CN110943362A - High-precision tunable low-phase-noise photo-generated microwave signal generation device and method - Google Patents

High-precision tunable low-phase-noise photo-generated microwave signal generation device and method Download PDF

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CN110943362A
CN110943362A CN201911342172.6A CN201911342172A CN110943362A CN 110943362 A CN110943362 A CN 110943362A CN 201911342172 A CN201911342172 A CN 201911342172A CN 110943362 A CN110943362 A CN 110943362A
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microwave
time delay
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light
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李鹏
席虹标
陈国帅
尹怡辉
熊平戬
刘鑫
毛九平
谢宝荣
李恩
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CETC 34 Research Institute
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/10053—Phase control
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/0014—Monitoring arrangements not otherwise provided for
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
    • H01S3/0092—Nonlinear frequency conversion, e.g. second harmonic generation [SHG] or sum- or difference-frequency generation outside the laser cavity
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H01S3/06754—Fibre amplifiers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H01S3/06791—Fibre ring lasers

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Abstract

The invention discloses a high-precision tunable low-phase-noise photoproduction microwave signal generating device and a method, which comprises a light source, a narrow-band photon filtering module, a switchable light time delay module, a microwave photon phase shifter, a light beat frequency device, a radio frequency amplifier, a coupler and a light time delay detection and control module, wherein the narrow-band photon filtering module is used for filtering out a narrow-band photon signal; the narrow-band photon filtering module consists of a double parallel Mach-Zehnder modulator, a circulator and a Bragg grating; the switchable light delay module consists of a polarization splitter, a controllable light delay line and a polarization combiner. The invention utilizes the methods of optical fiber energy storage and wireless optical true delay to realize a novel photoelectric oscillation source with frequency tunable precision, stability and phase noise obviously superior to those of the conventional microwave medium oscillator, thereby improving the performances of clutter visibility, speed measurement precision, speed resolution and the like of a radar system and providing technical support for the engineering application of weapons and equipment of the photoelectric oscillator.

Description

High-precision tunable low-phase-noise photo-generated microwave signal generation device and method
Technical Field
The invention relates to the technical field of microwave signal generation devices, in particular to a high-precision tunable low-phase-noise photo-generated microwave signal generation device and method.
Background
With the increasing demand of microwave systems such as doppler radar, satellite communication and satellite navigation for low phase noise microwave signals, the performance of the existing microwave device is difficult to meet the future development demand. For example, in an onboard radar, in order to improve the detection capability of the radar, a high-purity microwave local oscillation source is needed to generate a fully coherent pulse doppler radar signal, and the phase noise of the microwave signal is required to reach-110 dBc @1kHz or even lower.
A microwave oscillator is a core component of a microwave signal generator, and a high-Q oscillator with low loss and long energy storage time is often required to generate a microwave signal with high spectral purity. While conventional oscillators basically employ a microwave energy storage element (e.g., a dielectric cavity oscillator) or an acoustic energy storage element (e.g., a quartz oscillator). Since the optimum working frequency of the dielectric cavity oscillator is 8GHz, the higher frequency to be obtained can only be generated by a frequency doubling method, and the frequency doubling can cause the phase noise performance of the generated microwave signal to be obviously reduced. Therefore, in the conventional microwave signal generation method, the dielectric oscillator is often not satisfactory under the conditions of low noise, high spectral purity or tunable performance. The quartz crystal oscillator can obtain a high quality factor (Q value), but the local oscillator output is only 10-20MHz magnitude, a high-frequency signal cannot be directly obtained, and the quartz crystal oscillator is suitable as a reference clock. Although the quartz crystal oscillator can obtain high-frequency signal output by frequency conversion such as frequency multiplication, the phase noise will be seriously deteriorated. Generally, the frequency is increased by 10 times, and the phase noise is deteriorated by 20dB, so that the microwave signal obtained by the quartz crystal oscillator through the frequency doubling method cannot be directly applied to the occasions of radio frequency local oscillators requiring low phase noise, such as radars, electronic warfare and the like. In addition, the microwave energy storage element and the acoustic energy storage element can only work in frequency bands below several GHz, the frequency quality factor product is approximately constant, and the capacity is limited. When the frequency of the signal is higher than 10GHz, the quality factors of the two types of resonators are rapidly reduced, and the deterioration of the phase noise performance is relatively serious.
Disclosure of Invention
The invention aims to solve the problem that the frequency quality factor and the phase noise of a microwave signal generated by the existing microwave oscillator are difficult to meet the development requirement in the future, and provides a high-precision tunable low-phase-noise photo-generated microwave signal generating device and method.
In order to solve the problems, the invention is realized by the following technical scheme:
the high-precision tunable low-phase-noise photoproduction microwave signal generation device comprises a light source, a narrow-band photon filtering module, a switchable light time delay module, a microwave photon phase shifter, a light beat frequency device, a radio frequency amplifier, a coupler and a light time delay detection and control module; the narrow-band photon filtering module consists of a double parallel Mach-Zehnder modulator, a circulator and a Bragg grating; the switchable light delay module consists of a polarization splitter, a controllable light delay line and a polarization combiner.
The output end of the light source is connected with the light input end of the double-parallel Mach-Zehnder modulator, the light output end of the double-parallel Mach-Zehnder modulator is connected with the first port of the circulator, the Bragg grating is connected with the second port of the circulator, and the third port of the circulator is connected with the input end of the polarization splitter; the output end of the polarization splitter is connected with the input end of the controllable light delay line, the output end of the controllable light delay line is connected with the input end of the polarization combiner, and the output end of the polarization combiner is connected with the input end of the microwave photon phase shifter; the output end of the microwave photon phase shifter is connected with the input end of the optical beat frequency device, and the output end of the optical beat frequency device is connected with the input end of the radio frequency amplifier; the output end of the radio frequency amplifier is connected with the input end of the coupler, one output end of the coupler is connected with the electrical input end of one arm of the double-parallel Mach-Zehnder modulator, and the other output end of the coupler forms the microwave signal output end of the microwave signal generating device.
One input end of the optical time delay detection and control module is connected with the input end of the polarization splitter, and the other input end of the optical time delay detection and control module is connected with the output end of the polarization combiner; the coarse regulation control output end of the optical time delay detection and control module is connected with the control end of the controllable optical time delay line, and the fine regulation control output end of the optical time delay detection and control module is connected with the control end of the microwave photon phase shifter.
In the above scheme, the controllable optical delay line adopts a photonic crystal fiber as a resonant cavity.
In the above scheme, the light source is a wavelength-tunable laser.
The high-precision tunable low-phase-noise photo-generated microwave signal generation method realized by the microwave signal generation device comprises the following steps of:
step 1, a light source generates continuous light with adjustable wavelength;
step 2, phase modulation is carried out on continuous light emitted by the light source by the double parallel Mach-Zehnder modulators, so that optical signals with equal amplitude and opposite phases are formed on two sides of an optical carrier;
3, performing single-sideband photon filtering on the optical signal subjected to phase modulation through a Bragg grating so as to complete phase-to-intensity modulation;
step 4, transmitting the optical signal modulated by the intensity through a controllable optical delay line, then entering a microwave photon phase shifter, and sending the optical signal to an optical beat frequency device through the microwave photon phase shifter; in the process, the optical time delay detection and control module firstly detects an input optical signal and an output optical signal of the controllable optical time delay line and obtains the optical time delay of the system by comparing the input optical signal with the output optical signal; then, the PID algorithm is used for carrying out compensation calculation on the obtained system optical time delay to obtain a coarse adjustment time delay amount and a fine adjustment displacement amount; then sending the coarse adjustment delay amount to a controllable optical delay line to adjust the delay, and sending the fine adjustment displacement amount to a microwave photon phase shifter to adjust the delay;
step 5, the optical frequency beating device converts the optical signal into an electric signal;
and 6, the radio frequency amplifier amplifies the electric signal and then divides the amplified electric signal into two paths, one path is fed back to the electric input end of one arm of the double parallel Mach-Zehnder modulator, and the other path outputs the required microwave signal.
Compared with the prior art, the invention forms a feedback loop by the mutual matching of the controllable optical delay line, the microwave photon phase shifter and the optical delay detection and control module, and well solves the problem that the OEO frequency drifts along with external factors by adjusting the delay of the energy storage optical fiber based on the PID algorithm. The frequency stability of the invention can reach 10-10(4h) The generated frequency range is 1 GHz-40 GHz, the frequency resolution reaches 1Hz, and the phase noise reaches: -135dBc/Hz (10kHz offset); -115dBc/Hz (1kHz offset); -90dBc/Hz (100Hz frequency offset); 60dBc/Hz (10Hz frequency offset).
Drawings
FIG. 1 is a schematic diagram of a high-precision tunable low-phase noise photo-generated microwave signal generating device.
Fig. 2 is a diagram of a spectrum of a DPMZM (dual parallel mach-zehnder modulator) after modulation.
Fig. 3 is a graph of single sideband filtering and frequency response.
FIG. 4 is a schematic block diagram of the PID algorithm.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to specific examples.
Due to the characteristics of materials and structures, the photoelectric oscillator is used for generating high-precision tunable low-phase-noise microwave signals, and the technical problems to be solved are as follows:
(1) problem of single mode operation of optoelectronic oscillators: the longer the optical fiber distance in the cavity of the photoelectric oscillator, the higher the filtering Q value of the optical fiber ring cavity as energy storage, but with the increase of the length of the optical fiber in the cavity, the mode spacing capable of simultaneously starting oscillation is continuously reduced, and the side mode in such a short distance is difficult to remove by using the filter. Therefore, how to improve the structure of the optoelectronic oscillator and remove or suppress the power of the side mode oscillation is the key of the optoelectronic oscillator technology for generating high-purity microwave signals.
(2) Low phase noise problem: the phase noise is the most important technical index of the high-frequency microwave oscillator, and the photoelectric oscillation technology is generated just because the phase noise performance of the microwave solid-state device at high-frequency output is not good. The phase noise characteristic of the photoelectric oscillation is comprehensively influenced by a ring cavity system consisting of a laser, an amplifier and a transmission optical fiber, and the key technology of the low-phase-noise oscillator can be overcome only by deeply researching the mechanism of the phase noise characteristic of the photoelectric oscillation and improving the system structure of the photoelectric oscillation.
(3) The generated microwave signal has high-precision tunable frequency: the high-precision tunable microwave signal frequency is the most difficult to realize, and is also the key point for practical application of the photoelectric oscillator to generate high-quality microwave signals.
(4) The frequency stability problem of the generated microwave signal: the photoelectric oscillator utilizes the microwave signal generated by long optical fiber energy storage, and the energy storage optical fiber is easily deformed by factors such as external temperature, vibration, stress and the like, so that the generated frequency drift or shake is caused, and the detection of the variation of the length of the energy storage optical fiber is the key technology of the photoelectric oscillator.
The invention provides a high-precision tunable low-phase-noise photoproduction microwave signal generating device, which comprises a light source, a narrow-band photon filtering module, a switchable light time delay module, a microwave photon phase shifter, an optical beat frequency device, a radio frequency amplifier, a coupler and a light time delay detection and control module, wherein the narrow-band photon filtering module, the switchable light time delay module, the microwave photon phase shifter, the optical beat frequency device, the radio frequency amplifier and the coupler are arranged in sequence. The light source is a wavelength-tunable laser. The narrow-band photon filtering module consists of a double parallel Mach-Zehnder modulator, a circulator and a Bragg grating. The switchable light delay module consists of a polarization splitter, a controllable light delay line and a polarization combiner.
The output end of the light source is connected with the input end of the double-parallel Mach-Zehnder modulator, the output end of the double-parallel Mach-Zehnder modulator is connected with the first port of the circulator, the Bragg grating is connected with the second port of the circulator, and the third port of the circulator is connected with the input end of the polarization splitter. The output end of the polarization splitter is connected with the input end of the controllable light delay line, the output end of the controllable light delay line is connected with the input end of the polarization combiner, and the output end of the polarization combiner is connected with the input end of the microwave photon phase shifter. The output end of the microwave photon phase shifter is connected with the input end of the optical beat frequency device, and the output end of the optical beat frequency device is connected with the input end of the radio frequency amplifier. The output end of the radio frequency amplifier is connected with the input end of the coupler, one output end of the coupler is connected to one arm of the double parallel Mach-Zehnder modulator, and the other output end of the coupler forms the microwave signal output end of the microwave signal generating device.
One input end of the optical time delay detection and control module is connected with the input end of the polarization splitter, and the other input end of the optical time delay detection and control module is connected with the output end of the polarization combiner. The coarse regulation control output end of the optical time delay detection and control module is connected with the control end of the controllable optical time delay line, and the fine regulation control output end of the optical time delay detection and control module is connected with the control end of the microwave photon phase shifter.
The invention adopts the wavelength-adjustable laser, the DPMZM and the narrow-band photonic filter to realize the photoelectric oscillator system with the adjustable OEO frequency, in addition, the optical time delay detection and control module is adopted to be matched with the VDL wireless optical controllable time delay line, and the PID algorithm is utilized to automatically adjust the frequency drift of the microwave signal generated by the system, thereby achieving the purposes that the signal generated by the photoelectric oscillator keeps the characteristic of low phase noise and has the characteristics of high precision and adjustability and high stability.
The high-precision tunable low-phase-noise photo-generated microwave signal generation method realized by the microwave signal generation device comprises the following steps of:
step 1, a light source generates continuous light with adjustable wavelength;
step 2, phase modulation is carried out on continuous light emitted by the light source by the double parallel Mach-Zehnder modulators, so that optical signals with equal amplitude and opposite phases are formed on two sides of an optical carrier;
3, performing single-sideband photon filtering on the optical signal subjected to phase modulation through a Bragg grating so as to complete phase-to-intensity modulation;
step 4, transmitting the optical signal modulated by the intensity through a controllable optical delay line, then entering a microwave photon phase shifter, and sending the optical signal to an optical beat frequency device through the microwave photon phase shifter; in the process, the optical time delay detection and control module firstly detects an input optical signal and an output optical signal of the controllable optical time delay line and obtains the optical time delay of the system by comparing the input optical signal with the output optical signal; then, the PID algorithm is used for carrying out compensation calculation on the obtained system optical time delay to obtain a coarse adjustment time delay amount and a fine adjustment displacement amount; then sending the coarse adjustment delay amount to a controllable optical delay line to adjust the optical path of the controllable optical delay line, and sending the fine adjustment displacement amount to a microwave photon phase shifter to adjust the phase of the microwave photon phase shifter;
step 5, the optical frequency beating device converts the optical signal into an electric signal;
and 6, the radio frequency amplifier amplifies the electric signal and then divides the amplified electric signal into two paths, one path is fed back to the electric input end of one arm of the double parallel Mach-Zehnder modulator, and the other path outputs the required microwave signal.
The basic principle of the invention is as follows: continuous light output by the wavelength-tunable laser is subjected to phase modulation by the DPMZM, so that optical signals with equal amplitude and opposite phases are formed on two sides of an optical carrier, the optical signals subjected to the phase modulation are subjected to single-sideband photonic filtering through the Bragg grating, so that modulation from the phase to the intensity is completed, the optical signals enter the optical beat frequency device through the high-precision phase shifter after being subjected to switchable optical time delay transmission, the optical beat frequency device converts the optical signals into electric signals and then the electric signals are fed back to an electric input end of the DPMZM modulator through electric amplification to complete one cycle. Therefore, only the microwave resonance mode within the band-pass range of the filter can obtain effective oscillation, and after multiple cycles, the signal becomes exponentially larger, thereby achieving the purpose of generating microwave light. This structure enables self-sustained oscillation at a specific frequency determined by the length of the fiber, the laser wavelength and the bandpass characteristics of the filter. When the system is subjected to frequency drift caused by external factors, the optical delay detection and control module can detect the optical fiber delay variation and then is matched with the microwave photon phase shifter to form feedback. And the optical time delay of the system is adjusted by adopting a PID algorithm, so that the capability of automatically stabilizing the frequency is realized.
The invention provides a photoelectric oscillator with high Q value, low phase noise and easy tuning, which meets the requirements of a satellite communication system on the performance of a local oscillator, improves the performance of clutter visibility, speed measurement precision, speed resolution and the like of a radar system and provides technical support for the engineering application of weapons and equipment of the photoelectric oscillator by a photoelectric hybrid technical means, mainly breaking through key technologies of a single-mode operation technology of the photoelectric oscillator, a polarization state control-based phase noise suppression technology, a frequency-adjustable microwave photon filter technology, a microwave photon phase shifting technology and the like.
The wavelength tunable light source, the DPMZM and the optical trap filter (including the Bragg grating and the circulator) form a single-sideband microwave photonic filter with tunable frequency. The wavelength tunable light source outputs light to a DPMZM (double parallel Mach-Zehnder modulator) for phase modulation, and sidebands with the same amplitude and opposite phases are generated on both sides of the carrier wave on the spectrum. However, the microwave signal cannot be directly generated by the optical signal, and therefore, the invention filters one sideband of the phase-modulated optical signal through the optical trap filter, breaks through the balance that the sidebands with the same amplitude and opposite phases exist on two sides of the carrier, and realizes the modulation from the phase to the intensity, and the generated frequency is the difference frequency between the central frequency point of the narrow-band photon filter and the optical carrier, so that the central frequency point of the optical trap filter is kept unchanged, only the wavelength of the light source is changed, and different wavelengths can correspondingly generate different frequencies.
When the wavelength-tunable light source inputs an optical carrier into the DPMZM, for the upper arm of the DPMZM, no electric signal is loaded, and only the direct-current voltage DC is loaded1By regulating DC1To adjust the optical power of the optical carrier modulated by MZM 1. For the lower arm of the DPMZM, we load the DC voltage DC2To MZM2 and loads the RF signal onto MZM 2. By regulating DC2Is such that MZM2 operates in the carrier-suppressed double sideband mode, i.e., the DSB-CS mode. The optical carrier wave modulated by MZM2 enters a DC loaded direct current voltage3The phase shifter PS. This is achieved byThe effect of the addition of the phase shifter PS is to produce a phase shift θ between the two sidebands of the electrical signal-added carrier suppressed dual-sideband optical signal modulated by MZM23The phase difference of (1). By regulating DC3The voltage value of (a) is such that a phase difference theta is generated between the two sidebands3And finally, coupling the signals of the two arms together to obtain a signal finally modulated by the DPMZM. If the phase shift θ is caused by PS3Pi/2, the output signal of the DPMZM can be equivalent to the output signal of the phase modulator, but its optical carrier power is also phase modulated.
Let the optical carrier electric field expression be:
Figure BDA0002331750350000051
wherein E is0、ωcRespectively, optical carrier amplitude and phase. The RF signal loaded onto MZM2 is expressed as:
Ein(t)＝Vecos(ωet) (2)
wherein, VeBeing the amplitude, omega, of the electrical signaleIs the frequency of the electrical signal.
The optical field output from the DPMZM can be represented as:
Figure BDA0002331750350000061
to enable MZM2 to reject the optical carrier, θ needs to be made2Pi/2. And when theta3At pi/2, the RF signal loaded onto MZM2 is expressed as:
Figure BDA0002331750350000062
the spectrum diagram of the DPMZM modulated optical signal on both sides of the optical carrier is shown in FIG. 2, where ω iscIs a carrier wave, ωc-ωe、ωc+ωeRespectively-1 +1 order sidebands, as can be seen in fig. 2: the same amplitude and opposite phase are formed in the carrier wave attachment by phase modulationThe two sidebands, when the phase modulated signal is directly input to the PD at this time, cannot directly detect the RF signal because of the principle of photodetection. In order to obtain the information of the RF signal loaded on the optical carrier, we need to process the phase modulation signal so that the PD directly detects the microwave signal information, which is equivalent to a single bandpass filtering. This process by which the phase modulated signal can be detected is referred to as IM-PM, i.e. phase to intensity conversion.
The invention filters one sideband of the phase modulation signal by ultra-narrow optical notch filtering, thereby breaking amplitude balance and realizing single-bandpass filtering. As shown in fig. 3. When the optical carrier passes through the filter, a first-order sideband is correspondingly considered, so that the relation that the phases are opposite and the amplitudes are the same is broken, and the spectrum generates corresponding frequency after passing through the photoelectric detector. The relative positions of the wavelength and the optical trap filter are adjusted to obtain different frequencies, so that the phase-to-intensity conversion is realized, and finally, the microwave photon single-sideband filter with the adjustable central frequency is realized. Frequency tunability is achieved for our optoelectronic oscillator. But due to device considerations, the wavelength of the light source is currently tuned in steps of 1pm, approximately equal to 125 MHz. The adjustable range can reach 0-2 nm.
The short term stability of the opto-electronic oscillator is typically expressed in terms of the degree of drift of the signal frequency over time from the center frequency and the allen equation. This can be described by the following equation:
Figure BDA0002331750350000063
where k is the frequency stability of the opto-electronic oscillator over time, f0Is the center frequency, f, of the optoelectronic oscillator1Is the frequency value farthest from the center frequency within a certain time, and Δ f is the maximum value of the frequency change within a certain time.
The stability of the photoelectric oscillator is mainly determined by the stability of the time delay of the optical fiber ring of the oscillator, and the controllable optical delay line uses the photonic crystal optical fiber insensitive to temperature as a resonant cavity. The temperature sensitivity of the photonic crystal fiber is reduced by one third compared with the common fiber, and the stability of the generated microwave signal is improved by at least three times.
Due to the change of the environmental temperature and the environmental vibration, the time delay amount of the optical signal transmission in the optical fiber ring of the switchable optical time delay module can drift, so that the frequency drift generated by the photoelectric oscillator is caused. In order to improve the stability of the system on the basis of obtaining the adjustable frequency, the invention adopts the combination of the controllable optical delay line and the microwave photon phase shifter to realize the microwave photon phase shift, wherein the coarse optical path delay adjustment of the whole device is realized by the control of the controllable optical delay line, and the fine optical path delay adjustment of the whole device is realized by the microwave photon phase shifter, thereby realizing the fine and stable frequency adjustment of the whole microwave signal generating device.
The optical time delay detection and control module detects the optical fiber loop time delay amount of the current switchable optical time delay module, calculates the phase to be moved according to the detected time delay amount, and then adjusts the optical path of the controllable optical time delay line and the microwave photon phase shifter by controlling the high-precision stepping motor, so that the optical time delay of the system is changed in the optical domain, and finally, the generated microwave signal is stable and the resolution is high and precision is adjustable.
The oscillation frequency of the ring cavity can be known from the mechanism of the photoelectric oscillator:
f＝k/τ (6)
where k is 0, 1, 2, 3, τ is determined by the least common multiple of the two-ring cavity, and the oscillation frequency after passing through the phase shifter due to Δ τ is expressed as:
f＝k/(τ+Δτ) (7)
the frequency resolution Δ f can be expressed as:
Δf＝k[Δτ/τ(τ+Δτ)](8)
at present, the adjustment precision of the wireless optical controllable delay line can reach 15fs, so the minimum delta tau can be 15fs, and tau is us magnitude, so the frequency resolution is very high, for example, if a ring cavity is used for using 1km optical fiber, the frequency resolution delta f can reach 0.6 Hz.
The frequency of the microwave generated by the system is determined by the optical time delay of the system, when the frequency of the microwave needs to be set, only the length of a controllable optical time delay line needs to be set, the controllable optical time delay line consists of an optical switch and photonic crystal fibers with different lengths, and different optical time delay is generated by switching different optical switches, so that different microwave frequencies are generated.
The optical time delay detection and control module measures the current time delay amount in an optical signal injection, following and feedback mode, the optical signal emitted by the optical time delay detection and control module and the optical signal of the system are transmitted in the same optical path in an optical wavelength division multiplexing mode, so that the following detection of the time delay is achieved, when the optical path of the system is influenced by external factors such as external temperature, stress and the like to generate no time delay amount, the optical time delay detection and control module controls a controllable optical time delay line and a microwave photon phase shifter through a proportion-integration-differential feedback mode through a PID algorithm to adjust the time delay amount, and the time delay amount is kept consistent with an initial set value. In addition, if the time delay precision of the controllable optical delay line does not meet the requirement, the controllable optical delay line and the microwave photon phase shifter can be controlled to adjust through the optical delay detection and control module. The schematic block diagram of the PID algorithm is shown in fig. 4, and the control formula is:
Figure BDA0002331750350000071
wherein upsilon (t) is a control quantity.
The invention ensures the stability of the time delay of the optical fiber ring by using a detection and compensation mode, because the optical time delay detection and control module is used for detecting in real time, when the optical fiber ring causes time delay drift due to environmental factors, the optical controllable time delay line and the microwave photon phase shifter can be automatically controlled to carry out corresponding adjustment by automatically controlling a PID algorithm, so that the generated microwave signal can be kept stable while being finely adjusted. In addition, the invention utilizes the methods of optical fiber energy storage and wireless optical true delay to realize a novel photoelectric oscillation source with frequency tunable precision, stability and phase noise which are obviously superior to those of the conventional microwave medium oscillator, thereby improving the performances of clutter visibility, speed measurement precision, speed resolution and the like of a radar system and providing technical support for the weapon equipment engineering application of the photoelectric oscillator.
It should be noted that, although the above-mentioned embodiments of the present invention are illustrative, the present invention is not limited thereto, and thus the present invention is not limited to the above-mentioned embodiments. Other embodiments, which can be made by those skilled in the art in light of the teachings of the present invention, are considered to be within the scope of the present invention without departing from its principles.

Claims (4)

1. The high-precision tunable low-phase-noise photoproduction microwave signal generation device is characterized by comprising a light source, a narrow-band photon filtering module, a switchable light time delay module, a microwave photon phase shifter, a light beat frequency device, a radio frequency amplifier, a coupler and a light time delay detection and control module; the narrow-band photon filtering module consists of a double parallel Mach-Zehnder modulator, a circulator and a Bragg grating; the switchable light delay module consists of a polarization splitter, a controllable light delay line and a polarization combiner;
the output end of the light source is connected with the light input end of the double-parallel Mach-Zehnder modulator, the light output end of the double-parallel Mach-Zehnder modulator is connected with the first port of the circulator, the Bragg grating is connected with the second port of the circulator, and the third port of the circulator is connected with the input end of the polarization splitter; the output end of the polarization splitter is connected with the input end of the controllable light delay line, the output end of the controllable light delay line is connected with the input end of the polarization combiner, and the output end of the polarization combiner is connected with the input end of the microwave photon phase shifter; the output end of the microwave photon phase shifter is connected with the input end of the optical beat frequency device, and the output end of the optical beat frequency device is connected with the input end of the radio frequency amplifier; the output end of the radio frequency amplifier is connected with the input end of the coupler, one output end of the coupler is connected with the electrical input end of one arm of the double-parallel Mach-Zehnder modulator, and the other output end of the coupler forms the microwave signal output end of the microwave signal generating device;
one input end of the optical time delay detection and control module is connected with the input end of the polarization splitter, and the other input end of the optical time delay detection and control module is connected with the output end of the polarization combiner; the coarse regulation control output end of the optical time delay detection and control module is connected with the control end of the controllable optical time delay line, and the fine regulation control output end of the optical time delay detection and control module is connected with the control end of the microwave photon phase shifter.
2. The high-precision tunable low-phase-noise photo-generated microwave signal generation device as claimed in claim 1, wherein the controllable optical delay line uses a photonic crystal fiber as a resonant cavity.
3. The high accuracy tunable low phase noise photo-generated microwave signal generating device as claimed in claim 1, wherein the light source is a wavelength tunable laser.
4. The method for generating high-precision tunable low-phase noise photo-generated microwave signals, which is realized by the microwave signal generating device of claim 1, is characterized by comprising the following steps:
step 1, a light source generates continuous light with adjustable wavelength;
step 2, phase modulation is carried out on continuous light emitted by the light source by the double parallel Mach-Zehnder modulators, so that optical signals with equal amplitude and opposite phases are formed on two sides of an optical carrier;
3, performing single-sideband photon filtering on the optical signal subjected to phase modulation through a Bragg grating so as to complete phase-to-intensity modulation;
step 4, transmitting the optical signal modulated by the intensity through a controllable optical delay line, then entering a microwave photon phase shifter, and sending the optical signal to an optical beat frequency device through the microwave photon phase shifter; in the process, the optical time delay detection and control module firstly detects an input optical signal and an output optical signal of the controllable optical time delay line and obtains the optical time delay of the system by comparing the input optical signal with the output optical signal; then, the PID algorithm is used for carrying out compensation calculation on the obtained system optical time delay to obtain a coarse adjustment time delay amount and a fine adjustment displacement amount; then sending the coarse adjustment delay amount to a controllable optical delay line to adjust the delay, and sending the fine adjustment displacement amount to a microwave photon phase shifter to adjust the delay;
step 5, the optical frequency beating device converts the optical signal into an electric signal;
and 6, the radio frequency amplifier amplifies the electric signal and then divides the amplified electric signal into two paths, one path is fed back to the electric input end of one arm of the double parallel Mach-Zehnder modulator, and the other path outputs the required microwave signal.
CN201911342172.6A 2019-12-23 2019-12-23 High-precision tunable low-phase-noise photo-generated microwave signal generation device and method Pending CN110943362A (en)

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CN111953342A (en) * 2020-08-10 2020-11-17 东南大学 Double-ring photoelectric oscillator with active phase noise suppression circuit
CN112291015A (en) * 2020-08-19 2021-01-29 扬州船用电子仪器研究所(中国船舶重工集团公司第七二三研究所) STM32 processor-based microwave phase-stable transmission system and method
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CN111740786A (en) * 2020-06-10 2020-10-02 电子科技大学 Integrated optical waveguide beam forming device
CN111740786B (en) * 2020-06-10 2022-01-25 电子科技大学 Integrated optical waveguide beam forming device
CN111953342A (en) * 2020-08-10 2020-11-17 东南大学 Double-ring photoelectric oscillator with active phase noise suppression circuit
CN112291015A (en) * 2020-08-19 2021-01-29 扬州船用电子仪器研究所(中国船舶重工集团公司第七二三研究所) STM32 processor-based microwave phase-stable transmission system and method
CN112683313A (en) * 2020-12-15 2021-04-20 南京信息职业技术学院 Sensor array device of multi-photoelectric oscillator and measuring method
CN112787204A (en) * 2020-12-31 2021-05-11 武汉邮电科学研究院有限公司 Photoelectric oscillator based on-chip integrated system and method for generating microwave signal
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