CN107104739A - A kind of ultra-broadband digital laser phase-locked loop device and phase-lock technique - Google Patents

Abstract

The invention discloses an ultra-broadband digital laser phase-locked loop device, comprising: an optical mixer, used to mix a received optical signal and a local oscillator signal to obtain four-way mixed frequency signals; a balance detector, used to combine the The four-way mixing signal is converted into a first-way electrical signal and a second-way electrical signal which are mutually orthogonal; the first AD sampling circuit and the second AD sampling circuit are respectively used to perform the first sampling according to a preset sampling frequency. The circuit electrical signal and the second electrical signal are sampled to obtain the corresponding first digital signal and the second digital signal; a phase fine tracking loop and a phase rough tracking loop, wherein the phase fine tracking calculation module and the phase rough tracking The calculation module is realized by FPGA chip. The ultra-broadband digital laser phase-locked loop device disclosed by the invention can realize effective compensation when the frequency difference between the received optical signal and the local oscillator signal is large, and improve communication reliability. The invention also discloses an ultra-broadband digital laser phase-locking method.

Description

An ultra-broadband digital laser phase-locked loop device and phase-locked method

technical field

The invention relates to the technical field of optical communication, in particular to an ultra-wideband digital laser phase-locked loop device and an ultra-wideband digital laser phase-locked method.

Background technique

The purpose of communication is to transmit information quickly, efficiently, safely and accurately through channels. As an important part of the future information highway, satellite communication technology has become an important force to promote social progress and improve human living standards.

With the deepening of research on inter-satellite communication, people's requirements for data rates have been developed towards several Gbps. Therefore, the coherent optical communication system using laser as the information carrier has entered people's sight, and it has become an inevitable trend in the development of satellite communication to replace microwave links with laser links.

Laser has the characteristics of high coherence and high frequency. Therefore, compared with microwave communication, laser communication has the advantages of large bandwidth and high data transmission rate. Laser communication has a communication capability of up to hundreds of Gbps, which meets the needs of future massive space information transmission. In addition, the use of laser as the transmission medium to establish a communication link also has a small divergence angle, is not easy to be intercepted, high confidentiality, small beam energy dispersion, and can carry out effective transmission over long distances. The communication terminal is small in size and light in weight , low power consumption and other advantages, it is very suitable as an information carrier for satellite communication.

Traditional laser communication systems mostly use intensity modulation/direct detection (IM/DD), that is, the transmitter modulates the intensity of the optical carrier, and the receiver performs envelope detection on the optical carrier. Although this structure has the advantages of simplicity and easy integration, but because it can only use ASK modulation format, its single channel bandwidth is very limited, and its sensitivity is not high.

Compared with traditional direct intensity modulation (IM/DD) laser communication, coherent laser communication has the advantages of high sensitivity and fast speed, and is especially suitable for inter-satellite laser communication and the detection of weak signal light. Under the coherent system, the homodyne receiver modulated by Binary Phase Shift Keying (BPSK) signal can achieve the highest theoretical sensitivity, which is a hot spot in the research of coherent optical communication.

In a coherent laser communication link, according to whether the frequencies of local oscillator light and signal light are consistent, the communication system can be divided into homodyne detection and heterodyne detection. Phase synchronization problem, that is, laser phase-locking technology. There are two main methods of optical phase-locked loop, one is the analog phase-locked loop circuit, the other is the digital phase-locked loop circuit, although the digital optical phase-locked loop circuit has a simple and flexible structure, superior performance, and good scalability, but due to the The Doppler frequency shift of the received optical signal and the local optical signal in the communication system is greater than +/-7GHz. At the same time, the small drift of the laser may cause the frequency difference between the signal light and the local oscillator frequency to become very large, which may reach several On the order of ten GHz.

When implementing the present invention, the inventor found that the single-loop digital optical phase-locked loop in the prior art cannot directly compensate such a large frequency difference.

Therefore, there is an urgent need for a new solution capable of compensating large frequency differences in coherent optical receivers.

Contents of the invention

The purpose of the embodiments of the present invention is to provide an ultra-broadband digital laser phase-locked loop device and a phase-locked method, which can realize effective compensation when the frequency difference between the received optical signal and the local oscillator signal is large, and improve communication reliability .

In order to achieve the above purpose, an embodiment of the present invention provides an ultra-wideband digital laser phase-locked loop device, including:

An optical mixer, which is used to mix the received optical signal and the local oscillator signal to obtain four channels of mixed frequency signals;

a balanced detector, configured to convert the four-way mixing signals into a first-way electrical signal and a second-way electrical signal that are mutually orthogonal;

The first AD sampling circuit and the second AD sampling circuit are respectively used to sample the first electrical signal and the second electrical signal according to a preset sampling frequency to obtain corresponding first digital signals and second digital signals ;

The fine phase tracking loop is used to realize the fine tracking of the carrier during demodulation, including a phase fine tracking calculation module, a first D/A conversion module, a low-pass filter and an acousto-optic frequency shifter; the phase fine tracking calculation module Calculate the frequency difference between the received optical signal and the local oscillator signal according to the first digital signal and the second digital signal, and obtain the control signal of the acousto-optic frequency shifter according to the frequency difference, and the control signal of the acousto-optic frequency shifter is successively Output to the acousto-optic frequency shifter after passing through the first D/A conversion module and the low-pass filter; the acousto-optic frequency shifter is used to perform the original laser signal output by the laser according to the control signal of the acousto-optic frequency shifter Frequency shifting processing to obtain a local oscillator signal and output it to the optical mixer;

The phase rough tracking loop includes a phase rough tracking calculation module, a temperature control module and a laser, and the phase rough tracking calculation module calculates the distance between the received optical signal and the local oscillator signal according to the first digital signal and the second digital signal Frequency difference, and generate a laser temperature parameter adjustment signal according to the frequency difference, the temperature control module adjusts the temperature of the laser according to the laser temperature parameter adjustment signal, so that the frequency of the original laser signal output by the laser falls within the Within the frequency band of the phase precision tracking loop;

Wherein, the phase fine tracking calculation module and the phase rough tracking calculation module are realized by FPGA chip.

As an improvement of the above solution, the phase fine tracking calculation module includes a first multiplier, a loop filter, a DDS and a second D/A conversion module, and the input first digital signal and second digital signal pass through the first After the multiplier is multiplied, the frequency offset signal between the received optical signal and the local oscillator signal is obtained, and then passed through the loop filter of the loop filter to convert the frequency offset signal into an amplitude signal and output it to control the DDS. The output of the DDS is converted into an analog signal by the second D/A conversion module, so as to obtain the control signal of the acousto-optic frequency shifter.

As an improvement of the above scheme, the phase rough tracking loop includes a second multiplier, a sliding filter, an energy detection module and a frequency/temperature conversion module; the passband of the sliding filter corresponds to the N subbands divided by the rough tracking , where N=P1/P2, P1 is the coarse tracking bandwidth, and P2 is the fine tracking bandwidth;

The input first digital signal and the second digital signal are multiplied by the second multiplier to receive the frequency offset signal between the optical signal and the local oscillator signal, and then filtered by the sliding filter, the sliding filter Under the control of the filter parameter control module, the signal corresponding to the energy is output, and the energy detection module judges which sub-band the frequency difference is in by detecting the energy of the output signal of the sliding filter, thereby obtaining the range of the frequency difference, The result output by the energy detection module is converted into the laser temperature parameter adjustment signal by the frequency/temperature conversion module.

As an improvement of the above solution, the fine tracking bandwidth is ±25 MHz, the rough tracking bandwidth is ±5 GHz, and N=200.

As an improvement of the above solution, both the first AD sampling circuit and the second AD sampling circuit use EV10AQ190A chip, and the sampling frequency is 5 GHz.

As an improvement of the above scheme, an external clock interface circuit is also included, and the external clock interface circuit is respectively connected with the first AD sampling circuit and the second AD sampling circuit to provide a sampling clock; the external clock interface circuit adopts an ADCLK925 clock buffer chip .

The embodiment of the present invention correspondingly provides an ultra-broadband digital laser phase-locking method, including steps:

S1. Mixing the received optical signal and the local oscillator signal through an optical mixer to obtain four channels of mixed frequency signals;

S2. Converting the four-way mixing signals into mutually orthogonal first-way electrical signals and second-way electrical signals through a balanced detector;

S3. Sampling the first electrical signal and the second electrical signal respectively according to the preset sampling frequency by the first AD sampling circuit and the second AD sampling circuit to obtain corresponding first digital signal and second digital signal ;

S4. Calculate the frequency difference between the received optical signal and the local oscillator signal through the FPGA chip according to the first digital signal and the second digital signal, and respectively obtain an acousto-optic frequency shifter that realizes phase fine tracking according to the frequency difference Control signals and laser temperature parameter adjustment signals for coarse phase tracking;

S5. Using the temperature control module to adjust the temperature of the laser according to the laser temperature parameter adjustment signal, so that the frequency of the original laser signal output by the laser falls within the frequency band of the phase fine tracking loop;

S6. Perform digital-to-analog conversion and filtering on the control signal of the acousto-optic frequency shifter successively through the first D/A conversion module and the low-pass filter, and then output it to the acousto-optic frequency shifter;

S7. Perform frequency shift processing on the original laser signal output by the laser through the acousto-optic frequency shifter according to the control signal of the acousto-optic frequency shifter to obtain a local oscillator signal and output it to the optical mixer; wherein the local oscillator signal The frequency is the frequency of the original laser signal plus the frequency of the control signal of the acousto-optic frequency shifter.

As an improvement of the above solution, in the step S4, the control signal of the acousto-optic frequency shifter is obtained by calculating through the following steps:

S411. Multiply the input first digital signal and the second digital signal by the first multiplier to obtain a frequency offset signal between the received optical signal and the local oscillator signal;

S412. Perform loop filtering on the frequency offset signal through a loop filter, so as to convert the frequency offset signal into an amplitude signal and then output the control DDS, and the output of the DDS is converted into analog by the second D/A conversion module signal, so as to obtain the control signal of the acousto-optic frequency shifter.

As an improvement of the above solution, in the step S4, the laser temperature parameter adjustment signal is obtained by calculating through the following steps:

S421. Multiply the input first digital signal and the second digital signal by a second multiplier to obtain a frequency offset signal between the received optical signal and the local oscillator signal;

S422. Filter the frequency offset signal through a sliding filter, and the sliding filter outputs a signal corresponding to energy under the control of the filter parameter control module; wherein, the passband of the sliding filter corresponds to the rough tracking The divided N subbands, where N=P1/P2, P1 is the coarse tracking bandwidth, and P2 is the fine tracking bandwidth;

S423. Use the energy detection module to detect the energy of the output signal of the sliding filter to determine which sub-band the frequency difference is in, so as to obtain the range of the frequency difference, and convert the result output by the energy detection module into The laser temperature parameter adjustment signal.

As an improvement of the above solution, the fine tracking bandwidth is ±25 MHz, the rough tracking bandwidth is ±5 GHz, and N=200.

Compared with the prior art, an ultra-broadband digital laser phase-locked loop device and a phase-locked method provided by the embodiment of the present invention first mix the received optical signal and the local oscillator signal through an optical mixer to obtain four channels of mixed frequency signals, and convert the four-way mixing signals into mutually orthogonal first-way electrical signals and second-way electrical signals through a balanced detector, and then pass through the first AD sampling circuit and the second AD sampling circuit respectively according to preset The sampling frequency samples the first electrical signal and the second electrical signal to obtain the corresponding first digital signal and second digital signal, and then parallelizes the first digital signal and the second digital signal through the FPGA chip Calculate, calculate the frequency difference between the received optical signal and the local oscillator signal, and obtain the control signal of the acousto-optic frequency shifter for realizing phase fine tracking and the laser temperature parameter adjustment signal for realizing phase coarse tracking respectively according to the frequency difference, and Adjust the temperature of the laser through the temperature control module according to the laser temperature parameter adjustment signal, so that the frequency of the original laser signal output by the laser falls within the frequency band of the phase fine tracking, and through the first D/A The conversion module and the low-pass filter successively perform digital-to-analog conversion and filtering on the control signal of the acousto-optic frequency shifter and output it to the acousto-optic frequency shifter, and finally pass the acousto-optic frequency shifter according to the control signal of the acousto-optic frequency shifter. Perform frequency shift processing on the original laser signal output by the laser to obtain a local oscillator signal and output it to the optical mixer. Therefore, in the embodiment of the present invention, by adopting the dual-loop phase-locking structure of the coarse tracking loop and the fine tracking loop for phase-locking, effective compensation can be realized when the frequency difference between the received optical signal and the local oscillator signal is large, Eliminating the frequency offset caused by the Doppler effect and the temperature drift of the laser has the advantages of strong anti-interference and simple structure, which can effectively improve the accuracy of the tracking phase-locked loop and realize reliable communication.

Description of drawings

FIG. 1 is a structural block diagram of an ultra-broadband digital laser phase-locked loop device in Embodiment 1 of the present invention.

Fig. 2 is a schematic structural diagram of a phase coarse tracking calculation module of an ultra-broadband digital laser phase-locked loop device in Embodiment 1 of the present invention.

Fig. 3 is a schematic structural diagram of a phase precision tracking calculation module of an ultra-broadband digital laser phase-locked loop device in Embodiment 1 of the present invention.

Fig. 4 is a schematic flowchart of an ultra-broadband digital laser phase-locking method in Embodiment 2 of the present invention.

Fig. 5 is a schematic flow chart of step S4 in Embodiment 2 of the present invention.

Fig. 6 is a schematic flow chart of step S4 in Embodiment 2 of the present invention.

detailed description

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

Referring to FIG. 1 , it is a structural block diagram of an ultra-wideband digital laser phase-locked loop device in Embodiment 1 of the present invention. The ultra-broadband digital laser phase-locked loop device of the embodiment of the present invention includes an optical mixer 1, a first balanced detector 21, a second balanced detector 22, a first AD sampling circuit 31, a second AD sampling circuit 32, an external clock Interface circuit 33, FPGA4 including phase fine tracking calculation module 41 and phase rough tracking calculation module 42, first D/A conversion module 51, low-pass filter 52, acousto-optic frequency shifter 6, local oscillator laser 7 and temperature control Module 8.

The optical mixer 1 is used for coherently coupling (mixing) the received optical signal and the local oscillator signal to obtain four channels of mixed signals. Wherein, the local oscillator signal in this embodiment is a constant-amplitude wave generated by the local oscillator laser 7 and frequency-shifted by the acousto-optic frequency shifter 6 . Specifically, the local oscillator signal has a phase difference of 90° (0°, 90°, 180°, 270°). The optical mixer 1 of the present embodiment is a 90° optical mixer, and its main function is to interfere with a certain phase relationship between the received optical signal and the local oscillator signal, so that the received signal light and the relative phase shift are 0° and 90° respectively. °, 180°, 270° local oscillator signals for mixing. Among them, the 0° and 180° signals in the four-way mixing signals mixed by the optical mixer 1 enter the first balance detector 21, and the four-way mixed signals mixed by the optical mixer 1 The 90° and 270° signals in the signal enter the second balance detector 22 .

The first balanced detector 21 and the second balanced detector 22 convert the input four-way mixing signals into electrical signals respectively, so as to obtain mutually orthogonal first-way electrical signals (I-way signal) and second-way electrical signals. signal (Q channel signal).

The first AD sampling circuit 31 and the second AD sampling circuit 32 are respectively used to sample the first electrical signal (I channel signal) and the second electrical signal (Q channel signal) according to a preset sampling frequency, The corresponding first digital signal and second digital signal are obtained. Both the first AD sampling circuit 31 and the second AD sampling circuit 32 are connected to an external clock interface circuit 33, and the external clock interface circuit 33 provides sampling clocks for the first AD sampling circuit and the second AD sampling circuit respectively.

Specifically, the first AD sampling circuit 31 and the second AD sampling circuit 32 are ultra-high-speed AD sampling circuits, and the EV10AQ190A chip is used to sample the I road signal and the Q road signal at the specific implementation time, wherein each road sampling The frequencies are all 5GHz, so the comprehensive sampling frequency of the IQ channel is 10GHz. The external clock interface circuit 33 can adopt the ADCLK925 clock buffer chip, which is used to divide the high-stability clock frequency provided by the outside into two paths, which are respectively provided to the first AD sampling circuit 31 and the second AD sampling circuit 32 as its sampling clock frequency.

The digital tracking phase loop core controller of this embodiment is realized by FPGA4, which is used to realize the laser phase rough tracking and phase fine tracking of the ultra-wideband digital laser phase locked loop. Specifically, the FPGA 4 includes a fine phase tracking calculation module 41 and a rough phase tracking calculation module 42 . Wherein, the phase precision tracking calculation module 41, the first D/A conversion module 51, the low-pass filter 52 and the acousto-optic frequency shifter 6 constitute the phase precision tracking loop of the ultra-wideband digital laser phase-locked loop device of this embodiment 100, which is used to realize precise phase tracking through an acousto-optic frequency shifter, thereby realizing precise laser phase tracking of an ultra-wideband digital laser phase-locked loop. The phase coarse tracking calculation module 42, the local oscillator laser 7 and the temperature control module 8 constitute the phase coarse tracking loop 200 of the ultra-broadband digital laser phase-locked loop device of this embodiment, which is used to modulate the phase of the local oscillator laser 7, and to The laser frequency output by the semiconductor local oscillator laser 7 is roughly adjusted, so as to realize the coarse tracking of the laser phase of the ultra-wideband digital laser phase-locked loop.

Wherein, in the phase rough tracking loop 200, the phase rough tracking calculation module 42 calculates according to the first digital signal and the second digital signal output by the first AD sampling circuit 31 and the second AD sampling circuit 32 Find the frequency difference between the received optical signal and the local oscillator signal, and generate a laser temperature parameter adjustment signal according to the frequency difference, and the temperature control module 8 adjusts the temperature of the local oscillator laser 7 according to the laser temperature parameter adjustment signal, thereby Make the frequency of the original laser signal output by the local oscillator laser 7 fall within the frequency band range of the precise phase tracking loop 100 .

Specifically, as shown in FIG. 2 , the phase coarse tracking calculation module 42 includes a second multiplier 421 , a sliding filter 422 , an energy detection module 423 and a frequency/temperature conversion module 424 . in:

The first digital signal and the second digital signal output by the first AD sampling circuit 31 and the second AD sampling circuit 32 are first multiplied by the second multiplier 421 and then the frequency deviation between the received optical signal and the local oscillator signal Signal.

The second multiplier 421, as a phase detector, is used for phase comparison, compares the phase difference between the received optical signal and the local oscillator signal, specifically the first electrical signal (signal I) and the second electrical signal that are orthogonal to each other The signal (Q channel signal) is multiplied to obtain the frequency offset signal between the received optical signal and the local oscillator signal. The frequency offset signal here is the intermediate frequency signal after down-conversion of the local oscillator signal/received optical signal. If the frequency difference between the local oscillator signal and the received optical signal is 0, the intermediate frequency signal is 0. The homodyne coherent system requires that the frequency of the received optical signal and the frequency of the local oscillator signal must be completely matched, that is, the phase of the local oscillator signal changes with the phase of the received optical signal, and the phases of the two are consistent, so that the detection obtained by the balance detector and the multiplier The intermediate frequency signal is 0. If the intermediate frequency signal is not 0, it will eventually affect the demodulation, resulting in an increase in the bit error rate and affecting the overall coherent performance. Therefore, in this embodiment, the coarse phase tracking loop 200 is used to generate the laser frequency output by the laser based on the frequency offset signal (that is, the intermediate frequency signal after the down-conversion of the received optical signal/local oscillator signal) output by the second multiplier 421. The coarsely adjusted laser temperature parameter adjusts the signal so that the frequency of the original laser signal output by the local oscillator laser 7 falls within the frequency band of the phase fine tracking loop 100 .

Continuing to refer to FIG. 2 , in this embodiment, the passband of the sliding filter 422 corresponds to N subbands divided by rough tracking, where N=P1/P2, where P1 is the coarse tracking bandwidth, and P2 is the fine tracking bandwidth. For example, when the fine tracking bandwidth is ±25MHz and the coarse tracking bandwidth is ±5GHz, if the desired laser signal enters the fine tracking band, the rough tracking band needs to be divided into N=200 subbands, each subband corresponds to a filter, If a filter bank is used, it needs to occupy a lot of resources inside the FPGA. The present invention uses a sliding filter 422 to design, and the filter parameters are set by the FPGA so that the passband of the sliding filter 422 corresponds to the 200 subbands divided by rough tracking.

During specific implementation, the frequency offset signal output by the second multiplier 421 is filtered by the sliding filter 422 , and the sliding filter 422 outputs a signal corresponding to the energy under the control of the filter parameter control module 420 . The energy detection module 423 detects the energy of the output signal of the sliding filter 422 to determine which sub-band the frequency difference is in, so as to obtain the range of the frequency difference. The result output by the energy detection module 423 is converted into a laser temperature parameter adjustment signal by the frequency/temperature conversion module 424 .

The temperature control module 8 adjusts the temperature of the local oscillator laser 7 according to the laser temperature parameter adjustment signal, thereby adjusting the wavelength of the laser output from the local oscillator laser 7, so that the frequency of the original laser signal output by the local oscillator laser 7 falls into the frequency band of the phase precision tracking loop.

Generally, two methods are used to tune the frequency of the local oscillator laser, one is the temperature adjustment, and the other is the adjustment of the voltage as an external input. For temperature adjustment, its range is relatively large, and can reach the order of GHz (about 10 G), which is suitable for large-scale tuning. However, the speed of temperature tuning is slow, on the order of seconds (S), and the frequency and temperature are nonlinear. Therefore, the temperature is suitable for wide-range, low-speed control.

Therefore, this embodiment preferably adopts the method of temperature tuning (temperature control module 8). When the difference frequency between the received optical signal and the local oscillator is relatively large, the f of the local oscillator laser can be widened through temperature tuning at the control end of the temperature. The purpose of the low-speed scanning adjustment processing in the area is to reduce the frequency inconsistency between the received optical signal and the local oscillator signal caused by the Doppler frequency shift, so as to achieve the purpose of frequency control.

In addition, the specific principle and process of controlling the output frequency of the local oscillator laser through the temperature control module 8 in this embodiment are well known to those skilled in the art, and the description is omitted here.

In the fine phase tracking loop 100, the fine phase tracking calculation module 41 calculates the frequency difference between the received optical signal and the local oscillator signal according to the first digital signal and the second digital signal, and obtains the acoustic signal according to the frequency difference The control signal of the optical frequency shifter, the control signal of the acousto-optic frequency shifter passes through the first D/A conversion module 51 and the low-pass filter 52 successively, and then is output to the acousto-optic frequency shifter 6 . The acousto-optic frequency shifter 6 is used to perform frequency shift processing on the original laser signal output by the local oscillator laser 7 according to the control signal of the acousto-optic frequency shifter, so as to obtain a local oscillator signal and output it to the optical mixer 1 .

Specifically, as shown in FIG. 3 , the precise phase tracking calculation module 41 includes a first multiplier 411 , a loop filter 412 , a DDS 413 and a second D/A conversion module 414 . in:

The first digital signal and the second digital signal output by the first AD sampling circuit 31 and the second AD sampling circuit 32 are firstly multiplied by the first multiplier 411 to obtain the frequency between the received optical signal and the local oscillator signal. partial signal.

Wherein, the first multiplier 411 is used as a phase detector for phase comparison, and compares the phase difference between the received optical signal and the local oscillator signal, specifically the first electrical signal (signal I) and the second electrical signal that are orthogonal to each other. The circuit signal (Q channel signal) is multiplied to obtain the frequency offset signal between the received optical signal and the local oscillator signal. The frequency offset signal here is the intermediate frequency signal after down-conversion of the local oscillator signal/received optical signal. If the frequency difference between the local oscillator signal and the received optical signal is 0, the intermediate frequency signal is 0. The homodyne coherent system requires that the frequency of the received optical signal and the frequency of the local oscillator signal must be completely matched, that is, the phase of the local oscillator signal changes with the phase of the received optical signal, and the phases of the two are consistent, so that the detection obtained by the balance detector and the multiplier The intermediate frequency signal is 0. If the intermediate frequency signal is not 0, it will eventually affect the demodulation, resulting in an increase in the bit error rate and affecting the overall coherent performance. Therefore, in this embodiment, the fine phase tracking loop 100 performs fine tracking of the carrier during demodulation based on the frequency offset signal output by the first multiplier 411 (that is, the down-converted intermediate frequency signal of the received optical signal/local oscillator signal), and Outputting the control signal of the acousto-optic frequency shifter is used to drive the acousto-optic frequency shifter 6, so that the local oscillator signal output by the acousto-optic frequency shifter 6 to the optical mixer 1 follows the carrier frequency of the received optical signal within a certain frequency range .

Continuing to refer to FIG. 3 , the frequency offset signal output by the first multiplier 411 is loop-filtered through the loop filter 412, so that the frequency offset signal is converted into an amplitude signal and then output to control the DDS (Direct DigitalSynthesizer, direct digital synthesis) 413, the output of the DDS413 is converted into an analog signal by the second D/A conversion module 414, so as to obtain the control signal of the acousto-optic frequency shifter.

The control signal of the acousto-optic frequency shifter is output to the acousto-optic frequency shifter 6 after being D/A converted and filtered by the first D/A conversion module 51 and the low-pass filter 52 successively. The acousto-optic frequency shifter 6 is used to perform frequency shift processing on the original laser signal output by the local oscillator laser 7 according to the control signal of the acousto-optic frequency shifter, so as to obtain a local oscillator signal and output it to the optical mixer 1. Wherein, the frequency of the local oscillator signal is the frequency of the original laser signal plus the frequency of the control signal of the acousto-optic frequency shifter.

To sum up, an ultra-broadband digital laser phase-locked loop device provided by an embodiment of the present invention first mixes the received optical signal and the local oscillator signal through an optical mixer to obtain four channels of mixed frequency signals, and uses a balanced detector to mix the The four-way mixing signal is converted into a first-way electrical signal and a second-way electrical signal that are orthogonal to each other, and then the first AD sampling circuit and the second AD sampling circuit are respectively used for the first-way electrical signal according to the preset sampling frequency. The electrical signal and the second electrical signal are sampled to obtain the corresponding first digital signal and second digital signal, and then the FPGA chip is used to perform parallel calculations on the first digital signal and the second digital signal to calculate the received optical signal and The frequency difference between the local oscillator signals, and according to the frequency difference, respectively obtain the control signal of the acousto-optic frequency shifter to realize the phase fine tracking and the laser temperature parameter adjustment signal to realize the phase coarse tracking, and through the temperature control module according to the laser The temperature parameter adjustment signal adjusts the temperature of the laser, so that the frequency of the original laser signal output by the laser falls within the frequency band of the phase fine tracking, and passes through the first D/A conversion module and the low-pass filter successively Perform digital-to-analog conversion and filtering on the control signal of the acousto-optic frequency shifter, and then output it to the acousto-optic frequency shifter, and finally perform the original laser signal output by the laser through the acousto-optic frequency shifter according to the control signal of the acousto-optic frequency shifter. Frequency shifting processing is performed to obtain a local oscillator signal and output it to the optical mixer. Therefore, in the embodiment of the present invention, by adopting the dual-loop phase-locking structure of the coarse tracking loop and the fine tracking loop for phase-locking, effective compensation can be realized when the frequency difference between the received optical signal and the local oscillator signal is large, Eliminating the frequency offset caused by the Doppler effect and the temperature drift of the laser has the advantages of strong anti-interference and simple structure, which can effectively improve the accuracy of the tracking phase-locked loop and realize reliable communication.

Referring to FIG. 4, it is a schematic flow chart of an ultra-wideband digital laser phase-locking method in Embodiment 2 of the present invention. The carrier frequency offset compensation method includes steps S1 to S7:

S1. Mix the received optical signal and the local oscillator signal through an optical mixer to obtain four channels of mixed signals.

Wherein, the local oscillator signal in this embodiment is a constant-amplitude wave generated by a local oscillator laser and subjected to frequency shift processing by an acousto-optic frequency shifter. Specifically, the local oscillator signal has a phase difference of 90° (0°, 90°, 180°, 270°). The optical mixer used in this embodiment is a 90° optical mixer, and its main function is to interfere with a certain phase relationship between the received optical signal and the local oscillator signal, so that the relative phase shift of the received signal light is 0°, 90°, respectively. °, 180°, and 270° local oscillator signals are mixed to obtain four mixed frequency signals with 90° phase difference.

S2. Convert the four channels of mixed frequency signals into a first channel of electrical signals and a second channel of electrical signals that are orthogonal to each other by using a balanced detector.

During specific implementation, the input four-way mixing signals are respectively converted into electrical signals by the first balanced detector and the second balanced detector, so as to obtain mutually orthogonal first-way electrical signals (I-way signal) and second-way electrical signals. Two-way electrical signal (Q-way signal). Among them, the 0° and 180° signals in the four-way mixing signals after being mixed by the optical mixer enter the first balance detector, and the 0° and 180° signals in the four-way mixing signals after being mixed by the optical mixer 1 The 90° and 270° signals enter the second balanced detector.

S3. Sampling the first electrical signal and the second electrical signal respectively according to the preset sampling frequency by the first AD sampling circuit and the second AD sampling circuit to obtain corresponding first digital signal and second digital signal .

In this step, the first AD sampling circuit and the second AD sampling circuit used are both ultra-high-speed AD sampling circuits, and the EV10AQ190A chip is used to sample the I-channel signal and the Q-channel signal at the specific implementation time, wherein each channel sampling The frequencies are all 5GHz, so the comprehensive sampling frequency of the IQ channel is 10GHz. In addition, both the first AD sampling circuit and the second AD sampling circuit are connected to an external clock interface circuit, and the external clock interface circuit provides sampling clocks for the first AD sampling circuit and the second AD sampling circuit respectively. The external clock interface circuit can use an ADCLK925 clock buffer chip, which is used to divide the externally provided high-stability clock frequency into two channels, which are respectively provided to the first AD sampling circuit and the second AD sampling circuit as the sampling clock frequency.

S4. Calculate the frequency difference between the received optical signal and the local oscillator signal through the FPGA chip according to the first digital signal and the second digital signal, and respectively obtain an acousto-optic frequency shifter that realizes phase fine tracking according to the frequency difference Control signal and laser temperature parameter adjustment signal for coarse phase tracking.

In this embodiment, the laser phase rough tracking and phase fine tracking of the ultra-broadband digital laser phase-locked loop are realized by FPGA. A frequency offset signal between the received optical signal and the local oscillator signal is obtained based on the orthogonal first electrical signal (I signal) and the second electrical signal (Q signal). The frequency deviation signal here is the intermediate frequency signal after the down-conversion of the local oscillator signal/received optical signal, and based on the frequency deviation signal, the control signal of the acousto-optic frequency shifter for realizing phase fine tracking and the laser temperature for realizing phase coarse tracking are respectively generated. Parameter adjustment signal. Wherein, the laser temperature parameter adjustment signal is used to modulate the phase of the local oscillator laser, and roughly adjust the laser frequency output by the semiconductor local oscillator laser, so as to realize the coarse tracking of the laser phase of the ultra-wideband digital laser phase-locked loop. The control signal of the acousto-optic frequency shifter realizes fine tracking of the carrier during demodulation, and is used to drive the acousto-optic frequency shifter, so that the acousto-optic frequency shifter is output to the local oscillator of the optical mixer within a certain frequency range The signal follows the carrier frequency of the received optical signal.

Specifically, as shown in FIG. 5 , in the step S4, the laser temperature parameter adjustment signal is calculated through the following steps S421-S423:

S421. Multiply the input first digital signal and the second digital signal by a second multiplier to obtain a frequency offset signal between the received optical signal and the local oscillator signal;

S422. Filter the frequency offset signal through a sliding filter, and the sliding filter outputs a signal corresponding to energy under the control of the filter parameter control module; wherein, the passband of the sliding filter corresponds to the rough tracking The divided N subbands, where N=P1/P2, P1 is the coarse tracking bandwidth, and P2 is the fine tracking bandwidth;

S423. Use the energy detection module to detect the energy of the output signal of the sliding filter to determine which sub-band the frequency difference is in, so as to obtain the range of the frequency difference, and convert the result output by the energy detection module into The laser temperature parameter adjustment signal.

In this embodiment, the passband of the sliding filter corresponds to the N subbands divided by the rough tracking, where N=P1/P2, P1 is the rough tracking bandwidth, and P2 is the fine tracking bandwidth. For example, when the fine tracking bandwidth is ±25MHz and the coarse tracking bandwidth is ±5GHz, if the desired laser signal enters the fine tracking band, the rough tracking band needs to be divided into N=200 subbands, each subband corresponds to a filter, If a filter bank is used, it needs to occupy a lot of resources inside the FPGA. The present invention adopts a sliding filter to design, and the filter parameters are set by the FPGA so that the passband of the sliding filter corresponds to the 200 subbands divided by rough tracking.

During specific implementation, the second multiplier is used as a phase detector for phase comparison, and the phase difference between the received optical signal and the local oscillator signal is compared, and specifically the first road electrical signal (1 road signal) and the orthogonal first road signal will be mutually orthogonal. The second electrical signal (Q channel signal) is multiplied to obtain the deviation signal between the received optical signal and the local oscillator signal (ie, the local oscillator signal/the down-converted intermediate frequency signal of the received optical signal).

Then, the frequency offset signal output by the second multiplier is filtered through the sliding filter, and the sliding filter outputs a signal corresponding to the energy under the control of the filter parameter control module. The energy detection module detects the energy of the output signal of the sliding filter to determine which sub-band the frequency difference is in, so as to obtain the range of the frequency difference. The result output by the energy detection module is converted into a laser temperature parameter adjustment signal by the frequency/temperature conversion module.

Finally, the temperature of the local oscillator laser is adjusted by the temperature control module according to the laser temperature parameter adjustment signal, thereby adjusting the wavelength of the output laser light of the local oscillator laser, so that the frequency of the original laser signal output by the local oscillator laser falls within The phase precision tracking loop is within the frequency band range.

Further, as shown in FIG. 6, in the step S4, the control signal of the acousto-optic frequency shifter is calculated by the following steps:

S411. Multiply the input first digital signal and the second digital signal by the first multiplier to obtain a frequency offset signal between the received optical signal and the local oscillator signal;

S412. Perform loop filtering on the frequency offset signal through a loop filter, so as to convert the frequency offset signal into an amplitude signal and then output the control DDS, and the output of the DDS is converted into analog by the second D/A conversion module signal, so as to obtain the control signal of the acousto-optic frequency shifter.

During specific implementation, the first multiplier is used as a phase detector for comparison of the phases, and the phase difference between the received optical signal and the local oscillator signal is compared, specifically the first road electrical signal (signal I) and the first road signal that are orthogonal to each other. The second electrical signal (Q channel signal) is multiplied to obtain the deviation signal between the received optical signal and the local oscillator signal (ie, the local oscillator signal/the down-converted intermediate frequency signal of the received optical signal).

Then, the frequency offset signal output by the first multiplier is loop-filtered through the loop filter, so as to convert the frequency offset signal into an amplitude signal and output it to control the DDS (Direct Digital Synthesizer, Direct Digital Synthesis) , the output of the DDS is converted into an analog signal by the second D/A conversion module 414, so as to obtain the control signal of the acousto-optic frequency shifter.

S5. Using the temperature control module to adjust the temperature of the laser according to the laser temperature parameter adjustment signal, so that the frequency of the original laser signal output by the laser falls within the frequency band of the precise phase tracking.

Specifically, the temperature control module adjusts the temperature of the local oscillator laser according to the laser temperature parameter adjustment signal, thereby adjusting the wavelength of the laser output from the local oscillator laser, so that the frequency of the original laser signal output by the local oscillator laser falls into the frequency band of the phase precision tracking loop.

S6. Perform digital-to-analog conversion and filtering on the control signal of the acousto-optic frequency shifter successively through the first D/A conversion module and the low-pass filter, and then output it to the acousto-optic frequency shifter.

S7. Perform frequency shift processing on the original laser signal output by the laser through the acousto-optic frequency shifter according to the control signal of the acousto-optic frequency shifter to obtain a local oscillator signal and output it to the optical mixer; wherein the local oscillator signal The frequency is the frequency of the original laser signal plus the frequency of the control signal of the acousto-optic frequency shifter.

During specific implementation, the control signal of the acousto-optic frequency shifter is output to the acousto-optic frequency shifter after successively passing through the first D/A conversion module and the low-pass filter for D/A conversion and filtering. The acousto-optic frequency shifter is used to perform frequency shift processing on the original laser signal output by the local oscillator laser according to the control signal of the acousto-optic frequency shifter, so as to obtain a local oscillator signal and output it to the optical mixer. Wherein, the frequency of the local oscillator signal is the frequency of the original laser signal plus the frequency of the control signal of the acousto-optic frequency shifter.

For the detailed working principle and process of the ultra-wideband digital laser phase-locked method disclosed in this embodiment, please refer to the ultra-wideband digital laser phase-locked loop device disclosed in the above-mentioned embodiment, and details will not be repeated here.

In summary, an ultra-broadband digital laser phase-locking method provided by an embodiment of the present invention first mixes the received optical signal and the local oscillator signal through an optical mixer to obtain four channels of mixed frequency signals, and then uses a balanced detector to combine the four channels of mixed signals. The mixed frequency signal is converted into the first electrical signal and the second electrical signal which are orthogonal to each other, and then the first electrical signal and the second AD sampling circuit are respectively used for the first electrical signal according to the preset sampling frequency. Signal and the second electrical signal are sampled to obtain the corresponding first digital signal and second digital signal, and then the first digital signal and the second digital signal are calculated in parallel by the FPGA chip to calculate the received optical signal and this The frequency difference between the vibration signals, and according to the frequency difference, respectively obtain the control signal of the acousto-optic frequency shifter to realize the phase fine tracking and the laser temperature parameter adjustment signal to realize the phase coarse tracking, and through the temperature control module according to the laser temperature The parameter adjustment signal adjusts the temperature of the laser, so that the frequency of the original laser signal output by the laser falls within the frequency band of the phase fine tracking, and the first D/A conversion module and the low-pass filter sequentially The control signal of the acousto-optic frequency shifter is digital-to-analog converted and filtered, and then output to the acousto-optic frequency shifter, and finally the original laser signal output by the laser is shifted by the acousto-optic frequency shifter according to the control signal of the acousto-optic frequency shifter. frequency processing to obtain a local oscillator signal and output it to the optical mixer. Therefore, in the embodiment of the present invention, by adopting the dual-loop phase-locking structure of the coarse tracking loop and the fine tracking loop for phase-locking, effective compensation can be realized when the frequency difference between the received optical signal and the local oscillator signal is large, Eliminating the frequency offset caused by the Doppler effect and the temperature drift of the laser has the advantages of strong anti-interference and simple structure, which can effectively improve the accuracy of the tracking phase-locked loop and realize reliable communication.

It should be noted that the device embodiments described above are only illustrative, and the units described as separate components may or may not be physically separated, and the components shown as units may or may not be physically separated. A unit can be located in one place, or it can be distributed to multiple network units. Part or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. In addition, in the drawings of the device embodiments provided by the present invention, the connection relationship between the modules indicates that they have a communication connection, which can be specifically implemented as one or more communication buses or signal lines. It can be understood and implemented by those skilled in the art without creative effort.

Through the description of the above embodiments, those skilled in the art can clearly understand that the present invention can be realized by means of software plus necessary general-purpose hardware. Special components, etc. to achieve. In general, all functions completed by computer programs can be easily realized by corresponding hardware, and the specific hardware structure used to realize the same function can also be varied, such as analog circuits, digital circuits or special-purpose circuit etc. However, software program implementation is a better implementation mode for the present invention in most cases. Based on this understanding, the essence of the technical solution of the present invention or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product is stored in a readable storage medium, such as a floppy disk of a computer , U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), magnetic disk or optical disk, etc., including several instructions to make a computer device (which can be A personal computer, a server, or a network device, etc.) executes the methods described in various embodiments of the present invention.

The above description is a preferred embodiment of the present invention, and it should be pointed out that for those skilled in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications are also considered Be the protection scope of the present invention.

Claims (9)

1. An ultra-broadband digital laser phase-locked loop device, characterized in that, comprising: An optical mixer, which is used to mix the received optical signal and the local oscillator signal to obtain four channels of mixed frequency signals; a balanced detector, configured to convert the four-way mixing signals into a first-way electrical signal and a second-way electrical signal that are mutually orthogonal; The first AD sampling circuit and the second AD sampling circuit are respectively used to sample the first electrical signal and the second electrical signal according to a preset sampling frequency to obtain corresponding first digital signals and second digital signals ; The fine phase tracking loop is used to realize the fine tracking of the carrier during demodulation, including a phase fine tracking calculation module, a first D/A conversion module, a low-pass filter and an acousto-optic frequency shifter; the phase fine tracking calculation module Calculate the frequency difference between the received optical signal and the local oscillator signal according to the first digital signal and the second digital signal, and obtain the control signal of the acousto-optic frequency shifter according to the frequency difference, and the control signal of the acousto-optic frequency shifter is successively Output to the acousto-optic frequency shifter after passing through the first D/A conversion module and the low-pass filter; the acousto-optic frequency shifter is used to perform the original laser signal output by the laser according to the control signal of the acousto-optic frequency shifter Frequency shifting processing to obtain a local oscillator signal and output it to the optical mixer; The phase rough tracking loop includes a phase rough tracking calculation module, a temperature control module and a laser, and the phase rough tracking calculation module calculates the distance between the received optical signal and the local oscillator signal according to the first digital signal and the second digital signal Frequency difference, and generate a laser temperature parameter adjustment signal according to the frequency difference, the temperature control module adjusts the temperature of the laser according to the laser temperature parameter adjustment signal, so that the frequency of the original laser signal output by the laser falls within the Within the frequency band of the phase precision tracking loop; Wherein, the phase fine tracking calculation module and the phase coarse tracking calculation module are realized by an FPGA chip; It also includes an external clock interface circuit, which is respectively connected to the first AD sampling circuit and the second AD sampling circuit to provide a sampling clock; the external clock interface circuit uses an ADCLK925 clock buffer chip. 2. ultra-broadband digital laser phase-locked loop device as claimed in claim 1, is characterized in that, described phase precise tracking computation module comprises the first multiplier, loop filter, DDS and the second D/A conversion module, The input first digital signal and the second digital signal are multiplied by the first multiplier to obtain a frequency offset signal between the received optical signal and the local oscillator signal, and then passed through the loop filter of the loop filter to obtain The frequency deviation signal is converted into an amplitude signal and then output to control the DDS, and the output of the DDS is converted into an analog signal through the second D/A conversion module, thereby obtaining the control signal of the acousto-optic frequency shifter. 3. the ultra-broadband digital laser PLL device as claimed in claim 1 or 2, is characterized in that, described phase coarse tracking loop comprises the second multiplier, sliding filter, energy detection module and frequency/temperature conversion module ; The passband of the sliding filter corresponds to N subbands divided by coarse tracking, wherein N=P1/P2, P1 is the coarse tracking bandwidth, and P2 is the fine tracking bandwidth; The input first digital signal and the second digital signal are multiplied by the second multiplier to receive the frequency offset signal between the optical signal and the local oscillator signal, and then filtered by the sliding filter, the sliding filter Under the control of the filter parameter control module, the signal corresponding to the energy is output, and the energy detection module judges which sub-band the frequency difference is in by detecting the energy of the output signal of the sliding filter, thereby obtaining the range of the frequency difference, The result output by the energy detection module is converted into the laser temperature parameter adjustment signal by the frequency/temperature conversion module. 4. The ultra-broadband digital laser phase-locked loop device according to claim 3, wherein the fine tracking bandwidth is ±25 MHz, the rough tracking bandwidth is ±5 GHz, and N=200. 5. The ultra-broadband digital laser phase-locked loop device as claimed in claim 1, wherein the first AD sampling circuit and the second AD sampling circuit both adopt EV10AQ190A chip, and the sampling frequency is 5GHz. 6. A method for ultra-broadband digital laser phase-locking, characterized in that, comprising steps: S1. Mixing the received optical signal and the local oscillator signal through an optical mixer to obtain four channels of mixed frequency signals; S2. Converting the four-way mixing signals into mutually orthogonal first-way electrical signals and second-way electrical signals through a balanced detector; S3. Sampling the first electrical signal and the second electrical signal respectively according to the preset sampling frequency by the first AD sampling circuit and the second AD sampling circuit to obtain corresponding first digital signal and second digital signal ; S4. Calculate the frequency difference between the received optical signal and the local oscillator signal through the FPGA chip according to the first digital signal and the second digital signal, and respectively obtain an acousto-optic frequency shifter that realizes phase fine tracking according to the frequency difference Control signals and laser temperature parameter adjustment signals for coarse phase tracking; S5. Using the temperature control module to adjust the temperature of the laser according to the laser temperature parameter adjustment signal, so that the frequency of the original laser signal output by the laser falls within the frequency band of the phase fine tracking; S6. Perform digital-to-analog conversion and filtering on the control signal of the acousto-optic frequency shifter successively through the first D/A conversion module and the low-pass filter, and then output it to the acousto-optic frequency shifter; S7. Perform frequency shift processing on the original laser signal output by the laser through the acousto-optic frequency shifter according to the control signal of the acousto-optic frequency shifter to obtain a local oscillator signal and output it to the optical mixer; wherein the local oscillator signal The frequency of is the frequency of the original laser signal plus the frequency of the control signal of the acousto-optic frequency shifter. 7. ultra-broadband digital laser phase-locking method as claimed in claim 6, is characterized in that, in described step S4, obtain described acousto-optic frequency shifter control signal by the following steps calculation: S411. Multiply the input first digital signal and the second digital signal by the first multiplier to obtain a frequency offset signal between the received optical signal and the local oscillator signal; S412. Perform loop filtering on the frequency offset signal through a loop filter, so as to convert the frequency offset signal into an amplitude signal and then output the control DDS, and the output of the DDS is converted into analog by the second D/A conversion module signal, so as to obtain the control signal of the acousto-optic frequency shifter. 8. the ultra-broadband digital laser phase-locking method as claimed in claim 6 or 7, is characterized in that, in described step S4, obtains described laser temperature parameter adjustment signal by following calculation: S421. Multiply the input first digital signal and the second digital signal by a second multiplier to obtain a frequency offset signal between the received optical signal and the local oscillator signal; S422. Filter the frequency offset signal through a sliding filter, and the sliding filter outputs a signal corresponding to energy under the control of the filter parameter control module; wherein, the passband of the sliding filter corresponds to the rough tracking The divided N subbands, where N=P1/P2, P1 is the coarse tracking bandwidth, and P2 is the fine tracking bandwidth; S423. Use the energy detection module to detect the energy of the output signal of the sliding filter to determine which sub-band the frequency difference is in, so as to obtain the range of the frequency difference, and convert the result output by the energy detection module into The laser temperature parameter adjustment signal. 9. The ultra-broadband digital laser phase-locking method according to claim 8, wherein the fine tracking bandwidth is ±25MHz, the rough tracking bandwidth is ±5GHz, and N=200.