Intermediate infrared super-continuum spectrum light source of spatial light structure

Abstract

The invention discloses an intermediate infrared super-continuum spectrum light source with a spatial light structure, which comprises a pumping source, a light source, a light source and a light source, the collimating lens is used for collimating the pump light and outputting parallel light; the grating pair is formed by arranging two gratings in parallel and is used for splitting the light input into the grating pair according to the frequency, changing the optical path of the light of each frequency and outputting transmission light to the roof prism; the optical fiber is also used for compounding the light returned to the grating pair from the original path of the roof prism, realizing pulse compression and outputting compressed light to the reflector; the roof prism is used for reflecting the light penetrating through the grating pair to penetrate through the grating pair again; the reflecting mirror is used for reflecting the compressed light; the focusing lens is used for focusing the compressed light reflected by the reflecting mirror; and the compressed light focused by the focusing lens is spatially coupled at a focal point to enter the fluoride optical fiber, and intermediate infrared super-continuum spectrum laser is output. In the spatial optical coupling system, the grating pair is used for compressing the pulse, and further broadening of the super-continuum spectrum is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of lasers, and in particular relates to a mid-infrared supercontinuum light source with a spatial light structure. Background Art

[0002] Supercontinuum light source is a pump source output light pulse pumping nonlinear optical fiber, which is transmitted in nonlinear optical fiber. Due to the nonlinear effect of nonlinear optical fiber, the spectrum is broadened. Compared with ordinary lasers, it has the characteristics of high brightness, wide spectrum, and high coherence. The 2-5μm band contains the characteristic absorption lines of most molecules and is widely used in infrared countermeasures, medical imaging, and gas detection. Therefore, the research on mid-infrared supercontinuum light source has become one of the current research hotspots. In recent years, the improvement of the preparation process of nonlinear optical fiber and the rapid progress of high-power lasers have made great progress in the research of supercontinuum light source in terms of power enhancement and spectrum broadening. The huge development potential has made more and more scholars join the research of mid-infrared supercontinuum light source.

[0003] At present, the mid-infrared supercontinuum light source with an all-fiber structure uses soft glass fiber as nonlinear fiber, and the spectral range of the supercontinuum generated can completely cover the 2-5μm band. However, the technical means required for the all-fiber structure are relatively high, and the investment cost is also high. It is not the best experimental solution for scholars who have just entered this field. The mid-infrared supercontinuum light source with a spatial light structure, which has cheap equipment and less technical means, has the disadvantages of low output power and limited spectral broadening of the supercontinuum light source due to low coupling efficiency and large transmission loss, and has gradually faded out of the researchers' experimental solutions. This makes it difficult for scholars who are interested in the generation of supercontinuum light sources but have low experimental budgets to conduct research and exploration in this field. Therefore, it is very necessary to develop an experimental solution with high output power, large spectral broadening and low cost budget. Summary of the invention

[0004] Based on this, the present invention proposes a mid-infrared supercontinuum light source with a spatial optical structure. Compared with the existing all-fiber structure, the present invention uses grating pairs to compress pulses in a spatial optical coupling system to improve the supercontinuum broadening capability by increasing the laser peak power.

[0005] The present invention provides a mid-infrared supercontinuum light source with a spatial light structure, comprising: A pump source, used to generate pump light; A collimating lens, used to collimate the pump light generated by the pump source, and collimate the divergent pump light into parallel light; The grating pair consists of two gratings placed in parallel, which are used to split the light input to the grating pair according to the frequency and change the optical path of each frequency light, and output the transmitted light to the roof prism; it is also used to recombine the light returning from the roof prism to the grating pair and realize pulse compression, and output the compressed light to the reflector; A roof prism, used to reflect the light that has passed through the grating pair and pass it through the grating pair again; A reflector, used for reflecting the compressed light to change the direction of the light path; A focusing lens, used for focusing the compressed light reflected by the reflector; The compressed light focused by the focusing lens is spatially coupled into the fluoride optical fiber at the focus, the spectrum is broadened in the short-wave and long-wave directions, and a mid-infrared supercontinuum laser is output.

[0006] Furthermore, the mid-infrared supercontinuum light source of the spatial light structure also includes a half-wave plate, which is located between the collimating lens and the grating pair and is used to adjust the polarization angle of the parallel light and output polarized light of a specific angle to the grating pair.

[0007] Furthermore, the mid-infrared supercontinuum light source of the spatial light structure also includes a dichroic mirror, which is located between the collimating lens and the half-wave plate and is used to filter out stray light in the parallel light while having high transmittance to the pump light.

[0008] Furthermore, the pump source comprises: A seed source, used to output a pulsed laser with a central wavelength of 1.5 μm; The amplifier is used to amplify the power of the pulse laser output by the seed source and output pump light with a central wavelength of 2 μm.

[0009] In one embodiment of the present invention, the seed source is a laser with a central wavelength of 1550 nm, and the central wavelength of the pump light is 1985 nm.

[0010] Furthermore, the reflector is a D-type reflector.

[0011] Furthermore, the fluoride optical fiber is ZBLAN optical fiber or InF3 optical fiber.

[0012] Furthermore, the parallel distance of the grating pair is 40 cm, and the fluoride optical fiber outputs a mid-infrared supercontinuum laser of 1.37-3.82 μm.

[0013] Furthermore, the focal length of the collimating lens is 100 mm, and the focal length of the focusing lens is 40 mm.

[0014] Preferably, the roof prism is a high-reflectivity reflector coated with a gold film, and the reflector is a high-reflectivity reflector coated with a gold film; the collimating lens and the focusing lens are CaF2 lenses coated with an anti-reflection film.

[0015] Compared with the prior art, the present invention has the following beneficial effects: Compared with the existing all-fiber structure, the present invention proposes a method of improving the supercontinuum broadening capability by using grating pairs to compress pulses in a spatial optical coupling system to increase the peak power of the pump source. Fixing the input end of the optical fiber on a high-precision multi-dimensional adjustment table and optimizing the focal length of the collimating lens and the focusing lens can significantly improve the coupling efficiency. It effectively reduces the technical difficulty of fusing fluoride optical fiber to quartz optical fiber, especially solves the problem of high difficulty and failure rate of fusing InF3 optical fiber, can save costs, and provides a simple and efficient method for generating a mid-infrared supercontinuum light source. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments 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 these drawings without paying creative work.

[0017] Figure 1 A schematic diagram of the optical path of a mid-infrared supercontinuum light source in a spatial light structure provided by an embodiment of the present invention; The meanings of the symbols in the accompanying drawings are: 1- pump source, 2- collimating lens, 3- dichroic mirror, 4- half-wave plate, 5- grating, 6- roof prism, 7- D-type reflector, 8- focusing lens, 9- fluoride optical fiber. DETAILED DESCRIPTION

[0018] 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.

[0019] See also Figure 1 , a mid-infrared supercontinuum light source with a spatial light structure provided by an embodiment of the present invention comprises: A pump source 1, used for generating pump light; A collimating lens 2, used for collimating the pump light generated by the pump source, and collimating the divergent pump light into parallel light; Dichroic mirror 3, used to filter out stray light in parallel light and at the same time have high transmittance to pump light; The half-wave plate 4 is used to adjust the polarization angle of the parallel light and output polarized light of a specific angle; The grating pair consists of two gratings 5 ​​placed in parallel, which are used to split the polarized light according to the frequency and change the optical path of each frequency light, and output the transmitted light to the roof prism; the polarized light beam passes through the grating pair, and the light of different frequencies is separated due to the diffraction effect, and is output at different diffraction angles, so the optical path is different.

[0020] The grating pair is also used to recombine the light that returns to the grating pair from the roof prism and realize pulse compression, and output the compressed light to the reflector.

[0021] A roof prism 6, used for reflecting the light passing through the grating pair and passing it through the grating pair again; A D-type reflector 7, used for reflecting the compressed light to change the direction of the light path; A focusing lens 8, used for focusing the compressed light reflected by the reflector; Fluoride optical fiber 9, the compressed light focused by the focusing lens is spatially coupled into the fluoride optical fiber at the focus, the spectrum is broadened in the short-wave and long-wave directions, and mid-infrared supercontinuum laser is output.

[0022] The pump source includes a seed source and an amplifier. The seed source is power-amplified by a three-stage amplifier and a main amplifier to achieve a pulse output of 1.95-2.05 μm. In this embodiment, the seed source laser passes through a three-stage amplifier and a main amplifier to achieve a pulse laser with a central wavelength of 1985 nm, that is, to generate pump light in the 2 μm band.

[0023] The dichroic mirror 3 is located between the collimating lens 2 and the half-wave plate 4. The dichroic mirror 3 is used to filter out stray light in the parallel light and has high transmittance to the pump light in the 2μm band. It should be noted that it is also possible to have no dichroic mirror 3 in the optical path, but residual light of other bands may be mixed in, resulting in poor light quality. In addition, in other embodiments, the dichroic mirror 3 is used as a part of the 2µm pump source 1 to play the role of CPS (cladding light stripper), and it is also possible to attribute the dichroic mirror 3 to the internal system of the 2µm pump source 1.

[0024] The half-wave plate 4 is located between the collimating lens 2 and the grating pair. The half-wave plate 4 receives parallel linear polarized light, adjusts the direction of the linear polarized light, outputs polarized light of a specific angle, and improves the diffraction efficiency of the grating; the specific angle here refers to an angle consistent with the best diffraction direction of the grating 5.

[0025] It should be noted that it is also possible to have no half-wave plate 4 in the optical path, but the direction of the polarized light may be inconsistent with the polarization direction of the grating 5 that can achieve the best diffraction condition, resulting in low diffraction efficiency, thereby affecting the compression effect. The existence of the half-wave plate can improve the working efficiency of the grating.

[0026] The reflector used in this embodiment is a D-type reflector because the D-type reflector will not block the light beam from the half-wave plate to the grating pair. Other types of reflectors are also possible as long as the height is adjusted to ensure that the light beam from the half-wave plate to the grating pair is not blocked.

[0027] Fluoride optical fibers generally include ZBLAN optical fibers and InF3 optical fibers. In this embodiment, the fluoride optical fibers used are ZBLAN optical fibers. It should be noted that InF3 optical fibers can also be used here. The zero dispersion wavelength of ZBLAN optical fibers and InF3 optical fibers is 1.6-1.8µm, so a 2µm band laser is selected as the pump source. Pumping in the anomalous dispersion region makes it easier to obtain the maximum spectrum broadening.

[0028] The output light of the pump source 1 is divergent light. In order to make the spot at the focus of the final focusing lens 8 small enough to facilitate spatial coupling into the fluoride optical fiber 9, the focal length of the collimating lens 2 should be large enough and the focal length of the focusing lens 8 should be small enough. The size of the collimating lens 2 and the focusing lens 8 needs to take into account the spot size of the parallel light beam to ensure that the pulse light can be completely transmitted and reflected; the focal length selection should match the numerical aperture and core diameter of the fluoride optical fiber 9 to ensure the maximum coupling efficiency of the pulse light.

[0029] In order to reduce the power loss of pulse light transmitted in space, the collimating lens 2 and the focusing lens 8 are selected from CaF2 lenses coated with anti-reflection films, the dichroic mirror 3 is selected from a long-wave dichroic mirror with high transmittance in the 2μm band, the roof prism 6 is selected from a high-reflectivity mirror with a gold-plated film, and the D-type mirror 7 is selected from a high-reflectivity mirror with a silver-plated film. It should be noted that the roof prism is preferably a high-reflectivity mirror with a gold-plated film, and the D-type mirror is preferably a high-reflectivity mirror with a gold-plated film, because the reflectivity of the gold film is higher in the 2μm band. The D-type mirror 7 of this embodiment uses a silver-plated film, which is not as good as the gold-plated film.

[0030] In order to increase the peak power of the laser and compress the pulse width, the two gratings 5 ​​are fixed on two three-dimensional adjustable mirror frames and placed in parallel. Changing the transmission distance and the parallel distance between the two gratings will affect the compression effect. Therefore, the pulse cannot be compressed blindly. The compression quality factor should be paid attention to and an optimal compression distance should be selected.

[0031] The following combination Figure 1 The optical path of this embodiment is described.

[0032] See also Figure 1 , the 2µm pump source 1 outputs a divergent pump light. First, a lens 2 with high transmittance in the 2μm band is used to collimate the optical path. To ensure that the spot size after the final focus is suitable, a lens 2 with a focal length of 100mm is selected as the collimating lens. The collimation effect can be observed by a power meter at the laser spot close to the lens 2, and compared with the power at the laser spot as far as possible to see if there is attenuation. If the laser power before and after is consistent, it proves that the effect of optical path collimation is good, otherwise the position of lens 2 needs to be readjusted until the laser power at far and near is consistent; or a beam observer is used to observe the spot size and shape near and far from the lens 2. If the spot size and shape before and after are consistent, it proves that the effect of optical path collimation is good, otherwise the position of lens 2 needs to be readjusted until the spot size and shape at far and near are consistent. The laser collimated by lens 2 passes through a dichroic mirror 3, reflects the residual light of other bands, and has high transmittance to the laser in the 2μm band. A half-wave plate 4 is placed behind the dichroic mirror 3 to adjust the polarization angle. The pulse passing through the half-wave plate 4 enters two parallel gratings 5. The parallel distance of the grating pair is 40 cm. A high-reflection roof prism 6 with a gold film is placed behind the grating pair to return the laser to the original path and pass through the grating pair again. After measurement by the autocorrelator, the laser pulse width after passing through the grating pair can be compressed to 2ps. The laser is then reflected by a silver-coated D-type reflector 7 to change the direction of the light path. Finally, the laser is focused by a lens 8 with a focal length of 40 mm. The spot size at the focus is about 6.35 μm and spatially coupled into the ZBLAN optical fiber.

[0033] The ZBLAN optical fiber is cut using a fluoride optical fiber cutter to ensure that the end face of the optical fiber is smooth and clean. It is then fixed on a high-precision multi-dimensional adjustment frame. After the compressed light is focused, it is spatially coupled into the ZBLAN optical fiber at the focal point. The pulsed light is transmitted in the ZBLAN optical fiber. Under the nonlinear effect of the optical fiber, the spectrum is broadened in the short-wave and long-wave directions, and ultimately a mid-infrared supercontinuum laser of 1.37-3.82μm is output.

[0034] The present invention utilizes the spatial light structure of the lens combination to achieve supercontinuum broadening, thereby improving the problems of the high cost of research on mid-infrared supercontinuum light sources generated by all-fiber structures and the low coupling efficiency of mid-infrared supercontinuum light sources generated by spatial light structures.

[0035] In one embodiment of the present invention, a dichroic mirror is used to filter out 793nm laser light, and a pump light in the 2μm band is transmitted. The grating pair compresses the pulse to 2ps. After the compressed light pulse is focused, it is coupled into the fluoride optical fiber at the focus. By utilizing the nonlinear characteristics of the fluoride optical fiber, a mid-infrared supercontinuum with a spectral coverage range of 1.37-3.82μm is finally obtained in the ZBLAN optical fiber. When the pump power is 5W, the supercontinuum output power is 1.6W, which improves the power efficiency of the mid-infrared supercontinuum light source of the spatial light structure and improves the problem of low spatial light coupling efficiency.

[0036] A mid-infrared supercontinuum light source of a spatial light structure disclosed in an embodiment of the present invention is introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A mid-infrared supercontinuum light source with a spatial light structure, characterized in that: include: A pump source, used to generate pump light; A collimating lens, used to collimate the pump light generated by the pump source, and collimate the divergent pump light into parallel light; The grating pair consists of two gratings placed in parallel, which are used to split the light input to the grating pair according to the frequency and change the optical path of each frequency light, and output the transmitted light to the roof prism; it is also used to recombine the light returning from the roof prism to the grating pair and realize pulse compression, and output the compressed light to the reflector; A roof prism, used to reflect the light that has passed through the grating pair and pass it through the grating pair again; A reflector, used for reflecting the compressed light to change the direction of the light path; A focusing lens, used for focusing the compressed light reflected by the reflector; The compressed light focused by the focusing lens is spatially coupled into the fluoride optical fiber at the focus, the spectrum is broadened in the short-wave and long-wave directions, and a mid-infrared supercontinuum laser is output.

2. The mid-infrared supercontinuum light source according to claim 1, characterized in that: It also includes a half-wave plate, which is located between the collimating lens and the grating pair and is used to adjust the polarization angle of the parallel light and output polarized light of a specific angle to the grating pair.

3. The mid-infrared supercontinuum light source according to claim 2, characterized in that: It also includes a dichroic mirror, which is located between the collimating lens and the half-wave plate and is used to filter out stray light in the parallel light while having high transmittance to the pump light.

4. The mid-infrared supercontinuum light source according to claim 1, characterized in that: The pump source comprises: A seed source, used to output a pulsed laser with a central wavelength of 1.5 μm; The amplifier is used to amplify the power of the pulse laser output by the seed source and output pump light with a central wavelength of 2 μm.

5. The mid-infrared supercontinuum light source according to claim 1, characterized in that: The reflector is a D-type reflector.

6. The mid-infrared supercontinuum light source according to claim 1, characterized in that: The fluoride optical fiber is ZBLAN optical fiber or InF3 optical fiber.

7. The mid-infrared supercontinuum light source according to claim 4, characterized in that: The parallel distance between the grating pair is 40 cm, and the fluoride optical fiber outputs a mid-infrared supercontinuum laser of 1.37-3.82 μm.

8. The mid-infrared supercontinuum light source according to claim 4, characterized in that: The focal length of the collimating lens is 100 mm, and the focal length of the focusing lens is 40 mm.

9. The mid-infrared supercontinuum light source according to claim 3, characterized in that: The roof prism is a high-reflectivity reflector coated with a gold film, and the reflector is a high-reflectivity reflector coated with a gold film; the collimating lens and the focusing lens are CaF2 lenses coated with an anti-reflection film.

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