A mid-infrared extremely weak light signal high-fidelity amplification system and adjusting method

Abstract

This application relates to a high-fidelity amplification system and adjustment method for extremely weak mid-infrared light signals, aiming to solve the problems of existing mid-infrared light amplification systems, such as the inherent noise limitation caused by spontaneous emission of the medium, resulting in the submergence of extremely weak signals and inability to amplify them; high background noise due to numerous stray frequency components; and low gain coefficient and small bandwidth due to limited gain length and bandwidth. It includes a signal input unit for receiving mid-infrared signal light and near-infrared pump light, a pump input unit for providing near-infrared laser light, an optical fiber coupling unit for coupling the signal light and pump light, a parametric amplification unit for power amplification through parametric oscillation, a state control unit, and a state monitoring unit. Based on a cross-band parametric oscillation process under resonant conditions, this application can achieve high-fidelity and high-gain amplification of extremely weak mid-infrared light signals, with performance advantages of low threshold, low noise, high efficiency, and large bandwidth, as well as simple structure and ease of construction.

Description

Technical Field

[0001] This application relates to the field of optical amplification, and in particular to a high-fidelity amplification system and adjustment method for extremely weak mid-infrared light signals. Background Technology

[0002] Mid-infrared laser technology, especially light sources covering the 2-5 micrometer "molecular fingerprint region," plays an irreplaceable core role in fields such as precision spectral detection, environmental monitoring, biomedical imaging, and free-space communication. Whether used as a signal source, mode-locked laser, or seed light for nonlinear processes, the initial power of mid-infrared signal light, whether directly generated or remotely received, is often extremely weak, ranging from microwatts to nanowatts. Therefore, high-performance optical amplifiers are crucial for increasing signal power and meeting the signal-to-noise ratio and energy requirements of subsequent applications.

[0003] Current technological approaches heavily rely on rare-earth ion-doped fiber amplifiers, such as thulium-doped fiber in the 2-micron band and erbium-doped fluoride (or chalcogenide glass) fiber amplifiers in the 3-5 micron band. The basic principle is to achieve energy state inversion of doped ions (such as Tm³⁺ and Er³⁺) through optical pumping at a specific wavelength (e.g., 793nm pumping Tm³⁺), thereby amplifying the transmitted optical signal through stimulated emission. However, for applications requiring high sensitivity and high dynamic range, the inherent bottlenecks determined by its physical principles have become a key obstacle to technological advancement. Firstly, there is a fundamental contradiction between the lower sensitivity limit and spontaneous emission noise: spontaneous emission (ASE) photons generated inside the amplifier due to population inversion are continuously amplified in the gain medium, forming strong broadband background noise. For extremely weak input signals below -40 dBm (approximately 100 nW), the photon flux is far lower than the ASE noise flux, causing the signal to be completely submerged and unable to be amplified. This results in the effective input sensitivity of traditional doped fiber amplifiers being typically limited to above -40 dBm, which cannot meet the needs of extremely weak light detection or long-distance remote sensing.

[0004] Secondly, there is the limitation of gain bandwidth: due to the discrete energy level structure of rare earth ions, the gain spectrum is usually narrow, only tens of nanometers (e.g., thulium-doped fiber and erbium-doped fiber have a 3 dB bandwidth of ~50-100 nm). For signal light in different bands, multiple systems need to be replaced and specially customized. Thirdly, the gain coefficient is limited: due to the concentration quenching effect and the inherent loss of the fiber, the small-signal gain coefficient of single-mode fiber is difficult to exceed 20-30 dB / m; at the same time, to ensure controllable noise and optical nonlinear effects, the net gain of a single stage is often designed to be 10-20 dB. Therefore, to achieve higher gain (>30 dB), a multi-stage amplifier cascade scheme is usually required, with complex bandpass filters and isolators inserted between stages to suppress accumulated ASE noise, resulting in a large overall system size, complex structure, and high cost.

[0005] While recent advancements in integrated optics technology have made it possible to construct doped waveguide amplifiers or nanomaterial composite amplifiers on silicon nitride or chalcogenide glass chips, their inherent limitations, such as small operating bandwidth and difficult thermal management due to their ultra-small size and mode coupling methods, particularly the severely restricted power limit, present significant challenges. Therefore, achieving high-fidelity amplification of extremely weak mid-infrared light signals while simultaneously possessing high gain and large operating bandwidth has become a major bottleneck in current mid-infrared laser technology, presenting both significant implications and immense challenges. Summary of the Invention

[0006] The purpose of this application is to provide a high-fidelity amplification system and adjustment method for extremely weak mid-infrared light signals. This aims to solve the problems faced by existing mid-infrared light amplification systems, such as the inability to amplify extremely weak signals due to the inherent noise limitation caused by the spontaneous emission of doped gain media, as well as the problems of high background noise caused by multiple stray frequency components, and low gain coefficient and small operating bandwidth due to limited usable gain length and bandwidth. This will achieve high-fidelity and high-gain amplification of extremely weak mid-infrared light signals, break through the existing technical bottlenecks and capability limitations, and promote the application and development of mid-infrared laser technology.

[0007] In a first aspect, embodiments of this application provide a high-fidelity amplification system for extremely weak mid-infrared light signals, including a signal input unit, a pump input unit, an optical fiber coupling unit, a parametric amplification unit, a state control unit, and a state monitoring unit. The pump input unit inputs generated near-infrared pump light to the signal input unit. The signal input unit receives the mid-infrared signal light to be amplified and the near-infrared pump light, and injects them into the optical fiber coupling unit. The optical fiber coupling unit couples the mid-infrared signal light and the near-infrared pump light together into the parametric amplification unit and couples the output to the state monitoring unit. The parametric amplification unit utilizes a parametric oscillation process to amplify the power of the mid-infrared signal light. The state control unit changes the operating temperature of the parametric amplification unit to match the resonant wavelength of the parametric amplification unit with the center wavelength of the mid-infrared signal light and / or to match the resonant wavelength of the parametric amplification unit with the center wavelength of the near-infrared pump light. The state monitoring unit monitors the output spectrum of the parametric amplification unit to determine its operating state.

[0008] In some embodiments, the signal input unit includes a dual-color beam combiner and a first microscope objective arranged in sequence; the dual-color beam combiner is used to simultaneously receive the mid-infrared signal light and the near-infrared pump light and combine them for output; the first microscope objective is used to compress the spot size of the mid-infrared signal light and the near-infrared pump light, so that the combined beam of the mid-infrared signal light and the near-infrared pump light is incident on the fiber coupling unit.

[0009] In some embodiments, the pump input unit includes a pump laser and an fiber collimator connected in sequence; the pump laser is used to provide the near-infrared pump light, and the fiber collimator is used to collimate the near-infrared pump light and then inject it into the dichroic beam combiner.

[0010] In some embodiments, the fiber coupling unit includes a mid-infrared tapered fiber, a first displacement stage, and a second displacement stage; the mid-infrared tapered fiber is a mid-infrared single-mode fiber made of As2S3 sulfide glass; the starting end face of the mid-infrared tapered fiber is flat and polished to receive the mid-infrared signal light and the near-infrared pump light; the starting end face of the mid-infrared tapered fiber is placed at the focal point of the first microscope objective to couple and inject the mid-infrared signal light and the near-infrared pump light into the parametric amplification unit; In some embodiments, the central region of the mid-infrared tapered optical fiber is tapered until the evanescent wave can be coupled and output; the first displacement stage and the second displacement stage are respectively placed at the beginning and end of the mid-infrared tapered optical fiber to clamp the mid-infrared tapered optical fiber and tune the distance between the mid-infrared tapered optical fiber and the parametric amplification unit.

[0011] In some embodiments, the parametric amplification unit is a microdisk resonant cavity used to receive the mid-infrared signal light and the near-infrared pump light, and to amplify the power of the mid-infrared signal light by utilizing the parametric oscillation effect under resonance enhancement conditions; the microdisk resonant cavity is made of lithium niobate material, the quality factor of the microdisk resonant cavity is 10^5~10^6, the radius of the microdisk resonant cavity is 1cm~2cm, and the parametric amplification unit has negative dispersion in the 1.5~3.2μm wavelength range.

[0012] In some embodiments, the state control unit includes a semiconductor cooler and a current source; the semiconductor cooler is placed below the parametric amplification unit via a bracket and is used to control the actual operating temperature of the parametric amplification unit; the current source is used to provide the driving current for the semiconductor cooler, and its output terminals are respectively connected to the positive and negative terminals of the semiconductor cooler.

[0013] In some embodiments, the state monitoring unit includes a second microscope objective and a spectrometer arranged in sequence; the second microscope objective is used to receive the amplified mid-infrared signal light and filter out the residual near-infrared pump light, and the incident focal point of the second microscope objective is located at the end face of the mid-infrared tapered optical fiber; the spectrometer is used to monitor the spectral state of the amplified mid-infrared signal light.

[0014] Secondly, embodiments of this application provide an adjustment method for a high-fidelity amplification system for extremely weak mid-infrared light signals. The signal input unit includes a dual-color beam combiner and a first microscope objective arranged in sequence. The dual-color beam combiner is used to simultaneously receive the mid-infrared signal light and the near-infrared pump light and combine them for output to the fiber optic coupling unit. The status monitoring unit includes a second microscope objective and a spectrometer arranged in sequence. The second microscope objective is used to receive the amplified mid-infrared signal light and filter out residual near-infrared pump light. The spectrometer is used to monitor the spectral state of the amplified mid-infrared signal light. The method includes the following steps: Step 1: Adjusting the spatial positions of the dual-color beam combiner, the first microscope objective, and the second microscope objective, so that the mid-infrared signal light spot is compressed and transmitted to the fiber optic coupling unit before being incident on the light source. Step 1: Observe the center wavelength and power of the received mid-infrared signal light using a spectrometer; Step 2: Adjust the operating temperature of the parametric amplification unit and the spatial position of the parametric amplification unit and the fiber optic coupling unit, and observe the power change of the mid-infrared signal light using a spectrometer until the center wavelength of the mid-infrared signal light is at the resonant wavelength of the parametric amplification unit; Step 3: Turn on the pump laser and set the operating wavelength of the pump laser to half the center wavelength of the mid-infrared signal light, so that a parametric oscillation process induced by the injected signal occurs in the parametric amplification unit; Step 4: Adjust the operating wavelength of the pump laser until the operating wavelength of the pump laser is at the resonant wavelength of the parametric amplification unit.

[0015] In some embodiments, the fiber coupling unit includes a mid-infrared tapered fiber, a first displacement stage, and a second displacement stage. The state control unit includes a semiconductor cooler and a current source. Step two includes: Step 2.1, adjusting the first displacement stage and the second displacement stage to control the relative position between the central region of the mid-infrared tapered fiber and the parametric amplification unit until the power of the received mid-infrared signal light observed by the spectrometer reaches a minimum value, while keeping the relative position between the central region and the parametric amplification unit unchanged; Step 2.2, adjusting the current source to change the temperature of the semiconductor cooler to adjust the operating temperature of the parametric amplification unit until the power of the received mid-infrared signal light observed by the spectrometer reaches a minimum value again, while keeping the operating temperature of the parametric amplification unit unchanged.

[0016] The advantages of this application are: This application, based on the parametric oscillation process under resonance conditions, can solve the problem that existing methods cannot amplify extremely weak signals due to the limitation of inherent noise in spontaneous emission. It has the unique advantage of ultra-low threshold, realizing the amplification of extremely weak mid-infrared light signals, with a threshold capability of <-45dBm, which is more than an order of magnitude higher than the traditional method.

[0017] 2. This application amplifies extremely weak optical signals based on the parametric oscillation process under the induced conditions of the injected signal. In principle, it ensures that there are no other extra stray frequency components excited except for the signal wavelength, and has the distinct advantage of ultra-low noise. It can realize high-fidelity amplification of optical signals in the mid-infrared band.

[0018] 3. This application is based on the parametric oscillation process under resonant conditions to amplify the extremely weak mid-infrared light signal. Therefore, the conversion efficiency is extremely high. Only a single-stage system is needed to achieve a gain of nearly 40dB (ten thousand times). Compared with other traditional two-stage or three-stage system amplification schemes, it has the advantages of simple and compact structure and ultra-high gain coefficient.

[0019] 4. This application uses near-infrared pump laser to realize the parametric oscillation process across the band under resonant conditions, without the need for expensive and complex mid-infrared light source for pumping, which has the advantages of low cost and easy construction.

[0020] 5. This application supports the use of various types of near-infrared pump sources, such as 1500-1640nm semiconductor lasers and 1480nm fiber Raman lasers, to achieve mid-infrared weak light amplification covering an ultra-wide range of 2960-3380nm. The working bandwidth (>400nm) is about three to five times higher than that of traditional solutions, and it has broad application prospects in the mid-infrared field. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the system structure provided in the embodiments of this application; Figure 2 A schematic diagram illustrating the working principle of an embodiment of this application; Figure 3 The spectral results of the original mid-infrared signal light corresponding to step one provided in the embodiments of this application; Figure 4 The preliminary parametrically amplified spectral results corresponding to step three in the embodiments of this application; Figure 5 The optimized spectral results for the parametric oscillation process corresponding to step four in the embodiments of this application. Detailed Implementation

[0022] The embodiments of this application will be further described below with reference to the accompanying drawings and specific examples.

[0023] This embodiment provides a high-fidelity amplification system for extremely weak mid-infrared light signals, including a signal input unit for receiving mid-infrared signal light and near-infrared pump light, a pump input unit for providing high-power near-infrared pump laser, an optical fiber coupling unit for coupling the mid-infrared signal light and the near-infrared pump light together, a parametric amplification unit for amplifying the signal light power using a parametric oscillation process, a state control unit for changing the operating temperature of the parametric amplification unit, and a state monitoring unit for monitoring the output spectrum.

[0024] Figure 1 This is a schematic diagram of the structure of the mid-infrared extremely weak light signal high-fidelity amplification system 60 provided in the embodiments of this application, as shown below. Figure 1 As shown, the system includes: Signal input unit 110, pump input unit 20, fiber optic coupling unit 30, parametric amplification unit 8, state control unit 40 and state monitoring unit 50; Pump input unit 20 is used to input the generated near-infrared pump light to signal input unit 110; The signal input unit 110 is used to receive the mid-infrared signal light and near-infrared pump light to be amplified and inject them into the fiber optic coupling unit 30. The fiber optic coupling unit 30 is used to couple and inject the mid-infrared signal light and the near-infrared pump light into the parametric amplification unit 8, and then couple and output them to the status monitoring unit 50. Parametric amplification unit 8 is used to amplify the power of mid-infrared signal light by utilizing the parametric oscillation process; The state control unit 40 is used to change the operating temperature of the parametric amplification unit 8 so that the resonant wavelength of the parametric amplification unit 8 matches the center wavelength of the mid-infrared signal light and / or matches the center wavelength of the near-infrared pump light. The status monitoring unit 50 is used to monitor the output spectrum of the parametric amplification unit 8 and determine its working status.

[0025] It should be noted that the embodiments of this application can be applied to amplify extremely weak mid-infrared signal light. For example, the power of the mid-infrared signal light to be amplified can be less than 30nW.

[0026] See Figure 1 In this embodiment, the signal input unit 110 includes a dual-color beam combiner 1 and a first microscope objective 2 arranged in sequence; the dual-color beam combiner 1 is used to simultaneously receive the mid-infrared signal light to be amplified and the near-infrared pump light and combine them for output.

[0027] The near-infrared pump light has high power; for example, the power of the near-infrared pump light is greater than 10mW and less than 300mW. The first microscope objective 2 is used to compress the spot size of the mid-infrared signal light and the near-infrared pump light so that the combined light can be efficiently incident on the fiber coupling unit 30.

[0028] That is, the spot size of the mid-infrared signal light and near-infrared pump light after beam combining is reduced after passing through the first microscope objective 2, which is conducive to efficient entry into the fiber coupling unit 30.

[0029] The pump input unit 20 includes a pump laser 3 and an fiber collimator 4 connected in sequence. The pump laser 3 provides high-power near-infrared pump light, and the fiber collimator 4 collimates the near-infrared pump light before injecting it into the dichroic beam combiner 1. In this embodiment, the pump laser 3 is a semiconductor type with an operating wavelength of 1.5-1.64 μm, meaning it can be controlled to output laser light of any wavelength within the 1.5-1.64 μm range. Other embodiments may also use other forms of near-infrared, narrow-linewidth, continuous-wave lasers, such as fiber or solid-state lasers, as pumps, as long as they have wavelength tuning capability. The fiber coupling unit 30 includes a mid-infrared tapered fiber 5, a first displacement stage 6, and a second displacement stage 7. The mid-infrared tapered fiber 5 is a mid-infrared single-mode fiber made of sulfide glass such as arsenic trisulfide (As2S3). To achieve high-efficiency reception of mid-infrared signal light and near-infrared pump light, the starting end face of the mid-infrared tapered fiber 5 is flattened and polished, and placed at the focal point of the first microscope objective 2. To couple and inject the mid-infrared signal light and near-infrared pump light into the parametric amplification unit 8, the central region of the mid-infrared tapered fiber 5 is tapered so that the evanescent wave can be coupled and output. Specifically, the central region of the mid-infrared tapered fiber 5 has the smallest diameter and is uniformly distributed. It can also be referred to as the tapered region. As an example, the central region is tapered until the evanescent wave can be coupled for output. For example, the tapered section length of the mid-infrared tapered fiber 5 is 2-3 cm, and the core diameter is 2-3 μm. The first displacement stage 6 and the second displacement stage 7 are respectively placed at the beginning and end of the mid-infrared tapered fiber 5 to clamp it and precisely tune its distance from the parametric amplification unit 8. For example, the distance between the mid-infrared tapered fiber and the parametric amplification unit 8 is 0.5-1 μm.

[0030] It should be noted that, in order to improve coupling efficiency and achieve phase matching, evanescent wave coupling is used to couple the mid-infrared signal light and near-infrared pump light into / out of the microdisk resonant cavity. In principle, any waveguide structure capable of transmitting optical fields in the mid-infrared band using an evanescent wave method can replace mid-infrared tapered fiber 5. For example, on-chip ridge waveguides, etc.

[0031] The parametric amplification unit 8 can be a whispering-gallery mode microresonator with a high quality factor, and its material is a crystal material with second- or third-order nonlinear coefficients, which can generate parametric oscillation processes.

[0032] As an example, the parametric amplification unit 8 is a microdisk resonant cavity used to receive mid-infrared signal light and near-infrared pump light. It utilizes the parametric oscillation effect under resonant enhancement conditions to amplify the mid-infrared signal light power. To achieve a high-efficiency parametric oscillation effect and suppress other interfering effects, the microdisk resonant cavity is made of lithium niobate material, possessing a suitable quality factor (10^5~10^6) and radius (1~2 cm), and exhibiting negative dispersion in the 1.5-3.2 μm wavelength range. When other materials are selected, their size range can be adjusted according to the same design principles to meet dispersion requirements. The state control unit 40 includes a semiconductor cooler 9 and a current source 10. The semiconductor cooler 9 is placed below the parametric amplification unit 8 (i.e., the microdisk resonant cavity) via a bracket 13 to regulate its actual operating temperature. The current source 10 provides the driving current for the semiconductor cooler 9, and its output terminals are connected to the positive and negative terminals of the semiconductor cooler 9, respectively. This application does not limit the material of the bracket; good thermal conductivity is sufficient, and it can be metal, ceramic, etc. Other embodiments may employ different types of cooling devices, as long as they can achieve temperature control. The status monitoring unit 50 includes a second microscope objective 11 and a spectrometer 12 connected in sequence. The second microscope objective 11 receives the amplified mid-infrared signal light. In some embodiments, the second microscope objective 11 is coated with a film that only allows mid-infrared light transmission to improve coupling efficiency while filtering out residual near-infrared pump light. Its incident focus is located at the end face of the mid-infrared tapered optical fiber 5. In other embodiments, the second microscope objective 11 may not be coated, and a near-infrared filter can be added after the second microscope objective 11 to filter out near-infrared pump light. The spectrometer 12 monitors the operating status of the mid-infrared signal light, including its spectrum and / or power. Thus, the status control unit 40 can be adjusted according to the operating status of the mid-infrared signal light, so that the high-fidelity amplification system 60 for extremely weak mid-infrared light signals outputs a higher amplified mid-infrared signal light.

[0033] Specifically, high-fidelity amplification of extremely weak mid-infrared light signals can be achieved through the following process: Step 1: Adjust the spatial positions of the dual-color beam combiner 1, the first microscope objective 2, and the second microscope objective 11 so that the mid-infrared signal light spot is compressed and efficiently transmitted to the mid-infrared tapered fiber 5 in the fiber optic coupling unit 30, and then directly incident on the spectrometer 12. The center wavelength and initial power of the mid-infrared signal light are observed through the spectrometer 12.

[0034] Step 2: Adjust the operating temperature of the parametric amplification unit 8 and its spatial position with the fiber optic coupling unit 30, and observe the power change of the mid-infrared signal light through the status monitoring unit 50 until the center wavelength of the mid-infrared signal light is at the resonant wavelength of the parametric amplification unit 8.

[0035] Step 2 can be achieved through the following steps 2.1 to 2.2: Step 2.1: Adjust the first displacement stage 6 and the second displacement stage 7 to control the relative position between the central region of the mid-infrared tapered fiber 5 and the parametric amplification unit 8 until the power of the received mid-infrared signal light observed by the spectrometer 12 reaches the minimum value, and maintain the relative position between the central region and the parametric amplification unit 8.

[0036] It is understandable that during the adjustment of the first displacement stage 6 and the second displacement stage 7, the power and / or center wavelength of the mid-infrared signal light output by the fiber optic coupling unit 30 are constantly observed through the spectrometer 12. Controlling the relative position between the central region of the mid-infrared tapered fiber 5 and the parametric amplification unit 8 includes controlling the distance between them. When the power of the mid-infrared signal light reaches its minimum value, it indicates that most of the mid-infrared signal light has been coupled into the parametric amplification unit 8 through the evanescent wave. At this point, it can be ensured that a significant amount of mid-infrared signal light participates in the parametric oscillation process in the parametric amplification unit 8, thus improving amplification efficiency. Therefore, when the power of the mid-infrared signal light reaches its minimum value in this step, the relative position between the central region of the mid-infrared tapered fiber 5 and the parametric amplification unit 8 remains unchanged.

[0037] Step 2.2: Adjust the current source 10 to change the temperature of the semiconductor cooler 9, thereby adjusting the operating temperature of the parametric amplification unit 8, until the power of the received mid-infrared signal light observed by the spectrometer 12 reaches the minimum value again and / or the operating frequency corresponding to the center wavelength of the mid-infrared signal light completely coincides with the resonant frequency of the parametric amplification unit 8, while keeping the operating temperature of the parametric amplification unit 8 unchanged.

[0038] It is understood that during the adjustment of the current source 10, the power and / or center wavelength of the mid-infrared signal light output by the fiber optic coupling unit 30 are always observed by the spectrometer. When the power reaches the minimum value again or the operating frequency corresponding to the center wavelength of the mid-infrared signal light completely coincides with the resonant frequency of the parametric amplification unit 8, it indicates that the operating frequency corresponding to the center wavelength of the mid-infrared signal light completely coincides with the resonant frequency of the parametric amplification unit 8. At this time, the operating temperature of the parametric amplification unit 8 is kept constant.

[0039] Step 3: Turn on the pump laser 3 and set its operating wavelength to half of the center wavelength of the mid-infrared signal light. At this time, a parametric oscillation process induced by the injection signal will automatically occur in the microdisk resonant cavity 8. The power of the mid-infrared signal light can be significantly enhanced by the spectrometer 12. Step 4: Finely adjust the operating wavelength of the pump laser 3 until it is at the resonant wavelength of the parametric amplification unit (8). When adjusting the operating wavelength of the pump laser 3, when its frequency is completely consistent with the resonant frequency of the microdisk resonant cavity 8 (its operating wavelength is completely consistent with the resonant wavelength of the microdisk resonant cavity 8), the power observed on the spectrometer 12 will reach its maximum value, realizing high-fidelity amplification of the extremely weak mid-infrared light signal.

[0040] The working principle of this application can be found in [reference needed]. Figure 2For a microdisk resonator with negative dispersion in the broadband range (1.5-3.2 μm band), when a near-infrared pump laser is injected at its resonant frequency, a single near-infrared photon (e.g., 1.5 μm wavelength) can be converted into two mid-infrared photons across the band through a parametric oscillation process, with wavelengths meeting the phase-matching condition. Therefore, under no signal injection conditions, the wavelengths of the generated photons are not fixed; the two newly generated photons could both be 3.0 μm, or possibly different combinations such as 2.95 μm + 3.05 μm, 2.98 μm + 3.02 μm, etc. Under the induction condition of an injected signal, the resonant frequency that perfectly matches the signal light wavelength will preferentially oscillate, achieving a significant power resonant enhancement under ring cavity conditions. Therefore, by finely controlling the relative positions of the microdisk resonator frequency with the signal light frequency and pump light frequency through temperature and wavelength tuning, cross-band and high-efficiency amplification of extremely weak mid-infrared light signals under near-infrared pumping can be achieved. Furthermore, two potential adverse factors need to be suppressed. On the one hand, the microdisk resonator not only needs to have negative dispersion conditions in the near-infrared to mid-infrared band, but its quality factor should not be too low (which would lead to an excessively high parametric oscillation threshold and a decrease in conversion efficiency, requiring higher pump power) or too high (which would lead to an excessively narrow resonant envelope that is difficult to completely confine the signal light envelope, and interference effects such as Kerr effect and stimulated Raman scattering are prone to oscillation). Therefore, in this application, the appropriate quality factor range is constrained to be 10^5~10^6. On the other hand, the physical size (e.g., diameter) of the microdisk resonator directly determines its repetition frequency (i.e., the wavelength interval between two adjacent resonant longitudinal modes). If its size is too small, the resonant mode spacing will be too large, making it difficult to cover the entire repetition frequency range through temperature control. If the mid-infrared signal light is far from the resonant peak, effective resonant amplification will not be achieved. If it is too large, it will lead to difficulties in fabrication and will not be able to simultaneously meet the quality factor requirements. Therefore, in this application, the appropriate radius size is limited to 1~2 cm. Considering the above-mentioned influencing factors and the current state of the industry, the material for the microdisk resonant cavity should be lithium niobate, which not only has a high nonlinear coefficient but also meets various constraints, enabling the amplification of extremely weak mid-infrared light signals.

[0041] See Figure 3 , Figure 4 and Figure 5 This application embodiment presents the original mid-infrared signal spectral results, the preliminary spectral results after parametric oscillation amplification, and the optimized spectral results after the parametric oscillation process. When the signal light information is completely unknown, step one is first implemented, allowing the mid-infrared signal light to be transmitted through the mid-infrared tapered fiber 5 and then incident on the spectrometer 12, thereby obtaining its center wavelength and power. For example... Figure 3As shown, the signal light wavelength is ~2998.4nm and the initial power is ~27nW (-45.7dBm). By implementing step two, the relative positions of the mid-infrared tapered fiber 5 and the microdisk resonator 8 are tuned. When the mid-infrared signal light enters the microdisk resonator 8 through evanescent wave coupling, a sudden drop in the mid-infrared signal light power can be observed on the spectrometer 12. Subsequently, by adjusting the current source 10 to change the operating temperature of the microdisk resonator 8, when the mid-infrared signal light strictly coincides with the resonant frequency, it will be completely confined by the microdisk resonator 8. At this time, the spectrometer 12 will observe a significant decrease or even disappearance of the mid-infrared signal light power again. By implementing step three, the wavelength of the pump laser is set to half of the center wavelength of the signal light (~1.499μm). At this time, a parametric oscillation process under the induced condition of the injected signal will occur in the microdisk resonator 8, thereby achieving a significant enhancement of the mid-infrared signal light power. Figure 4 As shown, the power of the mid-infrared signal light has increased to ~-27dBm, an amplification of 18dB compared to the original power; meanwhile, although the center wavelength of the near-infrared pump light is within the resonance peak, it is not at the highest resonance point (see...). Figure 2 Therefore, further optimization is needed to improve the amplification effect. By implementing step four, the wavelength of the pump laser 3 is finely adjusted until it is completely consistent with the resonant frequency of the microdisk resonant cavity 8. At this point, a perfectly matched, high-efficiency, parametric cyclic resonant amplification process will occur, and the power observed on the spectrometer 12 will reach its maximum value. Figure 5 As shown, the signal light power has increased to ~-8.2dBm, which is ~19dB higher than before optimization and 37.5dB higher than the original power. At the same time, the spectrum of the amplified mid-infrared signal light is completely consistent with the initial state, thus completing the high-fidelity amplification of the extremely weak light signal.

[0042] This application, based on the parametric oscillation process under resonant conditions, not only solves the problem that existing methods are limited by the inherent noise of spontaneous emission from the doped gain medium, which causes extremely weak signals to be submerged and unable to be amplified, but also ensures in principle that there are no other extraneous stray frequency components excited except for the signal wavelength. Therefore, it has the unique advantages of extremely low threshold (~-45dBm, i.e., 30 nanowatts), low noise, and ultra-high efficiency (>4dB, i.e., 10,000 times). It can achieve high-fidelity and high-gain amplification of extremely weak mid-infrared light signals, and is simple in structure and easy to operate. Meanwhile, this application uses near-infrared pump lasers to replace the expensive and complex mid-infrared light sources typically required by other solutions, realizing cross-band (near-infrared to mid-infrared) parametric oscillation processes under resonant conditions. It supports various types of near-infrared light sources, such as 1500-1640nm semiconductor lasers and 1480nm fiber Raman lasers, and can amplify weak mid-infrared light covering an ultra-wide range of 2960-3380nm. Therefore, it has the characteristics of large bandwidth (>400nm), low cost, and easy construction, and has broad application prospects in the field of mid-infrared laser technology.

[0043] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of this application. Any modifications, equivalent substitutions, or improvements made by those skilled in the art to the embodiments without departing from the technical concept of this application should be included within the protection scope of this application.

Claims

1. A high-fidelity amplification system for extremely weak mid-infrared light signals, characterized in that, It includes a signal input unit (110), a pump input unit (20), an optical fiber coupling unit (30), a parametric amplification unit (8), a state control unit (40), and a state monitoring unit (50); The pump input unit (20) is used to input the generated near-infrared pump light to the signal input unit (110); The signal input unit (110) is used to receive the mid-infrared signal light to be amplified and the near-infrared pump light, and inject them into the fiber coupling unit (30); The fiber optic coupling unit (30) is used to couple and inject the mid-infrared signal light and the near-infrared pump light into the parametric amplification unit (8), and couple and output them to the status monitoring unit (50); The parametric amplification unit (8) is used to amplify the power of the mid-infrared signal light by utilizing the parametric oscillation process; The state control unit (40) is used to change the operating temperature of the parametric amplification unit (8) so that the resonant wavelength of the parametric amplification unit (8) matches the center wavelength of the mid-infrared signal light and / or makes the resonant wavelength of the parametric amplification unit (8) match the center wavelength of the near-infrared pump light. The status monitoring unit (50) is used to monitor the output spectrum of the parametric amplification unit (8) and determine its working status.

2. The high-fidelity amplification system for extremely weak mid-infrared light signals according to claim 1, characterized in that, The signal input unit (110) includes a dual-color beam combiner (1) and a first microscope objective (2) arranged in sequence; the dual-color beam combiner (1) is used to simultaneously receive the mid-infrared signal light and the near-infrared pump light and output them as a combined beam; the first microscope objective (2) is used to compress the spot size of the mid-infrared signal light and the near-infrared pump light so that the combined beam of the mid-infrared signal light and the near-infrared pump light is incident on the fiber coupling unit (30).

3. The high-fidelity amplification system for extremely weak mid-infrared light signals according to claim 2, characterized in that, The pump input unit (20) includes a pump laser (3) and an optical fiber collimator (4) connected in sequence; the pump laser (3) is used to provide the near-infrared pump light, and the optical fiber collimator (4) is used to collimate the near-infrared pump light and then inject it into the dichroic beam combiner (1).

4. The high-fidelity amplification system for extremely weak mid-infrared light signals according to claim 3, characterized in that, The fiber coupling unit (30) includes a mid-infrared tapered fiber (5), a first displacement stage (6), and a second displacement stage (7); the mid-infrared tapered fiber (5) is a mid-infrared single-mode fiber made of As2S3 sulfide glass. The starting end face of the mid-infrared tapered optical fiber (5) has been flattened and polished to enable the reception of the mid-infrared signal light and the near-infrared pump light. The starting end face of the mid-infrared tapered optical fiber (5) is placed at the focal point of the first microscope objective (2) so as to couple and inject the mid-infrared signal light and the near-infrared pump light into the parametric amplification unit (8). The central region of the mid-infrared tapered fiber (5) is tapered until the evanescent wave can be coupled and output; the first displacement stage (6) and the second displacement stage (7) are respectively placed at the beginning and end of the mid-infrared tapered fiber (5) to clamp the mid-infrared tapered fiber (5) and adjust the distance between the mid-infrared tapered fiber (5) and the parametric amplification unit (8).

5. The high-fidelity amplification system for extremely weak mid-infrared light signals according to claim 4, characterized in that, The parametric amplification unit (8) is a micro disk resonant cavity used to receive the mid-infrared signal light and the near-infrared pump light, and to realize the power amplification of the mid-infrared signal light by utilizing the parametric oscillation effect under the resonance enhancement condition. The microdisk resonant cavity is made of lithium niobate material, the quality factor of the microdisk resonant cavity is 10^5~10^6, the radius of the microdisk resonant cavity is 1cm~2cm, and the parametric amplification unit (8) has negative dispersion in the 1.5~3.2μm band.

6. The high-fidelity amplification system for extremely weak mid-infrared light signals according to claim 5, characterized in that, The state control unit (40) includes a semiconductor cooler (9) and a current source (10); the semiconductor cooler (9) is placed below the parametric amplification unit (8) via a bracket (13) and is used to control the actual operating temperature of the parametric amplification unit (8); the current source (10) is used to provide the driving current of the semiconductor cooler (9), and its output terminal is connected to the positive and negative terminals of the semiconductor cooler (9) respectively.

7. The high-fidelity amplification system for extremely weak mid-infrared light signals according to claim 6, characterized in that, The status monitoring unit (50) includes a second microscope objective (11) and a spectrometer (12) arranged in sequence; the second microscope objective (11) is used to receive the amplified mid-infrared signal light and filter out the residual near-infrared pump light, and the incident focal point of the second microscope objective (11) is located at the end face of the mid-infrared tapered optical fiber (5); the spectrometer (12) is used to monitor the spectrum and / or power of the amplified mid-infrared signal light.

8. A method for adjusting a high-fidelity amplification system for extremely weak mid-infrared light signals as described in any one of claims 1 to 7, characterized in that, The signal input unit (110) includes a dichroic beam combiner (1) and a first microscope objective (2) arranged in sequence. The dichroic beam combiner (1) is used to simultaneously receive the mid-infrared signal light and the near-infrared pump light and combine them to output to the fiber coupling unit (30). The status monitoring unit (50) includes a second microscope objective (11) and a spectrometer (12) arranged in sequence. The second microscope objective (11) is used to receive the amplified mid-infrared signal light and filter out the residual near-infrared pump light. The spectrometer (12) is used to monitor the spectrum and / or power of the amplified mid-infrared signal light. The method includes the following steps: Step 1: Adjust the spatial positions of the dual-color beam combiner (1), the first microscope objective (2), and the second microscope objective (11) so that the spot of the mid-infrared signal light is compressed and transmitted to the fiber optic coupling unit (30) and then incident on the spectrometer (12). The center wavelength and power of the received mid-infrared signal light are observed by the spectrometer (12). Step 2: Adjust the operating temperature of the parametric amplification unit (8) and the spatial position of the parametric amplification unit (8) and the optical fiber coupling unit (30), and observe the power change of the mid-infrared signal light through a spectrometer (12) until the center wavelength of the mid-infrared signal light is at the resonant wavelength of the parametric amplification unit (8); Step 3: Turn on the pump laser (3) and set the working wavelength of the pump laser to half of the center wavelength of the mid-infrared signal light, so that the parametric oscillation process under the condition of injection signal induction occurs in the parametric amplification unit (8); Step 4: Adjust the operating wavelength of the pump laser (3) until the operating wavelength of the pump laser is at the resonant wavelength of the parametric amplification unit (8).

9. The adjustment method according to claim 8, characterized in that, The fiber coupling unit (30) includes a mid-infrared tapered fiber (5), a first displacement stage (6), and a second displacement stage (7). The state control unit (40) includes a semiconductor cooler (9) and a current source (10). Step two includes: Step 2.1: Adjust the first displacement stage (6) and the second displacement stage (7) to control the relative position between the central region of the mid-infrared tapered optical fiber (5) and the parametric amplification unit (8) until the power of the received mid-infrared signal light observed by the spectrometer (12) reaches the minimum value, and keep the relative position between the central region and the parametric amplification unit (8) unchanged. Step 2.2: Adjust the current source (10) to change the temperature of the semiconductor cooler (9) to adjust the operating temperature of the parametric amplification unit (8) until the power of the received mid-infrared signal light observed by the spectrometer (12) reaches the minimum value again, and keep the operating temperature of the parametric amplification unit (8) unchanged.

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