CN104683027B - The unrelated optical signal rate recognition methods of modulation format and system - Google Patents

Abstract

The invention relates to an optical signal rate identification method and system independent of modulation format in the field of optical fiber communication. The system includes an optical amplifier, an optical filter, a 3dB optical splitter, an adjustable optical delay line TOD, an optical detector, an analog-to-digital converter, and a main control module. After the optical signal to be identified is amplified by the optical amplifier and the noise is filtered by the filter, it is divided into two paths by the 3dB optical splitter, and only one path is delayed by the TOD. The main control module drives the TOD to generate a series of step delays with a unit of 1 ps, and uses the two sampling signals obtained by the optical detection and the analog-to-digital converter to calculate the first-order and second-order autocorrelation functions ACF ₁ and ACF ₂ of the optical signal Amplitude and period, select the function period with larger amplitude as the symbol period and calculate the signal rate. The invention is applicable to various modulation format optical signals, has relatively large tolerance for signal damage, has low requirements on the rate of the analog-to-digital converter, and has the advantages of wide application range and low cost.

Description

Modulation format-independent optical signal rate identification method and system

technical field

The invention relates to the technical fields of optical fiber communication, signal identification and digital signal processing, in particular to optical signal symbol rate identification and a system.

Background technique

With the rapid development of optical communication technologies, optical communication networks carry more and more data transmission services. Different services have different bandwidth and rate requirements, so optical signals need to use different symbol rates and modulation formats to meet different requirements. This makes it possible to transmit optical signals with different rates and different modulation formats in the same optical network. In this heterogeneous optical network, the optical performance monitoring (OPM) technology of the physical layer is particularly important for system optimization and management. With the help of OPM technology, functions such as channel identification, bandwidth allocation and signal quality monitoring can be realized. In most cases, the optical signal symbol rate must be known to realize these OPM functions. Therefore, an optical signal symbol rate identification method that is independent of the modulation format and insensitive to signal damage has become a research hotspot in China.

Currently, there are mainly three schemes for optical signal symbol rate identification. For example, the zero-delay pulse width of the first-order autocorrelation function ACF ₁ curve is used to identify the symbol rate of the on-off keying (OOK) format signal. The principle is simple, but the accuracy is greatly affected by signal damage. Another scheme uses the characteristic that the periodicity of the second-order autocorrelation function ACF ₂ curve is equal to the signal symbol period to realize the identification of the symbol rate of the OOK signal and the non-return-to-zero binary differential phase-shift keying (NRZ-DPSK) signal. This method has improved anti-damage performance, but the applicable modulation formats are limited and cannot be used for return-to-zero (RZ) binary/quaternary phase-shift keying (RZ-DPSK/QPSK) and Advanced modulation format signals such as hexadecimal quadrature amplitude modulation (16QAM). This is because the period of the second-order autocorrelation function of this type of signal is not equal to the symbol period, so misjudgment will occur. Some research institutions have also proposed to use asynchronous sampling intensity histogram and artificial neural network to identify signal rate. This method can be applied to advanced modulation format signals, but it requires a complex artificial neural network training process before use, and it can only be applied to specific code units. The signal rate and modulation format cannot realize the symbol rate identification independent of the modulation format.

Therefore, it is necessary to study an optical signal symbol rate identification method and system that is applicable to various commonly used modulation formats, is insensitive to signal damage, has a simple structure, and is cost-effective.

Contents of the invention

The technical problem to be solved by the present invention is to propose a method and system that are applicable to various common optical modulation formats and can accurately identify the symbol rate of optical signals under full-blind conditions, so as to overcome the opaqueness to signal modulation formats existing in the prior art, and to Sensitivity to signal damage, and use of complex defects.

In order to solve the above-mentioned technical problem, the present invention proposes a kind of fully blind optical signal symbol rate identification method irrelevant to the modulation format, this method relates to optical amplifier, optical filter, 3dB optical splitter, adjustable optical delay line TOD, optical detector, The analog-to-digital converter, and the main control module, include the following steps:

The optical signal to be identified first enters the optical amplifier to amplify to a certain power, then filters out noise through the optical filter, and then enters the 3dB optical splitter, and is divided into two paths L1 and L2 on average according to the power; the optical signal of the L1 path The signal is input to the optical detector PD1 as a reference signal, and the L2 optical signal enters the TOD and is input to the optical detector PD2 after a certain delay;

The optical detectors PD1 and PD2 respectively convert optical signals into electrical signals and input them to the analog-to-digital converters ADC1 and ADC2 respectively, and the analog-to-digital converters ADC1 and ADC2 respectively perform asynchronous sampling at a rate lower than the signal symbol rate to obtain sampling sequences X ₁ , X ₂ , and inputting the sampling sequences X ₁ , X ₂ to the main control module;

The main control module drives the TOD to generate N step delays τ ₁ , τ ₂ ,..., τ _N with an interval of 1 ps, where N is a natural number greater than 3, and the samples recorded under each delay are used Sequences X ₁ and X ₂ calculate the first-order and second-order autocorrelation functions ACF ₁ and ACF ₂ of the optical signal respectively; use sine function fitting to obtain the amplitude and period of ACF ₁ and ACF ₂ respectively; finally select the function period with larger amplitude As a symbol period T, the output symbol rate is 1/T.

The present invention simultaneously proposes a signal symbol rate identification system that is independent of the signal modulation format, including an optical amplifier, an optical filter, a 3dB optical splitter, an adjustable optical delay line TOD, an optical detector, an analog-to-digital converter ADC, and a main control module;

The optical amplifier is used to amplify the optical signal to a certain power suitable for optical detection;

The optical filter is used to filter out-of-band noise of the optical signal;

The 3dB optical splitter is used to equally distribute the optical signal to the two branches according to the power;

The TOD delays a branch optical signal, and generates N step delays τ ₁ , τ ₂ ,..., τ _N with an interval of 1 ps under the control of the main control module;

The optical detector is used to convert the optical signals output by the two branches into electrical signals;

The analog-to-digital converter ADC is used to sample and quantify the output current of the photodetector and convert it into a digital signal;

The main control module is used to drive the TOD to generate _N step delays τ ₁ , τ ₂ , .

The adjustable light delay line is replaced by an adjustable electric delay line, which is placed at the output end of the light detection path.

The photodetector is a high-speed photodetector.

The analog-to-digital converter is in an asynchronous sampling mode, and the sampling rate is lower than the signal rate.

The invention does not need any prior information of the optical signal modulation format, and realizes accurate judgment of signal symbol period and rate under the unknown signal modulation format. The invention is applicable to optical signals of various commonly used modulation formats and rates, is insensitive to various damages, has low requirements on the sampling rate of the analog-to-digital converter, has the advantages of wide application range, simple structure and high cost performance.

Description of drawings

The technical solutions of the present invention will be further specifically described below in conjunction with the accompanying drawings and specific embodiments.

Fig. 1 is a schematic structural diagram of a symbol rate identification system implemented in the present invention.

Fig. 2(a) is a graph of the first-order autocorrelation function ACF ₁ of the 10GBaud RZ-BPSK/QPSK signal when the optical signal-to-noise ratio is 20dB.

Fig. 2(b) is a curve diagram of the second-order autocorrelation function ACF ₂ of the 10GBaud RZ-BPSK/QPSK signal when the optical signal-to-noise ratio is 20dB.

Fig. 3 (a) is the graph of the first-order autocorrelation function ACF ₁ of 10GBaud non-return-to-zero (NRZ) OOK and RZ-OOK signals.

Figure 3(b) is a graph of the second-order autocorrelation function ACF ₂ of the 10GBaud non-return-to-zero (NRZ) OOK and RZ-OOK signals.

detailed description

The optical signal symbol rate identification system shown in Figure 1 includes: optical amplifier OA 1, optical filter 2, 3dB optical splitter 3, adjustable optical delay line TOD 4, high-speed optical detectors 5, 6, and low-speed analog-to-digital conversion 7, 8, and the main control module 9.

The modulation format adaptive optical signal rate identification method implemented in the present invention specifically includes the following steps:

1) The optical signal to be identified is amplified to a certain power by the optical amplifier 1, and then the out-of-band noise is filtered out by the optical filter 2, and then input into the 3dB optical splitter 3, and the optical signal is equally divided into two paths L1 and L2 according to the power.

2) The L1 optical signal is input into the high-speed optical detector 5 as a reference branch, and the L2 optical signal enters the high-speed optical detector 6 after a certain delay through the adjustable optical delay line 4 .

3) The high-speed photodetectors 5, 6 convert the respective branch optical signals into electrical signals and input them into the low-speed analog-to-digital converters 7, 8 respectively.

4) The analog-to-digital converters 7 and 8 perform asynchronous sampling at a rate lower than the signal symbol rate and convert the sampled signals into digital signal sequences X ₁ and X ₂ to be input to the main control module 9 .

5) The main control module 9 drives the dimmable delay line 4 to generate a series of N delays with an interval of 1 picosecond, where N is a natural number greater than 3. And using the sample sequences X ₁ and X ₂ recorded separately at each time delay, the first-order autocorrelation function of the optical signal is calculated by formula (1)

Where t=τ ₁ , τ ₂ ,..., τ _N , E represents mathematical expectation, μ ₁ and μ ₂ are the average values of X ₁ and X ₂ respectively, are _X1 and _X2 standard deviations, respectively. The second-order autocorrelation function of the optical signal is calculated by formula (2)

where t=τ ₁ , τ ₂ , . . . , τ _N , respectively average value, respectively standard deviation of . Afterwards, the amplitude and period of ACF ₁ and ACF ₂ are obtained by fitting the sine function, and the amplitudes of the two are compared, and the period of the sine function with a larger amplitude is selected as the signal symbol period T, and the output symbol rate is 1/T.

As shown in Figure 2, it can be seen that the period of the first-order autocorrelation function is equal to the symbol period of 100ps, and the peak interval of the ACF ₂ pulses of the RZ-BPSK/QPSK signal is no longer equal to the symbol period T _s = 100ps, and the peak values are very close and difficult to judge correctly Signal symbol period. On the contrary, the pulse peak value of ACF ₁ is still equal to the symbol period, and the pulse peak value is larger than that of ACF ₂ , which can judge the symbol period more effectively and accurately.

As shown in FIG. 3 , it can be seen that the OOK signal ACF ₁ does not exhibit periodicity or its pulse amplitude is smaller than ACF ₂ , so that the symbol period cannot be correctly judged or the error is relatively large. When the ACF ₁ is not periodic, the amplitude obtained by fitting the sinusoidal function is much smaller than that of the periodic ACF ₂ . In summary, under the condition of unknown signal modulation format, the correct code can be obtained by comparing the amplitudes obtained by fitting the sinusoidal functions of ACF ₁ and ACF ₂ , and selecting the period of the sinusoidal function with a larger amplitude as the signal symbol period. meta rate.

Combining Figure 2 and Figure 3, it can be seen that the period of the first-order autocorrelation function is equal to the symbol period of 100 ps, while the period of the second-order autocorrelation function is not equal to the signal symbol period. Therefore, judging the signal symbol rate based on the second-order autocorrelation function will cause misjudgment.

The period and amplitude comparison of the first-order and second-order autocorrelation functions of different modulation formats (T _s is the signal symbol period, PM stands for polarization multiplexing) is shown in Table 1 below.

Table 1 summarizes and expresses the pulse period and amplitude characteristics of the first-order and second-order autocorrelation functions of different modulation formats after fitting the sine function.

Table 1

It can be seen from Table 1 that an autocorrelation function with a large magnitude always has the correct period equal to the signal symbol period. Therefore, the present invention can realize accurate judgment of signal symbol period and rate under unknown signal modulation format.

Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred implementation examples, those skilled in the art should understand that the present invention can be Modifications or equivalent replacements of the technical solutions without departing from the spirit and scope of the technical solutions of the present invention shall fall within the scope of the claims of the present invention.

Claims (5)

1. a kind of unrelated optical signal rate recognition methods of modulation format, it is characterised in that be related to image intensifer, optical filter, 3dB optical splitters, adjustable optical delay line TOD, photo-detector, analog-digital converter, and main control module, comprise the following steps：

Optical signal to be identified initially enters the image intensifer and is amplified to certain power, then filters out noise through the optical filter, Then the 3dB optical splitters are inputted, are divided into L1, L2 two-way by power averaging；L1 roads optical signal is inputted as reference signal The photo-detector PD1, L2 roads optical signal inputs the photo-detector PD2 into the TOD after certain time-delay；

Described photo-detector PD1, PD2 are converted light signals into respectively distinguishes input analog-to-digital converter ADC1, ADC2 after electric signal, Described analog-digital converter ADC1, ADC2 obtain sample sequence to carry out asynchronous-sampling less than the speed of signal element speed respectively X₁、X₂, and by sample sequence X₁、X₂It is input to the main control module；

The main control module drives the TOD to produce N number of stepping delay τ at intervals of 1ps₁, τ₂..., τ_N, N is oneself more than 3 So number, and utilize the sample sequence X of the lower record of each delay₁、X₂Single order, the second order auto-correlation letter of optical signal are calculated respectively Number ACF₁、ACF₂；ACF is respectively obtained using SIN function fitting₁And ACF₂Amplitude and the cycle；Finally selection amplitude is larger Function cycle is as code-element period T, and output symbol speed is 1/T.

2. a kind of system of the unrelated optical signal rate recognition methods of modulation format described in use claim 1, it is characterised in that Including image intensifer, optical filter, 3dB optical splitters, adjustable optical delay line TOD, photo-detector, analog-digital converter ADC, Yi Jizhu Control module；

The image intensifer, for optical signal amplification to be suitable for into optical detection detection to certain power；

The optical filter, for filtering out optical signal out-of-band noise；

The 3dB optical splitters, for optical signal to be assigned in two branch roads by power averaging；

The TOD, line delay is entered to a branch road optical signal, and produces under master control module controls N number of stepping at intervals of 1ps Be delayed τ₁, τ₂..., τ_N, N is the natural number more than 3；

The photo-detector, for the optical signal of two branch road outputs to be converted into electric signal；

The analog-digital converter ADC is used to be converted to data signal after photo-detector output current is sampled and quantified；

The main control module, for driving the TOD to produce N number of stepping delay τ at intervals of 1ps₁, τ₂..., τ_N, and calculate light The code-element period and speed of signal.

3. the system of the unrelated optical signal rate recognition methods of modulation format according to claim 2, it is characterised in that institute State adjustable optical delay line adjustable electric delay line to substitute, and be positioned over the output end of the road optical detection.

4. the system of the unrelated optical signal rate recognition methods of modulation format according to claim 2, it is characterised in that institute Photo-detector is stated for high speed photodetector.

5. the system of the unrelated optical signal rate recognition methods of modulation format according to claim 2, it is characterised in that institute Analog-digital converter is stated for asynchronous-sampling pattern, sampling rate is less than signal rate.