Visible wave band tunable femtosecond pulse laser generating device

Abstract

The invention discloses a visible wave band tunable femtosecond pulse laser generating device which comprises an input side single-mode optical fiber jumper assembly, a visible light frequency comb generating module, a collimating lens, a tunable filtering module, a focusing lens and an output side single-mode optical fiber jumper assembly which are sequentially arranged along a laser light path. The visible light frequency comb generation module comprises a germanium core optical fiber, the germanium core optical fiber is a conical optical fiber and comprises a fiber core and a cladding, the fiber core is a SiO2 fiber core with the GeO2 doping concentration being 98 mol.%, the cladding is a SiO2 cladding, and the input end of the germanium core optical fiber is welded to the output end of the input side single-mode optical fiber patch cord assembly. The device is high in integration level, integrated all-fiber and tunable stable and accurate single-wavelength femtosecond pulse laser output is achieved through an all-fiber structure, coupling can be completed without frequently adjusting a light path in the using process, manpower and material resources are saved, and the laser generator is small in structure, good in compatibility and high in practicability. And the system can be conveniently applied to a large-scale complex optical system.

Description

Technical Field

[0001] The present invention relates to the design and preparation technology of novel optical components, and in particular to a visible band tunable femtosecond pulse laser generating device, which is mainly used in the fields of nonlinear optics and ultrafast lasers. Background Art

[0002] Visible ultrashort pulse lasers, with their high peak power and extremely short temporal resolution, have significant application value in precision machining, nonlinear optics, precision measurement, medical surgery, quantum control, and optical communications. However, due to limitations in gain media and generation methods, the technology for generating femtosecond visible-wavelength lasers is currently immature. In particular, wavelength-tunable visible-wavelength femtosecond lasers have yet to be reported internationally. Dispersive waves, however, offer a promising approach for generating visible-wavelength femtosecond lasers.

[0003] Dispersive waves are the phenomenon in which energy is transferred from the input pulse to new spectral components when an optical pulse propagates in a nonlinear medium due to perturbations such as high-order dispersion, nonlinear effects, and various losses. It is well known that sufficiently powerful femtosecond laser pulses propagating in the anomalous group velocity dispersion region of a nonlinear medium can induce the generation of high-order solitons, leading to an initial spectral broadening caused by self-phase modulation and a temporal compression proportional to the number of solitons. At the compression point, when the spectrum is extensively broadened, solitons are perturbed by high-order dispersion or nonlinear terms, causing solitons to fission and transfer energy to linear dispersive waves shifted from the pump frequency. The generation of dispersive waves can occur at frequencies where the phase constant of the soliton pulse equals that of the linear wave, i.e., at the phase-matching point. It has been demonstrated that the generation of phase-matched dispersive waves corresponds to the appearance of a zero-dispersion wavelength. The study of dispersive waves provides a theoretical foundation for the development of broadband light sources, the optimization of optical communication systems, and the exploration of nonlinear dynamics, and profoundly reveals the complex mechanisms of light-matter interactions.

[0004] Currently known methods for dispersive wave manipulation include photonic crystal fibers and nonlinear manipulation, integrated optical waveguides and on-chip manipulation, spectral phase modulation, and whispering gallery mode microcavity structure design and manipulation. Photonic crystal fibers and nonlinear manipulation utilize fiber microstructure design combined with nonlinear effects to manipulate the wavelength and energy of dispersive waves. However, the design process is complex, and fabrication is challenging and costly. Integrated optical waveguides and on-chip manipulation utilize waveguides designed with materials such as thin-film lithium niobate to tune dispersion parameters in real time through the electro-optic effect. However, these methods have a limited tuning range, low energy tolerance, and difficulty in coupling. Spectral phase modulation applies spectral sinusoidal phase modulation to the incident pulse, changing its temporal shape to manipulate the radiation characteristics of the dispersive wave. However, these systems are complex, and sideband effects can degrade pulse compression quality and limit the operating bandwidth. Whispering gallery mode microcavity structure design and manipulation achieves dispersion control of whispering gallery mode microcavities by controlling the dimensions of the microdisk cavity. This requires high fabrication precision and carries the risk of intermodal crosstalk. Generating dispersive waves in the visible band is of great significance for tunable visible light femtosecond light sources. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a tunable femtosecond pulse laser generating device in the visible band in response to the shortcomings of the existing technology. The device can achieve stable and accurate single-wavelength femtosecond pulse laser output, and the device is highly integrated and fully optical, making it easy to be applied to large and complex optical systems.

[0006] The technical solution adopted by the present invention to solve the above technical problems is: a visible band tunable femtosecond pulse laser generating device, including an input side single-mode fiber jumper assembly, a visible light frequency comb generating module, a collimating lens, a tunable filter module, a focusing lens and an output side single-mode fiber jumper assembly arranged in sequence along the laser light path, the visible light frequency comb generating module includes a germanium core fiber, the germanium core fiber is a tapered fiber, the germanium core fiber includes a core and a cladding, the core is a SiO2 core with a GeO2 doping concentration of 98 mol.%, the cladding is a SiO2 cladding, the germanium core fiber The input end is fused with the output end of the input-side single-mode fiber jumper assembly, the input-side single-mode fiber jumper assembly is used to introduce the laser beam emitted by the laser light source into the germanium core fiber, the germanium core fiber is used to generate a frequency comb of different wavelengths in the visible light band, the collimating lens is used to collimate the laser beam output by the germanium core fiber, the tunable filter module is used to perform filtering processing of different wavelengths on the collimated laser beam to filter out femtosecond pulse laser of a specific wavelength, and the focusing lens is used to focus the femtosecond pulse laser and couple it into the output-side single-mode fiber jumper assembly for output.

[0007] The device of the present invention uses a germanium-core fiber to generate a frequency comb of different wavelengths in the visible light band, and then uses a tunable filter module to generate a femtosecond laser of a specific wavelength in the visible light band. The physical and chemical properties of the germanium-core fiber are similar to those of ordinary single-mode quartz fiber, making it easy to efficiently fusion-splice and possessing high bending strength. The germanium-core fiber used in the device of the present invention is tapered, and the tunable filter module enables control of the output wavelength. Tapering changes the fiber's structure, thereby affecting dispersion and altering the phase matching point. Calculation of the phase matching point predicts the location of the dispersion wave, generating new wavelength components that differ from those obtained with non-tapered germanium-core fiber.

[0008] When the device of the present invention is used, a laser beam is coupled into a germanium core optical fiber through an input-side single-mode optical fiber jumper assembly. Due to the influence of high-order dispersion and nonlinear effects, a plurality of high-order modes are excited. The dispersion of different modes is different. By adjusting the dispersion of different modes, frequency combs in different visible light bands are generated. The output end of the germanium core optical fiber has a large optical fiber numerical aperture, which causes the output laser beam to be relatively divergent. Therefore, a collimating lens is used for collimation. The collimated laser beam can be selectively filtered out of a desired specific wavelength of femtosecond pulse laser light through a tunable filter module. The femtosecond pulse laser light is focused by a focusing lens and coupled into the output-side single-mode optical fiber jumper assembly for output.

[0009] The device of the present invention utilizes an internal structure that allows for fiber optic patch cord input and output, resulting in an all-fiber external structure. This all-fiber structure enables integrated, all-fiber, tunable single-wavelength femtosecond pulse laser output. This device eliminates the need for frequent optical path adjustments to achieve coupling, saving manpower and resources. Furthermore, the laser generator's compact structure and excellent compatibility make it suitable for use in large and complex optical systems.

[0010] Preferably, the tunable filter module includes a multi-band filter, a knob, a connecting shaft, a first bevel gear, a second bevel gear, a first spur gear, a second spur gear, and a rack. The two ends of the connecting shaft are coaxially fixedly connected to the knob and the first bevel gear, respectively. The first bevel gear meshes with the second bevel gear, the second bevel gear is coaxially fixedly connected to the first spur gear, the first spur gear and the second spur gear are respectively meshed with the rack, the end of the rack is limited by a baffle, the multi-band filter is coaxially fixedly connected to the second spur gear, the multi-band filter is composed of multiple sub-filters with different filtering bands, and the filtering range of the multi-band filter is 400 to 800 nm. The above-mentioned tunable filter module has a simple structure, is easy to operate, and can achieve rapid adjustment of the filtering component. When in use, the knob is rotated to drive the first bevel gear to rotate, causing the second bevel gear and the first flat gear to rotate, and power is transmitted to the second flat gear through the rack, driving the second flat gear to rotate, and then driving the multi-band filter to rotate until the sub-filter of the required filtering band is in the laser light path, so as to filter out the required specific wavelength of femtosecond pulse laser.

[0011] As a further preference, the multi-band filter is composed of eight sub-filters, and the filtering bands of the eight sub-filters are 400-450nm, 450-500nm, 500-550nm, 550-600nm, 600-650nm, 650-700nm, 700-750nm and 750-800nm ​​respectively.

[0012] As a further preferred embodiment, the input-side single-mode fiber optic patch cord assembly is formed by connecting a first input-side single-mode fiber optic patch cord and a second input-side single-mode fiber optic patch cord, and the output-side single-mode fiber optic patch cord assembly is formed by connecting a first output-side single-mode fiber optic patch cord and a second output-side single-mode fiber optic patch cord, wherein the second input-side single-mode fiber optic patch cord, the germanium core fiber, the collimating lens, the multi-band filter, the focusing lens, and the first output-side single-mode fiber optic patch cord are respectively arranged in a box body, a cover plate is installed on the top of the box body, the first input-side single-mode fiber optic patch cord, the second output-side single-mode fiber optic patch cord, and the knob are respectively arranged outside the box body, the germanium core fiber and the first output-side single-mode fiber optic patch cord are respectively supported by fiber fixings, and the input end of the germanium core fiber is fused with the output end of the second input-side single-mode fiber optic patch cord. The main components of the device of the present invention are encapsulated in the box body through a modular design, which is easy to operate during testing and use and convenient to carry.

[0013] Preferably, the input-side single-mode optical fiber jumper assembly and the output-side single-mode optical fiber jumper assembly are both composed of SMF-28 single-mode quartz optical fiber.

[0014] Preferably, the core diameter is 8 μm, and the cladding diameter is 125 μm.

[0015] Compared with existing technologies, the present invention offers the following advantages: The present invention's visible-band tunable femtosecond pulse laser generator utilizes a germanium-core optical fiber to generate a frequency comb of different wavelengths in the visible light band, and then utilizes a tunable filter module to generate a specific wavelength femtosecond laser in the visible band. The device boasts a high level of integration, achieving integrated, fully fiber-based, tunable, stable, and precise single-wavelength femtosecond pulse laser output through an all-fiber structure. During use, the device eliminates the need for frequent optical path adjustments to achieve coupling, saving both manpower and material resources. Furthermore, the laser generator's compact structure and excellent compatibility facilitate its application in large and complex optical systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 2. A top view of the structure of the visible band tunable femtosecond pulse laser generating device with the cover opened in the embodiment;

[0017] Figure 2 This is a structural axonometric diagram of the visible band tunable femtosecond pulse laser generating device with the cover opened in the embodiment;

[0018] Figure 3 for Figure 2 Enlarged view of point A in the middle;

[0019] Figure 4 is the normalized curve for filtering out the 615.5nm wavelength component;

[0020] Figure 5 is the calculated Fourier limit pulse width at 615.5 nm;

[0021] Figure 6 This is the spectrum generated by GeO2 fiber at a pump wavelength of 1560nm;

[0022] Figure 7 To simulate the different mode integrated dispersion curves of GeO2 fiber at a pump wavelength of 1560nm;

[0023] Figure 8 To simulate the different mode integrated dispersion curves of GeO2 fiber with waist diameter of 110μm at pump wavelength of 1560nm;

[0024] Figure 9 To simulate the different mode integrated dispersion curves of GeO2 fiber with a waist diameter of 100μm at a pump wavelength of 1560nm;

[0025] Figure 10 To simulate the different mode integrated dispersion curves of GeO2 fiber with waist diameter of 90μm at pump wavelength of 1560nm;

[0026] Note: Figures 7 to 10In the figure, LP01, LP11, LP21, LP02, LP12, LP31, LP22, LP41, and LP51 represent different modes respectively. DETAILED DESCRIPTION

[0027] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

[0028] Embodiment: A visible band tunable femtosecond pulse laser generating device, such as Figure 1-Figure 3 As shown, it includes an input-side single-mode fiber jumper assembly, a visible light frequency comb generation module, a collimating lens 3, a tunable filter module 4, a focusing lens 5, and an output-side single-mode fiber jumper assembly arranged in sequence along the laser light path. The visible light frequency comb generation module includes a germanium core fiber 2, which is a tapered fiber. The germanium core fiber 2 includes a core and a cladding. The core diameter is 8 μm, the cladding diameter is 125 μm, the core is a SiO2 core with a GeO2 doping concentration of 98 mol.%, and the cladding is a SiO2 cladding. The input-side single-mode fiber jumper assembly is used to introduce a laser beam emitted by a laser light source (not shown in the figure) into the germanium core fiber 2. The germanium core fiber 2 is used to generate a frequency comb of different wavelengths in the visible light band. The collimating lens 3 is used to collimate the laser beam output by the germanium core fiber 2. The tunable filter module 4 is used to perform filtering processing of different wavelengths on the collimated laser beam to filter out femtosecond pulse lasers of specific wavelengths. The focusing lens 5 is used to focus the femtosecond pulse laser and couple it into the output-side single-mode fiber jumper assembly for output.

[0029] In this embodiment, the tunable filter module 4 includes a multi-band filter 41, a knob 42, a connecting shaft 43, a first bevel gear 44, a second bevel gear 45, a first flat gear 46, a second flat gear 47 and a rack 48. The two ends of the connecting shaft 43 are coaxially fixedly connected to the knob 42 and the first bevel gear 44, the first bevel gear 44 is meshed with the second bevel gear 45, the second bevel gear 45 is coaxially fixedly connected to the first flat gear 46, the first flat gear 46 and the second flat gear 47 are respectively meshed with the rack 48, and the end of the rack 48 is limited by the baffle 49. The multi-band filter 41 is coaxially fixedly connected to the second spur gear 47. The multi-band filter 41 is composed of multiple sub-filters 40 with different filtering bands. The filtering range of the multi-band filter 41 is 400-800nm. Specifically, the multi-band filter 41 is composed of eight sub-filters 40. The filtering bands of the eight sub-filters 40 are 400-450nm, 450-500nm, 500-550nm, 550-600nm, 600-650nm, 650-700nm, 700-750nm and 750-800nm. Figure 4 As shown, the spectral width after filtering at a wavelength of 615.5 nm is 5.1 nm, and the Fourier limit pulse width is calculated to be 78 fs. Figure 5 shown.

[0030] In this embodiment, the input side single-mode fiber optic jumper assembly is formed by connecting the first input side single-mode fiber optic jumper 11 and the second input side single-mode fiber optic jumper 12, and the output side single-mode fiber optic jumper assembly is formed by connecting the first output side single-mode fiber optic jumper 61 and the second output side single-mode fiber optic jumper 62. The second input side single-mode fiber optic jumper 12, the germanium core fiber 2, the collimating lens 3, the multi-band filter 41, the focusing lens 5 and the first output side single-mode fiber optic jumper 61 are respectively arranged in a box body 71, and a cover plate 72 is installed on the top of the box body 71. The first input side single-mode fiber optic jumper 11, the second output side single-mode fiber optic jumper 62 and the knob 42 are respectively arranged outside the box body 71, and the germanium core fiber 2 and the first output side single-mode fiber optic jumper 61 are respectively supported by fiber fixing parts 73.

[0031] In this embodiment, the input end of the Germanium-core fiber 2 is fused to the output end of the second input-side single-mode fiber optic patch cord 12. Both the input-side single-mode fiber optic patch cord assembly and the output-side single-mode fiber optic patch cord assembly are composed of SMF-28 single-mode quartz fiber. Due to the high nonlinear coefficient of the Germanium-core fiber 2, a length of 33 cm is sufficient for the device. The distance between the output end of the Germanium-core fiber 2 and the collimating lens 3 is 10 mm, and the focal length f of the collimating lens 3 is 10 mm.

[0032] When the visible band tunable femtosecond pulse laser generating device of this embodiment is used, the laser light source emits a 1560nm short pulse laser beam, which is coupled into the germanium core fiber 2 through the input side single-mode fiber jumper assembly. Through the influence of high-order dispersion and nonlinear effects, a large number of high-order modes are excited. The dispersion of different modes is different. By adjusting the dispersion of different modes, different frequency combs in the visible light band are generated (such as Figure 6 As shown); the output end of the germanium core optical fiber 2 has a large numerical aperture, which causes the output laser beam to diverge, so a collimating lens 3 is used for collimation; the collimated laser beam can be selectively filtered out by a tunable filter module 4 to obtain a femtosecond pulse laser of a specific wavelength; the femtosecond pulse laser is focused by a focusing lens 5 and coupled into the output-side single-mode optical fiber jumper assembly for output.

[0033] In nonlinear media, the propagation of solitons may be accompanied by the formation of dispersive waves. This is caused by the coherent transfer of energy from the soliton to a narrowband resonant feature similar to Cherenkov radiation. The spectral position of this resonant feature can be determined by the Cherenkov-type phase matching between the linear and nonlinear phases of the soliton and the linear phase of the emitted radiation to determine the frequency of the dispersive wave. Theoretical analysis of phase matching requires the calculation of the integrated dispersion β int :

[0034]

[0035] β is the propagation constant, ω s is the pump frequency, ω is the frequency variable, v g is the group velocity at the pump frequency. int = 0, the phase matching condition is met. Pumping at the phase matching point will generate dispersive waves at the phase matching point of the short wave.

[0036] Different modes have different phase matching points. To achieve a frequency comb with multiple wavelengths, it is necessary to excite higher-order modes other than the fundamental mode LP01, such as LP11, LP21, LP02, LP31, LP41, LP12, LP51, and LP22.

[0037] The number of modes transmitted in an optical fiber is determined by the normalized frequency V, which is defined by the following equation:

[0038]

[0039] d is the fiber diameter, NA is the numerical aperture, and the mode number of the step-index fiber is As the diameter d decreases or the wavelength λ increases, the number of modes supported in the fiber decreases. Therefore, when laser light is transmitted to the waist region of the tapered fiber, the number of modes supported at the same wavelength decreases, and some higher-order modes are cut off, resulting in a lack of a richer wavelength component. Therefore, a balance must be struck between the number of modes and the control range. When controlling within a certain diameter range (above 90μm), the smaller the tapered fiber diameter, the more the integrated dispersion of different modes exhibits the same trend, and the position of the dispersive wave shifts linearly. At this point, common higher-order modes are not cut off, so these higher-order modes can be utilized to generate a richer dispersive wave component.

[0040] When the pump wavelength is 1560nm, the phase matching points of different modes are basically consistent with the positions of the dispersion waves generated in the experiment, such as Figure 7 The waist diameters of the tapered germanium core fiber are calculated to be 110μm, 100μm, and 90μm, respectively. When the pump wavelength is 1560nm, the phase matching points of different modes are different from those in the standard germanium core fiber, as shown in Figure 2. Figure 8 、 Figure 9 and Figure 10 This means that the new dispersion wave wavelength components can be changed by changing the fiber diameter through tapering, which has great research potential.

[0041] In summary, the visible band tunable femtosecond pulse laser generator of the present invention has excellent stability, can realize all-fiber input and output, and can tune femtosecond laser outputs of different wavelengths by rotating germanium-core fibers with different tapered parameters and multi-band filters.

Claims

1. A visible band tunable femtosecond pulse laser generator, characterized in that: The invention comprises an input-side single-mode fiber jumper assembly, a visible light frequency comb generation module, a collimating lens, a tunable filter module, a focusing lens, and an output-side single-mode fiber jumper assembly, which are sequentially arranged along a laser light path. The visible light frequency comb generation module comprises a germanium core fiber, which is a tapered fiber and comprises a core and a cladding. The core is a SiO2 core with a GeO2 doping concentration of 98 mol%, and the cladding is a SiO2 cladding. The input end of the germanium core fiber is fused with the output end of the input-side single-mode fiber jumper assembly. The input-side single-mode fiber jumper assembly is used to introduce a laser beam emitted by a laser light source into the germanium core fiber. The germanium core fiber is used to generate a frequency comb of different wavelengths in the visible light band. The collimating lens is used to collimate the laser beam output by the germanium core fiber. The tunable filter module is used to perform filtering processing of different wavelengths on the collimated laser beam to filter out femtosecond pulse lasers of specific wavelengths. The focusing lens is used to focus the femtosecond pulse laser and couple it into the output-side single-mode fiber jumper assembly for output.

2. The visible band tunable femtosecond pulse laser generator according to claim 1, characterized in that: The tunable filter module includes a multi-band filter, a knob, a connecting shaft, a first bevel gear, a second bevel gear, a first spur gear, a second spur gear and a rack. The two ends of the connecting shaft are coaxially fixedly connected to the knob and the first bevel gear respectively, the first bevel gear is meshed with the second bevel gear, the second bevel gear is coaxially fixedly connected to the first spur gear, the first spur gear and the second spur gear are respectively meshed with the rack, the end of the rack is limited by a baffle, the multi-band filter is coaxially fixedly connected to the second spur gear, the multi-band filter is composed of multiple sub-filters with different filtering bands, and the filtering range of the multi-band filter is 400 to 800 nm.

3. The visible band tunable femtosecond pulse laser generator according to claim 2, characterized in that: The multi-band filter is composed of eight sub-filters, and the filtering bands of the eight sub-filters are 400-450nm, 450-500nm, 500-550nm, 550-600nm, 600-650nm, 650-700nm, 700-750nm and 750-800nm ​​respectively.

4. The visible band tunable femtosecond pulse laser generator according to claim 2, characterized in that: The input-side single-mode fiber optic jumper assembly is formed by connecting a first input-side single-mode fiber optic jumper and a second input-side single-mode fiber optic jumper. The output-side single-mode fiber optic jumper assembly is formed by connecting a first output-side single-mode fiber optic jumper and a second output-side single-mode fiber optic jumper. The second input-side single-mode fiber optic jumper, the germanium core fiber, the collimating lens, the multi-band filter, the focusing lens and the first output-side single-mode fiber optic jumper are respectively arranged in a box body. A cover plate is installed on the top of the box body. The first input-side single-mode fiber optic jumper, the second output-side single-mode fiber optic jumper and the knob are respectively arranged outside the box body. The germanium core fiber and the first output-side single-mode fiber optic jumper are respectively supported by fiber fixing parts. The input end of the germanium core fiber is fused with the output end of the second input-side single-mode fiber optic jumper.

5. The visible band tunable femtosecond pulse laser generator according to claim 1, characterized in that: The input side single-mode optical fiber jumper assembly and the output side single-mode optical fiber jumper assembly are both composed of SMF-28 single-mode quartz optical fiber.

6. The visible band tunable femtosecond pulse laser generator according to claim 1, characterized in that: The core diameter is 8 μm, and the cladding diameter is 125 μm.

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