Mid-infrared laser generation system based on dispersion-managed soliton bunch pulses

Abstract

A mid-infrared laser generation system based on dispersion-managed soliton bunch pulses. The system can achieve high-power, high-efficiency and high-proportion mid-infrared laser output, and has the advantages of an all-fiber configuration, a compact structure and a high power proportion in a longer-wavelength region of a mid-infrared spectrum. A pulsed fiber laser device generates a nanosecond pulse laser in a 1.5-micron band. A fiber pulse stretcher is made of a single-mode silica fiber, splits nanosecond pulses into a plurality of ultrafast soliton pulses by means of a nonlinear effect, and performs spectral energy conversion from 1.5 microns to 2.4 microns. A fiber laser amplifier further increases the output power of a stretched pulse laser and extends a spectrum to a 2.7-micron band, and also increases pulse energy beyond a 2.3-micron band. A fiber mode field adapter efficiently couples into a nonlinear fiber pulses generated in the fiber laser amplifier. The nonlinear fiber extends a laser to a mid-infrared 3-5-micron band, thereby achieving high-power, high-efficiency and high-proportion mid-infrared laser output.

Description

A mid-infrared laser generation system based on dispersion-controlled soliton group pulses Technical Field

[0001] This invention relates to the technical field of mid-infrared lasers, and more particularly to a mid-infrared laser generation system based on dispersion-controlled soliton group pulses. Background Technology

[0002] The mid-infrared 3–5 micrometer band covers a high-transmittance atmospheric window, encompassing the absorption spectra of various molecules. It is also a common response spectrum for various detectors in optoelectronic countermeasures. Therefore, lasers in this band have wide applications in basic scientific research, biomedicine, molecular spectroscopy, and optoelectronic countermeasures. Supercontinuum spectroscopy is a phenomenon where a strong laser pulse propagates through a nonlinear optical medium, resulting in a significant broadening of the pulse spectrum due to 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. Fiber-based supercontinuum light sources possess characteristics such as high efficiency, high beam quality, compact structure, high reliability, and high stability. Especially after the advent of highly nonlinear mid-infrared soft glass fibers (such as fluorozirconate fiber, indium fluoride fiber, tellurate fiber, and chalcogenide fiber), supercontinuum light sources generated from mid-infrared fibers have become a major research direction for broadband light sources. However, due to the different doping materials of soft glass fibers, the material loss of different types of soft glass fibers increases sharply in different mid-infrared wavelength regions, resulting in a narrow spectral range and low long-wavelength spectral content in the obtained mid-infrared supercontinuum light sources. Furthermore, traditional methods for directly generating mid-infrared lasers based on rare-earth ion doping gain suffer from 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] To overcome the shortcomings 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 being all-fiber, compact in structure, and having a high power proportion in the mid-infrared back spectral band.

[0004] The technical solution of the present invention is: This mid-infrared laser generation system based on dispersion-controlled soliton group pulses includes a pulsed 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 cooler and connected by fiber fusion splicing.

[0005] The pulsed fiber laser generates nanosecond pulsed lasers in the 1.5-micrometer band;

[0006] The fiber pulse stretcher is a single-mode silica fiber located between the pulsed fiber laser and the fiber laser amplifier. It splits the nanosecond pulse into multiple ultrafast soliton pulses through nonlinear effects and performs spectral energy conversion of nanosecond pulsed laser from 1.5 micrometers to 2.4 micrometers.

[0007] The fiber laser amplifier further enhances the output power of the broadened pulsed laser and extends the spectrum to the 2.7-micron band, while also increasing the pulse energy after the 2.3-micron band.

[0008] The fiber mode field adapter efficiently couples the pulses generated in the fiber laser amplifier into the nonlinear fiber.

[0009] The nonlinear optical fiber extends the laser to the mid-infrared 3-5 micrometer band, achieving high-power, high-efficiency, and high-proportion mid-infrared laser output.

[0010] In terms of engineering applications, this invention achieves an all-fiber structure through fiber fusion splicing, with each component employing water-cooling or semiconductor cooler devices. This results in a mid-infrared broadband fiber laser system that is compact, highly integrated, stable, and has high conversion efficiency. It is also insensitive to interference factors such as vibration in the working environment, significantly improving the stability and reliability of laser operation, making it suitable for industrial mass production. Regarding technical advantages, the invention utilizes a dispersion control mechanism based on high peak power soliton group pulses to enhance the pulse energy in the back spectral band, effectively increasing the power proportion of the mid-infrared back spectral band. Ultimately, this yields a high-power broadband laser output with enhanced mid-infrared back spectral band, beneficial for applications in gas detection, biomedicine, and military fields. Attached Figure Description

[0011] Figure 1 is a schematic diagram of the mid-infrared laser generation system based on dispersion-controlled soliton group pulses according to the present invention. Detailed Implementation

[0012] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. 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 should fall within the scope of protection of the present invention.

[0013] It should be noted that the term "comprising" and any variations thereof in the specification, claims and accompanying drawings of this invention are intended to cover non-exclusive inclusion. For example, a process, method, apparatus, product or device that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products or devices.

[0014] As shown in Figure 1, this mid-infrared laser generation system based on dispersion-controlled soliton group pulses includes a pulsed 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 thermoelectric cooler (TEC, Thermo Electric Cooler) and connected by fiber fusion splicing.

[0015] The pulsed fiber laser generates nanosecond pulsed lasers in the 1.5-micrometer band;

[0016] The fiber pulse stretcher is a single-mode silica fiber located between the pulsed fiber laser and the fiber laser amplifier. It splits the nanosecond pulse into multiple ultrafast soliton pulses through nonlinear effects and performs spectral energy conversion of nanosecond pulsed laser from 1.5 micrometers to 2.4 micrometers.

[0017] The fiber laser amplifier further enhances the output power of the broadened pulsed laser and extends the spectrum to the 2.7-micron band, while also increasing the pulse energy after the 2.3-micron band.

[0018] The fiber mode field adapter efficiently couples the pulses generated in the fiber laser amplifier into the nonlinear fiber.

[0019] The nonlinear optical fiber extends the laser to the mid-infrared 3-5 micrometer band, achieving high-power, high-efficiency, and high-proportion mid-infrared laser output.

[0020] In terms of engineering applications, this invention achieves an all-fiber structure through fiber fusion splicing, with each component employing water-cooling or semiconductor cooler devices. This results in a mid-infrared broadband fiber laser system that is compact, highly integrated, stable, and has high conversion efficiency. It is also insensitive to interference factors such as vibration in the working environment, significantly improving the stability and reliability of laser operation, making it suitable for industrial mass production. Regarding technical advantages, the invention utilizes a dispersion control mechanism based on high peak power soliton group pulses to enhance the pulse energy in the back spectral band, effectively increasing the power proportion of the mid-infrared back spectral band. Ultimately, this yields a high-power broadband laser output with enhanced mid-infrared back spectral band, beneficial for applications in gas detection, biomedicine, and military fields.

[0021] Preferably, the pulsed fiber laser includes: 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 connected in sequence through single-mode fibers to form a linear cavity structure; all the above devices are connected by fiber fusion splicing.

[0022] 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 fiber. The 1550nm distributed feedback semiconductor laser serves as a seed source. Through a control circuit, a 1.5-micron nanosecond pulse seed laser is generated by modulation. The seed laser undergoes preliminary power amplification in the single-mode erbium-doped fiber and is then transmitted to the fiber pulse stretcher through an optical fiber isolator.

[0023] Preferably, the fiber laser amplifier includes: a fiber combiner 4-1, a 793nm semiconductor laser 4-2, a large mode area double-clad thulium-doped fiber 4-3, and a fiber isolator 4-4. The 793nm semiconductor laser provides pump light to the large mode area double-clad thulium-doped fiber through the fiber combiner, and the fiber isolator isolates the feedback light formed by subsequent optical paths. All the above devices are connected by fiber fusion splicing.

[0024] Preferably, the fiber mode field adapter connects a large mode field area fiber to a single-mode fiber to match the nonlinear fiber; all the above devices are connected by fiber fusion splicing.

[0025] Preferably, the nonlinear optical fiber utilizes a dispersion modulation mechanism to extend 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 fiber, fluoride fiber, tellurate fiber, or chalcogenide fiber with longitudinal dispersion design. The longitudinal dispersion design of the nonlinear optical fiber includes three parts: a dispersion flat region for soliton self-frequency shifting; a dispersion transition region for accumulating soliton group pulses; and a dispersion steepening region for enhancing soliton group pulse intensity. The nonlinear optical fiber and the fiber mode field adapter are connected by fiber fusion splicing. The output end of the nonlinear optical fiber is cut at a 15° angle to prevent Fresnel reflection.

[0026] Preferably, the 1550nm distributed feedback semiconductor laser of the pulsed fiber laser is controlled by a driving circuit and a computer, and is adjusted according to the actual situation, the pulse characteristics of the seed laser, and the pump power.

[0027] The present invention will now be described in more detail.

[0028] Figure 1 is a schematic diagram of the structure of a high-efficiency mid-infrared laser generation system based on dispersion-controlled soliton group pulses provided by the present invention. The high-efficiency mid-infrared laser generation system based on dispersion-controlled soliton group pulses includes, in sequence, a pulsed fiber laser 1, a fiber pulse stretcher 2, a fiber laser amplifier 3, a fiber mode field adapter 4, and a nonlinear fiber 5;

[0029] The pulsed fiber laser generates nanosecond pulsed lasers in the 1.5-micrometer band;

[0030] The fiber pulse stretcher performs spectral energy conversion of nanosecond pulsed laser from 1.5 micrometers to 2.4 micrometers;

[0031] The fiber laser amplifier further enhances the output power of the broadened pulsed laser and extends the spectrum to the 2.7-micron band, while also increasing the pulse energy after the 2.3-micron band.

[0032] The fiber mode field adapter efficiently couples the pulses generated in the fiber laser amplifier into the nonlinear fiber.

[0033] The nonlinear optical fiber extends the laser to the mid-infrared 3-5 micrometer band, achieving high-power, high-efficiency, and high-proportion mid-infrared laser output.

[0034] The pulsed 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 an optical fiber isolator 1-5, which are sequentially connected via single-mode fibers to form a linear cavity structure; all the above devices are connected by fiber fusion splicing. The 976nm single-mode semiconductor laser provides pump light, which is input through the wavelength division multiplexer and pumps the single-mode erbium-doped fiber. The 1550nm distributed feedback semiconductor laser serves as a seed source, and through a control circuit, it is modulated to generate a 1.5-micron nanosecond pulsed seed laser. This seed laser undergoes preliminary power amplification in the single-mode erbium-doped fiber, and then the generated 1.5-micron nanosecond pulsed laser is transmitted to the optical fiber pulse stretcher via the optical fiber isolator.

[0035] Therefore, the connection relationship and working principle of the optical components of the pulsed fiber laser 1 are as follows: A 1550nm distributed feedback semiconductor laser 1-1, a wavelength division multiplexer 1-2, a 976nm single-mode semiconductor laser 1-3 connected to the wavelength division multiplexer 1-2 via optical fiber, a single-mode erbium-doped 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 core-pumped and coupled into the cavity through the wavelength division multiplexer 1-2 to pump the single-mode erbium-doped fiber 1-4. The 1550nm distributed feedback semiconductor laser 1-1 acts as a seed source, generating a 1.5-micron nanosecond pulsed seed laser through modulation via a control circuit. The optical fiber isolator 1-5 serves as the output of the pulsed fiber laser. The laser is packaged using an all-fiber packaging method, which has been experimentally proven feasible.

[0036] It should be noted that the 1550nm distributed feedback semiconductor laser of the pulsed fiber laser can be controlled by the driving circuit and computer, and can be adjusted according to the actual situation and the pulse characteristics of the seed laser, pump power, etc.

[0037] The fiber pulse stretcher 2 is located between the pulsed fiber laser 1 and the fiber laser amplifier 3. In the 1.5-micrometer to 2.4-micrometer wavelength band, the fiber pulse stretcher 2 can split nanosecond pulses into multiple ultrafast soliton pulses through nonlinear effects and undergo frequency conversion to longer wavelengths to broaden the pulse spectral width, thereby providing abundant soliton group pulses for the next stage fiber laser amplifier and further improving pulse power and spectral width.

[0038] The fiber laser amplifier includes: a fiber combiner 4-1, a 793nm semiconductor laser 4-2, a large mode area double-clad thulium-doped fiber 4-3, and a fiber isolator 4-4. The 793nm semiconductor laser provides pump light to the large mode area double-clad thulium-doped fiber through the fiber combiner, and the fiber isolator isolates the feedback light formed by subsequent optical paths. All the above devices are connected by fiber fusion splicing.

[0039] Therefore, the working principle of the pump source of the high-efficiency mid-infrared laser generation system based on dispersion-controlled soliton group pulses of the present invention is as follows: the pulsed fiber laser 1 is used to generate stable nanosecond pulse lasers, the fiber pulse stretcher 2 splits the nanosecond pulses into multiple ultrafast soliton pulses through nonlinear effects and performs frequency conversion to long wavelengths, and outputs the multiple ultrafast soliton pulse lasers after splitting to the fiber laser amplifier 3. The fiber laser amplifier 3 is used to amplify the laser after pulse spectrum stretching and increase the laser pulse energy after 2.3 micrometers. After the fiber laser amplifier 3, a high-power laser with long-wavelength spectral edge covering the 2.7-micrometer band is output, which serves as the pump source of the nonlinear fiber 5.

[0040] The fiber mode field adapter 4 efficiently couples the pulses generated in the fiber laser amplifier into the nonlinear fiber.

[0041] The nonlinear fiber 5 has a designed dispersion curve, characterized by its relatively flat shape in the near-zero dispersion region, an increasing absolute dispersion value with increasing wavelength, a sharply increasing slope in the 4-micrometer region, and a wide infrared transmission window. The nonlinear fiber 6 is a germanate fiber, fluoride fiber, or tellurate fiber. Under the influence of nonlinear effects such as self-phase modulation, modulation instability, and soliton self-frequency shift, the nonlinear fiber 5 extends the spectrum generated by the fiber laser amplifier 3 to the 5-micrometer band, achieving high-power, high-efficiency, and high-proportion mid-infrared laser output. The nonlinear fiber 5 and the fiber mode field adapter 4 are connected by fiber fusion splicing. The output end of the nonlinear fiber 5 is cut at a 15° angle to prevent Fresnel reflection.

[0042] Therefore, the working principle of the spectral broadening portion of the high-efficiency mid-infrared laser generation system based on dispersion-controlled soliton group pulses, according to the present invention, is as follows:

[0043] Dispersion control is manifested in two aspects: First, a 1.5-micron pulsed fiber laser is used instead of a conventional 2-micron thulium-doped fiber laser. When the split soliton group pulses are used as the seed lasers for the fiber laser amplifier, the output supercontinuum laser spectrum is flatter. The main reason is that the soliton group pulses actually contain a large number of soliton pulses with high peak power at different wavelengths. As these pulses evolve within the fiber laser amplifier, they acquire different gain values ​​and undergo varying degrees of nonlinear evolution, which has an averaging effect on the supercontinuum spectrum. This is beneficial for increasing the pulse energy beyond the 2.3-micron band in the fiber laser amplifier, allowing the pump laser to initially obtain pulses with a high energy proportion at longer wavelengths, which is beneficial for subsequent spectral expansion and increased power proportion in later spectral bands. The second aspect is the nonlinear fiber section. The ability to obtain high-power, high-efficiency, and high-proportion mid-infrared laser output is attributed to the dispersion control mechanism of the high-peak-power soliton group pulses. The dispersion curve of the nonlinear fiber can be divided into three stages. First, in the dispersion plateau region, the pulse output from the fiber laser amplifier propagates into the near-zero dispersion region of the nonlinear fiber, where the dispersion curve is relatively flat, and spectral broadening is mainly dominated by soliton splitting and Raman soliton self-frequency shift. In the dispersion transition region, as the absolute value of fiber dispersion gradually increases, the peak power of longer-wavelength soliton pulses decreases due to dispersion, and the frequency shift rate slows down, causing soliton pulses to gradually accumulate at longer wavelengths. In the dispersion steepening region, the slope of the dispersion curve increases sharply in the 5-micrometer region, further weakening the redshift of the soliton pulses, causing the overall spectral broadening of the pulse to stagnate near 5 micrometers, forming a long-wavelength boundary. At the same time, the short-wavelength pulse component continues to redshift, while the long-wavelength portion stagnates, realizing the transfer of energy from the short-wavelength to the long-wavelength region, thereby enhancing the mid-infrared laser and ultimately obtaining a high-power, high-efficiency, and high-proportion mid-infrared laser in the 3-5 μm band.

[0044] In summary, this invention utilizes dispersion modulation technology to generate high-peak-power soliton group pulses as pump light through soliton pulse splitting. Different degrees of nonlinear effects occur in different regions of the mid-infrared nonlinear fiber dispersion curve to increase the energy of long-wavelength soliton pulses, causing frequency shifts in short-wavelength soliton pulses and stagnation in the long-wavelength portion. This results in high-power, high-efficiency, and high-percentage-weight mid-infrared lasers in the 3-5μm band. The invention employs an all-fiber structure, giving the laser advantages such as compact structure, high integration, good stability, and high conversion efficiency.

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope 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 pulsed 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 connected by water cooling or semiconductor cooler and by fiber fusion splicing. The pulsed fiber laser generates nanosecond pulsed lasers in the 1.5-micrometer band; The fiber pulse stretcher is a single-mode silica fiber located between the pulsed fiber laser and the fiber laser amplifier. It splits the nanosecond pulse into multiple ultrafast soliton pulses through nonlinear effects and performs spectral energy conversion of nanosecond pulsed laser from 1.5 micrometers to 2.4 micrometers. The fiber laser amplifier further enhances the output power of the broadened pulsed laser and extends the spectrum to the 2.7-micron band, while also increasing the pulse energy beyond 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 extends the laser to the mid-infrared 3-5 micrometer band, achieving high-power, high-efficiency, and high-proportion 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 pulsed fiber laser includes: 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 connected in sequence through single-mode fibers to form a linear cavity structure; all the above devices are connected by 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 fiber. The 1550nm distributed feedback semiconductor laser serves as a seed source. Through a control circuit, it is modulated to generate a 1.5-micron nanosecond pulse seed laser. The seed laser undergoes preliminary power amplification in the single-mode erbium-doped fiber and is then transmitted to the 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, characterized in that: The fiber laser amplifier includes: a fiber combiner (4-1), a 793nm semiconductor laser (4-2), a large mode area double-clad thulium-doped fiber (4-3), and a fiber isolator (4-4). The 793nm semiconductor laser provides pump light to the large mode area double-clad thulium-doped fiber through the fiber combiner, and the fiber isolator isolates the feedback light formed by subsequent optical paths. All the above devices are 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 fiber mode field adapter connects large mode field area optical fiber and single-mode optical fiber to match nonlinear optical fiber; all the above devices are connected by 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 fiber utilizes a dispersion modulation mechanism to extend 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 fiber is germanate fiber, fluoride fiber, tellurate fiber, or chalcogenide fiber with longitudinal dispersion design. The longitudinal dispersion design of the nonlinear fiber includes three parts: a dispersion flat region, used for soliton self-frequency shifting process; and a dispersion transition region, used to accumulate soliton group pulse count. The region of sharp increase in dispersion 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. The 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 pulsed fiber laser is controlled by a driving circuit and a computer, and is adjusted according to the actual situation, the pulse characteristics of the seed laser, and the pump power.

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