CN116599590A - Optical self-interference elimination device and method for distributed in-band full duplex ROF system - Google Patents

Optical self-interference elimination device and method for distributed in-band full duplex ROF system Download PDF

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CN116599590A
CN116599590A CN202310384049.0A CN202310384049A CN116599590A CN 116599590 A CN116599590 A CN 116599590A CN 202310384049 A CN202310384049 A CN 202310384049A CN 116599590 A CN116599590 A CN 116599590A
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modulator
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dmzm
optical
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朱子行
李�赫
赵尚弘
高从芮
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Air Force Engineering University of PLA
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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
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
    • 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
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2575—Radio-over-fibre, e.g. radio frequency signal modulated onto an optical carrier
    • H04B10/25752—Optical arrangements for wireless networks
    • H04B10/25758—Optical arrangements for wireless networks between a central unit and a single remote unit by means of an optical fibre
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

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  • Engineering & Computer Science (AREA)
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  • Optical Communication System (AREA)

Abstract

An optical self-interference cancellation device for a distributed in-band full duplex ROF system includes a central station, a remote base station, and a transmission medium. The central station comprises an optical power amplifier and a photoelectric detector; the remote base station comprises a double-parallel double-drive Mach-Zehnder modulator, an electric attenuator, an electric delay line, a laser, a local oscillation signal source (11), a 180-degree electric coupler, three direct current sources, a transmitting module, a transmitting antenna and a receiving antenna. An optical self-interference cancellation method for a distributed in-band full duplex ROF system is also disclosed. The invention directly realizes self-interference elimination in the optical domain, and avoids the influence of optical fiber transmission on SIC performance; the bandwidth requirement of the central station signal demodulation and the sampling rate requirement of the analog-to-digital converter are reduced by carrying out harmonic down-conversion on the high-frequency radio frequency signal to the same intermediate frequency; the frequency conversion efficiency is improved while the DIPF effect is compensated, so that useful signals of a plurality of remote base stations are transmitted to the same central station, the structural complexity of the base stations is greatly simplified, and the signal transmission quality is improved.

Description

Optical self-interference elimination device and method for distributed in-band full duplex ROF system
Technical Field
The invention relates to the field of microwave photon signal processing, in particular to an optical self-interference elimination device and method for a distributed in-band full duplex ROF system, wherein the device has self-interference elimination capability, harmonic mixing capability and frequency conversion efficiency optimization.
Background
The radio-on-fiber (ROF) system uses low-loss light optical fiber as medium, uses broadband high-frequency optical wave as carrier wave to transmit radio-frequency signals, and uses stable optoelectronic integrated devices to replace part of electrical devices, so that the system has great advantages in aspects of system size, quality, power consumption, stability, cost and bandwidth, and is widely concerned. In general, a remote base station of a full duplex RoF system receives an uplink signal of a user on a certain frequency band, and simultaneously transmits a downlink signal on another different frequency band, so that a large frequency gap between a transmission frequency band and a receiving frequency band causes no interference between receiving and transmitting ends of the base station. However, the limited spectrum resources and the ever-increasing demand for higher data rates have motivated the development of the in-band full duplex (IBFD) regime. Under the system, the uplink signal and the downlink signal are positioned in the same frequency band, so that the IBFD RoF system can theoretically obtain double frequency spectrum utilization rate. In this case, however, the transmitted signal leaks from the transmitter to its own receiver and is converted to the same intermediate frequency together with the useful Signal (SOI), and cannot be simply filtered out by an electrical filter, thereby causing interference to demodulation and recovery of the useful signal, which is called a self-interference (SI) signal. The potential of IBFD RoF systems can only be truly exploited after the self-interference problem is resolved.
The self-interference cancellation (SIC) scheme based on the electrical principle is widely studied and has remarkable results, but because of the electronic bottleneck, the SIC system is limited in frequency range and bandwidth, while the photon-assisted SIC scheme has the advantages of low loss, wide bandwidth, high frequency band and the like, and becomes the focus of attention. Most of the photon-assisted SIC schemes today achieve self-interference cancellation in the electrical domain after photo-detection, while the self-interference signal is still included in the optical signal before photo-detection. Since these methods focus only on the cancellation of self-interference signals, they are more suitable for use in a user terminal scenario where the received signal is directly used or processed. At the remote base station of the IBFD RoF system, however, the received radio frequency signal is converted to an optical signal and then transmitted over an optical fiber to a central station. The optical fiber dispersion can cause the phase relation between the optical sidebands to change, when the frequency of a radio frequency signal is low, the influence caused by the optical fiber dispersion is small and can be ignored, and for a high-frequency radio frequency signal, the optical fiber dispersion can influence the effectiveness of SIC, and the optical fiber dispersion has serious Dispersion Induced Power Fading (DIPF) effect after long-distance optical fiber transmission, thereby causing self-interference elimination, frequency conversion of a useful signal and transmission performance deterioration.
Disclosure of Invention
In view of the problems of the prior art, there is provided herein an optical self-interference cancellation device for a distributed in-band full duplex ROF system, comprising a central station, a remote base station, and a transmission medium; wherein the method comprises the steps of
The central station comprises an optical power amplifier 4 and a photoelectric detector 5; the remote base station comprises a double-parallel double-drive Mach-Zehnder modulator DP-DMZM 2, an electric attenuator 9, an electric delay line 10, a laser 1, a local oscillation signal source 11, a 180-degree electric coupler 12, a first direct current source a 13, a second direct current source b 14, a third direct current source c15, a transmitting module 8, a transmitting antenna 7 and a receiving antenna 6; and wherein
The output end of the distributed feedback laser 1 is connected with the optical input end of the double parallel-double driving Mach-Zehnder modulator DP-DMZM 2;
the DP-DMZM 2 is internally provided with two parallel arms, and a double-drive-Mach-Zehnder modulator is respectively embedded into the two arms to serve as a sub-modulator, namely a sub-modulator a and a sub-modulator b; the upper arm of the main modulator is provided with a main modulator direct current bias point input port 2-7; the sub-modulator a is provided with two radio frequency input ports (2-1, 2-2) and a sub-modulator direct current bias point input port 2-5; the sub-modulator b is provided with two radio frequency input ports (2-3, 2-4) and a sub-modulator direct current bias point input port 2-6; the optical carrier radio frequency signal output by the upper arm sub-modulator a and the optical carrier radio frequency signal output by the lower arm sub-modulator b are coupled and output again at the output end of the DP-DMZM 2;
a single-mode optical fiber 3, the input end of which is connected with the optical output end of the DP-DMZM 2;
an optical power amplifier 4, the input end of which is connected with the output end of the single-mode optical fiber 3;
the input end of the photoelectric detector 5 is connected with the output end of the optical power amplifier 4;
a receiving antenna 6, the receiving end of which faces the wireless channel, and the output end of which is connected with the second radio frequency input end 2-2 of the DP-DMZM 2 up-branch sub-modulator a;
a transmitting antenna 7, the transmitting end of which faces the wireless channel, wherein the signal leaked from the transmitting antenna 7 into the receiving antenna 6 is SI signal, and the input end of the transmitting antenna 7 is connected with one output end of the transmitting module 8;
a transmitting module 8, one output end of which is connected with the input end of the transmitting antenna 7, and the other output end of which is connected with the input end of the electric attenuator 9;
an electric attenuator 9 which receives the REF signal from the transmitting module 8, the output of the electric attenuator 9 being connected to the input of an electric delay line 10;
an electrical delay line 10 which receives the amplitude adjustable REF signal from the electrical attenuator 9 and has an output connected to the first radio frequency input 2-1 of the upper branch of the DP-DMZM 2;
the output end of the local oscillation signal source 11 is connected with the input end of the 180-degree electric coupler 12;
a 180 DEG electric coupler 12 which receives the LO signal from the local oscillation signal source 11 and the output end of which is respectively connected with the first radio frequency input end 2-3 and the second radio frequency input end 2-4 of the DP-DMZM 2 down-branch sub-modulator b;
a first direct current source a 13, the output end of which is connected with the direct current input end 2-5 of the DP-DMZM 2 up-branch sub-modulator a;
a second DC source b 14, the output end of which is connected with the DC input end 2-6 of the DP-DMZM 2 down-branch sub-modulator b;
and the output end of the third direct current source c15 is connected with the direct current input ends 2-7 of the main modulator of the DP-DMZM 2.
In one embodiment of the invention, the transmission medium employs a single mode optical fiber 3.
The optical self-interference elimination method for the distributed in-band full-duplex ROF system is based on the optical self-interference elimination device of the distributed in-band full-duplex ROF system, and specifically comprises the following steps:
(1) The optical carrier is generated by the distributed feedback laser 1 and injected into the DP-DMZM 2;
the distributed feedback laser 1 generates an optical carrier wave, which is injectedDP-DMZM 2 is equally divided into an upper path and a lower path with equal power at the optical input end of the modulator, and the upper path and the lower path enter an upper sub-modulator a and a lower sub-modulator b respectively; assume that the generated optical carrier is E c (t)＝E c expjω c t, wherein E c Is the amplitude, omega of the carrier wave c Representing the angular frequency of the optical carrier;
(2) The optical carrier entering the DP-DMZM 2 upper sub-modulator a is modulated by the mixed receiving signal and RI signal which are received by the receiving antenna 6 and comprise SOI signal and SI signal in the upper sub-modulator a, and the first direct current source a 13 introduces direct current bias in the upper sub-modulator; the method comprises the following steps:
assume that the SOI signal received by the receiving antenna 6 isThe SI signal isExtracting the REF signal back to the system device by the transmitting module 8 as +.>Wherein V is SOI 、V SI 、V REF Voltages, ω, of the SOI signal, the SI signal, and the REF signal, respectively SOI ω SI 、ω REF Angular frequencies of SOI signal, SI signal, REF signal, respectively, +.>The initial phases of the SOI signal, the SI signal and the REF signal are respectively;
wherein, the mixed receiving signal comprising SOI signal and SI signal is injected by the second radio frequency input port 2-2 of the sub-modulator a on the DP-DMZM 2; the REF signal which is extracted by the transmitting module 8 and transmitted back to the system device is firstly subjected to amplitude tuning through the electric attenuator 9, then subjected to delay tuning through the electric delay line 10, and then injected by the first radio frequency input port 2-1 of the sub-modulator a on the DP-DMZM 2; the voltage of the first DC source a 13 is set to V π ，V π For half-wave voltage of DP-DMZM-2, thereby modulating at the upper sub-levelThe upper and lower paths of the modulator a introduce pi phase to bias the sub-modulator a at the minimum transmission point;
therefore, the optical carrier microwave signals at the output end of the sub-modulator a on the DP-DMZM 2 are respectively:
wherein beta is SOI ＝πV SOI /V π 、β SI ＝πV SI /V π 、β REF ＝πV REF /V π Modulation coefficients of the SOI signal, the SI signal and the REF signal respectively;
the first-order sidebands are obtained by spreading the Bessel function and reserving the first-order sidebands under small signal modulation:
wherein J 0 (β i )、J 1 (β i ) A 0 or 1 order first class Bessel function for the corresponding signal; j (J) n (β i )、J k (β i )、J m (β i ) N, k or m order Bessel functions of the first class of the corresponding signals; i can be expressed as SOI\SI\REF;
(3) The electric attenuator 9 and the electric delay line 10 are regulated, so that the self-interference signal in the optical-carrier microwave signal output by the upper sub-modulator a is directly eliminated in an optical domain; the method comprises the following steps:
as seen from equation (2), adjusting the electrical attenuator 9, electrical delay line 10 can change the amplitude and delay of the REF signal to meet at the same timeJ 0 (β SOI )J 1 (β SI )＝J 1 (β REF ) Under two conditions, the SI modulation sidebands and the REF modulation sidebands meet the conditions of equal amplitude, delay matching and pi phase difference, so that the self-interference elimination on the optical domain is realized at the output end of the upper sub-modulator a, and at the moment, the upper sub-modulator a is arrangedThe output signal of the sub-modulator a is:
(4) The optical carrier wave entering the DP-DMZM 2 for being downloaded is modulated by the LO signal in the lower sub-modulator b, and the second direct current source b 14 introduces direct current bias in the lower sub-modulator b; the method is as follows;
assume that the LO signal generated by local oscillator signal source 11 isWherein V is LO Is the voltage of the LO signal omega LO For the angular frequency of the LO signal, +.>Is the initial phase of the LO signal;
the LO signal generated by the local oscillation signal source 11 is firstly output to the 180-degree electric coupler 12, and the 180-degree electric coupler 12 equally divides the LO signal into two paths with equal power and opposite phases; one path of LO signal with unchanged phase output by the 180 DEG electric coupler 12 is injected by the first radio frequency input port 2-3 of the DP-DMZM 2 lower sub-modulator b; the other path of phase-inverted LO signal output by the 180 DEG electric coupler 12 is injected by the second radio frequency input port 2-4 of the DP-DMZM 2 lower sub-modulator b; the voltage of the second DC source b 14 is set to V biasb Thereby introducing adjustable phase modulation in the upper and lower paths of the lower sub-modulator bTo achieve different modulation formats;
therefore, the optical carrier microwave signal at the output end of the sub-modulator b of the DP-DMZM 2 is as follows:
wherein beta is LO ＝πV LO /V π Is the modulation factor of the LO signal; by means of BesselThe spread of the Alf is:
wherein J n (β LO ) N-order first class Bessel function for LO signal
(5) Adjusting the direct current bias introduced by the second direct current source b 14 in the DP-DMZM 2 lower branch sub-modulator b to enable the sub-modulator b to generate different LO signal modulation sidebands; the method comprises the following steps:
when the second direct current source b 14 is used for modulating the direct current introduced by the sub-modulation b of the lower branch of the DP-DMZM 2 to be V π When, i.eIn this case, the LO signal generated by the sub-modulator b modulates the sidebands, and the carrier and the even-order sidebands are suppressed, and only the odd-order sidebands remain, expressed as:
wherein l is a positive integer; as described above, the carrier suppressed double sideband signal of (2 l-1) order is preserved;
when the second DC source b 14 introduces a DC bias of V in the DP-DMZM 2 lower arm sub-modulator b π 2, i.eIn this case, the LO signal generated by the sub-modulator b modulates the sidebands, and the odd-order sidebands are suppressed, and only the even-order sidebands and the carrier wave remain, expressed as:
as described above, the 2 l-order carrier suppressed double sideband signal is preserved; if the amplitude of the LO signal generated by the local oscillation source 11 is adjusted at this time, the modulation factor of the LO signal is such that beta LO =2.405, i.e. J 0 (β LO ) When=0, the carrier is suppressed, and only 2 l-order carrier suppression double-sideband signals are reserved; therefore, the optical carrier radio frequency signals output by the DP-DMZM 2 down-branch sub-modulator b are unified as follows:
wherein r is a positive integer;
(6) The optical carrier microwave signals output by the upper sub-modulator and the lower sub-modulator are coupled at the output end of the DP-DMZM 2, and a third direct current source c15 introduces direct current bias into the upper path and the lower path of the main modulator; the method comprises the following steps:
after optical domain cancellation of self-interference and specific order carrier suppression double-sideband signal generation are realized, optical carrier microwave signals output by an upper sub-modulator and a lower sub-modulator are coupled at the output end of the DP-DMZM 2, and a direct current bias voltage of a main modulator introduces a phase difference in the upper path and the lower path, so that the output signals of the DP-DMZM 2 are as follows:
wherein the method comprises the steps ofIs the phase difference introduced between the output signals of the upper and lower sub-modulators,/and->By regulating the voltage V of a third DC source c15 connected to the DC input ports 2-7 of the DP-DMZM 2 main modulator bias Phase tuning is realized;
(7) The coupled optical signal output by the DP-DMZM 2 is transmitted in a long distance through the single mode optical fiber 3, and meanwhile, a dispersion phase is introduced;
the transfer function of a single mode fiber is expressed as:
H(jω)＝exp[-αL/2+jβ 2 L(ω-ω c ) 2 /2] (10)
wherein, alpha and L are dividedAttenuation coefficient and length, beta, of single mode fiber 2 The second-order dispersion coefficient of the single-mode fiber, wherein omega represents the angular frequency of a signal passing through the single-mode fiber; the output signal through the single mode fiber 3 is:
(8) The optical carrier microwave signal which is transmitted in a long distance through the single-mode fiber 3 is subjected to power amplification to realize photoelectric conversion, and meanwhile, the parameter compensation DIPF effect is adjusted to improve the frequency conversion efficiency; the method comprises the following steps:
the optical carrier microwave signal output by the single-mode fiber 3 is injected into the optical power amplifier 4 for power amplification, and the gain of the optical power amplifier 4 is denoted as G EDFA Subsequently, the optical carrier microwave signal output from the optical power amplifier 4 is injected into the photodetector 5 to realize photoelectric conversion; the electrical signal output by the photodetector 5 is:
wherein a= -4RG EDFA E c 2 e -αL J 1 (β SOI )J 0 (β SI )J r (β LO ) R is the responsivity of the photodetector 4, G EDFA Is the gain of the optical power amplifier 4; from equation (14), the up-down-converted signal generated by the beat frequency of the SOI signal and the LO signal is preserved, but for a particular caseThe amplitude of the obtained down-conversion intermediate frequency IF signal periodically changes along with the angular frequency of the optical fiber length L, SOI signal and the LO signal, so that the frequency is influenced by the dispersion induced power fading DIPF effect; by regulating the voltage V of the third DC source c15 bias Thereby changing->Can meet->At this time, the amplitude of the IF signal will remain the largest, compensating for the DIPF effect, and the output signal of the photodetector 5 is:
the conversion gain of a receiver is defined as the power ratio between the IF signal and the RF signal, in particular:
wherein R is out And R is in Matching impedance of output and input ends, P out And P in The power at the output and input, respectively.
The apparatus and method of the present invention can be applied to a distributed in-band full duplex RoF system. After antenna units of a plurality of remote base stations of the distributed system receive useful radio frequency signals, self-interference elimination is directly realized in an optical domain through the device, and the influence of optical fiber transmission on SIC performance is avoided; the device can also carry out harmonic down-conversion on the high-frequency radio frequency signal to the same intermediate frequency so as to reduce the bandwidth requirement of central station signal demodulation and the sampling rate requirement of an analog-to-digital converter; in addition, the frequency conversion efficiency can be improved while the DIPF effect is compensated by adjusting parameters, so that useful signals of a plurality of remote base stations are transmitted to the same central station through optical fibers to realize signal processing, the structural complexity of the base stations is greatly simplified, and the signal transmission quality is improved.
Drawings
FIG. 1 is a schematic diagram of a scenario in which the present invention is applied to a distributed in-band full duplex ROF system;
FIG. 2 is a schematic diagram of an optical self-interference cancellation device according to the present invention;
fig. 3 is an internal structure of an integrated dual parallel-dual drive mach-zehnder modulator.
Detailed description of the preferred embodiments
The invention is further described below with reference to the accompanying drawings:
fig. 1 is a schematic diagram of a scenario in which the present invention is applied to a distributed in-band full duplex ROF system, and in which a central station and a plurality of remote base stations are zoomed out and separated by optical fibers; at the remote base station, performing electro-optical modulation and self-interference elimination on the signal received from the central station to obtain an optical carrier radio frequency signal after self-interference elimination; the remote base stations disposed at the same adjacent positions transmit the optical carrier radio frequency signals to the central station through the optical fibers by wavelength division multiplexing, and down-conversion and subsequent signal processing are carried out in the central station.
Fig. 2 is a schematic structural diagram of an optical self-interference cancellation device according to the present invention when a single base station is shown, where the device specifically includes:
the distributed feedback laser 1 is used for providing a high-quality low-phase-noise light source, and the output end of the distributed feedback laser is connected with the optical input end of the double parallel-double driving Mach-Zehnder modulator DP-DMZM 2;
fig. 3 is a diagram showing an internal structure of a dual parallel-dual drive mach-zehnder modulator DP-DMZM 2 for modulating an optical carrier, which has two parallel arms inside, and one dual drive-mach-zehnder modulator is embedded as a sub-modulator (sub-modulator a and sub-modulator b) respectively. The upper arm of the main modulator is provided with a main modulator direct current bias point input port 2-7; the sub-modulator a is provided with two radio frequency input ports (2-1, 2-2) and a sub-modulator direct current bias point input port 2-5; the sub-modulator b has two radio frequency input ports (2-3, 2-4) and a sub-modulator dc bias point input port 2-6. The voltage input by the direct current bias point input port 2-7 of the main modulator leads the optical carrier radio frequency signal output by the sub-modulator a into the phase difference tuned by the bias voltage of the main modulator, the optical carrier radio frequency signal output by the sub-modulator a of the upper arm and the optical carrier radio frequency signal output by the sub-modulator b of the lower arm after the phase difference tuned by the bias voltage of the main modulator are coupled and output again at the output end of the DP-DMZM 2.
The input end of the single-mode fiber 3 is connected with the optical output end of the DP-DMZM 2 and is used for introducing different chromatic dispersion for optical sidebands with different wavelengths, generating optical carrier radio frequency signals with different chromatic dispersion induction phases and realizing remote transmission of the signals;
the input end of the optical power amplifier 4 is connected with the output end of the single-mode optical fiber 3 and is used for amplifying the power of the optical signal after optical fiber transmission to form an optical carrier radio frequency signal after power amplification;
the input end of the photoelectric detector 5 is connected with the output end of the optical power amplifier 4 and is used for converting the optical carrier radio frequency signal into an electric signal and outputting the electric signal;
a receiving antenna 6, the receiving end of which faces the wireless channel, and the output end of which is connected with the second radio frequency input end 2-2 of the DP-DMZM 2 up-branch sub-modulator a and is used for receiving a mixed receiving signal containing a self-interference Signal (SI) and a useful Signal (SOI);
a transmitting antenna 7, the transmitting end of which faces the wireless channel, and the transmitting signal will enter the free space for propagation, wherein the signal leaked by the transmitting antenna 7 into the receiving antenna 6 is SI signal, and the input end of the transmitting antenna 7 is connected with one output end of the transmitting module 8;
a transmitting module 8, one output end of which is connected with the input end of the transmitting antenna 7, and the other output end of which is connected with the input end of the electric attenuator 9, wherein the transmitting module 8 is used for generating and processing a transmitting signal, and extracting the transmitting signal and transmitting the transmitting signal back to the electric attenuator 9 to be used as a Reference (REF) signal for self-interference elimination;
an electric attenuator 9 which receives the REF signal from the transmitting module 8, adjusts the power of the REF signal, generates an amplitude-adjustable REF signal and outputs the REF signal, and the output end of the electric attenuator 9 is connected with the input end of the electric delay line 10;
an electric delay line 10 which receives the amplitude-adjustable REF signal from the electric attenuator 9, carries out delay adjustment on the signal, generates and outputs the delay-adjustable REF signal, and the output end of the electric delay line is connected with the first radio frequency input end 2-1 of the DP-DMZM 2 upper branch;
a local oscillation signal source 11, the output end of which is connected with the input end of a 180 DEG electric coupler 12 and is used for providing a Local Oscillation (LO) signal with adjustable frequency and amplitude;
the 180 DEG electric coupler 12 receives the LO signal from the local oscillation signal source 11, is used for dividing the LO signal into two paths with equal power and opposite phases and outputting the two paths, and the output end of the electric coupler is respectively connected with the first radio frequency input end 2-3 and the second radio frequency input end 2-4 of the DP-DMZM 2 lower branch sub-modulator b;
a first direct current source a 13, the output end of which is connected with the direct current input ends 2-5 of the DP-DMZM 2 up-branch sub-modulator a and is used for carrying out direct current bias on the sub-modulator a;
a second direct current source b 14, the output end of which is connected with the direct current input ends 2-6 of the DP-DMZM 2 down-branch sub-modulator b and is used for carrying out direct current bias on the sub-modulator b;
and the output end of the third direct current source c15 is connected with the direct current input ends 2-7 of the main modulator of the DP-DMZM 2 and is used for carrying out direct current bias on the main modulator.
The central station comprises an optical power amplifier 4 and a photoelectric detector 5; the remote base station comprises a double-parallel double-drive Mach-Zehnder modulator DP-DMZM 2, an electric attenuator 9, an electric delay line 10, a laser 1, a local oscillation signal source 11, a 180-degree electric coupler 12, three direct current sources (a first direct current source a 13, a second direct current source b 14 and a third direct current source c 15), a transmitting module 8, a transmitting antenna 7 and a receiving antenna 6; the transmission medium mainly adopts a single-mode optical fiber 3.
There is also provided an optical self-interference cancellation method for a distributed in-band full duplex ROF system, the method comprising the steps of:
(1) The optical carrier is generated by the distributed feedback laser 1 and injected into the DP-DMZM 2;
the distributed feedback laser 1 generates an optical carrier wave which is injected into the DP-DMZM 2 and is equally divided into an upper path and a lower path with equal power at the optical input end of the modulator, and the upper path and the lower path enter the upper sub-modulator a and the lower sub-modulator b respectively. For convenience of the following description, it is assumed that the generated optical carrier is E c (t)＝E c expjω c t, wherein E c Is the amplitude, omega of the carrier wave c Indicating the angular frequency of the optical carrier.
(2) The optical carrier entering the DP-DMZM 2 upper sub-modulator a is modulated by the mixed receiving signal and RI signal which are received by the receiving antenna 6 and comprise SOI signal and SI signal in the upper sub-modulator a, and the first direct current source a 13 introduces direct current bias in the upper sub-modulator; the method comprises the following steps:
for convenience of the following description, it is assumed that the SOI signal received by the receiving antenna 6 isSI signal is +.>Extracting the REF signal back to the system device by the transmitting module 8 as +.>Wherein V is SOI 、V SI 、V REF Voltages, ω, of the SOI signal, the SI signal, and the REF signal, respectively SOI 、ω SI 、ω REF Angular frequencies of SOI signal, SI signal, REF signal, respectively, +.>The initial phases of the SOI signal, the SI signal, and the REF signal, respectively.
Wherein, the mixed receiving signal comprising SOI signal and SI signal is injected by the second radio frequency input port 2-2 of the sub-modulator a on the DP-DMZM 2; the REF signal which is extracted by the transmitting module 8 and transmitted back to the system device is firstly subjected to amplitude tuning through the electric attenuator 9, then subjected to delay tuning through the electric delay line 10, and then injected into the first radio frequency input port 2-1 of the sub-modulator a on the DP-DMZM 2. The voltage of the first DC source a 13 is set to V π (V π Half-wave voltage of DP-DMZM-2) so that pi phase is introduced in the upper and lower paths of the upper sub-modulator a to bias the sub-modulator a at the minimum transmission point.
Therefore, the optical carrier microwave signals at the output end of the sub-modulator a on the DP-DMZM 2 are respectively:
wherein beta is SOI ＝πV SOI /V π 、β SI ＝πV SI /V π 、β REF ＝πV REF /V π The modulation coefficients of the SOI signal, SI signal, and REF signal, respectively, j being an imaginary number.
The first-order sidebands can be obtained by spreading the Bessel function and retaining them under small signal modulation (beta < 1):
wherein J 0 (β i )、J 1 (β i ) (i may be expressed as SOI\SI\REF) is a Bessel function of the first type, either 0 or 1, of the corresponding signal. J (J) n (β i )、J k (β i )、J m (β i ) Is a first class Bessel function of order n, k or m of the corresponding signal.
(3) The electric attenuator 9 and the electric delay line 10 are regulated, so that the self-interference signal in the optical-carrier microwave signal output by the upper sub-modulator a is directly eliminated in an optical domain; the method comprises the following steps:
as can be seen from equation (2), adjusting the electrical attenuator 9 and electrical delay line 10 can change the amplitude and delay of the REF signal to meet the requirements at the same timeJ 0 (β SOI )J 1 (β SI )＝J 1 (β REF ) When two conditions are met, the SI modulation sidebands and the REF modulation sidebands are equal in amplitude, are matched in time delay and have pi phase difference, so that self-interference elimination on an optical domain is realized at the output end of the upper sub-modulator a, and at the moment, the output signal of the upper sub-modulator a is as follows:
(4) The optical carrier wave entering the DP-DMZM 2 for being downloaded is modulated by the LO signal in the lower sub-modulator b, and the second direct current source b 14 introduces direct current bias in the lower sub-modulator b; the method comprises the following steps:
for convenience of description, it is assumed that LO signal generated by local oscillation signal source 11Number isWherein V is LO Is the voltage of the LO signal omega LO For the angular frequency of the LO signal, +.>Is the initial phase of the LO signal.
The LO signal generated by the local oscillation signal source 11 is firstly output to the 180 ° electric coupler 12, and the LO signal is equally divided into two paths with equal power and opposite phases by the 180 ° electric coupler 12. One path of LO signal with unchanged phase output by the 180 DEG electric coupler 12 is injected by the first radio frequency input port 2-3 of the DP-DMZM 2 lower sub-modulator b; another phase-inverted LO signal output via 180 ° electrical coupler 12 is injected by the second radio frequency input port 2-4 of the DP-DMZM 2 lower sub-modulator b. The voltage of the second DC source b 14 is set to V biasb Thereby introducing adjustable phase modulation in the upper and lower paths of the lower sub-modulator bTo achieve different modulation formats.
Therefore, the optical carrier microwave signal at the output end of the sub-modulator b of the DP-DMZM 2 is as follows:
wherein beta is LO ＝πV LO /V π Is the modulation factor of the LO signal. Also using Bessel function expansion can be obtained:
wherein J n (β LO ) N-order first class Bessel function for LO signal
(5) Adjusting the direct current bias introduced by the second direct current source b 14 in the DP-DMZM 2 lower branch sub-modulator b to enable the sub-modulator b to generate different LO signal modulation sidebands; the method comprises the following steps:
when the second direct current source b 14 is used for modulating the direct current introduced by the sub-modulation b of the lower branch of the DP-DMZM 2 to be V π When, i.eIn this case, the LO signal generated by the sub-modulator b modulates the sidebands, so that the carrier and the even-order sidebands are suppressed, and only the odd-order sidebands remain, which can be expressed as:
wherein l is a positive integer. As described above, the (2 l-1) order carrier-suppressed double sideband signals are preserved, such as + -1 order, + -3 order, + -5 order, etc.
When the second DC source b 14 introduces a DC bias of V in the DP-DMZM 2 lower arm sub-modulator b π 2, i.eIn this case, the LO signal generated by the sub-modulator b modulates the sidebands, and the odd-order sidebands are suppressed, and only the even-order sidebands and the carrier are reserved, which can be expressed as:
as described above, the carrier-suppressed double sideband signal of order 2 is retained, such as ±2, ±4, ±6, and the like. If the amplitude of the LO signal generated by the local oscillation source 11 is adjusted at this time, the modulation factor of the LO signal is such that beta LO =2.405, i.e. J 0 (β LO ) When=0, the carrier is suppressed, and only the carrier suppressed double sideband signal of order 2l remains. Therefore, the optical carrier radio frequency signal output by the DP-DMZM 2 down-arm sub-modulator b can be unified as follows:
wherein r is a positive integer.
(6) The optical carrier microwave signals output by the upper sub-modulator and the lower sub-modulator are coupled at the output end of the DP-DMZM 2, and a third direct current source c15 introduces direct current bias into the upper path and the lower path of the main modulator; the method comprises the following steps:
after optical domain cancellation of self-interference and specific order carrier suppression double-sideband signal generation are realized, optical carrier microwave signals output by an upper sub-modulator and a lower sub-modulator are coupled at the output end of the DP-DMZM 2, and a direct current bias voltage of a main modulator introduces a phase difference in the upper path and the lower path, so that the output signals of the DP-DMZM 2 are as follows:
wherein the method comprises the steps ofIs the phase difference introduced between the output signals of the upper and lower sub-modulators +.>By regulating the voltage V of a third DC source c15 connected to the DC input ports 2-7 of the DP-DMZM 2 main modulator bias Phase tuning is achieved.
(7) The coupled optical signal output by the DP-DMZM 2 is transmitted in a long distance through the single mode optical fiber 3, and meanwhile, a dispersion phase is introduced;
the transfer function of a single mode fiber can be generally expressed as:
H(jω)＝exp[-αL/2+jβ 2 L(ω-ω c ) 2 /2] (10)
wherein alpha and L are respectively the attenuation coefficient and length, beta of a single-mode optical fiber 2 Being the second order dispersion coefficient of a single mode fiber, ω represents the angular frequency of the signal passing through the single mode fiber. The output signal through the single mode fiber 3 can be written as:
(8) The optical carrier microwave signal which is transmitted in a long distance through the single-mode fiber 3 is subjected to power amplification to realize photoelectric conversion, and meanwhile, the parameter compensation DIPF effect is adjusted to improve the frequency conversion efficiency; the method comprises the following steps:
the optical carrier microwave signal output by the single-mode fiber 3 is injected into the optical power amplifier 4 for power amplification, and the gain of the optical power amplifier 4 can be expressed as G EDFA Subsequently, the optical carrier microwave signal output from the optical power amplifier 4 is injected into the photodetector 5 to realize photoelectric conversion. The electrical signal output by the photodetector 5 is:
wherein a= -4RG EDFA E c 2 e -αL J 1 (β SOI )J 0 (β SI )J r (β LO ) R is the responsivity of the photodetector 4, G EDFA Is the gain of the optical power amplifier 4. As can be seen from equation (14), the up-down converted signal generated by the beat frequency of the SOI signal and the LO signal is preserved, but for a particular caseThe amplitude of the resulting down-converted Intermediate Frequency (IF) signal will vary periodically with the angular frequency of the fiber length L, SOI signal and the LO signal, and thus be affected by the effect of Dispersion Induced Power Fading (DIPF). By regulating the voltage V of the third DC source c15 bias Thereby changing->Can satisfy->At this time, the amplitude of the IF signal will remain the largest, compensating for the DIPF effect, and the output signal of the photodetector 5 is:
in radio frequency receivers with self-interference cancellation and down-conversion functions, the power of the weak received radio frequency signal is typically relatively low. The frequency conversion gain is worth more attention to improve the signal reception quality. The conversion gain of a receiver is defined as the power ratio between the IF signal and the RF signal, in particular:
wherein R is out And R is in Matching impedance of output and input ends, P out And P in The power at the output and input, respectively. In theory, the conversion gain can be improved by adjusting the modulation index of the LO signal, and since dispersion induced power fading is compensated, the amplitude of the IF signal can be kept at a maximum at any frequency, and thus the conversion gain of the scheme is optimized over conventional Double Sideband (DSB) modulated links. Therefore, the invention can realize harmonic down-conversion of the input microwave signal, and can simultaneously realize self-interference elimination and DIPF effect compensation, thereby obtaining the maximum conversion gain.
The invention provides an optical self-interference elimination device and method applied to a distributed in-band full duplex ROF system, wherein the device utilizes a concise system structure, has self-interference elimination capability and harmonic mixing capability under the same hardware configuration, optimizes frequency conversion efficiency, solves the influence of self-interference signals and DIPF effects on signal transmission and receiving quality, and can obtain optimal frequency conversion efficiency so as to be more beneficial to the recovery of weak received signals; in addition, since the optical domain self-interference counteracts that no self-interference signal exists in the double-sideband modulated optical signal, the optical fiber dispersion does not cause the self-interference to reappear after photoelectric detection, which means that the self-interference cancellation performance is immune to the optical fiber dispersion; the invention can combine multiplexing to realize separation and remote transmission control of the central station and the remote base station, thereby providing realization strategy for large-scale, wide-bandwidth and large dynamic range distributed array system.

Claims (3)

1. An optical self-interference elimination device for a distributed in-band full duplex ROF system comprises a central station, a far-end base station and a transmission medium; it is characterized in that
The central station comprises an optical power amplifier (4) and a photoelectric detector (5); the remote base station comprises a double-parallel double-drive Mach-Zehnder modulator DP-DMZM (2), an electric attenuator (9), an electric delay line (10), a laser (1), a local oscillation signal source (11), a 180-degree electric coupler (12), a first direct current source a (13), a second direct current source b (14), a third direct current source c (15), a transmitting module (8), a transmitting antenna (7) and a receiving antenna (6); and wherein
The output end of the distributed feedback laser (1) is connected with the optical input end of the double parallel-double driving Mach-Zehnder modulator DP-DMZM (2);
two parallel arms are arranged in the DP-DMZM (2), and a double-drive-Mach-Zehnder modulator is respectively embedded into the two arms to serve as a sub-modulator, namely a sub-modulator a and a sub-modulator b; the upper arm of the main modulator is provided with a main modulator direct current bias point input port (2-7); the sub-modulator a is provided with two radio frequency input ports (2-1, 2-2) and a sub-modulator direct current bias point input port (2-5); the sub-modulator b is provided with two radio frequency input ports (2-3, 2-4) and a sub-modulator direct current bias point input port (2-6); the output of the upper arm sub-modulator a and the optical carrier radio frequency signal output by the lower arm sub-modulator b are coupled and output again at the output end of the DP-DMZM (2);
a transmission medium, the input end of which is connected with the optical output end of the DP-DMZM (2);
an optical power amplifier (4) with an input connected to the output of the transmission medium;
the input end of the photoelectric detector (5) is connected with the output end of the optical power amplifier (4);
a receiving antenna (6), the receiving end of which faces the wireless channel, and the output end of which is connected with a second radio frequency input end (2-2) of the DP-DMZM (2) upper branch sub-modulator a;
the transmitting antenna (7) faces the wireless channel, wherein a signal leaked into the receiving antenna (6) by the transmitting antenna (7) is an SI signal, and the input end of the transmitting antenna (7) is connected with one output end of the transmitting module (8);
the transmitting module (8) is connected with the input end of the transmitting antenna (7) at one output end and the input end of the electric attenuator (9) at the other output end;
an electric attenuator (9) receiving the REF signal from the transmitting module (8), the output of the electric attenuator (9) being connected to the input of an electric delay line (10);
an electrical delay line (10) which receives the amplitude-adjustable REF signal from the electrical attenuator (9) and has an output connected to the first radio frequency input (2-1) of the upper branch of the DP-DMZM (2);
the output end of the local oscillation signal source (11) is connected with the input end of the 180-degree electric coupler (12);
the 180-degree electric coupler (12) receives an LO signal from a local oscillator signal source (11), and the output end of the electric coupler is respectively connected with a first radio frequency input end (2-3) and a second radio frequency input end (2-4) of the DP-DMZM (2) lower branch sub-modulator b;
a first direct current source a (13) with an output end connected with a direct current input end (2-5) of the upper branch sub-modulator a of the DP-DMZM (2);
a second direct current source b (14) with an output end connected with the direct current input end (2-6) of the DP-DMZM (2) lower branch sub-modulator b;
and the output end of the third direct current source c (15) is connected with the direct current input end (2-7) of the main modulator of the DP-DMZM (2).
2. Optical self-interference cancellation device for a distributed in-band full duplex ROF system according to claim 1, characterized in that the transmission medium is a single mode optical fiber (3).
3. An optical self-interference cancellation method for a distributed in-band full duplex ROF system, which is based on the optical self-interference cancellation device of the distributed in-band full duplex ROF system according to claim 1, and is characterized by comprising the following steps:
(1) The optical carrier is generated by a distributed feedback laser (1) and injected into a DP-DMZM (2);
the distributed feedback laser (1) generates an optical carrier wave which is injected into the DP-DMZM (2) and is equally divided into upper and lower parts with equal power at the optical input end of the modulatorTwo paths of the two-way signal enter an upper sub-modulator a and a lower sub-modulator b respectively; assume that the generated optical carrier is E c (t)＝E c expjω c t, wherein E c Is the amplitude, omega of the carrier wave c Representing the angular frequency of the optical carrier;
(2) The optical carrier entering the DP-DMZM (2) upper sub-modulator a is modulated by a mixed receiving signal and an RI signal which are received by a receiving antenna (6) and comprise an SOI signal and an SI signal in the upper sub-modulator a, and a direct current bias is introduced into the upper sub-modulator by a first direct current source a (13); the method comprises the following steps:
assume that the SOI signal received by the receiving antenna (6) isSI signal is +.>The REF signal transmitted back to the system device is extracted by the transmitting module (8) as +.>Wherein V is SOI 、V SI 、V REF Voltages, ω, of the SOI signal, the SI signal, and the REF signal, respectively SOI 、ω SI 、ω REF Angular frequencies of SOI signal, SI signal, REF signal, respectively, +.>The initial phases of the SOI signal, the SI signal and the REF signal are respectively;
wherein a mixed reception signal comprising an SOI signal and an SI signal is injected from a second radio frequency input port (2-2) of the sub-modulator a on the DP-DMZM (2); the REF signal which is extracted by a transmitting module (8) and transmitted back to a system device is firstly subjected to amplitude tuning through an electric attenuator (9), then subjected to delay tuning through an electric delay line (10), and injected by a first radio frequency input port (2-1) of a sub-modulator a on the DP-DMZM (2); the voltage of the first DC source a (13) is set to V π ，V π For half-wave voltage of DP-DMZM-2, thereby modulating at the upper sub-levelThe upper and lower paths of the modulator a introduce pi phase to bias the sub-modulator a at the minimum transmission point;
therefore, the optical carrier microwave signals at the output end of the sub-modulator a on the DP-DMZM (2) are respectively:
wherein beta is SOI ＝πV SOI /V π 、β SI ＝πV SI /V π 、β REF ＝πV REF /V π Modulation coefficients of the SOI signal, the SI signal and the REF signal respectively;
the first-order sidebands are obtained by spreading the Bessel function and reserving the first-order sidebands under small signal modulation:
wherein J 0 (β i )、J 1 (β i ) A 0 or 1 order first class Bessel function for the corresponding signal; j (J) n (β i )、J k (β i )、J m (β i ) N, k or m order Bessel functions of the first class of the corresponding signals; i can be expressed as SOI\SI\REF;
(3) An electric attenuator (9) and an electric delay line (10) are regulated, so that self-interference signals in the optical-load microwave signals output by the upper sub-modulator a are directly eliminated in an optical domain; the method comprises the following steps:
as seen from the formula (2), the adjustment of the electric attenuator (9) and the electric delay line (10) can change the amplitude and the delay of the REF signal to simultaneously satisfyJ 0 (β SOI )J 1 (β SI )＝J 1 (β REF ) Under two conditions, the SI modulation sideband and the REF modulation sideband meet the conditions of equal amplitude, delay matching and pi phase difference, so that the output end of the upper sub-modulator a is realThe self-interference on the optical domain is eliminated, and at this time, the output signal of the upper sub-modulator a is:
(4) The optical carrier wave entering the DP-DMZM (2) for being downloaded is modulated by the LO signal in the lower sub-modulator b, and the second direct current source b (14) introduces direct current bias in the lower sub-modulator b; the method comprises the following steps:
assume that the LO signal generated by the local oscillation signal source (11) isWherein V is LO Is the voltage of the LO signal omega LO For the angular frequency of the LO signal, +.>Is the initial phase of the LO signal;
the LO signal generated by the local oscillation signal source (11) is firstly output to the 180-degree electric coupler (12), and the 180-degree electric coupler (12) equally divides the LO signal into two paths with equal power and opposite phases; one path of phase-unchanged LO signal output by the 180-degree electric coupler (12) is injected by a first radio frequency input port (2-3) of a sub-modulator b under the DP-DMZM (2); another path of phase-inverted LO signal output by the 180 DEG electric coupler (12) is injected by a second radio frequency input port (2-4) of the DP-DMZM (2) lower sub-modulator b; the voltage of the second DC source b (14) is set to V biasb Thereby introducing adjustable phase modulation in the upper and lower paths of the lower sub-modulator b To achieve different modulation formats;
therefore, the optical carrier microwave signal at the output end of the sub-modulator b of the DP-DMZM (2) is as follows:
wherein beta is LO ＝πV LO /V π Is the modulation factor of the LO signal; using Bessel function to develop to obtain:
wherein J n (β LO ) N-order first class Bessel function for LO signal
(5) Adjusting the direct current bias introduced by the second direct current source b (14) in the down-leg sub-modulator b of the DP-DMZM (2) to enable the sub-modulator b to generate different LO signal modulation sidebands; the method comprises the following steps:
when the second DC source b (14) is used for modulating the DC bias introduced by the sub-modulation b under the DP-DMZM (2) to V π When, i.eIn this case, the LO signal generated by the sub-modulator b modulates the sidebands, and the carrier and the even-order sidebands are suppressed, and only the odd-order sidebands remain, expressed as:
wherein l is a positive integer; as described above, the carrier suppressed double sideband signal of (2 l-1) order is preserved;
when the second DC source b (14) is under the DP-DMZM (2) and the DC bias introduced by the sub-modulator b is V π 2, i.eIn this case, the LO signal generated by the sub-modulator b modulates the sidebands, and the odd-order sidebands are suppressed, and only the even-order sidebands and the carrier wave remain, expressed as:
as described above, the 2 l-order carrier suppressed double sideband signal is preserved; if the amplitude of the LO signal generated by the local oscillation signal source (11) is adjusted at this time, the modulation factor of the LO signal is made to satisfy beta LO =2.405, i.e. J 0 (β LO ) When=0, the carrier is suppressed, and only 2 l-order carrier suppression double-sideband signals are reserved; therefore, the optical carrier radio frequency signals output by the DP-DMZM (2) down-branch sub-modulator b are unified as follows:
wherein r is a positive integer;
(6) The optical carrier microwave signals output by the upper sub-modulator and the lower sub-modulator are coupled at the output end of the DP-DMZM (2), and direct current bias is introduced into the upper path and the lower path of the main modulator by a third direct current source c (15); the method comprises the following steps:
after optical domain cancellation of self-interference and specific order carrier suppression double-sideband signal generation are realized, optical carrier microwave signals output by an upper sub-modulator and a lower sub-modulator are coupled at the output end of the DP-DMZM (2), and a phase difference is introduced into the upper path and the lower path by the direct current bias voltage of the main modulator, so that the output signals of the DP-DMZM (2) are as follows:
wherein the method comprises the steps ofIs the phase difference introduced between the output signals of the upper and lower sub-modulators,/and->By regulating the voltage V of a third DC source c (15) connected to the DC input ports (2-7) of the main modulator of the DP-DMZM (2) bias Realizing phase positionTuning;
(7) The coupled optical signal output by the DP-DMZM (2) is transmitted in a long distance through the single mode fiber (3), and meanwhile, a dispersion phase is introduced;
the transfer function of a single mode fiber is expressed as:
H(jω)＝exp[-αL/2+jβ 2 L(ω-ω c ) 2 /2] (10)
wherein alpha and L are respectively the attenuation coefficient and length, beta of a single-mode optical fiber 2 The second-order dispersion coefficient of the single-mode fiber, wherein omega represents the angular frequency of a signal passing through the single-mode fiber; the output signal through the single mode fiber (3) is:
(8) The optical carrier microwave signal after the long-distance transmission is realized through the single-mode fiber (3) is subjected to power amplification to realize photoelectric conversion, and meanwhile, the parameter compensation DIPF effect is regulated, so that the frequency conversion efficiency is improved; the method comprises the following steps:
the optical carrier microwave signal output by the single-mode fiber (3) is injected into the optical power amplifier (4) to carry out power amplification, and the gain of the optical power amplifier (4) is expressed as G EDFA Subsequently, the optical carrier microwave signal output from the optical power amplifier (4) is injected into the photoelectric detector (5) to realize photoelectric conversion; the electrical signal output by the photodetector (5) is:
wherein a= -4RG EDFA E c 2 e -αL J 1 (β SOI )J 0 (β SI )J r (β LO ) R is the responsivity of the photodetector 4, G EDFA Is the gain of the optical power amplifier (4); from equation (14), the up-down-converted signal generated by the beat frequency of the SOI signal and the LO signal is preserved, but for a particular caseThe amplitude of the obtained down-conversion intermediate frequency IF signal periodically changes along with the angular frequency of the optical fiber length L, SOI signal and the LO signal, so that the frequency is influenced by the dispersion induced power fading DIPF effect; by regulating the voltage V of the third DC source c (15) bias Thereby changing->Can meet->At this time, the amplitude of the IF signal is kept to be maximum, the DIPF effect is compensated, and the output signal of the photodetector (5) is:
the conversion gain of a receiver is defined as the power ratio between the IF signal and the RF signal, in particular:
wherein R is out And R is in Matching impedance of output and input ends, P out And P in The power at the output and input, respectively.
CN202310384049.0A 2023-04-11 2023-04-11 Optical self-interference elimination device and method for distributed in-band full duplex ROF system Pending CN116599590A (en)

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