Wide-range continuously tunable mid-infrared optical frequency shifting device and method based on electro-optic effect

Abstract

The application discloses a wide-range continuous adjustable middle infrared optical frequency shift device and method based on an electro-optic effect, and solves the problems of a complex structure, slow tuning speed, small tuning range and low tuning precision of an existing middle infrared laser tuning device, and specifically comprises an optical pumping unit, a frequency shift mechanism, an electric signal output unit, a phase shift attenuation mechanism and a filtering and amplifying unit; the optical pumping unit is used for emitting middle infrared pumping laser; the electric signal output unit is used for providing microwave signals and direct current voltages to the frequency shift mechanism; the frequency shift mechanism is used for modulating the frequency of the middle infrared pumping laser, generating optical frequency sidebands with different frequencies and powers, and realizing redistribution of middle infrared pumping laser power on different frequencies; the phase shift attenuation mechanism is used for generating optical signals with opposite phases to initial carriers and residual sidebands, and suppressing residual optical signal power; and the filtering and amplifying unit is used for filtering and amplifying the optical signals.

Description

Technical Field

[0001] This invention relates to a mid-infrared optical frequency shifting device and method, specifically to a wide-range continuously adjustable mid-infrared optical frequency shifting device and method based on the electro-optic effect. Background Technology

[0002] Mid-infrared lasers not only cover multiple transparent windows of atmospheric transmission but also highly overlap with the fundamental vibrational absorption peaks of most molecules, forming a highly specific "fingerprint spectral region." Leveraging this unique spectral characteristic, mid-infrared lasers exhibit outstanding advantages in high-sensitivity gas detection and free-space optical communication, and are currently widely used in environmental monitoring, industrial process control, medical diagnosis, and cutting-edge scientific research. With the continuous development of various application scenarios, the industry has set higher standards for the comprehensive performance of mid-infrared light sources, focusing on core indicators such as output power, linewidth, and wavelength tunability; among these, tuning speed, tuning accuracy, and tuning range are key parameters for evaluating the performance of mid-infrared lasers.

[0003] Compared to lasers with fixed wavelengths and no tuning capability, tunable lasers can achieve continuous and precise wavelength adjustment within a specific wavelength range, significantly improving the functional scalability and applicability of equipment in complex scenarios. In environmental monitoring, a single tunable laser can scan the characteristic absorption spectra of various gases to detect multiple pollutants one by one, eliminating the need for multiple fixed-wavelength lasers, effectively reducing equipment redundancy, system cost, and structural complexity. In the field of free-space optical communication, wavelength tuning capability enables communication channel switching and anti-interference performance optimization, significantly improving the flexibility and stability of the communication system. Therefore, wavelength tuning capability not only enriches the functional dimensions of mid-infrared lasers but is also a core key to driving mid-infrared laser technology from laboratory research to practical application and large-scale deployment.

[0004] Currently, the mainstream technologies for achieving mid-infrared tunable laser output fall into three main categories: optical parametric oscillators (OPOs), external cavity tunable semiconductor lasers (ECDLs), and semiconductor laser current / temperature tuning technology. Optical parametric oscillators, relying on nonlinear optical frequency conversion effects, can efficiently convert a fixed-wavelength pump laser into two longer-wavelength output lasers, offering advantages such as high output power and wide wavelength coverage. However, they suffer from complex system structures, large size, and high environmental stability requirements, making them difficult to implement in real-world applications outside of laboratory settings. External cavity tunable semiconductor lasers achieve wavelength scanning through external grating mechanical adjustment structures, boasting a large tuning range, fast tuning speed, and high tuning accuracy. However, they also suffer from complex system construction, high costs, and difficulty in large-scale deployment. In contrast, semiconductor laser tuning schemes based on temperature or cavity length adjustment offer advantages such as small size, low power consumption, and compact structure, making them suitable for integrated applications. However, these schemes suffer from slow tuning speed, limited tuning range, and insufficient tuning accuracy, and their overall performance still needs optimization and improvement. Summary of the Invention

[0005] To address the technical problems of existing mid-infrared laser tuning devices, such as complex structure, slow tuning speed, small tuning range, and low tuning accuracy, this invention provides a wide-range continuously tunable mid-infrared optical frequency shifting device and method based on electro-optic effect.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A wide-range continuously tunable mid-infrared optical frequency shifting device based on the electro-optic effect, characterized by: It includes an optical pumping unit, a frequency shifting mechanism, an electrical signal output unit, a phase shift attenuation mechanism, and a filtering and amplification unit; The optical pumping unit is used to emit mid-infrared pump laser, and its carrier is the initial carrier. The electrical signal output unit is connected to the frequency shifting mechanism and is used to provide microwave signals and DC voltage to the frequency shifting mechanism; The frequency shifting mechanism is connected between the optical pumping unit and the filtering and amplification unit, and is used to modulate the frequency of the mid-infrared pump laser to generate optical frequency sidebands with different frequencies and powers, thereby realizing the redistribution of the mid-infrared pump laser power at different frequencies. The phase shift attenuation mechanism is connected between the optical pump unit and the filter amplification unit, and is connected to the frequency shifting mechanism through an optical beam splitter. It is used to generate an optical signal with the opposite phase to the initial carrier and the residual sideband, and to suppress the power of the residual optical signal. The filtering and amplification unit is used to filter and amplify the optical signal.

[0007] Furthermore, the optical beam splitter is a 2×2 optical beam splitter; The frequency shifting mechanism includes a first frequency shifting unit and a second frequency shifting unit; The optical signal input end of the first frequency shifting unit is connected to the optical fiber output end of the optical pumping unit, and its optical signal output end is connected to the optical fiber first input end of the 2×2 optical beam splitter. The optical signal input end of the second frequency shift unit is connected to the optical fiber of the first output end of the 2×2 optical beam splitter, and its output end is connected to the optical fiber of the input end of the filter amplification unit. The second input and second output terminals of the 2×2 optical beam splitter are connected to the optical fiber of the phase shift attenuation mechanism. The electrical signal output unit is electrically connected to the first frequency shift unit and the second frequency shift unit, respectively.

[0008] Furthermore, the phase shift attenuation mechanism includes a first phase shift attenuation unit, a second phase shift attenuation unit, and a third phase shift attenuation unit; The optical signal input end of the first phase shift attenuation unit is connected to the output end of the optical pumping unit via optical fiber, and its output end is connected to the second input end of the 2×2 optical beam splitter via optical fiber. The optical signal input terminal of the second phase shift attenuation unit is connected to the second output terminal of the 2×2 optical beam splitter via optical fiber, and its optical signal output terminal is connected to the input terminal of the filter amplification unit via optical fiber. The optical signal input terminal of the third phase shift attenuation unit is connected to the output terminal of the optical pump unit via optical fiber, and its optical signal output terminal is connected to the input terminal of the filter amplification unit via optical fiber.

[0009] Furthermore, the first frequency shifting unit includes a first sub-phase shifter, a first sub-modulator, a second sub-phase shifter, a second sub-modulator, a first sub-biaser, and a second sub-biaser; The first sub-phase shifter, the first sub-modulator, the second sub-phase shifter, and the second sub-modulator are sequentially connected by optical fibers along the optical signal emission direction. The optical signal input end of the first sub-phase shifter is the optical signal input end of the first frequency shifting unit, and the optical signal output end of the second sub-modulator is the optical signal output end of the first frequency shifting unit. The input terminal of the first sub-biaser is electrically connected to the electrical signal output unit, and its output terminal is electrically connected to the electrical signal input terminal of the first sub-modulator. The input terminal of the second sub-biaser is electrically connected to the electrical signal output unit, and its output terminal is electrically connected to the electrical signal input terminal of the second sub-modulator. The second frequency shift unit has the same structure as the first frequency shift unit.

[0010] Furthermore, the first phase shift attenuation unit includes a third sub-phase shifter and a sub-attenuator that are sequentially connected by optical fibers along the optical signal emission direction; The input terminal of the third sub-phase shifter is the optical signal input terminal of the first phase shift attenuation unit; The optical signal output terminal of the sub-attenuator is the optical signal output terminal of the first phase shift attenuation unit; The structures of the second phase shift attenuation unit and the third phase shift attenuation unit are the same as those of the first phase shift attenuation unit.

[0011] Furthermore, the filtering and amplification unit includes a first optical beam combiner, a second optical beam combiner, an optical fiber filter, and an optical fiber amplifier; The first input end of the first optical combiner is optically connected to the optical signal output end of the second sub-modulator in the second frequency shift unit, its second input end is optically connected to the optical signal output end of the sub-attenuator in the second phase shift attenuation unit, and its output end is optically connected to the first input end of the second optical combiner. The second input end of the second optical combiner is optically connected to the optical signal output end of the sub-attenuator in the third phase shift attenuation unit, and its output end is sequentially optically connected to an optical fiber filter and an optical fiber amplifier. The fiber optic filter is used to filter out optical signals with frequencies greater than or equal to or less than or equal to the initial carrier. The fiber optic amplifier is used to amplify optical signals.

[0012] Furthermore, the electrical signal output unit includes a microwave signal source and a DC voltage source; The output terminal of the microwave signal source is electrically connected to the microwave signal input terminal of each first sub-biaser and each second sub-biaser in the first frequency shift unit and the second frequency shift unit, respectively. The output terminal of the DC voltage source is electrically connected to the DC voltage signal input terminal of each first sub-biaser and each second sub-biaser in the first frequency shift unit and the second frequency shift unit, respectively.

[0013] Furthermore, the optical pumping unit includes a mid-infrared laser and a 1×3 optical beam splitter; The mid-infrared laser is used to emit mid-infrared pump laser; The input end of the 1×3 optical beam splitter is connected to the output end of the mid-infrared laser via optical fiber. Its first output end is connected to the optical signal input end of the first frequency shifting unit via optical fiber. Its second output end is connected to the optical signal input end of the first phase shift attenuation unit via optical fiber. Its third output end is connected to the optical signal input end of the third phase shift attenuation unit via optical fiber. Both the first and second sub-modulators are mid-infrared Mach-Zehnder modulators.

[0014] A wide-range continuously tunable mid-infrared optical frequency shifting method based on the electro-optic effect, employing the aforementioned wide-range continuously tunable mid-infrared optical frequency shifting device based on the electro-optic effect, is characterized by including the following steps: Step 1: The optical pumping unit emits mid-infrared pump laser; Step 2: The frequency shifting mechanism and the phase shift attenuation mechanism receive the mid-infrared pump laser. The electrical signal output unit provides a microwave signal and a DC voltage to the frequency shifting mechanism. The frequency shifting mechanism is adjusted so that it modulates the frequency of the mid-infrared pump laser based on the microwave signal and the DC voltage, thereby redistributing the mid-infrared pump laser power at different frequencies. The phase shift attenuation mechanism is adjusted so that it generates an optical signal with a phase opposite to the initial carrier and the residual sideband, thereby suppressing the residual optical signal power. Step 3: Adjust the filter amplification unit to filter out optical signals with frequencies greater than or equal to or less than the initial carrier, and amplify the remaining optical signals to obtain mid-infrared optical frequency shift signals.

[0015] Furthermore, step 1 specifically includes: A mid-infrared laser emits a mid-infrared pump laser, and a 1×3 optical beam splitter splits the mid-infrared pump laser into pump laser A, pump laser B, and pump laser C. Step 2 specifically includes: Step 2.1: The first sub-phase shifter in the first frequency shifting unit receives pump laser A, the third sub-phase shifter in the first phase shift attenuation unit receives pump laser B, and the third sub-phase shifter in the third phase shift attenuation unit receives pump laser C. Step 2.2: Adjust the DC voltage source so that the first sub-modulator and the second sub-modulator in the first frequency shift unit and the second frequency shift unit both operate at the maximum transmission point; Step 2.3: Adjust the microwave signal frequency output by the first sub-biaser and the second sub-biaser in the first frequency shift unit from the microwave signal source. f m The microwave signal voltage and microwave signal phase cause the microwave signal frequency to... f m 0GHz < f m <50GHz, the microwave signal voltage received by the first and second sub-modulators in the first frequency shift unit is its own half-wave voltage V. π The phase difference between the microwave signals received by the first sub-modulator and the second sub-modulator in the first frequency shift unit is π / 2, which is 5.3 to 5.4 times that of the first frequency shift unit. Step 2.4: Adjust the second sub-phase shifter in the first frequency shifting unit so that the phase difference between the light passing through the first sub-modulator and the second sub-modulator in the first frequency shifting unit is 2nπ. Then, in the first frequency shifting unit, the power of the pump laser A is redistributed at different frequencies to obtain laser D. Step 2.5: Adjust the sub-attenuator in the first phase shift attenuation unit so that the power of the pump laser B is attenuated to 6%~7% of that before passing through the sub-attenuator. Adjust the third sub-phase shifter in the first phase shift attenuation unit so that the phase difference between the light passing through the first phase shift attenuation unit and the light passing through the first frequency shift unit is (2n+1)π, and obtain the laser E. Step 2.6: The 2×2 optical beam splitter receives laser D and laser E. Laser D and laser E interfere with each other to generate interference light. The 2×2 optical beam splitter then splits the interference light into laser F and laser G with the same power, which are respectively incident on the first sub-phase shifter in the second frequency shifting unit and the third sub-phase shifter in the second phase shift attenuation unit. Step 2.7: Adjust the microwave signal frequency output by the first and second sub-biasers in the second frequency shift unit from the microwave signal source. f m The output voltage and output phase cause the microwave signal frequency to... f m 0GHz < f m <50GHz, the microwave signal voltage received by the first and second sub-modulators in the second frequency shift unit is its own half-wave voltage V. π The phase difference between the electrical signals received by the first and second sub-modulators in the second frequency shift unit is π / 2, which is 5.3 to 5.4 times that of the second frequency shift unit. Step 2.8: Adjust the second sub-phase shifter in the second frequency shifting unit so that the phase difference between the light passing through the first sub-modulator and the second sub-modulator in the second frequency shifting unit is 2nπ. Then, in the second frequency shifting unit, the power of laser F is redistributed at different frequencies to obtain laser H. Step 2.9: Adjust the sub-attenuator in the second phase shift attenuation unit so that the power of laser G is attenuated to 6%~7% of the power before passing through the sub-attenuator. Adjust the third sub-phase shifter in the second phase shift attenuation unit so that the phase difference between the light passing through the second phase shift attenuation unit and the light passing through the second frequency shift unit is (2n+1)π, and obtain laser I. Step 2.10: The first optical beam combiner receives laser H and laser I, and combines them into laser J; Step 2.11: Adjust the sub-attenuator in the third phase shift attenuation unit so that the power of the pump laser C is attenuated to 0.4%-0.5% of that before passing through the sub-attenuator. Adjust the third sub-phase shifter in the third phase shift attenuation unit so that the phase of the light after passing through the third phase shift attenuation unit is (2n+1)π different from the carrier phase of the laser J, and obtain the laser K. Step 2.12: The second optical beam combiner receives laser J and laser K, and combines them into laser L; Step 3 specifically involves: The fiber optic filter is adjusted to filter out optical signals in laser L with frequencies greater than or equal to or less than the initial carrier wave. The signals are then amplified by a fiber optic amplifier to obtain a mid-infrared optical frequency-shifting signal.

[0016] The beneficial effects of this invention are: 1. The present invention provides a wide-range continuously tunable mid-infrared optical frequency shifting device and method based on the electro-optic effect. Based on the Pockels electro-optic effect, it generates continuously and rapidly tunable optical frequency sidebands, which can achieve sideband frequency shift of up to 16 times the modulation frequency. It has the advantages of fast response speed and high precision. At the same time, it can effectively suppress the initial carrier and other useless optical frequency sidebands, with a suppression ratio of more than 20dB, which significantly reduces background noise.

[0017] 2. This invention utilizes a fixed-frequency mid-infrared laser as a carrier light source. By specially configuring the first and second sub-modulators, it can generate freely tunable optical sidebands. It eliminates the need for large and costly tunable lasers, requiring only miniaturized and economical pump lasers. This solves the current problem of a lack of rapidly tunable sweep lasers in the mid-infrared band, and features a simple system structure and strong practicality.

[0018] 3. This invention uses the electro-optic effect to shift frequencies, which can be adapted to a wide range of light sources. For example, the electro-optic modulator using lithium niobate material can operate at wavelengths of 2-5 μm. As an external tuning device, this device and method can be adapted to various light sources, including mid-infrared semiconductors and fiber lasers. Furthermore, it decouples frequency tuning from power tuning, so the output power is not affected during the tuning process, giving it the advantage of strong versatility.

[0019] 4. This invention achieves a continuously shiftable optical frequency sideband by specially setting the mid-infrared Mach-Zehnder modulator. The shift value can reach 16 times the modulation frequency, and the shift range exceeds 2nm (150GHz). Compared with the current miniaturized mid-infrared semiconductor laser, which uses piezoelectric ceramics to adjust the external cavity length and thus achieve laser frequency tuning (usually <10GHz), the frequency tuning range is improved by more than an order of magnitude.

[0020] 5. This invention achieves continuous frequency shifting of optical frequency sidebands by specially configuring the mid-infrared Mach-Zehnder modulator, while suppressing the frequency components of the initial carrier and other useless optical frequency sidebands, with a suppression ratio exceeding 20dB, effectively reducing continuous laser background noise. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of an embodiment of a wide-range continuously adjustable mid-infrared optical frequency shifting device based on the electro-optic effect according to the present invention; Figure 2This is a schematic diagram of the structure of the first frequency shifting unit / second frequency shifting unit in an embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of the first phase shift attenuation unit, the second phase shift attenuation unit, and the third phase shift attenuation unit in an embodiment of the present invention; Figure 4 This is a schematic diagram illustrating the principle of sub-modulator frequency shifting and carrier and sideband suppression in an embodiment of the present invention; wherein: a) is the optical frequency distribution diagram of the first sub-modulator emitted from the first sub-modulator in the first frequency shifting unit after completing step 2.3, at which time the optical power is redistributed to even-order sidebands; b) is the optical frequency distribution diagram of the second sub-modulator emitted from the first sub-modulator in the first frequency shifting unit after completing step 2.4, retaining ±8th and ±12th order sidebands while suppressing ±4th order sidebands; c) is the optical frequency distribution diagram of the 2×2 optical beam splitter emitted after completing step 2.6. Figure 4 Based on step b, carrier suppression is achieved; d is the optical frequency distribution diagram of the first sub-modulator in the second frequency shift unit after completing step 2.8, at which point most of the optical power is distributed in the ±8th and ±16th order sidebands; e is the optical frequency distribution diagram of the first optical combiner, at which point most of the optical power is distributed in the carrier and ±16th order sidebands; f is the optical frequency distribution diagram of the second optical combiner, in... Figure 4 Carrier suppression is achieved based on the middle e.

[0022] Figure 5 This is the final spectrum obtained in the embodiments of the present invention.

[0023] The attached figures are labeled as follows: 1. Mid-infrared laser; 2. 1×3 optical beam splitter; 3. Microwave signal source; 4. 2×2 optical beam splitter; 5. DC voltage source; 6. First optical beam combiner; 7. Second optical beam combiner; 8. Fiber optic filter; 9. Fiber optic amplifier; 10. First frequency shifting unit; 11. Second frequency shifting unit; 12. First phase shift attenuation unit; 13. Second phase shift attenuation unit; 14. Third phase shift attenuation unit; 15. First sub-phase shifter; 16. First sub-modulator; 17. Second sub-phase shifter; 18. Second sub-modulator; 19. First sub-biaser; 20. Second sub-biaser; 21. Third sub-phase shifter; 22. Sub-attenuator. Detailed Implementation

[0024] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and 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.

[0025] This invention provides a wide-range, continuously tunable mid-infrared optical frequency shifting device based on the electro-optic effect, such as... Figure 1 As shown, the wide-range continuously adjustable mid-infrared optical frequency shifting device includes an optical pumping unit, an optical beam splitter, a frequency shifting mechanism, an electrical signal output unit, a phase shift attenuation mechanism, and a filtering and amplification unit.

[0026] The optical pumping unit is used to emit mid-infrared pump laser, with the initial carrier as its carrier. The optical pumping unit includes a mid-infrared laser 1 and a 1×3 optical beam splitter 2. The mid-infrared laser 1 is used to emit mid-infrared pump laser. The input end of the 1×3 optical beam splitter 2 is optically connected to the output end of the mid-infrared laser 1. Its first output end is optically connected to the optical signal input end of the first frequency shifting unit 10. Its second output end is optically connected to the optical signal input end of the first phase shift attenuation unit 12. Its third output end is optically connected to the optical signal input end of the third phase shift attenuation unit 14. In this embodiment, the mid-infrared laser 1 is a mid-infrared semiconductor laser with a working wavelength of 2μm. In other embodiments, different types of mid-infrared lasers operating at other wavelengths can also be used, such as fiber narrow linewidth lasers with a working wavelength of around 2.1μm.

[0027] The optical beam splitter is a 2×2 optical beam splitter 4.

[0028] A frequency shifting mechanism is connected between the optical pumping unit and the filtering and amplification unit to modulate the frequency of the mid-infrared pump laser, thereby redistributing the power of the mid-infrared pump laser at different frequencies. Specifically, the frequency shifting mechanism includes a first frequency shifting unit 10 and a second frequency shifting unit 11. The optical signal input end of the first frequency shifting unit 10 is connected to the output optical fiber of the optical pumping unit, and its optical signal output end is connected to the first input optical fiber of the 2×2 optical beam splitter 4. The optical signal input end of the second frequency shifting unit 11 is connected to the first output optical fiber of the 2×2 optical beam splitter 4, and its output end is connected to the input optical fiber of the filtering and amplification unit. The second input end and the second output end of the 2×2 optical beam splitter 4 are connected to the phase shift attenuation mechanism via optical fibers. An electrical signal output unit is electrically connected to the first frequency shifting unit 10 and the second frequency shifting unit 11, respectively.

[0029] The first frequency shifting unit 10 and the second frequency shifting unit 11 have the same structure and corresponding connection relationship. This embodiment uses the first frequency shifting unit 10 as an example to describe its structure in detail, such as... Figure 2As shown, the first frequency shifting unit 10 includes a first sub-phase shifter 15, a first sub-modulator 16, a second sub-phase shifter 17, a second sub-modulator 18, a first sub-biaser 19, and a second sub-biaser 20. The first sub-phase shifter 15, the first sub-modulator 16, the second sub-phase shifter 17, and the second sub-modulator 18 are sequentially connected by optical fibers along the optical signal emission direction. The optical signal input terminal of the first sub-phase shifter 15 is the optical signal input terminal of the first frequency shifting unit 10, and the optical signal output terminal of the second sub-modulator 18 is the optical signal output terminal of the first frequency shifting unit 10. The input terminal of the first sub-biaser 19 is electrically connected to the electrical signal output unit, and its output terminal is electrically connected to the electrical signal input terminal of the first sub-modulator 16. The input terminal of the second sub-biaser 20 is connected to the electrical signal output unit. The output terminal of the first sub-modulator 16 is electrically connected to the electrical signal input terminal of the second sub-modulator 17; the first sub-phase shifter 15 and the second sub-phase shifter 17 are used to control the phase of the light after passing through the delay line; the first sub-biaser 19 and the second sub-biaser 20 are used to simultaneously input the signals generated by the microwave signal source 3 and the DC voltage source 5 into the corresponding mid-infrared Mach-Zehnder modulators; in this embodiment, the first sub-modulator 16 and the second sub-modulator 18 are both lithium niobate Mach-Zehnder modulators with a working wavelength around 2μm, used for electro-optic modulation to generate optical frequency sidebands with different frequencies and powers. Other electro-optic modulators made of materials with Pockels-type electro-optic effects, such as lithium tantalate, potassium titanium phosphate (KTP), and barium borate (BBO) Mach-Zehnder modulators, can also be used.

[0030] The electrical signal output unit is connected to the frequency shifting mechanism and is used to provide microwave signals and DC voltage to the frequency shifting mechanism. Specifically, the electrical signal output unit includes a microwave signal source 3 and a DC voltage source 5. The output terminal of the microwave signal source 3 is electrically connected to the microwave signal input terminal of each first sub-biaser 19 and each second sub-biaser 20, respectively. The microwave signal source 3 is used to generate microwave signals of different frequencies and powers to drive the frequency shifting mechanism to output optical frequency sidebands. The output terminal of the DC voltage source 5 is electrically connected to the DC voltage signal input terminal of each first sub-biaser 19 and each second sub-biaser 20, respectively. The DC voltage source 5 is used to output DC voltage to control the working state of the first sub-modulator 16 and the second sub-modulator 18 in the first frequency shifting unit 10 and the second frequency shifting unit 11.

[0031] A phase-shift attenuation mechanism is connected between the optical pump unit and the filter amplification unit, and is connected to the frequency shifting mechanism through a 2×2 optical beam splitter 4. It is used to generate an optical signal with a phase opposite to the initial carrier and residual sidebands, suppressing residual optical signal power and increasing the proportion of laser power at the target frequency. Specifically, the phase-shift attenuation mechanism includes a first phase-shift attenuation unit 12, a second phase-shift attenuation unit 13, and a third phase-shift attenuation unit 14. The optical signal input end of the first phase-shift attenuation unit 12 is connected to the output optical fiber of the optical pump unit, and its output end is connected to the second input optical fiber of the 2×2 optical beam splitter 4. The optical signal input end of the second phase-shift attenuation unit 13 is connected to the second output optical fiber of the 2×2 optical beam splitter 4, and its optical signal output end is connected to the input optical fiber of the filter amplification unit. The optical signal input end of the third phase-shift attenuation unit 14 is connected to the output optical fiber of the optical pump unit, and its optical signal output end is connected to the input optical fiber of the filter amplification unit.

[0032] The first phase shift attenuation unit 12, the second phase shift attenuation unit 13, and the third phase shift attenuation unit 14 have the same structure and corresponding connection relationships. This embodiment takes the first phase shift attenuation unit 12 as an example to describe its structure in detail, such as... Figure 3 As shown, the first phase shift attenuation unit 12 includes a third sub-phase shifter 21 and a sub-attenuator 22 connected sequentially by optical fibers along the optical signal emission direction; the input end of the third sub-phase shifter 21 is the optical signal input end of the first phase shift attenuation unit 12; the optical signal output end of the sub-attenuator 22 is the optical signal output end of the first phase shift attenuation unit 12; the third sub-phase shifter 21 is used to control the phase of the light after passing through the first phase shift attenuation unit 12, the second phase shift attenuation unit 13, or the third phase shift attenuation unit 14; the sub-attenuator 22 is used to control the optical power after passing through the first phase shift attenuation unit 12, the second phase shift attenuation unit 13, or the third phase shift attenuation unit 14.

[0033] The filtering and amplification unit is used to filter and amplify the optical signal to achieve high signal-to-noise ratio and high-power laser output. Specifically, the filtering and amplification unit includes a first optical combiner 6, a second optical combiner 7, an optical fiber filter 8, and an optical fiber amplifier 9. The first input end of the first optical combiner 6 is optically connected to the optical signal output end of the second sub-modulator 18 in the second frequency shift unit 11, and its second input end is optically connected to the optical signal output end of the sub-attenuator 22 in the second phase shift attenuation unit 13. Its output end is optically connected to the first input end of the second optical combiner 7. The second input end of the second optical combiner 7 is optically connected to the optical signal output end of the sub-attenuator 22 in the third phase shift attenuation unit 14, and its output end is sequentially optically connected to the optical fiber filter 8 and the optical fiber amplifier 9. The optical fiber filter 8 is used to filter out optical signals with frequencies greater than or equal to or less than or equal to the initial carrier wave. The optical fiber amplifier 9 is used to amplify the optical signal. In this embodiment, the optical fiber filter 8 is a tunable optical fiber filter with a working wavelength around 2μm. Other filter devices, such as bandpass filters and notch filters, can also be used. The fiber amplifier 9 used in this embodiment is a thulium-doped fiber amplifier, but a holmium-doped fiber amplifier or the like can also be used.

[0034] The mid-infrared optical frequency shifting method using the aforementioned large-range continuously tunable mid-infrared optical frequency shifting device based on the electro-optic effect comprises the following steps: Step 1: The optical pumping unit emits mid-infrared pump laser; specifically: Mid-infrared laser 1 emits mid-infrared pump laser, and 1×3 optical beam splitter 2 splits the mid-infrared pump laser into pump laser A, pump laser B, and pump laser C.

[0035] Step 2: The frequency shifting mechanism and phase shift attenuation mechanism receive mid-infrared pump laser. The electrical signal output unit provides a microwave signal and DC voltage to the frequency shifting mechanism. The electrical signal output unit and the frequency shifting mechanism are adjusted so that the frequency shifting mechanism modulates the frequency of the mid-infrared pump laser based on the microwave signal and DC voltage, achieving a redistribution of mid-infrared pump laser power at different frequencies. The phase shift attenuation mechanism is adjusted so that it generates an optical signal with a phase opposite to the initial carrier and residual sidebands, suppressing residual optical signal power. Specifically, this includes: Step 2.1: The first sub-phase shifter 15 in the first frequency shifting unit 10 receives pump laser A, the third sub-phase shifter 21 in the first phase shift attenuation unit 12 receives pump laser B, and the third sub-phase shifter 21 in the third phase shift attenuation unit 14 receives pump laser C.

[0036] Step 2.2: Adjust the DC voltage source 5 so that the first sub-modulator 16 and the second sub-modulator 18 in the first frequency shift unit 10 and the second frequency shift unit 11 both operate at the maximum transmission point.

[0037] Step 2.3: Adjust the microwave signal frequency output by the first sub-biaser 19 and the second sub-biaser 20 in the first frequency shift unit 10 from the microwave signal source 3. f m The microwave signal voltage and microwave signal phase cause the microwave signal frequency to... f m 0GHz < f m <50GHz (in this embodiment) f m =10GHz), the microwave signal voltage received by the first sub-modulator 16 and the second sub-modulator 18 is its own half-wave voltage V. π The phase difference between the microwave signals received by the first sub-modulator 16 and the second sub-modulator 18 is π / 2, which is 5.3 to 5.4 times (5.366 times in this embodiment).

[0038] like Figure 4 As shown in Figure a, it can be seen that when step 2.3 is completed, the optical power is redistributed to the even-order sidebands.

[0039] Step 2.4: Adjust the second sub-phase shifter 17 in the first frequency shifting unit 10 so that the phase difference between the light passing through the first sub-modulator 16 and the second sub-modulator 18 in the first frequency shifting unit 10 is 2nπ. Then, in the first frequency shifting unit 10, the power of the pump laser A is redistributed at different frequencies to obtain laser D.

[0040] like Figure 4 As shown in Figure b, it can be seen that by adjusting the second sub-phase shifter 17 in the first frequency shifter unit 10, the ±8th and ±12th order sidebands can be retained while the remaining even-order sidebands can be suppressed. Furthermore, by adjusting the half-wave voltage, the ±8th order sideband can be retained while the ±4th order sideband can be suppressed.

[0041] Step 2.5: Adjust the sub-attenuator 22 in the first phase shift attenuation unit 12 so that the power of the pump laser B is attenuated to 6%~7% (6.5% in this embodiment) before passing through the sub-attenuator 22. Adjust the third sub-phase shifter 21 in the first phase shift attenuation unit 12 so that the phase difference between the light passing through the first phase shift attenuation unit 12 and the light passing through the first frequency shift unit 10 is (2n+1)π, and obtain the laser E.

[0042] Step 2.6: The 2×2 optical beam splitter 4 receives laser D and laser E. Laser D and laser E interfere with each other to produce interference light. The 2×2 optical beam splitter 4 then splits the interference light into laser F and laser G with the same power, which are respectively incident on the first sub-phase shifter 15 in the second frequency shifting unit 11 and the third sub-phase shifter 21 in the second phase shift attenuation unit 13; Figure 4As shown in Figure c, after adjusting the sub-attenuator 22 and the third sub-phase shifter 21 in the first phase shift attenuation unit 12, the signals output by laser A and laser B interfere in the 2×2 optical beam splitter 4 to achieve carrier suppression. At this time, the optical power is mainly distributed in the ±8th order sideband.

[0043] Step 2.7: Adjust the microwave signal frequency output by the first sub-biaser 19 and the second sub-biaser 20 in the second frequency shift unit 11 from the microwave signal source 3. f m The output voltage and output phase cause the microwave signal frequency to... f m 0GHz < f m <50GHz (in this embodiment) f m =10GHz), the microwave signal voltage received by the first sub-modulator 16 and the second sub-modulator 18 in the second frequency shift unit 11 is its own half-wave voltage V. π The phase difference between the electrical signals received by the first sub-modulator 16 and the second sub-modulator 18 in the second frequency shift unit 11 is π / 2, which is 5.3 to 5.4 times (5.366 times in this embodiment).

[0044] Step 2.8: Adjust the second sub-phase shifter 17 in the second frequency shift unit 11 so that the phase difference between the light passing through the first sub-modulator 16 and the second sub-modulator 18 in the second frequency shift unit 11 is 2nπ. Then, in the second frequency shift unit 11, the power of the laser F is redistributed at different frequencies, resulting in the following... Figure 4 The laser H is shown in d.

[0045] Step 2.9: Adjust the sub-attenuator 22 in the second phase shift attenuation unit 13 so that the energy of the laser G is attenuated to 6%~7% (6.5% in this embodiment) before passing through the sub-attenuator 22. Adjust the third sub-phase shifter 21 in the second phase shift attenuation unit 13 so that the phase difference between the light passing through the second phase shift attenuation unit 13 and the light passing through the second frequency shift unit 11 is (2n+1)π, and obtain the laser I.

[0046] Step 2.10: The first optical beam combiner 6 receives laser H and laser I, and combines them into laser J; as shown... Figure 4 As shown in Figure e, after adjusting the sub-attenuator 22 and the third sub-phase shifter 21 in the second phase shift attenuation unit 13, the signals output by laser H and laser I interfere in the first optical beam combiner 6, thereby achieving suppression of ±8th order sidebands.

[0047] Step 2.11: Adjust the sub-attenuator 22 in the third phase shift attenuation unit 14 so that the power of the pump laser C is attenuated to 0.4%-0.5% (0.42% in this embodiment) before passing through the sub-attenuator 22. Adjust the third sub-phase shifter 21 in the third phase shift attenuation unit 14 so that the phase of the light after passing through the third phase shift attenuation unit 14 is different from the carrier phase of the laser J by (2n+1)π, thus obtaining the laser K.

[0048] Step 2.12: The second optical beam combiner 7 receives laser J and laser K and combines them into laser L.

[0049] like Figure 4 As shown in Figure f, after adjusting the sub-attenuator 22 and the third sub-phase shifter 21 in the third phase shift attenuation unit 14, the signals output by laser J and laser K interfere in the second optical combiner 7 to achieve carrier suppression. At this time, most of the optical power is distributed in the ±16th order sideband.

[0050] Step 3: Adjust the filtering and amplification unit to filter out optical signals with frequencies greater than or equal to or less than the initial carrier wave, and amplify the remaining optical signals to obtain a mid-infrared optical frequency-shifting signal; specifically: Adjust the fiber optic filter 8 to filter out optical signals in laser L with frequencies greater than or equal to or less than the initial carrier wave. Then, amplify the signal through the fiber optic amplifier 9 to obtain a mid-infrared optical frequency-shifting signal.

[0051] In this embodiment, optical signals with wavelengths less than or equal to the initial carrier wave are filtered out, then amplified by fiber amplifier 9, and finally the spectrum is obtained as shown. Figure 5 As shown, the pump laser wavelength λ0 used in this embodiment is 2μm. When the input microwave signal frequency is 10GHz, a frequency shift of 160 GHz is achieved by using the steps and methods described above.

[0052] The principle of this invention is as follows: This method utilizes a fixed-frequency mid-infrared laser, generating modulation sidebands through cascaded electro-optic Mach-Zehnder modulators. By specifically configuring the Mach-Zehnder modulators, the generated sidebands are redistributed. Finally, unwanted frequency components are suppressed through destructive interference, thus achieving frequency shifting. This approach addresses the current lack of rapidly tunable sweep lasers in the mid-infrared band. Furthermore, by employing an electro-optic frequency shifting scheme, it offers the advantage of adaptability to various laser wavelengths. It overcomes the limitations of temperature and cavity length tuning in small-volume semiconductor lasers, which typically restrict tuning speed and accuracy, and the problem of simultaneous frequency-shifting light intensity variations during tuning. Moreover, it requires only a miniaturized, narrow-linewidth laser of a fixed frequency for pumping, eliminating the need for a high-performance, large-volume, precision-tunable light source. Therefore, it features high precision, wide applicability, simple structure, low cost, and ease of operation.

[0053] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present invention should be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A wide-range continuously tunable mid-infrared optical frequency shifting device based on the electro-optic effect, characterized in that: It includes an optical pumping unit, a frequency shifting mechanism, an electrical signal output unit, a phase shift attenuation mechanism, and a filtering and amplification unit; The optical pumping unit is used to emit mid-infrared pump laser, and its carrier is the initial carrier. The electrical signal output unit is connected to the frequency shifting mechanism and is used to provide microwave signals and DC voltage to the frequency shifting mechanism; The frequency shifting mechanism is connected between the optical pumping unit and the filtering and amplification unit, and is used to modulate the frequency of the mid-infrared pump laser to generate optical frequency sidebands with different frequencies and powers, thereby realizing the redistribution of the mid-infrared pump laser power at different frequencies. The phase shift attenuation mechanism is connected between the optical pump unit and the filter amplification unit, and is connected to the frequency shifting mechanism through an optical beam splitter. It is used to generate an optical signal with the opposite phase to the initial carrier and the residual sideband, and to suppress the power of the residual optical signal. The filtering and amplification unit is used to filter and amplify the optical signal.

2. The wide-range continuously tunable mid-infrared optical frequency shifting device based on electro-optic effect according to claim 1, characterized in that: The optical beam splitter is a 2×2 optical beam splitter (4); The frequency shifting mechanism includes a first frequency shifting unit (10) and a second frequency shifting unit (11); The optical signal input end of the first frequency shift unit (10) is connected to the output end of the optical pump unit via optical fiber, and its optical signal output end is connected to the first input end of the 2×2 optical beam splitter (4) via optical fiber. The optical signal input end of the second frequency shift unit (11) is connected to the first output end of the 2×2 optical beam splitter (4) via optical fiber, and its output end is connected to the input end of the filter amplification unit via optical fiber. The second input and second output of the 2×2 optical beam splitter (4) are connected to the optical fiber of the phase shift attenuation mechanism; The electrical signal output unit is electrically connected to the first frequency shift unit (10) and the second frequency shift unit (11), respectively.

3. The wide-range continuously tunable mid-infrared optical frequency shifting device based on electro-optic effect according to claim 2, characterized in that: The phase shift attenuation mechanism includes a first phase shift attenuation unit (12), a second phase shift attenuation unit (13), and a third phase shift attenuation unit (14). The optical signal input end of the first phase shift attenuation unit (12) is connected to the output end of the optical pump unit via optical fiber, and its output end is connected to the second input end of the 2×2 optical beam splitter (4) via optical fiber. The optical signal input end of the second phase shift attenuation unit (13) is connected to the second output end of the 2×2 optical beam splitter (4) via optical fiber, and its optical signal output end is connected to the input end of the filter amplification unit via optical fiber. The optical signal input end of the third phase shift attenuation unit (14) is connected to the output end of the optical pump unit via optical fiber, and its optical signal output end is connected to the input end of the filter amplification unit via optical fiber.

4. The wide-range continuously tunable mid-infrared optical frequency shifting device based on electro-optic effect according to claim 3, characterized in that: The first frequency shift unit (10) includes a first sub-phase shifter (15), a first sub-modulator (16), a second sub-phase shifter (17), a second sub-modulator (18), a first sub-biaser (19), and a second sub-biaser (20). The first sub-phase shifter (15), the first sub-modulator (16), the second sub-phase shifter (17), and the second sub-modulator (18) are connected by optical fibers in sequence along the optical signal emission direction. The optical signal input end of the first sub-phase shifter (15) is the optical signal input end of the first frequency shift unit (10), and the optical signal output end of the second sub-modulator (18) is the optical signal output end of the first frequency shift unit (10). The input terminal of the first sub-biaser (19) is electrically connected to the electrical signal output unit, and its output terminal is electrically connected to the electrical signal input terminal of the first sub-modulator (16). The input terminal of the second sub-biaser (20) is electrically connected to the electrical signal output unit, and its output terminal is electrically connected to the electrical signal input terminal of the second sub-modulator (18). The second frequency shift unit (11) and the first frequency shift unit (10) have the same structure.

5. The wide-range continuously tunable mid-infrared optical frequency shifting device based on electro-optic effect according to claim 4, characterized in that: The first phase shift attenuation unit (12) includes a third sub-phase shifter (21) and a sub-attenuator (22) connected sequentially by optical fibers along the optical signal emission direction. The input terminal of the third sub-phase shifter (21) is the optical signal input terminal of the first phase shift attenuation unit (12); The optical signal output terminal of the sub-attenuator (22) is the optical signal output terminal of the first phase shift attenuation unit (12); The structures of the second phase shift attenuation unit (13) and the third phase shift attenuation unit (14) are the same as those of the first phase shift attenuation unit (12).

6. The wide-range continuously tunable mid-infrared optical frequency shifting device based on electro-optic effect according to claim 5, characterized in that: The filtering and amplification unit includes a first optical combiner (6), a second optical combiner (7), an optical fiber filter (8), and an optical fiber amplifier (9). The first input end of the first optical combiner (6) is optically connected to the optical signal output end of the second sub-modulator (18) in the second frequency shift unit (11), its second input end is optically connected to the optical signal output end of the sub-attenuator (22) in the second phase shift attenuation unit (13), and its output end is optically connected to the first input end of the second optical combiner (7). The second input end of the second optical combiner (7) is optically connected to the optical signal output end of the sub-attenuator (22) in the third phase shift attenuation unit (14), and its output end is optically connected to the optical fiber filter (8) and the optical fiber amplifier (9) in sequence. The fiber optic filter (8) is used to filter out optical signals with frequencies greater than or equal to or less than or equal to the initial carrier. The fiber amplifier (9) is used to amplify the optical signal.

7. The wide-range continuously tunable mid-infrared optical frequency shifting device based on electro-optic effect according to claim 6, characterized in that: The electrical signal output unit includes a microwave signal source (3) and a DC voltage source (5). The output terminal of the microwave signal source (3) is electrically connected to the microwave signal input terminal of each first sub-biaser (19) and each second sub-biaser (20) in the first frequency shift unit (10) and the second frequency shift unit (11), respectively. The output terminal of the DC voltage source (5) is electrically connected to the DC voltage signal input terminal of each first sub-biaser (19) and each second sub-biaser (20) in the first frequency shift unit (10) and the second frequency shift unit (11), respectively.

8. The wide-range continuously tunable mid-infrared optical frequency shifting device based on the electro-optic effect according to any one of claims 4-7, characterized in that: The optical pumping unit includes a mid-infrared laser (1) and a 1×3 optical beam splitter (2). The mid-infrared laser (1) is used to emit mid-infrared pump laser; The input end of the 1×3 optical beam splitter (2) is connected to the output end of the mid-infrared laser (1) by optical fiber. Its first output end is connected to the optical signal input end of the first frequency shift unit (10) by optical fiber. Its second output end is connected to the optical signal input end of the first phase shift attenuation unit (12) by optical fiber. Its third output end is connected to the optical signal input end of the third phase shift attenuation unit (14) by optical fiber. Both the first sub-modulator (16) and the second sub-modulator (18) are mid-infrared Mach-Zehnder modulators.

9. A wide-range continuously tunable mid-infrared optical frequency shifting method based on electro-optic effect, employing the wide-range continuously tunable mid-infrared optical frequency shifting device based on electro-optic effect as described in any one of claims 1-8, characterized in that, Includes the following steps: Step 1: The optical pumping unit emits mid-infrared pump laser; Step 2: The frequency shifting mechanism and the phase shift attenuation mechanism receive the mid-infrared pump laser. The electrical signal output unit provides a microwave signal and a DC voltage to the frequency shifting mechanism. The frequency shifting mechanism is adjusted so that it modulates the frequency of the mid-infrared pump laser based on the microwave signal and the DC voltage, thereby redistributing the mid-infrared pump laser power at different frequencies. The phase shift attenuation mechanism is adjusted so that it generates an optical signal with a phase opposite to the initial carrier and the residual sideband, thereby suppressing the residual optical signal power. Step 3: Adjust the filter amplification unit to filter out optical signals with frequencies greater than or equal to or less than the initial carrier, and amplify the remaining optical signals to obtain mid-infrared optical frequency shift signals.

10. The wide-range continuously tunable mid-infrared optical frequency shifting method based on electro-optic effect according to claim 9, characterized in that: Step 1 is as follows: Mid-infrared laser (1) emits mid-infrared pump laser, and 1×3 optical beam splitter (2) divides the mid-infrared pump laser into pump laser A, pump laser B and pump laser C; Step 2 specifically includes: Step 2.1: The first sub-phase shifter (15) in the first frequency shifting unit (10) receives pump laser A, the third sub-phase shifter (21) in the first phase shift attenuation unit (12) receives pump laser B, and the third sub-phase shifter (21) in the third phase shift attenuation unit (14) receives pump laser C. Step 2.2: Adjust the DC voltage source (5) so that the first sub-modulator (16) and the second sub-modulator (18) in the first frequency shift unit (10) and the second frequency shift unit (11) are both working at the maximum transmission point; Step 2.3: Adjust the microwave signal frequency output by the first sub-biaser (19) and the second sub-biaser (20) in the first frequency shift unit (10) to the microwave signal source (3). f m The microwave signal voltage and microwave signal phase cause the microwave signal frequency to... f m 0GHz < f m <50GHz, the microwave signal voltage received by the first sub-modulator (16) and the second sub-modulator (18) in the first frequency shift unit (10) is its own half-wave voltage V π The phase difference between the microwave signals received by the first sub-modulator (16) and the second sub-modulator (18) in the first frequency shift unit (10) is π / 2, which is 5.3 to 5.4 times that of the first frequency shift unit (10). Step 2.4: Adjust the second sub-phase shifter (17) in the first frequency shifting unit (10) so that the phase difference between the light passing through the first sub-modulator (16) and the second sub-modulator (18) in the first frequency shifting unit (10) is 2nπ. Then, in the first frequency shifting unit (10), the power of the pump laser A is redistributed at different frequencies to obtain laser D. Step 2.5: Adjust the sub-attenuator (22) in the first phase shift attenuation unit (12) so that the power of the pump laser B is attenuated to 6%~7% before passing through the sub-attenuator (22). Adjust the third sub-phase shifter (21) in the first phase shift attenuation unit (12) so that the phase difference between the light passing through the first phase shift attenuation unit (12) and the light passing through the first frequency shift unit (10) is (2n+1)π, and obtain the laser E. Step 2.6: The 2×2 optical beam splitter (4) receives laser D and laser E. Laser D and laser E interfere with each other to generate interference light. The 2×2 optical beam splitter (4) then splits the interference light into laser F and laser G with the same power, which are respectively incident on the first sub-phase shifter (15) in the second frequency shifting unit (11) and the third sub-phase shifter (21) in the second phase shift attenuation unit (13). Step 2.7: Adjust the microwave signal frequency output by the first sub-biaser (19) and the second sub-biaser (20) in the second frequency shift unit (11) to the microwave signal source (3). f m The output voltage and output phase cause the microwave signal frequency to... f m 0GHz < f m <50GHz, the microwave signal voltage received by the first sub-modulator (16) and the second sub-modulator (18) in the second frequency shift unit (11) is its own half-wave voltage V. π The phase difference between the electrical signals received by the first sub-modulator (16) and the second sub-modulator (18) in the second frequency shift unit (11) is π / 2, which is 5.3 to 5.4 times that of the second frequency shift unit (11). Step 2.8: Adjust the second sub-phase shifter (17) in the second frequency shifter unit (11) so that the phase difference between the light passing through the first sub-modulator (16) and the second sub-modulator (18) in the second frequency shifter unit (11) is 2nπ. Then, in the second frequency shifter unit (11), the power of laser F is redistributed at different frequencies to obtain laser H. Step 2.9: Adjust the sub-attenuator (22) in the second phase shift attenuation unit (13) so that the power of laser G is attenuated to 6%~7% of the power before passing through the sub-attenuator (22). Adjust the third sub-phase shifter (21) in the second phase shift attenuation unit (13) so that the phase difference between the light passing through the second phase shift attenuation unit (13) and the light passing through the second frequency shift unit (11) is (2n+1)π, and obtain laser I. Step 2.10: The first optical beam combiner (6) receives laser H and laser I and combines them into laser J; Step 2.11: Adjust the sub-attenuator (22) in the third phase shift attenuation unit (14) so ​​that the power of the pump laser C is attenuated to 0.4%-0.5% before passing through the sub-attenuator (22). Adjust the third sub-phase shifter (21) in the third phase shift attenuation unit (14) so ​​that the phase of the light after passing through the third phase shift attenuation unit (14) differs from the carrier phase of the laser J by (2n+1)π, and obtain the laser K. Step 2.12: The second optical beam combiner (7) receives laser J and laser K and combines them into laser L; Step 3 specifically involves: Adjust the fiber optic filter (8) to filter out the optical signal in laser L with a frequency greater than or equal to or less than the initial carrier, and then amplify it through the fiber optic amplifier (9) to obtain the mid-infrared optical frequency shift signal.

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