A single-frequency microwave signal source and signal generation method based on active phase-shift grating

Abstract

The present invention belongs to the technical field of microwave photonics, and specifically relates to a single-frequency microwave signal source based on an active phase-shift grating and a signal generating method, wherein the signal source comprises a pump source, a wavelength division multiplexer, a dual-wavelength active phase-shift grating, an optical isolator and a high-speed photodetector; the pump light output by the pump source is connected to an input terminal A of the wavelength division multiplexer via a single-mode optical fiber; the output terminal of the dual-wavelength active phase-shift grating is connected to a common terminal C of the wavelength division multiplexer via a single-mode optical fiber; the output terminal B of the wavelength division multiplexer is connected to an input terminal of the optical isolator via a single-mode optical fiber; compared with the prior art, the advantages and positive effects of the present invention are: (1) the single-frequency microwave signal source based on the active phase-shift grating has a simple structure, a compact size and is easy to integrate; (2) the output signal is stable, has good coherence, a narrow line width and low phase noise; (3) the dual-wavelength interval of the laser generated by the dual-wavelength active phase-shift grating is extremely short, and a single-frequency decimeter-wave microwave signal output can be realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave photonics, and in particular relates to a single-frequency microwave signal source and a signal generating method based on an active phase-shift grating. Background Art

[0002] High-performance microwave signal sources are widely used in electronic countermeasures, wireless communications, satellite communications, atomic physics, etc. However, traditional electronic signal generators represented by frequency synthesizers and analog-to-digital converters have narrow working bandwidths at high frequencies, high transmission losses, and poor noise characteristics, which fundamentally limit the upper limit of microwave signal source performance improvement.

[0003] In recent years, the emerging microwave photonics uses photonic technology to realize the generation and processing of microwave signals. It has the advantages of high precision, low noise, RF fiber carrier and anti-electromagnetic interference. It can directly realize the generation of highly stable local oscillators and arbitrary waveforms, avoiding the degradation of signal quality caused by frequency doubling and up-conversion operations, and can well make up for the shortcomings of traditional electronic microwave signal sources.

[0004] Currently, the main way to generate single-frequency microwave signals using photonic methods is to beat two or more laser signals with a certain phase relationship. The two optical signals being beaten need to meet the conditions of constant phase difference, stable frequency and consistent polarization state. When they pass through the photodetector after the beat, a heterodyne signal will be generated, whose frequency is equal to the frequency difference between the wavelengths of the two optical signals.

[0005] Specific implementation methods include the use of photon filters (CN112865876A), optoelectronic oscillators (CN102931568A) and multi-wavelength lasers (CN 101572375A). In order to achieve stable microwave signal output, photon filters and optoelectronic oscillator solutions usually use complex optical paths including polarization controllers and Mach-Zehnder interferometer architectures, and their filter and oscillator systems are expensive, with low overall reliability and ease of integration. On the other hand, the signal source needs to directly output single longitudinal mode multi-wavelength lasers. Common architectures include ring cavity lasers using rare earth-doped optical fibers as saturated absorbers and distributed feedback lasers using chirped Bragg gratings and sampling gratings to build resonant cavities, but they have large welding losses, are prone to mode hopping, and have high phase noise. The last method is to use a short cavity active phase-shifted grating with semiconductor laser diode pumping to produce a single longitudinal mode multi-wavelength laser. The main difficulty of this method is to achieve multi-wavelength output, which requires precise control of the grating intensity and phase shift position, and the preparation and processing of active phase-shifted gratings is difficult. Summary of the invention

[0006] In view of the above problems, the present invention provides a single-frequency microwave signal source and a signal generating method based on an active phase-shift grating.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is: a single-frequency microwave signal source based on an active phase-shift grating, comprising a pump source, a wavelength division multiplexer, a dual-wavelength active phase-shift grating, an optical isolator and a high-speed photodetector;

[0008] The wavelength division multiplexer is provided with an input terminal A, an output terminal B and a common terminal C; the pump light output by the pump source is connected to the input terminal A of the wavelength division multiplexer via a single-mode optical fiber; the output terminal of the dual-wavelength active phase-shift grating is connected to the common terminal C of the wavelength division multiplexer via a single-mode optical fiber; the output terminal B of the wavelength division multiplexer is connected to the input terminal of the optical isolator via a single-mode optical fiber;

[0009] The output end of the optical isolator is connected to the input end of the high-speed photoelectric detector via a single-mode optical fiber, and the output end of the high-speed photoelectric detector outputs a single-frequency microwave signal.

[0010] Preferably, the dual-wavelength active phase-shift grating is a π-phase-shifted erbium-doped dual-wavelength active phase-shift grating, the gate region of the dual-wavelength active phase-shift grating is an asymmetric structure, and the π phase shift is close to the input end of the dual-wavelength active phase-shift grating.

[0011] Preferably, the dual-wavelength active phase-shift grating is prepared on an erbium-doped photosensitive optical fiber by a 244nm ultraviolet laser through a scanning and jittering phase mask method; during the ultraviolet laser scanning process, the jitter of the phase mask is precisely controlled to produce a π phase shift of one-quarter of the grating period on the dual-wavelength active phase-shift grating.

[0012] Preferably, the pump source is a 980nm semiconductor laser, and the pump source outputs 200mw pump light.

[0013] Preferably, the wavelength division multiplexer is a 980 / 1550nm wavelength division multiplexer, and the optical isolator is a 1550nm optical isolator.

[0014] Preferably, the frequency range of the high-speed photodetector should match the frequency of the dual-wavelength narrow-linewidth laser emitted by the received dual-wavelength active phase-shift grating, and the response frequency of the high-speed photodetector should not be less than 1 GHz.

[0015] A method for generating a single-frequency microwave signal based on an active phase-shift grating comprises the following steps:

[0016] Step 1: Using the above-mentioned single-frequency microwave signal source based on active phase-shift grating, the 200mw pump light output by the pump source 980nm semiconductor laser is transmitted to the 980nm input terminal A of the 980 / 1550nm wavelength division multiplexer through a standard 980nm single-mode optical fiber;

[0017] Step 2: The dual-wavelength active phase-shift grating outputs dual-wavelength narrow-linewidth laser light, which is output to the common terminal C of the wavelength division multiplexer through a 980nm single-mode optical fiber; the wavelength division multiplexer couples the pump light and the dual-wavelength narrow-linewidth laser light input from the input terminal A and the common terminal C respectively;

[0018] In step three, the coupled laser signal is then transmitted from the 1550nm output terminal B of the wavelength division multiplexer to the input terminal of the 1550nm optical isolator. Finally, the laser signal is transmitted from the output terminal of the optical isolator via the 1550nm single-mode optical fiber to the high-speed photodetector. After the high-speed photodetector receives the single longitudinal mode dual-wavelength laser signal generated by the dual-wavelength active phase-shift grating, it generates a microwave electrical signal output with a frequency equal to the frequency difference between the two optical signal wavelengths through the beat frequency.

[0019] Compared with the prior art, the advantages and positive effects of the present invention are:

[0020] (1) The single-frequency microwave signal source based on the active phase-shift grating of the present invention has a simple structure, compact size, convenient integration, and relatively low overall cost, avoiding the use of a complex optical path including a polarization controller and a Mach-Zehnder interferometer architecture and the use of expensive filters and oscillator systems;

[0021] (2) The single-frequency microwave signal source based on the active phase-shift grating of the present invention has a stable output signal, good coherence, narrow line width and low phase noise;

[0022] (3) The dual-wavelength interval of the single-longitudinal-mode dual-wavelength laser generated by the dual-wavelength active phase-shift grating in the single-frequency microwave signal source based on the active phase-shift grating of the present invention is extremely short, and the output of the single-frequency decimeter-wave microwave signal can be realized;

[0023] (4) The dual-wavelength active phase-shift grating is prepared on an erbium-doped photosensitive optical fiber using a 244nm ultraviolet laser by scanning and dithering a phase mask. During the ultraviolet laser scanning process, the dithering of the phase mask is precisely controlled to produce a π phase shift of one quarter of the grating period on the dual-wavelength active phase-shift grating. The above-mentioned dual-wavelength active phase-shift grating preparation method reduces the difficulty of preparing the active phase-shift grating. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solution of the embodiment of the present invention, the following briefly introduces the drawings required for describing the embodiment. Figure 1 Schematic diagram of a single-frequency microwave signal source based on an active phase-shift grating.

[0025] Figure 2 This is the single longitudinal mode dual-wavelength laser spectrum generated by the dual-wavelength active phase-shift grating.

[0026] Description of reference numerals:

[0027] 1—Pump source, 2—Wavelength division multiplexer, 3—Dual wavelength active phase shift grating, 4—Optical isolator,

[0028] 5—High-speed photodetector. DETAILED DESCRIPTION

[0029] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described below with reference to the accompanying drawings and embodiments.

[0030] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways than those described herein. Therefore, the present invention is not limited to the specific embodiments of the following disclosure.

[0031] Example 1

[0032] Combine the following Figures 1 to 2 Specifically explain the single-frequency microwave signal source based on active phase-shift grating, such as Figure 1 As shown, a single-frequency microwave signal source based on an active phase-shift grating includes a pump source 1, a wavelength division multiplexer 2, a dual-wavelength active phase-shift grating 3, an optical isolator 4 and a high-speed photodetector 5.

[0033] like Figure 1 As shown, the wavelength division multiplexer 2 is provided with an input terminal A, an output terminal B and a common terminal C; the pump light output by the pump source 1 is connected to the input terminal A of the wavelength division multiplexer 2 via a single-mode optical fiber; the output terminal of the dual-wavelength active phase-shift grating 3 is connected to the common terminal C of the wavelength division multiplexer 2 via a single-mode optical fiber; the output terminal B of the wavelength division multiplexer 2 is connected to the input terminal of the optical isolator 4 via a single-mode optical fiber.

[0034] like Figure 1 As shown, the output end of the optical isolator 4 is connected to the input end of the high-speed photodetector 5 via a single-mode optical fiber, and the output end of the high-speed photodetector 5 outputs a single-frequency microwave signal.

[0035] The dual-wavelength active phase-shift grating 3 is a π phase-shifted erbium-doped dual-wavelength active phase-shift grating. The grating region of the dual-wavelength active phase-shift grating 3 is an asymmetric structure, and the π phase shift is close to the input end of the dual-wavelength active phase-shift grating 3 .

[0036] The dual-wavelength active phase-shift grating 3 is prepared on an erbium-doped photosensitive optical fiber by a 244nm ultraviolet laser through a scanning and jittering phase mask method; during the ultraviolet laser scanning process, the jitter of the phase mask is precisely controlled to produce a π phase shift of a quarter of the grating period on the dual-wavelength active phase-shift grating 3.

[0037] The single longitudinal mode dual wavelength laser signal generated by the dual wavelength active phase shift grating 3 has a difference between the two wavelengths between 5-15 pm ( Figure 1The difference between the two wavelengths is 12.05pm), and after frequency conversion, it is about 624-1871MHz, which belongs to the decimeter wave band in microwaves. The single longitudinal mode dual-wavelength laser signal generated by the dual-wavelength active phase-shift grating 3 has good coherence, narrow line width, low phase noise, and stable mode. It can directly generate a single-frequency microwave signal by beating without any additional processing. From a system perspective, it has a simple structure, light volume, and is easy to integrate. The optical carrier is easy to modulate, adapts to long-distance transmission, and is resistant to electromagnetic interference. It can be used as an ideal signal source in the field of radio frequency microwave photonics.

[0038] The pump source 1 is a 980nm semiconductor laser, and the pump source 1 outputs 200mw pump light.

[0039] The wavelength division multiplexer 2 is a 980 / 1550nm wavelength division multiplexer, and the optical isolator 4 is a 1550nm optical isolator.

[0040] The frequency range of the high-speed photodetector 5 should match the frequency of the dual-wavelength narrow-linewidth laser emitted by the received dual-wavelength active phase-shift grating 3 , and the response frequency of the high-speed photodetector 5 should be no less than 1 GHz.

[0041] A method for generating a single-frequency microwave signal based on an active phase-shift grating, such as Figure 1 As shown, the following steps are included:

[0042] Step 1: Using the above-mentioned single-frequency microwave signal source based on active phase-shift grating, the 200mw pump light output by the pump source 1980nm semiconductor laser is transmitted to the 980nm input terminal A of the 980 / 1550nm wavelength division multiplexer 2 through the standard 980nm single-mode optical fiber; the pump light is input from the input terminal A of the wavelength division multiplexer 2, and reaches the dual-wavelength active phase-shift grating 3 through the common terminal C, and pumps the dual-wavelength active phase-shift grating 3;

[0043] Step 2: The pumped dual-wavelength active phase-shift grating 3 outputs dual-wavelength narrow-linewidth laser. The single longitudinal mode dual-wavelength laser spectrum is shown in FIG. Figure 2 As shown, the 980nm single-mode optical fiber is output to the common terminal C of the wavelength division multiplexer 2; the wavelength division multiplexer 2 couples the pump light and the dual-wavelength narrow linewidth laser input from the input terminal A and the common terminal C respectively;

[0044] In step 3, the coupled laser signal is then transmitted from the 1550nm output terminal B of the wavelength division multiplexer 2 to the input terminal of the 1550nm optical isolator 4. Finally, the laser signal is transmitted from the output terminal of the optical isolator 4 to the high-speed photodetector 5 via the 1550nm single-mode optical fiber. After receiving the single longitudinal mode dual-wavelength laser signal generated by the dual-wavelength active phase-shift grating 3, the high-speed photodetector 5 generates a microwave electrical signal output with a frequency equal to the frequency difference between the two optical signal wavelengths through the beat frequency.

[0045] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes for application in other fields. However, any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A single-frequency microwave signal source based on an active phase-shift grating, characterized in that: It comprises a pump source (1), a wavelength division multiplexer (2), a dual-wavelength active phase-shift grating (3), an optical isolator (4) and a high-speed photodetector (5); The wavelength division multiplexer (2) is provided with an input end A, an output end B and a common end C; the pump light output by the pump source (1) is connected to the input end A of the wavelength division multiplexer (2) via a single-mode optical fiber; the output end of the dual-wavelength active phase-shift grating (3) is connected to the common end C of the wavelength division multiplexer (2) via a single-mode optical fiber; the output end B of the wavelength division multiplexer (2) is connected to the input end of an optical isolator (4) via a single-mode optical fiber; The output end of the optical isolator (4) is connected to the input end of a high-speed photodetector (5) via a single-mode optical fiber, the output end of the high-speed photodetector (5) outputs a single-frequency microwave signal, the frequency range of the high-speed photodetector (5) matches the frequency of the dual-wavelength narrow-linewidth laser emitted by the received dual-wavelength active phase-shift grating (3), and the response frequency of the high-speed photodetector (5) is not less than 1 GHz; The dual-wavelength active phase-shift grating (3) is a π phase-shifted erbium-doped dual-wavelength active phase-shift grating, the grating region of the dual-wavelength active phase-shift grating (3) is an asymmetric structure, and the π phase shift is close to the input end of the dual-wavelength active phase-shift grating (3); The dual-wavelength active phase-shift grating (3) is prepared on an erbium-doped photosensitive optical fiber by a 244nm ultraviolet laser through a scanning and jittering phase mask method; during the ultraviolet laser scanning process, the jittering of the phase mask is precisely controlled to produce a π phase shift of a quarter of the grating period on the dual-wavelength active phase-shift grating (3).

2. The single-frequency microwave signal source based on active phase-shift grating according to claim 1, characterized in that: The pump source (1) is a 980nm semiconductor laser, and the pump source (1) outputs 200mw pump light.

3. The single-frequency microwave signal source based on active phase-shift grating according to claim 2, characterized in that: The wavelength division multiplexer (2) is a 980 / 1550nm wavelength division multiplexer, and the optical isolator (4) is a 1550nm optical isolator.

4. A method for generating a single-frequency microwave signal based on an active phase-shift grating, characterized in that: Generating a single-frequency microwave signal using the single-frequency microwave signal source based on an active phase-shift grating as claimed in claim 3 comprises the following steps: Step 1: using the single-frequency microwave signal source based on active phase-shift grating, the 200mw pump light outputted by the 980nm semiconductor laser of the pump source (1) is transmitted to the 980nm input terminal A of the 980 / 1550nm wavelength division multiplexer (2) via a standard 980nm single-mode optical fiber; Step 2: The dual-wavelength active phase-shift grating (3) outputs dual-wavelength narrow-linewidth laser light, which is output to the common end C of the wavelength division multiplexer (2) through a 980nm single-mode optical fiber; the wavelength division multiplexer (2) couples the pump light and the dual-wavelength narrow-linewidth laser light respectively input from the input end A and the common end C; Step 3: The coupled laser signal is then transmitted from the 1550nm output terminal B of the wavelength division multiplexer (2) to the input terminal of the 1550nm optical isolator (4). Finally, the laser signal is transmitted from the output terminal of the optical isolator (4) via the 1550nm single-mode optical fiber to the high-speed photodetector (5). After the high-speed photodetector (5) receives the single longitudinal mode dual-wavelength laser signal generated by the dual-wavelength active phase-shift grating (3), it generates a microwave electrical signal output with a frequency equal to the frequency difference between the two wavelengths of the optical signal through beat frequency.

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