Common delay line and optical phase-locked loop link device for simultaneous phase locking of double chirp signals

Abstract

The invention provides a common delay line and optical phase-locked loop link device for simultaneous phase locking of double chirp signals. The common delay line and optical phase-locked loop link device comprises an upper scanning frequency modulation continuous wave source, a lower scanning frequency modulation continuous wave source, a common Mach-Zehnder interferometer module, an optical orthogonal front end and an optical phase-locked loop module. The up-sweep frequency modulation continuous wave source and the down-sweep frequency modulation continuous wave source are modulated by adopting triangular waves with opposite phases to generate an up-sweep frequency modulation continuous wave source and a down-sweep frequency modulation continuous wave source, and double-chirp signal output is realized in a half modulation period; and the shared Mach-Zehnder interferometer module is arranged on the optical path, receives the double-chirp signal and outputs the double-chirp signal. The phase noise correlation between the two chirp sources can be improved, the phase noise of each of the two chirp sources can be suppressed, the chirp linearity can be improved, the utilization efficiency of the delay line can be improved, and the device integration level of the whole optical module and the whole electric module can be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of digital signal processing, and in particular relates to a shared delay line and optical phase-locked loop link device for simultaneous phase locking of double chirp signals. Background Art

[0002] Frequency modulated continuous wave laser radar has the characteristics of high sensitivity, high precision, low power consumption, eye safety, anti-stray light interference, and simultaneous mapping of object distance / speed information. It has been widely used in the fields of autonomous driving, assisted navigation, and traffic accident warning. To obtain the distance / speed information of the object under test at the same time, the frequency modulated continuous wave signal needs to have up and down scanning chirps. At present, the main schemes for generating double chirps include triangular wave modulated distributed feedback semiconductor lasers and external modulation schemes based on carrier suppression technology. The former can obtain up and down scanning chirps within one modulation cycle, but the acquisition time of distance / speed information needs to be greater than one modulation cycle, which greatly limits the performance of this scheme in scenarios such as traffic accident warning that require fast response time. The latter, through carrier suppression technology, can simultaneously generate up and down scanning chirp signals within half a modulation cycle, but this scheme requires the use of expensive modulators, and the bias point of the modulator will be interfered by environmental factors, and the bandwidth of the frequency sweep will also be limited by the bandwidth of the modulator.

[0003] In addition to the above two methods for generating double chirps, two distributed feedback semiconductor lasers with similar wavelengths can be used and driven by voltage signals in opposite scanning directions. The outputs of the two chirp sources can then be coupled to obtain a double chirp source. However, this method currently has some key problems, such as poor correlation between the phase noise of the two chirps, large phase noise of the two chirp sources, poor chirp linearity, and the inability to use a consistent pre-distortion waveform for correction. Summary of the invention

[0004] The object of the present invention is to solve the defects of the above-mentioned prior art and provide a shared delay line and optical phase-locked loop link device for simultaneous phase locking of dual chirp signals.

[0005] The present invention adopts the following technical solution:

[0006] A shared delay line and optical phase-locked loop link device for simultaneous phase locking of dual chirp signals comprises up- and down-sweep frequency modulated continuous wave sources, a shared Mach-Zehnder interferometer module, an optical orthogonal front end, and an optical phase-locked loop module.

[0007] The up-sweep and down-sweep frequency modulated continuous wave sources are modulated by triangle waves with opposite phases to generate up-sweep frequency modulated continuous wave sources and down-sweep frequency modulated continuous wave sources, and realize double chirp signal output within half a cycle.

[0008] The shared Mach-Zehnder interferometer module is arranged on the optical path, receives the double-chirp signal, and outputs it.

[0009] The optical orthogonal front end receives the output of the shared Mach-Zehnder interferometer module, extracts the beat frequency electrical signal, and outputs it.

[0010] The optical phase-locked loop module is electrically connected to the optical orthogonal front end and the up- and down-sweep frequency-modulated continuous wave source, receives the beat frequency electrical signal output by the optical orthogonal front end, and feeds the signal back to the up- and down-sweep frequency-modulated continuous wave source to achieve simultaneous phase locking.

[0011] In one embodiment, the shared Mach-Zehnder interferometer module includes a Mach-Zehnder interferometer module I, a Mach-Zehnder interferometer module II, and a shared optical fiber delay line.

[0012] Mach-Zehnder interferometer I and Mach-Zehnder interferometer II are placed in parallel.

[0013] Mach-Zehnder interferometer I receives the chirped signal of the up-sweep frequency modulated continuous wave source and outputs it.

[0014] Mach-Zehnder interferometer II receives the chirped signal of the down-scanned frequency modulated continuous wave source and outputs it.

[0015] The shared optical fiber delay line combines the signals received by Mach-Zehnder interferometer I and Mach-Zehnder interferometer II and outputs them.

[0016] In one embodiment, the optical phase-locked loop module includes a mixer, an electrical amplifier, an integrator, and an arbitrary function generator.

[0017] Arbitrary function generator generates reference signal and transmits the signal to mixer I and mixer II.

[0018] The mixer includes mixer I and mixer II.

[0019] Mixer I mixes the reference signal with the beat frequency electrical signal output by the optical orthogonal front end to generate an error signal.

[0020] Mixer II mixes the reference signal with the beat frequency electrical signal output by the optical orthogonal front end to generate an error signal.

[0021] The electric amplifier comprises an electric amplifier I and an electric amplifier II.

[0022] The electric amplifier I receives the error signal generated by the mixer I, amplifies it and outputs it.

[0023] The electric amplifier II receives the error signal generated by the mixer II, amplifies it and outputs it.

[0024] The integrator comprises an integrator I and an integrator II.

[0025] The integrator I receives the error signal after amplification by the electric amplifier I, integrates it and outputs it to the up-scanning frequency-modulated continuous wave source.

[0026] The integrator II receives the error signal after amplification by the electric amplifier II, integrates it and outputs it to the down-scanning frequency-modulated continuous wave source.

[0027] In one embodiment, the up- and down-sweep frequency modulated continuous wave sources are generated using two independent current modulated distributed feedback semiconductor lasers.

[0028] In one embodiment, Mach-Zehnder interferometer I and Mach-Zehnder interferometer II are both composed of two 5:5 type fiber-optic couplers connected in series. The fiber-optic coupler is used to couple the optical signal and output it to the shared fiber-optic delay line, and is used to output the result. The length of the shared fiber-optic delay line is 10m.

[0029] In one embodiment, the optical orthogonal front end includes a 90° optical phase shifter and two balanced detectors. After the two optical signals pass through the optical orthogonal front end, electrical beat frequency signals with a phase difference of 90° are output.

[0030] In one embodiment, the phase noise of the electrical signal output by the arbitrary function generator is -125dBc / Hz@10kHz within the frequency range of 0.1kHz-10MHz. The electrical amplifier I and the electrical amplifier II are the same device, which can provide a 60dB adjustable amplification / reduction factor. The integration time of the integrator is 10kHz, which is designed by the resistor and capacitor time constant.

[0031] Beneficial effects of the present invention:

[0032] The present invention provides a double-chirp linear frequency sweep source. In the whole device, the output power of the laser used to generate the up-sweep frequency modulated continuous wave is 57.83mW, and the output power of the laser used to generate the down-sweep frequency modulated continuous wave is 60.00mW. The operating temperature of the module is 20°C. After beam splitting and beam combining, the output power of the final phase-locked double-chirp signal is 53mW.

[0033] The coherence enhancement between incoherent sources is achieved by using a shared phase-locked loop module, and the simultaneous phase locking of dual chirps is achieved by using a shared delay line, which improves the utilization efficiency of the delay line and the device integration of the entire optical module and electrical module. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a structural schematic diagram of the present invention;

[0035] Figure 2These are time-frequency analysis diagrams of the up-sweep frequency modulated continuous wave source and the down-sweep frequency modulated continuous wave source after phase locking in Example 1, wherein (a) is a time-frequency analysis diagram of the up-sweep frequency modulated continuous wave source, and (b) is a time-frequency analysis diagram of the down-sweep frequency modulated continuous wave source.

[0036] Figure 3 The bar graphs are the difference between the time-frequency signals output by the upper sweep continuous wave source and the lower sweep continuous wave source and the first-order fitting function, where (a) is the bar graph of the difference between the upper sweep continuous wave source and (b) is the bar graph of the difference between the lower sweep continuous wave source.

[0037] Figure 4 It is a time series comparison diagram of the error between the time-frequency signal output by the upper sweep continuous wave source and the lower sweep continuous wave source and the difference between the first fitting function.

[0038] Figure 5 It is the frequency noise power spectrum density diagram after the difference between the time-frequency signal output by the up-sweep frequency continuous wave source and the down-sweep frequency continuous wave source and the first-order fitting function, where (a) is the up-chirp difference frequency noise power spectrum density diagram of the up-sweep frequency modulation and down-sweep frequency modulation continuous wave source, and (b) is the down-chirp difference frequency noise power spectrum density diagram of the up-sweep frequency modulation and down-sweep frequency modulation continuous wave source.

[0039] In the figure: 1-up and down sweep frequency modulated continuous wave source, 2-shared Mach-Zehnder interferometer module, 3-shared fiber delay line, 4-optical orthogonal front end, 5-mixer, 6-electric amplifier, 7-integrator, 8-arbitrary function generator.

[0040] 1011-upward scanning frequency modulation continuous wave source, 1012-downward scanning frequency modulation continuous wave source.

[0041] 2021-Mach-Zehnder Interferometer I, 2022-Mach-Zehnder Interferometer II.

[0042] 5011-Mixer I, 5012-Mixer II.

[0043] 6011-Electric amplifier I, 6012-Electric amplifier II.

[0044] 7011-Integrator I, 7012-Integrator II.

[0045] Note: Up FMCW Source, UP sweep Frequency-Modulated Continuous-Wave Source, Down FMCW Source, Down sweep Frequency-Modulated Continuous-Wave Source, fiber jumper (Fiber), fiber coupler (FC), fiber delay line (DL), optical orthogonal front end (90° Hybrid), mixer, arbitrary function generator (AFG), amplifier (AMP), integrator. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention is described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] like Figure 1 As shown, a shared delay line and optical phase-locked loop link device for simultaneous phase locking of dual chirp signals of the present invention comprises an up- and down-sweep frequency modulated continuous wave source 1, a shared Mach-Zehnder interferometer module 2, an optical orthogonal front end 4, and an optical phase-locked loop module.

[0048] The up-sweep and down-sweep frequency modulated continuous wave source 1 uses triangular waves with opposite phases for modulation to generate an up-sweep frequency modulated continuous wave source 1011 and a down-sweep frequency modulated continuous wave source 1012, and realizes double chirp signal output within half a modulation period.

[0049] The shared Mach-Zehnder interferometer module 2 is arranged on the optical path, receives the double-chirp signal, and outputs it.

[0050] The shared Mach-Zehnder interferometer module 2 includes a Mach-Zehnder interferometer I 2021 , a Mach-Zehnder interferometer II 2022 , and a shared optical fiber delay line 3 .

[0051] Mach-Zehnder interferometer I 2021 is placed parallel to Mach-Zehnder interferometer II 2022.

[0052] Mach-Zehnder interferometer I 2021 receives the chirp signal of the up-sweep frequency modulated continuous wave source 1011 and outputs it.

[0053] The Mach-Zehnder interferometer II 2022 receives the chirped signal of the down-sweep continuous wave source 1012 and outputs it.

[0054] The shared optical fiber delay line 3 combines the double-chirp signals received by the Mach-Zehnder interferometer I 2021 and the Mach-Zehnder interferometer II 2022 and outputs them.

[0055] The optical orthogonal front end 4 receives the output of the shared optical fiber delay line 3 , extracts the beat frequency electrical signal, and outputs it to the mixer 5 .

[0056] The optical phase-locked loop module is electrically connected to the optical orthogonal front end 4 and the up / down sweep frequency modulated continuous wave source 1, receives the beat frequency electrical signal output by the optical orthogonal front end 4, and feeds the signal back to the up / down sweep frequency modulated continuous wave source 1 to achieve simultaneous phase locking.

[0057] The optical phase-locked loop module includes a mixer 5, an electrical amplifier 6, an integrator 7, and an arbitrary function generator 8.

[0058] The arbitrary function generator 8 generates a reference signal and transmits the signal to the mixer I 5011 and the mixer II 5012. The arbitrary function generator 8 can calculate a standard frequency according to the sweep width of the frequency modulated continuous wave and the length of the shared delay line, and the standard frequency and the beat frequency outputted by the optical orthogonal front end 4 are mixed in the mixer 5 to produce an error signal.

[0059] The mixer 5 receives the reference signal generated by the arbitrary function generator 8 and the beat frequency electrical signal generated by the optical orthogonal front end 4, mixes the reference signal and the beat frequency signal to generate an error signal.

[0060] The mixer 5 includes a mixer I 5011 and a mixer II 5012 .

[0061] Mixer I 5011 mixes the reference signal with the beat frequency electrical signal output by the optical orthogonal front end 4 to generate an error signal.

[0062] Mixer II 5012 mixes the reference signal with the beat frequency electrical signal output by the optical orthogonal front end 4 to generate an error signal.

[0063] The electric amplifier 6 receives the error signal generated by the mixer 5, amplifies it and outputs it.

[0064] The electrical amplifier 6 includes electrical amplifier I 6011 and electrical amplifier II 6012 .

[0065] The electric amplifier I 6011 receives the error signal generated by the mixer I 5011, amplifies it and outputs it. The electric amplifier I 6011 is used to adjust the gain in the phase-locked loop formed by the up-sweep frequency modulation continuous wave source 1011.

[0066] The electric amplifier II 6012 receives the error signal generated by the mixer II 5012, amplifies it and outputs it. The electric amplifier II 6012 is used to adjust the gain in the phase-locked loop formed by the down-sweep continuous wave source.

[0067] The integrator 7 receives the error signal after amplification by the electric amplifier 6, integrates it and outputs it to the up-sweep and down-sweep frequency modulation continuous wave source 1 to achieve simultaneous phase locking. The integrator 7 is used to accumulate the error information in the time domain. The integration time of the integrator 7 is 10kHz, which is designed by the resistor and capacitor time constant.

[0068] Integrator 7 includes integrator I 7011 and integrator II 7012 .

[0069] Integrator I 7011 receives the error signal after amplification by the electrical amplifier 6011, integrates it and outputs it to the up-scanning frequency-modulated continuous wave source 1011.

[0070] Integrator II 7012 receives the error signal after amplification by the electrical amplifier 6012, integrates it and outputs it to the down-scanning frequency modulated continuous wave source 1012.

[0071] In one embodiment, the up-sweep and down-sweep frequency modulated continuous wave sources 1 are generated by two independent current modulated distributed feedback semiconductor lasers.

[0072] In one embodiment, the Mach-Zehnder interferometer I 2021 and the Mach-Zehnder interferometer II 2022 are both composed of two 5:5 type fiber couplers connected in series, and the fiber couplers are used to couple optical signals and output them to the common fiber delay line 3, and are used to output the results. The length of the common fiber delay line 3 is 10m.

[0073] In one embodiment, the optical quadrature front end 4 includes a 90° optical phase shifter and two balanced detectors, and the two optical signals output electrical beat frequency signals with a phase difference of 90° after passing through the optical quadrature front end 4. In the present invention, only the in-phase electrical signal output by the optical quadrature front end 4 is used, and the other quadrature signal can be reserved as a signal acquisition path or other optimization algorithm interface.

[0074] In one embodiment, the phase noise of the electrical signal output by the arbitrary function generator 8 is -125dBc / Hz@10kHz within the frequency range of 0.1kHz-10MHz. The electrical amplifier I 6011 and the electrical amplifier II 6012 are the same devices and can provide a 60dB adjustable amplification / reduction factor.

[0075] Example

[0076] The peak-to-peak value of the modulation signal of the up-sweep and down-sweep frequency modulated continuous wave source 1 is 20mA, and the modulation frequency is 2.5KHz. The output power of the two frequency modulated continuous wave sources is about 60mW, and the operating temperature is 20℃.

[0077] The up- and down-sweep frequency modulated continuous wave sources 1 are input into the common Mach-Zehnder interferometer module 2 through the optical fiber jumper, and are combined as output in one arm of the common optical fiber delay line 3. After that, the signal enters the corresponding optical orthogonal front end 4 to extract the beat frequency signal, and the respective beat frequency signals are fed back to the up- and down-sweep frequency modulated continuous wave sources 1 through the optical phase-locked loop module to achieve simultaneous phase locking.

[0078] The results of the embodiments are tested respectively:

[0079] like Figure 2 As shown in the figure, the result is obtained by using a single-frequency narrow-linewidth laser to beat the up- and down-frequency modulated continuous wave sources, collecting the time series on an oscilloscope and using the short-time Fourier algorithm. It can be seen from the figure that the up-sweep frequency modulated continuous wave source and the down-sweep frequency modulated continuous wave source have good linearity, and there is a certain phase delay between them.

[0080] Using statistical characterization:

[0081] like Figure 3 As shown in FIG. 1 , the result is obtained by using an oscilloscope and a post-processing algorithm. The beat signal from the optical orthogonal front end 4 is collected by an oscilloscope. The post-processing process includes performing Hilbert transform on the beat signal to extract the up and down sweep frequency sequences, performing linear fitting on the frequency sequence, and drawing the error bar statistics after deducting the linearity. It can be seen from the figure that both the up-chirp and the down-chirp have similar residual distributions. Therefore, it can be seen that the quality of the up-sweep frequency modulated continuous wave source and the down-sweep frequency modulated continuous wave source is almost the same, proving that there is a certain phase noise correlation between them.

[0082] Using time series representation:

[0083] like Figure 4 As shown in FIG. 1 , the result is obtained by using an oscilloscope and a post-processing algorithm. The beat signal from the optical orthogonal front end 4 is collected by an oscilloscope. The post-processing process includes performing Hilbert transform on the beat signal to extract the up and down sweep frequency sequences, performing linear fitting on the frequency sequence, and drawing the frequency sequence after deducting the linear fitting. It can be seen from the figure that both the up chirp and the down chirp have similar time series trends. Therefore, it can be seen that the quality of the frequency modulated continuous wave source of the up-sweep frequency modulated continuous wave source and the down-sweep frequency modulated continuous wave source is almost the same, proving that there is a certain phase noise correlation between them.

[0084] Using frequency characterization:

[0085] like Figure 5 As shown in the figure, the result is obtained by using an oscilloscope and a post-processing algorithm. The beat frequency signal from the optical orthogonal front end is collected by an oscilloscope. The post-processing process includes performing Hilbert transform on the beat frequency signal to extract the up and down sweep frequency sequences, performing linear fitting on the frequency sequence and obtaining the frequency sequence after deducting the linear fitting, and obtaining the frequency noise power spectrum density of the remaining frequency sequence. It can be seen from the figure that both the up-chirp and the down-chirp have similar frequency noise power spectrum density distributions. Therefore, it can be seen that the quality of the up-sweep frequency modulated continuous wave source and the down-sweep frequency modulated continuous wave source is almost the same, proving that there is a certain phase noise correlation between them.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A shared delay line and optical phase-locked loop link device for simultaneous phase locking of dual chirp signals, characterized in that , including up- and down-scanning frequency modulated continuous wave sources, shared Mach-Zehnder interferometer modules, optical orthogonal front ends, and optical phase-locked loop modules; The up-sweep and down-sweep frequency modulated continuous wave sources are modulated by using triangle waves with opposite phases to generate up-sweep frequency modulated continuous wave sources and down-sweep frequency modulated continuous wave sources, and realize double chirp signal output within half a modulation period; A shared Mach-Zehnder interferometer module is arranged on the optical path, receives the double-chirp signal, and outputs it; An optical orthogonal front end receives the output of the common Mach-Zehnder interferometer module, extracts the beat frequency electrical signal, and outputs it; The optical phase-locked loop module is electrically connected to the optical orthogonal front end and the up-sweep and down-sweep frequency modulated continuous wave sources, receives the beat frequency electrical signal output by the optical orthogonal front end, and feeds the signal back to the up-sweep and down-sweep frequency modulated continuous wave sources respectively to achieve simultaneous phase locking.

2. The shared delay line and optical phase-locked loop link device for simultaneous phase locking of dual chirp signals according to claim 1, characterized in that: The shared Mach-Zehnder interferometer module includes Mach-Zehnder interferometer module I, Mach-Zehnder interferometer module II, and a shared optical fiber delay line; Mach-Zehnder interferometer I and Mach-Zehnder interferometer II are placed in parallel; Mach-Zehnder interferometer I, receives the chirped signal of the up-sweep frequency modulated continuous wave source and outputs it; Mach-Zehnder interferometer II receives the chirped signal of the down-scanned frequency modulated continuous wave source and outputs it; The shared optical fiber delay line combines the signals received by Mach-Zehnder interferometer I and Mach-Zehnder interferometer II and outputs them.

3. The shared delay line and optical phase-locked loop link device for simultaneous phase locking of dual chirp signals according to claim 1, characterized in that: An optical phase-locked loop module, including a mixer, an electrical amplifier, an integrator, and an arbitrary function generator; An arbitrary function generator generates a reference signal and transmits the signal to mixer I and mixer II; Mixer, including mixer I and mixer II; Mixer I, mixing the reference signal with the beat frequency electrical signal output by the optical orthogonal front end to generate an error signal; Mixer II, mixing the reference signal with the beat frequency electrical signal output by the optical orthogonal front end to generate an error signal; Electric amplifier, including electric amplifier I and electric amplifier II; The electric amplifier I receives the error signal generated by the mixer I, amplifies it and then outputs it; The electric amplifier II receives the error signal generated by the mixer II, amplifies it and outputs it; Integrator, including integrator I and integrator II; Integrator I receives the error signal after amplification by electric amplifier I, integrates it and outputs it to the up-scanning frequency modulated continuous wave source; The integrator II receives the error signal after amplification by the electric amplifier II, integrates it and outputs it to the down-scanning frequency-modulated continuous wave source.

4. The shared delay line and optical phase-locked loop link device for simultaneous phase locking of dual chirp signals according to claim 1, characterized in that: The up-sweep and down-sweep frequency modulated continuous wave sources are generated by two independent current modulated distributed feedback semiconductor lasers.

5. The shared delay line and optical phase-locked loop link device for simultaneous phase locking of dual chirp signals according to claim 2, characterized in that: Mach-Zehnder interferometer I and Mach-Zehnder interferometer II are both composed of two 5:5 type fiber-optic couplers connected in series; the fiber-optic coupler is used to couple optical signals and output them to a common fiber-optic delay line, and is also used to output the results. The length of the common fiber-optic delay line is 10m.

6. The shared delay line and optical phase-locked loop link device for simultaneous phase locking of dual chirp signals according to claim 1, characterized in that: The optical orthogonal front end includes a 90° optical phase shifter and two balanced detectors. After the two optical signals pass through the optical orthogonal front end, electrical beat frequency signals with a phase difference of 90° are output.

7. The shared delay line and optical phase-locked loop link device for simultaneous phase locking of dual chirp signals according to claim 3, characterized in that: The phase noise of the electrical signal output by the arbitrary function generator is -125dBc / Hz@10kHz within the frequency range of 0.1kHz-10MHz; the electrical amplifier I and the electrical amplifier II are the same devices, providing a 60dB adjustable amplification / reduction factor, and the integration time of the integrator is 10kHz, which is designed by the resistor and capacitor time constant.

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