F-P cavity closed-loop feedback ultra-narrow linewidth laser light source for measurement

Abstract

An F-P cavity closed-loop feedback ultra-narrow linewidth laser light source for measurement belongs to the technical field of laser light sources and comprises a pumping source, the pumping source is connected with the input end of a laser resonant cavity, the output end of the laser resonant cavity is connected with the input end of a wavelength division multiplexer, the output end of the wavelength division multiplexer is connected with a forwarding port of a circulator, and the forwarding port of the circulator is connected with the output end of the laser resonant cavity. An isolation port of the circulator is connected with the input end of the first isolator, the output end of the first isolator is connected with the input end of the laser passing coupler, the output end of the laser passing coupler is connected with the input end of the adjustable attenuator, the output end of the adjustable attenuator is connected with the input end of the second isolator, and the output end of the second isolator is connected with the output end of the laser passing coupler. The output end of the second isolator is connected with the input end of the F-P cavity, and the output end of the F-P cavity is connected with the input port of the circulator. According to the method, the narrow linewidth characteristic is ensured, and meanwhile, system power and noise suppression optimization are considered, so that the method has better performance and wider application prospects in high-precision measurement, coherent optical communication and other applications.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser light sources, and more particularly to an F-P cavity closed-loop feedback ultra-narrow linewidth laser light source for measurement. Background Art

[0002] The short-period frequency noise of a laser, i.e., the linewidth characteristic of the laser, is crucial for the performance of various high-precision measurement applications, including spectroscopy, laser interferometers, quantum communication, and bioimaging. In spectroscopy, a narrower linewidth is the key to ensuring high-resolution spectral line analysis; laser interferometers rely on extremely high coherence to improve measurement accuracy. Quantum communication requires a sufficiently small linewidth to maintain the coherence of qubits, while bioimaging needs to optimize the linewidth to ensure image quality. Therefore, it is particularly important to optimize and control the linewidth of lasers according to the specific requirements of different precision measurement applications. This not only improves the overall performance of the system but also lays the foundation for innovative applications in various fields. For example, the linewidth of modern lidar is usually between kilohertz and hundreds of kilohertz. If the linewidth is narrowed to dozens of hertz through advanced technical means, the detection accuracy of lidar will be significantly improved, enabling accurate identification of farther distances and smaller targets. This narrowing of the linewidth not only enhances the performance of the laser but also expands its application potential in fields such as autonomous driving and topographic mapping.

[0003] Therefore, researching and implementing linewidth narrowing of lasers can effectively suppress short-period frequency noise and improve the coherence of lasers to meet the accuracy requirements of different applications.

[0004] In terms of narrowing the linewidth of lasers, researchers have widely explored various techniques, including self-injection feedback, phase modulation, and F-P (Fabry-Perot) cavity filtering methods. The basic principle of self-injection feedback is to use part of the output light to be fed back into the oscillator of the laser through the optical path to improve the frequency stability and coherence of the laser, thereby narrowing the linewidth of the output light. For example, in 2015, researchers at the Shanghai Institute of Optics and Fine Mechanics successfully adopted the method of self-injection locking, injecting part of the output light as the traction frequency of the pump light back into the DFB laser, achieving a laser output linewidth of 125 Hz. However, linewidth narrowing based on self-injection usually requires a long feedback loop, and the length of the feedback optical path needs to match the laser linewidth. If the feedback loop is too short, it may cause intensity fluctuations of the laser, thus affecting the overall performance of the laser. Therefore, it is particularly important to optimize the design of the feedback loop and its matching with the laser performance to ensure the stability and reliability of the linewidth narrowing system. Phase modulation improves the coherence of the laser by adjusting the laser phase, thereby effectively reducing the linewidth. However, this method may require the introduction of an additional noise suppression system, which will increase the number of optical components and control circuits, and thus lead to an increase in system complexity and maintenance difficulty. In addition, it is also very important to accurately calculate the transfer function between the modulation signal and the laser linewidth, which limits the universality of this method. The third technique uses the filtering effect of the F-P cavity to achieve linewidth narrowing. Through the interference effect of light, the F-P cavity can select specific frequencies by controlling the optical path difference in the cavity, thereby effectively reducing the linewidth. However, in high-power applications, the F-P cavity may face the challenge of nonlinear effects, which may affect its performance. In addition, if the laser frequency is significantly different from the standing wave frequency, it may lead to significant power loss.

[0005] In order to achieve a stable laser output with narrowed linewidth, the present invention proposes a self-injection linewidth narrowing technique based on an F-P cavity, combining the advantages of self-injection feedback and optical F-P cavity filtering. This technique not only effectively solves the strict requirement for the length matching of the delay fiber in self-injection feedback, but also overcomes the problem of optical power loss that may occur during the optical F-P cavity filtering process. The content of the invention

[0006] The present invention provides an F-P cavity closed-loop feedback ultra-narrow linewidth laser light source for measurement to solve the defects in the prior art.

[0007] The present invention is achieved through the following technical solutions:

[0008] An F-P cavity closed-loop feedback ultra-narrow linewidth laser source for measurement, comprising a pump source, wherein the pump source is connected to the input end of a laser resonator, the output end of the laser resonator is connected to the input end of a wavelength division multiplexer, the output end of the wavelength division multiplexer is connected to the through port of a circulator, the isolation port of the circulator is connected to the input end of a first isolator, the output end of the first isolator is connected to the input end of a laser through a coupler, the output end of the laser through the coupler is connected to the input end of an adjustable attenuator, the output end of the adjustable attenuator is connected to the input end of a second isolator, the output end of the second isolator is connected to the input end of an F-P cavity, and the output end of the F-P cavity is connected to the output port of the circulator.

[0009] For the F-P cavity closed-loop feedback ultra-narrow linewidth laser source for measurement as described above, the pump source is incident from the high reflector on the left side of the laser resonator, and through the multiple reflection of the high reflector and the low reflector in the laser resonator, after the amplification process of the gain fiber, the laser is finally output from the low reflector.

[0010] For the F-P cavity closed-loop feedback ultra-narrow linewidth laser source for measurement as described above, the wavelength division multiplexer filters out part of the residual pump light, and then the laser signal passes through the circulator and eliminates the interference of the return light and other stray lights on the front end of the system through the first isolator. Subsequently, the laser signal is divided into two paths by the laser through the coupler. One path is directly output, and the other path of the laser after attenuation and filtering through the adjustable attenuator and the second isolator then enters the F-P cavity. The laser signal realizes the standing wave effect in the F-P cavity, and uses the frequency selection characteristic of the F-P cavity to finely screen the laser spectrum. At the same time, the standing wave effect significantly prolongs the residence time of photons in the cavity, thereby increasing the photon lifetime. The laser signal after frequency filtering and photon lifetime extension is re-injected into the laser resonator through the through port of the circulator to form a closed-loop feedback mechanism.

[0011] For the F-P cavity closed-loop feedback ultra-narrow linewidth laser source for measurement as described above, the pumping method of the pump source is forward pumping or backward pumping, and the pump source is any one of semiconductor laser pumping, sunlight pumping, and flash lamp pumping.

[0012] For the F-P cavity closed-loop feedback ultra-narrow linewidth laser source for measurement as described above, the laser resonator is a distributed feedback (DBR) type laser resonator or a distributed Bragg reflector (DFB) type laser resonator.

[0013] An F-P cavity closed-loop feedback ultra-narrow linewidth laser source for measurement as described above. The main function of the circulator is to ensure that the optical signal can be efficiently and stably transmitted to subsequent optical components, and at the same time, effectively guide the narrow linewidth signal light that has undergone frequency screening back to the laser resonator to achieve the closed-loop feedback control of the system. The circulator is any one of a multi-port fiber optic circulator, an electro-optic circulator, a silicon-based integrated circulator, and a free space circulator.

[0014] An F-P cavity closed-loop feedback ultra-narrow linewidth laser source for measurement as described above. The main function of the coupler is to divide the laser signal into two paths. One path is directly output, and the other path, after subsequent power adjustment and frequency filtering processing, is reinjected into the laser resonator as a feedback signal to achieve the closed-loop control of the system. The coupler is any one of a fused taper coupler, a planar waveguide coupler, and a fiber array coupler.

[0015] An F-P cavity closed-loop feedback ultra-narrow linewidth laser source for measurement as described above. The main function of the variable optical attenuator is to precisely adjust the optical power input into the laser resonator to ensure that the optical power in the laser resonator reaches the optimal value, thereby optimizing the performance of the system and improving the stability of the laser output. The variable optical attenuator is any one of an optical variable optical attenuator, an electro-optic variable optical attenuator, and a mechanical variable optical attenuator.

[0016] An F-P cavity closed-loop feedback ultra-narrow linewidth laser source for measurement as described above. The main function of the F-P cavity is to perform high-precision screening of the laser frequency, filter out the laser of a specific wavelength, and effectively extend the photon lifetime. Through this process, the compressed laser signal will be reinjected into the laser resonator as a traction frequency signal, and further optimize the frequency stability and linewidth performance of the laser by extending the photon lifetime.

[0017] An F-P cavity closed-loop feedback ultra-narrow linewidth laser source for measurement as described above. The F-P cavity is any one of a fiber optic F-P cavity, an air cavity F-P cavity, and a standard F-P cavity.

[0018] The advantages of the present invention are as follows: Through the wavelength selection and filtering function of the F-P cavity and in combination with the technology of extending the self-injected photon lifetime, the present invention realizes the stable narrowing of the laser linewidth and effectively suppresses the short-period frequency noise. It not only avoids the stringent requirements for the length matching of the delay fiber due to self-injection feedback but also effectively reduces the optical power loss problem that may be caused by the filtering of the F-P cavity. At the same time, by optimizing the system structure, the present invention reduces the strict requirements for the fiber length matching due to self-injection feedback, makes the laser system more compact, improves the overall stability, reduces the interference of the external environment on the laser frequency, ensures the linewidth narrowing effect, and improves the overall efficiency and stability of the system. Moreover, while ensuring the narrow linewidth characteristics, the present invention takes into account the optimization of system power and noise suppression, making it have better performance and broader application prospects in applications such as high-precision measurement and coherent optical communication. Brief Description of the Drawings

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0020] Figure 1 is the structural schematic diagram of the present invention;

[0021] Figure 2 is the schematic diagram of the linewidth measurement of the laser light source before suppression in the embodiment of the present invention;

[0022] Figure 3 is the schematic diagram of the linewidth measurement of the laser light source after suppression in the embodiment of the present invention;

[0023] Figure 4 is the schematic diagram of the frequency noise measurement of the laser light source before and after suppression in the embodiment of the present invention (the gray curve represents the measurement result of the frequency noise of the light source after the laser linewidth is narrowed by using the F-P cavity closed-loop feedback, while the black curve represents the measurement result of the frequency noise of the laser light source before suppression).

[0024] Reference numerals: 1, pump source; 2, laser resonator; 3, wavelength division multiplexer; 4, circulator; 5, first isolator; 6, coupler; 7, adjustable attenuator; 8, second isolator; 9, F-P cavity. Detailed Embodiments

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0026] As Figure 1 shown, a fiber - optic Fabry - Perot (F - P) cavity closed - loop feedback ultra - narrow line - width laser source for measurement includes a pump source 1, where the pump source 1 is connected to the input end of a laser resonator 2, the output end of the laser resonator 2 is connected to the input end of a wavelength division multiplexer 3, the output end of the wavelength division multiplexer 3 is connected to the through - port (port 2) of a circulator 4, the isolation port (port 3) of the circulator 4 is connected to the input end of a first isolator 5, the output end of the first isolator 5 is connected to the input end of a laser through a coupler 6, the output end of the laser through the coupler 6 is connected to the input end of a tunable attenuator 7, the output end of the tunable attenuator 7 is connected to the input end of a second isolator 8, the output end of the second isolator 8 is connected to the input end of an F - P cavity 9, and the output end of the F - P cavity 9 is connected to the input port (port 1) of the circulator 4.

[0027] Specifically, the pump source 1 in this embodiment is incident from the left - hand high - reflector of the laser resonator 2. Through multiple reflections between the high - reflector and the low - reflector in the laser resonator 2 and after the amplification process of the gain fiber, the laser is finally output from the low - reflector.

[0028] Specifically, the wavelength division multiplexer 3 in this embodiment filters out some residual pump light, and then the laser signal passes through the circulator 4 and the first isolator 5 to eliminate the interference of the return light and other stray light on the front - end of the system, ensuring the unidirectional propagation of the laser signal. Subsequently, the laser signal is divided into two paths by the laser through the coupler 6. One path is directly output, and the other path of the laser after attenuation and filtering through the tunable attenuator 7 and the second isolator 8 then enters the F - P cavity 9, further ensuring the unidirectionality of the laser and controlling its intensity, ensuring its stability and consistency in subsequent processes. The laser signal realizes the standing - wave effect in the F - P cavity 9, and uses the frequency - selection characteristic of the F - P cavity 9 to finely screen the laser spectrum. At the same time, the standing - wave effect significantly prolongs the residence time of photons in the cavity, thereby increasing the photon lifetime. The laser signal after frequency filtering and photon - lifetime extension passes through the through - port (port 2) of the circulator 4 and is re - injected into the laser resonator 2 to form a closed - loop feedback mechanism. Through this closed - loop feedback, the laser experiences frequency screening and photon - lifetime delay in the optical loop, which will effectively narrow the laser line - width and finally realize the line - width optimization and frequency - stability improvement of the system.

[0029] More specifically, the pumping method of the pump source 1 in this embodiment is forward pumping or backward pumping, and the pump source 1 is any one of semiconductor laser pumping, sunlight pumping, and flashlamp pumping.

[0030] Even more specifically, the laser resonator 2 in this embodiment is a distributed feedback DBR type laser resonator or a Bragg reflector DFB type laser resonator.

[0031] Even more specifically, the main function of the circulator 4 in this embodiment is to ensure that the optical signal can be efficiently and stably transmitted to subsequent optical elements, and at the same time effectively guide the narrow linewidth signal light after frequency screening back to the laser resonator 2 to achieve the closed-loop feedback control of the system. The circulator 4 is any one of a multi-port fiber optic circulator, an electro-optic circulator, a silicon-based integrated circulator, and a free space circulator.

[0032] Furthermore, the main function of the coupler 6 in this embodiment is to divide the laser signal into two paths, one path is directly output, and the other path is used as a feedback signal to be reinjected into the laser resonator 2 after subsequent power adjustment and frequency filtering processing to achieve the closed-loop control of the system. The feedback signal returns to the laser resonator 2 after precise adjustment to optimize the working state of the laser and further narrow the linewidth of the laser. The coupler 6 is any one of a fused biconical taper coupler, a planar waveguide coupler, and a fiber array coupler.

[0033] Even further, the main function of the tunable attenuator 7 in this embodiment is to precisely adjust the optical power input to the laser resonator 2 to ensure that the optical power in the laser resonator 2 reaches the optimal value, thereby optimizing the performance of the system and improving the stability of laser output. The tunable attenuator 7 is any one of an optical tunable attenuator, an electro-optic tunable attenuator, and a mechanical tunable attenuator.

[0034] Even more further, the main function of the F-P cavity 9 in this embodiment is to perform high-precision screening on the laser frequency, filter out the laser of a specific wavelength, and effectively extend the photon lifetime. Through this process, the narrowed laser signal will be reinjected into the laser resonator 2 as a traction frequency signal to further optimize the frequency stability and linewidth performance of the laser through the extension of the photon lifetime.

[0035] Even further, the F-P cavity 9 in this embodiment is any one of a fiber optic F-P cavity, an air cavity F-P cavity, and a standard F-P cavity.

[0036] Perform performance tests on an F-P cavity closed-loop feedback ultra-narrow linewidth laser source for measurement according to an embodiment of the present invention, and the results are as Figures 2 - 4 shown.

[0037] It can be known from Figure 2 that the linewidth measurement of the laser source before the suppression of the F-P cavity closed-loop feedback ultra-narrow linewidth laser source. The linewidth measurement before suppression adopted the method of delayed self-heterodyne. Through the measurement results, it can be calculated that the linewidth of the laser source before the linewidth was not narrowed was 30.7 kHz;

[0038] It can be known from Figure 3 that the linewidth measurement of the laser source after the suppression of the F-P cavity closed-loop feedback ultra-narrow linewidth laser source. The linewidth measurement after suppression adopted the self-coherence detection method based on the strong coherence envelope. Through the measurement results, it can be calculated that the linewidth of the laser source after narrowing was 50 Hz;

[0039] It can be known from Figure 4 that the frequency noise measurement of the laser source before and after the suppression of the F-P cavity closed-loop feedback ultra-narrow linewidth laser source. The gray curve represents the measurement result of the frequency noise of the light source after the laser linewidth is narrowed by using the F-P cavity closed-loop feedback, while the black curve represents the measurement result of the frequency noise of the laser source before suppression. From the above curves, it can be seen that the maximum suppression amplitude of the frequency noise of the laser source at 10 Hz to 25 kHz reaches 6 orders of magnitude. At this time, the frequency noise drops to 820 Hz at 100 Hz and 25 kHz 2 / Hz or less, and the frequency noise at the frequency points of 1 kHz and 25 kHz is not greater than 200 Hz 2 / Hz.

[0040] In summary, the present invention adopts the closed-loop feedback technology based on F-P cavity filtering, effectively suppresses the short-period frequency noise of the laser, and significantly narrows the linewidth of the output laser; in addition, combined with the selection of the feedback laser frequency by the F-P cavity and the narrowing of the linewidth, the overall performance of the linewidth narrowing is further improved; moreover, the output power of the laser source obtained by the present invention exceeds 10 W, and it maintains the operation state of a single longitudinal mode during the actual operation process, having a high output power and very high working stability.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A FP cavity closed-loop feedback ultra-narrow linewidth laser light source for measurement, characterized by: It includes a pump source (1), the pump source (1) is connected to the input end of a laser resonator (2), the output end of the laser resonator (2) is connected to the input end of a wavelength division multiplexer (3), the output end of the wavelength division multiplexer (3) is connected to the through port of a circulator (4), the isolation port of the circulator (4) is connected to the input end of a first isolator (5), the output end of the first isolator (5) is connected to the input end of a laser passing through a coupler (6), the output end of the laser passing through the coupler (6) is connected to the input end of a tunable attenuator (7), the output end of the tunable attenuator (7) is connected to the input end of a second isolator (8), the output end of the second isolator (8) is connected to the input end of an F-P cavity (9), and the output end of the F-P cavity (9) is connected to the input port of the circulator (4).

2. The F-P cavity closed-loop feedback ultra-narrow linewidth laser light source for measurement according to claim 1, wherein: The pump source (1) is incident from the left high reflector of the laser resonator (2), and through the multiple reflection effects of the high reflector and the low reflector in the laser resonator (2), after the amplification process of the gain fiber, the laser is finally output from the low reflector.

3. The F-P cavity closed-loop feedback ultra-narrow linewidth laser light source for measurement according to claim 1, characterized in that: The wavelength division multiplexer (3) filters out some residual pump light, and then the laser signal passes through the circulator (4) and the first isolator (5) to eliminate the interference of the return light and other stray light on the front end of the system. Subsequently, the laser signal is divided into two paths by the laser passing through the coupler (6). One path is directly output, and the other path of the laser after attenuation and filtering through the tunable attenuator (7) and the second isolator (8) then enters the F-P cavity (9). The laser signal realizes the standing wave effect in the F-P cavity (9), and the frequency selection characteristic of the F-P cavity (9) is used to finely screen the laser spectrum. At the same time, the standing wave effect significantly prolongs the residence time of photons in the cavity, thereby increasing the photon lifetime. The laser signal after frequency filtering and photon lifetime extension is re-injected into the laser resonator (2) through the through port of the circulator (4) to form a closed-loop feedback mechanism.

4. A F-P cavity closed-loop feedback ultra-narrow linewidth laser source for measurement according to claim 1, characterized in that: The pumping method of the pump source (1) is forward pumping or backward pumping, and the pump source (1) is any one of semiconductor laser pumping, sunlight pumping, and flash lamp pumping.

5. The F-P cavity closed-loop feedback ultra-narrow linewidth laser light source for measurement according to claim 1, characterized in that: The laser resonator (2) is a distributed feedback type laser resonator or a Bragg reflector type laser resonator.

6. The F-P cavity closed-loop feedback ultra-narrow linewidth laser light source for measurement according to claim 1, characterized in that: The main function of the circulator (4) is to ensure that the optical signal can be efficiently and stably transmitted to the subsequent optical components, and at the same time effectively guide the narrow linewidth signal light after frequency screening back to the laser resonator (2) to realize the closed-loop feedback control of the system. The circulator (4) is any one of a multi-port fiber circulator, an electro-optic circulator, a silicon-based integrated circulator, and a free space circulator.

7. A closed-loop feedback F-P cavity ultra-narrow linewidth laser source for measurement according to claim 1, characterized in that: The main function of the coupler (6) is to divide the laser signal into two paths. One path is directly output, and the other path, after subsequent power adjustment and frequency filtering processing, is re-injected into the laser resonator (2) as a feedback signal to realize the closed-loop control of the system. The coupler (6) is any one of a fused biconical taper coupler, a planar waveguide coupler, and a fiber array coupler.

8. A closed-loop feedback F-P cavity ultra-narrow linewidth laser source for measurement according to claim 1, characterized in that: The main function of the adjustable attenuator (7) is to precisely adjust the optical power input into the laser resonator (2) to ensure that the optical power in the laser resonator (2) reaches the optimal value, thereby optimizing the system performance and improving the stability of the laser output. The adjustable attenuator (7) can be any one of an optical adjustable attenuator, an electro-optic adjustable attenuator, and a mechanical adjustable attenuator.

9. A closed-loop feedback F-P cavity ultra-narrow linewidth laser source for measurement according to claim 1, characterized in that: The main function of the F-P cavity (9) is to perform high-precision screening of the laser frequency, filter out the laser of a specific wavelength, and effectively extend the photon lifetime. Through this process, the narrowed laser signal will be reinjected into the laser resonator (2) as a pulling frequency signal, and the frequency stability and linewidth performance of the laser will be further optimized by extending the photon lifetime.

10. A closed-loop feedback F-P cavity ultra-narrow linewidth laser source for measurement according to claim 1, characterized in that: The F-P cavity (9) can be any one of a fiber-type F-P cavity, an air-cavity type F-P cavity, and a standard F-P cavity.

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