Widely tunable fiber laser source in the mid-infrared band

Abstract

The present invention relates to the technical field of optical fiber lasers, and proposes a mid-infrared band wide-range precisely tunable optical fiber laser light source, which adopts a widely tunable 1μm laser pump source to obtain an ultra-wideband mid-infrared laser output greater than 1000nm, including a 1μm band tunable pulse seed source, an optical fiber amplifier module, an optical fiber end cap, an end cap coupling device, a hollow-core optical fiber, and a small gas cavity. The 1μm band tunable pulse seed source is a nanosecond pulse laser with a tuning range covering 1024nm-1080nm. Based on the direct tuning of the 1μm band pump source, the wavelength of the 3μm-4μm laser is directly precisely tuned, and the tuning is convenient without adding a seed source. The 1μm band pump source is more likely to obtain high-power laser output, and the hollow-core optical fiber has a high damage threshold, which can effectively improve the mid-infrared output power. The gas Raman laser has a narrow linewidth and the hollow-core optical fiber has a small dispersion, so that the output mid-infrared laser has a narrow linewidth characteristic.

Description

Technical Field

[0001] The invention mainly relates to the technical field of optical fiber lasers, in particular to a large-range accurately tunable optical fiber laser light source in a mid-infrared band. Background Art

[0002] Mid-infrared band lasers (3μm~5μm) are the focus of research in the laser field because of their important application value. Lasers in this band cover important atmospheric transmission windows, are suitable for long-distance transmission of lasers, and are widely used in fields such as communications and remote sensing. The molecular absorption peaks of greenhouse gases, pollutants on the ground or in water, various biological tissues, and other gaseous, solid, or liquid substances are located in this band, so they can be used for the molecular fingerprints of these molecules for pollutant and environmental monitoring. In addition, mid-infrared lasers are also widely used in military fields such as missile tail flame detection and multi-spectral lidar. At present, gas lasers, solid lasers, quantum cascade lasers, and fiber lasers can all achieve mid-infrared laser output. Among them, fiber lasers are favored for their good beam quality, strong stability, and compact structure.

[0003] At present, there are mainly the following ways to generate fiber laser output in the mid-infrared band: mid-infrared fiber lasers based on rare earth ion doping, mid-infrared fiber lasers based on stimulated Raman scattering effect in solid core optical fiber, fiber gas lasers based on population inversion, and mid-infrared supercontinuum fiber lasers. Mid-infrared fiber lasers doped with rare earth ions such as Er3+, Ho3+, and Dy3+ have developed rapidly in recent years, and have achieved tens of watts of continuous wave output and kilowatt-level peak power pulse output. However, due to the energy level characteristics of rare earth ions, the wavelength of the output laser is basically limited to below 4μm. At the same time, due to the low damage threshold of the fluoride glass mainly used, it is difficult to further significantly increase the output power level under the current process level. Mid-infrared fiber lasers based on stimulated Raman scattering in solid-core optical fibers have been proven to be an effective means of expanding laser wavelengths to more than 4μm. However, the Raman gain and damage threshold of the soft glass optical fibers used in such lasers are relatively low, which is not conducive to increasing the output power. Writing gratings of corresponding wavelengths on soft glass optical fibers also puts forward higher process requirements and increases the technical difficulty. At the same time, like solid-core fiber Raman lasers in other bands, its output laser linewidth is relatively wide, which is not conducive to direct application. Fiber gas lasers based on population inversion are an emerging way to generate mid-infrared lasers. By using microstructured hollow-core optical fibers filled with low-pressure gas and utilizing the absorption of gas molecules for lasers of specific wavelengths, the radiation output of mid-infrared lasers is realized. Although this type of laser combines many advantages of gas lasers and fiber lasers and realizes mid-infrared laser output with a maximum tuning range of nearly 700nm, it is difficult to achieve continuous fine tuning of the output laser due to the discrete energy level characteristics of the molecules. At the same time, the pump source used must have stable wavelength and extremely narrow linewidth characteristics, and the preparation process requirements are high, which is not conducive to promotion. Mid-infrared supercontinuum fiber lasers can achieve wide-spectrum output of mid-infrared lasers above 100 nanometers. Although this type of laser can also achieve a power output of tens of watts, the output spectrum is too wide, so the spectral density at a single wavelength is relatively small. At the same time, high-power pump sources are difficult to prepare under current process conditions, and the end face of the soft glass optical fiber used is also extremely easy to be damaged, making it difficult to further increase the output power.

[0004] Although there have been related reports on fiber gas Raman lasers based on direct pumping of 1.5μm erbium-doped fiber lasers, it is difficult to achieve widely tunable mid-infrared laser output due to the characteristics of erbium ions themselves and the lack of a high-power tunable pump source. Summary of the invention

[0005] In view of the technical problems existing in the prior art, the present invention proposes a fiber laser light source that is precisely tunable over a wide range in the mid-infrared band.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] On the one hand, the present invention provides a mid-infrared band wide-range precisely tunable fiber laser light source, including a 1μm band tunable pulse seed source, a fiber amplifier module, a fiber end cap, an end cap coupling device, a hollow core fiber, and a small gas cavity;

[0008] 1μm band tunable pulse seed source, used to provide the pump source with 1μm band pulse seed light with the required pulse width and wavelength, and its tuning range covers 1024nm-1080nm;

[0009] The optical fiber amplifier module is used for power amplifying the 1 μm band pulse seed light output by the 1 μm band tunable pulse seed source as pump light; the output pigtail of the optical fiber amplifier module is connected to the first optical fiber end cap;

[0010] An end cap coupling device is an end cap alignment device used for aligning and coupling a first optical fiber end cap and a second optical fiber end cap, wherein the second optical fiber end cap is connected to an input end of the first hollow core optical fiber;

[0011] The first hollow-core optical fiber is an antiresonant hollow-core optical fiber, which is used to be filled with a first working gas, wherein the first working gas is methane, and provides a place for the pump light to interact with the methane gas molecules. Under the effect of the vibration stimulated Raman scattering of the methane gas molecules, the pump light is converted into a Raman laser output of 1460nm-1498nm as a new pump light;

[0012] A first small gas cavity is connected to the output end of the first hollow core optical fiber and is used to fix and seal the first hollow core optical fiber and output new pump light to the second hollow core optical fiber;

[0013] The second hollow-core optical fiber has a third optical fiber end cap connected to its input end, and the new pump light is input into the second hollow-core optical fiber through the third optical fiber end cap; the second hollow-core optical fiber is an antiresonant hollow-core optical fiber, which is used to be filled with a second working gas, wherein the second working gas is hydrogen, and provides a place for the pump light to interact with hydrogen gas molecules, and the pump light is converted into a mid-infrared laser output of 3710nm-4718nm under the effect of vibration stimulated Raman scattering of hydrogen gas molecules;

[0014] The second small gas cavity is connected to the output end of the second hollow core optical fiber and is used to fix and seal the second hollow core optical fiber and output a mid-infrared laser of 3710nm-4718nm at the same time.

[0015] Furthermore, the fiber amplifier module contains multiple fiber amplifier units and an amplification switching unit, each fiber amplifier unit is used to achieve pulse laser power amplification in different sub-bands within the 1μm band, and the amplification switching unit is used to achieve switching of each fiber amplifier unit, switching the fiber amplifier unit of the sub-band corresponding to the seed light wavelength to achieve power amplification of the seed light.

[0016] Furthermore, the optical fiber amplifier module contains two optical fiber amplifier units, which are respectively used to achieve pulse laser power amplification in two sub-bands of 1024nm-1050nm and 1050nm-1080nm.

[0017] Furthermore, the 1 μm band tunable pulse seed source is a nanosecond pulse laser with a tuning range covering 1024 nm-1080 nm.

[0018] Furthermore, a first lens group is fixed inside the end cap coupling device for realizing collimation and focusing of the pump light. The end cap coupling device has a three-dimensional adjustment structure at the input side connected to the first optical fiber end cap and the output side connected to the second optical fiber end cap. The three-dimensional adjustment structure can realize alignment of the first optical fiber end cap and the second optical fiber end cap, so that the pump light output by the first optical fiber end cap is efficiently coupled into the first hollow-core optical fiber through the second optical fiber end cap.

[0019] Furthermore, the first hollow-core optical fiber is a near-infrared hollow-core optical fiber with low transmission loss at 1 μm-1.1 μm and 1.4 μm-1.6 μm, and the second hollow-core optical fiber is a mid-infrared hollow-core optical fiber with low transmission loss at 1.4 μm-1.6 μm and 3.5 μm-5 μm.

[0020] Furthermore, the first small gas cavity and the second small gas cavity both have an air inlet / exhaust port, which are connected to corresponding exhaust equipment / inflating equipment through pipelines, and can evacuate the interior of the corresponding hollow-core optical fiber into a vacuum state and fill it with corresponding working gas at a certain air pressure.

[0021] Furthermore, it also includes a barium fluoride lens coated with a 2μm-5μm anti-reflection film and a filter. A barium fluoride lens for mid-infrared laser is arranged outside the output side of the second small gas cavity to collimate the output laser into parallel light; the filter only allows the mid-infrared laser of 3710μm-4718nm to be transmitted and output, and filters out the residual first-order Raman laser of 1460μm-1498nm.

[0022] Furthermore, the first optical fiber end cap and the second optical fiber end cap are coated with 1μm-1.1μm high transmittance and 1.4μm-1.6μm high reflection films; the third optical fiber end cap is coated with 1μm-1.1μm high reflection and 1.4μm-1.6μm high transmittance films.

[0023] Furthermore, it also includes a second lens group, which is arranged outside the output end of the first small gas cavity and is used to collimate and focus the new pump light output by the first hollow core optical fiber and then input it into the second hollow core optical fiber through the third optical fiber end cap.

[0024] The present invention uses a pump source that is precisely tunable over a wide range in the 1μm band to achieve tunable laser output in the mid-infrared band exceeding 1000nm. Compared with the prior art, the technical effects of the present invention are:

[0025] 1. The present invention is based on the easily available widely tunable 1μm pulsed laser, and realizes wavelength conversion based on the two-stage stimulated Raman scattering of gas, directly converting it into an ultra-wideband mid-infrared laser with a tuning range greater than 1000nm. The structure is simple and easy to implement.

[0026] 2. The present invention adopts a common 1μm finely tunable seed source to obtain a 1024nm-1080nm pulsed laser. When the tuning accuracy of the seed source is 0.01nm, the corresponding mid-infrared laser tuning accuracy is up to 0.13nm. Through the simple tuning of the 1μm seed source, the fine adjustment of the mid-infrared laser wavelength is achieved, the operation is quick, and the system is streamlined.

[0027] 3. Each amplifier unit in the fiber amplifier module of the present invention is an ytterbium-doped fiber amplifier. Based on the advantages of the simple energy level structure of ytterbium ions and the wide absorption and emission spectrum, it is relatively easy to obtain high-power laser output with a wide tuning range and high tuning accuracy. Based on the combination of the ytterbium-doped fiber amplifier outputting pump light and the air-filled hollow-core fiber as the gain medium, it is easy to obtain higher-power pump light. The core damage threshold of the hollow-core fiber is higher than that of the solid-core fiber, which ensures the high-power bearing capacity of the gain medium and is conducive to a substantial increase in the power of the mid-infrared tunable laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0029] Figure 1 This is a schematic diagram of the structure of a fiber laser light source that can be precisely tuned over a wide range in the mid-infrared band;

[0030] Figure 2 This is an output spectrum diagram of a 1 μm band tunable pulse seed source in one embodiment;

[0031] Figure 3 This is a spectrum diagram of the output of a tunable pulse pump source in one embodiment;

[0032] Figure 4 1 is an output spectrum diagram of the Raman laser output by the first hollow-core optical fiber under the pumping of a 1035 nm wavelength pulse pump light in one embodiment;

[0033] Figure 5 is a graph showing the evolution of 1482.7nm Raman laser output power versus pump power in one embodiment;

[0034] Figure 6 4 is a graph showing the evolution of the Raman laser output power of the first hollow-core optical fiber as a function of the pump power at different methane gas pressures in one embodiment.

[0035] Numbers in the figure:

[0036] 1 is a 1μm band tunable pulse seed source; 2 is a fiber amplifier module; 3 is a first fiber amplifier unit; 4 is a second fiber amplifier unit; 5, a first fiber end cap; 6, an end cap coupling device; 7, a first lens; 8, a second lens; 9, a second fiber end cap; 10, a first hollow-core fiber; 11, a first small gas cavity; 12, a third lens; 13, a fourth lens; 14, a third fiber end cap; 15, a second hollow-core fiber; 16, a second small gas cavity; 17, a fifth lens; and 18, a filter. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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 are within the scope of protection of the present invention.

[0038] The present invention uses a pump source that is precisely tunable over a wide range in the 1 μm band to achieve tunable laser output over an ultra-large wavelength range exceeding 1000 nm in the mid-infrared band.

[0039] Reference Figure 1 In one embodiment, a mid-infrared band wide range precisely tunable fiber laser light source is provided, including a 1μm band tunable pulse seed source 1, a fiber amplifier module 2, a fiber end cap, an end cap coupling device 6, a hollow core fiber, a small gas cavity, a lens, and a filter 18; the lenses used are all plano-convex lenses for collimating or focusing the light beam.

[0040] The 1μm band tunable pulse seed source 1 and the fiber amplifier module 2 together constitute a 1μm band wide range precision tunable pulse pump source. The 1μm band tunable pulse seed source is easy to obtain, and has the characteristics of stable wavelength, narrow linewidth, and fine tuning. Through the mature ytterbium-doped fiber amplifier, it can achieve wide-tuned pump light output, and then based on the stimulated Raman scattering characteristics of the gas, the easily obtained 1μm wide-tuned pump light is converted into a wide-tuned laser in the mid-infrared.

[0041] The 1μm band tunable pulse seed source 1 is used to provide the pump source with 1μm band pulse seed light of required pulse width and wavelength. The 1μm band is mainly set to correspond to the mid-infrared output wavelength above 1000nm. Preferably, its tuning range covers 1024nm-1080nm. The pulse width modulation requirement of the pump source mainly depends on the parameters of the modulator used. Usually, in order to facilitate amplification, the pulse width used is ns level and the pulse repetition frequency is kHz-MHz level.

[0042] The optical fiber amplifier module 2 is used to power amplify the 1 μm band pulse seed light output by the tunable pulse seed source in the 1 μm band as pump light; the output pigtail of the optical fiber amplifier module 2 is connected to the first optical fiber end cap 5. Specifically, the optical fiber amplifier module 2 contains two optical fiber amplifier units, and the first optical fiber amplifier unit 3 and the second optical fiber amplifier unit 4 are used to realize the pulse laser power amplification of the two sub-bands of 1024nm-1050nm and 1050nm-1080nm respectively. The amplification switching unit is used to realize the switching of the first optical fiber amplifier unit 3 and the second optical fiber amplifier unit 4, and the optical fiber amplifier unit of the sub-band corresponding to the seed light wavelength is switched to realize the power amplification of the 1 μm band pulse seed light.

[0043] The end cap coupling device 6 is an end cap alignment device, which is used for alignment and coupling of the first optical fiber end cap 5 and the second optical fiber end cap 6. The second optical fiber end cap 9 is connected to the input end of the first hollow core optical fiber 10. A first lens group consisting of a first lens 7 and a second lens 8 is fixed inside the cavity of the end cap coupling device 6. The first lens group is used to realize the collimation and focusing of the pump light. The input side of the end cap coupling device 6 connected to the first optical fiber end cap and the output side connected to the second optical fiber end cap have a three-dimensional adjustment structure. The three-dimensional adjustment structure can realize the alignment of the first optical fiber end cap 5 and the second optical fiber end cap 6, so that the pump light output by the first optical fiber end cap 5 is efficiently coupled into the first hollow core optical fiber 10 through the first lens group and the second optical fiber end cap 9.

[0044] The first hollow-core optical fiber 10 is an antiresonant hollow-core optical fiber, which is used to be filled with a first working gas, wherein the first working gas is methane, and provides a place for the pump light to interact with the methane gas molecules. Under the effect of the vibration stimulated Raman scattering of the methane gas molecules, the pump light is converted into a Raman laser output of 1460nm-1498nm as a new pump light.

[0045] A first small gas cavity 11 is connected to the output end of the first hollow core optical fiber 10 and is used to fix and seal the first hollow core optical fiber 10 and output new pump light to the second hollow core optical fiber 15;

[0046] The second hollow-core optical fiber 15 has a third optical fiber end cap 14 connected to its input end, and new pump light is input into the second hollow-core optical fiber 15 through the third optical fiber end cap 14; the second hollow-core optical fiber 15 is an antiresonant hollow-core optical fiber, which is used to be filled with a second working gas, wherein the second working gas is hydrogen, and provides a place for the pump light to interact with hydrogen gas molecules. Under the effect of vibration stimulated Raman scattering of hydrogen gas molecules, the pump light is converted into a mid-infrared laser output of 3710nm-4718nm;

[0047] The second small gas cavity 16 is connected to the output end of the second hollow core optical fiber 15 and is used to fix and seal the second hollow core optical fiber 15 and output a mid-infrared laser of 3710-4718 nm.

[0048] The fifth lens 17 is a barium fluoride lens coated with a 2μm-5μm anti-reflection film. A barium fluoride lens for mid-infrared laser is arranged outside the output side of the second small gas cavity 16 to collimate the laser output from the second hollow-core optical fiber 15 into parallel light.

[0049] The filter 18 is a mid-infrared bandpass filter, which is used to separate the mid-infrared signal light, allowing only the 3710nm-4718nm mid-infrared laser to be transmitted and output, and filtering out the residual 1460nm-1498nm primary Raman laser.

[0050] Furthermore, the 1μm band tunable pulse seed source of the present invention is a nanosecond pulse laser with a tuning range covering 1024nm-1080nm. In the above embodiment, based on the direct tuning of the 1μm band pump source, the wavelength of the 3μm-4μm laser is directly precisely tuned, and the tuning is convenient without adding a seed source. The 1μm band pump source is more likely to obtain high-power laser output, and the hollow-core fiber damage threshold is higher, which can effectively improve the mid-infrared output power. The gas Raman laser linewidth is narrow, and the hollow-core fiber dispersion is small, so that the output mid-infrared laser has a narrow linewidth characteristic.

[0051] Furthermore, it also includes a second lens group consisting of a third lens 12 and a fourth lens 13. The second lens group is arranged outside the output end of the first small gas cavity 11, and is used to collimate and focus the new pump light output by the first hollow-core optical fiber and then input it into the second hollow-core optical fiber 15 through the third optical fiber end cap 14.

[0052] The mid-infrared tunable laser light source proposed in the above embodiment is realized by two-stage stimulated Raman scattering. The pump source used in the 1μm band with a wide range of precise tunability is a 1μm high peak power pulse laser. When the single wavelength pump light of 1024nm-1080nm interacts with the high-pressure methane gas in the first hollow-core optical fiber, the incident pump light is converted into a Raman laser output of 1460nm-1498nm under the vibration stimulated Raman scattering of the methane gas molecules. The Raman laser near the 1.5μm band output is then used as a new pump light, which interacts with the hydrogen molecules in the second hollow-core optical fiber again, and the incident Raman laser is converted into a mid-infrared laser output of 3710nm-4718nm through the vibration stimulated Raman scattering of the hydrogen molecules. Based on the mature 1μm fine-tunable seed source, by adjusting its output wavelength, the 1μm high-peak power pulse laser wavelength is changed to change the corresponding 1.5 μm band Raman laser wavelength, thereby further changing the output mid-infrared band laser wavelength.

[0053] The methane gas pressure should be close to 2.5 bar to ensure that methane has sufficient Raman gain without self-focusing effects. The hydrogen gas pressure should be close to 20 bar, under which the rotational stimulated Raman scattering of hydrogen is greatly suppressed and the vibrational stimulated Raman scattering is greatly enhanced, which is conducive to improving the conversion efficiency.

[0054] In one embodiment, the following is used Figure 1The structure shown in the figure, wherein the pulse width and repetition frequency of the 1μm band tunable pulse seed source 1 itself are flexibly tunable, and its output pigtail is directly connected to the fiber amplifier module 2. The fiber amplifier module 2 starts the fiber amplifier unit of the corresponding sub-band by manually inputting the wavelength and the circuit automatically selecting the program, wherein there are two amplifier units, which respectively realize the high peak power pulse pump light output of 1024nm-1050nm and 1050nm-1080nm. The output pigtail of the fiber amplifier module 2 is low-loss fused with the first fiber end cap 5 coated with 1μm-1.1μm high transmittance and 1.4μm-1.6μm high reflection film, which is used to protect the pigtail end face from the return light damage and prevent other band lasers from entering the fiber amplifier unit. The second fiber end cap 9 of the same type as the first fiber end cap 5 is fused with the first hollow core fiber 10, and then inserted into the end cap coupling device 6 from the input side and the output side of the end cap coupling device 6 together with the first fiber end cap 5. A first lens group is fixedly arranged in the end cap coupling device 6, which can realize the collimation and focusing of the pump light. By adjusting the three-dimensional adjustment structure on both sides of the end cap coupling device 6, the pump light is efficiently coupled into the first hollow core fiber 10. The first hollow core fiber 10 is a near-infrared hollow core fiber with low transmission loss at 1μm-1.1μm and 1.4μm-1.6μm. The other end of the first hollow core fiber 10 is fixed and sealed in the first small gas cavity 11. The first small gas cavity 11 is a metal cavity with a microstructure, in which the output end of the first hollow core fiber 10 is fixed and isolated from the outside.

[0055] The small gas chambers used in the present invention all have an air inlet / exhaust port, which is connected to the corresponding exhaust device / inflating device through a pipeline, and can extract the inside of the corresponding hollow-core optical fiber into a vacuum state and fill it with the corresponding working gas at a certain pressure. Specifically, the small gas chambers all contain gas inlet and outlet pipes and precision valves, and firstly extract the hollow-core optical fiber and the air in the cavity by connecting to the exhaust device, and then inject the high-pressure working gas through the connected high-pressure gas cylinder.

[0056] The third lens 12 in the second lens group collimates the output light of the first hollow core fiber 10, and the fourth lens 13 focuses the collimated light beam again. The second hollow core fiber 15 is a mid-infrared hollow core fiber with low transmission loss at 1.4μm-1.6μm and 3.5μm-5 μm, and its input end is fused with the third fiber end cap 14. The three fiber end caps 14 are coated with 1μm-1.1μm high reflection and 1.4μm-1.6μm high transmission films, which can effectively protect the end face of the hollow core fiber from damage, and at the same time reflect the residual pump light of the previous stage back to improve the pump utilization rate. By adjusting the spatial position of the three fiber end caps 14, efficient coupling of 1460nm-1498nm Raman laser is achieved. The second small gas cavity 16 is arranged at the output end of the second hollow core fiber 15, and the air therein is extracted and filled with high-pressure hydrogen. The fifth lens 17 is a barium fluoride lens suitable for mid-infrared lasers, which can collimate the laser output from the second hollow core fiber 15 into parallel light. The filter 18 allows only the mid-infrared laser of 3710 nm to 4718 nm to be transmitted and output, and filters out the residual primary Raman laser of 1460 nm to 1498 nm.

[0057] The working gas used in the first hollow-core optical fiber of the present invention is methane. If ethane or deuterium is used instead and the tuning wavelength used by the pump source is adjusted accordingly, a similar effect can be obtained.

[0058] based on Figure 1 The structure shown in the figure provides a mid-infrared band wide range accurately tunable fiber laser light source. The output spectrum of the 1 μm band tunable pulse seed source 1 of one embodiment is shown in FIG. Figure 2 The tunable pulse pump source is composed of a 1μm band tunable pulse seed source 1 and a fiber amplifier module 2. Figure 3 : is the output spectrum of the tunable pulse pump source. In this embodiment, the maximum output power of the tunable pulse pump source is 2W, and the corresponding peak power is up to 8 kW. Further, the output spectrum of the Raman laser output by the first hollow-core optical fiber 10 under the 1035nm wavelength pulse pump light obtained in this embodiment is as follows: Figure 4 As shown, in this embodiment, the working gas used in the first hollow-core optical fiber 10 is methane, and the Raman laser output by the first hollow-core optical fiber 10 in the mid-infrared band large-range precisely tunable optical fiber laser light source is a 1482.7 nm Raman laser. Figure 4 It can be seen that when the 1μm band pulse laser is pumped, the output Raman laser is also a single spectrum line. Figure 5, which is an evolution curve of the 1482.7nm Raman laser output power of the first hollow-core optical fiber 10 of this embodiment with the pump power. The pump power of the tunable pulse pump source outputting 1035nm pump light should be above 750mW. By continuously increasing the pump power above 750mW, it is expected to achieve higher-power 1482.7nm Raman laser output. When the pump power is above 1500mW, the maximum output average power of the 1482.7nm Raman laser output by the first hollow-core optical fiber 10 is close to 350mW.

[0059] In addition, the pressure of the methane gas introduced into the first hollow core optical fiber 10 will also affect the Raman laser power outputted by the first hollow core optical fiber. By optimizing and adjusting the pressure of the methane gas introduced into the first hollow core optical fiber 10, it is easy to obtain the highest Raman laser output power. The output Raman laser is used as a new pump light, so that the output power of the mid-infrared band laser is also improved. Figure 6 , is a graph showing the evolution of the Raman laser output power of the first hollow-core optical fiber with the pump power at different methane gas pressures in one embodiment. It can be seen that the methane gas pressure is not as high as possible, nor is it as low as possible. The preferred range of the methane gas pressure is between 1 bar and 2.5 bar, and the optimal value of the methane gas pressure is 2.5 bar. When the methane gas pressure is 2.5 bar, with the increase of the pump power, it is easy to obtain the highest Raman laser output power at this pressure. When the methane gas pressure is greater than 2.5 bar, with the increase of the pump power, the effect of increasing the Raman laser output power is constantly decreasing.

[0060] Matters not covered by the present invention are known technologies.

[0061] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0062] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A wide range of precisely tunable fiber laser light sources in the mid-infrared band, characterized by: Including 1μm band tunable pulse seed source, fiber amplifier module, fiber end cap, end cap coupling device, hollow core fiber, small gas cavity; 1 μm band tunable pulse seed source, used to provide the pump source with 1 μm band pulse seed light with the required pulse width and wavelength, and its tuning range covers 1024nm-1080nm; The optical fiber amplifier module is used for power amplifying the 1 μm band pulse seed light output by the 1 μm band tunable pulse seed source as pump light; the output pigtail of the optical fiber amplifier module is connected to the first optical fiber end cap; An end cap coupling device is an end cap alignment device used for aligning and coupling a first optical fiber end cap and a second optical fiber end cap, wherein the second optical fiber end cap is connected to an input end of the first hollow core optical fiber; The first hollow-core optical fiber is an antiresonant hollow-core optical fiber, which is used to be filled with a first working gas, wherein the first working gas is methane, and provides a place for the pump light to interact with the methane gas molecules. Under the effect of the vibration stimulated Raman scattering of the methane gas molecules, the pump light is converted into a Raman laser output of 1460nm-1498nm as a new pump light; A first small gas cavity is connected to the output end of the first hollow core optical fiber and is used to fix and seal the first hollow core optical fiber and output new pump light to the second hollow core optical fiber; The second hollow-core optical fiber has a third optical fiber end cap connected to its input end, and the new pump light is input into the second hollow-core optical fiber through the third optical fiber end cap; the second hollow-core optical fiber is an antiresonant hollow-core optical fiber, which is used to be filled with a second working gas, wherein the second working gas is hydrogen, and provides a place for the pump light to interact with hydrogen gas molecules, and the pump light is converted into a mid-infrared laser output of 3710nm-4718nm under the effect of vibration stimulated Raman scattering of hydrogen gas molecules; The second small gas cavity is connected to the output end of the second hollow core optical fiber and is used to fix and seal the second hollow core optical fiber and output a mid-infrared laser of 3710nm-4718nm at the same time.

2. The mid-infrared band large-range precisely tunable fiber laser light source according to claim 1, characterized in that: The fiber amplifier module contains multiple fiber amplifier units and an amplification switching unit. Each fiber amplifier unit is used to achieve pulse laser power amplification in different sub-bands within the 1μm band. The amplification switching unit is used to achieve switching of each fiber amplifier unit. Switching the fiber amplifier unit of the sub-band corresponding to the seed light wavelength achieves power amplification of the seed light.

3. The mid-infrared band large-range precisely tunable fiber laser light source according to claim 1, characterized in that: The optical fiber amplifier module contains two optical fiber amplifier units, which are respectively used to realize pulse laser power amplification in two sub-bands of 1024nm-1050nm and 1050nm-1080nm.

4. The mid-infrared band large-range precisely tunable fiber laser light source according to claim 1, 2 or 3, characterized in that: The 1μm band tunable pulse seed source is a nanosecond pulse laser with a tuning range covering 1024nm-1080nm.

5. The mid-infrared band wide range accurately tunable fiber laser light source according to claim 4, characterized in that: A first lens group is fixed inside the end cap coupling device for realizing collimation and focusing of the pump light. The end cap coupling device has a three-dimensional adjustment structure at the input side connected to the first optical fiber end cap and the output side connected to the second optical fiber end cap. The three-dimensional adjustment structure can realize alignment of the first optical fiber end cap and the second optical fiber end cap, so that the pump light output by the first optical fiber end cap is efficiently coupled into the first hollow-core optical fiber through the second optical fiber end cap.

6. The mid-infrared band large-range precisely tunable fiber laser light source according to claim 1 or 2 or 3 or 5, characterized in that: The first hollow-core optical fiber is a near-infrared hollow-core optical fiber with low transmission loss at 1 μm-1.1 μm and 1.4 μm-1.6 μm, and the second hollow-core optical fiber is a mid-infrared hollow-core optical fiber with low transmission loss at 1.4 μm-1.6 μm and 3.5 μm-5 μm.

7. The mid-infrared band wide range accurately tunable fiber laser light source according to claim 6, characterized in that: The first small gas cavity and the second small gas cavity both have an air inlet / exhaust port, which are connected to corresponding exhaust equipment / inflating equipment through pipelines, and can evacuate the interior of the corresponding hollow-core optical fiber into a vacuum state and fill it with corresponding working gas at a certain air pressure.

8. The mid-infrared band wide range accurately tunable fiber laser light source according to claim 7, characterized in that: It also includes a barium fluoride lens coated with a 2μm-5μm anti-reflection film and a filter. A barium fluoride lens for mid-infrared laser is arranged outside the output side of the second small gas cavity to collimate the output laser into parallel light; the filter only allows the transmission output of the mid-infrared laser of 3710nm-4718nm, and filters out the residual primary Raman laser of 1460nm-1498nm.

9. The mid-infrared band wide range accurately tunable fiber laser light source according to claim 6, characterized in that: The first optical fiber end cap and the second optical fiber end cap are coated with 1μm-1.1μm high transmittance film and 1.4μm-1.6μm high reflection film; the third optical fiber end cap is coated with 1μm-1.1μm high reflection film and 1.4μm-1.6μm high transmittance film.

10. The mid-infrared band large-range precisely tunable fiber laser light source according to claim 1 or 2 or 3 or 5 or 7 or 8 or 9, characterized in that: It also includes a second lens group, which is arranged outside the output end of the first small gas cavity and is used to collimate and focus the new pump light output by the first hollow core optical fiber and then input it into the second hollow core optical fiber through the third optical fiber end cap.

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