WO2007132503A1 - 光電界受信器、光多値信号受信器および光伝送システム - Google Patents
光電界受信器、光多値信号受信器および光伝送システム Download PDFInfo
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- WO2007132503A1 WO2007132503A1 PCT/JP2006/309498 JP2006309498W WO2007132503A1 WO 2007132503 A1 WO2007132503 A1 WO 2007132503A1 JP 2006309498 W JP2006309498 W JP 2006309498W WO 2007132503 A1 WO2007132503 A1 WO 2007132503A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/60—Receivers
- H04B10/66—Non-coherent receivers, e.g. using direct detection
- H04B10/67—Optical arrangements in the receiver
- H04B10/671—Optical arrangements in the receiver for controlling the input optical signal
- H04B10/672—Optical arrangements in the receiver for controlling the input optical signal for controlling the power of the input optical signal
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/60—Receivers
- H04B10/66—Non-coherent receivers, e.g. using direct detection
- H04B10/69—Electrical arrangements in the receiver
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L7/00—Arrangements for synchronising receiver with transmitter
- H04L7/0008—Synchronisation information channels, e.g. clock distribution lines
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L7/00—Arrangements for synchronising receiver with transmitter
- H04L7/0075—Arrangements for synchronising receiver with transmitter with photonic or optical means
Definitions
- Optical electric field receiver, optical multilevel signal receiver, and optical transmission system are Optical electric field receiver, optical multilevel signal receiver, and optical transmission system
- the present invention relates to an optical information transmission technique, and more particularly to an optical electric field receiver, an optical multilevel signal receiver, and an optical transmission system suitable for receiving multilevel optical information transmitted through an optical fiber. .
- Multi-level modulation technology which was popular in the 1960s, has enabled high-efficiency transmission with a frequency utilization efficiency exceeding 10. Multi-level modulation is considered promising in optical fiber transmission, and many studies have been made on its conventional power. For example, RA Grif nn, et.
- Non-Patent Document 1 QPSK (Quadrature Phase Shift Keying) with phase modulation was reported, Kenro Sekine, Nobuhiko Kikuchi, Shinya Sasaki, Shigenori Hayase and Chie Has egawa, "Proposal and Demonstration of 10— Gsymbol / sec 16—ary (40 Gbit / s ) Optical Modulation I Demodulation Scheme, "paper We3.4.5, ECOC 2004, 2004 (Non-Patent Document 2) reported 16-level amplitude 'phase modulation that combines 4-level amplitude modulation and 4-level phase modulation. ing.
- FIGS. 1A to 1D are diagrams showing characteristics of various known modulation schemes applicable to optical transmission.
- the phase point of light modulation (complex display of the optical electric field at the identification time) is plotted on the phase plane (on the IQ plane).
- BASK binary amplitude modulation
- (B) is a quaternary phase that transmits 2-bit information (11, 10, 01, 00) in one symbol by using quaternary phase angles (0, ⁇ / 2, ⁇ , 1 ⁇ ⁇ 2). Modulation (QPSK) is shown.
- (C) shows 16-value quadrature amplitude modulation (16QAM) widely used in radio.
- 16QA IV the phase points are arranged in a grid pattern, and 4 bits of information can be transmitted with one symbol.
- the upper 2 bits (11 ⁇ , 10 ⁇ , 01 ⁇ , ⁇ ) are represented by the Q axis coordinates
- the lower 2 bits xxl l, ⁇ 10, xx01, xxOO
- This phase point arrangement is known to have high reception sensitivity because the distance between the phase points can be increased, but an implementation example in the optical communication field has not yet been reported.
- (D) shows 16-value amplitude phase modulation (16APSK) in which the phase point of binary amplitude modulation and the phase point of 8-value phase modulation are arranged concentrically, and (E) shows the amplitude and phase. Showing the relationship.
- the tolerance to wavelength dispersion is usually only about 5 km with a dispersion fiber, so signal quality degradation is minimized by a tunable dispersion compensator placed at the optical signal receiving end.
- Adaptive compensation technology that automatically controls the system is being studied! Speak.
- the tunable dispersion compensator still has many problems to be solved in terms of the size, complexity, cost, and control speed of the device.
- an electrical adaptive equalization circuit such as a feedforward equalization circuit (FFE) or a decision feedback equalization circuit (DFE) is arranged in an electric circuit section of an optical signal receiver, or a maximum likelihood estimation circuit ( Electric stage compensation technology that estimates received symbols by MLSE) is being studied.
- the chromatic dispersion compensation at the electrical stage according to the prior art is incomplete so as to shape the eye opening of the received light waveform. Therefore, the compensation effect also effectively increases the chromatic dispersion resistance of the receiver to 1.5 to 2 times, for example, to extend the transmission distance to 1 Okm with normal optical fiber transmission of 4 OGbitZ seconds. It was insufficient.
- Non-Patent Document 3 an optical multilevel signal 123 transmitted through an optical fiber transmission line is converted into a horizontal (P) polarization component 133 by a polarization separation circuit 131. Separated into vertical (S) polarization component 134 and input to coherent optical field receivers 135-1 and 135-2, respectively.
- the coherent optical electric field reception system requires a local oscillation laser light source 130 having substantially the same wavelength as the transmission light source.
- the output light (local light) 132 from the laser light source 130 is separated into two local light sources 132-1 and 132-2 by the optical splitter 102 and input to the coherent optical field receivers 135-1 and 135-2.
- the coherent optical electric field receiver 135-1 includes an optical phase diversity circuit 136 and a digital arithmetic circuit 141.
- the optical phase diversity circuit 136 outputs a 1 (in-phase) component output light consisting of the in-phase components of the local light and the optical multilevel signal from the P polarization component 133 and the local light 132-1 of the input optical multilevel signal.
- 137 and the Q (orthogonal) component output light 138 consisting of the orthogonal components of the local light and the optical multilevel signal, and the I component output light 137 is sent to the balanced optical receiver 105-1 and the Q component output light 138. Supplies to the balanced optical receiver 105-2.
- the analog electrical signals output from the non-reflex type optical receivers 105-1, 105-2 are time-sampled by the A / D converters 106-1, 1062, respectively, and converted into digital signals.
- the optical electric field of the received signal is defined as r (n) exp ( ⁇ ( ⁇ )), and local light is emitted. Is expressed as exp (- ⁇ (n)).
- r is the amplitude of the photoelectric field
- ⁇ is the phase of the optical field
- n is the sampling time
- the amplitude of the local light 132 is assumed to be a constant value “1”.
- ⁇ (n) represents the random phase noise inherent in the laser light source and the phase fluctuation caused by the difference frequency component between the local light and the signal light.
- the transmitter light source on the transmitter side also has phase noise, but is ignored here for simplicity.
- phase variation ⁇ ( ⁇ ) ⁇ ( ⁇ ).
- ⁇ ′ ( ⁇ ) ⁇ ( ⁇ ). Therefore, when a coherent photoelectric field receiver is used, all information (here, I and Q components) indicating the optical electric field r (n) eX p (n)) is directly obtained from the received optical multilevel signal 123.
- the influence of the phase fluctuation ⁇ (n) of the local light 132 cannot be ignored. For example, assuming that the received optical multilevel signal is multilevel modulated by 16-level quadrature modulation (16QAM) shown in (C) of FIG.
- the digital arithmetic circuit 141 detects a slow rotational component (up to several hundred MHz) of the phase point from the output signals of the AZD converters 106-1 and 106-2, and uses this rotational component as the phase fluctuation ⁇ (n ),
- the output signals 142-1 and 142-2 indicating ( ⁇ ( ⁇ )) are output to the symbol determination circuit 143.
- the balanced optical receiver 105-2 operates in the same manner as the balanced optical receiver 105-1,
- the symbol determination circuit 143 compares the I and Q components output from each digital arithmetic circuit 141 with the phase point arrangement shown in FIG. Discriminate and output playback multilevel digital signal 144.
- the digital arithmetic circuit 141 performs a correction process on the input signal by the inverse function of the propagation function of the optical fiber transmission line, so that linear degradation due to chromatic dispersion or the like is theoretically reduced. There is a great advantage that it can be completely compensated and the compensation amount is not limited.
- FIG. 3 shows a configuration diagram of a conventional optical multilevel signal receiver for receiving amplitude-phase modulated light represented by Non-Patent Document 2, and (A) in FIG.
- 8-level amplitude-phase modulated light 8APSK
- 8APSK 8-level amplitude-phase modulated light
- differential code is usually used for modulation of phase components.
- 3 bits of information are stored in each sym- ponole in association with the binary 4 values that have the amplitude of 2 and the phase difference between the previous symbol and 0, ⁇ / 2, ⁇ , or 1 ⁇ / 2. Is transmitted.
- An optical multilevel signal receiver that receives an 8APSK signal is a non-coherent method that does not detect an optical electric field.
- an input optical APSK signal 124 is an optical branch circuit.
- the signal is split into three optical signals. Of these, two optical signals are input to the optical delay detectors 104-1 and 104-2, and the remaining optical signal is input to the optical intensity receiver 151.
- Optical delay detectors 10 04-1 and 104-2 each have a first optical path that gives a delay of symbol time ⁇ to the input signal and a second ⁇ / 4 phase shifter or + ⁇ / 4 phase shifter. Receive light path and power The state (symbol) of the received optical multilevel signal is interfered with the symbol received before time T.
- the phase modulation component is converted into a light intensity signal.
- the output light of the optical delay detector 104-1 with a + ⁇ / 4 phase shifter has a high output intensity when the phase difference between the received symbol and the immediately preceding symbol becomes SO or + ⁇ ⁇ 2, and the level is high.
- the output intensity decreases when the phase difference is - ⁇ ⁇ 2 or ⁇ .
- the output light from the optical delay detector 104-1 is received by the balanced receiver 105-1, and the binary output of the output is determined by the binary decision circuit 152-1. 153-1 is obtained.
- the output light of the optical delay detector 104-2 with a ⁇ / 4 phase shifter has a large output intensity when the phase difference power SO between the received symbol and the immediately preceding symbol becomes SO or ⁇ ⁇ 2, and the phase difference is The output intensity decreases when ⁇ ⁇ 2 or ⁇ .
- the optical intensity receiver 151 converts the optical intensity of the received signal (the square of the optical electric field amplitude) into an electrical signal.
- the output of the light intensity receiver 151 is judged by a binary judgment circuit 152-3, and a binary reproduced digital signal 153-1 for one bit included in the optical amplitude component is reproduced. Since this optical multilevel signal receiver uses optical delay detection, it has the advantage of eliminating the need for a local oscillation light source that eliminates the effects of phase fluctuation ⁇ ( ⁇ ) and polarization dependence. This is applied to the reception of up to APSK signals.
- Non-patent Document 4 Multi-symbol Phase Estimation, “proc. ECOC '05, We4P 118, 25—29 September 20 05, Glasgow, Scotland, 2005 (Non-patent Document 4) shows a receiver of binary phase-modulated light.
- This receiver applies a decision feedback method used in wireless communication in order to receive a binary differential phase modulation (DPSK) input optical signal 159 with high sensitivity.
- the input signal is split into two optical signals and input to the optical delay detectors 104-1 and 104-2.
- the optical delay detectors 104-1 and 104-2 have a first optical path that gives a delay of symbol time T to the input signal, and a phase shifter with a phase angle of 0 or a ⁇ / 2 phase shifter, as in FIG.
- the second light path It has become.
- ⁇ (n) is the phase modulation component
- the optical electric field of the binary phase modulation signal is expressed as exp ( ⁇ ( ⁇ )).
- the outputs of the optical delay detectors 104-1 and 104-2 are respectively input to the balanced receivers 105-1 and 105-2, the output signals of the two balanced receivers are cos (A ⁇ ( ⁇ )) , Sin (A ⁇ ( ⁇ )).
- ⁇ ( ⁇ ) ( ⁇ ) ⁇ ( ⁇ 1) and the amplitude component is constant, it is specified as “1”.
- the receiver shown in Fig. 4 employs a decision feedback method.
- phase difference information cos ⁇ ⁇ ( ⁇ -1), sin A ⁇ ( ⁇ -By multiplying binary digital information output from the binary decision circuit 152 by 1), the differential phase modulation component (“0” or “ ⁇ ”) is eliminated and only the error component is extracted. Yes.
- a four-quadrant multiplier 156 From the extracted error component and the new phase difference information ⁇ ( ⁇ ), a four-quadrant multiplier 156 generates a compensation signal, and inputs the compensation signal to the weighting circuits 155-1, 155-2.
- the weighted compensation signal to the received signal by the adder circuits 154-1 and 154-2, the influence of the previous bit (symbol) is partially removed.
- Non-Patent Document 1 RA Griffin, et. Al, "lOGb / s Optical Differential Quadrature Phase Shift Key (DQPSK) Transmission using GaAs / AlGaAs Integration, OFC2002, paper PD-FD6, 2003
- Non-Patent Document 2 Kenro Sekine, Nobuhiko Kikuchi, Shinya Sasaki, Shigenori Hayase an d Chie Hasegawa, "Proposal and Demonstration of 10— Gsymbol / sec 16— ary (40 Gbit / s) Optical Modulation I Demodulation Scheme," paper We3. 4.5, ECOC 2004, 200 4
- Non-Patent Document 3 M. G. Taylor, "Coherent detection method using DSP to demodulate signal and for subsequent equalization of propagation impairments, paper We4.P.l l 1, ECOC 2003, 2003
- Non-Patent Document 4 S Calabro, "Improved Detection of Differential Phase Shift Keying Through Multi-symbol Phase Estimation," proc. ECOC '05, We4P 118, 25—29 September 2005, Glasgow, Scotland, 2005
- a first object of the present invention is to provide a practical optical electric field receiver and optical multilevel signal receiver that do not require a local oscillation light source having no polarization dependency.
- a second object of the present invention is to provide a photoelectric field receiver capable of detecting all electric field information (received symbol amplitude value, phase angle, or inter-symbol phase difference) of an optical multilevel modulation signal required for symbol determination, and It is to provide an optical multilevel signal receiver.
- the coherent optical field receiver described in Fig. 2 is in principle polarization dependent, and if the P-polarized component described above is lost due to fluctuations in polarization, the coherent optical field receiver 135-1 cannot operate. End up. Therefore, in the coherent optical electric field receiving system shown in FIG. 2, the coherent optical electric field receiver 1 35-1 that receives the P-polarized component 133 of the optical multilevel signal and the coherent optical electric field receiver that receives the S-polarized component. 135-2 is prepared, and a symbol determination circuit 143 selects one of these two receivers to determine a symbol, and has a polarization diversity configuration.
- the coherent optical electric field reception system requires a local oscillation light source 130 having a wavelength substantially matching that of the received light, so that there is a problem that wavelength management becomes complicated.
- a polarization diversity configuration it becomes possible to receive an input optical signal even if the polarization state fluctuates. In this case, however, the polarization separation circuit 131 and the extra optical components such as the optical splitter 102 are used. Is necessary, and the hardware scale of the receiver increases.
- the received signal strength and relative phase difference are each subjected to binary determination.
- the optical delay detector used in these methods is for detecting an intensity signal that changes in accordance with the relative phase difference between two consecutive symbols on the time axis. This is because the absolute phase cannot be detected.
- the eight-value detection of the relative phase difference required for the determination of the 16AP SK signal in FIG. 1 (D) cannot be performed.
- a third object of the present invention is to provide a highly versatile optical field receiver, an optical multilevel signal receiver, and an optical transmission system that can be applied to a plurality of types of optical modulation schemes having different multilevel values. It is to provide.
- the coherent optical field receiver has an advantage for this problem.
- non-coherent receivers such as the optical multilevel signal receiver described in FIG. 3 and the decision feedback type multilevel phase modulation receiver described in FIG. Therefore, when the number of multilevel symbols increases by 2 to the Nth power, N sets of receiver circuits are required as a general rule.
- the structure of the vessel becomes complicated. This configuration complexity is a serious problem in practical use in an optical multilevel signal receiver that is desired to increase the number of multilevels in the future.
- these non-coherent receivers have a problem that they lack generality because the receiver structure changes depending on the modulation method and phase point arrangement of the received optical signal.
- Non-Patent Document 2 four-level intensity multi-level modulation signals are received by one optical intensity receiver.
- a fourth object of the present invention is to realize an optical electric field receiver that detects all information of an optical electric field in a non-coherent manner and compensates for linear degradation that occurs during transmission.
- the optical signal has an amplitude modulation component
- the output signal intensity varies depending on the amplitude modulation component. Therefore, the optical electric field information cannot be obtained unless it is a coherent optical reception system using a local oscillation light source. It is believed that. If a conventional multi-level modulated optical signal including binary amplitude modulation can be received and all electric field information can be obtained, the receiver's electrical circuit stage computes linear degradation that occurs during transmission. For example, advanced dispersion compensation can be realized.
- the received optical signals are input to a pair of optical delay detectors whose phases are shifted from each other by 90 degrees.
- the delayed detection output is converted into an electric signal, and optical electric field information is calculated using an electric field calculation unit.
- two delayed detection signals indicating an orthogonal component X component and y component (or I component and Q component) of a complex signal are generated from a pair of optical delay detectors.
- the electric field calculation unit calculates the phase component (inter-symbol phase difference) of the complex signal, and subtracts the phase angle of the immediately preceding symbol calculated in the past from the calculated phase component. Is calculated.
- the amplitude value of the complex signal is calculated from the two delayed detection signals, and the amplitude value of the received symbol is calculated by dividing this value by the amplitude value of the symbol just calculated in the past.
- the amplitude value of the received symbol may be calculated based on the output of a light intensity detector provided separately from the optical delay detector.
- the optical electric field receiver and the optical multi-level signal receiver of the present invention determine the inter-symbol phase difference received symbol calculated by the electric field calculation unit.
- a multi-level symbol determination circuit is provided.
- the optical electric field receiver and optical multilevel signal receiver of the present invention Includes a multi-value symbol determination circuit that determines a received symbol from the amplitude value and phase component (inter-symbol phase difference or symbol phase angle) of the optical electric field calculated by the electric field calculation unit, or the in-phase component and the orthogonal component.
- the force that causes fluctuations in the phase and amplitude at low speed is a problem.
- This fluctuation component is used for multilevel symbol determination, for example, by adopting a technique such as decision feedback calculation. Can be removed.
- the delay time T of the optical delay detector and the sampling time of the AZD converter are set to lZ2f (f is the maximum frequency of the input optical signal). Ingredients)
- f is the maximum frequency of the input optical signal.
- the optical electric field compensation circuit performs an inverse operation on the propagation characteristics of the optical transmission line with respect to the regenerated optical electric field signal, chromatic dispersion can be more completely compensated.
- it is necessary to specify the amount of chromatic dispersion to be compensated in the optical electric field compensation circuit but if the chromatic dispersion value is known, a fixed compensation value should be specified in advance. If the chromatic dispersion value is unknown, An adaptive compensation type optical electric field compensation circuit whose compensation value is automatically changed according to the reception state may be employed.
- the compensation value can be set with an external device force for the optical electric field compensation circuit.
- the control terminal connected to the optical network is used. Then, the total chromatic dispersion amount of the optical fiber along the optical signal path is calculated, and this value is transmitted to the optical transmission device on the optical signal receiving side, and the optical electric field compensation circuit of the optical electric field receiver and the optical multilevel signal receiver.
- the optimal compensation amount can be set. According to this method, when the optical signal path in the optical network is changed, the recalculated compensation amount can be quickly set in the optical electric field compensation circuit, so that an adaptive compensation type optical electric field compensation circuit can be dispensed with. At the time of pulling in the optimum state in adaptive compensation control It is possible to shorten the interval.
- the present invention uses an optical delay detector and is independent of the polarization state of the input light. Unlike the conventional coherent detection method, the present invention does not require a local oscillation light source. Becomes easier.
- the circuit scale has been increased as the number of received signals increases, but the optical electric field receiver and multilevel optical receiver of the present invention are Since the two-dimensional coordinate information on the phase plane of the received optical electric field can be directly reproduced, even if the number of optical modulation signals is increased to improve transmission efficiency, the received signal can be obtained on a practical hardware scale. There is an advantage in that it is possible to determine the symbols.
- the electric field calculation and multilevel determination of the received optical signal can be performed by an electrical digital circuit, so that the same receiver configuration can be applied to optical signals having different multilevel numbers and modulation methods. It is possible to
- FIG. 5 shows a first embodiment of the optical electric field receiver 100 according to the present invention.
- the optical signal path is indicated by a thick line
- the electrical signal path is indicated by a thin line.
- ⁇ ⁇ ⁇ ⁇ ( ⁇ (input optical signal 101 represented by n ", like the conventional decision feedback type multilevel phase modulation receiver described in FIG. 4, two optical signals by an optical branching circuit 102 And is input to the optical delay detectors 104-1 and 104- 2.
- the optical delay detectors 104-1 and 104-2 have a first optical path that gives a delay of symbol time T to the input signal, and State (symbol) of a phase-shifted optical multilevel signal consisting of a phase shifter with a phase angle of 0 or a second optical path with a phase shifter of ⁇ / 2 so that the phase is shifted by ⁇ / 2 between the two detectors Is interfered with the symbol received before time ⁇ .
- optical signals output from the optical delay detectors 104-1 and 104-2 are converted into electrical signals by optical balanced receivers (photodetectors) 105-1 and 105-2, respectively, and then converted to AZD. Converted to a digital signal in 106-1 and 106-2.
- the digital signals output from AZD 106- 1 and 106--2 are the delay adjustment circuits 108-1 and 108-2, respectively. After adjusting the deviation of the path timing to the symbol time T or less, it is supplied to the electric field calculation unit 111 as the electrical reception signals 110 1 and 110-2.
- these signals are input to the electric field calculation unit 111, the previous n-1st symbol information is removed, and only the nth received symbol information is extracted, and the reproduced optical electric field signal 117 is obtained.
- the reproduction optical electric field signal 117-1 indicates the electric field amplitude r (n)
- the reproduction optical electric field signal 117-1 indicates the phase angle ⁇ (n).
- the electric field calculation unit 111 includes a square calculation circuit 112 for calculating the amplitude r (n) r (nl) of the delay detection signal from the electrical reception signals 110-1 and 110-2.
- the arc tangent calculation circuit 113 for calculating the phase difference ⁇ ( ⁇ ) of the delayed detection signal from the electrical reception signals 11 0-1 and 110-2, and the delay division circuit 115 connected to the square calculation circuit 112 And a delay addition circuit 116 connected to the arctangent calculation circuit 113.
- the delay division circuit 115 removes the amplitude r (nl) component of the immediately preceding received symbol from the amplitude r (n) r (nl), thereby reproducing the reproduction optical electric field indicating the electric field amplitude r (n) of the received symbol.
- the delay addition circuit 116 removes the phase component ⁇ (n-1) of the received symbol immediately before the phase difference ⁇ (n) force, thereby reproducing the reproduced photoelectric signal indicating the phase angle ⁇ (n) of the received symbol.
- 117 Outputs 2
- the optical electric field receiver shown here includes a multi-level symbol determination circuit for determining the bit values corresponding to the reproduction optical electric field signals r (n) and ⁇ ( ⁇ ) after the electric field calculation unit 111.
- a multi-level symbol determination circuit for determining the bit values corresponding to the reproduction optical electric field signals r (n) and ⁇ ( ⁇ ) after the electric field calculation unit 111.
- an optical multilevel signal receiver can be configured.
- the delay time and sampling time of the optical delay detectors 104-1 and 104-2 are set to 1Z2 or less of the symbol time ⁇ , and the compensation calculation circuit corrects the reproduced optical electric field signal with the inverse characteristic of the propagation function of the transmission line.
- FIG. 6 is an explanatory diagram of the operation timing of the optical electric field receiver of the first embodiment.
- the A / D converter circuits 106-1 and 106-2 receive the output signals of the optical balanced receivers 105-1 and 105-2 at the desired period and timing determined by the sampling clocks 107-1 and 107-2, respectively. AZD conversion.
- FIG. 6 (A) shows changes in the electrical reception signal 110-1 (x component) and the electrical reception signal 110-2 (y component) input to the electric field calculation unit 111
- FIG. ) Shows changes in the reproduction electric field signal 117-1 (amplitude component r) and the reproduction electric field signal 117-2 (phase component ⁇ ) output from the electric field calculation unit 111.
- the frequency of the sampling clock is matched with the symbol rate of the received optical multilevel signal, and the received signal is sampled at the center timing of each symbol period.
- the square operation circuit 112 calculates the square root of the sum of squares of the input signals x and y in the symbol period, thereby eliminating the cosine term and the sine term, and calculating the product of amplitudes r (n) r (nl ) Indicating signal 114-1 is output.
- the arc tangent calculation circuit 113 calculates the arc tangent tan-Ky / x of the input signals x and y, thereby calculating a complex signal (hereinafter referred to as “delayed detection signal”) having the input signals x and y as orthogonal components.
- the signal 114-2 indicating the phase difference ⁇ (for example, ⁇ ⁇ ⁇ ) is output.
- the delay division circuit 115 divides the amplitude product r (n) r (nl) output from the square operation circuit 112 by the amplitude r (nl) of the immediately preceding symbol, thereby obtaining the amplitude r (n) of the received symbol. Can be calculated. Also, in the delay addition circuit, the phase angle ⁇ ( ⁇ ) of the received symbol can be calculated by adding the phase ⁇ ( ⁇ -1) of the immediately preceding symbol to ⁇ ( ⁇ ) output from the arctangent calculation circuit 113. . As described above, in this embodiment, the optical electric field information indicating the amplitude value and the phase angle can be extracted from the input optical signal 101 using the optical delay detection type optical receiver which is a non-coherent receiver.
- the coupling between the optical components on the optical signal path 103 includes coupling between the optical components by an optical fiber, coupling by a Balta optical element space beam, and between integrated optical components.
- Various connection forms such as coupling by a waveguide can be adopted.
- the optical delay detector 104 and the balanced receiver 105 are combined, the amplitude of the detector output signal There is an advantage that unnecessary DC signals can be removed.
- a normal light intensity detector can be applied.
- the delay adjustment circuits 108-1 and 108-2 match the signal propagation times in the two signal paths between the optical branching circuit 102 and the electric field calculation unit 111, and match the calculation timings of the X component and the y component. For example, it can be realized by a nother circuit. However, the delay adjustment circuits 108-1 and 108-2 can be omitted if a circuit configuration in which the two signal path lengths can be completely matched at the manufacturing stage is adopted. Also, instead of using the delay adjustment circuits 108-1, 108-2, the relative phase of the X and y components can be changed by another method, for example, the sampling supplied to the AZD converters 106-1, 106-2. Control according to the application timing of clocks 107-1 and 107-2.
- an analog delay line is used as a force delay adjustment circuit in which the digital delay adjustment circuit 108-1 (108-2) is placed after the AZD converter 106-1 (106-2). Thereafter, a circuit configuration in which the AZD converter 106 is arranged may be employed. Also, omit the AZD converter 106, and implement some or all of the calculation functions of the electric field calculation unit 111 with analog circuits.
- the polar coordinate (r (n), ⁇ (n)) calculation type electric field calculation unit 111 is used, but the electric field calculation unit 111 includes orthogonal coordinates (I ( n), Q (n)) arithmetic type can also be applied. In this case, a coordinate conversion circuit is used as necessary.
- the function of the electric field calculation unit 111 can be realized by, for example, an FPGA, an ASIC, a DSP, or a processor whose function can be reconfigured.
- the calculation procedure to be performed by the electric field calculation unit 111 includes various nominations and approximate calculation methods different from those in the embodiment according to the purpose. Further, a configuration may be adopted in which output values calculated in advance are stored in memory corresponding to different input signal values, and calculation results are obtained in a table lookup format according to the input signal values.
- the electric field calculation unit 111 may be provided with other functional circuits, for example, an automatic gain control (AGC) circuit for normalizing the amplitude and intensity of the signal as necessary.
- AGC automatic gain control
- N data is divided into 3 series of data packets (data blocks), and each data packet is arranged in parallel.
- the reproduction electric field signal processed in step 3 and output from each electric field calculation unit may be combined by the packet combining circuit 121.
- the electric field data string is divided and processed in this way, it is necessary to adjust so that the optical electric field phase is continuous at the connection portion of each data packet.
- the problem can be solved by providing an overlapping part of the bits and correcting so that the phases of the overlapping bits match.
- FIG. 8 shows an optical multilevel signal receiver using the optical electric field receiver 100 shown in FIG. 5 as a second embodiment of the present invention.
- the second embodiment is characterized in that when the optical multilevel signal 123 including the phase variation ⁇ (n) is received, the influence of the phase variation ⁇ (n) can be removed from the reproduced multilevel digital signal. To do.
- the received optical multilevel signal 123 includes an optical branching circuit 102, an optical delay detector 104 (104-1, 10 4 2), and an optical balanced receiver 105 (105-1, 105-2). , AZD change ⁇ 106 (106 1, 106-2), delay adjustment circuit 108 (108-1, 108-2), and electric field receiver 111 similar to that shown in FIG.
- the electric field calculation unit 11 1 reproduces the reproduction electric field signal 117-1 indicating the amplitude component r (n) and the reproduction indicating the phase component ⁇ ′ ( ⁇ ) affected by the phase fluctuation ⁇ (n).
- Electric field signal 117-2 is output.
- These reproduction electric field signals 117-1 and 117-2 are input to a symbol determination unit 176 independent of phase fluctuation.
- the symbol determination unit 176 also has the power of the symbol determination circuit 143, the phase fluctuation estimation circuit 174, the delay circuits 157-1 and 157-1, and the subtraction circuit 171.
- the symbol determination circuit 143 includes a reproduction electric field signal 117-1 (amplitude component r (n)) and a reproduction electric field signal 172 (with phase fluctuation component ⁇ (n) removed from the reproduction electric field signal 117-2 by decision feedback described later.
- the phase component ⁇ ( ⁇ )) is input, and the symbol determination result is output as a reproduced multilevel digital signal 144.
- the operation of the symbol determination unit 176 when the received optical multilevel signal 123 is a 16QAM signal will be described with reference to FIG. [0065]
- the correctness of the 16QAM signal! / And the phase point are at the positions indicated by white circles in FIG. 9 (A).
- the optical electric field information at time n output from the electric field calculation unit 111 indicates a phase point indicated by a black circle in FIG. 9 (A).
- the phase shift of the optical signal due to the phase fluctuation of the light source in the transmitter, noise, waveform distortion, etc., ⁇ (n) causes a rotational shift in the phase plane, and the phase point observed on the receiver is correct. It is shifted from the phase point.
- the phase fluctuation estimation circuit 174 uses the phase point information of the past (time n-1) to determine the time n.
- the phase fluctuation estimated value 175 (0 (n)) is calculated, and the subtraction circuit 171 removes the phase fluctuation estimated value ⁇ ( ⁇ ) from the phase component ⁇ ′ ( ⁇ ) at time n, thereby obtaining the correct phase.
- the angle ⁇ ( ⁇ ) 17 2 is calculated.
- Symbol determination circuit 143 selects the most reliable received symbol from amplitude information r (n) and phase information ⁇ ( ⁇ ) of the received signal. Simply put, the distance between each symbol position (white circle) in the 16QAM signal and the phase point (black circle) indicated by the received signal is calculated, and the symbol with the closest distance is determined as the received symbol. The symbol determination circuit 143 outputs a 4-bit digital value assigned to the received symbol as V /! And a 16-QAM signal as a reproduction multilevel digital signal 144. In this example, a symbol indicated by a double circle is determined as a received symbol, the phase angle is ⁇ ( ⁇ ), and the output digital value is “1011”.
- the phase fluctuation estimation circuit 174 determines the reception signal phase ⁇ ′ ( ⁇ ) one symbol period before and one symbol period before through the delay circuits 157-1 and 157-2. Phase angle ⁇ (n-1) is
- the phase of the received photoelectric field can be calculated with high accuracy even under the influence of the phase noise of the light source and the optical amplifier noise.
- the phase variation-independent symbol determination unit 176 force phase variation is removed by decision feedback, but the decision feedback technique can also be applied to correct amplitude calculation errors and other errors.
- the distance between the input phase point and the symbol position determined by the symbol determination unit 176 is calculated, and the phase angle and symbol amplitude are adjusted so that the average value is minimized.
- the optimum reception state can be maintained by adjusting the frequency.
- the best reception sensitivity can be maintained by dynamically adapting to waveform degradation.
- the phase angle ⁇ ′ ( ⁇ ) indicated by the reproduction optical electric field signal 117-2 is set to an N-fold circuit (or the optical field phase term exp ⁇ ′ ( ⁇ ) Input to the Nth power circuit), the phase modulation component (the phase point interval is ⁇ ⁇ ) can be eliminated, and the phase fluctuation component can be estimated easily. If this estimated value is averaged over the past ⁇ bit period and subtracted from the detected phase angle ⁇ ′ ( ⁇ ), the fluctuation component can be removed.
- phase modulation interval is unequal as in the 16QAM signal
- the phase points at the four corners at which the amplitude is maximum for example, the points "1111” and "0000” shown in FIG.
- the average position of the specific phase point may be tracked in time, and the deviation amount may be estimated as the phase fluctuation.
- Other methods known in the wireless communication field may be applied to estimate the phase variation component.
- the effects of noise and calculation errors accumulate, and in the worst case, there is a possibility of causing error propagation over a long period of time.
- Examples of methods for preventing such error propagation include application of encoding such as differential encoding to amplitude and phase, and insertion of a known reference code periodically on the transmission side. It is also possible to apply methods such as prevention of divergence and attenuation of amplitude values by normal amplitude calculation, statistical distribution of received phase points, and sequential decision feedback from specific phase point positions.
- the minimum distance rule is applied to the determination of the received symbol, but other known symbol determination methods used for multilevel signals in the wireless communication field may be applied. .
- MLSE using the electric field state of multiple consecutive symbols, preferential determination of either phase or amplitude radius, maximum likelihood determination (Viterbi decoding), soft decision FEC (prefix error correction), trellis code Techniques such as ⁇ Z decoding ⁇ ⁇ processing are also applicable.
- a non-Euclidean distance corresponding to the noise generation factor optical amplifier noise, thermal noise, crosstalk, etc.
- the symbol determination circuit may have an analog structure in which, for example, a plurality of matched filters corresponding to each symbol are arranged in parallel, a filter with the maximum output is selected, and an input symbol is specified.
- FIG. 10 shows an example of the initial phase determination method employed in the second embodiment.
- Fig. 10 (A) shows the transmitted optical field
- Fig. 10 (B) shows the symbol (phase point) arrangement of the 16QAM signal.
- the two corners “1111” and “0000” that are symmetrical to each other are used as known data, and five symbols “1111” are used prior to user information.
- “0000”, “1111”, “0000”, “0000” is transmitted as a known data pattern. Since these symbols are not amplitude-modulated, the amplitude of the reproduction optical electric field is a force that makes the amplitude value of the first symbol unknown, as shown in FIG. Therefore, on the receiving side, the reproduction electric field intensity may be corrected so that the amplitude values after the second symbol become the radii of symbols “1111” and “0000” in the 16QAM signal.
- phase angle ⁇ ⁇ 4 of the symbol “00 00” or the phase angle ⁇ 3 ⁇ ⁇ 4 of the symbol “1111” should ideally be detected as the phase angle. is there.
- the phase angle of the first symbol is indefinite
- the phase angle ⁇ ⁇ (indefinite value) of the first symbol is used as the initial phase
- the same phase angle appears continuously for 2 bits during the reception period of the known data pattern only when the 4th and 5th symbols are received.
- the phase angle detected at this time corresponds to the phase angle of the symbol “0000”. Therefore, the value of the phase angle detected in the fourth and fifth symbols, the phase angle ⁇ ⁇ 4 and force that the symbol “0000” should have, and the phase shift amount (initial phase angle ⁇ 0) can be specified.
- the detected phase angle of the fifth symbol indicated by a black circle in the third quadrant and the normal phase angle ⁇ ⁇ 4 that the symbol “0000” should have The detection phase angle can be corrected by calculating the difference ⁇ 0 and subtracting ⁇ 0 from the phase angle of the reproduced optical field detected thereafter.
- Determination of the initial phase and initial amplitude is a common problem in the optical communication field and the wireless communication field.
- a reference signal having a known phase angle or amplitude value is inserted into the transmitted signal periodically or intermittently, or using a technique such as differential modulation that makes it unnecessary to determine the initial phase or initial amplitude. Also good.
- the initial phase and amplitude may be adjusted adaptively by the statistical distribution power of the reconstructed phase points so that normal reception is possible.
- FIG. 11 shows an optical multilevel signal receiver having a configuration in which a light intensity receiving function and a clock extracting function are added as a third embodiment of the optical electric field receiver of the present invention.
- the input optical multilevel signal 123 is branched into three optical signals by the optical branch circuit 150.
- the first and second optical signals are input to the optical delay detectors 104-1 and 104-2, respectively, and the third optical signal is input to the optical intensity receiver 151.
- the outputs of the optical delay detectors 104-1 and 10 4-2 are converted into electrical signals by the optical balanced receivers 105 (105-1, 105-2), as in Fig. 8, and the AZD conversion 106 (106 — 1, 106-2) and the delay adjustment circuit 108 (108-1, 108-2) to the electric field calculation unit 111.
- Output of light intensity receiver 151 The force signal is converted into a digital signal by the AZD converter 106-3, adjusted in timing by the delay adjustment circuit 108-3, and then input to the electric field calculation unit 111.
- the output of the delay adjustment circuit 108-3 indicates the square value r 2 (n) of the intensity r (n) of the nth symbol.
- the square root circuit 160 provided in the electric field calculation unit 11 1 calculates the square root of the output signal 110-3 from the delay adjustment circuit 108-3, thereby calculating the amplitude value r (n ) According to the above configuration, the optical electric field amplitude r (n) can be obtained more easily and more accurately than the optical electric field receiver of the first embodiment shown in FIG. Propagation measures become unnecessary.
- a part of the output signal of the light intensity receiver 151 is input to the clock extraction circuit 161, and a clock signal having a frequency f corresponding to the reciprocal of the symbol rate (1ZT) is extracted.
- This is supplied to A / D conversion 106-1, 106-2, 106-3.
- the clock signal generation timing is adjusted so that the AZD converter samples the input signal at the center of each symbol period.
- the clock extraction circuit 161 may be supplied with the output of the non-lance type receiver 105-1 or 105-2 instead of the output of the light intensity receiver 151. Further, the clock extraction circuit 161 may be provided individually for each photodetector, or a dedicated photodetector for clock extraction may be prepared.
- FIG. 12 shows an optical multilevel signal receiver provided with a decision feedback equalization circuit as a fourth embodiment of the present invention.
- a clock having a frequency f that is twice (or higher) the symbol rate (1ZT) of the input optical multilevel signal 123 is generated from the clock source 191 and is converted into an AZD conversion 106 —1, 106 — Sampling clocks 107-1 and 107-2 are supplied to 2.
- a / D converters ⁇ 106-1, 106-2 perform sampling regardless of timing synchronization with the input symbol in response to the sampling clock.
- the outputs of the AZD converters 106-1 and 106-2 are input to the resampling circuits 192-1 and 192-2 via the delay adjustment circuits 108-1 and 108-2, respectively.
- Each re-sample The sampling circuit interpolates the input data string according to the Nyquist theorem and can reproduce the sampling points at any timing.
- resampling is performed so that the sampling point is positioned at the center of each symbol period.
- Sampling timing can be adjusted using, for example, a data transition point discriminating circuit or a maximum eye opening detection circuit.
- the orthogonal electric field conversion circuit 198 connected to the electric field calculation unit 111 converts the coordinates of the optical electric field output from the electric field calculation unit 111 into the orthogonal coordinates based on the polar coordinates, and then the optical electric field.
- the value is supplied to the symbol determination unit 176 independent of the phase fluctuation through the determination feedback equalization circuit 193.
- the equalizer circuit 193 performs waveform equalization using decision feedback.
- a pre-error correction code (FEC) used in a known high-speed optical signal is mounted, and error correction of the reproduced multilevel digital signal 144 is performed. It is possible to further improve the performance.
- FEC pre-error correction code
- FIG. 13 shows an optical multilevel signal receiver for optical APSK signals as a fifth embodiment of the present invention.
- the optical multilevel signal receiver of the fifth embodiment uses optical delay detection for the optical APSK signal 124.
- Devices 104-1 and 104-2 receive differential signals, and input the output signals of delay adjustment circuits 108-1 and 108-2 to automatic gain control circuits (AGC) 195-1 and 195-2 to obtain the average intensity. Is normalized so that is constant. By providing AGC195-1 and 195-2, the reception characteristics can be stabilized even if the reception intensity of the input optical signal 124 varies.
- AGC automatic gain control circuits
- the output signals x and y of the AGC 195-1 and 195-2 are supplied in parallel to the square operation circuit 112 and the arctangent operation circuit 113 of the optical electric field operation unit 111, respectively.
- the optical electric field calculation unit 111 calculates the amplitude r (n) of the received optical electric field calculated by the square calculation circuit 112 and the delay division circuit 115 as the first signal 117-1, and the inter-symbol phase difference ⁇ calculated by the arctangent calculation circuit 113. ( ⁇ ) is output to the second signal 117-2 and the symbol determination circuit 143.
- Fig. 14 (A) shows the phase point arrangement of a 16-value APSK signal with a binary amplitude ("1" and "a") and an 8-level phase.
- the APSK signal has a concentric phase point arrangement as shown by the broken line. Therefore, the APSK signal can increase the resistance against phase fluctuation by applying differential reception to the phase component, so that the removal of the phase fluctuation becomes unnecessary.
- FIG. 14B is a code table for differential phase modulation showing the correspondence between the value of the phase difference ⁇ (n) and the three information bits D3, D2, and D1.
- the symbol determination circuit 143 determines the strength of the amplitude r (n) input as the first signal 1 17-1 and determines the value of the phase difference ⁇ input as the second signal as shown in FIG. Use the reverse key table to decode.
- information bit D4 is amplitude-modulated according to the working amplitude modulation coding table shown in FIG. That is, when the information bit D4 is “0”, the amplitude of the n-th symbol is made the same as the immediately preceding (n ⁇ 1) symbol, and when the information bit D4 power is “1”, the immediately preceding (n— 1) Amplitude value obtained by inverting symbol amplitude r (n—1) (If the amplitude r (n-1) force S of the previous symbol S is “1”, then “a” and r (n-1) is “a”. In this case, “1”).
- the delay division circuit 115 is omitted from the optical electric field calculation unit 111 by applying a differential sign to the amplitude on the transmission side, and the output signal 114-1: r (of the square calculation circuit 112 is omitted. It is also possible to adopt a configuration in which n) r (n-1) is directly input to the symbol determination circuit 143.
- FIG. 15 shows an optical multilevel signal receiver for an N-level optical phase modulation signal as a sixth embodiment of the present invention.
- the N-value optical phase modulation signal 197 is differentially received, thereby making it unnecessary to determine the amplitude of the received light, and the electric field calculation unit 111 shown in FIG. 13 includes the square calculation circuit 112 and the delay division circuit 115. Omitted and only the arc tangent calculation circuit 113 is left.
- the reception sensitivity can be improved by reducing the influence of the phase fluctuation by using the decision feedback circuit described in FIGS.
- the sixth embodiment is similar to the conventional binary phase modulation light receiver shown in FIG. 4 at first glance, but the receiver in FIG. Cos (A ⁇ ( ⁇ )) output from the balanced receiver 105-1 is input to a binary determination circuit 152 that is limited to a signal and serves as a symbol determination circuit. Therefore, the receiver according to the prior art generates the inter-symbol phase difference ⁇ ( ⁇ ) based on the x and y components of the complex signal output from the non-lance type receiver, as in this embodiment, The digital value of the received symbol is not judged by the value of ⁇ ( ⁇ ). According to this embodiment, even when a multi-level phase modulation signal having two or more values is received, the digital value of the received symbol can be easily obtained by using the value of ⁇ ( ⁇ ) generated by the electric field calculation unit 111. Can be determined.
- FIG. 16 shows a complete optical field receiver 200 that captures all the information of an optical electric field as a seventh embodiment of the present invention.
- the complete optical electric field receiver 200 shown here directly samples the optical electric field of the input optical signal 101 at a rate twice the symbol rate, thereby obtaining the information possessed by the optical electric field. Capture all.
- the delay amounts of the optical delay detectors 201-1 and 202-2 are 1Z2 of the symbol period T, and are input to the AZD variable ⁇ 106.
- the operations from the optical delay detectors 204-1, 204-2 to the electric field calculation unit 111 are similar to those in the first embodiment.
- the electric field signals 117-1 and 117-2 output from the electric field calculation unit 111 are subjected to compensation calculation by the electric field compensation circuit 202, and the electric field signals 2 03-1 and 203-2 after the compensation are optically transmitted. As the output of the multi-level signal receiver.
- (A) and (B) of Fig. 17 show the sampling timings of the electric reception signals x and y and the reproduction electric field signals r (n) and ⁇ (, respectively. n ⁇ l indicates the order of time-series samples at intervals of TZ2, not symbol numbers.
- the delay amount of the optical delay detectors 201-1, 202-2 is TZ2, so the optical delay Detection is performed between received symbols shifted by a half symbol on the time axis, and as a result, electric field information can be obtained sequentially for each half symbol as a reproduction electric field signal as shown in FIG.
- FIG. 18 is an explanatory diagram of the case where the complete optical field receiver 200 of the seventh embodiment is applied to compensation for optical multilevel signal degradation due to chromatic dispersion in the transmission path.
- the transmitted optical field 204 from the optical multilevel signal transmitter 210 has a ternary amplitude level as indicated by the amplitude eye pattern in the frame 501.
- the optical electric field 204 undergoes waveform degradation corresponding to the chromatic dispersion amount j8, and the amplitude eye pattern of the optical electric field received by the multilevel signal receiver 200 is shown in a frame 502. It deteriorates greatly.
- the chromatic dispersion of the transmission path 206 affects the transmission optical field 204 as linear degradation indicated by the transfer function exp ( ⁇ j ⁇ ⁇ 2 ).
- the complete optical electric field receiver 200 receives the transmission optical electric field 204 whose waveform has deteriorated, and the electric field calculation unit 208 calculates the reproduction optical electric field signal 117.
- the electric field calculation unit 208 is a circuit from the optical delay detectors 204-1 and 204-2 to the electric field calculation unit 111 shown in FIG. It corresponds to the road part.
- the sampling points of AZD transformations 106-1 and 106-2 are adjusted to be located at the center of each symbol.
- the output 117 (r (n) and ⁇ ( ⁇ )) of the electric field calculation unit 208 is supplied to the electric field compensation circuit 202, and has a transfer function exp G iS ⁇ 2 having characteristics opposite to those of the transfer path 205. ).
- This compensation is an operation in the frequency domain and can be realized by FFT or convolution.
- the electric field compensation circuit 202 can dynamically change the transfer function by setting the compensation amount j8 for the external force through the compensation amount input terminal 207 as well.
- the electric field signal 203 compensated for the waveform deterioration is output from the electric field compensation circuit 202, so that the determination process of the multi-level signal can be performed at the sampling timing that matches the center of each symbol.
- the electric field compensation circuit 202 can compensate for, for example, band degradation of an optical transmitter or receiver, band reduction by narrowband optical filtering, influence of filter ripple, and the like.
- the electric field compensator 202 is configured with a digital calculator. Or DSP.
- the electric field compensator 202 omits a part of the compensation processing to save power consumption and computing power according to the degree of degradation of the received signal, or when there are multiple signal degradation factors, Alternatively, the compensation mode corresponding to the highest deterioration factor may be selectively executed, or a plurality of compensation modes may be executed in duplicate.
- the sampling frequency is 2 of the maximum frequency component of the signal based on Nyquist's theorem, based on the Nyquist theorem, with the sampling interval of AZD transformation 106 and the delay amount of optical delay detector 104 as 1Z2 of the symbol length. It is required to be more than twice. Therefore, when the transmission signal includes a modulation component that is faster than the symbol rate, higher-speed sampling is required. Conversely, when the effective band of the optical electric field is low, such as a duobinary signal, the sampling rate is reduced. Can be lowered.
- the sampling rate must be slightly higher than TZ2.
- the sampling rate of the AZD converter 106 is doubled as the symbol rate.
- the output signal of the optical delay detector 104 is one symbol. Since it is a composite signal with the previous electric field, complete electric field information cannot be obtained by simply sampling at high speed. This problem can be solved by interleaved sampling described later.
- FIG. 19 shows an adaptive compensation type photoelectric receiver suitable for compensating for a self-phase modulation effect, which is a kind of nonlinear effect generated in an optical fiber, as a modification of the complete optical field receiver 200 described above.
- the structure of is shown.
- complete electric field information is not necessarily required for compensation of the self-phase modulation effect, the other types of optical electric field receivers described in the first to sixth embodiments are applied to the adaptive compensation type. But ...
- the optical multilevel signal transmitter 210 transmits an 8-level APSK signal to the optical fiber.
- the phase point arrangement of the transmission light electric field 204 is a quaternary phase point arranged radially on a concentric circle of binary amplitude.
- the phase point arrangement of the optical electric field that has passed through the optical fiber is such that the phase point on the outer concentric circle rotates more than the phase point on the inner concentric circle, as indicated by the black circle in the frame 512, and the phase is changed at the inner and outer circumferences Deviation occurs in point arrangement.
- the self-phase modulation effect is a nonlinear effect. However, the effect can be counteracted by multiplying the received signal by the inverse operator exp (—jar (n) 2 ).
- the deviation minimizing control circuit 212 automatically sets the value of the compensation amount a to be applied to the compensation amount input terminal 207 of the electric field compensation circuit 202 so that the error of the compensated electric field signal output from the electric field compensator 202 is minimized.
- Adaptive compensation is realized by controlling the system.
- the quadrature circuit 211 causes the phase of each phase point to be quadrupled. For example, it should always be a constant value. However, if the phase point shifts due to the self-phase modulation effect, the output of the quadruple circuit will vary for each symbol.
- the phase point arrangement of the electric field signal 203 output from the electric field compensation circuit 202 can always be corrected to the optimum arrangement.
- the signal degradation due to the self-phase modulation effect is the same for the optical signal other than the APSK signal, and the adaptive compensation type optical electric field receiver according to the present invention can be applied to other modulation systems.
- FIG. 20 shows an embodiment in which the complete optical field receiver 200 according to the present invention is applied to wavelength dispersion compensation of a binary intensity modulation signal.
- Ordinary binary modulation is used when the light intensity at the space level with an extinction ratio of about 10 dB is low. If the extinction ratio is about this level, the electric field amplitude ratio is about 3, so that the signal level has no operational problem for the optical electric field receiver 200 of the present invention. However, if the extinction ratio is very high (for example, about 20 dB), or if the light intensity at the sampling point decreases to near zero due to waveform deterioration that occurs in the optical fiber transmission line, the optical electric field receiver 200 operates normally. There is a possibility that will not.
- This embodiment is characterized in that, in order to operate the optical electric field receiver 200 normally when the extinction ratio is very high, the space level is intentionally set high and the extinction ratio is deteriorated.
- the optical electric field 205 received by the optical electric field receiver 200 due to the chromatic dispersion of the optical fiber is as shown in the frame 522. Deteriorates greatly.
- the electric field calculation unit 208 of the optical electric field receiver 200 shifts the sampling point from the center of the symbol as indicated by the white circle of the reproduction optical electric field signal 117 shown in the frame 523, and the symbol width is 25%. By setting the time point to 75%, the sampled optical electric field intensity is unlikely to become zero.
- the influence of the chromatic dispersion is compensated by calculating the transfer function having the opposite characteristic to the chromatic dispersion in the electric field compensation circuit 202 with respect to the output signal 117 from the electric field calculation unit 208.
- An electric field signal is obtained.
- the signal waveform reproduced from the electric field signal 203 output from the electric field compensation circuit 202 is: Since the sampling points are shifted, in this embodiment, the amplitude signal r (n) is input to the re-sampling circuit 192, and the sample value at the center of the symbol waveform is determined by the binary determination circuit 152. A reproduced binary digital signal 153 is obtained.
- the output of the resampling circuit 192 is branched to the eye opening detection circuit 214, and the eye opening detection circuit 214 detects the size of the eye opening of the signal after electric field compensation.
- the eye dispersion detection result is input to the control circuit 215, and the control circuit 215 controls the compensation amount of the electric field compensation circuit 202 so as to maximize the value of the eye opening, thereby realizing adaptive dispersion compensation.
- the complete optical electric field receiver according to the present invention functions as a coherent receiver, and can compensate for chromatic dispersion dynamically and without limitation by arithmetic processing using an electric circuit.
- the complete optical electric field receiver according to the present invention is applied to reception of various optical signals such as binary intensity-modulated light other than multilevel signals, duobinary signals, and binary phase-modulated signals. it can .
- various optical signals such as binary intensity-modulated light other than multilevel signals, duobinary signals, and binary phase-modulated signals. it can .
- a wavelength dispersion compensator is unnecessary and the optical transmission distance can be greatly increased.
- the optical signal intensity is always “0” between bits.
- the original signal waveform can be reduced by reducing the extinction ratio of RZ modulation or shifting the sampling timing. It can be played back.
- FIG. 21 shows an embodiment of a wavelength division multiplexing optical transmission system to which the optical electric field receiver of the present invention is applied.
- a wavelength division multiplexing transmission apparatus 220A is an optical transmitter 226-1A coupled to a wavelength multiplexer 223A. 226-3A and optical field receivers 200-1A to 200-3A of the present invention coupled to wavelength demultiplexer 224A.
- the wavelength multiplexing transmission device 220B includes optical transmitters 226-1B to 226-3B coupled to the wavelength multiplexer 223B and an optical electric field receiver 200-1B to the present invention coupled to the wavelength demultiplexer 224B. 200—Including 3B.
- the wavelength division multiplexing transmission apparatuses 220A and 220B are connected by an upstream optical transmission path and a downstream optical transmission path.
- the upstream optical transmission line consists of optical finos 206-1 to 206-3 and optical amplifiers 225-1, 22 5-2, and the downstream optical transmission line consists of optical fines 206-4 to 206-6 and optical amplifiers. 225-3, 225-4, and so on.
- the optical transmitters 226-1A to 226-3A of the wavelength division multiplexing transmission device 220A are different from each other. An optical signal is transmitted at wavelengths ⁇ 1 to 3. These optical signals are multiplexed by the wavelength multiplexer 223 ⁇ , then output to the upstream optical transmission line, separated for each wavelength by the wavelength demultiplexer 224 ⁇ of the opposite optical transmission device 220 ⁇ , and the optical electric field receiver 200 — 1 ⁇ ⁇ 200— It is input in 3 ⁇ .
- the optical transmitters 226-1 to 226-3 of the wavelength multiplexing transmission apparatus 220 also transmit optical signals at different wavelengths ⁇ 1 to 3 respectively.
- optical signals are combined by the wavelength multiplexer 223 ⁇ , then output to the downstream optical transmission line, separated for each wavelength by the wavelength demultiplexer 224 ⁇ of the optical transmission device 220 ⁇ , and the optical electric field receiver 200-1 ⁇ ⁇ 200—Entered in 3 ⁇ .
- the upstream optical transmission line and the downstream optical transmission line may have different optical wavelengths to be multiplexed.
- the wavelength multiplexing transmission device 220 includes a terminal control unit 221 (221) and a database 222 (222)! / Speak.
- the optical transmitters 226-1 ⁇ to 226-3 ⁇ (226 -1 ⁇ to 226-3 ⁇ ) and the optical electric field receivers 200-1 ⁇ to 200 ⁇ 3 ⁇ (200 ⁇ 1 ⁇ to 200 ⁇ 3 ⁇ ) receive transmission data from the outside. It is input and the received data is output to the outside, but it is omitted in the figure.
- a data table indicating the chromatic dispersion amount of each optical fiber forming the optical transmission line is stored in correspondence with the reception wavelengths ⁇ 1 to 3.
- FIG. 22 shows a flowchart of a compensation amount setting routine executed by the station control unit 221 A (221B). This routine is executed when the wavelength multiplex transmission device is activated or reset, or when the transmitter / receiver 226 (226-1A to 226-3A) or 200 (200-1A to 200-3A) is reset.
- Terminal station controller 221A reads the chromatic dispersion amount data table from database 222A, and sets parameter i for specifying the wavelength channel to an initial value "1" (step 601).
- the terminal station controller 221 A determines the received optical transmission line from the chromatic dispersion amount of each optical fiber corresponding to the wavelength ⁇ i of the i-th channel indicated by the chromatic dispersion amount data table.
- the total wavelength dispersion amount Di of all the optical fibers along the terminal station control unit 221-1 is calculated (step 603).
- the compensation amount “ ⁇ Di” is set to the terminal 207 of the optical field receiver 200-1A of the i-th channel (wavelength i), and the optical field receiver 200-1A is activated.
- the optical electric field receivers 200-1A to 200-3A can estimate the wavelength dispersion compensation amount with high accuracy from the time of startup, and thus no adaptive control is required. Even if adaptive control is used, it is possible to transition to an optimal control state in a short time and to prevent malfunction.
- FIG. 23 shows an embodiment of an optical network configuration including a plurality of optical add / drop devices (ADMs) 230-1 to 230-4 to which the optical electric field receiver of the present invention is applied.
- the optical head drop devices 230-1 to 230-4 are connected in a ring shape by optical fiber transmission lines 206-1 to 206-4.
- the optical signal path may be dynamically changed.
- the dispersion compensation amount in the optical receiver 200 affected by the path change is optimized by the control console 231 connected to the optical drop apparatus 230-1.
- 222 is a database 222 in which chromatic dispersion values for each wavelength are recorded for all optical fibers constituting the network.
- the control console 231 accesses the database 222, calculates the total chromatic dispersion value according to the new optical signal path and the used wavelength, and uses this value via the network as the new path. This is distributed as a dispersion compensation amount to the optical receiver 200 (200-1 to 200-3) connected to the optical add-drop device (230-2 to 230-4) that is the end of the network.
- the optical signal of wavelength 3 output from the optical transmitter 200-3 is input to the optical add / drop device 230-4, and the three optical signals along the optical path 232-3 It reaches the optical field receiver 200-3 connected to the optical drop device 230-3 via the fiber transmission paths 206-1, 206-2, 206-3.
- the control console 231 reads out the chromatic dispersion amount of the optical fiber transmission paths 206-1, 1, 206-2, 206-3 corresponding to the wavelength 3 from the database 222.
- the compensation setting signal determined from the total value is sent to the optical electric field receiver 200-3 through the communication path 23-3 shown by the broken line.
- the compensation amount setting signal is input to the compensation amount setting terminal 207-3, and thus the photoelectric amount setting signal is An optimum dispersion compensation value is set in the electric field compensation circuit 202 of the field receiver 200-3.
- FIG. 24 shows another embodiment of the optical multilevel signal receiver to which the optical electric field receiver according to the present invention is applied.
- the optical multilevel signal 123 is received by the optical delay detectors 201-1 and 201-2 of the complete optical electric field receiver described in FIG. 16, and the output of the electric field calculation unit 111 is used as the electric field compensation circuit 202.
- the phase fluctuation component is removed and the symbol of the multilevel signal is determined by inputting the electric field signals 203-1 and 203-2 after the electric field compensation to the symbol judgment unit 176 independent of the phase fluctuation. .
- a highly functional optical multilevel modulation signal receiver can be configured by connecting a symbol determination circuit, an equalization circuit such as FFE or DFE, an error correction circuit, etc., downstream of the optical electric field receiver. Is possible.
- FIG. 25 shows still another embodiment of the optical multilevel signal receiver to which the optical electric field receiver of the present invention is applied.
- the signal 203-1 indicating the amplitude component r (n)
- the signal 203-2 which is directly input to the determination unit 176 and indicates the phase component ⁇ (n), is input to the delay detection circuit 234 in the electrical domain, and the differential phase signal ⁇ (n) output from the delay detection circuit 234 Is supplied to the phase fluctuation independent symbol determination unit 176, thereby removing the phase fluctuation component and determining the symbol of the multilevel signal.
- the electric field compensation circuit 202 In order to perform complete dispersion compensation in the electric field compensation circuit 202, it is necessary to reproduce all-optical electric field information r (n) and ⁇ (n) in advance by the electric field calculation unit 111 in the previous stage. However, when a signal to which delay detection is applicable, such as an APSK signal, is used as a received signal, the electric field compensation circuit 202 compensates for it. Of the compensated electric field signal, the phase component ⁇ i (n) is input to the delay detection circuit 234 in the electrical domain, and the differential phase signal ⁇ ⁇ ( ⁇ ) is calculated and applied to symbol determination. This makes it possible to eliminate the effects of phase fluctuations.
- a signal to which delay detection is applicable such as an APSK signal
- FIG. 26 shows an optical multilevel signal receiver to which interleave sampling is applied as a fourteenth embodiment of the present invention.
- an optical delay detector 244-1 having a delay amount of 3 mm
- three AZD conversions 1 06—1 ⁇ to 106—3 ⁇ and 106—1 ⁇ to 106—3 ⁇ are connected to the balanced optical receivers 105-1 and 105-2 respectively.
- Three pairs of A ZD conversion outputs “xl, yl”, “x2, y2”, and “x3, y3” are respectively applied to the electric field calculation unit 111 1 to 11 1 3!
- the output signals 117-1 to 117-3 of L 11 3 are respectively input to symbol determination units 176-1 to 176-3 independent of phase fluctuations. By interleaving these three symbol judgment units, the circuit speed required for symbol judgment can be reduced to 1Z3.
- [0128] 240 is a frequency-divided clock source that generates a clock with a frequency of 1Z3T in synchronization with the received symbol timing.
- delay circuit 157 With delay time T and 2T, the phase difference of symbol time T A three-phase clock signal sequence with is generated.
- Three sets of AZD converters 106—iA, 106—iB (i l to 3) use these three-phase clock signals as sampling clocks, and output signals from balanced optical receivers 105-1, 105-2 Digitally.
- the delayed detection signals output from balanced optical receivers 105-1 and 105-2 are these three sets of AZD variation ⁇ , as shown by black circles, double circles, and white circles in Fig. 27 In addition, they are sampled by interleaving into three sequences on the time axis.
- the electric field calculation units 111-1 to L-11-3 perform the reproduction calculation of the optical electric field independently of each other. Can be executed.
- the regenerated optical electric field signals 1171 to 117-3 are subjected to phase fluctuation removal and symbol determination by individual symbol determination units 176-1 to 176-3, respectively.
- the three digital signals output from the symbol determination unit 176-1 to 176-3 are combined by a multiplexing circuit 243 and reproduced multi-value digital Signal 144 is output.
- the three series of phase points interleaved on the time axis are individually processed by the electric field calculation units 1111-1111 and correlated with each other. If the signal is supplied to the symbol determination circuits 176-1 to 176-3 without any error, there is a possibility of errors in phase and amplitude.
- the reproduction optical electric field signals 117-1 to 117-3 are branched to the electric field synchronization circuit 241, the average amplitude and average phase of the same phase point are compared with each other, and the difference is used as the correction signal 242.
- This is supplied to the symbol determination unit 176-1 to 176-3.
- Each symbol determination unit 176 performs normalization of the input signal amplitude and correction of the reference phase so that the amplitude and phase reference of the three systems of output signals always match according to the correction signal.
- the correction signal 242 is supplied to the electric field calculation units 111 1 to 111 3 instead of being supplied to the symbol determination unit 176, and each of the electric field calculation units 111 1 to 111 3 receives each output signal (reproduced optical electric field signal).
- 117— 1 to 1 17-3 Try to correct it.
- the number of interleavings and the sampling rate can be arbitrarily selected.
- the delay time of the optical delay detectors 201-1 and 201-2 is T and the sampling rate is 1ZT. If you do.
- the optical electric field receiver of the present invention uses an optical delay detector, and therefore does not depend on the polarization state of the input light and requires a local oscillation light source. do not do.
- the optical multilevel signal receiver shown in the embodiment can directly reproduce the two-dimensional coordinate information of the optical signal phase point in the electric field arithmetic circuit that processes the output signal of the optical delay detector.
- the symbol decision circuit connected to the arithmetic circuit enables batch judgment of multi-level symbols, and the optical multi-level signal receiver with a large multi-level number such as 32-value and 64-value with high transmission efficiency is comparatively small hardware. Can be realized on a scale.
- electric field calculation and multi-value determination can be executed by an electric digital circuit, so an adaptive receiver according to transmission line loss, signal SN ratio, deterioration factor, etc. can be easily obtained. realizable.
- an electric field compensation circuit is connected to an optical electric field receiver, linear transmission degradation such as chromatic dispersion and band degradation can be completely compensated theoretically, and the adaptive content can be changed dynamically. Dispersion compensation can also be realized.
- the present invention can be applied to, for example, an optical electric field waveform measuring apparatus and an optical space transmission apparatus in addition to a receiver for optical fiber communication.
- a receiver in the field of wireless communication generally uses a local oscillator and is configured to coherently receive an orthogonal component of an input electric field. This corresponds to the coherent optical transmission method shown in FIG. 2 in this specification.
- the polarization dependency of the received signal and the cost of the local oscillator do not matter, so such a coherent electric field receiver can be configured relatively easily.
- the present invention obtains the same effect as coherent detection using an optical delay detector without using a local oscillator, and has a different problem from that of a receiver in the wireless communication field.
- Delay detectors are also used in the wireless communication field. However, in the wireless communication field, it is common to generate a baseband signal by coherent quadrature detection using a local oscillator and apply delayed detection to the baseband signal.
- the optical delay detection of the present invention is applied to a complex optical signal that cannot be orthogonally separated, and has a different effect from the delay detection in wireless communication.
- the present invention can be applied to multi-value modulation signal reception with high transmission efficiency in the optical communication field.
- FIG. 1 An explanatory diagram of a modulation method applicable to optical transmission.
- FIG. 2 A configuration diagram (A) showing an example of a conventional coherent optical field receiver and a diagram (B) showing the effect of phase fluctuation.
- FIG. 3 Phase point arrangement (A) of 8-level amplitude phase modulation (APSK) signal and configuration diagram (B) of a conventional 8-APSK signal receiving optical multilevel signal receiver.
- APSK 8-level amplitude phase modulation
- FIG. 5 is a configuration diagram showing a first embodiment of an optical electric field receiver according to the present invention.
- FIG. 6 Diagram showing changes in electrical reception signal (A) and reproduction electric field signal (B) in the first embodiment. 7] Configuration diagram when the electric field calculation unit 111 in the first embodiment is parallelized.
- ⁇ 11 Configuration of optical multilevel signal receiver showing the third embodiment of the optical electric field receiver according to the present invention.
- ⁇ 12 Optical multilevel signal receiver showing the fourth embodiment of the optical electric field receiver according to the present invention.
- Configuration Diagram 13 Configuration diagram of an optical APSK signal receiver showing a fifth embodiment of the optical electric field receiver according to the present invention.
- Configuration diagram of an optical signal receiver for an N-value optical phase modulation signal showing a fifth embodiment of the optical electric field receiver according to the present invention.
- FIG. 16 is a configuration diagram of a complete optical field receiver showing a sixth embodiment of the optical field receiver according to the present invention.
- FIG. 19 is a configuration diagram of an adaptive compensation type optical electric field receiver showing an eighth embodiment of the optical electric field receiver according to the present invention.
- FIG. 20 is a configuration diagram of a photoelectric field receiver for a binary intensity modulation signal, showing a ninth embodiment of the optical electric field receiver according to the present invention.
- FIG. 23 A configuration diagram of an optical network such as a plurality of ADM cards, showing an eleventh embodiment of an optical electric field receiver according to the present invention.
- FIG. 24 is a configuration diagram of an optical multilevel signal receiver showing a twelfth embodiment of the optical electric field receiver according to the present invention.
- FIG. 25 is a configuration diagram of an optical multilevel signal receiver showing a thirteenth embodiment of an optical electric field receiver according to the present invention.
- FIG. 26 is a block diagram of an interleave sampling type optical multilevel signal receiver showing a fourteenth embodiment of the optical electric field receiver according to the present invention.
- FIG. 27 is an explanatory diagram of an interleave operation in the fourteenth embodiment.
- Optical field receiver 101: Input optical signal
- 102 Optical branch circuit
- 103 Optical signal path
- 10 Optical delay detector
- 105 Balanced optical receiver
- 106 AZD conversion
- 107 Sampler 108: Delay adjustment circuit
- 109 Electrical signal path
- 111 Electric field calculation unit
- 112 Square calculation circuit
- 113 Inverse tangent calculation circuit
- 115 Delay division circuit
- 121 Packet synthesis circuit, 123: Optical multilevel signal, 124: Optical APSK signal, 130: Local oscillation laser light source, 131: Polarization separation circuit, 132: Local light emission, 133: P polarization of optical multilevel signal Component, 13 4: S polarization component of optical multilevel signal, 136: phase diversity circuit, 137: 1 component output light, 1 38: Q component output light, 141: digital operation circuit, 143: symbol judgment circuit, 144: Reproduction Multilevel digital signal, 150: Optical branch circuit, 151: Optical intensity receiver, 152: Binary decision circuit, 1 53: Binary reproduction digital signal, 154: Adder, 155: Weighting circuit, 156: Four quadrant multiplication 157: delay circuit, 158: multiplication circuit, 159: binary differential phase modulated light, 160: square root circuit, 161: clock extraction circuit, 171: subtraction circuit, 174: phase fluctuation estimation circuit, 175: phase fluctuation Estimated value, 176: Symbol variation circuit independent
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Abstract
Description
Claims
Priority Applications (5)
Application Number | Priority Date | Filing Date | Title |
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PCT/JP2006/309498 WO2007132503A1 (ja) | 2006-05-11 | 2006-05-11 | 光電界受信器、光多値信号受信器および光伝送システム |
US12/300,212 US8873968B2 (en) | 2006-05-11 | 2006-05-11 | Optical field receiver, optical multilevel signal receiver, and optical transmission system |
EP06732529A EP2017980A4 (en) | 2006-05-11 | 2006-05-11 | OPTICAL ELECTRIC FIELD RECEIVER, OPTICAL MULTI-LEVEL SIGNAL RECEIVER AND OPTICAL TRANSMISSION SYSTEM |
JP2008515391A JP4791536B2 (ja) | 2006-05-11 | 2006-05-11 | 光電界受信器、光多値信号受信器および光伝送システム |
CN2006800545488A CN101438517B (zh) | 2006-05-11 | 2006-05-11 | 光电场接收器、光多值信号接收器以及光传送*** |
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PCT/JP2006/309498 WO2007132503A1 (ja) | 2006-05-11 | 2006-05-11 | 光電界受信器、光多値信号受信器および光伝送システム |
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US (1) | US8873968B2 (ja) |
EP (1) | EP2017980A4 (ja) |
JP (1) | JP4791536B2 (ja) |
CN (1) | CN101438517B (ja) |
WO (1) | WO2007132503A1 (ja) |
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EP2017980A1 (en) | 2009-01-21 |
US8873968B2 (en) | 2014-10-28 |
US20090208224A1 (en) | 2009-08-20 |
CN101438517A (zh) | 2009-05-20 |
CN101438517B (zh) | 2012-09-05 |
EP2017980A4 (en) | 2013-01-16 |
JP4791536B2 (ja) | 2011-10-12 |
JPWO2007132503A1 (ja) | 2009-09-17 |
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