A random microwave pulse generation system and method based on an optoelectronic oscillator

Abstract

This invention proposes a random microwave pulse generation system and method based on an optoelectronic oscillator, belonging to the field of microwave photonic signal generation and processing technology. The system includes 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 mainly consists of a Mach-Zehnder modulator, a circulator, an erbium-doped fiber amplifier, a photodetector, an electrical amplifier, and a directional coupler.

Description

TECHNICAL FIELD

[0001] The application provides a random microwave pulse generation system and method based on an optoelectronic oscillator, and belongs to the technical field of microwave photonic signal generation and processing. BACKGROUND

[0002] A microwave pulse signal refers to a microwave signal with a certain amplitude and time interval. Microwave pulse signals are widely used in detection systems, communication, and pulse modulation. In the field of detection, pulse signals are a commonly used detection signal. By processing the echo signal at the receiving end, the distance and speed of the detected target can be determined. Among them, a random microwave pulse signal is a kind of microwave pulse signal, which has the characteristics of random intensity, random frequency and random pulse duty cycle. Due to the wideband 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 ambiguity function of the random signal has a nail-like feature, which can improve the 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 low-precision and low-detection-range detection systems. However, due to the limitations of electronic bottlenecks, the microwave pulses generated by electronic methods have low frequency and limited spectral 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 proposed, and the generation method of high-quality microwave pulses has become more and more mature.

[0004] The generation of random microwave pulses requires introducing random amplitude modulation on the basis of generating random signals, which is more complex than the traditional microwave pulse generation structure, and there are relatively few reports of such systems. The optoelectronic oscillator is one of the key technologies in the field of microwave photonics, which can generate high-frequency and large-bandwidth microwave signals by using optoelectronic / electro-optical conversion. At present, the chaos signal generation system based on the optoelectronic oscillator is relatively mature, and the chaos signal is generated due to the nonlinear effect introduced by the optoelectronic / electro-optical device. The chaos pulse, chaos radar and chaos communication systems based on the chaos signal are also constantly improving, but the chaos signal has a time delay feature and is also at risk of being deciphered. The research team of the Institute of Semiconductors, Chinese Academy of Sciences also uses fiber Rayleigh scattering to introduce random distributed feedback in the optoelectronic oscillator loop, thereby affecting the loop cavity length, and realizes the generation of random microwave signals of 0-40GHz, which attracts the attention of researchers.

[0005] Although a wideband random signal generation system is constantly being proposed, the method for generating random microwave pulses is currently relatively few, and random microwave pulses have high application value in the detection field. Therefore, it is necessary to design a random microwave pulse generation system. SUMMARY

[0006] Therefore, the present application 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 generating microwave signals with large frequency bandwidth and compact system structure.

[0007] The technical scheme of the present application is as follows:

[0008] In a first aspect, the present application provides a random microwave pulse generation system based on an optoelectronic oscillator, which 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 mainly comprises a Mach-Zehnder modulator, a circulator, an erbium-doped fiber amplifier, a photodetector, an electrical amplifier and a directional coupler.

[0009] Laser: used for generating a single-frequency optical signal and transmitting the single-frequency optical signal to the polarization controller;

[0010] Polarization controller: used for changing the polarization state of the output optical signal of the laser, so that the polarization state of the optical signal is aligned with the principal axis of the double-parallel Mach-Zehnder modulator;

[0011] Mach-Zehnder modulator: used for outputting the input optical signal after electro-optical modulation to the circulator;

[0012] Circulator: for emitting the incident laser signal to the random fiber grating string, receiving the reflected laser signal of the random fiber grating string, and outputting;

[0013] Random fiber grating string: for reflecting the incident laser signal and reflecting the disordered optical signal;

[0014] Erbium-doped fiber amplifier: for amplifying the reflected light of the random fiber grating string;

[0015] Photodetector: for converting the optical signal into an electrical signal;

[0016] Electric amplifier: for amplifying the electrical signal output by the photodetector, so that the optical electric oscillator loop gain is greater than the output threshold;

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

[0018] Function generator: for providing a bias voltage for the Mach-Zehnder modulator.

[0019] Further, the function generator provides a square wave or a sine wave as the bias voltage, and the maximum value of the bias voltage corresponds to the quadrature 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] Further, the random fiber grating string is obtained by cascading a plurality of fiber gratings with random grating spacings, and the number of gratings and the grating spacing satisfy the following formula:

[0021] T(L)≈exp(-L / 2ξ)

[0022] 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.

[0023] Further, when the electrical signal needs to be observed, one way output after the directional coupler is split by 10dB and used for observation.

[0024] In the second aspect, the embodiment of the application provides a random microwave pulse generation method based on an optical electric 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 working frequency of the Mach-Zehnder modulator, first use a polarization controller to control the polarization state of the laser signal, so that the polarization state is parallel to the principal axis of the Mach-Zehnder modulator;

[0026] Step two, control the working voltage of the photodetector and the electrical amplifier in the normal working state;

[0027] Step three, regulate the output voltage of the function generator, and judge whether there is an output in the photonic oscillator loop, record the voltage value of the output signal of the photonic oscillator as voltage 1, and select one of them when there are multiple values, and record the voltage value of the output signal of the photonic oscillator as voltage 2, and select one of them when there are multiple values;

[0028] Step four, set the output signal of the function generator 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 in voltage 1 and voltage 2 respectively.

[0029] Beneficial effects:

[0030] The random microwave pulse generation system based on the photonic oscillator disclosed by the application utilizes the random fiber grating string to introduce random distributed feedback in the photonic oscillator loop, so that the loop cavity length of the photonic oscillator randomly changes, and due to the reflection loss of the fiber grating, the power of the optical signal randomly changes, and finally a microwave signal with random frequency and random intensity is generated; and then the working point of the modulator is controlled by using the function generator, and a random microwave pulse is generated. Compared with other random microwave pulse generation systems, the application has the advantages of large microwave frequency bandwidth and compact system structure. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the application, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0032] Figure 1 It is a system block diagram of the random microwave pulse generation system based on the photonic oscillator.

[0033] Figure 2 It is the incident reflection principle of the customized random fiber grating string.

[0034] Figure 3 It is the continuous random microwave output when the fixed bias voltage is applied, 3a is a thumbnail, and 3b is a detailed waveform diagram.

[0035] Figure 4 It is the random microwave pulse output when different period square waves are applied.

[0036] Figure 5 It is the random microwave pulse output when different period sine waves are applied. DETAILED DESCRIPTION

[0037] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0038] It should be noted that, in the absence of conflict, the following embodiments and features can be combined with each other; and, based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

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

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

[0041] Laser: Generates laser signals and transmits them 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 which point the Mach-Zehnder modulator has the highest modulation efficiency.

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

[0044] Circulator: Used for emitting incident laser signals and receiving reflected laser signals. It has three ports: port 1, port 2, and port 3. Port 1 is the port for incident light to enter. The laser signal incident from port 1 exits 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 Bragg grating strings are used to reflect laser signals. A random fiber Bragg grating string is obtained by cascading multiple fiber Bragg gratings with random spacing. The number of gratings and their spacing satisfy the photon localization theory. The photon localization theory states that light waves can also be localized in disordered scattering materials. In random fiber Bragg gratings, the feedback medium (i.e., the length of the random fiber Bragg grating) is greater than the optical localization length, which is expressed as...

[0046] T(L)≈exp(-L / 2ξ)

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

[0048] Erbium-doped fiber amplifier: used to amplify the reflected light from random fiber grating strings.

[0049] Photodetector: Used to detect optical signals.

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

[0051] Directional coupler: Used to split electrical signals, dividing them into two parts: a signal attenuated by 10dB and the remaining signal, which are then injected into different devices. Typically, the signal attenuated by 10dB is used for observation and is usually connected to devices such as spectrum analyzers and oscilloscopes.

[0052] Function generator: Used to provide a bias voltage in the form of a square wave or sine wave. The maximum value of its bias voltage corresponds to the quadrature operating point of the Mach-Zehnder modulator, and the minimum value corresponds to the minimum operating point of the Mach-Zehnder modulator. By changing the loop operating point, a periodic output signal is caused by the loop, thereby generating random microwave pulses.

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

[0054]

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

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

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

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

[0059] Where, ω k To satisfy the frequency component required for oscillation, τ is the loop delay φ(ω). k Ignoring loop dispersion, it can be considered as 0, and φ0 is the phase constant, typically 0 or π. Therefore, the loop oscillation signal is related to the loop time delay. However, for the optoelectronic oscillator loop with a random fiber grating, the loop length is not fixed. The optical signal undergoes multiple reflections in a random grating string with multiple gratings and is randomly emitted to the output port 3 of the circulator. Therefore, for the signal of the microwave pulse generation system in this invention, the frequency of its output signal is random. Based on 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 time delay introduced by the OEO loop excluding the fiber Bragg grating, k is the number of gratings in the random fiber Bragg grating in the outgoing optical signal, k ≤ the total number of gratings in the system fiber Bragg grating string, and m i τ is an integer representing the number of times the optical signal passes between the (i-1)th grating and the ith grating. i This represents the time delay generated when the optical signal passes through the (i-1)th grating and the ith grating.

[0062] Because the number of reflections of the optical signal is random, and there is reflection loss between grating reflections, the signal strength 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 randomly varying amplitude is introduced, a microwave signal is output when the voltage is high and no microwave signal is output when the voltage is low, thus completing the generation of a random microwave pulse signal.

[0063] This invention proposes a random microwave pulse signal generation system based on an optoelectronic oscillator. The workflow of a 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. 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 two: Control the operating voltage of the photodetector and the amplifier to be in normal working condition.

[0066] Step 3: Adjust the output voltage of the function generator. Determine whether there is an output in the photoelectric oscillator loop. Record the voltage value when the photoelectric oscillator has an output signal as voltage 1. If there are multiple values, select one of them. Record the voltage value when the photoelectric oscillator has no output signal as voltage 2. If there are multiple values, select one of them.

[0067] Step 4: Set the output signal of the function generator to a square wave signal, with the high and low levels of the signal corresponding to the larger and smaller values ​​of voltage 1 and voltage 2, respectively.

[0068] Based on the characteristics of this invention, a physical experiment was designed to verify the performance of this design in generating random microwave pulses. The final results are as follows: Figure 2 , Figure 3 , Figure 4 and Figure 5 As shown. The experimental parameters for this test are as follows: the laser output power 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 electrical amplifier is 20GHz.

[0069] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An opto-electronic oscillator based random microwave pulse generation system, characterized in that, It comprises 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 composed of a Mach-Zehnder modulator, a circulator, an erbium-doped fiber amplifier, a photodetector, an electrical amplifier and a directional coupler; The laser is used to generate a single-frequency optical signal and transmit it to the polarization controller; The polarization controller is 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 principal axis of the double-parallel Mach-Zehnder modulator; The Mach-Zehnder modulator is used to output the input optical signal after electro-optic modulation to the circulator; The circulator is used to emit the incident laser signal to the random fiber grating string, receive the reflected laser signal of the random fiber grating string and output it; The random fiber grating string is used to reflect the incident laser signal and reflect the disordered optical signal; The erbium-doped fiber amplifier is used to amplify the reflected light of the random fiber grating string; The photodetector is used to convert the optical signal into an electrical signal; The electrical amplifier is used to amplify the electrical signal output by the photodetector, so that the gain of the optoelectronic oscillator loop is greater than the output threshold; The directional coupler is used to split the electrical signal, one of which is input to the microwave input port of the Mach-Zehnder modulator, and the other is output as a random microwave pulse generation system; The function generator is used to provide a bias voltage for the Mach-Zehnder modulator.

2. The random microwave pulse generation system based on an opto-electronic oscillator of claim 1, wherein, The bias voltage provided by the function generator is a square wave or a sine wave, and the maximum value of the bias voltage corresponds to the quadrature 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 opto-electronic oscillator of claim 1, wherein, The random fiber grating string is obtained by cascading a plurality of fiber gratings with random grating spacings, and the number of gratings and the grating spacing satisfy the following formula: wherein, is the transmittance of the whole random fiber grating string, is the length of the random fiber grating string, is the photon localization length.

4. The random microwave pulse generation system based on an opto-electronic oscillator of claim 1, wherein, When the electrical signal needs to be observed, one of the outputs split by the directional coupler is attenuated by 10 dB and used for observation.

5. A method of random microwave pulse generation for a random microwave pulse generation system based on an opto-electronic oscillator according to any one of claims 1 to 4, characterized in that, The specific process is as follows: Step one, use the laser to output a single-frequency laser signal, set the output laser frequency within the working frequency of the Mach-Zehnder modulator, and use the polarization controller to control the polarization state of the laser signal so that its polarization state is parallel to the principal axis of the Mach-Zehnder modulator; Step two, control the working voltage of the photodetector and the electrical amplifier in the normal working state; Step three, adjust the output voltage of the function generator, judge whether the optoelectronic oscillator loop has output according to the output voltage, record the voltage value of the output signal of the optoelectronic oscillator as voltage 1, and select one of the multiple values when there are multiple values, and record the voltage value of the output signal of the optoelectronic oscillator as voltage 2, and select one of the multiple values when there are multiple values; Step four, set the output signal of the function generator as a square wave signal or a sine wave, and the high level and the low level of the signal correspond to the larger value and the smaller value in the voltage 1 and the voltage 2 respectively.

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