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

Abstract

The application discloses an F-P cavity closed loop feedback ultra-narrow linewidth laser light source for measurement, and belongs to the technical field of laser light sources.The F-P cavity closed loop feedback ultra-narrow linewidth laser light source comprises a pump source, the pump source is connected with an input end of a laser resonant cavity, an output end of the laser resonant cavity is connected with an input end of a wavelength division multiplexer, an output end of the wavelength division multiplexer is connected with a forwarding port of a circulator, an isolation port of the circulator is connected with an input end of a first isolator, an output end of the first isolator is connected with an input end of a laser passing coupler, an output end of the laser passing coupler is connected with an input end of an adjustable attenuator, an output end of the adjustable attenuator is connected with an input end of a second isolator, an output end of the second isolator is connected with an input end of an F-P cavity, and an output end of the F-P cavity is connected with an input port of the circulator.The F-P cavity closed loop feedback ultra-narrow linewidth laser light source can ensure the narrow linewidth characteristic, and can also optimize system power and noise suppression, so that the F-P cavity closed loop feedback ultra-narrow linewidth laser light source has better performance and wider application prospect in high-precision measurement and coherent light communication and the like.

Description

Technical Field

[0001] This invention belongs to the field of laser source technology, specifically a FP cavity closed-loop feedback ultra-narrow linewidth laser source for measurement. Background Technology

[0002] The short-period frequency noise of a laser, i.e., its linewidth characteristics, is crucial to the performance of various high-precision measurement applications, including spectroscopy, laser interferometry, quantum communication, and bioimaging. In spectroscopy, a narrow linewidth is key to ensuring high-resolution spectral line analysis; laser interferometry relies on extremely high coherence to improve measurement accuracy. Quantum communication requires sufficiently small linewidths to maintain the coherence of qubits, while bioimaging requires optimized linewidth to ensure image quality. Therefore, optimizing and controlling the laser linewidth for the specific needs of different precision measurement applications is particularly important. 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 typically between kilohertz and hundreds of kilohertz. If the linewidth is narrowed to tens of hertz using advanced technologies, the detection accuracy of lidar will be significantly improved, enabling accurate identification of smaller targets at greater distances. This linewidth narrowing 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 laser coherence to meet the precision requirements of different applications.

[0004] In the area of ​​laser linewidth narrowing, researchers have extensively explored various techniques, including self-injection feedback, phase modulation, and FP (Fabry-Perot) cavity filtering. The basic principle of self-injection feedback is to use a portion of the output light to be fed back into the laser's oscillator through the optical path to improve the laser's frequency stability and coherence, thereby narrowing the output linewidth. For example, in 2015, researchers at the Shanghai Institute of Optics and Fine Mechanics successfully employed a self-injection locking method, re-injecting a portion of the output light as the pump light's pulling frequency into a DFB laser, achieving a laser output linewidth of 125Hz. However, linewidth narrowing based on self-injection typically requires a long feedback loop, and the length of the feedback optical path must match the laser linewidth. If the feedback loop is too short, it may cause intensity fluctuations in the laser, affecting the overall performance of the laser. Therefore, optimizing the design of the feedback loop and its matching with laser performance is particularly important to ensure the stability and reliability of the linewidth narrowing system. Phase modulation improves the laser's coherence by adjusting the laser phase, thereby effectively reducing the linewidth. However, this method may require the introduction of additional noise suppression systems, which increases the number of optical components and control circuits, leading to increased system complexity and maintenance difficulty. Furthermore, accurately calculating the transfer function between the modulation signal and the laser linewidth is crucial, limiting the method's versatility. The third technique utilizes the filtering effect of a FP cavity to achieve linewidth narrowing. Through the interference effect of light, the FP cavity can select a specific frequency by controlling the optical path difference within the cavity, thereby effectively reducing the linewidth. However, in high-power applications, the FP cavity may face challenges from nonlinear effects, which could affect its performance. Additionally, if the laser frequency differs significantly from the standing wave frequency, it can lead to significant power loss.

[0005] To achieve stable linewidth-reduced laser output, this invention proposes a self-injection linewidth-reducing technique based on an FP cavity, combining the advantages of self-injection feedback and optical FP cavity filtering. This technique not only effectively solves the stringent requirements of self-injection feedback on delay fiber length matching, but also overcomes the potential optical power loss problem that may occur during optical FP cavity filtering. Summary of the Invention

[0006] This invention provides an FP cavity closed-loop feedback ultra-narrow linewidth laser source for measurement, in order to overcome the deficiencies in the prior art.

[0007] This invention is achieved through the following technical solution:

[0008] An FP cavity closed-loop feedback ultra-narrow linewidth laser source for measurement includes a pump source connected to the input of a laser resonant cavity, the output of the laser resonant cavity connected to the input of a wavelength division multiplexer (WDM), the output of the WDM connected to the repeater port of a circulator, the isolation port of the circulator connected to the input of a first isolator, the output of the first isolator connected to the input of a laser-coupled device, the output of the laser-coupled device connected to the input of an adjustable attenuator, the output of the adjustable attenuator connected to the input of a second isolator, the output of the second isolator connected to the input of the FP cavity, and the output of the FP cavity connected to the output port of the circulator.

[0009] As described above, in a FP cavity closed-loop feedback ultra-narrow linewidth laser source for measurement, the pump source is incident from the high-reflectivity mirror on the left side of the laser resonant cavity, and after multiple reflections by the high-reflectivity mirror and the low-reflectivity mirror within the laser resonant cavity, and after a gain fiber amplification process, the laser is finally output from the low-reflectivity mirror.

[0010] As described above, a FP cavity closed-loop feedback ultra-narrow linewidth laser source for measurement involves a wavelength division multiplexer filtering out some residual pump light. The laser signal then passes through a circulator and a first isolator to eliminate interference from return light and other stray light at the system front end. The laser signal is then split into two paths by a laser coupler. One path is directly output, while the other path, after attenuation and filtering by an adjustable attenuator and a second isolator, enters the FP cavity. A standing wave effect is achieved within the FP cavity, utilizing the frequency selectivity of the FP cavity to finely filter the laser spectrum. Simultaneously, the standing wave effect significantly extends the photon dwell time within the cavity, thereby increasing photon lifetime. The laser signal, after frequency filtering and lifetime extension, is re-injected into the laser resonant cavity through the circulator's forwarding port, forming a closed-loop feedback mechanism.

[0011] As described above, the FP cavity closed-loop feedback ultra-narrow linewidth laser source for measurement is pumped in either forward or backward pumping mode, and the pump source can be any one of semiconductor laser pumping, sunlight pumping, or flash lamp pumping.

[0012] The laser resonator described above for measurement using a closed-loop feedback ultra-narrow linewidth laser source with FP cavity is either a distributed feedback (DBR) laser resonator or a Bragg reflector (DFB) laser resonator.

[0013] As described above, in a FP cavity closed-loop feedback ultra-narrow linewidth laser source for measurement, the main function of the circulator is to ensure that the optical signal can be transmitted efficiently and stably to subsequent optical components, while effectively guiding the frequency-filtered narrow linewidth signal light back to the laser resonant cavity to achieve closed-loop feedback control of the system. The circulator can be any one of a multi-port fiber optic circulator, an electro-optic circulator, a silicon-based integrated circulator, and a free-space circulator.

[0014] As described above, in a FP cavity closed-loop feedback ultra-narrow linewidth laser source for measurement, the main function of the coupler is to split the laser signal into two paths, one of which is directly output, and the other path is re-injected into the laser resonant cavity as a feedback signal after subsequent power adjustment and frequency filtering, so as to realize the closed-loop control of the system. The coupler can be any one of a fused biconical tapered coupler, a planar waveguide coupler, and a fiber array coupler.

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

[0016] As described above, the FP cavity closed-loop feedback ultra-narrow linewidth laser source for measurement has the main function of high-precision screening of laser frequency, filtering out lasers of specific wavelengths, and effectively extending photon lifetime. Through this process, the narrowed laser signal is re-injected into the laser resonant cavity as a traction frequency signal, and the frequency stability and linewidth performance of the laser are further optimized by extending the photon lifetime.

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

[0018] The advantages of this invention are as follows: By utilizing the wavelength selection and filtering capabilities of the FP cavity, combined with self-injected photon lifetime extension technology, this invention achieves stable narrowing of the laser linewidth and effectively suppresses short-period frequency noise. This not only avoids the stringent requirements of self-injection feedback on the length matching of the delay fiber but also effectively reduces the optical power loss problems that may be caused by FP cavity filtering. Simultaneously, by optimizing the system structure, this invention reduces the stringent requirements of self-injection feedback on fiber length matching, making the laser system more compact, while improving overall stability and reducing interference from the external environment on the laser frequency. This ensures the linewidth narrowing effect while improving the overall efficiency and stability of the system. Furthermore, while ensuring narrow linewidth characteristics, this invention also optimizes system power and noise suppression, giving it superior performance and broader application prospects in high-precision measurement and coherent optical communication applications. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the structure of the present invention;

[0021] Figure 2 This is a schematic diagram of the linewidth measurement of the laser source before suppression according to an embodiment of the present invention;

[0022] Figure 3 This is a schematic diagram of the linewidth measurement of the suppressed laser source according to an embodiment of the present invention;

[0023] Figure 4 This is a schematic diagram of the frequency noise measurement of the laser source before and after suppression according to an embodiment of the present invention (the gray curve represents the frequency noise measurement result of the source after narrowing the laser linewidth using FP cavity closed-loop feedback, while the black curve represents the frequency noise measurement result of the laser source before suppression).

[0024] Reference numerals: 1. Pump source; 2. Laser resonant cavity; 3. Wavelength division multiplexer; 4. Circulator; 5. First isolator; 6. Coupler; 7. Adjustable attenuator; 8. Second isolator; 9. FP cavity. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] like Figure 1 As shown, an FP cavity closed-loop feedback ultra-narrow linewidth laser source for measurement includes a pump source 1, which is connected to the input end of a laser resonant cavity 2. The output end of the laser resonant cavity 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 forwarding 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-coupled device 6. The output end of the laser-coupled device 6 is connected to the input end of an adjustable attenuator 7. The output end of the adjustable 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 FP cavity 9. The output end of the FP cavity 9 is connected to the input port (port 1) of the circulator 4.

[0027] Specifically, in this embodiment, the pump source 1 is incident from the high-reflection mirror on the left side of the laser resonant cavity 2, and after multiple reflections by the high-reflection mirror and the low-reflection mirror in the laser resonant cavity 2, and after the gain fiber amplification process, the laser is finally output from the low-reflection mirror.

[0028] Specifically, in this embodiment, 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 return light and other stray light on the system front end, ensuring the unidirectional propagation of the laser signal. Subsequently, the laser signal is split into two paths by the laser coupler 6. One path is directly output, and the other path is attenuated and filtered by the adjustable attenuator 7 and the second isolator 8 before entering the FP cavity 9, further ensuring the unidirectionality of the laser and controlling its intensity, ensuring its stability and consistency in subsequent stages. The laser signal achieves a standing wave effect in the FP cavity 9, and the frequency selection characteristics of the FP cavity 9 are used to finely filter 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. After frequency filtering and photon lifetime extension, the laser signal is re-injected into the laser resonant cavity 2 through the forwarding port (port 2) of the circulator 4, forming a closed-loop feedback mechanism. Through this closed-loop feedback, the laser undergoes frequency filtering and photon lifetime delay in the optical loop, which effectively narrows the laser linewidth, ultimately achieving system linewidth optimization and frequency stability improvement.

[0029] More specifically, the pump source 1 described in this embodiment is pumped in a forward pumping or backward pumping manner, and the pump source 1 is any one of semiconductor laser pumping, sunlight pumping, and flash lamp pumping.

[0030] More specifically, the laser resonator 2 described in this embodiment is a distributed feedback (DBR) laser resonator or a Bragg reflector (DFB) laser resonator.

[0031] More specifically, the main function of the circulator 4 described in this embodiment is to ensure that the optical signal can be transmitted to the subsequent optical components efficiently and stably, and to effectively guide the narrow linewidth signal light that has been frequency filtered back to the laser resonant cavity 2, so as to realize 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 described in this embodiment is to split the laser signal into two paths, one of which is directly output, and the other path is re-injected into the laser resonant cavity 2 as a feedback signal after subsequent power adjustment and frequency filtering to achieve closed-loop control of the system. The feedback signal is returned to the laser resonant cavity 2 after precise adjustment, optimizing the working state of the laser and further narrowing the laser linewidth. The coupler 6 is any one of a fused biconical tapered coupler, a planar waveguide coupler, and a fiber array coupler.

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

[0034] Furthermore, the main function of the FP cavity 9 described in this embodiment is to perform high-precision screening of laser frequencies, filter out lasers of specific wavelengths, and effectively extend photon lifetime. Through this process, the narrowed laser signal will be re-injected into the laser resonant cavity 2 as a traction frequency signal. By extending the photon lifetime, the frequency stability and linewidth performance of the laser will be further optimized.

[0035] Furthermore, the FP cavity 9 described in this embodiment is any one of an optical fiber FP cavity, an air cavity FP cavity, and a standard FP cavity.

[0036] The performance of a FP cavity closed-loop feedback ultra-narrow linewidth laser source for measurement according to an embodiment of the present invention was tested, and the results are as follows: Figures 2-4 As shown.

[0037] pass Figure 2 It can be seen that the linewidth of the laser source before suppression of the FP cavity closed-loop feedback ultra-narrow linewidth laser source was measured. The linewidth measurement before suppression adopted the delayed self-heterodyne method. The linewidth of the laser source before the linewidth was not narrowed can be calculated to be 30.7kHz based on the measurement results.

[0038] pass Figure 3 It can be seen that the linewidth of the laser source after suppression of the FP cavity closed-loop feedback ultra-narrow linewidth laser source is measured. The linewidth measurement after suppression adopts the self-coherent detection method based on strong coherent envelope. The linewidth of the laser source after narrowing can be calculated to be 50Hz from the measurement results.

[0039] pass Figure 4 It can be seen that the frequency noise measurement of the laser source before and after suppression using the FP cavity closed-loop feedback ultra-narrow linewidth laser source is shown. The gray curve represents the frequency noise measurement result of the source after narrowing the laser linewidth using the FP cavity closed-loop feedback, while the black curve represents the frequency noise measurement result of the laser source before suppression. From the above curves, it can be seen that the maximum suppression of the laser source's frequency noise in the range of 10Hz to 25kHz reaches 6 orders of magnitude. At this time, the frequency noise is reduced to 820Hz at 100Hz and 25kHz. 2 Below / Hz, and the frequency noise at 1kHz and 25kHz is no greater than 200Hz. 2 / Hz.

[0040] In summary, this invention employs a closed-loop feedback technique based on FP cavity filtering, which effectively suppresses short-period frequency noise of the laser and significantly narrows the linewidth of the output laser. Furthermore, by combining the selection of the feedback laser frequency by the FP cavity with the narrowing of the linewidth, the overall performance of linewidth narrowing is further improved. Moreover, the output power of the laser source obtained by this invention exceeds 10W, and it maintains a single longitudinal mode operation during actual operation, exhibiting high output power and high operational stability.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A closed-loop feedback ultra-narrow linewidth laser source for measurement using an FP cavity, characterized in that: The system includes a pump source (1), which is connected to the input of a laser resonant cavity (2). The output of the laser resonant cavity (2) is connected to the input of a wavelength division multiplexer (3). The output of the wavelength division multiplexer (3) is connected to the forwarding port of a circulator (4). The isolation port of the circulator (4) is connected to the input of a first isolator (5). The output of the first isolator (5) is connected to the input of a laser-through-coupler (6). The output of the laser-through-coupler (6) is connected to the input of an adjustable attenuator (7). The output of the adjustable attenuator (7) is connected to the input of a second isolator (8). The output of the second isolator (8) is connected to the input of an FP cavity (9). The output of the FP cavity (9) is connected to the input of the circulator (4). After the wavelength division multiplexer (3) filters out some residual pump light, the laser signal passes through the circulator (4) and then through the first isolator (5) to eliminate the interference of return light and other stray light on the front end of the system. Subsequently, the laser signal is split into two paths by the laser coupler (6). One path is directly output, and the other path is attenuated and filtered by the adjustable attenuator (7) and the second isolator (8). The laser signal then enters the FP cavity (9). The laser signal realizes the standing wave effect in the FP cavity (9). The frequency selection characteristics of the FP cavity (9) are used to finely filter 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. After frequency filtering and photon lifetime extension, the laser signal is re-injected into the laser resonant cavity (2) through the forwarding port of the circulator (4) to form a closed-loop feedback mechanism. The main function of the FP cavity (9) is to perform high-precision screening of laser frequency, filter out lasers of specific wavelengths, and effectively extend photon lifetime. Through this process, the narrowed laser signal will be re-injected into the laser resonant cavity (2) as a traction frequency signal. The frequency stability and linewidth performance of the laser will be further optimized by extending the photon lifetime.

2. The FP cavity closed-loop feedback ultra-narrow linewidth laser source for measurement according to claim 1, characterized in that: The pump source (1) is incident from the high-reflection mirror on the left side of the laser resonator (2), and after multiple reflections by the high-reflection mirror and the low-reflection mirror in the laser resonator (2), and after the gain fiber amplification process, the laser is finally output from the low-reflection mirror.

3. The FP cavity closed-loop feedback ultra-narrow linewidth laser source for measurement according to claim 1, characterized in that: The pump source (1) is pumped in either forward or backward manner, and the pump source (1) can be any one of semiconductor laser pumping, sunlight pumping, or flash lamp pumping.

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

5. The FP cavity closed-loop feedback ultra-narrow linewidth laser 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 transmitted to the subsequent optical components efficiently and stably, and to effectively guide the narrow linewidth signal light that has been frequency filtered back to the laser resonant cavity (2) to realize 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.

6. The FP cavity closed-loop feedback ultra-narrow linewidth laser source for measurement according to claim 1, characterized in that: The main function of the coupler (6) is to split the laser signal into two paths, one of which is directly output, and the other is re-injected into the laser resonant cavity (2) as a feedback signal after subsequent power adjustment and frequency filtering, so as to realize the closed-loop control of the system. The coupler (6) is any one of the following: fused tapered coupler, planar waveguide coupler and fiber array coupler.

7. The FP cavity closed-loop feedback 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 of the input 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) is any one of an optical adjustable attenuator, an electro-optic adjustable attenuator, and a mechanical adjustable attenuator.

8. The FP cavity closed-loop feedback ultra-narrow linewidth laser source for measurement according to claim 1, characterized in that: The FP cavity (9) is any one of fiber optic FP cavity, air cavity FP cavity, and standard FP cavity.

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