A high power tunable mid-infrared electro-optic frequency comb generation system and method

Abstract

The application discloses a high-power tunable mid-infrared electro-optical frequency comb generation system and method, solves the problem that the existing mid-infrared optical frequency comb system is large in size, high in cost and difficult to realize high-power output due to the performance limitation of a pump light source and an integrated device, and the application adopts a mature and low-cost mid-infrared fiber amplifier to replace a high-performance and narrow-line-width pump light source, simultaneously combines a ring cavity structure and resonance principle to realize automatic selection of an initial wavelength and controlled generation of comb teeth sidebands, and the mid-infrared fiber amplifier plays a dual role of starting and power cycle amplification of the pump light signal, solves the problems that other schemes are difficult to obtain a mid-infrared extremely narrow line-width light source, it is difficult to realize synchronous locking of pumping and resonance, and a control system is complex, makes various elements more easily obtained and without a high-frequency electric control loop, and has the advantages of low cost and easy construction.

Description

Technical Field

[0001] This invention relates to a mid-infrared electro-optic frequency comb generation system and method, specifically to a high-power tunable mid-infrared electro-optic frequency comb generation system and method. Background Technology

[0002] Optical frequency combs, as important multi-wavelength coherent light sources, have achieved milestone status in the development of laser technology and are now widely used in high-speed communication, microwave photonics, precision measurement, photonic computing, and many other fields. Traditional optical frequency combs are implemented using solid-state or fiber-mode-locked lasers, exhibiting equidistant longitudinal mode wavelengths in the frequency domain and a stable pulse sequence in the time domain. In recent years, advancements in micro-nano photonics technology, particularly the improved fabrication of low-loss waveguides and high-quality microcavities, have led to the rapid development of integrated device-based optical frequency comb technology, which possesses inherent advantages in miniaturization and low power consumption. Among the most representative technologies are integrated Kerr microcavity optical frequency combs, which utilize the Kerr effect (four-wave mixing process) in a high-quality microcavity to generate a large number of comb teeth at the microcavity resonant position, with the repetition frequency determined by the cavity length; and integrated electro-optic frequency combs, which are based on high-speed electro-optic devices and combine intensity and phase modulation types to achieve cascaded modulation sidebands driven by the electro-optic effect, with the repetition frequency determined by the modulator bandwidth.

[0003] Although integrated optical frequency comb technology has made significant progress, enabling wide spectral output and stable pulse excitation, current miniaturized integrated optical frequency combs are mainly concentrated in the near-infrared band due to limitations in pump source performance (power, linewidth, etc.), device fabrication level (quality factor, nonlinear coefficient, etc.), and supporting optical components (coupling lenses, beam splitters / combiners, etc.). The mid-infrared band faces various technical bottlenecks, making the production of optical frequency combs extremely difficult. For example, the linewidth of mid-infrared pump lasers is typically only in the MHz to GHz range, which is three orders of magnitude lower than the kHz or even Hz range of C-band narrow-linewidth lasers. Moreover, it basically lacks continuous frequency tuning capability, thus failing to meet the ultra-narrow linewidth pumping and resonant synchronization locking requirements of Kerr microcavity optical frequency combs. Furthermore, the performance of mid-infrared electro-optic modulators lags significantly behind that of near-infrared bands. They exhibit higher insertion loss, lower modulation rate, and lower bandwidth. Using multiple intensity and phase modulators cascaded together to generate an electro-optic frequency comb not only results in an excessively large and costly system but also severely limits output power (comb power is only in the μW range). Simultaneously, precise phase control within the cavity is required, leading to complex structures and cumbersome operations. Particularly disadvantageous is the lack of fine narrowband filters in the mid-infrared band, coupled with the relatively wide linewidth of the pump source. This makes it difficult to directly amplify weak signals from low-power optical frequency combs, or results in excessively high background noise after amplification, hindering practical applications. Meanwhile, fields such as precision measurement and microwave photonics require optical frequency comb sources with excellent tunability of repetition frequency (i.e., frequency interval) to meet specific parameter requirements in different scenarios. However, the mode-locking conditions of Kerr microcavity optical frequency combs are extremely stringent, resulting in a very small tuning tolerance range (repetition frequency on the order of 10 GHz to 1 THz, but tunable range only in the MHz range).

[0004] In summary, there is currently no effective solution for mid-infrared optical frequency combs to overcome the performance limitations of pump light sources and integrated devices, achieve higher power output, and support flexible tuning of repetition frequency. Therefore, it is necessary to develop new technologies and fully leverage the advantages of miniaturization and low power consumption of integrated devices to enable their widespread application as a general-purpose, high-performance coherent light source in the field of information technology. Summary of the Invention

[0005] To address the technical problems of existing mid-infrared optical frequency comb systems, which suffer from large size, high cost, difficulty in achieving high power output, and inflexible repetition frequency tuning due to limitations in the performance of pump light sources and integrated devices, thus failing to meet the specific needs of different application scenarios, this invention provides a high-power tunable mid-infrared electro-optic frequency comb generation system and method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A high-power tunable mid-infrared electro-optic frequency comb generation system, characterized in that:

[0008] It includes a pumping unit, an electro-optic modulation unit, a beam splitting unit, a ring cavity control unit, and a status monitoring unit;

[0009] The output end of the pump unit is connected to the input end of the electro-optic modulation unit to generate pump light and inject it into the electro-optic modulation unit.

[0010] The output of the electro-optic modulation unit is connected to the input of the beam splitter unit, and is used to electro-optically modulate the received pump light.

[0011] The beam splitting unit is used to split the modulated beam into a first beam and a second beam.

[0012] The ring cavity control unit is disposed in the optical path of the first beam, and its output end is connected to the input end of the pump unit, thereby forming a ring cavity between the pump unit, the electro-optic modulation unit, the beam splitting unit and the ring cavity control unit; the ring cavity control unit is used to control the propagation direction and delay phase of the first beam and adjust the polarization state of the first beam.

[0013] The status monitoring unit is set in the optical path of the second beam to monitor the spectral characteristics of the second beam and provide a basis for the regulation of the ring cavity control unit.

[0014] Furthermore, the pumping unit includes a mid-infrared fiber amplifier;

[0015] The input end of the mid-infrared fiber amplifier is optically connected to the output end of the ring cavity control unit, and its output end is optically connected to the input end of the electro-optic modulation unit.

[0016] Furthermore, the electro-optic modulation unit includes a mid-infrared electro-optic modulator, a microwave signal generator, a DC power supply, and a radio frequency biaser;

[0017] The optical input end of the mid-infrared electro-optic modulator is optically connected to the output end of the mid-infrared fiber amplifier, its optical output end is optically connected to the input end of the beam splitter, and its electrical input end is electrically connected to the output end of the radio frequency biaser.

[0018] The output terminal of the microwave signal generator is electrically connected to the radio frequency input terminal of the radio frequency biaser.

[0019] The output terminal of the DC power supply is electrically connected to the DC input terminal of the RF bias.

[0020] Furthermore, the beam splitting unit includes an optical fiber beam splitter;

[0021] The input end of the fiber optic beam splitter is connected to the output end of the mid-infrared electro-optic modulator via fiber optic cable, its first output end is connected to the input end of the ring cavity control unit via fiber optic cable, and its second output end is connected to the input end of the status monitoring unit via fiber optic cable.

[0022] Furthermore, the annular cavity control unit includes a polarization controller, an isolator, and an optical fiber delay line that are sequentially optically connected along the direction of the first beam.

[0023] The input end of the polarization controller is optically connected to the first output end of the fiber optic beam splitter.

[0024] The output end of the fiber delay line is connected to the input fiber of the mid-infrared fiber amplifier.

[0025] Furthermore, the status monitoring unit includes a spectrometer;

[0026] The spectrometer is connected to the second output fiber of the fiber optic beam splitter.

[0027] A method for generating a high-power tunable mid-infrared electro-optic frequency comb, employing the aforementioned high-power tunable mid-infrared electro-optic frequency comb generation system, is characterized by including the following steps:

[0028] Step 1: Start the pump unit and electro-optic modulation unit. The pump unit emits spontaneous emission light, which circulates within the annular cavity.

[0029] Step 2: Adjust the ring cavity control unit so that the spontaneous emission light oscillates in the ring cavity until the state monitoring unit can detect the initial laser being excited in the ring cavity. Then the output beam of the pump unit is the pump light.

[0030] Step 3: Based on the state of the target electro-optic frequency comb, the pump light is electro-optically modulated by the electro-optic modulation unit until the state monitoring unit can detect the generation of the initial comb tooth sideband of the target electro-optic frequency comb.

[0031] Step 4: Adjust the ring cavity control unit to change the overall cavity length and resonant mode of the ring cavity until the automatic cascading generation process of optical frequency sidebands is established in the ring cavity. Then the target electro-optic frequency comb has been stably output, and the generation of the mid-infrared electro-optic frequency comb is completed.

[0032] Further, step 1 specifically involves turning on the mid-infrared fiber amplifier and the mid-infrared electro-optic modulator, turning off the microwave signal generator and the DC power supply, and having the mid-infrared fiber amplifier emit spontaneously emitted light, which then circulates within the ring cavity.

[0033] Further, step 2 specifically involves adjusting the polarization controller to change the polarization state of the spontaneously emitted light, causing the spontaneously emitted light to oscillate cyclically within the ring cavity until a laser wavelength can be observed on the spectrometer and the optical power reaches its maximum value, indicating that the initial laser has been excited within the ring cavity. At this point, the beam emitted by the mid-infrared fiber amplifier is the pump light.

[0034] Further, step 3 specifically involves turning on the microwave signal generator and the DC power supply, and adjusting the microwave drive signal voltage output by the microwave signal generator and the DC bias signal voltage of the DC power supply according to the state of the target electro-optic frequency comb, until the initial comb tooth sideband of the target electro-optic frequency comb can be observed on the spectrometer.

[0035] Step 4 specifically involves adjusting the fiber delay line to change the overall cavity length and resonant mode of the ring cavity until the frequency comb spectrum observed on the spectrometer reaches its widest state. At this point, the cavity length of the ring cavity and the frequency of the microwave driving signal are integer multiples of each other, and an automatic cascade generation process of optical frequency sidebands is established within the ring cavity. The target electro-optic frequency comb has been stably output, completing the generation of the mid-infrared electro-optic frequency comb.

[0036] The beneficial effects of this invention are:

[0037] 1. The present invention provides a high-power tunable mid-infrared electro-optic frequency comb generation system and method, which utilizes a mid-infrared fiber amplifier to pump a mid-infrared electro-optic modulator, and realizes cascade excitation and synchronous cyclic amplification of the optical frequency comb teeth through a ring cavity structure and resonance principle. The optical conversion efficiency is greater than 20%, and the output power in the ring cavity can reach tens of mW. Compared with the existing electro-optic frequency comb scheme, the power is increased by about one order of magnitude, and it has the advantages of high output power and energy efficiency.

[0038] 2. The present invention provides a high-power tunable mid-infrared electro-optic frequency comb generation system and method, which can achieve a wide range of repetition frequency tuning (MHz to GHz level) by freely setting the microwave driving frequency of the mid-infrared electro-optic modulator. Compared with the existing Kerr optical frequency comb generation method, the tuning range is improved by three orders of magnitude. Moreover, by changing the DC signal voltage, different working modes (odd, even, orthogonal modes, etc.) and spectral morphologies (single peak or double peak) can be achieved. It has the characteristics of flexible control and high tolerance, and can meet the specific needs of various application scenarios.

[0039] 3. The present invention provides a high-power tunable mid-infrared electro-optic frequency comb generation system and method, which ingeniously utilizes the ring cavity structure and resonance principle. Compared with the existing single-pass or series electro-optic frequency comb generation methods, each newly generated comb tooth sideband can become the initial seed signal for the next stage process, thereby realizing automatic cascade excitation and synchronous cyclic amplification of optical frequency comb teeth. Therefore, under the same power consumption, it has the advantages of larger spectral bandwidth and more comb teeth.

[0040] 4. The present invention provides a high-power tunable mid-infrared electro-optic frequency comb generation system and method, which uses a mature and inexpensive mid-infrared fiber amplifier to replace a high-performance, narrow-linewidth pump light source. At the same time, it combines a ring cavity structure and resonance principle to achieve automatic selection of the initial wavelength and controlled generation of the comb sideband. The mid-infrared fiber amplifier plays a dual role in pump light signal oscillation and power cyclic amplification, solving the problems faced by other solutions, such as the difficulty in obtaining mid-infrared extremely narrow-linewidth light sources, the difficulty in locking pump and resonance synchronization, and the complexity of the control system. This makes the components easier to obtain and eliminates the need for high-frequency electronic control circuits, giving it the advantages of low cost and ease of construction.

[0041] 5. The present invention provides a high-power tunable mid-infrared electro-optic frequency comb generation system and method, which can determine the system's working status simply by monitoring the waveform with a spectrometer. It does not require precise time-domain and frequency-domain measurement equipment such as oscilloscopes, spectrum analyzers, and network analyzers, nor does it require complex electrical control programs or precise operation by professional personnel. It is characterized by simple operation and ease of use. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of an embodiment of a high-power tunable mid-infrared electro-optic frequency comb generation system according to the present invention;

[0043] Figure 2 These are state diagrams corresponding to the generation process of the mid-infrared electro-optic frequency comb in the embodiments of the present invention; wherein, (a) is the optical signal curve when the mid-infrared electro-optic modulator is not loaded with microwave driving signal in step 1, (b) is a schematic diagram of a laser wavelength generated on the spectrometer in step 2, (c) is a schematic diagram of the initial comb tooth sideband generation state in the odd-order modulation mode in step 3, (d) is a schematic diagram of the first target electro-optic frequency comb generation state in the odd-order modulation mode in step 3, (e) is a schematic diagram of the initial comb tooth sideband generation state in the even-order modulation mode in step 3, and (f) is a schematic diagram of the second target electro-optic frequency comb generation state in the even-order modulation mode in step 3.

[0044] Figure 3 This is a diagram showing the relationship between the initial comb tooth sideband and the longitudinal die position supported by the annular cavity in an embodiment of the present invention;

[0045] Figure 4 This is a spectral result diagram of odd-order modulation in an embodiment of the present invention;

[0046] Figure 5 This is a spectral result of even-order modulation in an embodiment of the present invention.

[0047] The attached figures are labeled as follows:

[0048] 1. Mid-infrared fiber optic amplifier; 2. Mid-infrared electro-optic modulator; 3. Microwave signal generator; 4. DC power supply; 5. Radio frequency biaser; 6. Fiber optic bundle splitter; 7. Polarization controller; 8. Isolator; 9. Fiber optic delay line; 10. Spectrometer. Detailed Implementation

[0049] 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.

[0050] This invention provides a high-power tunable mid-infrared electro-optic frequency comb generation system, such as... Figure 1 As shown, the mid-infrared electro-optic frequency comb generation system includes a pump unit, an electro-optic modulation unit, a beam splitting unit, a ring cavity control unit, and a status monitoring unit connected in sequence, and a ring cavity is formed between the pump unit, the electro-optic modulation unit, the beam splitting unit, and the ring cavity control unit;

[0051] The pump unit is a mid-infrared fiber amplifier 1; the input end of the mid-infrared fiber amplifier 1 is optically connected to the output end of the ring cavity control unit, and its output end is optically connected to the input end of the electro-optic modulation unit. In this embodiment, the mid-infrared fiber amplifier 1 is a thulium-doped fiber amplifier with an output power of 500mW and an operating wavelength of 1950-2050nm. The mid-infrared fiber amplifier 1 is used to generate spontaneous emission light;

[0052] The electro-optic modulation unit includes a mid-infrared electro-optic modulator 2, a microwave signal generator 3, a DC power supply 4, and a radio frequency biasing device 5. The optical input of the mid-infrared electro-optic modulator 2 is optically connected to the output of the mid-infrared fiber amplifier 1, its optical output is optically connected to the input of the beam splitter unit, and its electrical input is electrically connected to the output of the radio frequency biasing device 5. The output of the microwave signal generator 3 is electrically connected to the radio frequency input of the radio frequency biasing device 5. The output of the DC power supply 4 is electrically connected to the DC input of the radio frequency biasing device 5. The microwave signal generator 3 is used to input a microwave drive signal to the mid-infrared electro-optic modulator 2 to regulate its operating state. The DC power supply 4 is used to send a DC bias signal to the mid-infrared electro-optic modulator 2 to control its DC bias voltage. The radio frequency biasing device 5 is used to inject both the microwave drive signal and the DC bias signal into the mid-infrared electro-optic modulator 2. In this embodiment, the mid-infrared electro-optic modulator 2 is a waveguide-type Mach-Zehnder modulator based on lithium niobate material, and its single-arm half-wave voltage V... π ~4.5V.

[0053] The beam splitting unit is an optical fiber beam splitter 6. The input end of the optical fiber beam splitter 6 is connected to the output end of the mid-infrared electro-optic modulator 2 via optical fiber. Its first output end is connected to the input end of the ring cavity control unit via optical fiber, and its second output end is connected to the input end of the status monitoring unit via optical fiber. In this embodiment, the optical fiber beam splitter 6 has a beam splitting ratio of 1:9 (i.e., 10% output to the status monitoring unit and 90% output to the ring cavity control unit). In other embodiments, different beam splitting ratios (e.g., 1:99, 5:95, 20:80, etc.) can also be used, as long as the beam can be split into two branches.

[0054] The ring cavity control unit includes a polarization controller 7, an isolator 8, and an optical fiber delay line 9 connected sequentially along the direction of the first beam. The input end of the polarization controller 7 is optically connected to the first output end of the optical fiber beam splitter 6; the output end of the optical fiber delay line 9 is optically connected to the input end of the mid-infrared optical fiber amplifier 1. The polarization controller 7 is used to regulate the polarization state of the beam within the ring cavity; the isolator 8 is used to suppress back-amplified signals, ensuring that the beam within the ring cavity propagates in only one direction; the optical fiber delay line 9 is used to delay the phase of the beam within the ring cavity, thereby finely tuning the overall cavity length and resonant mode distribution of the ring cavity.

[0055] The ring cavity specifically corresponds to the space between the mid-infrared fiber amplifier 1, the mid-infrared electro-optic modulator 2, the fiber beam splitter 6, the polarization controller 7, the isolator 8, and the fiber delay line 9.

[0056] The status monitoring unit is a spectrometer 10; the spectrometer 10 is connected to the second output end of the fiber optic beam splitter 6 via optical fiber. The spectrometer 10 is used to measure the spectral waveform of the second beam, providing a basis for adjusting the working state of the ring cavity.

[0057] The steps for generating a mid-infrared electro-optic frequency comb using the high-power tunable mid-infrared electro-optic frequency comb generation system described above are as follows:

[0058] Step 1: Start the pump unit, electro-optic modulation unit, beam splitter unit, ring cavity control unit, and status monitoring unit. The pump unit emits spontaneous emission light, which circulates within the ring cavity; specifically:

[0059] Turn on the mid-infrared fiber amplifier 1 and the mid-infrared electro-optic modulator 2, and turn off the microwave signal generator 3 and the DC power supply 4. The mid-infrared fiber amplifier 1 emits spontaneous emission light, which circulates in the ring cavity.

[0060] like Figure 2 As shown in (a), when the mid-infrared electro-optic modulator 2 is not loaded with a microwave driving signal, the mid-infrared fiber amplifier 1 does not have any signal light injected at this time, so it only outputs the amplified signal of spontaneous emission light, which is optically represented as the gain spectrum envelope of the mid-infrared doped fiber (taking thulium-doped fiber as an example).

[0061] Step 2: Adjust the ring cavity control unit to make the spontaneous emission light oscillate cyclically within the ring cavity until the state monitoring unit can detect the initial laser emitted within the ring cavity. Then, the output beam from the pump unit is the pump light; specifically:

[0062] Adjusting the polarization controller 7 changes the polarization state of the spontaneously emitted light, causing it to oscillate cyclically within the ring cavity until a laser wavelength can be observed on the spectrometer 10 and the optical power reaches its maximum value. This indicates that the polarization within the ring cavity is now in its optimal state, and the initial center wavelength has been achieved through ring cavity resonance. f 0 Excitation occurs when the beam emitted by the mid-infrared fiber amplifier 1 is pump light.

[0063] like Figure 2 As shown in (b), since conventional electro-optic modulators all have polarization selectivity, when the polarization state of the beam in the ring cavity is adjusted by the polarization controller 7 to perfectly match that of the mid-infrared electro-optic modulator 2, the optical power in the ring cavity will reach its maximum. Furthermore, among the many optical wave modes that meet the ring cavity resonance condition, one longitudinal mode will be cyclically amplified, while other modes will fail to oscillate due to gain competition. Therefore, after step 2 is completed, the initial center wavelength can be achieved. f 0 When excited, the spectrometer 10 exhibits a narrow linewidth longitudinal mode, meaning that a laser wavelength can be observed on the spectrometer 10 and the optical power reaches its maximum value.

[0064] Step 3: Based on the target electro-optic frequency comb state, the pump light is electro-optically modulated by the electro-optic modulation unit until the state monitoring unit can detect the generation of the initial comb tooth sideband of the target electro-optic frequency comb; specifically:

[0065] Turn on the microwave signal generator 3 and the DC power supply 4. Adjust the microwave drive signal voltage output by the microwave signal generator 3 and the DC bias signal voltage of the DC power supply 4 according to the state of the target electro-optic frequency comb until the initial comb tooth sideband of the target electro-optic frequency comb can be observed on the spectrometer 10.

[0066] In this embodiment, the following three target electro-optic frequency combs are set:

[0067] A. Based on the state of the first target electro-optic frequency comb, adjust the operating voltage V of DC power supply 4. DC Set to V π =4.5V (odd-order modulation mode, the upper and lower arms of the mid-infrared electro-optic modulator 2 will be in an out-of-phase state with a phase difference of π, and the initial center carrier frequency will be suppressed), the microwave drive signal voltage V output by the microwave signal generator 3. RF Set to 0.58V π=2.61V, the microwave drive signal frequency f output by microwave signal generator 3 RF Set to 5GHz, the initial center wavelength f0 will be achieved through electro-optic modulation as follows: Figure 2 When a small number of comb teeth are initially generated as shown in (c), that is, when the initial comb tooth sidebands of the first target electro-optic frequency comb are generated, two relatively strong electro-optic comb teeth can be observed on the spectrometer 10, with their frequency wavelengths located at f0+f RF and f0-f RF At that point, the initial center wavelength f0 is suppressed.

[0068] B. Based on the state of the second target electro-optic frequency comb, adjust the operating voltage V of DC power supply 4. DC Set to 0 (even-order modulation mode, the upper and lower arms of the electro-optic modulator will be in phase with a phase difference of 0, and the initial center carrier frequency is preserved), and the microwave drive signal voltage V output by microwave signal generator 3 is... RF Set to V π =4.5V, the microwave drive signal frequency f output by microwave signal generator 3 RF Set to 5GHz, the initial center wavelength f0 will be achieved through electro-optic modulation as follows: Figure 2 As shown in (e), a small number of comb teeth are initially generated, that is, the initial comb tooth sidebands of the second target electro-optic frequency comb are generated. Then, three relatively strong electro-optic comb teeth can be observed on the spectrometer 10, with their frequency wavelengths located at f0, f0+2f, and f0, respectively. RF and f0-2f RF Place.

[0069] C. Based on the state of the third target electro-optic frequency comb, adjust the operating voltage V of DC power supply 4. DC Set to V π / 2 (orthogonal modulation mode, the upper and lower arms of the electro-optic modulator will be in an orthogonal state with a phase difference of π / 2, and the initial center carrier frequency and all sidebands are preserved); the microwave drive signal voltage V output by microwave signal generator 3. RF Set to 0.58V π ~0.76V π The values ​​between (voltage values ​​vary depending on the equipment model and parameters used in each embodiment); the microwave drive signal frequency f output by microwave signal generator 3. RF When set to 5 GHz, five strong electro-optic combs can be observed on the spectrometer 10, with frequencies and wavelengths located at f0, f0±f, and f0±f, respectively. RF and f0±2f RF Place.

[0070] Among them, V πThis is the actual half-wave voltage of the mid-infrared electro-optic modulator 2, typically 1.5V-5V, which can be determined based on the equipment model and parameters used in the embodiment.

[0071] Step 4: Adjust the ring cavity control unit to change the overall cavity length and resonant mode of the ring cavity until an automatic cascade generation process of optical frequency sidebands is established within the ring cavity. At this point, the target electro-optic frequency comb has been stably output, completing the generation of the mid-infrared electro-optic frequency comb. Specifically:

[0072] Adjusting the fiber delay line 9 to change the overall cavity length and resonant mode of the ring cavity until the frequency comb spectrum observed on the spectrometer 10 reaches its widest state indicates that the cavity length of the ring cavity is now in harmony with the microwave drive signal frequency f. RF To ensure a strict integer multiple relationship, the ring cavity established an automatic cascade generation process for the optical frequency sidebands through resonance enhancement, realizing the stable output of the electro-optic frequency comb and completing the generation of the mid-infrared electro-optic frequency comb.

[0073] like Figure 3 As shown, when step 3 is just completed, since the cavity length of the annular cavity is initially a random number and is related to the microwave drive signal frequency f... RF The initial comb-tooth sidebands are not integer multiples of each other, and their positions do not coincide with the longitudinal modes supported by the ring cavity. Therefore, cyclic resonance and power enhancement cannot be obtained in the ring cavity. By implementing step 4, adjusting the fiber delay line 9 can change the ring cavity length, thereby tuning the resonant mode distribution. When the ring cavity length is related to the microwave drive signal frequency f... RF When the relationship is a strict integer multiple (e.g., f) RF The frequency is 5.0 GHz, and the finely tuned ring cavity length corresponds to a repetition frequency of 100.0 MHz. The initial comb sidebands will undergo a cyclic process of power amplification, electro-optic modulation, re-amplification, and re-modulation by the mid-infrared fiber amplifier 1. Each newly generated comb sideband can become the initial seed signal for the next cascade process, thereby achieving resonant enhancement and cyclic amplification, ultimately forming a stable output of a broadband mid-infrared electro-optic frequency comb. The comb tooth spacing is determined by the microwave drive signal frequency f. RF The operating mode of the mid-infrared electro-optic modulator 2 is determined by this.

[0074] like Figure 2 As shown in (d), the initial comb edge band generated after step 3A consists of two electro-optic comb teeth (f0±f). RF Therefore, the final electro-optic frequency comb will exhibit a bimodal structure, and the spectral bandwidth and the number of comb teeth will be significantly broadened;

[0075] like Figure 2 As shown in (f), the initial comb edge band generated after step 3B consists of 3 electro-optic comb teeth (f0 and f0±2f). RFTherefore, the final electro-optic frequency comb will exhibit a single-peak structure centered at f0, with its intensity decreasing towards both sides.

[0076] like Figure 4 and Figure 5 As shown, in both odd-order and even-order modulation modes, the initial center wavelength f0 generated in this embodiment is 2000nm, and the frequency interval of the electro-optic comb that can be generated is 2f. RF (i.e., 10GHz), with the number of lines reaching 23 and 30 respectively, and because the initial center carrier frequency is suppressed in odd-order mode, the overall envelope is flatter. Furthermore, by flexibly changing V... DC V RF f RF With these settings, electro-optic frequency combs with different spectral envelope waveforms, comb frequency intervals, and relative comb intensities can be achieved. The output optical power of this system after 1:9 beam splitting is 4.5mW, and its optical conversion efficiency reaches 20% after compensation for device insertion and coupling losses in the ring optical path.

[0077] This invention replaces the high-performance, narrow-linewidth pump light source used in other solutions with a mature and inexpensive mid-infrared fiber amplifier. By controlling the driving mode of the mid-infrared electro-optic modulator and adopting a ring optical path (i.e., ring cavity) architecture, it achieves automatic initial wavelength selection and controlled generation of sidebands at specific frequencies. Furthermore, it cleverly utilizes resonance enhancement to achieve cascaded excitation of the electro-optic comb teeth and synchronous cyclic amplification. The resulting mid-infrared electro-optic frequency comb has advantages such as tunable spectrum, wide coverage, high repetition frequency, multiple usable carrier frequencies, and high output power and energy efficiency. This invention not only solves the problems faced by other methods, such as the difficulty in obtaining extremely narrow-linewidth mid-infrared light sources, the difficulty in locking pump and resonance synchronization, the complexity of the control system, the inability to tune the repetition frequency, and the low power of the comb teeth making subsequent amplification difficult, but also features a compact structure, simple operation, and supports a wide range of parameter tuning for different application scenarios, demonstrating significant practical value.

[0078] 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 high-power tunable mid-infrared electro-optic frequency comb generation system, characterized in that: It includes a pumping unit, an electro-optic modulation unit, a beam splitting unit, a ring cavity control unit, and a status monitoring unit; The output end of the pump unit is connected to the input end of the electro-optic modulation unit to generate pump light and inject it into the electro-optic modulation unit. The output of the electro-optic modulation unit is connected to the input of the beam splitter unit, and is used to electro-optically modulate the received pump light. The beam splitting unit is used to split the modulated beam into a first beam and a second beam. The ring cavity control unit is disposed in the optical path of the first beam, and its output end is connected to the input end of the pump unit, thereby forming a ring cavity between the pump unit, the electro-optic modulation unit, the beam splitting unit and the ring cavity control unit; the ring cavity control unit is used to control the propagation direction and delay phase of the first beam and adjust the polarization state of the first beam. The status monitoring unit is set in the optical path of the second beam to monitor the spectral characteristics of the second beam and provide a basis for the regulation of the ring cavity control unit.

2. The high-power tunable mid-infrared electro-optic frequency comb generation system according to claim 1, characterized in that: The pumping unit includes a mid-infrared fiber amplifier (1). The input end of the mid-infrared fiber amplifier (1) is optically connected to the output end of the ring cavity control unit, and its output end is optically connected to the input end of the electro-optic modulation unit.

3. The high-power tunable mid-infrared electro-optic frequency comb generation system according to claim 2, characterized in that: The electro-optic modulation unit includes a mid-infrared electro-optic modulator (2), a microwave signal generator (3), a DC power supply (4), and a radio frequency biaser (5). The optical input end of the mid-infrared electro-optic modulator (2) is connected to the output end of the mid-infrared fiber amplifier (1) by optical fiber, its optical output end is connected to the input end of the beam splitter by optical fiber, and its electrical input end is connected to the output end of the radio frequency biaser (5). The output terminal of the microwave signal generator (3) is electrically connected to the radio frequency input terminal of the radio frequency bias unit (5); The output terminal of the DC power supply (4) is electrically connected to the DC input terminal of the radio frequency biaser (5).

4. The high-power tunable mid-infrared electro-optic frequency comb generation system according to claim 3, characterized in that: The beam splitting unit includes an optical fiber beam splitter (6). The input end of the fiber optic beam splitter (6) is optically connected to the output end of the mid-infrared electro-optic modulator (2), its first output end is optically connected to the input end of the ring cavity control unit, and its second output end is optically connected to the input end of the status monitoring unit.

5. The high-power tunable mid-infrared electro-optic frequency comb generation system according to claim 4, characterized in that: The annular cavity control unit includes a polarization controller (7), an isolator (8), and an optical fiber delay line (9) connected sequentially along the direction of the first beam. The input end of the polarization controller (7) is optically connected to the first output end of the fiber optic beam splitter (6); The output end of the fiber delay line (9) is optically connected to the input end of the mid-infrared fiber amplifier (1).

6. The high-power tunable mid-infrared electro-optic frequency comb generation system according to claim 5, characterized in that: The status monitoring unit includes a spectrometer (10); The spectrometer (10) is optically connected to the second output end of the optical fiber beam splitter (6).

7. A method for generating a high-power tunable mid-infrared electro-optic frequency comb, employing the high-power tunable mid-infrared electro-optic frequency comb generation system as described in any one of claims 1-6, characterized in that, Includes the following steps: Step 1: Start the pump unit and electro-optic modulation unit. The pump unit emits spontaneous emission light, which circulates within the annular cavity. Step 2: Adjust the ring cavity control unit so that the spontaneous emission light oscillates in the ring cavity until the state monitoring unit can detect the initial laser being excited in the ring cavity. Then the output beam of the pump unit is the pump light. Step 3: Based on the state of the target electro-optic frequency comb, the pump light is electro-optically modulated by the electro-optic modulation unit until the state monitoring unit can detect the generation of the initial comb tooth sideband of the target electro-optic frequency comb. Step 4: Adjust the ring cavity control unit to change the overall cavity length and resonant mode of the ring cavity until the automatic cascading generation process of optical frequency sidebands is established in the ring cavity. Then the target electro-optic frequency comb has been stably output, and the generation of the mid-infrared electro-optic frequency comb is completed.

8. The method for generating a high-power tunable mid-infrared electro-optic frequency comb according to claim 7, characterized in that: Step 1 specifically involves turning on the mid-infrared fiber amplifier (1) and the mid-infrared electro-optic modulator (2), and turning off the microwave signal generator (3) and the DC power supply (4). The mid-infrared fiber amplifier (1) emits spontaneously radiated light, which circulates within the ring cavity.

9. The method for generating a high-power tunable mid-infrared electro-optic frequency comb according to claim 8, characterized in that: Step 2 specifically involves adjusting the polarization controller (7) to change the polarization state of the spontaneously emitted light, causing the spontaneously emitted light to oscillate in the ring cavity until a laser wavelength can be observed on the spectrometer (10) and the optical power reaches its maximum value, indicating that the initial laser is excited in the ring cavity. At this time, the output beam of the mid-infrared fiber amplifier (1) is the pump light.

10. The method for generating a high-power tunable mid-infrared electro-optic frequency comb according to claim 9, characterized in that: Step 3 specifically involves turning on the microwave signal generator (3) and the DC power supply (4), and adjusting the microwave drive signal voltage output by the microwave signal generator (3) and the DC bias signal voltage of the DC power supply (4) according to the state of the target electro-optic frequency comb, until the initial comb tooth sideband of the target electro-optic frequency comb can be observed on the spectrometer (10). Step 4 specifically involves adjusting the fiber delay line (9) to change the overall cavity length and resonant mode of the ring cavity until the frequency comb spectrum observed on the spectrometer (10) reaches its widest state. At this time, the cavity length of the ring cavity and the frequency of the microwave driving signal are integer multiples of each other. An automatic cascade generation process of optical frequency sidebands is established in the ring cavity, and the target electro-optic frequency comb has been stably output, thus completing the generation of the mid-infrared electro-optic frequency comb.

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