A visible band tunable femtosecond pulse laser generating device

Abstract

The application discloses a kind of visible band tunable femtosecond pulse laser generation device, including input side single-mode optical fiber jumper component, visible light frequency comb generation module, collimating lens, tunable filter module, focusing lens and output side single-mode optical fiber jumper component in turn along laser light path, visible light frequency comb generation module includes germanium core optical fiber, germanium core optical fiber is tapered optical fiber, including core and cladding, core is SiO2 core of GeO2 doping concentration 98mol.%, cladding is SiO2 cladding, the input end of germanium core optical fiber is fused with the output end of input side single-mode optical fiber jumper component.The device has high integration, and through the structure of all-fiber realizes integrated all-fiber and tunable stable, accurate single-wavelength femtosecond pulse laser output, does not need to adjust optical path frequently to complete coupling in use process, saves manpower and material resources, and the laser generator structure is small and exquisite, compatibility is good, and it is convenient to be applied in large-scale complex optical system.

Description

Technical Field

[0001] This invention relates to the design and fabrication technology of novel optical components, specifically to a visible-band tunable femtosecond pulse laser generator, which is mainly applied in the fields of nonlinear optics and ultrafast lasers. Background Technology

[0002] Visible ultrashort pulse lasers, with their high peak power and extremely short temporal resolution, have significant applications in precision machining, nonlinear optics, precision measurement, medical surgery, quantum control, and optical communication. However, due to limitations in gain media and generation methods, the technology for generating femtosecond-level visible light lasers is not yet mature, especially wavelength-tunable visible femtosecond lasers, which have not yet been reported internationally. Dispersive waves, on the other hand, represent a highly promising method for generating visible femtosecond laser sources.

[0003] Dispersive waves are the phenomenon where energy is transferred from the input pulse to new spectral components when a light pulse propagates in a nonlinear medium due to perturbations caused by higher-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 higher-order solitons, leading to initial spectral broadening caused by self-phase modulation and time compression proportional to the soliton number. At the compression point, when the spectrum is extensively broadened, the soliton is perturbed by higher-order dispersion or nonlinear terms, causing soliton fission and transferring energy to a linearly dispersed wave shifted from the pump frequency. The generation of dispersive waves can occur at frequencies where the phase constant of the soliton pulse equals the phase constant of the linear wave, i.e., at the phase-matching point, and it has been proven 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 developing broadband light sources, optimizing optical communication systems, and exploring nonlinear dynamics, profoundly revealing the complex mechanisms of light-matter interaction.

[0004] Currently known methods for controlling dispersive waves include photonic crystal fiber and nonlinear modulation, integrated optical waveguide and on-chip modulation, spectral phase modulation technology, and whispering-gallery mode microcavity structure design and control. Photonic crystal fiber and nonlinear modulation utilizes fiber microstructure design combined with nonlinear effects to control the wavelength and energy of dispersive waves; however, its design process is complex, and its fabrication is difficult and costly. Integrated optical waveguide and on-chip modulation designs waveguides based on materials such as thin-film lithium niobate, and tunes dispersive parameters in real time through electro-optic effects; however, its tuning range is small, and it suffers from low energy handling and coupling difficulties. Spectral phase modulation technology applies sinusoidal phase modulation to the incident pulse, changing the time-domain shape to control the dispersive wave radiation characteristics; however, its system is complex, and sideband effects lead to pulse compression quality degradation and limited operating bandwidth. Whispering-gallery mode microcavity structure design and control achieves dispersive control of whispering-gallery mode microcavities by controlling the size of the microcavity; however, it requires high fabrication precision and carries the risk of intermodal crosstalk. The generation of dispersive waves in the visible band is of great significance for tunable visible femtosecond light sources. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a visible band tunable femtosecond pulse laser generating device in view of the shortcomings of the prior art. The device can achieve stable and accurate single-wavelength femtosecond pulse laser output. Moreover, the device has high integration and is all fiber optic, which makes it easy to apply to large and complex optical systems.

[0006] The technical solution adopted by this invention to solve the above-mentioned technical problems is as follows: a visible-band tunable femtosecond pulse laser generation device, comprising an input-side single-mode fiber optic patch cord assembly, a visible light frequency comb generation module, a collimating lens, a tunable filtering module, a focusing lens, and an output-side single-mode fiber optic patch cord assembly arranged sequentially along the laser optical path. The visible light frequency comb generation module comprises a germanium-core fiber, which 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.%, and the cladding is a SiO2 cladding. The input end of the device is fused to the output end of the input-side single-mode fiber optic patch cord assembly. The input-side single-mode fiber optic patch cord assembly is used to introduce the laser beam emitted by the laser source into the germanium core fiber. The germanium core fiber is used to generate frequency combs of different wavelengths in the visible light band. The collimating lens is used to collimate the laser beam output from the germanium core fiber. The tunable filter module is used to filter the collimated laser beam at different wavelengths 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 optic patch cord assembly for output.

[0007] This invention's device generates frequency combs of different wavelengths in the visible light band using germanium-core optical fiber, and then generates femtosecond lasers of specific wavelengths in the visible light band through a tunable filter module. The physicochemical properties of germanium-core optical fiber are similar to those of ordinary single-mode silica optical fiber, making it easy to perform efficient fusion splicing and possessing high bending strength. The germanium-core optical fiber used in this invention is tapered. The output wavelength can be controlled through the tunable filter module. The tapering alters the fiber's structure, thus affecting dispersion and changing the phase matching point. By calculating the phase matching point, the location of the dispersion wave can be predicted, generating new wavelength components different from those obtained with non-tapered germanium-core optical fiber.

[0008] In use, the laser beam is coupled into the germanium-core fiber through the input-side single-mode fiber patch cord assembly. Due to the influence of higher-order dispersion and nonlinear effects, numerous higher-order modes are excited. The dispersion of different modes varies, and by adjusting the dispersion of different modes, frequency combs with different frequencies in the visible light band are generated. Because the output end of the germanium-core fiber has a large numerical aperture, the output laser beam is relatively divergent; therefore, a collimating lens is used for collimation. The collimated laser beam is then selectively filtered through a tunable filter module to select a femtosecond pulse laser of a specific wavelength. The femtosecond pulse laser is focused by a focusing lens and coupled into the output-side single-mode fiber patch cord assembly for output.

[0009] This invention's device achieves fiber optic patch cord input and output through internal structural design, realizing an all-fiber external structure. This all-fiber structure enables integrated, tunable, single-wavelength femtosecond pulsed laser output. The device eliminates the need for frequent optical path adjustments for coupling, saving manpower and resources. Furthermore, the laser generator is compact, highly compatible, and easily applied to 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. Both ends of the connecting shaft are coaxially and fixedly connected to the knob and the first bevel gear, respectively. The first bevel gear meshes with the second bevel gear, and the second bevel gear is coaxially and fixedly connected to the first spur gear. The first spur gear and the second spur gear mesh with the rack, and the end of the rack is limited by a baffle. The multi-band filter is coaxially and 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 400–800 nm. The above-mentioned tunable filter module has a simple structure, is easy to operate, and can achieve rapid adjustment of the filtered components. In use, rotating the knob drives the first bevel gear to rotate, causing the second bevel gear and the first spur gear to rotate. Power is transmitted to the second spur gear through the rack, causing the second spur gear to rotate, which in turn drives the multi-band filter to rotate until the sub-filter of the desired filtering band is in the laser optical path, so as to filter out the femtosecond pulse laser of the desired specific wavelength.

[0011] As a further preferred embodiment, the multi-band filter consists of eight sub-filters, the filtering bands of which 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. The second input-side single-mode fiber optic patch cord, germanium-core fiber, collimating lens, multi-band filter, focusing lens, and the first output-side single-mode fiber optic patch cord are each housed within a housing. A cover plate is installed on the top of the housing. The first input-side single-mode fiber optic patch cord, the second output-side single-mode fiber optic patch cord, and a knob are respectively located outside the housing. The germanium-core fiber and the first output-side single-mode fiber optic patch cord are supported by fiber optic fasteners. The input end of the germanium-core fiber optic patch cord is fused to the output end of the second input-side single-mode fiber optic patch cord. The main components of the device of this invention are modularly designed and packaged within a housing, making operation convenient during testing and use, and easy to carry.

[0013] Preferably, 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 silica fiber.

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

[0015] Compared with existing technologies, the present invention has the following advantages: The visible-band tunable femtosecond pulse laser generator of the present invention generates frequency combs of different wavelengths in the visible light band through germanium-core optical fiber, and then generates femtosecond lasers of specific wavelengths in the visible light band through a tunable filtering module. This device has high integration, achieving integrated, all-fiber, tunable, stable, and precise single-wavelength femtosecond pulse laser output through an all-fiber structure. During use, the device does not require frequent adjustments to the optical path for coupling, saving manpower and resources. Furthermore, the laser generator has a compact structure, good compatibility, and is easy to apply to large and complex optical systems. Attached Figure Description

[0016] Figure 1 This is a top view of the visible band tunable femtosecond pulse laser generator in the embodiment after the cover plate is opened;

[0017] Figure 2 This is an isometric view of the visible band tunable femtosecond pulse laser generator in the embodiment after the cover plate is opened;

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

[0019] Figure 4 To filter out the normalized curve of the 615.5nm wavelength component;

[0020] Figure 5 The Fourier limiting pulse width at 615.5 nm was calculated.

[0021] Figure 6 The spectrum generated by GeO2 optical fiber at a pump wavelength of 1560 nm;

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

[0023] Figure 8 To simulate the integral dispersion curves of different modes of a GeO2 fiber with a pump wavelength of 1560nm and a waist diameter of 110μm;

[0024] Figure 9 To simulate the integral dispersion curves of different modes of a 100μm diameter GeO2 fiber with a pump wavelength of 1560nm in the lower waist region;

[0025] Figure 10 To simulate the integral dispersion curves of different modes of a 90μm diameter GeO2 fiber with a pump wavelength of 1560nm in the lower waist region;

[0026] Note: Figures 7-10In this context, LP01, LP11, LP21, LP02, LP12, LP31, LP22, LP41, and LP51 represent different modes. Detailed Implementation

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

[0028] Example: A visible-band tunable femtosecond pulse laser generator, such as... Figures 1-3 As shown, the system includes an input-side single-mode fiber optic patch cord 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 optic patch cord assembly arranged sequentially along the laser optical 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, and 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 optic patch cord assembly is used to introduce the laser beam emitted by the laser source (not shown in the figure) into the germanium-core fiber 2. The germanium-core fiber 2 is used to generate frequency combs of different wavelengths in the visible light band. The collimating lens 3 is used to collimate the laser beam output from the germanium-core fiber 2. The tunable filter module 4 is used to filter the collimated laser beam at different wavelengths 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 optic patch cord 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 spur gear 46, a second spur gear 47, and a rack 48. The two ends of the connecting shaft 43 are coaxially and fixedly connected to the knob 42 and the first bevel gear 44, respectively. The first bevel gear 44 meshes with the second bevel gear 45, and the second bevel gear 45 is coaxially and fixedly connected to the first spur gear 46. The first spur gear 46 and the second spur gear 47 mesh with the rack 48, and the end of the rack 48 is limited by a baffle 49. The multi-band filter... 41 is coaxially and fixedly connected to the second spur gear 47. The multi-band filter 41 is composed of multiple filter chips 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 filter chips 40, and the filtering bands of these eight filter chips 40 are 400-450nm, 450-500nm, 500-550nm, 550-600nm, 600-650nm, 650-700nm, 700-750nm, and 750-800nm, respectively. Figure 4 As shown, the filtered spectral width at a wavelength of 615.5 nm is 5.1 nm, and the Fourier-limited pulse width calculation yields a value of 78 fs. Figure 5 As shown.

[0030] In this embodiment, the input-side single-mode fiber optic patch cord assembly is formed by connecting the first input-side single-mode fiber optic patch cord 11 and the second input-side single-mode fiber optic patch cord 12, and the output-side single-mode fiber optic patch cord assembly is formed by connecting the first output-side single-mode fiber optic patch cord 61 and the second output-side single-mode fiber optic patch cord 62. The second input-side single-mode fiber optic patch cord 12, germanium core fiber 2, collimating lens 3, multi-band filter 41, focusing lens 5, and first output-side single-mode fiber optic patch cord 61 are respectively disposed in a housing 71. A cover plate 72 is installed on the top of the housing 71. The first input-side single-mode fiber optic patch cord 11, the second output-side single-mode fiber optic patch cord 62, and the knob 42 are respectively disposed outside the housing 71. The germanium core fiber 2 and the first output-side single-mode fiber optic patch cord 61 are respectively supported by fiber optic fixing components 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 patch cord 12. Both the input-side and output-side single-mode fiber patch cord assemblies are composed of SMF-28 single-mode silica fiber. Since the germanium-core fiber 2 has a high nonlinear coefficient, a length of 33cm is sufficient for the device requirements. The distance between the output end of the germanium-core fiber 2 and the collimating lens 3 is 10mm, and the focal length of the collimating lens 3 is f = 10mm.

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

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

[0034]

[0035] β is the propagation constant, ω s v is the pump frequency, ω is the frequency variable, and v g The group velocity is at the pump frequency. When β int When = 0, the phase matching condition is satisfied. Pumping at the phase matching point will produce a dispersive wave at the phase matching point of the shortwavelength.

[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 formula:

[0038]

[0039] d represents the fiber diameter, NA represents the numerical aperture, and the number of modes in a step-index fiber is... As the diameter d decreases or the wavelength λ increases, the number of supported modes in the optical fiber decreases. Therefore, when laser light is transmitted to the waist region of a tapered fiber, the number of supported modes at the same wavelength decreases, and some higher-order modes are cut off, resulting in a lack of richer wavelength components. Thus, a balance must be struck between the number of modes and the tuning range. Within a certain diameter range (above 90 μm), the smaller the diameter of the tapered fiber, the more similar the trend of integrated dispersion of different modes becomes, with the dispersive wave position shifting linearly. At this point, common higher-order modes are not cut off, and therefore these higher-order modes can be used to generate rich dispersive wave components.

[0040] At a pump wavelength of 1560 nm, the phase-matching points of different modes basically coincide with the positions of the dispersive waves generated in the experiment, such as... Figure 7 As shown. The calculated waist diameters of the tapered germanium-core fiber are 110 μm, 100 μm, and 90 μm, respectively. The phase matching points of different modes at a pump wavelength of 1560 nm differ from those in standard germanium-core fiber, as shown below. Figure 8 , Figure 9 and Figure 10 As shown, this means that by tapering the fiber diameter, new dispersive wavelength components can be generated, which has extremely high 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 output 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 system includes an input-side single-mode fiber optic patch cord 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 optic patch cord assembly arranged sequentially along the laser optical path. The visible light frequency comb generation module includes a germanium-core fiber, which 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.%, and the cladding is a SiO2 cladding. The input end of the germanium-core fiber is fused to the output end of the input-side single-mode fiber optic patch cord assembly. The input-side single-mode fiber optic patch cord assembly is used to introduce the laser beam emitted by the laser source into the germanium-core fiber. The germanium-core fiber is used to generate frequency combs of different wavelengths in the visible light band. The collimating lens is used to collimate the laser beam output from the germanium-core fiber. The tunable filter module is used to filter the collimated laser beam at different wavelengths 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 optic patch cord assembly for output. 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. Both ends of the connecting shaft are coaxially and fixedly connected to the knob and the first bevel gear, respectively. The first bevel gear meshes with the second bevel gear, and the second bevel gear is coaxially and fixedly connected to the first spur gear. The first spur gear and the second spur gear mesh with the rack, and the end of the rack is limited by a baffle. The multi-band filter is coaxially and fixedly connected to the second spur gear. The multi-band filter consists of eight sub-filters with different filtering bands: 400-450nm, 450-500nm, 500-550nm, 550-600nm, 600-650nm, 650-700nm, 700-750nm, and 750-800nm. The filtering range of the multi-band filter is 400-800nm.

2. The visible-band tunable femtosecond pulse laser generating device according to claim 1, characterized in that, 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. 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. The second input-side single-mode fiber optic patch cord, germanium-core fiber, collimating lens, multi-band filter, focusing lens, and first output-side single-mode fiber optic patch cord are respectively housed in a housing. A cover plate is installed on the top of the housing. The first input-side single-mode fiber optic patch cord, the second output-side single-mode fiber optic patch cord, and a knob are respectively located outside the housing. The germanium-core fiber and the first output-side single-mode fiber optic patch cord are respectively supported by fiber optic fasteners. The input end of the germanium-core fiber optic patch cord is fused to the output end of the second input-side single-mode fiber optic patch cord.

3. The visible-band tunable femtosecond pulse laser generating device according to claim 1, characterized in that, 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 silica fiber.

4. The visible-band tunable femtosecond pulse laser generating device according to claim 1, characterized in that, The core diameter is 8 μm, and the cladding diameter is 125 μm.

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