A mid-infrared supercontinuum light source with spatial light structure

Abstract

A kind of mid-infrared supercontinuum light source of spatial light structure, comprising: pump source, for generating pump light;Collimating lens, for collimating pump light, output parallel light;Grating pair, by two grating parallel placement, for according to frequency to the light input to grating pair Spectral splitting is realized and the optical path of each frequency light is changed, output transmission light to roof prism;It is also used for the light that returns to grating pair from roof prism by original road to be compounded and pulse compression is realized, output compressed light to reflector;Roof prism, for the light that transmits grating pair is reflected again and transmits grating pair;Reflector, for reflecting the compressed light;Focusing lens, for focusing the compressed light reflected by the reflector;Fluoride fiber, the compressed light after focusing of focusing lens is spatially coupled into fluoride fiber at focal point, output mid-infrared supercontinuum laser.The utility model discloses in spatial light coupling system using grating pair compression pulse, the further widening of supercontinuum is realized.

Description

Technical Field

[0001] This invention belongs to the field of laser technology, and specifically relates to a mid-infrared supercontinuum light source with a spatial optical structure. Background Technology

[0002] Supercontinuum light sources are pump sources that output pulsed light to pump nonlinear optical fibers. The light propagates within these fibers, and the nonlinear effects of the fibers cause spectral broadening, resulting in a phenomenon that, compared to conventional lasers, offers high brightness, a wide spectral width, and high coherence. The 2-5 μm wavelength band contains the characteristic absorption lines of most molecules, making it widely applicable in infrared countermeasures, medical imaging, and gas detection. Therefore, research on mid-infrared supercontinuum light sources has become a hot topic. In recent years, advancements in nonlinear fiber fabrication technology and rapid progress in high-power lasers have led to significant progress in supercontinuum light source research, both in power enhancement and spectral broadening. This immense potential has attracted an increasing number of researchers to join the ranks of mid-infrared supercontinuum light source researchers.

[0003] Currently, all-fiber mid-infrared supercontinuum light sources use soft glass optical fibers as nonlinear fibers, generating supercontinuum spectra that can fully cover the 2-5 μm band. However, the all-fiber structure requires advanced technology and is costly, making it less than ideal for beginners. Space-optical mid-infrared supercontinuum light sources, with cheaper equipment and less demanding technology, suffer from lower coupling efficiency and greater transmission loss, resulting in lower output power and limited spectral broadening. Consequently, they are gradually fading from researchers' experimental options. This makes research into supercontinuum generation challenging for those with limited budgets. Therefore, developing an experimental scheme with high output power, broad spectral broadening, and low cost is essential. Utility Model Content

[0004] Based on this, this invention proposes a mid-infrared supercontinuum light source with a spatial optical structure. Compared with existing all-fiber structures, this invention utilizes gratings to compress pulses in the spatial optical coupling system, thereby increasing the laser's peak power and improving the supercontinuum broadening capability.

[0005] This utility model provides a mid-infrared supercontinuum light source with a spatial optical structure, comprising:

[0006] Pump source, used to generate pump light;

[0007] A collimating lens is used to collimate the pump light generated by the pump source, and to collimate the divergent pump light into parallel light.

[0008] A grating pair consists of two parallel gratings. It is used to split the light input to the grating pair according to the frequency and change the optical path of each frequency light, outputting 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, outputting compressed light to the reflector.

[0009] A roof prism is used to reflect light that has passed through a grating pair back through the grating pair.

[0010] A reflector is used to reflect the compressed light to change the direction of the light path;

[0011] A focusing lens is used to focus the compressed light reflected by the mirror;

[0012] In a fluoride optical fiber, the compressed light focused by the focusing lens is spatially coupled into the fluoride optical fiber at the focal point, and the spectrum is broadened in the short and long wavelength directions, outputting mid-infrared supercontinuum laser.

[0013] 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 at a specific angle to the grating pair.

[0014] 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 to filter out stray light in the parallel light while allowing high transmission of pump light.

[0015] Furthermore, the pump source includes:

[0016] Seed source, used to output pulsed laser with a center wavelength of 1.5μm;

[0017] An amplifier is used to amplify the power of the pulsed laser output from the seed source, and output pump light with a center wavelength of 2μm.

[0018] In one embodiment of this utility model, the seed source is a laser with a center wavelength of 1550nm, and the pump light has a center wavelength of 1985nm.

[0019] Furthermore, the reflector is a D-type reflector.

[0020] Furthermore, the fluoride optical fiber is ZBLAN optical fiber or InF3 optical fiber.

[0021] Furthermore, the parallel distance between the grating pairs is 40 cm, and the fluoride optical fiber outputs mid-infrared supercontinuum laser with a wavelength of 1.37-3.82 μm.

[0022] Furthermore, the collimating lens has a focal length of 100mm, and the focusing lens has a focal length of 40mm.

[0023] Preferably, the ridge prism is a high-reflectivity mirror with a gold-plated coating, and the collimating lens and the focusing lens are CaF2 lenses with anti-reflection coatings.

[0024] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0025] Compared to existing all-fiber structures, this invention proposes a method to improve supercontinuum broadening capability in a spatial optical coupling system by using gratings to compress pulses and increase the peak power of the pump source. Fixing the input end of the fiber on a high-precision multi-dimensional adjustment stage and optimizing the focal lengths of the collimating and focusing lenses can significantly improve coupling efficiency. This effectively reduces the technical difficulty of splicing fluoride fibers to silica fibers, especially addressing the high failure rate and difficulty of splicing InF3 fibers, thus saving costs and providing a simple and efficient method for generating mid-infrared supercontinuum light sources. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 A schematic diagram of the optical path of a mid-infrared supercontinuum light source with a spatial light structure provided for an embodiment of this utility model;

[0028] The meanings of the labels in the attached diagram are as follows:

[0029] 1-Pump source, 2-Collimating lens, 3-Dichroic mirror, 4-Half-wave plate, 5-Grating, 6-Roof prism, 7-D-type mirror, 8-Focusing lens, 9-Fluoride optical fiber. Detailed Implementation

[0030] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0031] Please see Figure 1This utility model provides a mid-infrared supercontinuum light source with a spatial light structure, comprising:

[0032] Pump source 1, used to generate pump light;

[0033] Collimating lens 2 is used to collimate the pump light generated by the pump source and collimate the divergent pump light into parallel light.

[0034] Dichroic mirror 3 is used to filter out stray light in parallel light, while allowing high transmission of pump light;

[0035] Half-wave plate 4 is used to adjust the polarization angle of parallel light and output polarized light at a specific angle;

[0036] The grating pair consists of two parallel gratings 5, used to split the polarized light according to its frequency and change the optical path of each frequency of light, outputting transmitted light to the roof prism; when the polarized beam passes through the grating pair, the light of different frequencies is separated due to the diffraction effect and output at different diffraction angles, thus the optical path is different.

[0037] The grating pair is also used to recombine the light returning from the roof prism to the grating pair and to achieve pulse compression, outputting compressed light to the reflector.

[0038] The ridge prism 6 is used to reflect light that has passed through the grating pair back through the grating pair;

[0039] D-type reflector 7 is used to reflect the compressed light to change the direction of the light path;

[0040] Focusing lens 8 is used to focus the compressed light reflected by the mirror;

[0041] Fluoride fiber 9, the compressed light focused by the focusing lens is spatially coupled into the fluoride fiber at the focal point, the spectrum is broadened in the short and long wavelength directions, and the mid-infrared supercontinuum laser is output.

[0042] The pump source includes a seed source and an amplifier. The seed source undergoes power amplification via 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, after passing through a three-stage amplifier and a main amplifier, can achieve a pulsed laser with a center wavelength of 1985 nm, i.e., generate pump light in the 2 μm band.

[0043] 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 while maintaining high transmittance for the pump light in the 2µm band. It should be noted that the dichroic mirror 3 can be omitted from the optical path, but this may result in residual light from other bands, leading to poor light quality. Furthermore, in other embodiments, the dichroic mirror 3 can be incorporated as part of the 2µm pump source 1, functioning as a CPS (cladding stripper), thus integrating the dichroic mirror 3 into the internal system of the 2µm pump source 1.

[0044] The half-wave plate 4 is located between the collimating lens 2 and the grating pair. The half-wave plate 4 receives parallel linearly polarized light, adjusts the direction of the linearly polarized light, and outputs polarized light at a specific angle, thereby improving the diffraction efficiency of the grating; the specific angle here refers to the angle that coincides with the optimal diffraction direction of the grating 5.

[0045] It should be noted that the half-wave plate 4 can be omitted from the optical path, but the direction of the polarized light may not be consistent with the polarization direction that allows the grating 5 to achieve optimal diffraction conditions, resulting in low diffraction efficiency and thus affecting the compression effect. The presence of the half-wave plate can improve the working efficiency of the grating.

[0046] The reflector used in this embodiment is a D-type reflector because it does not block the light beam from the half-wave plate to the grating pair. Other types of reflectors are also acceptable, as long as the height is adjusted to ensure that they do not block the light beam from the half-wave plate to the grating pair.

[0047] Fluoride optical fibers typically include ZBLAN fiber and InF3 fiber. In this embodiment, ZBLAN fiber is used, although InF3 fiber can also be used. The zero-dispersion wavelengths of ZBLAN and InF3 fibers are 1.6-1.8µm, therefore a 2µm band laser is chosen as the pump source, as pumping in the anomalous dispersion region makes it easier to obtain the maximum spectral broadening.

[0048] The output light from pump source 1 is divergent. To ensure a sufficiently small spot size at the focal point of the final focusing lens 8 for easy spatial coupling into the fluoride fiber 9, the focal length of collimating lens 2 should be large enough, and the focal length of focusing lens 8 should be small enough. The dimensions of collimating lens 2 and focusing lens 8 need to take into account the spot size of the parallel beam to ensure complete transmission and reflection of the pulsed light. The focal length selection should match the numerical aperture and core diameter of the fluoride fiber 9 to ensure maximum coupling efficiency of the pulsed light.

[0049] To reduce power loss during pulsed light transmission in space, collimating lens 2 and focusing lens 8 are CaF2 lenses coated with anti-reflection films. Dichroic mirror 3 is a long-pass dichroic mirror with high transmittance in the 2μm band. Roof prism 6 is a high-reflectivity mirror with a gold coating, and D-type mirror 7 is a high-reflectivity mirror with a silver coating. It should be noted that a gold-coated high-reflectivity mirror is preferred for both the roof prism and the D-type mirror because gold coatings have higher reflectivity in the 2μm band. In this embodiment, the D-type mirror 7 uses a silver coating, which is less effective than a gold coating.

[0050] To improve the laser's peak power and compress the pulse width, two gratings 5 ​​are fixed on two three-dimensional adjustment frames and placed parallel to each other. Changing the transmission distance and the parallel distance between the two grating pairs will affect the compression effect. Therefore, pulse compression should not be pursued indiscriminately; the compression quality factor must be considered, and an optimal compression distance should be selected.

[0051] This invention innovatively introduces a roof prism, whose dual-reflective surface design can precisely correct the optical path angle and reduce beam deviation. Simultaneously, the high reflectivity (>98%) of the gold-plated film significantly reduces energy loss. Especially under high-power pumping, the damage threshold of the roof prism is much higher than that of ordinary mirrors, preventing optical element ablation. Considering the high peak power after pulse compression, this invention innovatively introduces a roof prism to reduce damage to optical elements caused by excessive energy, thereby achieving greater compression efficiency without worrying about exceeding its damage threshold.

[0052] Furthermore, this invention achieves pulse compression through the synergistic effect of a roof prism and a grating pair. The grating pair is placed in parallel and its beam splitting adjusts the optical path. Combined with the secondary passage of reflected light through the grating pair via the roof prism, a closed-loop compression structure is formed. This invention achieves pulse width compression to 2 ps and peak power increase to 1.6 W through the diffraction effect of the grating pair and the optimized reflection path of the roof prism. The parallel spacing of the grating pair (40 cm) and its coordination with the roof prism significantly extend the optical path difference of light at various frequencies, thereby enhancing the nonlinear effect and promoting spectral broadening in both short and long wavelengths.

[0053] The following combination Figure 1 The optical path of this embodiment will be described.

[0054] Please see Figure 1The pump light output from the 2µm pump source 1, which emits diverging light, is first collimated using a lens 2 with high transmittance in the 2µm band. To ensure a suitable spot size after focusing, lens 2 with a focal length of 100mm is selected as the collimating lens. The collimation effect can be observed using a power meter to check the power of the laser spot near lens 2 and compare it with the power of the laser spot as far as possible. If the laser power is consistent, the collimation effect is good; otherwise, the position of lens 2 needs to be readjusted until the laser power is consistent at both near and far distances. Alternatively, a beam observer can be used to observe the size and shape of the spot near and far from lens 2. If the size and shape of the spot are consistent, the collimation effect is good; otherwise, the position of lens 2 needs to be readjusted until the size and shape of the spot are consistent at both near and far distances. The laser beam collimated by lens 2 passes through a dichroic mirror 3, reflecting residual light from other bands while maintaining high transmittance for the 2µm band laser. 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, with a parallel distance of 40cm between the gratings. A gold-plated high-reflectivity roof prism 6 is placed behind the gratings to return the laser along its original path. The laser pulse passes through the gratings again, and according to the autocorrelation instrument, the width of the laser pulse after passing through the gratings can be compressed to 2ps. The laser is then reflected by a silver-plated D-type mirror 7, changing the direction of the light path. Finally, the laser is focused by a lens 8 with a focal length of 40mm, and the spot size at the focal point is about 6.35μm. The laser is then spatially coupled into the ZBLAN fiber.

[0055] ZBLAN optical fibers are cut using a fluoride fiber cleaver to ensure the fiber end face is flat and clean. The fibers are then fixed on a high-precision multi-dimensional adjustment frame. After compression and focusing, the light is spatially coupled into the ZBLAN optical fiber at the focal point. The pulsed light propagates in the ZBLAN optical fiber. Under the nonlinear effect of the optical fiber, the spectrum broadens towards short and long wavelengths, ultimately outputting a mid-infrared supercontinuum laser with a wavelength of 1.37-3.82 μm.

[0056] This invention utilizes a spatial light structure with lens combinations to achieve supercontinuum broadening, thus improving upon the current problems of high research costs and low coupling efficiency of mid-infrared supercontinuum light sources generated by all-fiber structures.

[0057] This invention significantly improves pulse compression efficiency (compressed to 2 ps) through the combination design of ridge prism and grating pair, thereby increasing peak power, and finally achieves spectral broadening (1.37~3.82 µm) through the nonlinear effect of fluoride fiber.

[0058] This invention uses a half-wave plate to adjust the polarization direction (matching the optimal angle of grating diffraction), combining the half-wave plate with the grating to maximize diffraction efficiency and optimize the power loss problem caused by polarization mismatch in spatial light structures.

[0059] In one embodiment of this invention, a dichroic mirror is used to filter out the 793nm laser light, while a pump light in the 2μm band is transmitted. A grating pair compresses the pulse to 2ps. After the compressed light pulse is focused, it is coupled into a fluoride fiber at the focal point. Utilizing the nonlinear characteristics of the fluoride fiber, a mid-infrared supercontinuum with a spectral coverage of 1.37-3.82μm is finally obtained in the ZBLAN 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 in the spatial light structure and improves the problem of low spatial light coupling efficiency.

[0060] The introduction of a dichroic mirror is intended to significantly improve beam purity and prevent backlighting. The dichroic mirror can more precisely filter 793nm laser light (transmittance <1%) and achieve high transmittance (transmittance >99%) for 2µm pump light. Furthermore, this embodiment combines the dichroic mirror with a polarizer; polarization optimization and stray light filtering concentrate the pump light energy, thereby maximizing output power to 1.6 W. The synergistic effect of polarization modulation and beam quality control significantly improves system stability and output efficiency.

[0061] The foregoing has provided a detailed description of a mid-infrared supercontinuum light source with a spatial light structure disclosed in the embodiments of this utility model. Specific examples have been used to illustrate the principle and implementation of this utility model. The description of the above embodiments is only for the purpose of helping to understand the core idea of ​​this utility model. At the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​this utility model. Therefore, the content of this specification should not be construed as a limitation of this utility model.

Claims

1. A mid-infrared supercontinuum light source with a spatial optical structure, characterized in that, include: Pump source, used to generate pump light; A collimating lens is used to collimate the pump light generated by the pump source, and to collimate the divergent pump light into parallel light. A grating pair consists of two parallel gratings. It is used to split the light input to the grating pair according to the frequency and change the optical path of each frequency light, outputting 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, outputting compressed light to the reflector. A roof prism is used to reflect light that has passed through a grating pair back through the grating pair. A reflector is used to reflect the compressed light to change the direction of the light path; A focusing lens is used to focus the compressed light reflected by the mirror; Fluoride optical fiber, where compressed light focused by the focusing lens is spatially coupled into the fluoride optical fiber at the focal point, the spectrum is broadened in the short and long wavelength directions, and mid-infrared supercontinuum laser is output; A half-wave plate, located between the collimating lens and the grating pair, is used to adjust the polarization angle of parallel light and output polarized light at a specific angle to the grating pair. A dichroic mirror, located between the collimating lens and the half-wave plate, is used to filter out stray light in parallel light while allowing high transmission of pump light.

2. The mid-infrared supercontinuum light source according to claim 1, characterized in that, The pump source includes: Seed source, used to output pulsed laser with a center wavelength of 1.5μm; An amplifier is used to amplify the power of the pulsed laser output from the seed source, and output pump light with a center wavelength of 2μm.

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

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

5. The mid-infrared supercontinuum light source according to claim 2, characterized in that, The parallel distance between the grating pairs is 40 cm, and the fluoride optical fiber outputs mid-infrared supercontinuum laser with a wavelength of 1.37-3.82 μm.

6. The mid-infrared supercontinuum light source according to claim 2, characterized in that, The collimating lens has a focal length of 100mm, and the focusing lens has a focal length of 40mm.

7. The mid-infrared supercontinuum light source according to claim 1, characterized in that, The ridge prism is a high-reflectivity mirror with a gold-plated coating; the collimating lens and the focusing lens are CaF2 lenses with anti-reflection coatings.

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