Random microwave pulse generation system and method based on photoelectric oscillator

Abstract

The invention provides a random microwave pulse generation system and method based on a photoelectric oscillator, and belongs to the technical field of microwave photon signal generation and processing. The system comprises a laser, a polarization controller, a closed-loop optoelectronic oscillator (OEO) loop, a random fiber grating string and a function generator, wherein the closed-loop optoelectronic oscillator (OEO) loop is mainly composed of a Mach-Zehnder modulator, a circulator, an erbium-doped optical fiber amplifier, a photoelectric detector, an electric amplifier and a directional coupler.

Description

Technical Field

[0001] The invention provides a random microwave pulse generation system and method based on an optoelectronic oscillator, belonging to the technical field of microwave photon signal generation and processing. Background Art

[0002] Microwave pulse signals refer to microwave signals with a certain amplitude and a certain time interval. Microwave pulse signals are widely used in detection systems, communications, pulse modulation and other fields. In the field of detection, pulse signals are a commonly used detection signal. The echo signal is processed by the receiving end to determine the distance and speed of the detected target. Among them, random microwave pulse signals are a type of microwave pulse signal, which has the characteristics of random intensity, random frequency and random pulse duty cycle. Due to the wide-band noise characteristics of random microwave pulses, it is easier to hide signal characteristics when used as a detection signal for target detection, thereby improving the anti-interference characteristics of the detection system. Compared with traditional detection signals, the fuzzy function of random signals has a pin-like feature, which can improve detection accuracy and reduce the risk of interception.

[0003] At present, the generation of microwave pulses can be divided into two categories, one is based on electronics, and the other is based on microwave photonics. The microwave pulse generation system based on electronics has the characteristics of low cost and miniaturization, and is widely used in detection systems with low precision and low detection range. However, due to the limitation of electronic bottlenecks, the microwave pulses generated by electronics methods have low frequency and limited spectrum width, which cannot meet the requirements of high detection accuracy and high anti-interference ability. The microwave pulse method based on microwave photonics can generate high-frequency and large-bandwidth microwave pulse signals through photoelectric conversion. In recent years, microwave pulse generation methods using structures such as mode-locked lasers, optical frequency combs, and optoelectronic oscillators have been continuously proposed, and the generation methods of high-quality microwave pulses have become more and more mature.

[0004] The generation of random microwave pulses requires the introduction of random amplitude modulation on the basis of generating random signals, which is more complicated than the traditional microwave pulse generation structure, and there are relatively few reports on such systems. The optoelectronic oscillator is one of the key technologies in the field of microwave photonics. It can generate high-frequency and large-bandwidth microwave signals by using optoelectronic / electro-optical conversion. At present, the chaotic signal generation system based on optoelectronic oscillators is relatively mature. As a kind of random signal, the chaotic signal is generated by the nonlinear effect introduced by optoelectronic / electro-optical devices. Chaotic pulses, chaotic radars, chaotic communications and other systems based on chaotic signals are also being improved, but chaotic signals have time delay characteristics and are also at risk of being deciphered. The research team of the Institute of Semiconductors of the Chinese Academy of Sciences also used fiber Rayleigh scattering to introduce random distributed feedback in the optoelectronic oscillator loop, thereby affecting the loop cavity length and realizing the generation of 0-40GHz random microwave signals. The structure of using optoelectronic oscillators to generate random signals has attracted the attention of researchers.

[0005] Although broadband random signal generation systems are constantly being proposed, there are relatively few methods for generating random microwave pulses, which have high application value in the field of detection. Therefore, the design of a random microwave pulse generation system is necessary. Summary of the invention

[0006] In view of this, the present invention provides a random microwave pulse generation system and method based on an optoelectronic oscillator, which can generate random microwave pulses and has the advantages of a large generated microwave frequency bandwidth and a compact system structure.

[0007] The technical solution for implementing the present invention is as follows:

[0008] In a first aspect, an embodiment of the present application provides a random microwave pulse generation system based on an optoelectronic oscillator, comprising a laser, a polarization controller, a closed-loop optoelectronic oscillator (OEO) loop, a random fiber grating string, and a function generator; wherein the closed-loop optoelectronic oscillator (OEO) loop is mainly composed of a Mach-Zehnder modulator, a circulator, an erbium-doped fiber amplifier, a photodetector, an electrical amplifier, and a directional coupler;

[0009] Laser: used to generate single-frequency optical signals and transmit them to the polarization controller;

[0010] Polarization controller: used to change the polarization state of the laser output optical signal so that the polarization state of the optical signal is aligned with the main axis of the dual parallel Mach-Zehnder modulator;

[0011] Mach-Zehnder modulator: used to electro-optically modulate the input optical signal and then output it to the circulator;

[0012] Circulator: used to emit the incident laser signal to the random fiber grating string, receive the reflected laser signal from the random fiber grating string, and output it;

[0013] Random fiber grating string: used to reflect the incident laser signal and reflect disordered light signals;

[0014] Erbium-doped fiber amplifier: used to amplify the reflected light of random fiber grating strings;

[0015] Photodetector: used to convert light signals into electrical signals;

[0016] Electrical amplifier: used to amplify the electrical signal output by the photodetector so that the optoelectronic oscillator loop gain is greater than the output threshold;

[0017] Directional coupler: used to split the electrical signal, one path is input to the microwave input port of the Mach-Zehnder modulator, and the other path is used as the output of the random microwave pulse generation system;

[0018] Function Generator: Used to provide bias voltage for the Mach-Zehnder modulator.

[0019] Furthermore, the bias voltage provided by the function generator of the present invention is a square wave or a sine wave, the maximum value of the bias voltage corresponds to the orthogonal operating point of the Mach-Zehnder modulator, and the minimum value of the bias voltage corresponds to the minimum operating point of the Mach-Zehnder modulator.

[0020] Furthermore, the random fiber grating string of the present invention is obtained by cascading a plurality of fiber gratings with random grating spacings, and the number of gratings and the grating spacing thereof satisfy the following formula:

[0021] T(L)≈exp(-L / 2ξ)

[0022] Where T(L) is the transmittance of the entire random fiber grating string, L is the length of the random fiber grating string, and ξ is the photon localization length.

[0023] Furthermore, when the electrical signal needs to be observed, the output of the directional coupler after beam splitting is weakened by 10 dB for observation.

[0024] In a second aspect, the present application provides a method for generating random microwave pulses based on an optoelectronic oscillator, and the specific process is as follows:

[0025] Step 1: Use a laser to output a single-frequency laser signal, set the output laser frequency within the operating frequency of the Mach-Zehnder modulator, and first use a polarization controller to control the polarization state of the laser signal so that its polarization state is parallel to the main axis of the Mach-Zehnder modulator;

[0026] Step 2, controlling the working voltage of the photodetector and the electric amplifier to be in a normal working state;

[0027] Step 3, regulating the output voltage of the function generator, judging whether the optoelectronic oscillator loop has output, recording the voltage value of the optoelectronic oscillator with output signal as voltage 1, and selecting one of them when there are multiple values, and recording the voltage value of the optoelectronic oscillator without output signal as voltage 2, and selecting one of them when there are multiple values;

[0028] Step 4: Set the function generator output signal to a square wave signal or a sine wave, and the high level and low level of the signal correspond to the larger value and the smaller value of voltage 1 and voltage 2 respectively.

[0029] Beneficial effects:

[0030] The random microwave pulse generation system based on an optoelectronic oscillator proposed in the present invention uses a random fiber grating string to introduce random distributed feedback in the optoelectronic oscillator loop, so that the loop cavity length of the optoelectronic oscillator changes randomly, and the reflection loss of the fiber grating causes the optical signal power to change randomly, and finally generates a microwave signal with random frequency and random intensity; then the function generator is used to control the modulator working point, thereby generating random microwave pulses. Compared with other random microwave pulse generation systems, the present invention has the advantages of large microwave frequency bandwidth and compact system structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 The system block diagram of the random microwave pulse generation system based on optoelectronic oscillator.

[0033] Figure 2 The incident-reflection principle of a customized random fiber Bragg grating string.

[0034] Figure 3 The continuous random microwaves output when a fixed bias voltage is applied, 3a is a thumbnail, and 3b is a detailed waveform.

[0035] Figure 4 These are random microwave pulses output when square waves of different periods are applied.

[0036] Figure 5 These are random microwave pulses output when sine waves of different periods are applied. DETAILED DESCRIPTION

[0037] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0038] It should be noted that the following embodiments and features in the embodiments may be combined with each other in the absence of conflict; and, based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in the field without making any creative work are within the scope of protection of the present disclosure.

[0039] It should be noted that various aspects of the embodiments within the scope of the appended claims are described below. It should be apparent that the aspects described herein may be embodied in a wide variety of forms, and any specific structure and / or function described herein is merely illustrative. Based on the present disclosure, it should be understood by those skilled in the art that an aspect described herein may be implemented independently of any other aspect, and two or more of these aspects may be combined in various ways. For example, any number of aspects described herein may be used to implement the device and / or practice the method. In addition, other structures and / or functionalities other than one or more of the aspects described herein may be used to implement this device and / or practice this method.

[0040] The present application embodiment provides a random microwave pulse generation system based on an optoelectronic oscillator, the system structure is as follows Figure 1 As shown, it consists of a laser, a polarization controller, a Mach-Zehnder modulator, a circulator, a random fiber grating string, a photodetector, an electric amplifier, a directional coupler and a function generator, wherein:

[0041] Laser: Generates laser signal and transmits the laser signal to the polarization controller.

[0042] Polarization controller: used to adjust the polarization state of the laser signal so that the polarization state of the laser signal is aligned with the main axis of the Mach-Zehnder modulator. At this time, the Mach-Zehnder modulator has the highest modulation efficiency.

[0043] Mach-Zehnder modulator: used for electro-optical modulation, the optical signal is a single-wavelength laser, and the electrical signal is a feedback electrical signal of a directional coupler. In the present invention, the Mach-Zehnder modulator has three signal input ports and one signal output port. The signal source of the optical input port is a laser, the source of the microwave input port is a coupler, and the source of the bias voltage input port is a function generator.

[0044] Circulator: used to transmit incident laser signals and receive reflected laser signals. It has three ports, namely port 1, port 2 and port 3. Port 1 is the port where the incident light enters, and the laser signal incident from port 1 is emitted from port 2. At the same time, port 2 receives the reflected light and transmits the reflected light to port 3 for output.

[0045] Random fiber grating string: used to reflect laser signals. A random fiber grating string is obtained by cascading multiple fiber gratings with random grating spacing. The number of gratings and the grating spacing satisfy the photon localization theory. The photon localization theory can be explained as light waves can also produce localization phenomena in disordered scattering materials. In a random fiber grating, the feedback medium (i.e., the random fiber grating length) is greater than the light localization length. The light localization length is expressed as

[0046] T(L)≈exp(-L / 2ξ)

[0047] Wherein, T(L) is the transmittance of the entire random fiber grating string, L is the length of the random fiber grating string, and ξ is the photon localization length. When the length meets the above requirements, the light signal incident on the random fiber grating string will produce a localized phenomenon, thereby reflecting a disordered light signal, which in turn causes the optoelectronic oscillator loop to change randomly, completing the generation of a random signal.

[0048] Erbium-doped fiber amplifier: used to amplify the reflected light of a random fiber grating string.

[0049] Photodetector: used to detect light signals.

[0050] Electrical amplifier: used to amplify the electrical signal output by the photodetector so that the optoelectronic oscillator loop gain is greater than the output threshold.

[0051] Directional coupler: It is used to split the electrical signal into two parts, the signal attenuated by 10dB and the remaining signal, and inject them into different devices respectively. Generally, the signal attenuated by 10dB is used for observation and is generally connected to a spectrum analyzer, oscilloscope and other devices.

[0052] Function generator: used to provide bias voltage in the form of square wave or sine wave. The maximum value of the bias voltage corresponds to the orthogonal operating point of the Mach-Zehnder modulator, and the minimum value of the bias voltage corresponds to the minimum operating point of the Mach-Zehnder modulator. By changing the loop operating point, the loop periodically outputs a signal, thereby generating random microwave pulses.

[0053] The electrical signal generated by the system can be expressed as:

[0054]

[0055] Among them, G A is the amplifier gain, R is the amplifier resistance, is the responsivity of the photodetector, E out is the power of the output optical signal, α and L are the loss coefficient and length of the optical fiber respectively, V B is the bias voltage, V πis the half-wave voltage of the Mach-Zehnder modulator, so when V B When it is a certain value (such as V π / 2), the system output signal is a DC signal, and there is no other frequency signal, so when the bias voltage is set to a square wave, the output signal is in the form of a pulse.

[0056] In the present invention, the generation principle of the random signal is as follows:

[0057] The source of the OEO loop signal is noise oscillation, and the signal meets the oscillation requirements as follows:

[0058] ω k τ+φ(ω k )+φ0=2nπk=0,1,2,...

[0059] Among them, ω k To meet the frequency component of the oscillation requirement, τ is the loop delay φ(ω k ) can be considered to be 0 when the loop dispersion is ignored, and φ0 is the phase constant, which is generally 0 or π. Therefore, the loop start-up signal is related to the loop delay, and for the optoelectronic oscillator loop that introduces random fiber gratings, its loop length is not fixed. The optical signal is reflected multiple times in the random grating string with multiple gratings and randomly emitted to the output port 3 of the circulator. Therefore, for the signal of the microwave pulse generation system in the present invention, the frequency of its output signal is random. According to the above relationship, the actual signal oscillation frequency f in the loop can be obtained osc :

[0060]

[0061] Where n is a positive integer, τ0 is the delay introduced by the OEO loop except the fiber Bragg grating, k is the number of gratings in the random fiber Bragg grating in the outgoing light signal, k≤the total number of gratings in the system fiber Bragg grating string, m i is an integer, indicating the number of times the light signal passes between the i-1th grating and the i-th grating, τ i It represents the time delay caused by the optical signal passing through the i-1th grating and the i-th grating.

[0062] Since the number of times the optical signal is reflected is random and there is reflection loss between grating reflections, the signal intensity input to the photodetector is random. Therefore, the output signal of the OEO has the characteristics of random frequency and random intensity. When the output signal form of the function generator is changed and a bias voltage with random amplitude jump is introduced, a microwave signal is output at a high level and no microwave signal is output at a low level, thus completing the generation of a random microwave pulse signal.

[0063] The present invention proposes a random microwave pulse signal generation system based on an optoelectronic oscillator. The working process of the specific embodiment is as follows:

[0064] Step 1: Use a laser to output a single-frequency laser signal, set the output laser frequency within the operating frequency of the Mach-Zehnder modulator, and first use a polarization controller to control the polarization state of the laser signal so that its polarization state is parallel to the main axis of the Mach-Zehnder modulator.

[0065] Step 2: Control the working voltage of the photodetector and the electric amplifier to be in normal working state.

[0066] Step three, adjust the output voltage of the function generator, judge whether the optoelectronic oscillator loop has output, record the voltage value of the optoelectronic oscillator with output signal as voltage 1, when there are multiple values, select one of them, record the voltage value of the optoelectronic oscillator without output signal as voltage 2, when there are multiple values, select one of them.

[0067] Step 4: Set the function generator output signal to a square wave signal, where the high level and low level of the signal correspond to the larger value and the smaller value of voltage 1 and voltage 2, respectively.

[0068] According to the characteristics of the present invention, a physical experiment was designed to test the performance of the design in generating random microwave pulses. The final results are shown in Figure 2 , Figure 3 , Figure 4 and Figure 5 The experimental parameters of this test are as follows: the output power of the laser is 14dBm, the modulation bandwidth of the Mach-Zehnder modulator is 40GHz, the gain of the erbium-doped fiber amplifier is 20dB, the 3dB bandwidth of the photodetector is 33GHz, and the 3dB bandwidth of the electric amplifier is 20GHz.

[0069] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A random microwave pulse generation system based on an optoelectronic oscillator, characterized in that: It includes a laser, a polarization controller, a closed-loop optoelectronic oscillator loop, a random fiber grating string and a function generator; wherein the closed-loop optoelectronic oscillator loop is mainly composed of a Mach-Zehnder modulator, a circulator, an erbium-doped fiber amplifier, a photodetector, an electric amplifier and a directional coupler; Laser: used to generate single-frequency optical signals and transmit them to the polarization controller; Polarization controller: used to change the polarization state of the laser output optical signal so that the polarization state of the optical signal is aligned with the main axis of the dual parallel Mach-Zehnder modulator; Mach-Zehnder modulator: used to electro-optically modulate the input optical signal and then output it to the circulator; Circulator: used to emit the incident laser signal to the random fiber grating string, receive the reflected laser signal from the random fiber grating string, and output it; Random fiber grating string: used to reflect the incident laser signal and reflect disordered light signals; Erbium-doped fiber amplifier: used to amplify the reflected light of random fiber grating strings; Photodetector: used to convert light signals into electrical signals; Electrical amplifier: used to amplify the electrical signal output by the photodetector so that the optoelectronic oscillator loop gain is greater than the output threshold; Directional coupler: used to split the electrical signal, one path is input to the microwave input port of the Mach-Zehnder modulator, and the other path is used as the output of the random microwave pulse generation system; Function Generator: Used to provide bias voltage for the Mach-Zehnder modulator.

2. The random microwave pulse generation system based on an optoelectronic oscillator according to claim 1, characterized in that: The bias voltage provided by the function generator is a square wave or a sine wave, the maximum value of the bias voltage corresponds to the orthogonal operating point of the Mach-Zehnder modulator, and the minimum value of the bias voltage corresponds to the minimum operating point of the Mach-Zehnder modulator.

3. The random microwave pulse generation system based on an optoelectronic oscillator according to claim 1, characterized in that: The random fiber grating string is obtained by cascading multiple fiber gratings with random grating spacing, and the number of gratings and the grating spacing satisfy the following formula: T(L)≈exp(-L / 2ξ) Where T(L) is the transmittance of the entire random fiber grating string, L is the length of the random fiber grating string, and ξ is the photon localization length.

4. The random microwave pulse generation system based on an optoelectronic oscillator according to claim 1, characterized in that: When it is necessary to observe the electrical signal, one of the outputs after the directional coupler splits the beam is attenuated by 10 dB for observation.

5. A method for generating random microwave pulses based on an optoelectronic oscillator, characterized in that: The specific process is: Step 1: Use a laser to output a single-frequency laser signal, set the output laser frequency within the operating frequency of the Mach-Zehnder modulator, and use a polarization controller to control the polarization state of the laser signal so that its polarization state is parallel to the main axis of the Mach-Zehnder modulator; Step 2, controlling the working voltage of the photodetector and the electric amplifier to be in a normal working state; Step 3, regulating the output voltage of the function generator, judging whether the optoelectronic oscillator loop has output, recording the voltage value of the optoelectronic oscillator with output signal as voltage 1, and selecting one of them when there are multiple values, and recording the voltage value of the optoelectronic oscillator without output signal as voltage 2, and selecting one of them when there are multiple values; Step 4: Set the function generator output signal to a square wave signal or a sine wave, and the high level and low level of the signal correspond to the larger value and the smaller value of voltage 1 and voltage 2 respectively.

Images