Intermediate infrared laser generation system based on dispersion regulation and control soliton group pulse

Abstract

A mid-infrared laser generating system based on dispersion regulation and control soliton group pulses can obtain high-power, high-efficiency and high-proportion mid-infrared laser output, and has the advantages of being all-fiber, compact in structure and high in mid-infrared rear spectrum power proportion. The pulse fiber laser generates nanosecond pulse laser in a 1.5-micron wave band; the optical fiber pulse stretcher is a single-mode quartz optical fiber, the nanosecond pulse is split into a plurality of ultrafast soliton pulses through a nonlinear effect, and spectral energy conversion from 1.5 microns to 2.4 microns is carried out; the fiber laser amplifier further improves the output power of the broadened pulse laser, expands the spectrum to a 2.7-micron wave band, and improves the pulse energy after the 2.3-micron wave band; the optical fiber mode field adapter efficiently couples the pulse generated in the optical fiber laser amplifier into the nonlinear optical fiber; the nonlinear optical fiber expands the laser to a mid-infrared 3-5 micron wave band, and mid-infrared laser output with high power, high efficiency and high proportion is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of mid-infrared lasers, and in particular to a mid-infrared laser generation system based on dispersion-controlled soliton group pulses. Background Art

[0002] The mid-infrared 3-5 micron band covers the high-transmittance atmospheric window, covers a variety of molecular characteristic absorption spectra, and is also a common response spectrum band for various detectors in photoelectric countermeasures. Therefore, lasers in this band have very wide applications in basic scientific research, biomedicine, molecular spectroscopy, photoelectric countermeasures and other fields. Supercontinuum spectrum is a phenomenon in which the pulse spectrum is greatly broadened due to the nonlinear effects such as self-phase modulation, modulation instability, cross-phase modulation, four-wave mixing, stimulated Raman scattering and soliton splitting, as well as group velocity dispersion when strong laser pulses are transmitted in nonlinear optical media. Fiber-based supercontinuum light sources have the characteristics of high efficiency, high beam quality, compact structure, high reliability, and high stability. Especially after the emergence of highly nonlinear mid-infrared soft glass fibers (such as fluorozirconate fibers, indium fluoride fibers, tellurite fibers, and chalcogenide fibers), supercontinuum light sources generated based on mid-infrared fibers have become the main direction of broadband light source research. However, due to the different doping materials of soft glass fibers, the material loss of different types of soft glass fibers in different mid-infrared wavelength regions increases sharply, resulting in a narrow spectral range and low long-wave spectral component of the obtained mid-infrared supercontinuum light source. In addition, the traditional scheme of directly generating mid-infrared lasers based on rare earth ion doping gain has problems such as low conversion efficiency, low output power, poor environmental adaptability, and complex structure. Therefore, further research on the efficient generation of mid-infrared lasers is of great significance. Summary of the invention

[0003] In order to overcome the defects of the prior art, the technical problem to be solved by the present invention is to provide a mid-infrared laser generation system based on dispersion-controlled soliton group pulses, which can obtain high-power, high-efficiency, and high-proportion mid-infrared laser output, and has the advantages of all-fiber, compact structure, and high power proportion in the mid-infrared rear spectral band.

[0004] The technical solution of the present invention is: the mid-infrared laser generation system based on dispersion-controlled soliton group pulses comprises a pulse fiber laser (1), a fiber pulse stretcher (2), a fiber laser amplifier (3), a fiber mode field adapter (4), and a nonlinear fiber (5) which are connected in sequence, each part is cooled by water or a semiconductor refrigerator, and connected by fiber fusion splicing;

[0005] The pulse fiber laser generates nanosecond pulse laser in the 1.5 micron band;

[0006] The fiber pulse stretcher is a single-mode quartz fiber located between the pulse fiber laser and the fiber laser amplifier. It splits the nanosecond pulse into multiple ultrafast soliton pulses through nonlinear effects and performs spectrum energy conversion from 1.5 microns to 2.4 microns for the nanosecond pulse laser. The fiber laser amplifier further increases the output power of the pulsed laser after stretching and expands the spectrum to the 2.7 micron band, while increasing the pulse energy after the 2.3 micron band.

[0007] The fiber mode field adapter efficiently couples the pulses generated in the fiber laser amplifier into the nonlinear fiber;

[0008] The nonlinear optical fiber expands the laser to the mid-infrared 3-5 micron band, obtaining high-power, high-efficiency, and high-ratio mid-infrared laser output.

[0009] In terms of engineering application, the present invention realizes the all-fiber structure of the system by optical fiber fusion splicing, and each part adopts water cooling or semiconductor refrigerator device, so that the mid-infrared wide-spectrum fiber laser system has the advantages of compact structure, high integration, good stability, high conversion efficiency, insensitive to interference factors such as vibration in the working environment, greatly improving the stability and reliability of laser operation, and suitable for industrial mass production. In terms of technical advantages, the dispersion control mechanism of high-peak power soliton group pulses is used to improve the pulse energy of the rear spectrum of the spectrum, effectively increasing the power proportion of the rear band of the mid-infrared spectrum; finally, the high-power wide-spectrum laser output with enhanced mid-infrared rear spectrum is obtained, which is beneficial to the application in gas detection, biomedicine and military fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a structural schematic diagram of a mid-infrared laser generation system based on dispersion-controlled soliton group pulses according to the present invention. DETAILED DESCRIPTION

[0011] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0012] It should be noted that the term "comprises" and any variations in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, apparatus, product or equipment that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products or equipment.

[0013] like Figure 1 As shown, the mid-infrared laser generation system based on dispersion-controlled soliton group pulses includes a pulse fiber laser 1, a fiber pulse stretcher 2, a fiber laser amplifier 3, a fiber mode field adapter 4, and a nonlinear fiber 5 connected in sequence, each part is cooled by water or a semiconductor refrigerator (TEC, Thermo Electric Cooler), and connected by fiber fusion splicing;

[0014] The pulse fiber laser generates nanosecond pulse laser in the 1.5 micron band;

[0015] The fiber pulse stretcher is a single-mode quartz fiber located between the pulse fiber laser and the fiber laser amplifier. It splits the nanosecond pulse into multiple ultrafast soliton pulses through nonlinear effects and performs spectrum energy conversion from 1.5 microns to 2.4 microns for the nanosecond pulse laser. The fiber laser amplifier further increases the output power of the pulsed laser after stretching and expands the spectrum to the 2.7 micron band, while increasing the pulse energy after the 2.3 micron band.

[0016] The fiber mode field adapter efficiently couples the pulses generated in the fiber laser amplifier into the nonlinear fiber;

[0017] The nonlinear optical fiber expands the laser to the mid-infrared 3-5 micron band, obtaining high-power, high-efficiency, and high-ratio mid-infrared laser output.

[0018] In terms of engineering application, the present invention realizes the all-fiber structure of the system by optical fiber fusion splicing, and each part adopts water cooling or semiconductor refrigerator device, so that the mid-infrared wide-spectrum fiber laser system has the advantages of compact structure, high integration, good stability, high conversion efficiency, insensitive to interference factors such as vibration in the working environment, greatly improving the stability and reliability of laser operation, and suitable for industrial mass production. In terms of technical advantages, the dispersion control mechanism of high-peak power soliton group pulses is used to improve the pulse energy of the rear spectrum of the spectrum, effectively increasing the power proportion of the rear band of the mid-infrared spectrum; finally, the high-power wide-spectrum laser output with enhanced mid-infrared rear spectrum is obtained, which is beneficial to the application in gas detection, biomedicine and military fields.

[0019] Preferably, the pulse fiber laser comprises: a 1550nm distributed feedback semiconductor laser 1-1, a wavelength division multiplexer 1-2, a 976nm single-mode semiconductor laser 1-3, a single-mode erbium-doped fiber 1-4, and a fiber isolator 1-5, which are sequentially connected via single-mode optical fiber to form a linear cavity structure; the above devices are all connected by optical fiber fusion splicing.

[0020] Preferably, the 976nm single-mode semiconductor laser provides pump light, which is input through a wavelength division multiplexer and pumps the single-mode erbium-doped optical fiber, wherein the 1550nm distributed feedback semiconductor laser is used as a seed source, and is modulated through a control circuit to generate a 1.5-micron nanosecond pulse seed laser, which is initially power amplified in the single-mode erbium-doped optical fiber, and then the generated 1.5-micron nanosecond pulse laser is transmitted to the optical fiber pulse stretcher through an optical fiber isolator.

[0021] Preferably, the fiber laser amplifier comprises: a fiber combiner 4-1, a 793nm semiconductor laser 4-2, a large mode area double-clad thulium-doped optical fiber 4-3 and a fiber isolator 4-4, the 793nm semiconductor laser provides pump light for the large mode area double-clad thulium-doped optical fiber through the fiber combiner, and the fiber isolator isolates the feedback light formed by the subsequent optical path; the above devices are all connected by fiber fusion splicing.

[0022] Preferably, the fiber mode field adapter connects the large mode field area fiber and the single mode fiber to match the nonlinear fiber; the above devices are all connected by fiber fusion splicing.

[0023] Preferably, the nonlinear optical fiber utilizes a dispersion control mechanism to expand the spectrum generated by the fiber laser amplifier to the 5-micron band, thereby achieving high-power, high-efficiency, and high-ratio mid-infrared laser output. The nonlinear optical fiber is a germanate optical fiber, a fluoride optical fiber, a tellurite optical fiber, or a chalcogenide optical fiber designed with longitudinal dispersion. The longitudinal dispersion design of the nonlinear optical fiber includes three parts: a dispersion flat region, which is used for the soliton self-frequency shift process; a dispersion transition region, which is used to accumulate the number of soliton group pulses; and a dispersion steep increase region, which is used to enhance the soliton group pulse intensity. The nonlinear optical fiber and the optical fiber mode field adapter are connected by optical fiber fusion splicing, and the optical fiber output end of the nonlinear optical fiber is cut at a 15° angle to prevent Fresnel reflection.

[0024] Preferably, the 1550nm distributed feedback semiconductor laser of the pulse fiber laser is controlled by a driving circuit and a computer, and is adjusted according to actual conditions and the pulse characteristics of the seed laser and the pump power.

[0025] The present invention is described in more detail below.

[0026] Figure 1A schematic diagram of the structure of a high-efficiency mid-infrared laser generation system based on dispersion-controlled soliton group pulses based on dispersion control technology provided by the present invention. A high-efficiency mid-infrared laser generation system based on dispersion-controlled soliton group pulses based on dispersion control technology comprises a pulse fiber laser 1, a fiber pulse stretcher 2, a fiber laser amplifier 3, a fiber mode field adapter 4 and a nonlinear fiber 5 in sequence;

[0027] The pulse fiber laser generates nanosecond pulse laser in the 1.5 micron band;

[0028] The fiber pulse stretcher performs spectral energy conversion from 1.5 microns to 2.4 microns for nanosecond pulse lasers;

[0029] The fiber laser amplifier further improves the output power of the broadened pulse laser and expands the spectrum to the 2.7 micron band, while improving the pulse energy after the 2.3 micron band;

[0030] The fiber mode field adapter efficiently couples the pulses generated in the fiber laser amplifier into the nonlinear fiber;

[0031] The nonlinear optical fiber expands the laser to the mid-infrared 3-5 micron band, obtaining high-power, high-efficiency, and high-ratio mid-infrared laser output.

[0032] The pulse fiber laser comprises: a 1550nm distributed feedback semiconductor laser 1-1, a wavelength division multiplexer 1-2, a 976nm single-mode semiconductor laser 1-3, a single-mode erbium-doped fiber 1-4, and a fiber isolator 1-5, which are sequentially connected through single-mode optical fibers to form a linear cavity structure; the above devices are all connected by optical fiber fusion. The 976nm single-mode semiconductor laser provides pump light, which is input through the wavelength division multiplexer and pumps the single-mode erbium-doped optical fiber, wherein the 1550nm distributed feedback semiconductor laser is used as a seed source, and is modulated by a control circuit to generate a 1.5-micron nanosecond pulse seed laser, which is initially power amplified in the single-mode erbium-doped optical fiber, and then the generated 1.5-micron nanosecond pulse laser is transmitted to the fiber pulse stretcher through the fiber isolator.

[0033] It can be seen that the connection relationship and working principle of the various optical components of the pulse fiber laser 1 are as follows: a 1550nm distributed feedback semiconductor laser 1-1, a wavelength division multiplexer 1-2, and a 976nm single-mode semiconductor laser 1-3 connected to the wavelength division multiplexer 1-2 through an optical fiber, a single-mode erbium-doped optical fiber 1-4, and an optical fiber isolator 1-5 are sequentially arranged along the optical path. In the linear cavity, the 976nm single-mode semiconductor laser 1-3 is coupled into the cavity through the wavelength division multiplexer 1-2 by core pumping to pump the single-mode erbium-doped optical fiber 1-4, and the 1550nm distributed feedback semiconductor laser 1-1 plays the role of a seed light source. Through the control circuit, it is modulated to generate a 1.5 micron nanosecond pulse seed laser, and the optical fiber isolator 1-5 plays the role of a pulse fiber laser output. Its packaging method adopts a full-fiber packaging method, and it is feasible in the experiment.

[0034] It should be noted that the 1550nm distributed feedback semiconductor laser of the pulse fiber laser can be controlled by a drive circuit and a computer, and can be adjusted according to actual conditions and the pulse characteristics of the seed laser, pump power, etc.

[0035] The fiber pulse stretcher 2 is arranged between the pulse fiber laser 1 and the fiber laser amplifier 3. The fiber pulse stretcher 2 can split the nanosecond pulse into multiple ultrafast soliton pulses through nonlinear effects in the 1.5 micron to 2.4 micron band, and perform frequency conversion to long waves to broaden the pulse spectrum width, thereby providing abundant soliton group pulses for the next-stage fiber laser amplifier, further improving the pulse power and spectrum width.

[0036] The fiber laser amplifier comprises: a fiber combiner 4-1, a 793nm semiconductor laser 4-2, a large mode area double-clad thulium-doped optical fiber 4-3 and a fiber isolator 4-4. The 793nm semiconductor laser provides pump light for the large mode area double-clad thulium-doped optical fiber through the fiber combiner, and the fiber isolator isolates the feedback light formed by the subsequent optical path. The above devices are all connected by fiber fusion splicing.

[0037] Therefore, the working principle of the pump light source of an efficient mid-infrared laser generation system based on dispersion-controlled soliton group pulses according to the present invention based on dispersion control technology is as follows: a pulse fiber laser 1 is used to generate a stable nanosecond pulse laser, and a fiber pulse stretcher 2 splits the nanosecond pulse into multiple ultrafast soliton pulses through a nonlinear effect, and performs frequency conversion to long waves, and outputs the multiple ultrafast soliton pulse lasers after the splitting to a fiber laser amplifier 3. The fiber laser amplifier 3 is used to amplify the laser after pulse spectrum broadening and enhance the laser pulse energy after 2.3 microns, and outputs a high-power laser with a long-wave spectrum edge covering the 2.7-micron band after the fiber laser amplifier 3, which serves as a pump light source for the nonlinear fiber 5.

[0038] The fiber mode field adapter 4 efficiently couples the pulses generated in the fiber laser amplifier into the nonlinear fiber;

[0039] The nonlinear optical fiber 5 is a mid-infrared optical fiber with a designed dispersion curve, characterized by being relatively flat in the near-zero dispersion region, increasing the absolute value of dispersion with increasing wavelength, and having a sharp increase in the slope of the dispersion curve in the 4-micron region, and having a wide infrared transmission window. The nonlinear optical fiber 6 is a germanate optical fiber, a fluoride optical fiber or a tellurite optical fiber. Under the action of nonlinear effects such as self-phase modulation, modulation instability, and soliton self-frequency shift, the nonlinear optical fiber 5 expands the spectrum generated by the fiber laser amplifier 3 to the 5-micron band, and obtains a high-power, high-efficiency, and high-ratio mid-infrared laser output. The nonlinear optical fiber 5 and the optical fiber mode field adapter 4 are connected by optical fiber fusion splicing. The optical fiber output end of the nonlinear optical fiber 5 is cut at a 15° angle to prevent Fresnel reflection.

[0040] Therefore, the working principle of the spectrum broadening part of the high-efficiency mid-infrared laser generation system based on dispersion-controlled soliton group pulses based on the dispersion-controlled technology of the present invention is:

[0041] Dispersion control is reflected in two places: one is that a 1.5-micron pulsed fiber laser is used instead of a conventional 2-micron thulium-doped fiber laser. When the split soliton group pulse is used as the seed laser of the fiber laser amplifier, the spectrum of the output supercontinuum laser is flatter. The main reason is that the soliton group pulse actually contains a large number of soliton pulses with high peak power of different wavelengths. When they evolve inside the fiber laser amplifier, they can obtain different gain sizes and undergo different degrees of nonlinear evolution. They have an averaging effect on the supercontinuum spectrum, which is beneficial to the fiber laser amplifier to increase the pulse energy after the 2.3-micron band, so that the pump laser first obtains pulses with high energy proportion in the long wave, which is beneficial to the subsequent spectrum expansion and the increase of power proportion in the later spectrum; the other is the nonlinear fiber part, which can obtain high-power, high-efficiency, and high-proportion mid-infrared laser output due to the dispersion control mechanism of high-peak power soliton group pulses. The dispersion curve of nonlinear fiber can be divided into three stages. First, in the dispersion platform region, the pulse output by the fiber laser amplifier propagates to the near-zero dispersion region of the nonlinear fiber. The dispersion curve is relatively flat, and the spectrum broadening is mainly dominated by soliton splitting and Raman soliton self-frequency shift. In the dispersion transition region, as the absolute value of the fiber dispersion gradually increases, the peak power of the soliton pulse with a longer wavelength decreases due to dispersion, and the frequency shift speed slows down, causing the soliton pulse to gradually accumulate at the long wavelength. In the dispersion steep increase region, the slope of the dispersion curve increases sharply in the 5-micron region, further weakening the redshift of the soliton pulse, causing the overall spectrum broadening of the pulse to stagnate near 5 microns, forming a long-wave boundary. At the same time, the short-wave pulse component continues to redshift, while the long-wave part stagnates, realizing the transfer of energy from the short-wave to the long-wave region, thereby enhancing the mid-infrared band laser, and finally obtaining a high-power, high-efficiency, and high-proportion mid-infrared laser in the 3-5μm band.

[0042] In summary, the present invention utilizes dispersion control technology to generate high peak power soliton group pulses as pump light by soliton pulse splitting, and uses different degrees of nonlinear effects in different regions of the mid-infrared nonlinear fiber dispersion curve to increase the energy of the long-wave soliton pulses in the spectrum, so that the short-wave soliton pulses are frequency-shifted and the long-wave part is stagnant, and a high-power, high-efficiency, high-proportion mid-infrared laser in the 3-5μm band can be obtained. The present invention adopts an all-fiber structure, which makes the laser have the advantages of compact structure, high integration, good stability and high conversion efficiency.

[0043] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the protection scope of the technical solution of the present invention.

Claims

1. A mid-infrared laser generation system based on dispersion-controlled soliton group pulses, characterized in that: It includes a pulse fiber laser (1), a fiber pulse stretcher (2), a fiber laser amplifier (3), a fiber mode field adapter (4), and a nonlinear fiber (5) which are connected in sequence, and each part is connected by water cooling or a semiconductor refrigerator and fiber fusion splicing. The pulse fiber laser generates nanosecond pulse laser in the 1.5 micron band; The fiber pulse stretcher is a single-mode quartz fiber arranged between the pulse fiber laser and the fiber laser amplifier. It splits the nanosecond pulse into multiple ultrafast soliton pulses through nonlinear effects and performs spectrum energy conversion from 1.5 microns to 2.4 microns for the nanosecond pulse laser. The fiber laser amplifier further improves the output power of the pulsed laser after stretching and expands the spectrum to the 2.7 micron band, while improving the pulse energy after the 2.3 micron band. The fiber mode field adapter efficiently couples the pulses generated in the fiber laser amplifier into the nonlinear fiber. The nonlinear optical fiber expands the laser to the mid-infrared 3-5 micron band, obtaining high-power, high-efficiency, and high-ratio mid-infrared laser output.

2. The mid-infrared laser generation system based on dispersion-controlled soliton group pulses according to claim 1, characterized in that: The pulse fiber laser comprises: a 1550nm distributed feedback semiconductor laser (1-1), a wavelength division multiplexer (1-2), a 976nm single-mode semiconductor laser (1-3), a single-mode erbium-doped optical fiber (1-4), and an optical fiber isolator (1-5), which are sequentially connected via single-mode optical fibers to form a linear cavity structure; the above devices are all connected by optical fiber fusion splicing.

3. The mid-infrared laser generation system based on dispersion-controlled soliton group pulses according to claim 2, characterized in that: The 976nm single-mode semiconductor laser provides pump light, which is input through a wavelength division multiplexer and pumps the single-mode erbium-doped optical fiber. The 1550nm distributed feedback semiconductor laser is used as a seed source. Through a control circuit, it is modulated to generate a 1.5-micron nanosecond pulse seed laser, which is initially power amplified in the single-mode erbium-doped optical fiber, and then the generated 1.5-micron nanosecond pulse laser is transmitted to the optical fiber pulse stretcher through an optical fiber isolator.

4. The mid-infrared laser generation system based on dispersion-controlled soliton group pulses according to claim 3 is characterized in that: The fiber laser amplifier comprises: a fiber combiner (4-1), a 793nm semiconductor laser (4-2), a large mode area double-clad thulium-doped optical fiber (4-3) and a fiber isolator (4-4); the 793nm semiconductor laser provides pump light for the large mode area double-clad thulium-doped optical fiber through the fiber combiner, and the fiber isolator isolates feedback light formed by a subsequent optical path; the above devices are all connected by fiber fusion splicing.

5. The mid-infrared laser generation system based on dispersion-controlled soliton group pulses according to claim 4, characterized in that: The optical fiber mode field adapter connects the large mode field area optical fiber and the single mode optical fiber to match the nonlinear optical fiber; the above devices are all connected by optical fiber fusion splicing.

6. The mid-infrared laser generation system based on dispersion-controlled soliton group pulses according to claim 5, characterized in that: The nonlinear optical fiber uses a dispersion control mechanism to expand the spectrum generated by the fiber laser amplifier to the 5-micron band, achieving high-power, high-efficiency, and high-ratio mid-infrared laser output. The nonlinear optical fiber is a germanate optical fiber, a fluoride optical fiber, a tellurite optical fiber, or a chalcogenide optical fiber designed with longitudinal dispersion. The longitudinal dispersion design of the nonlinear optical fiber includes three parts: a dispersion flat zone, which is used for the soliton self-frequency shift process; a dispersion transition zone, which is used to accumulate the number of soliton group pulses; The dispersion steep increase region is used to enhance the intensity of soliton group pulses; The nonlinear optical fiber and the optical fiber mode field adapter are connected by optical fiber fusion splicing, and the optical fiber output end of the nonlinear optical fiber is cut at a 15° angle to prevent Fresnel reflection.

7. The mid-infrared laser generation system based on dispersion-controlled soliton group pulses according to claim 6, characterized in that: The 1550nm distributed feedback semiconductor laser of the pulse fiber laser is controlled by a driving circuit and a computer, and is adjusted according to actual conditions, the pulse characteristics of the seed laser, and the pump power.

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