CN1790948A - Optical signal-to-noise ratio monitoring method in synchronous optical transmission system - Google Patents
Optical signal-to-noise ratio monitoring method in synchronous optical transmission system Download PDFInfo
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Abstract
The monitor method for optical SNR in synchronous optical transmission system comprises: dividing communication optical signal into two parts with optical coupler to use the signal with smaller power as monitor signal; sending the monitor signal to high-speed optical switch for signal cutting to let frame head information pass; dividing the cut optical signal into two paths by a 1X2 coupler with one path send to MPU and another path send to optical detection unit to measure cut optical power and send measurement result to MPU; comparing and calculating two paths of signal with MPU to obtain the SNR according to existed correction relation. This invention can measure SNR precisely, and restrains effectively the effect of PMD and nonlinear effect.
Description
Technical field
What the present invention relates to is the method in a kind of optical communication technique field, specifically is the method for optical signal-to-noise ratio monitoring in a kind of synchronous optical transmission system.
Background technology
In optical transmission system, in order to improve transmission range, often adopt the fiber amplifier technology in a large number, make the transmission performance of system and the influence that transmission quality is subjected to noise sources such as image intensifer, and present the noise storage phenomenon.Therefore, Optical Signal To Noise Ratio becomes a main restricting factor of restriction system transmission range and transmission quality.The Optical Signal To Noise Ratio of monitoring receiving terminal just becomes a crucial technological means understanding system works performance, estimated signal transmission quality like this.In the reconfigurable optical network, each channel all will be through multiplexing, demultiplexing and route before being received, and signal is every through primary multiplexer/demodulation multiplexer, all will stand certain filter effect.In this course, spontaneous emission noise (ASE) noise in the channel passband constantly accumulates, and the outer filtered device of ASE noise of channel has been restricted to lower level, therefore band power level interior and the outer ASE noise of band is different, obviously the power level of ASE noise has determined final Optical Signal To Noise Ratio (OSNR) in the band, also is signal quality.And the monitoring method of traditional Optical Signal To Noise Ratio generally is by monitor signal spectrum, reads the signal strength signal intensity of certain wavelength and the noise intensity of adjacent its both sides, gets the noise intensity of the mean value of both sides noise intensity as this signal place; Use snr computation formula OSNR=P then
S-P
N, obtain the signal to noise ratio of this signal, the P in the formula
SBe signal strength signal intensity, P
NMean value for signal both sides noise intensity.Obviously, in above method, adopted the outer noise mean value of passband to replace noise intensity in the channel, and in the reconfigurable optical network in the band ASE noise different be with outside the ASE noise, this method can be brought bigger measure error.In addition, the spectrum method for scanning costs an arm and a leg, and speed is slow, is unsuitable for performance monitoring and uses.Therefore, OSNR in how simply, at low cost, accurately monitoring is with is important and problem demanding prompt solution in the extensive wavelength division multiplexed optical network.
Find through literature search prior art, U.S. Patent number is US6813021, patent name is " Method and apparatus for monitoring optical signal-to-noise ratio (OSNR) using polarization-nulling method (based on the apparatus and method of the monitoring Optical Signal To Noise Ratio of polarization extinction) ", has proposed a kind of method of monitoring OSNR in the band in this patent.This method is used quarter-wave plate and polarizer of a rotation, monitors the OSNR of light signal by measurement ratio of luminous power on two polarization directions.Yet the prerequisite of this technology is that the degree of polarization of putative signal is (DOP) 1, and this condition does not satisfy in the optical transmission system of reality.When PMD (polarization mode dispersion) was present in the Transmission Fibers, light signal had two orthogonal polarization components that postpone mutually in time, i.e. two of polarization major states, this moment signal degree of polarization less than 1.Therefore, even adjusted signal polarization, signal polarization is balanced out.Therefore, this technology is when having PMD to exist, and the error in the measured OSNR value is very big.In addition, in the multichannel wdm system, because the cross-phase of interchannel modulation (XPM) causes the polarization state of signal the polarization scattering effect to occur, the degree of polarization that makes signal is used this technology and also can be caused bigger OSNR measure error less than 1.
Above result shows that prior art is many at present can not monitor OSNR in the band exactly, is subjected to the influence of various impairment factors easily, forms bigger measure error.We can say also there is not to be applied to the interior OSNR monitoring scheme of band of real system at present.
Summary of the invention
The objective of the invention is to overcome defective of the prior art and deficiency, the method of optical signal-to-noise ratio monitoring in a kind of synchronous optical transmission system is provided, make it can be used for dynamic reconfigurable wavelength division multiplexing (WDM) optical transmission system, accurately the measuring light signal to noise ratio has suppressed the influence to measurement result of PMD and nonlinear effect effectively.
The present invention is achieved by the following technical solutions, and step is as follows:
(1) with optical coupler with Communication ray signal separated into two parts, wherein the light signal of smaller power part is as monitor signal;
(2) the monitoring light signal is admitted to high-speed optical switch, and this high-speed optical switch is driven by frame synchronizing signal, and its effect is that signal is cut, and only allows frame head information to pass through.
(3) coupler of the light signal after the cutting by one 1 * 2 is divided into two-way, wherein one the tunnel sends into photoelectric detector, and its output is sent into spectral analysis unit after the amplifier amplification, be used for the monitor signal beat frequency noise, and monitoring result is sent into microprocessor unit;
(4) another road light signal after the cutting is sent into optical detecting unit, is used to measure the luminous power after the cutting, and measurement result is sent into microprocessor unit;
(5) microprocessor unit compares calculating to the signal of two-way input, according to existing correction relationship, obtains the signal to noise ratio of this channel optical signal.
Specific requirement to optical switch in the described step (2) is: have high switching speed (ns level), high extinction ratio (＞20dB), and switching characteristic and polarization irrelevant.Can adopt semiconductor amplifier (SOA) optical switch in actual the use; Or employing electroabsorption modulator (EAM).
In the described step (3), do not need to use the high-speed light detector, the requirement of bandwidth is got final product less than 300MHz; Equally, do not have strict demand, be generally less than 300MHZ and get final product for the bandwidth of employed spectral analysis unit.
The formula that calculates Optical Signal To Noise Ratio in the described step (5) is:
In the following formula, N
BeatBe beat frequency noise power, record by step (3); P
TotalBe luminous power, record by step (4), OSNR by following formula by calculating; A, B are correction coefficient, and be relevant with the characteristic of photodetector and the optical filter characteristic that adopted.
In the step (5), need inquire about existing correction coefficient during signal calculated OSNR, this correction coefficient is by measuring in advance.
The present invention is a kind of OSNR monitoring technology that is applicable to the synchronous mode optical transmission system, it can measure OSNR in the band exactly, and has good robustness for ubiquitous PMD in the optical transmission system and polarization scattering effect, can work exactly when having these effects, using value is higher.The present invention and improve monitoring efficient greatly shortens monitoring time.
Description of drawings
Fig. 1 is a fundamental diagram of the present invention
Fig. 2 is the schematic diagram of signal of the present invention at cutting front and back time domain and frequency domain
Wherein, (a) cutting before time-domain signal; (b) frequency-region signal before the cutting; (c) cutting back time-domain signal; (d) cutting back frequency-region signal.
Fig. 3 is that the present invention is applied to the experimental system figure that a WDM transmission system detects OSNR
OSNR curve chart in the band that Fig. 4 records when being to use the present invention to have the polarization scattering transmission impairment
Wherein, (a) relation of beat frequency noise and OSNR; (b) OSNR and the error of using OSNR that the present invention records and error (c) to use the DOP method to record.
Embodiment
The present invention is a kind of OSNR monitoring method that is applicable to the synchronous mode optical transmission system.Referring to Fig. 1, fundamental diagram of the present invention.One group of light signal that the WDM signal is exported among many people having a common goal by demodulation multiplexer 2 after optical transmission unit 1 transmission; This light signal is delivered to the optical coupler 3 of coupling proportion between 20: 1～10: 1 through optical fiber, light signal is divided into two parts: wherein the signal of most of power is delivered to receiving element through optical fiber output, and the light of about 5%～10% smaller power part is delivered to OSNR monitoring device 11 as monitor signal via optical fiber, OSNR monitoring in being with.Signal to be monitored is at first sent into optical switch 4, and this optical switch is driven by frame synchronizing signal, is used to realize the cutting to light signal, only allows header signal pass through to suppress load signal.Light signal after the cutting is sent into 1 * 2 coupler 5, is divided into the two ways of optical signals of constant power, wherein one the tunnel sends into optical detecting unit 9 via optical fiber, is used for measuring light power; The current signal of optical detecting unit 9 outputs is sent into microprocessor unit 10.Another road light signal of coupler output is delivered to photodetector 6 via optical fiber, the signal of telecommunication of photodetector output is sent into spectral analysis unit 8 after being amplified by electric amplifier 7, spectral analysis unit is used to detect beat noise power, and its output result sends into microprocessor unit 10.The luminous power and the beat noise power of 10 pairs of inputs of microprocessor unit calculate, and obtain the Optical Signal To Noise Ratio (OSNR) of signal according to existing correction coefficient.
The computing formula of OSNR is:
In the following formula, A, B are calibration factor, and be relevant with the characteristic of photodetector and the optical filter characteristic that adopted, N
BeatAnd P
TotalRecord by spectral analysis unit and optical detecting unit respectively.
In above-mentioned OSNR monitoring device, optical switch 4 requires to have high switching speed, and is undistorted in cutting process to guarantee frame head information, therefore requires optical switch to have the switching speed of ns magnitude; Require optical switch 4 to have high extinction ratio simultaneously,, therefore require extinction ratio greater than 20dB to realize effective inhibition to load information; Also require the switching characteristic and the polarization irrelevant of optical switch 4 simultaneously, the error of bringing with ubiquitous PMD and polarization scattering effect in effective inhibition optical transmission process.In actual the use, optical switch 4 can adopt semiconductor amplifier (SOA) optical switch, as the SOA-S-OEC-1550 of Ciphotonics; Or adopt electroabsorption modulator (EAM), as the EAM10 of CYOptics.
As shown in Figure 2, signal of the present invention is at the schematic diagram of cutting front and back time domain and frequency domain.In the synchronous mode transmission system, data code flow is formed (Fig. 2 (a)) by frame head and load, and wherein the data in the frame head have fixing repetition rate, are 1/125s as the frame head repetition rate in the SDH system.On frequency spectrum, these frame heads are corresponding to fixing frequency interval, and between these frequency intervals frequency field corresponding to the frequency spectrum of load; Simultaneously, the noise of signal also is positioned at this zone (Fig. 2 (b)).Generally, because noise is covered by signal spectrum, therefore can not measure real noise power.And the present invention is by the method for signal cutting, suppressed load and only kept frame head information (Fig. 2 (c)).Like this, on frequency spectrum, real noise floor has appeared to come out (Fig. 2 (d)), can be by measuring noise also by calculating the OSNR of picked up signal.
As shown in Figure 3, be that the present invention is applied to a WDM transmission system, and the light signal of transmission is subjected to polarization scattering when damage, be used to detect the experimental system figure of OSNR.In order to introduce tangible polarization scattering effect, to show the superiority of the inventive method, the power output of first erbium-doped fiber amplifier (EDFA) is 20dBm among the figure.The OSNR monitoring device is used for the OSNR of monitor signal as for after the demodulation multiplexer.
Fig. 4 is that the present invention is applied to the resulting measurement result of WDM transmission system shown in Figure 3.Fig. 4 (a) is the beat frequency noise that records and the relation of OSNR, concerns the OSNR that can obtain signal through overcorrect thus.As can be seen, kept the better linearity relation between beat frequency noise power that records and the OSNR.Interior OSNR value of the band that Fig. 4 (b) is to use the present invention to record and measure error.Can see that in the scope of 10～27dB, the present invention has reflected the OSNR of signal preferably, worst error is no more than 0.7dB.Fig. 4 (c) adopts OSNR value and measure error in the band that the method for degree of polarization (DOP) records, with Fig. 4 (b) more as can be known, the present invention has improved certainty of measurement greatly.
Claims (6)
1, the method for optical signal-to-noise ratio monitoring in a kind of synchronous optical transmission system is characterized in that step is as follows:
(1) with optical coupler with Communication ray signal separated into two parts, wherein the light signal of smaller power part is as monitor signal;
(2) the monitoring light signal is admitted to high-speed optical switch, and this high-speed optical switch is driven by frame synchronizing signal, and its effect is that signal is cut, and only allows frame head information to pass through;
(3) coupler of the light signal after the cutting by one 1 * 2 is divided into two-way, wherein one the tunnel sends into photoelectric detector, and its output is sent into spectral analysis unit after the amplifier amplification, be used for the monitor signal beat frequency noise, and monitoring result is sent into microprocessor unit;
(4) another road light signal after the cutting is sent into optical detecting unit, is used to measure the luminous power after the cutting, and measurement result is sent into microprocessor unit;
(5) microprocessor unit compares calculating to the signal of two-way input, according to existing correction relationship, obtains the signal to noise ratio of this channel optical signal.
2, the method for optical signal-to-noise ratio monitoring in the synchronous optical transmission system according to claim 1 is characterized in that, in the described step (1), the coupling proportion of optical coupler is between 20: 1～10: 1.
3, the method for optical signal-to-noise ratio monitoring in the synchronous optical transmission system according to claim 1 is characterized in that, in the described step (2), the switching speed of high-speed optical switch reaches the ns level, extinction ratio＞20dB, and switching characteristic and polarization irrelevant.
4, the method for optical signal-to-noise ratio monitoring in the synchronous optical transmission system according to claim 1 is characterized in that, in the described step (3), the bandwidth of employed photoelectric detector is less than 300MHz, and the bandwidth of employed spectral analysis unit is less than 300MHZ.
5, the method for optical signal-to-noise ratio monitoring in the synchronous optical transmission system according to claim 1 is characterized in that, in the described step (5), the formula that calculates Optical Signal To Noise Ratio is:
Wherein, N
BeatBe beat frequency noise power, record by step (3); P
TotalBe luminous power, record by step (4), OSNR by following formula by calculating; A, B are correction coefficient.
According to the method for optical signal-to-noise ratio monitoring in claim 1 or the 5 described synchronous optical transmission systems, it is characterized in that 6, in the step (5), need inquire about existing correction coefficient during signal calculated OSNR, this correction coefficient is by measuring in advance.
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| CN101563868B (en) * | 2006-12-22 | 2012-11-21 | 法国电信公司 | Optical signal processing method and device, associated central equipment and access network |
| CN103634066A (en) * | 2012-08-28 | 2014-03-12 | 上海贝尔股份有限公司 | Optical line terminal and optical network unit |
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| CN101563868B (en) * | 2006-12-22 | 2012-11-21 | 法国电信公司 | Optical signal processing method and device, associated central equipment and access network |
| WO2011157128A3 (en) * | 2011-05-31 | 2012-04-05 | 华为技术有限公司 | Method and device for processing optical signals |
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| CN103634066B (en) * | 2012-08-28 | 2017-04-12 | 上海贝尔股份有限公司 | Optical line terminal and optical network unit |
| CN103634066A (en) * | 2012-08-28 | 2014-03-12 | 上海贝尔股份有限公司 | Optical line terminal and optical network unit |
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| WO2015077924A1 (en) * | 2013-11-26 | 2015-06-04 | 华为技术有限公司 | Measuring method and apparatus of optical signal to noise ratio |
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| CN105009484B (en) * | 2013-11-26 | 2017-06-27 | 华为技术有限公司 | The measuring method and device of a kind of OSNR |
| CN105911348A (en) * | 2016-04-11 | 2016-08-31 | 烽火通信科技股份有限公司 | High speed signal quality test device |
| CN106685524A (en) * | 2016-12-23 | 2017-05-17 | 武汉邮电科学研究院 | Method and system for measuring optical signal-to-noise ratio in optical pulse amplitude modulation signal |
| CN106685524B (en) * | 2016-12-23 | 2019-07-16 | 武汉邮电科学研究院 | The method and system of optical signal to noise ratio are measured in a kind of light pulse am signals |
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