Frequency measurement system of injection-locked laser single-cycle-state loop self-excited subharmonic modulation
A frequency measurement system based on self-excited subharmonic modulation of a single-cycle loop using an injection-locked laser overcomes the limitations of microwave photonic filters in frequency selectivity and tuning range, achieving broadband tunable and high-precision frequency measurement. It is suitable for high-purity spectrum microwave signal generation and high-sensitivity microwave photonic sensing.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- DALIAN UNIV OF TECH
- Filing Date
- 2024-01-03
- Publication Date
- 2026-07-14
Smart Images
Figure CN117848525B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of microwave photonics technology, specifically relating to a frequency measurement system based on self-excited subharmonic modulation of a single-cycle loop of an injection-locked laser. Background Technology
[0002] Microwave photonic filters (MPFs) have wide applications in millimeter-wave communication, high-performance radar, optical wireless communication systems, and wireless local area networks. Compared with traditional electronic filters, microwave photonic filters have advantages such as low loss, large bandwidth, resistance to electromagnetic interference, tunability, and reconfigurability, and are gradually becoming a key technology for high-frequency broadband signal control and processing. With the increasing demands for frequency selectivity of filters in cutting-edge technologies such as high-purity spectrum microwave signal generation, high-sensitivity microwave photonic sensing, and high-resolution microwave photonic radar, broadband tunable MPFs have gradually become a research hotspot and challenge in the field of microwave photonics in recent years.
[0003] To date, researchers have proposed a variety of tunable, narrow-bandwidth MPFs (Wang Wenxuan, Tao Ji, Huang Long. Narrow-band tunable microwave photonic filter based on optically injected Fabry-Perot laser [J]. Chinese Journal of Lasers, 2017, 44(10): 1006-002. (Hu Zonghua, Nie Kuiying, Ruan Yi, et al. Tunable bandpass microwave photonic filter based on dispersive fiber ring cascade structure [J]. Semiconductor Optoelectronics, 2019, 40(2): 189-192-199.). For example, a narrowband, tunable MPF implemented using a phase modulator and a superstructure fiber Bragg grating (SFBG) has a 3dB bandwidth of 143MHz and a tunable range of 0.4–6.4GHz (GAO L.CHEN X F.YAO J P. Tunable microwave photonic filter with a flarrow and fiat-top passband[J].IEEE Microwave and Wireless Components Letters, 2013, 23(7): 362–364.). However, in this scheme, the reflection bandwidth and notch bandwidth of the SFBG determine the frequency tunable range and passband width, and its fabrication process is relatively complicated. In 2016, Zhang (ZHANG TT, XIONG JT, ZHENG JL, et al. Wideband tunable single bandpass microwave photonic filter based on FWM dynamics of optical-injected DFB laser[J]. Electronics Letters, 2016, 52(1): 57-59.) et al. used four-wave mixing based on optically injected distributed feedback semiconductor laser to realize a broadband tunable MPF with a 3dB bandwidth and out-of-band suppression ratio of 61.2MHz and 25dB, respectively. By changing the optical injection parameters, a frequency tuning range of 12-40GHz was achieved. Recently, a ring resonant cavity MPF based on a 2×2 fiber coupler was reported, which achieved a tuning range of 40GHz through a coherent detection link. Compared with the traditional non-cavity MPF, its filtering bandwidth can be as low as 1.2MHz. (Zhang Ziping, Niu Xiaochen, Huang Jie, et al. High-performance microwave photonic filter based on fiber ring resonator [J]. Acta Optica Sinica, 2020, 40(21): 2106001.).Optoelectronic oscillator systems are a classic model of single-mode oscillations that can establish a steady state from noise, and low phase noise is one of its core advantages (HAO T, CEN Q, GUAN S, et al. Optoelectronic parametric oscillator[J]. Light: Science & Applications, 2020, 9, 102). Current mathematical models of optically injected semiconductor lasers are based on the theory proposed by Lang and Kabayshi in 1980. Optically injected semiconductor laser systems mainly exhibit four typical nonlinear dynamics. Among these four dynamic states, the simplest steady-state locked state has been widely studied and applied in areas such as wavelength synchronization and coherence enhancement. Furthermore, the steady-state locked state of optically injected semiconductor lasers has also been used to improve modulation characteristics, such as increasing modulation bandwidth, chirping, and reducing noise. Period-doubling oscillations are mainly used for frequency doubling and division of microwave signals. Chaotic oscillation states are widely used in chaotic secure communication, high-speed random number generation, and chaotic radar. In recent years, the application of single-cycle oscillation states of optically injected semiconductor lasers has gradually gained attention. Researchers have successively studied its applications in signal generation (Zhou Pei, Li Nianqiang, Pan Shilong. Broadband radar signal generation and application based on optically injected semiconductor lasers [J]. Semiconductor Optoelectronics, 2022, 43(01):), photonic microwave amplification, single-sideband modulation and optical frequency conversion. Summary of the Invention
[0004] This invention primarily realizes a system capable of simultaneously measuring the frequencies of multiple signals under test within a single system. The proposed broadband tunable frequency measurement system based on injection-locked laser single-cycle loop self-excited subharmonic modulation achieves the measurement of broadband microwave signals of unknown frequencies by changing the center wavelength or optical power of the main laser and combining it with high-linearity frequency-time mapping technology.
[0005] The technical solution of the present invention is as follows:
[0006] A frequency measurement system for single-cycle loop self-excited subharmonic modulation of an injection-locked laser includes an adjustable laser source, modulator, polarization controller, optical circulator, DFB slave laser, long optical fiber, dispersion-compensating optical fiber, optical amplifier, photodetector, electrical amplifier, high-pass filter, narrow-pass filter, and arbitrary waveform generator.
[0007] The output of the tunable laser source is connected to the optical input port of the modulator. After being modulated by the RF input of the loop signal modulator, the light is output from the optical output port of the modulator and input to the polarization controller. The polarization-controlled light is input to port 1 of the optical circulator and then to port 2 of the DFB for injection locking from the laser. After locking, the laser is input from port 2 of the optical circulator and output from port 3 to the long optical fiber and dispersion compensation fiber. The optical signal is then input to the optical input port of the photodetector for beat frequency. The beat frequency electrical signal is input to the electrical amplifier for amplification. The amplified RF signal is output to the high-pass filter through the power divider to filter out low-frequency noise signals. After being combined with the signal under test, it is input to the RF port of the modulator for modulation and input to the narrowband power filter for frequency-time mapping and detection on the oscilloscope. The system can perform spectral and frequency spectrum detection at the optical splitter and the power divider respectively.
[0008] Furthermore, the arbitrary waveform generator is used to tune the output optical power or optical wavelength of the tunable laser source, or both simultaneously, and to synchronize the periodic tuning signal to the oscilloscope. During the tuning process, the DFB should be kept in the P1 state from the final operating state of the laser.
[0009] Furthermore, in the frequency measurement system, the loop delay is an integer multiple of the tuning period of the tunable laser source output signal, ensuring that the DFB laser is in a subharmonic modulation state. The long optical fiber is used to adjust the loop delay, and the dispersion compensation fiber is used to adjust the loop dispersion to zero.
[0010] Furthermore, the optical amplifier and electrical amplifier are used to ensure that the open-loop gain is greater than 1, generating periodic self-oscillation to produce a periodic frequency-modulated signal. The high-pass filter is used to filter out low-frequency noise signals to improve spectral purity and frequency measurement accuracy.
[0011] Furthermore, the injection coefficient ζ of the tunable laser source and the DFB from the laser's light injection system is adjusted by adjusting the optical power output of the tunable laser source through an arbitrary waveform generator, or by adjusting through a polarization controller.
[0012] Analysis of the mathematical model for optically injected semiconductor laser technology reveals that the properties of the optical signal injected into the semiconductor laser alter its operating characteristics. Furthermore, a redshift in the resonant cavity mode of the semiconductor laser generates an optical gain region. The properties of the injected optical signal itself are primarily determined by the injection coefficient ζ and the detuning frequency f. iThese two parameters, located in the power and frequency dimensions respectively, are used for characterization. By changing the external light injection parameters, the laser can exhibit a variety of nonlinear dynamic outputs, such as single-cycle oscillation (P1 state), period-doubling oscillation, chaotic state, and injection lock. When the system is in the P1 state, the redshift of the laser center wavelength output from the laser will change with ζ and f. i It changes with the changes. The schematic diagram of the output spectral sidebands at this time is shown below. Figure 2 As shown, where λ m , λ s and λ c These are the center wavelengths of the master laser, the laser in its free state, and the laser after redshift, respectively, λ. m With λ s The frequency difference is f i .
[0013] When the signal to be measured f is modulated and fed into the output laser of the master laser, and then injected into the slave laser along with the laser, when the system is operating in P1 state, it will form as follows: Figure 3 The diagram shows a schematic of the spectral sidebands. Then, after the above spectrum is subjected to a beat frequency, it will generate frequencies of f. c =λ c -λ m and λ c -(λ m +f)=f c -f beat frequency signal. Based on the spectral variation characteristics of the P1 state, it can be known that when the injected optical signal's ζ and f... i When changes occur, f c This will also change accordingly. Thus, by periodically tuning the output optical power or wavelength of the tunable laser source using an arbitrary waveform generator, a periodically swept frequency f can be obtained. c and f c -f. Then, the corresponding frequency signal is filtered out using a narrowband pass filter, resulting in two pulse signals per cycle. Finally, the time interval between the two pulse signals within one sweep cycle is measured and compared with f. c By matching the frequency sweep characteristics of the signal, the frequency of the signal under test can be measured by frequency-time mapping.
[0014] Meanwhile, due to the characteristic that a semiconductor laser's resonant cavity mode generates an optical gain region upon redshift, by adjusting the variation period of the tunable laser source in the system to be exactly equal to or an integer multiple of the loop signal's running time, it can be ensured that the signal cyclically loaded onto the modulator through the loop at any given time is exactly the wavelength of the DFB's output signal after redshift from the laser. This conforms to the principle of laser injection-locked subharmonic oscillation (i.e., when the Nth-order sideband modulated on the injection light is close to the wavelength after redshift from the laser, the wavelength of the P1 state operation becomes more stable, where N=1), thus making the system's periodic operation more stable.
[0015] This invention achieves frequency measurement using a narrowband pass-through filter. Only a periodically changing frequency modulation signal is generated in the loop. The difference frequency signal after the beat frequency of this signal and the signal under test is filtered into a pulse signal by the narrowband pass-through filter, thus completing the frequency-time mapping.
[0016] This invention allows for the tuning of the system's frequency measurement range by adjusting the output optical power or wavelength range of the tunable laser source using an arbitrary waveform generator.
[0017] The beneficial effects of this invention are:
[0018] The frequency measurement system of this invention can maintain high frequency measurement accuracy over a long period of continuous operation. Its system stability is directly related to the stability of the loop oscillation signal, and the optical injection lock-in mode under subharmonic modulation can continuously maintain the stability of its own signal; its expected frequency measurement error is close to the bandwidth of the narrowband pass filter, which can reach around 8MHz under existing technology. Attached Figure Description
[0019] Figure 1 This is a schematic diagram of the design device for the broadband signal frequency measurement system provided by the present invention;
[0020] Figure 2 This is a schematic diagram of the spectral sidebands when the laser is injected into the P1 state.
[0021] Figure 3 This is a schematic diagram of the injection-locked P1 state spectral sideband after the signal to be measured is input;
[0022] Figure 4 This is a graph showing the frequency measurement results from the MATLAB program in Example 2. Detailed Implementation
[0023] To make the technical problems solved by the present invention, the technical solutions adopted, and the technical effects achieved clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.
[0024] Example 1:
[0025] Figure 1 This is a link diagram of a frequency measurement system based on self-excited subharmonic modulation in a single-cycle loop of an injection-locked laser, provided by the present invention. The output optical power or wavelength of the tunable laser source 1 is tuned by an arbitrary waveform generator 13, and the output signal of the arbitrary waveform generator 13 is connected to an oscilloscope 17 for clock locking, so that subsequent frequency measurements can be performed. By adjusting the tuning range of the output optical power or wavelength of the tunable laser source 1, the DFB is kept in state P1 from laser 5. At this time, f c and f c -f will change periodically as the output signal of the tunable laser source 1 changes.
[0026] Now assume the beat frequency signal is between 12-18 GHz. When a test signal with a frequency of 10 GHz is input to the system, the modulator will... m λ is modulated on both sides respectively m -10GHz and λ m Positive and negative sideband signals at +10 GHz. Where λ m +10GHz and λ c After passing through the photodetector, the frequency λ is obtained by frequency capture. c -λ m The signal is -10 GHz, and also varies with the periodic change of the center wavelength of the main laser. Given λ... c -λ m The frequency sweep range is 12-18GHz, then the above λ c -λ m The signal frequency range of -10GHz is 2-8GHz. When this signal frequency is the same as the center frequency of the narrowband pass filter (assuming it is 6GHz), a pulse peak can be obtained. It is easy to see that two pulse peaks will appear within one sweep cycle. By measuring the time interval between the pulse peaks and the sweep characteristic curve, frequency-time mapping can be completed, and the frequency of the signal under test can be calculated.
[0027] Example 2:
[0028] like Figure 4 This is based on a single frequency measurement data from this system, in which the system operates stably with oscillations in the range of approximately 12-24 GHz, corresponding to the measured frequency of 6-18 GHz. The system's frequency sweep characteristic curve is shown below. Figure 4 The left-middle figure shows the result obtained by performing a short-time Fourier transform on the swept frequency signal acquired by oscilloscope 17. The 14GHz signal generated by microwave signal source 14 is input into the system, and after being filtered by the loop beat frequency and narrowband pass filter 12, the result is displayed on oscilloscope 17 as shown below. Figure 4 The time interval between the pulse peaks of the double-pulse time-domain envelope shown in the middle right figure is the corresponding parameter of the frequency-time mapping. This can be compared using a MATLAB program. Figure 4 The frequency value calculated from the data in the left and right graphs is 14.005 GHz, meaning the measurement error is 5 MHz.
[0029] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope described in the present invention, based on the technical solution and inventive concept of the present invention, should be included within the scope of protection of the present invention.
Claims
1. A frequency measurement system for self-excited subharmonic modulation of a single-cycle state loop in an injection-locked laser, characterized in that, It includes a tunable laser source (1), a modulator (2), a polarization controller (3), an optical circulator (4), a DFB laser (5), a long optical fiber (6), a dispersion compensation fiber (7), an optical amplifier (8), a photodetector (9), an electrical amplifier (10), a high-pass filter (11), a narrow-band pass filter (12), and an arbitrary waveform generator (13). The output end of the tunable laser source (1) is connected to the optical input port of the modulator (2). The light modulated by the RF input end of the loop signal modulator is output from the optical output port of the modulator (2) and input into the polarization controller (3). The polarization-controlled light is input into port 1 of the optical circulator (4) and then into the DFB laser (5) for injection locking through port 2. After locking, the laser is input from port 2 of the optical circulator (4) and output from port 3 into the long optical fiber (6) and the dispersion compensation optical fiber (7). The optical signal is then amplified by optical amplification. The signal is amplified by the device (8) and split by the optical splitter. It is then input to the optical input port of the photodetector (9) for frequency beat. The frequency beat signal is input to the electric amplifier (10) for amplification. The amplified radio frequency signal is output to the high-pass filter (11) through the power divider to filter out low-frequency noise signals. After being combined with the signal to be measured, it is input to the radio frequency port of the modulator (2) for modulation, and input to the narrowband power filter (12) for frequency-time mapping and detected in the oscilloscope (17). The system can perform spectrum and frequency spectrum detection at the optical splitter and the power divider respectively. The arbitrary waveform generator (13) is used to tune the output optical power or optical wavelength of the tunable laser source (1) or both simultaneously, and to synchronize the periodic tuning signal to the oscilloscope (17). During the tuning process, the DFB should be kept in the P1 state from the final operating state of the laser (5).
2. The frequency measurement system for single-cycle self-excited subharmonic modulation of an injection-locked laser as described in claim 1, characterized in that, The loop delay in the frequency measurement system is related to the period of the adjustable laser source (1) output signal being tuned to an integer multiple, so that the DFB is in the subharmonic modulation state from the laser (5); wherein the long optical fiber (6) is used to adjust the loop delay, and the dispersion compensation optical fiber (7) is used to adjust the loop dispersion to 0.
3. The frequency measurement system for self-excited subharmonic modulation of a single-cycle state loop in an injection-locked laser as described in claim 1, characterized in that, The optical amplifier (8) and electrical amplifier (10) are used to make the open-loop gain of the loop greater than 1, generate periodic self-excited oscillation, and generate periodic frequency modulation signals; wherein the high-pass filter (11) is used to filter out low-frequency noise signals to improve the spectral purity and frequency measurement accuracy.
4. The frequency measurement system for self-excited subharmonic modulation of a single-cycle state loop in an injection-locked laser as described in claim 3, characterized in that, The injection coefficients of the tunable laser source (1) and the DFB from the laser (5) light injection system , The optical power output of the adjustable laser source (1) can be adjusted by adjusting the optical power of the adjustable laser source (1) through an arbitrary waveform generator (13), or by adjusting the polarization controller (3).