Low complexity optical arbitrary waveform measurement system and method based on single-ended pd array

Abstract

The application discloses a kind of low complexity optical arbitrary waveform measurement system and method based on single-end PD array, system includes the signal transmission end of to-be-measured signal, local light frequency comb end, signal receiver array, receiving end digital signal processing DSP, wherein including mixer array, photodetector array, analog-digital converter array in receiver array;Traditional coherent light receiver array adopts 2×4 90° optical mixer, and four-way mixed signals with phase difference of 90° are output, respectively through 4 photodetectors PD and are detected to obtain photocurrent in-phase and quadrature components, subsequent digital signal processing is carried out, and broadband signal reconstruction is completed.The 2×2 90° optical mixer is used in the system to replace the 90° mixer in the traditional coherent light receiver, and 2-way mixed signals are obtained, and enter 2 single-end photodetectors PD to detect and obtain photocurrent in-phase and quadrature components;The application can well reduce the device complexity in the traditional optical arbitrary waveform measurement system, and simplify system composition.

Description

Technical Field

[0001] This invention relates to the field of optical communication technology, and more specifically, to a low-complexity optical arbitrary waveform measurement system and method based on a single-ended PD array. Background Technology

[0002] With the rapid increase in multimedia services and the development of the communications industry, the demands for communication speeds are constantly rising, placing enormous pressure and challenges on existing fiber optic communication networks. The surge in traffic is driving fiber optic communication to continuously evolve and upgrade in five dimensions: ultra-high speed, ultra-large capacity, ultra-long distance, ultra-wide flexibility, and ultra-strong intelligence, giving rise to coherent optical communication. Coherent optical communication systems supporting high-order modulation formats, due to their higher spectral efficiency (SE) and receiver sensitivity, offer higher transmission rates and longer transmission distances. They are not only used in long-distance and metropolitan area networks but also in short-distance networks, including data center interconnects, and represent the future direction of fiber optic communication development. As bandwidth utilization increases and signal bandwidth widens, measuring and monitoring high-speed, high-bandwidth optical signals has become a key technology for ensuring the reliability of fiber optic communication networks. Parallel reception is used to increase the measurement bandwidth of optical channels, enabling spectral slicing optical arbitrary waveform measurement technology to improve the broadband optical signal measurement capability of single and multi-channel optical signals without increasing electronic bandwidth. The inherent bandwidth scalability of these technologies and their ability to continuously receive full-field waveforms enable communication systems to support flexible bandwidth allocation and modulation format independence. Optical arbitrary waveform measurement technology is one of the hot research directions in the receiver end of communication systems.

[0003] For optical arbitrary waveform measurement techniques, optical frequency combs play a multifaceted role, and their scalability at the receiver end is highly attractive. Regarding freely operating optical frequency combs, spectral slicing signal processing has proven to be a feasible solution for broadband coherent detection. Spectral slicing detection supported by optical frequency combs represents a very powerful method, allowing complete reconstruction of arbitrary optical waveforms over bandwidths exceeding the reach of electronic signal processing. In optical communication systems, it is important to note that optical arbitrary waveform measurement schemes offer significant advantages for applications involving coherent reception of broadband data signals. The achievable measurement bandwidth of this system increases linearly by using more spectral slices; specifically, at the system receiver end, the measurement bandwidth is further extended by increasing the number of coherent optical receivers.

[0004] While optical arbitrary waveform measurement techniques based on slice coherent detection offer superior performance in receiving high-bandwidth signals, they still face several inherent key technical challenges. One challenge lies in reducing system complexity, which impacts the practical application of optical arbitrary waveform measurement systems in future optical communication systems. In optical arbitrary waveform measurement systems, for traditional coherent receivers at the receiving end... Composed of multiple components such as optical 90° mixers, photodetectors, and analog-to-digital converters, the more parallel coherent optical receivers there are, the more underlying components are required, leading to higher costs and greater complexity. This, to some extent, limits the development of coherent receivers for optical arbitrary waveform measurement towards integration. Therefore, for high-bandwidth signal reception, it is highly significant to research low-complexity optical arbitrary waveform measurement systems without increasing system framework complexity and losses. Summary of the Invention

[0005] To address the problem of high receiver complexity in existing optical arbitrary waveform measurement systems, this invention proposes a low-complexity optical arbitrary waveform measurement system based on a single-ended PD array.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A low-complexity optical arbitrary waveform measurement system based on a single-ended PD array includes a laser source, an optical fiber coupler, a signal generation module, a tunable optical filter array, an optical frequency comb generation module, a parallel receiver array, and a digital signal processing module. The laser source and the optical fiber coupler are connected, and the optical fiber coupler is connected to the signal generation module and the optical frequency comb generation module respectively. After the signal generation module and the tunable optical filter array are connected in sequence, the output of the tunable optical filter array and the output of the optical frequency comb generation module are input to the parallel receiver array, and the output of the parallel receiver array is input to the digital signal processing module.

[0008] The signal generation module includes an arbitrary waveform generator, an IQ modulator, and an optical amplifier EDFA.

[0009] The optical frequency comb generation module includes an MZM modulator and a wavelength selection switch (WSS).

[0010] The parallel receiver array includes sequentially connected... Optical mixer array, single-ended PD array, analog-to-digital converter array.

[0011] The optical frequency comb generation module uses electro-optic modulation. The center wavelength of the optical frequency comb is 1548nm-1550nm, and the frequency spacing is 24GHz-26GHz. The frequency spacing of the optical frequency comb is adjustable and is determined by both the bandwidth of the signal under test and the number of receivers.

[0012] Preferably, the parallel receiver array comprises four columns of parallel receivers.

[0013] Meanwhile, the present invention also provides a low-complexity optical arbitrary waveform measurement method based on a single-ended PD array. The method is based on the above-mentioned low-complexity optical arbitrary waveform measurement method based on a single-ended PD array and includes the following steps:

[0014] S1. Obtain an optical signal through the laser source, and divide the optical signal into optical path one and optical path two through the optical fiber coupler;

[0015] S2. The optical signal from optical path one is sequentially input into the signal generation module and the tunable optical filter array to obtain four spectral slice signals of different signal frequency bands. The optical signal from optical path two is input into the optical frequency comb generation module to obtain four parallel local oscillator signals. Where S represents the signal light and L represents the local oscillator light; spectral slice With local oscillator signal Correspondingly, when the digital subscripts of the slice signal and the local oscillator signal are the same, then there is a one-to-one correspondence between the two;

[0016] S3. The parallel receiver array receives four spectral slice signals and four parallel local oscillator signals; The optical mixer array mixes different spectral slice signals with their corresponding local oscillator signals to obtain two mixed output signals for each of the four parallel receivers. This represents the slice signal corresponding to the i-th receiver. This represents the local oscillator signal corresponding to the i-th receiver. This represents the first mixer output of the i-th receiver. This represents the second mixer output of the i-th receiver, where i represents the number of parallel receivers, ranging from 1 to 4.

[0017] The mixing operation is as follows:

[0018] (1)

[0019] The single-ended PD array performs beat frequency synthesis of the mixed output signal into an intermediate frequency signal, down-converting the high-frequency optical modulation signal to be received to a lower-frequency intermediate frequency signal, and the single-ended PD array outputs photocurrent. , , ;

[0020] (2)

[0021] in, , These are the photocurrents of the sliced ​​signal light and the local oscillator light corresponding to the i-th receiver, respectively. Let be the phase difference between the i-th receiver slice signal and the local oscillator signal. = ;

[0022] The photocurrent is output through each receiver. The in-phase signal components of each slice signal are calculated. Orthogonal signal components Finally, the baseband signals of each slice signal are obtained. ,

[0023] - (3)

[0024] (4)

[0025] (5)

[0026] in, = , Selfie noise is additionally introduced for the i-th receiver;

[0027] S4. The baseband signals obtained from different signal frequency bands of each receiver are sent to the analog-to-digital converter array for analog-to-digital conversion. The digital signal processing module processes the digital signals after analog-to-digital conversion to ultimately achieve signal waveform measurement. The specific steps of the digital signal processing module in processing the digital signals after analog-to-digital conversion include:

[0028] S41. Shift the baseband signals obtained from the four parallel receivers left and right to their original positions in the sliced ​​spectrum;

[0029] S42. Perform inverse channel response compensation on the moved sliced ​​spectrum signal, and then stitch the compensated sliced ​​signal together using a sliding window algorithm.

[0030] S43. Perform amplitude normalization processing on the spliced ​​signal, estimate and compensate for the quadrature imbalance of the I / Q channels, and correct the sampling clock deviation to achieve synchronization of the clock signals of the transmitting and receiving ends;

[0031] S44. Equalize the channel using an equalization algorithm;

[0032] S45. A square root raised cosine filter is used to implement the matched filtering function, and the signal after matched filtering is downsampled;

[0033] S46. Calculate the bit error rate of the reconstructed signal using the downsampled signal to evaluate the performance of the received signal.

[0034] After adopting the above scheme, the beneficial effects of the present invention are as follows: Compared with the traditional coherent optical receiver, the present invention reduces the number of photodetectors, reducing the number of single-channel photodetectors from 4 to 2. In the optical arbitrary waveform measurement system with four-channel parallel reception, 8 photodetectors are reduced, simplifying the system receiver configuration. The present invention achieves a considerable signal reconstruction function with fewer components, effectively reducing system cost and complexity, and is more conducive to system integration and miniaturization. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the low-complexity optical arbitrary waveform measurement system based on a single-ended PD array according to the present invention.

[0036] Figure 2 This is a schematic diagram of the single-ended PD principle;

[0037] Figure 3 This is a schematic diagram of the principle of the optical arbitrary waveform measurement system;

[0038] Figure 4 This is the signal spectrum diagram after compensation for transmission loss of the four sliced ​​signals in the simulation;

[0039] Figure 5 This is a spectrum diagram of the spliced ​​signal obtained by splicing four sliced ​​signals through a sliding window in the digital signal processing module during simulation.

[0040] Figure 6 This is a signal constellation diagram showing the successful demodulation of spliced ​​signals by the digital signal processing module during simulation. Detailed Implementation

[0041] The present invention will be further described below with reference to the accompanying drawings. It should be understood that the embodiments are merely illustrative and not limiting of the present invention.

[0042] like Figure 1 As shown, a low-complexity optical arbitrary waveform measurement system based on a single-ended PD array includes a laser source, an optical fiber coupler, a signal generation module, a tunable optical filter array, an optical frequency comb generation module, a parallel receiver array, and a digital signal processing module. The laser source and the optical fiber coupler are connected, and the optical fiber coupler is connected to the signal generation module and the optical frequency comb generation module respectively. After the signal generation module and the tunable optical filter array are connected in sequence, the output of the tunable optical filter array and the output of the optical frequency comb generation module are input to the parallel receiver array, and the output of the parallel receiver array is input to the digital signal processing module.

[0043] The signal generation module includes an arbitrary waveform generator, an IQ modulator, and an optical amplifier EDFA.

[0044] The optical frequency comb generation module includes an MZM modulator and a wavelength selection switch (WSS).

[0045] The parallel receiver array includes sequentially connected... Optical mixer arrays, single-ended PD arrays, and analog-to-digital converter arrays.

[0046] The optical frequency comb generation module uses electro-optic modulation. The center wavelength of the optical frequency comb is 1548nm-1550nm, and the frequency spacing is 24GHz-26GHz. The frequency spacing of the optical frequency comb is adjustable and is determined by both the bandwidth of the signal under test and the number of receivers. The parallel receiver array includes four parallel rows of receivers.

[0047] Based on this system, the method of the present invention is as follows:

[0048] S1. An optical signal is obtained through the laser source, and the optical signal is split into optical path one and optical path two through the optical fiber coupler. After the output optical signal of the laser source passes through the optical fiber coupler, the optical signal is split into two beams according to a 50 / 50 splitting ratio, and enters the signal generation module and the optical frequency comb generation module respectively.

[0049] S2. The optical signal from optical path one is sequentially input into the signal generation module and the tunable optical filter array to obtain four spectral slice signals of different signal frequency bands. The optical signal from optical path two is input into the optical frequency comb generation module to obtain four parallel local oscillator signals. Where S represents the signal light and L represents the local oscillator light; spectral slice With local oscillator signal Correspondingly, when the digital subscripts of the sliced ​​signal and the local oscillator signal are the same, they correspond one-to-one. In the signal generation module, an arbitrary waveform generator acts as a signal source to generate an electrical signal. The electrical signal to be measured is applied to the RF input terminal of the IQ modulator, and a DC voltage is applied to the DC bias port. The electrical signal to be measured is modulated onto the optical signal, which can generate any QAM optical modulation signal. Then, an optical amplifier (EDF) amplifies the optical modulation signal. An adjustable optical filter array is used for spectral slicing. The optical modulation signal amplified by the optical amplifier (EDFA) is spectrally sliced ​​by adjusting the adjustable passband position of the optical filter, filtering out different signal frequency bands of the optical modulation signal.

[0050] In the optical frequency comb generation module, a DC voltage is applied to the RF input port of the MZM modulator. Through amplitude and phase modulation, a flat optical frequency comb with equal frequency spacing is generated. The optical frequency comb is separated and equalized by a wavelength selective switch (WSS) to serve as the local oscillator signal for each receiver. The corresponding local oscillator signal used for coherent reception of different spectral slices is determined by the wavelength selective switch. The optical frequency comb generation module uses electro-optic modulation. The center wavelength of the optical frequency comb is 1550 nm, and the frequency spacing of the optical frequency comb is 26 GHz. The frequency spacing is adjustable and is determined by both the bandwidth of the signal under test and the number of receivers.

[0051] S3. The parallel receiver array receives four spectral slice signals and four parallel local oscillator signals; The optical mixer array mixes different spectral slice signals with their corresponding local oscillator signals to obtain two mixed output signals for each of the four parallel receivers. This represents the slice signal corresponding to the i-th receiver. This represents the local oscillator signal corresponding to the i-th receiver. This represents the first mixer output of the i-th receiver. This represents the second mixer output of the i-th receiver, where i represents the number of parallel receivers, ranging from 1 to 4. The parallel receiver array is used to receive different spectral slices and their corresponding local oscillator signals. The optical mixer array mixes different spectral slice signals with their corresponding local oscillator signals. The photodetector array then performs beat frequency synthesis on the mixed output signal to form an intermediate frequency (IF) signal, thus down-converting the high-frequency optical modulation signal to a lower-frequency IF signal. The analog-to-digital converter (ADC) array performs analog-to-digital conversion on the electrical signal output from the photodetector array, converting it into a digital signal. Specifically, the parallel receiver array includes... The 90° optical mixer array and photodetector array are used to mix the corresponding slice signals through the 90° optical mixer, and the single-ended PD array beats the mixed signals to synthesize the intermediate frequency signals corresponding to each slice signal. Figure 2 This is a schematic diagram of the single-ended PD principle. The slice signal and the local oscillator optical frequency comb signal are mixed to produce two mixed outputs.

[0052] The mixing operation is as follows:

[0053] (1)

[0054] The single-ended PD array performs beat frequency synthesis of the mixed output signal into an intermediate frequency signal, down-converting the high-frequency optical modulation signal to be received to a lower-frequency intermediate frequency signal, and the single-ended PD array outputs photocurrent. , , ;

[0055] (2)

[0056] in, , These are the photocurrents of the sliced ​​signal light and the local oscillator light corresponding to the i-th receiver, respectively. Let be the phase difference between the i-th receiver slice signal and the local oscillator signal. = ;

[0057] The photocurrent is output through each receiver. The in-phase signal components of each slice signal are calculated. Orthogonal signal components Finally, the baseband signals of each slice signal are obtained. ,

[0058] - (3)

[0059] (4)

[0060] (5)

[0061] in, = , Selfie noise is additionally introduced for the i-th receiver;

[0062] S4. The baseband signals obtained from different frequency bands of each receiver are sent to the analog-to-digital converter array for analog-to-digital conversion. The digital signal processing module (DSP) processes the digital signals after analog-to-digital conversion to reconstruct the signal under test. The digital signal processing includes signal slicing and shifting, amplitude and phase compensation, signal splicing, normalization, DC removal, IQ orthogonalization, clock synchronization, channel equalization, matched filtering, downsampling, and BER calculation, ultimately realizing signal waveform measurement. The specific steps of the digital signal processing module in processing the digital signals after analog-to-digital conversion include:

[0063] S41. Shift the baseband signals obtained from the four parallel receivers left and right to their original positions in the sliced ​​spectrum;

[0064] S42. Perform inverse channel response compensation on the moved sliced ​​spectrum signal, and then stitch the compensated sliced ​​signal together using a sliding window algorithm.

[0065] S43. Perform amplitude normalization processing on the spliced ​​signal, estimate and compensate for the quadrature imbalance of the I / Q channels, and correct the sampling clock deviation to achieve synchronization of the clock signals of the transmitting and receiving ends;

[0066] S44. Equalize the channel using an equalization algorithm;

[0067] S45. A square root raised cosine filter is used to implement the matched filtering function, and the signal after matched filtering is downsampled;

[0068] S46. Calculate the bit error rate of the reconstructed signal using the downsampled signal to evaluate the performance of the received signal.

[0069] A low-complexity optical arbitrary waveform measurement system based on a single-ended PD array was built in Matlab to numerically simulate a 100 GBd 16QAM Nyquist single-carrier signal. The broadband optical signal was generated by modulating the optical carrier using an IQ modulator, the driving signal was generated by an arbitrary waveform generator (AWG), and the optical modulation signal was amplified by an EDFA. A root-raised cosine (RRC) pulse shaping filter with a roll-off factor of 0.01 was used to generate a single-channel 100 GBd 16QAM signal. Transmission was performed back-to-back. First, the EDFA-amplified optical modulation signal passed through an optical filter array to achieve broadband signal slicing at the transmitter. The sliced ​​signals corresponded to different frequency bands of the optical signal under test, with some overlap between adjacent slices. The optical signal emitted by the continuous laser passed through a 50 / 50 optical coupler, and another portion of the output optical signal was modulated by an MZM to generate an optical frequency comb. Then, a WSS (Wideband Filter) selected four specific sub-combs as the input local oscillators.

[0070] The four slice signals are transmitted through the corresponding optical frequency comb. After mixing by a 90° optical mixer array and beating by a single-ended PD array, four sliced ​​baseband signals are obtained at the receiving end. These sliced ​​signals are then moved to their original positions. Since each sliced ​​signal experiences amplitude and phase loss after transmission through the channel, the baseband transfer function of each sliced ​​signal is used to compensate for this loss. For the compensated sliced ​​signals, a sliding window method using adjacent sliced ​​signals is used to stitch the signals together. The stitched signal is consistent with the transmitter signal before the signal under test enters the receiver array. The sliced ​​signals undergo a DSP processing flow through an optical arbitrary waveform measurement system. A traditional DSP processing flow includes: DC removal, IQ orthogonalization, clock synchronization, signal equalization, matched filtering, downsampling, QAM demodulation, calculation of signal BER, EVM, and SNR, and finally, evaluation of signal reconstruction performance to complete signal reception reconstruction.

[0071] Figure 3 This is a schematic diagram of the principle of the present invention; the signal to be tested is divided into slice signals of different frequency bands, which are received by their respective local oscillator optical combs.

[0072] Figure 4 The image shows the signal spectrum after compensation for transmission loss of the four slice signals in the simulation; a 4GHz spectrum overlap is set between adjacent slice signals.

[0073] Figure 5 The spliced ​​signal spectrum is obtained by sliding window splicing of the overlapping frequency part of the four slice signals in the digital signal processing module during simulation. The spliced ​​signal is consistent with the transmitter signal before the signal under test enters the receiver array.

[0074] Figure 6The system uses a digital signal processing module to successfully demodulate the spliced ​​signal in the simulation, evaluates the system performance, ensures that the signal is reconstructed to meet the requirements of communication transmission, and achieves successful reconstruction.

[0075] The parts of this invention not described in detail are common knowledge to those skilled in the art.

[0076] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A low complexity optical arbitrary waveform measurement method based on single-ended PD array, characterized in that, The method is based on a single-end PD array low-complexity optical arbitrary waveform measurement system, which comprises a laser source, a fiber coupler, a signal generation module, an adjustable optical filter array, an optical comb generation module, a parallel receiver array, and a digital signal processing module; the laser source is connected to the fiber coupler, the fiber coupler is connected to the signal generation module and the optical comb generation module, the signal generation module and the adjustable optical filter array are connected in sequence, the output of the adjustable optical filter array and the output of the optical comb generation module are jointly input into the parallel receiver array, and the output of the parallel receiver array is input into the digital signal processing module. The signal generation module comprises an arbitrary waveform generator, an IQ modulator, and an optical amplifier EDFA. The optical comb generation module comprises an MZM modulator and a wavelength selective switch WSS. The parallel receiver array includes sequentially connected optical mixer array, single-ended PD array, analog-to-digital converter array The method comprises the following steps: S1. Obtain an optical signal through the laser source, and divide the optical signal into optical path one and optical path two through the fiber coupler; S2. The optical signal of the light path one is sequentially input into the signal generation module and the adjustable optical filter array, and four optical spectrum slicing signals of different signal bands are obtained ; the optical signal of the light path two is input into the optical frequency comb generation module, and four parallel local signals are obtained ; wherein S represents signal light, L represents local light; the spectrum slicing signal corresponds to the local signal , when the digital subscripts of the slicing signal and the local signal are the same, they correspond one by one. S3. The parallel receiver array receives four light spectrum slice signals and four parallel local oscillator signals; the The light mixer array mixes different light spectrum slice signals with corresponding local oscillator signals to obtain two mixed output signals of each of the four parallel receivers represents the slice signal corresponding to the i-th receiver, represents the local oscillator signal corresponding to the i-th receiver, represents the first mixed output of the i-th receiver, represents the second mixed output of the i-th receiver, i represents the number of parallel receivers, i ranges from 1 to 4. The mixing operation is as follows: （1） The single-end PD array performs beat frequency synthesis on a mixed output signal, down-converts a high-frequency optical modulation signal to be received to a low-frequency intermediate frequency signal, and outputs a photoelectric current 、 , ; （2） wherein, , are the photocurrents of the i-th receiver corresponding to the sliced signal light and the local light, respectively, is the phase difference between the sliced signal and the local signal of the i-th receiver, = tan-1 (Im(Ii) / Re(Ii)), ; Output photoelectric current through each channel , calculate in-phase signal components of each channel slice signal , quadrature signal components , finally obtain baseband signals of each channel slice signal , － （3） （4） （5） wherein = 0.5 , is the additional self-interference noise introduced to the ith receiver. S4. Input the baseband signals obtained by each receiver in different signal frequency bands into an analog-to-digital converter array for analog-to-digital conversion, and process the digital signals after analog-to-digital conversion by the digital signal processing module to finally realize signal waveform measurement.

2. The single-ended PD array based low complexity optical arbitrary waveform measurement method according to claim 1, wherein, The specific steps of processing the digital signals after analog-to-digital conversion by the digital signal processing module comprise: S41. Shift the baseband signals obtained by the four parallel receivers to the left and right, and shift them to the original position of the sliced spectrum; S42. Perform channel response inverse compensation on the shifted sliced spectrum signals, and splice the compensated sliced signals by a sliding window algorithm; S43. Perform amplitude normalization on the spliced signals, estimate and compensate for I / Q two-way quadrature imbalance, correct sampling clock deviation to realize synchronization of the clock signals at the transmitting end and the receiving end; S44. Equalize the channel by using an equalization algorithm; S45. Realize matching filter function by using a square root raised cosine filter, and down-sample the signals after matching filtering; S46. Calculate the bit error rate of the reconstructed signals through the down-sampled signals, and evaluate the performance of the received signals.

3. The single-ended PD array based low complexity optical arbitrary waveform measurement method according to claim 1, wherein, In the single-end PD array low-complexity optical arbitrary waveform measurement, the optical comb generation module is generated in an electro-optic modulation mode, the center wavelength of the optical comb is 1548nm-1550nm, and the frequency interval of the optical comb is 24GHz-26GHz.

4. The single-ended PD array based low complexity optical arbitrary waveform measurement method of claim 1, wherein, In the single-end PD array low-complexity optical arbitrary waveform measurement, the parallel receiver array comprises four columns of parallel receivers.

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