Polycrystalline composite wavelength visible light output device and method

Abstract

The application discloses a polycrystal composite wavelength visible light output device and method, and belongs to the technical field of visible light laser, which comprises a fiber combiner and N wavelength branches; each wavelength branch comprises a blue light pumping module, a line width compression module, a first focusing lens, a resonant cavity and a focusing coupling module; the blue light pumping module is used for generating a blue light beam with a power meeting preset requirements; the line width compression module is used for performing line width compression on the blue light beam; the first focusing lens is used for focusing the blue light beam after line width compression to form pumping blue light; the resonant cavity has a full reflection mirror and a resonant cavity rear mirror at two ends, and a crystal and a tuning module are sequentially arranged between the two; the crystal outputs working laser under excitation of the pumping blue light; the tuning module is used for selecting target laser of a specified wavelength from the working laser; the focusing coupling module is used for focusing and coupling the target laser transmitted through the resonant cavity rear mirror into a corresponding output optical fiber of the fiber combiner; the N crystals are different from each other; and the application can realize composite wavelength output with any specified spectral characteristics.

Description

Technical Field

[0001] This invention belongs to the field of visible light laser technology, and more specifically, relates to a polycrystalline composite wavelength visible light output device and method. Background Technology

[0002] Different scenarios require different laser output wavelengths. Achieving multi-wavelength, tunable laser output, adaptable to the optical absorption and interaction characteristics of different materials, and meeting the precision application needs of various fields, is of great significance in scientific research, industrial processing, and medical biology. For example, in ophthalmology, different wavelengths of laser light have varying absorption characteristics, penetration depths, and biological effects in eye tissues, making it difficult for single-wavelength lasers to meet the treatment and diagnostic needs of all ophthalmic diseases. Therefore, laser systems capable of outputting multiple wavelengths have significant application value.

[0003] Traditional semiconductor laser-pumped rare-earth ion crystals for visible light output are mostly limited to single-wavelength output (such as using Pr-doped crystals to output 639nm red light). However, in practical applications, such as medical and detection fields, dual-wavelength or even multi-wavelength visible light is required to meet specific needs. This severely limits the application of traditional single-wavelength output systems.

[0004] To address the limitations of single-wavelength output systems, researchers have proposed multi-wavelength output systems. However, existing multi-wavelength output systems often suffer from other drawbacks (such as difficulty in achieving high-power, high-quality, and stable output). For example, patent document CN120165287B discloses a multi-wavelength selective laser based on Ho-doped crystals and its wavelength tuning method. It achieves multi-wavelength output across a wide wavelength band using a single laser by combining Ho-doped crystals with different substrates. However, this scheme, due to the use of a single-wavelength pump source (1940nm), can only utilize the Ho³⁺ pump energy. + Specific energy levels of ions ( 5 I8→ 5 I7) effective absorption, which means that this scheme can only use Ho³ + Ion-doped gain media. Although different emission wavelengths can be obtained by changing different substrates (LLF, YAP, YLF), these wavelengths are all limited to Ho³. + Within the emission spectrum of ions, it is difficult to extend to the visible light band or other near-infrared bands, let alone achieve multi-wavelength composite output across bands (such as red + green + blue light). For applications requiring coverage of a wider spectral range (such as multi-color laser displays and multi-wavelength medical diagnostics), the wavelength coverage capability of this solution is clearly insufficient. Summary of the Invention

[0005] In view of the shortcomings of the existing technology and the need for improvement, the present invention provides a polycrystalline composite wavelength visible light output device and method, the purpose of which is to realize composite wavelength output with arbitrary specified spectral characteristics.

[0006] To achieve the above objectives, according to one aspect of the present invention, a multi-crystal composite wavelength visible light output device is provided, comprising: an optical fiber combiner and N wavelength branches; N is an integer greater than or equal to 3; An optical fiber combiner consists of N output optical fibers, with each of the N wavelength branches corresponding to one of the N output optical fibers. The optical fiber combiner is used to combine the target laser output from the N wavelength branches and output it. Each wavelength branch includes: The blue light pump module is used to generate a blue light beam with power that meets preset requirements; The linewidth compression module is placed in the propagation optical path of the blue light beam to compress the linewidth of the blue light beam, forming a linewidth-compressed blue light beam. The first focusing lens is placed on the propagation optical path of the blue light beam after linewidth compression, and is used to focus the blue light beam after linewidth compression to form pump blue light; The resonant cavity has its central optical axis aligned with the optical axis of the pump blue light beam. At each end of the resonant cavity is a total reflection mirror and a rear mirror, with a crystal and a tuning module sequentially positioned between them. Both the crystal and the tuning module are located on the central optical axis. The crystal outputs a working laser beam under the excitation of the pump blue light, and the tuning module is used to select a target laser beam of a specified wavelength from the working laser beam. The outer surface of the total reflection mirror is highly transparent to the pump blue light, while its inner surface is highly reflective to the target laser beam. The inner surface of the rear mirror has a preset transmittance for the target laser beam. The focusing and coupling module is used to focus the target laser light transmitted through the rear mirror of the resonant cavity and couple it to the corresponding output fiber; The crystals in the N wavelength branches are all different.

[0007] Furthermore, the tuning module includes a turntable and an FP etalon mounted on the turntable, the turntable being used to adjust the tilt angle of the FP etalon relative to the cavity axis of the resonant cavity.

[0008] Furthermore, the N output fibers in the fiber combiner are combined using fused taper technology.

[0009] Furthermore, N is an odd number.

[0010] Furthermore, N=5, and the crystals in the 5 wavelength branches are: Ho:YLF crystal, Pr:LiYF4 crystal, Sm:YAP crystal, Dy-Tb:YAG crystal and Tb:LiYF4 crystal.

[0011] Furthermore, the blue light pump module includes: A blue light single-tube array consists of M blue light single tubes spaced at intervals. The fast-axis collimating lens group includes M fast-axis collimating lenses; the M fast-axis collimating lenses are respectively set on the light output windows of the M blue light tubes to reduce the fast-axis divergence angle of the beam; The slow-axis collimating lens group includes M slow-axis collimating lenses; the M slow-axis collimating lenses are respectively set in the output light path of the M blue light tubes, and there are gaps between them and the M fast-axis collimating lenses, which are used to reduce the slow-axis divergence angle of the beam; And a beam combining unit, which is set on the output optical path of the blue light single tube array, is used to couple M beams that have passed through the fast axis collimating lens group and the slow axis collimating lens group into a blue light beam with power meeting the preset requirements. Where M is a positive integer.

[0012] Furthermore, in the blue light array, the arrangement interval of the blue light tubes satisfies the following condition: the fill factor is higher than a preset value.

[0013] Furthermore, the linewidth compression module includes: a diffraction grating, an output coupling mirror, and a dispersion compensation grating arranged sequentially along the optical path; the diffraction grating is configured to satisfy the following conditions: a blue light beam is incident on the diffraction grating at a Littrow angle and diffracts; the output coupling mirror is placed perpendicular to the desired diffracted light; and the dispersion compensation grating and the diffraction grating are placed with their scribe lines parallel.

[0014] Furthermore, the focusing coupling module includes: a second focusing lens and an optical fiber connector group; the second focusing lens is used to focus the target laser transmitted through the rear mirror of the resonant cavity; the optical fiber connector group is disposed on the focal plane of the second focusing lens and connected to the corresponding output optical fiber.

[0015] According to another aspect of the present invention, a method for outputting composite wavelength visible light based on the multi-crystal composite wavelength visible light output device provided by the present invention is provided, comprising: Adjust the center transmission wavelength of the tuning module on each branch to make the wavelength of the target laser output from each branch consistent with the corresponding specified wavelength. Adjust the power of the blue light beams output by each blue light pump module so that the power ratio of each target laser in the beam output by the fiber combiner is consistent with the corresponding preset value.

[0016] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects: (1) The multi-crystal composite wavelength visible light output device provided by the present invention includes multiple wavelength branches, each branch using a different crystal as a gain medium, so that each branch can obtain an independent wavelength component. The wavelength components output by each branch will eventually be combined into an output beam. The present invention can precisely control the wavelength of each wavelength component through the crystal and tuning module on the branch. Furthermore, by independently controlling the power of each wavelength component, a composite wavelength output with arbitrary specified spectral characteristics can be synthesized.

[0017] (2) In the preferred embodiment of the polycrystalline composite wavelength visible light output device provided by the present invention, a turntable is used in conjunction with an FP etalon to control the wavelength of the target laser on the branch, thereby avoiding the hysteresis of temperature tuning and the insufficient precision of mechanical scaling tuning.

[0018] (3) In the preferred embodiment of the multi-crystal composite wavelength visible light output device provided by the present invention, the N output optical fibers in the fiber combiner are combined by fused taper technology, which has the advantages of low loss, high temperature resistance and no mechanical drift during the combining process, which is conducive to realizing high power and stable multi-wavelength composite output.

[0019] (4) In the preferred embodiment of the multi-crystal composite wavelength visible light output device provided by the present invention, the blue light pumping module includes a blue light single tube array, which outputs multiple spaced blue light beams and couples them into a single blue light beam, thereby achieving high-power wavelength output. The output blue light beam is collimated in the fast axis direction and the slow axis direction after passing through the fast axis collimating lens group and the slow axis collimating lens group, thereby reducing the fast and slow axis divergence angles of each beam and improving the beam quality.

[0020] (5) In the preferred embodiment of the multi-crystal composite wavelength visible light output device provided by the present invention, the linewidth compression module includes a diffraction grating, an output coupling mirror and a dispersion compensation grating arranged sequentially in the eye optical path. The diffraction grating can achieve linewidth compression by selecting the dispersion wavelength, and the dispersion compensation grating can compensate for the dispersion effect caused by the diffraction grating, reduce the divergence angle and lateral expansion of the light spot, and improve the beam quality and fiber coupling efficiency of the output laser.

[0021] (6) The composite wavelength visible light output method provided by the present invention can synthesize composite wavelength output with arbitrary specified spectral characteristics by adjusting the center transmission wavelength of the tuning module on each branch and the output power of the blue light pump module. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall structure of the multi-crystal composite wavelength visible light output device provided in an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of the structure of the blue light pump module provided in an embodiment of the present invention.

[0024] Figure 3 This is a schematic diagram of a linewidth compression module provided in an embodiment of the present invention.

[0025] Figure 4 A schematic diagram of the Pr:LiYF4 crystal resonator and particle energy level transitions provided in an embodiment of the present invention.

[0026] Figure 5 This is a schematic diagram of the focusing coupling module provided in an embodiment of the present invention.

[0027] Figure 6 This is a schematic diagram of an optical fiber combiner provided in an embodiment of the present invention.

[0028] In all the accompanying drawings, the same reference numerals are used to denote the same structures or elements, wherein: 1-First group of blue light single-tube array, 2-Fast axis collimating lens group, 3-Slow axis collimating lens group, 4-Reflecting mirror group, 5-Second group of blue light single-tube array, 6-Third group of blue light single-tube array, 7-Fourth group of blue light single-tube array, 8-Fifth group of blue light single-tube array, 9-Diffraction grating, 10-Output coupling mirror, 11-Dispersion compensation grating, 12-First focusing lens, 13-Total reflection mirror, 14-Ho:YLF crystal, 15-Pr:LiYF4 crystal, 16-Sm:YAP crystal, 17-Dy-Tb:YAG crystal, 18-Tb:LiYF4 crystal, 19-Rotating disk, 20-FP etalon, 21-Resonant cavity rear mirror, 22-Second focusing lens, 23-Fiber optic connector group, 24-Capillary sleeve, 25-Tapered region, 26-Tapered waist section, 27-Output fiber, 28-Output lens. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0030] In this invention, the terms "first," "second," etc. (if present) in the invention and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0031] To achieve composite wavelength output with arbitrary specified spectral characteristics, this invention provides a multi-crystal composite wavelength visible light output device and method. The overall concept is to utilize different wavelengths output by different gain media and tuning modules, and combine them to output high-power composite wavelength laser.

[0032] Based on the above concept, the present invention first provides a multi-crystal composite wavelength visible light output device, wherein multiple independent wavelength branches are set up, each using a different crystal as a gain medium to obtain multiple independent wavelength components. The multiple wavelength components are combined into an output beam. By independently adjusting the power of each wavelength component, a composite wavelength output with arbitrary specified spectral characteristics can be synthesized.

[0033] To ensure the output of arbitrary composite wavelengths, the multi-crystal composite wavelength visible light output device provided by this invention has a wavelength branch number greater than or equal to 3, and to facilitate beam combining, the number of wavelength branches is usually set to an odd number. Without loss of generality, the following embodiments are described using 5 branches as an example.

[0034] The following is an example.

[0035] Example 1: A multi-crystal composite wavelength visible light output device, such as Figure 1 As shown, it includes: an optical fiber combiner and five wavelength branches; The fiber optic combiner includes five output fibers 27, with each of the five wavelength branches corresponding to one of the five output fibers 27. The fiber optic combiner is used to combine the target laser output from the five wavelength branches and output it. Each wavelength branch includes: The blue light pump module is used to generate a blue light beam with power that meets preset requirements; The linewidth compression module is placed in the propagation optical path of the blue light beam to compress the linewidth of the blue light beam, forming a linewidth-compressed blue light beam. The first focusing lens 12 is disposed on the propagation optical path of the blue light beam after linewidth compression, and is used to focus the blue light beam after linewidth compression to form pump blue light; The resonant cavity has its central optical axis aligned with the optical axis of the pump blue light beam. At each end of the resonant cavity is a total reflection mirror 13 and a rear mirror 21, with a crystal and a tuning module sequentially positioned between them. Both the crystal and the tuning module are located on the central optical axis. The crystal outputs a working laser beam under the excitation of the pump blue light, and the tuning module is used to select a target laser beam of a specified wavelength from the working laser beam. The outer surface of the total reflection mirror is highly transparent to the pump blue light (transmittance greater than a preset transmittance threshold), while its inner surface is highly reflective to the target laser beam (emissivity greater than a preset reflectivity threshold). The inner surface of the rear mirror has a preset transmittance for the target laser beam. The focusing and coupling module is used to focus the target laser light transmitted through the rear mirror of the resonant cavity and couple it to the corresponding output fiber; The crystals in the five wavelength branches are all different.

[0036] The following provides a further explanation of the specific implementation of each module.

[0037] like Figure 1 and Figure 2 As shown, in this embodiment, the blue light pumping module includes: The blue light single-tube array consists of 6 blue light single tubes spaced apart. The fast-axis collimating lens group 2 includes 6 fast-axis collimating lenses (FACs); the 6 fast-axis collimating lenses are respectively set on the light output windows of the 6 blue light tubes to reduce the fast-axis divergence angle of the beam; The slow-axis collimating lens group 3 includes 6 slow-axis collimating lenses (SAC); the 6 slow-axis collimating lenses are respectively set in the output light path of the 6 blue light tubes, and there are gaps between them and the 6 fast-axis collimating lenses, which are used to reduce the slow-axis divergence angle of the beam; And a beam combining unit, which is set on the output optical path of the blue light single tube array, is used to couple the six beams that have passed through the fast axis collimating lens group and the slow axis collimating lens group into a blue light beam with a power that meets the preset requirements.

[0038] In this embodiment, the five wavelength branches correspond to five groups of blue single-tube arrays, namely the first group of blue single-tube array 1, the second group of blue single-tube array 5, the third group of blue single-tube array 6, the fourth group of blue single-tube array 7, and the fifth group of blue single-tube array 8.

[0039] Optionally, such as Figure 1 and Figure 2 As shown, in this embodiment, the beam converging unit is specifically a mirror group 4, which includes 6 mirrors. The 6 mirrors are respectively disposed on the output light path of the 6 blue light tubes and are respectively at a 45° angle to the corresponding incident light; the reflected light paths of the 6 mirrors coincide.

[0040] In this embodiment, the beam converging unit adjusts the beam angle and achieves beam coupling while compressing the beam to facilitate subsequent beam linewidth compression.

[0041] This embodiment arranges multiple independent blue LEDs densely in space, allowing for the combination of as many light sources as possible within a limited lateral space, which is beneficial for achieving high-power beam output. It is easy to understand that in practical applications, the number of blue LEDs in the array can be flexibly adjusted according to actual power requirements, and is not limited to the six in this embodiment. The spacing between the LEDs in the array is closely related to the output power and beam combining efficiency. A smaller spacing results in higher output power, but may lead to beam quality degradation, and the coupling efficiency may drop sharply when coupled into the optical fiber. Conversely, a larger spacing results in higher beam quality, but the output power will decrease within the limited space. As a preferred implementation, in this embodiment, the spacing between the blue LEDs in the array satisfies the condition that the fill factor is higher than a preset value. In practical applications, this preset value is generally set to a value close to 1, thereby achieving a dense arrangement of blue LEDs. This embodiment adopts a dense arrangement, sacrificing the edge power achieved by the Gaussian beam to achieve a beam combining beam with a fill factor close to 1.

[0042] The blue light pumping module in this embodiment utilizes a fast-axis collimating lens group and a slow-axis collimating lens group to reduce the fast-axis divergence angle and slow-axis divergence angle of the light beam, thereby improving the beam quality.

[0043] Optionally, such as Figure 1 and Figure 3 As shown, in this embodiment, the linewidth compression module includes: a diffraction grating 9, an output coupling mirror 10, and a dispersion compensation grating 11 arranged sequentially along the optical path; The diffraction grating 9 is configured to satisfy the following: a blue light beam is incident on the diffraction grating 9 at a Littrow angle and diffracts, and the +1st order diffracted light is incident on the output coupling mirror 10; the diffraction grating 9 achieves linewidth compression through dispersion wavelength selection; The output coupling mirror 10 is placed perpendicular to the desired diffracted light beam; the output coupling mirror 10 is coated with a reflective film to reflect a portion of the blue light beam back along the original path, forming feedback with the outer surface of the output mirror of each blue light tube, while outputting another portion of the blue light beam as a blue light beam with compressed linewidth. The dispersion compensation grating 11 and the diffraction grating 9 are placed with their scribe lines parallel. The dispersion compensation grating 11 compensates for the dispersion effect caused by the diffraction grating 9, reduces the divergence angle and lateral expansion of the light spot, and improves the beam quality and fiber coupling efficiency of the output laser.

[0044] In this embodiment, due to laser dispersion, only light within a narrow wavelength range reflected by the output coupling mirror can return to the active region of the laser resonator within the allowable angular deviation range, thus providing effective optical feedback. Consequently, longitudinal modes near this narrow wavelength range gain an advantage in mode competition, forming laser oscillations, while other longitudinal modes far from this wavelength range are suppressed. Therefore, the output linewidth is effectively compressed. In this embodiment, the output coupling mirror is placed perpendicular to the desired diffracted light, ensuring optimal feedback performance.

[0045] The blue light beam, after linewidth compression, is focused by the first focusing lens and enters the resonant cavity, where it is focused onto the crystal inside the cavity. One end of the resonant cavity is a total reflection mirror, whose outer surface is highly transparent to the pump blue light, while its inner surface is highly reflective to the target laser. This ensures effective reflection of the target laser while isolating the back reflection of the pump blue light. Optionally, in this embodiment, the transmittance of the pump blue light to the outer surface of the total reflection mirror is higher than 99.5%, and the reflectivity of the target laser to the inner surface is higher than 99.5%.

[0046] The crystal serves as the laser gain medium within the resonant cavity, generating stimulated emission under blue light pumping. It is the core gain medium for laser oscillation, with different crystals corresponding to different wavelengths of output light. In each resonant cavity, the crystal is positioned on the central optical axis, which coincides with the optical axis of the pump blue light beam, facilitating the entry of the pump blue light into the gain medium. Preferably, in this embodiment, the crystal is positioned on the focal plane of the first focusing lens.

[0047] Optionally, in this embodiment, the crystals on the five wavelength branches are Ho:YLF crystal 14, Pr:LiYF4 crystal 15, Sm:YAP crystal 16, Dy-Tb:YAG crystal 17 and Tb:LiYF4 crystal 18, respectively.

[0048] For Ho:YLF crystals, under approximately 480 nm blue light pumping, Ho³ + Ion absorption pump light, from ground state 5 I8 excites to the highest excited state 5 G6 then undergoes a nonradiative transition and rapidly relaxes to the upper energy level of the laser. 5 F5. Depending on the cavity mode and loss selection, the particles may be generated by... 5 F5 stimulated radiation to 5 The I8 energy level emits 540nm green light; it may also be derived from... 5 F5 stimulated radiation to 5 The I7 energy level emits 750nm deep red light, after which particles in the laser-induced energy level rapidly relax to the ground state. The resonant cavity is highly transparent to the pump light and highly reflective to the target laser, forming a standing-wave oscillation structure. When the inverted particle number density ΔN accumulates to exceed a threshold condition... ( This is the total loss coefficient. For stimulated emission cross section, When the crystal length is constant, spontaneous emission propagates along the cavity axis and is amplified by stimulated emission during its round trip through the gain medium. Because a tuning module is inserted into the resonant cavity, gain competition is controlled through tuning, thereby controlling the loss of different longitudinal modes and achieving the purpose of selecting a specific wavelength.

[0049] Furthermore, for Pr:LiYF4 crystals, when pumped by blue light at approximately 444 nm, Pr³ + Ions from ground state 3 H4 transitions to a highly excited state. 3 P2, followed by a fast multiphonon relaxation non-radiative laser up-level. 3 P0. Similar to Ho:YLF crystals, it achieves different wavelengths of emission through different energy level transitions. 3 P0 jumps to 3 The F2 energy level generates a 639nm laser emission or is produced by... 3 P0 jumps to 3 The F4 energy level generates a 721nm laser output. The resonant cavity is highly transparent to the pump light and highly reflective to the target laser, forming a standing wave oscillation, enabling continuous laser output at 639nm and 721nm. Similarly, a specific wavelength can be selected through a tuning module within the resonant cavity.

[0050] Furthermore, for Sm:YAP crystals, when pumped by blue light at approximately 405 nm, Sm³ + Ions from ground state 6 H 5 / 2 Transition to a highly excited state 4 F 7 / 2 Multiple states are then populated non-radiatively into the upper energy level of the laser via rapid multiphonon relaxation. 4 G 5 / 2 The system exhibits a four-level characteristic, with the energy levels under laser conditions... 6 H 7 / 2 It is an excited state, far from the ground state. 6 H 5 / 2 At relatively low thermal populations at room temperature, population inversion is easily established with negligible reabsorption losses. The resonant cavity exhibits high transmittance of pump light and high reflectivity of target laser light, forming a standing wave oscillation. At approximately 604 nm (… 4 G 5 / 2 → 6 H 7 / 2 The red-orange band enables tunable laser output. Similarly, a specific wavelength can be selected through a tuning module within the resonant cavity.

[0051] Furthermore, Dy-Tb:YAG crystals, Dy³+ After ions absorb 447nm blue light, they change from the ground state. 6 H 15 / 2 Transition to a highly excited state 4 F 7 / 2 Multiple states are then populated non-radiatively into the upper energy level of the laser via rapid multiphonon relaxation. 4 F 9 / 2 However, Dy³ + Laser lower energy level when working alone 6 H 13 / 2 The long lifespan of Tb³ particles can easily lead to particle population accumulation and a "self-termination" effect. Therefore, Tb³ is introduced. + As a co-doped sensitizing ion, using Dy³ + : 6 H 13 / 2 With Tb³ + : 7 The resonant energy transfer between F4 rapidly consumes lower-level particles, maintaining unobstructed energy levels. The resonant cavity is highly transparent to pump light and highly reflective to target laser light, forming a standing-wave oscillation structure. At approximately 575 nm (… 4 F 9 / 2 → 6 H 13 / 2 The yellow light band enables tunable laser output. Similarly, a specific wavelength can be selected through a tuning module within the resonant cavity.

[0052] Furthermore, Tb:LiYF4 crystal, Tb³ + After ions absorb 485nm blue light, they change from the ground state. 7 F6 transitions to a highly excited state. 5 D4 (or via higher energy levels) 5 D3 cascade relaxation to 5 D4), achieving laser upper energy level 5 The particle population of D4. This system exhibits a four-level characteristic, with the energy levels determined by laser. 7 F5 (corresponding to green light emission at approximately 541 nm) has a low thermal population at room temperature, making it easy to establish population inversion. The resonant cavity is highly transparent to the pump light and highly reflective to the target laser, forming a standing wave oscillation structure. At approximately 541 nm ( 5 D4→ 7 Laser output is achieved in the F5 green light band. Similarly, a specific wavelength can be selected through the tuning module within the resonant cavity.

[0053] Correspondingly, the first group of blue light-emitting units (BLRN) arrays contains six BLRNs with an output wavelength of approximately 480 nm; the second group contains six BLRNs with an output wavelength of approximately 444 nm; the third group contains six BLRNs with an output wavelength of approximately 400-450 nm; the fourth group contains six BLRNs with an output wavelength of approximately 400-450 nm; and the fifth group contains six BLRNs with an output wavelength of approximately 488 nm. The six BLRNs in each array are arranged in a super-filled space-dense configuration along a line. The output blue light beam is collimated sequentially by a fast-axis collimating lens group and a slow-axis collimating lens group in the fast-axis and slow-axis directions, reducing the fast and slow axis divergence angles of each beam and improving beam quality.

[0054] Optionally, such as Figure 1 and Figure 4 As shown, in this embodiment, the tuning module includes a turntable 19 and an FP etalon 20 disposed on the turntable. The turntable 19 is used to adjust the tilt angle of the FP etalon 20 relative to the cavity axis of the resonant cavity.

[0055] The transmission peak of the FP etalon is composed of Decision, among which For the interference level, For refractive index, For thickness, The incident angle. The turntable (20) precisely changes the tilt angle of the etalon relative to the cavity axis. (i.e., by tuning the incident angle), the central transmission wavelength can be continuously changed. ( Longitudinal mode frequency spacing of the resonant cavity. , At the speed of light, The optical cavity length of the resonant cavity. The transmission peak width (full width at half maximum, FWHM) of the etalon is much smaller than the gain bandwidth and typically smaller than the longitudinal mode spacing, thus allowing only a single longitudinal mode (or a few longitudinal modes) to pass through. Within the resonant cavity, the longitudinal mode that satisfies the etalon transmission peak and is closest to the gain peak wavelength achieves the highest net gain. Through mode competition, this longitudinal mode rapidly depletes the inverted particle number, suppressing other longitudinal mode oscillations, ultimately achieving tunable laser output.

[0056] This embodiment introduces a tunable etalon, which allows for gain competition to select a specific wavelength through angle tuning. This enables the selection of a single-frequency longitudinal mode while suppressing other modes, resulting in an extremely narrow laser linewidth (down to the MHz or even kHz level) and extremely high spectral purity and coherence. By simply changing the tilt angle, gap, or temperature of the etalon, continuous and precise wavelength tuning can be achieved within the bandwidth of the gain medium without replacing any components. This is beneficial for subsequent beam combining and output of composite wavelength lasers, while avoiding the hysteresis of temperature tuning and the insufficient precision of mechanical scaling tuning.

[0057] The propagation process of the light beam within the resonant cavity is explained using a Pr:LiYF4 crystal as an example. Figure 4 As shown, the approximately 444nm laser output from the blue semiconductor laser module, after collimation and linewidth compression, is focused by a focusing mirror and incident from the front cavity mirror M1 onto the Pr:LiYF4 crystal. The Pr:LiYF4 crystal, acting as the gain medium, absorbs the pump light, achieving population inversion and causing a transition. The 444nm pump light then propels the ground-state particles from... 3 H4 energy level pump to 3 The P2 energy level, after a non-radiative transition, allows these particles to relax rapidly to... 3 The P0 energy level. Depending on the cavity mode selection, the particle may be composed of... 3 P0 jumps to 3 The F4 energy level produces 721 nm laser emission, which may also be due to... 3 P0 jumps to 3 The F2 energy level generates a 639nm laser beam. Particles in the lower energy level of the laser beam will rapidly relax to the ground state energy level. Therefore... 3 P2 energy level and laser-induced energy level 3 F2 3 F4 contains almost no particles. Assuming particles exist only in the ground state and the upper laser level, the intracavity photon number and inverted particle number for generating 639 nm and 721 nm lasers using a single blue semiconductor tube-pumped Pr:LiYF4 crystal can be expressed as follows: Figure 4 A schematic diagram of energy level transitions. The four-level equations inside the Pr:LiYF4 crystal are as follows: ; in, Indicates time, This represents the particle number density of the upper energy level of a laser as a function of time, expressed in units of... ; The absorption cross-section of Pr:LiYF4 crystal to pump light, and the absorption cross-section of Pr:LiYF4 crystal at 444nm. ; The photon flux of the pump light is taken as 3W in this embodiment. . ; The number density of particles in the ground state energy level as a function of time, expressed in units of 1. ; This indicates the emission cross-section size of the Pr:LiYF4 crystal at 639 nm. In this embodiment, ; This indicates the emission cross-section size of the Pr:LiYF4 crystal at 721 nm. In this embodiment, ; , These represent the photon number densities at 639 nm and 721 nm, respectively, in units of... ; For Pr:LiYF4 lasers, the fluorescence lifetime of the upper energy level is typically 35–50. ; Represents the speed of light; The length of the Pr:LiYF4 crystal is [missing information]. The length of the cavity; , These represent the photon lifetimes of the laser cavity at 639 nm and 721 nm, respectively, in units of... ; The total particle number density inside the cavity is related to the doping concentration of the Pr:LiYF4 crystal.

[0058] Spontaneous emission light originates from the Pr:LiYF4 crystal and propagates along the cavity axis (total reflection mirror → rear mirror of the resonant cavity). Upon reaching the total reflection mirror, the laser wavelength is completely reflected back into the cavity. During the reverse propagation, when incident on the etalon, based on the principle of multi-beam interference, this element allows only wavelengths that meet its transmission peak condition to pass through with low loss. The transmission peak wavelength can be changed by angle tuning. Within the fluorescence spectrum of the gain medium, intense gain competition exists between different wavelength modes. Angle tuning ensures that the etalon allows only a narrow band wavelength with sufficiently low loss to meet the laser oscillation threshold condition, while the loss at other wavelengths is much higher than the gain. By continuously changing the tilt angle of the etalon, the desired laser output wavelength can be continuously and repeatably selected within the gain bandwidth. After passing through the FP etalon, the light propagates to the rear mirror of the resonant cavity, where most of the light is reflected back into the cavity, and a small portion is transmitted to form a laser beam. The light oscillates back and forth between the total reflection mirror and the rear mirror of the resonant cavity, undergoing stimulated emission amplification each time it passes through the gain medium (Pr:LiYF4).

[0059] Optionally, such as Figure 1 and Figure 5 As shown, in this embodiment, the focusing coupling module includes: a second focusing lens 22 and an optical fiber connector group 23; The second focusing lens 22 is used to focus the target laser that has passed through the rear mirror of the resonant cavity; The fiber optic connector group 23 is disposed on the focal plane of the second focusing lens 22 and is connected to the corresponding output fiber optic cable.

[0060] In this embodiment, the center of the target laser beam is aligned with the central optical axis of the output fiber connected to the fiber optic connector group, so as to facilitate coupling the target laser into the fiber. During fiber coupling, the optical parameter products of the fast and slow axes of the focused spot are approximately equal, and the spot shape is rectangular. In addition, for the beam to be efficiently coupled into the fiber, the following conditions must be met: (1) the maximum diameter of the spot must be smaller than the core diameter of the fiber; (2) the incident angle of the beam must be smaller than the optical fiber core diameter. Maximum angle of incidence It can be calculated using the numerical aperture (NA) of the fiber. From geometric optics, we know that the numerical aperture (NA) of the fiber and the maximum incident angle (...) The relationship is: ; in, This is the maximum angle of incidence that the optical fiber can receive the light beam from. The refractive index of air, The refractive index of the fiber core, The cladding refractive index is used. When the beam is coupled into the fiber, the incident angle is less than or equal to... The light rays undergo total internal reflection (TIR) ​​at the core-cladding interface and are confined within the core to propagate forward; the angle of incidence is greater than... The light rays are eventually lost due to refraction.

[0061] To ensure that the entire focused light spot enters the optical fiber, in this embodiment, the focal length of the second focusing lens is... Compared to the diameter of the light spot before focusing satisfy: ; Furthermore, while satisfying the above relationships, the focal length should be as small as possible to minimize the light spot size, making it easier for the light to enter the optical fiber and improve coupling efficiency. Accordingly, in this embodiment, the focal length of the second focusing lens... .

[0062] like Figure 1 and Figure 6 As shown, in this embodiment, the fiber optic combiner uses multiple output fibers combined using fiber optic fusion tapering technology. After fusion tapering, the output fibers form a tapered region 25 and a tapered waist section 26. In this embodiment, the fiber optic combiner also includes five capillary tubes 24, and the five output fibers 27 are respectively sleeved inside the five capillary tubes 24 to protect the output fibers 27.

[0063] This embodiment uses an optical fiber combining method to output a composite wavelength beam. Because optical fibers are highly flexible and easily bent, the direction of the beam output can be easily changed by twisting the fiber, making it suitable for confined spaces or demanding working conditions. Furthermore, the output beam through the optical fiber combiner produces a symmetrical circular spot, improving beam quality.

[0064] Optionally, in this embodiment, the output end of the fiber optic combiner is further provided with an output lens 28, the optical axis of which is consistent with the direction of the beam.

[0065] The target laser from the five output fibers is combined and output to achieve composite wavelength output. By adjusting the power of the pump blue light in each branch, the proportion of the corresponding wavelength component can be adjusted. Therefore, this embodiment can synthesize composite wavelength output with any specified spectral characteristics.

[0066] In this embodiment, the resonant cavities of the five wavelength branches each contain different crystal types and independent etalon parameters to obtain specific wavelength outputs. These parameters can be increased or decreased according to actual needs, and the wavelength of the pump source output light, as well as the structure and dimensions of other components in the device such as the fast-axis collimating lens group and the slow-axis collimating lens group, also need to be changed accordingly.

[0067] In general, this embodiment uses five different crystals as gain media. By adjusting the output wavelength of each pump source, blue light injected into the gain medium undergoes stimulated absorption, radiating laser beams of different wavelengths, which oscillate in their respective resonant cavities. Subsequently, by adjusting the parameters of the etalon, mode gain matching is adjusted to obtain five different wavelengths of laser light. Furthermore, by controlling the output power of the five pump sources independently, the output power of each wavelength of laser light is adjusted, and after beam combining, a composite laser output of the desired wavelength can be obtained to meet different application requirements, achieving a more flexible output with a wider wavelength range.

[0068] Example 2: A method for outputting visible light with composite wavelengths, this embodiment is based on the polycrystalline composite wavelength visible light output device provided in Embodiment 1 above, and includes: Adjust the center transmission wavelength of the tuning module on each branch to make the wavelength of the target laser output from each branch consistent with the corresponding specified wavelength; that is, adjust the transmission peak of the FP etalon to be consistent with the corresponding specified wavelength by turning the dial. Adjust the power of the blue light beams output by each blue light pump module so that the power ratio of each target laser in the beam output by the fiber combiner is consistent with the corresponding preset value; in practical applications, the preset value of the wavelength component ratio corresponds to the desired output beam.

[0069] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A multi-crystal composite wavelength visible light output device, characterized in that, include: Fiber optic combiner and N wavelength branches; N is an integer greater than or equal to 3; The fiber optic combiner includes N output fibers, and N wavelength branches correspond one-to-one with the N output fibers; The fiber optic combiner is used to combine the target laser output from N wavelength branches and output it. Each wavelength branch includes: The blue light pump module is used to generate a blue light beam with power that meets preset requirements; A linewidth compression module is disposed in the propagation optical path of the blue light beam to compress the linewidth of the blue light beam, thereby forming a linewidth-compressed blue light beam. A first focusing lens is disposed on the propagation optical path of the linewidth-compressed blue light beam to focus the linewidth-compressed blue light beam and form pump blue light. A resonant cavity has its central optical axis aligned with the optical axis of the pump blue light beam. At each end of the resonant cavity is a total reflection mirror and a rear mirror, with a crystal and a tuning module sequentially positioned between them. Both the crystal and the tuning module are located on the central optical axis. The crystal outputs a working laser beam under the excitation of the pump blue light, and the tuning module selects a target laser beam of a specified wavelength from the working laser beam. The outer surface of the total reflection mirror is highly transparent to the pump blue light, while its inner surface is highly reflective to the target laser beam. The inner surface of the rear mirror has a preset transmittance for the target laser beam. A focusing and coupling module is used to focus the target laser light transmitted through the rear mirror of the resonant cavity and couple it to the corresponding output optical fiber; The crystals in the N wavelength branches are all different.

2. The multi-crystal composite wavelength visible light output device as described in claim 1, characterized in that, The tuning module includes a turntable and an FP etalon disposed on the turntable, the turntable being used to adjust the tilt angle of the FP etalon relative to the cavity axis of the resonant cavity.

3. The multi-crystal composite wavelength visible light output device as described in claim 1 or 2, characterized in that, The N output optical fibers in the optical fiber combiner are combined using fused taper technology.

4. The multi-crystal composite wavelength visible light output device as described in claim 3, characterized in that, N is an odd number.

5. The multi-crystal composite wavelength visible light output device as described in claim 4, characterized in that, N=5, and the crystals in the 5 wavelength branches are: Ho:YLF crystal, Pr:LiYF4 crystal, Sm:YAP crystal, Dy-Tb:YAG crystal and Tb:LiYF4 crystal.

6. The multi-crystal composite wavelength visible light output device as described in claim 1 or 2, characterized in that, The blue light pumping module includes: A blue light single-tube array consists of M blue light single tubes spaced at intervals. The fast-axis collimating lens group includes M fast-axis collimating lenses; the M fast-axis collimating lenses are respectively disposed on the light output windows of the M blue light tubes, and are used to reduce the fast-axis divergence angle of the light beam; The slow-axis collimating lens group includes M slow-axis collimating lenses; the M slow-axis collimating lenses are respectively disposed in the output light paths of the M blue light tubes, and there are gaps between them and the M fast-axis collimating lenses, which are used to reduce the slow-axis divergence angle of the light beam; And a beam converging unit, disposed on the output optical path of the blue light single tube array, is used to couple M beams that have passed through the fast axis collimating lens group and the slow axis collimating lens group into a blue light beam with power meeting the preset requirements. Where M is a positive integer.

7. The multi-crystal composite wavelength visible light output device as described in claim 6, characterized in that, In the blue light array, the arrangement interval of the blue light tubes satisfies the condition that the fill factor is higher than a preset value.

8. The multi-crystal composite wavelength visible light output device as described in claim 6, characterized in that, The linewidth compression module includes: a diffraction grating, an output coupling mirror, and a dispersion compensation grating arranged sequentially along the optical path; The diffraction grating is configured such that a blue light beam incident on the diffraction grating at a Littrow angle will undergo diffraction. The output coupling mirror is placed perpendicular to the desired diffraction beam; The dispersion compensation grating and the diffraction grating are placed with their grating lines parallel.

9. The multi-crystal composite wavelength visible light output device as described in claim 1 or 2, characterized in that, The focusing coupling module includes: a second focusing lens and an optical fiber connector group; The second focusing lens is used to focus the target laser light that has passed through the rear mirror of the resonant cavity; The fiber optic connector assembly is disposed on the focal plane of the second focusing lens and connected to the corresponding output fiber optic cable.

10. A method for outputting composite wavelength visible light based on the polycrystalline composite wavelength visible light output device according to any one of claims 1 to 9, characterized in that, include: Adjust the center transmission wavelength of the tuning module on each branch to make the wavelength of the target laser output from each branch consistent with the corresponding specified wavelength. Adjust the power of the blue light beams output by each blue light pump module so that the power ratio of each target laser in the beam output by the fiber combiner is consistent with the corresponding preset value.

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