A tunable spatially multiplexed multi-wavelength laser based on Ho:LLF and a wavelength tuning method

Abstract

This invention relates to a tunable spatially multiplexed multi-wavelength laser based on Ho:LLF and a wavelength tuning method, belonging to the field of optoelectronic device manufacturing and optical engineering laser technology. To achieve multiple selectable wavelength outputs in the tunable spatially multiplexed multi-wavelength laser, the 1940nm pump source is connected to a fiber-coupled lens group via an optical fiber. Along the optical path on the right side of the fiber-coupled lens group, a microlens array, a polarizer group, an input plane mirror, a c-axis-cut Ho:LLF crystal, an output plane mirror, a 1900nm narrowband filter, and a set of polarizing beam-splitting prisms are arranged sequentially. The rotation angle of the polarizer group is set to a gradient change from 0° to 90°. The surface of the input plane mirror is coated with a 2050nm narrowband reflective film, and the surface of the output plane mirror is coated with a 2050nm 5% transmission film. The c-axis-cut Ho:LLF crystal is cuboid in shape. This invention realizes the design of a miniaturized multi-wavelength laser.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic device manufacturing and optical engineering laser technology, specifically relating to a tunable spatially multiplexed multi-wavelength laser based on Ho:LLF and a wavelength tuning method. Background Technology

[0002] Lasers play an indispensable role in modern communication and computing systems. However, traditional lasers rely on complex tuning mechanisms or multiple independent laser sources to generate multi-wavelength light. This not only increases system complexity and cost but also makes it difficult to ensure stable performance over long periods, especially in the face of environmental changes. Furthermore, with the rapid expansion of wavelength division multiplexing (WDM) technology in cutting-edge fields such as fiber optic communication and optical computing, the information industry's demand for efficient and highly integrated laser output is growing. However, traditional lasers are mostly limited to single-wavelength operation due to the inherent absorption and emission spectra of laser crystals. Their multi-wavelength signal generation capability is limited by the need to deploy multiple independent laser sources, restricting their use in compact applications. Moreover, wavelength tuning suffers from high energy loss, which not only increases system complexity and cost but also limits system flexibility and integration.

[0003] The patent application CN216648854U, entitled "An Adjustable Proportion Orthogonally Polarized Dual-Wavelength Laser," uses a single-wavelength laser as the fundamental frequency and employs a nonlinear crystal inside / outside the resonant cavity for frequency conversion, enabling simultaneous output of dual-wavelength lasers. Furthermore, dual-wavelength laser output can be achieved by selecting the emission spectrum of different laser working media using a frequency-selective device. However, this method is difficult to implement, and the intracavity beam splitting method increases intracavity losses, resulting in a significant decrease in output power.

[0004] The patent application CN116885540A, entitled "A Compact Multi-Wavelength Laser," uses a single crystal to achieve four-wavelength coaxial output with a high degree of integration, enabling four-wavelength output at room temperature without requiring harsh environmental conditions. However, it only provides a four-wavelength output method and cannot freely switch wavelengths, requiring external devices for filtering or beam splitting to extract a specific wavelength.

[0005] The patent application CN213071699U, entitled "A Dual-Crystal Multi-Wavelength Laser," utilizes a structural design combining a focuser, a fixing block, and the laser to solve the problem of existing dual-crystal multi-wavelength lasers being unable to collect data on laser values ​​and the distance to the beam refraction point during practical use. However, by only using optical lenses and other components to modulate the beam without changing the "dual-crystal" premise, the number of output wavelengths is limited. Summary of the Invention

[0006] The problem to be solved by this invention is to realize multiple selectable wavelength outputs of a tunable spatially multiplexed multi-wavelength laser. It proposes a tunable spatially multiplexed multi-wavelength laser based on Ho:LLF and a wavelength tuning method.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A tunable spatially multiplexed multiwavelength laser based on Ho:LLF includes a 1940nm pump source, an optical fiber, an optical fiber coupling lens group, a microlens array, a polarizer group, an input plane mirror, a c-axis cut Ho:LLF crystal, an output plane mirror, a 1900nm narrowband filter, and a set of polarizing beam splitters.

[0009] The 1940nm pump source is connected to a fiber-coupled lens group via an optical fiber. The right side of the fiber-coupled lens group is arranged along the optical path with a microlens array, a polarizer group, an input plane mirror, a c-axis cut Ho:LLF crystal, an output plane mirror, a 1900nm narrowband filter, and a set of polarizing beam splitters.

[0010] The rotation angle of the polarizer group is set to vary from 0 to 90°.

[0011] Furthermore, the surface of the input plane mirror is coated with a 2050nm narrowband reflective film, the surface of the output plane mirror is coated with a 2050nm 5% transmission film, and the c-axis cut Ho:LLF crystal is cuboid in shape.

[0012] Furthermore, the microlens array is composed of microconvex lenses, the focal length of which corresponds to the position of the front end face of the c-axis-cut Ho:LLF crystal.

[0013] Furthermore, the microlens array is replaced by a set of beam mirrors and an optical path compensation plate.

[0014] Furthermore, the n beam splitting paths in a beam splitter are designed with numbers from bottom to top. The transmittance of the first beam splitter is 1 / n and the reflectance is (n-1) / n. The transmittance of the second beam splitter is (n-2) / (n-1) and the reflectance is 1 / (n-1). The transmittance of the third beam splitter is (n-3) / (n-2) and the reflectance is 1 / (n-2). ... The transmittance of the i-th beam splitter is (ni) / (n-i+1) and the reflectance is 1 / (n-i+1).

[0015] Furthermore, the optical path compensation plate is set as a glass plate placed at a 45° angle to the horizontal plane. The thickness of the glass plate is determined by the distance s between the beam splitters. The thickness difference between each pair of adjacent optical paths is 0.58×s. No optical path compensation plate is placed in the uppermost optical path. In order from top to bottom, the thickness of the first optical path compensation plate is 0.58×s, the thickness of the second optical path compensation plate is 0.58×2s, and so on, with the thickness of the nth optical path compensation plate being 0.58×ns.

[0016] A wavelength tuning method for a tunable spatially multiplexed multi-wavelength laser based on Ho:LLF, implemented using the aforementioned tunable spatially multiplexed multi-wavelength laser based on Ho:LLF, includes the following steps:

[0017] A 1940nm pump source outputs pump light, which is transmitted through an optical fiber and coupled into an optical fiber coupling lens group to output parallel light. After being split by a microlens array, the parallel light passes through a polarizer group to adjust the polarization direction of the pump light, and then is input into a plane mirror to obtain 1940nm wavelength light focused on the front end of a c-axis cut Ho:LLF crystal.

[0018] The c-axis cut Ho:LLF crystal absorbs the input light in the 1940nm band, undergoes stimulated absorption and stimulated transition in the resonant cavity and continuously gains gain, and then outputs laser light through the output plane mirror and 1900nm narrowband filter.

[0019] Then, a set of polarization beam splitters is used to separate the σ polarization and π polarization of the orthogonally polarized dual-wavelength lasers generated by each branch, thereby achieving multi-wavelength laser output in the horizontal and vertical directions of 2052-2056.3nm and 2063.1-2065.7nm, respectively.

[0020] Furthermore, when Ho:LLF absorbs 1940nm laser light, it undergoes… 5 I8 and 5 The energy level transition between I7 and the multi-wavelength laser output by this laser system is actually... 5 I8 and 5 The result of the numerous fine energy levels generated by the energy level splitting in I7, and the transitions from upper to lower energy levels, can be simplified by analyzing the rate equation during these transitions, yielding the following expression:

[0021]

[0022] Where N1 is 5 The number of particles in the I8 level, N2 is 5 The number of particles in the I7 level, W 12 For a 1940nm laser pump rate, W 21 For the output laser rate, σ 12 and σ21 W represents the emission or absorption cross-sectional area, and the output laser wavelength varies. 21 and σ 12 Different values ​​correspond to different fine energy levels; P is the total power absorbed during the energy level transition, h is Planck's constant, A is the cross-sectional area of ​​the beam, and υ P It is the center frequency of the pump light, υ L It is the center frequency of the emitted laser, τ ij It is the relaxation time between energy levels, τ ij sp It is the spontaneous emission time, τ ij nr It is the non-radiative transition time;

[0023] Formulas (1) and (2) are based on 5 I8 energy level, 5 The rate equations for the increase and decrease of the number of particles in the I7 energy level are (3) and (4), which respectively represent the expressions for the pump rate and output laser rate of the 1940nm laser. (5) represents the relationship between the relaxation time, spontaneous emission time and non-radiative transition time of the particles in the energy level.

[0024] Furthermore, when an angular change α occurs between the polarization direction of the incident light and the crystal principal axis, it causes a change in the wavelength of the σ-polarization state and π-polarization state output by the Ho:LLF crystal, resulting in the expression:

[0025] λ σ (θ1)=λ σ (θ0)+Δλ σ (α) (6)

[0026] λ π (θ1)=λ π (θ0)+Δλ π (α) (7)

[0027] Where θ0 is defined as the initial angle between the polarization direction of the input light and the principal axis of the crystal, and the angle becomes θ1 after rotation α. σ (θ0) and λ σ (θ1) is defined as the center wavelength of the output of the σ polarization state at angles θ0 and θ1, respectively. π (θ0) and λ π (θ1) is defined as the center wavelength of the π-polarized state output at angles θ0 and θ1, respectively, and Δλ is the center wavelength of the output of the π-polarized state. σ (α) and Δλ π (α) represents the change in the center wavelength of the σ polarization state and the change in the center wavelength of the π polarization state after rotation α;

[0028] The expression for the refractive index relationship between the a-axis and c-axis planes of Ho:LLF crystal is:

[0029]

[0030] Where, n a and n c These are the refractive indices along the a-axis and c-axis, respectively, and n c (θ) is the refractive index when the polarization direction of the input light is at an angle θ with the principal axis of the crystal;

[0031] Based on the constraint of the output light on the standing wave condition of the resonant cavity between the input and output mirrors, the expression is obtained as follows:

[0032] 2kL'=2mπ (9)

[0033] L'=n0L1+n c (θ)L2 (10)

[0034] Where k is the mode of the wave vector, L' is the total optical path, and n0L1 and n c (θ)L2 represents the optical path lengths outside and inside the crystal in the resonant cavity, respectively, where m is the first positive integer; L1 and L2 represent the propagation paths of light during oscillation in the resonant cavity outside and inside the crystal, respectively.

[0035] Combining equations (8), (9), and (10), we obtain:

[0036]

[0037] When the angle θ changes by α, equation (6) changes to:

[0038]

[0039] Where k' is the magnitude of the transformed wave vector, and m' is the second positive integer;

[0040] Introducing wavelength λ into equation (12), we obtain the following expression:

[0041]

[0042] Where m1' and m2' are the third positive integer and the fourth positive integer, respectively, and θ π0 and θ σ0 Let σ and π represent the angles between the output σ polarization and the crystal principal axis, respectively; based on equations (8) and (9), the variable Δλ is obtained after introducing α. π (α) / Δλ σ (α) and m1' / m2' also change synergistically; when the polarizer is rotated, the refractive index n changes with θ. c When (θ) changes, the optical path L' changes. In order to satisfy the standing wave condition, the mode k of the wave vector will change accordingly, that is, the wavelength λ changes.

[0043] A tunable spatially multiplexed multiwavelength laser based on Ho:LLF includes a 795nm LD pump source, an optical fiber, an optical fiber coupling lens group, a second input plane mirror, a b-axis diced Tm:YAP crystal, a second output plane mirror, a beam splitter, an optical path compensation plate, a polarizer group, an input plane mirror, a c-axis diced Ho:LLF crystal, an output plane mirror, a 1000nm narrowband filter, a 1900nm narrowband filter, and a set of polarizing beam splitters.

[0044] The 795nm LD pump source is connected to a fiber-coupled lens group via an optical fiber. The fiber-coupled lens group has a second input plane mirror, a b-axis cut Tm:YAP crystal, a second output plane mirror, a beam splitter, an optical path compensation plate, a polarizer group, an input plane mirror, a c-axis cut Ho:LLF crystal, an output plane mirror, a 1000nm narrowband filter, a 1900nm narrowband filter, and a set of polarizing beam splitters arranged sequentially along the optical path on the right side.

[0045] The surface of the second input plane mirror is coated with a 1950nm narrowband reflective film, and the surface of the second output plane mirror is coated with a 1950nm 5% transmission film; the c-axis cut Ho:LLF crystal is cuboid in shape.

[0046] In a beam splitter, the n beam paths are numbered from bottom to top. The transmittance of the first beam splitter is 1 / n and the reflectance is (n-1) / n. The transmittance of the second beam splitter is (n-2) / (n-1) and the reflectance is 1 / (n-1). The transmittance of the third beam splitter is (n-3) / (n-2) and the reflectance is 1 / (n-2)... The transmittance of the i-th beam splitter is (ni) / (n-i+1) and the reflectance is 1 / (n-i+1).

[0047] The optical path compensation plate is set as a glass plate placed at a 45° angle to the horizontal plane. The thickness of the glass plate is determined by the distance s between the beam splitters. The thickness difference between any two adjacent optical paths is 0.58 × s. No optical path compensation plate is placed in the uppermost optical path. In order from top to bottom, the thickness of the first optical path compensation plate is 0.58 × s, the thickness of the second optical path compensation plate is 0.58 × 2s, and so on. The thickness of the nth optical path compensation plate is 0.58 × ns.

[0048] The beneficial effects of this invention are:

[0049] The present invention discloses a tunable spatial multiplexed multi-wavelength laser based on Ho:LLF, which utilizes the rotation angle gradient design of multiple polarizers to achieve multi-wavelength output in two bands in the horizontal and vertical directions. Furthermore, all laser wavelength components can be extracted individually. In addition, multi-wavelength tuning can be achieved by adjusting the polarizers.

[0050] The present invention discloses a tunable spatially multiplexed multi-wavelength laser based on Ho:LLF, which uses a Ho:LLF crystal and a pump source to generate multi-wavelength laser output in two bands, 2052-2056.3nm and 2063.1-2065.7nm, in the horizontal and vertical directions, respectively.

[0051] The present invention discloses a tunable spatial multiplexed multi-wavelength laser based on Ho:LLF, which can achieve independent output of any wavelength component of the multi-wavelength laser.

[0052] This invention discloses a tunable spatially multiplexed multi-wavelength laser based on Ho:LLF. By simply rotating the polarizer angle, it can tune the output of multiple wavelengths of laser light, achieving tunable multi-wavelength laser output in both horizontal and vertical directions. Utilizing the spatial multiplexing characteristics and the output properties of the Ho:LLF crystal, the space required for multi-wavelength output is optimized, realizing the design of a miniaturized multi-wavelength laser. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the first structure of a tunable spatially multiplexed multiwavelength laser based on Ho:LLF according to the present invention.

[0054] Figure 2 This is a schematic diagram of the structure of Ho:LLF crystal cut along the c-axis according to the present invention;

[0055] Figure 3 This is a schematic diagram showing the polarization direction of the input light and the angle between the crystal axis and the crystal axis in this invention.

[0056] Figure 4 This is a schematic diagram of the c-axis cut of the refractive index ellipse of the Ho:LLF crystal according to the present invention;

[0057] Figure 5 This is a schematic diagram of a second structure of a tunable spatially multiplexed multiwavelength laser based on Ho:LLF according to the present invention.

[0058] Figure 6 This is a schematic diagram of a third structure of a tunable spatially multiplexed multiwavelength laser based on Ho:LLF according to the present invention.

[0059] Figure 7 The wavelength variation of the Ho:LLF crystal under c-axis cutting angle tuning in this invention is shown in the figure, where a represents π polarization and b represents σ polarization. Detailed Implementation

[0060] 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 specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described specific embodiments are merely a part of the embodiments of the invention, and not all of them. The components of the specific embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations, and the invention may also have other embodiments.

[0061] Therefore, the following detailed description of specific embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected specific embodiments of the invention. All other specific embodiments obtained by those skilled in the art based on these specific embodiments without inventive effort are within the scope of protection of this invention.

[0062] To further understand the invention's content, features, and effects, the following specific embodiments are provided, along with accompanying drawings. Figure 1 - Appendix Figure 7 Detailed explanation is as follows:

[0063] Example 1:

[0064] A tunable spatially multiplexed multiwavelength laser based on Ho:LLF includes a 1940nm pump source 1, an optical fiber 2, an optical fiber coupling lens group 3, a microlens array 4, a polarizer group 5, an input plane mirror 6, a c-axis cut Ho:LLF crystal 7, an output plane mirror 8, a 1900nm narrowband filter 9, and a set of polarization beam splitters 10.

[0065] The 1940nm pump source 1 is connected to the fiber-coupled lens group 3 via the optical fiber 2. The fiber-coupled lens group 3 is arranged in sequence along the optical path on the right side, including the microlens array 4, the polarizer group 5, the input plane mirror 6, the c-axis cut Ho:LLF crystal 7, the output plane mirror 8, the 1900nm narrowband filter 9, and a set of polarizing beam splitters 10.

[0066] The rotation angle of the polarizer group is set to vary from 0 to 90°.

[0067] Furthermore, the surface of the input plane mirror 6 is coated with a 2050nm narrowband reflective film, the surface of the output plane mirror 8 is coated with a 2050nm 5% transmission film, and the c-axis cut Ho:LLF crystal 7 is in the shape of a cuboid.

[0068] Furthermore, the microlens array 4 is composed of microconvex lenses, the focal length of which corresponds to the position of the c-axis cut Ho:LLF crystal 7.

[0069] Furthermore, to ensure that each laser beam after splitting is focused onto the crystal end face, the placement of the Ho:LLF crystal should be adjusted according to the focal length of the microlens array during operation. The 1940nm pump light is multi-output through the microlens array, and outputs linearly polarized light with different polarization directions through a series of polarizers with different rotation angles. The polarizer is an extremely important device in this design. The reason for the different output wavelengths depending on the rotation angle of the polarizer is as follows: When lasers with different polarization directions output from different polarizers are input to the c-axis to cut the Ho:LLF end face, the refractive index corresponding to the polarization direction of the light wave also changes according to the different rotation angles. Considering that the Ho:LLF crystal has the ability to output dual-wavelength lasers under the pump condition of 1940nm due to the special energy level structure, when an angle change α occurs between the polarization direction of the incident light and the principal axis of the crystal, the wavelengths of the σ polarization state and π polarization state output by the Ho:LLF crystal change.

[0070] Furthermore, the 1900nm narrowband filter filters out the 1940nm pump light, so that the laser only contains the output component of the Ho:LLF crystal.

[0071] Furthermore, due to the ingenious design of the structure and the innovative application of the polarizer, multi-wavelength laser output in two bands can be achieved in the vertical and horizontal directions respectively, based on the gradient rotation of the polarizer, and each wavelength component of the output can be separated individually.

[0072] Example 2:

[0073] A wavelength tuning method for a tunable spatially multiplexed multi-wavelength laser based on Ho:LLF, implemented using the tunable spatially multiplexed multi-wavelength laser based on Ho:LLF described in Example 1, includes the following steps:

[0074] A 1940nm pump source outputs pump light, which is transmitted through an optical fiber and coupled into an optical fiber coupling lens group to output parallel light. After being split by a microlens array, the parallel light passes through a polarizer group to adjust the polarization direction of the pump light, and then is input into a plane mirror to obtain 1940nm wavelength light focused on the front end of a c-axis cut Ho:LLF crystal.

[0075] The c-axis cut Ho:LLF crystal absorbs the input light in the 1940nm band, undergoes stimulated absorption and stimulated transition in the resonant cavity and continuously gains gain, and then outputs laser light through the output plane mirror and 1900nm narrowband filter.

[0076] Then, a set of polarization beam splitters is used to separate the σ polarization and π polarization of the orthogonally polarized dual-wavelength lasers generated by each branch, thereby achieving multi-wavelength laser output in the horizontal and vertical directions of 2052-2056.3nm and 2063.1-2065.7nm, respectively.

[0077] Furthermore, when Ho:LLF absorbs 1940nm laser light, it undergoes… 5 I8 and 5 The energy level transition between I7 and the multi-wavelength laser output by this laser system is actually... 5 I8 and 5 The result of the numerous fine energy levels generated by the energy level splitting in I7, and the transitions from upper to lower energy levels, can be simplified by analyzing the rate equation during these transitions, yielding the following expression:

[0078]

[0079] Where N1 is 5 The number of particles in the I8 level, N2 is 5 The number of particles in the I7 level, W 12 For a 1940nm laser pump rate, W 21 For the output laser rate, σ 12 and σ 21 W represents the emission or absorption cross-sectional area, and the output laser wavelength varies. 21 and σ 12 Different values ​​correspond to different fine energy levels; P is the total power absorbed during the energy level transition, h is Planck's constant, A is the cross-sectional area of ​​the beam, and υ P It is the center frequency of the pump light, υ L It is the center frequency of the emitted laser, τ ij It is the relaxation time between energy levels, τ ij sp It is the spontaneous emission time, τ ij nr It is the non-radiative transition time;

[0080] Formulas (1) and (2) are based on 5 I8 energy level, 5 The rate equations for the increase and decrease of the number of particles in the I7 energy level are (3) and (4), which respectively represent the expressions for the pump rate and output laser rate of the 1940nm laser. (5) represents the relationship between the relaxation time, spontaneous emission time and non-radiative transition time of the particles in the energy level.

[0081] Furthermore, when an angular change α occurs between the polarization direction of the incident light and the crystal principal axis, it causes a change in the wavelength of the σ-polarization state and π-polarization state output by the Ho:LLF crystal, resulting in the expression:

[0082] λσ (θ1)=λ σ (θ0)+Δλ σ (α) (6)

[0083] λ π (θ1)=λ π (θ0)+Δλ π (α) (7)

[0084] Where θ0 is defined as the initial angle between the polarization direction of the input light and the principal axis of the crystal, and the angle becomes θ1 after rotation α. σ (θ0) and λ σ (θ1) is defined as the center wavelength of the output of the σ polarization state at angles θ0 and θ1, respectively. π (θ0) and λ π (θ1) is defined as the center wavelength of the π-polarized state output at angles θ0 and θ1, respectively, and Δλ is the center wavelength of the output of the π-polarized state. σ (α) and Δλ π (α) represents the change in the center wavelength of the σ polarization state and the change in the center wavelength of the π polarization state after rotation α;

[0085] The expression for the refractive index relationship between the a-axis and c-axis planes of Ho:LLF crystal is:

[0086]

[0087] Where, n a and n c These are the refractive indices along the a-axis and c-axis, respectively, and n c (θ) is the refractive index when the polarization direction of the input light is at an angle θ with the principal axis of the crystal;

[0088] Based on the constraint of the output light on the standing wave condition of the resonant cavity between the input and output mirrors, the expression is obtained as follows:

[0089] 2kL'=2mπ (9)

[0090] L'=n0L1+n c (θ)L2 (10)

[0091] Where k is the mode of the wave vector, L' is the total optical path, and n0L1 and n c (θ)L2 represents the optical path lengths outside and inside the crystal in the resonant cavity, respectively, where m is the first positive integer; L1 and L2 represent the propagation paths of light during oscillation in the resonant cavity outside and inside the crystal, respectively.

[0092] Combining equations (8), (9), and (10), we obtain:

[0093]

[0094] When the angle θ changes by α, equation (6) changes to:

[0095]

[0096] Where k' is the magnitude of the transformed wave vector, and m' is the second positive integer;

[0097] Introducing wavelength λ into equation (12), we obtain the following expression:

[0098]

[0099] Where m1' and m2' are the third positive integer and the fourth positive integer, respectively, and θ π0 and θ σ0 Let σ and π represent the angles between the output σ polarization and the crystal principal axis, respectively; based on equations (8) and (9), the variable Δλ is obtained after introducing α. π (α) / Δλ σ (α) and m1' / m2' also change synergistically; when the polarizer is rotated, the refractive index n changes with θ. c When (θ) changes, the optical path L' changes. In order to satisfy the standing wave condition, the mode k of the wave vector will change accordingly, that is, the wavelength λ changes.

[0100] Furthermore, the variables Δλπ(α) / Δλσ(α) and m' / n' also change collaboratively, enabling the output of a wide range of frequencies under the condition of satisfying the equation. According to the absorption and emission spectra of the σ / π polarization state of Ho:LLF crystals published by Walsh.BM et al. in "Branching ratios, cross sections, and radiative lifetimes of rare earth ions in solids::Application to Tm3+ and Ho3+ ions in LiYF4", the Ho:LLF crystal exhibits a broad emission wavelength range at approximately 2050 nm, which is consistent with the theoretical derivation.

[0101] Furthermore, based on the above derivation, when the polarizer rotates, the refractive index nc(θ) changes with θ, thus changing the optical path L'. To satisfy the standing wave condition, the mode k of the wave vector changes accordingly, i.e., the wavelength λ changes. This angle tuning refers to changing the angle between the polarization state of the 1940nm laser (the pump light of the Ho:LLF crystal) and the crystal axis direction. In other words, each part of the Ho:LLF crystal outputs laser light of different wavelengths due to the change in polarization direction. Moreover, due to the characteristics of the Ho:LLF crystal, each laser path is an orthogonally polarized dual-wavelength laser. Through the polarizer angle gradient design, each optical path outputs a group of orthogonally polarized dual-wavelength lasers with monotonic wavelength changes, achieving wavelength tuning by angle control.

[0102] As the derivation shows, the change in the polarization direction of the pump light and the angle between the crystal principal axes of the Ho:LLF crystal affects the wavelength of the output laser. Therefore, by rotating the angle of the polarizer, the wavelength of each output laser can be tuned. After passing through a polarizing beam splitter, the orthogonally polarized dual-wavelength lasers of different wavelengths from each output laser are separated, enabling each wavelength component of the multi-wavelength laser to be output individually. Figure 7 The results show the wavelength variation of the output laser under angle tuning of 13°-80°, which is consistent with the theoretical derivation. The π-polarized wavelength variation range in the horizontal direction is 2053-2056.3nm, and the σ-polarized wavelength variation range in the vertical direction is 2063.1-2065.7nm. The test results verify the feasibility of the device.

[0103] Example 3:

[0104] The difference between this embodiment and the first embodiment is that the microlens array 4 is replaced by a set of beam mirrors 11 and an optical path compensation plate 12.

[0105] Furthermore, the n beam splitting paths in a beam splitter 11 are designed with numbers from bottom to top. The transmittance of the first beam splitter is 1 / n and the reflectance is (n-1) / n. The transmittance of the second beam splitter is (n-2) / (n-1) and the reflectance is 1 / (n-1). The transmittance of the third beam splitter is (n-3) / (n-2) and the reflectance is 1 / (n-2)... The transmittance of the i-th beam splitter is (ni) / (n-i+1) and the reflectance is 1 / (n-i+1).

[0106] For example, if five beam splitters are used to create five optical paths, the first beam splitter has a transmittance of 20% and a reflectance of 80% in the 2μm band, the second beam splitter has a transmittance of 75% and a reflectance of 25%, the third beam splitter has a transmittance of 66.7% and a reflectance of 33.3%, the fourth beam splitter has a transmittance of 50% and a reflectance of 50%, and the fifth beam splitter has a transmittance of 0% and a reflectance of 100%.

[0107] Furthermore, the optical path compensation plate 12 is set as a glass plate placed at a 45° angle to the horizontal plane. The thickness of the glass plate is determined by the distance s between the beam splitters. The thickness difference between each pair of adjacent optical paths is 0.58×s. No optical path compensation plate is placed in the uppermost optical path. In order from top to bottom, the thickness of the first optical path compensation plate is 0.58×s, the thickness of the second compensation plate is 0.58×2s, and so on. The thickness of the nth optical path compensation plate is 0.58×ns.

[0108] Example 4:

[0109] The difference between this embodiment and embodiment 3 is that the 1940nm pump source 1 is replaced by a 795nm LD pump source 13. The tunable spatial multiplexed multiwavelength laser based on Ho:LLF is configured such that the 795nm LD pump source 13 is connected to the fiber-coupled lens group 3 via fiber 2. The fiber-coupled lens group 3 is arranged along the optical path on the right side with a second input plane mirror 14, a b-axis cut Tm:YAP crystal 15, a second output plane mirror 16, a beam splitter 11, an optical path compensation plate 12, a polarizer group 5, an input plane mirror 6, a c-axis cut Ho:LLF crystal 7, an output plane mirror 8, a 1000nm narrowband filter 17, a 1900nm narrowband filter 9, and a set of polarizing beam splitters 10.

[0110] The surface of the second input plane mirror 14 is coated with a 1950nm narrowband reflective film, and the surface of the second output plane mirror 16 is coated with a 1950nm narrowband reflective film.

[0111] Furthermore, considering that 795nm LD pump sources are more common and the system is more mature in practical applications, a 795nm LD pump source is used to pump a Tm:YAP crystal to output a 1940nm laser, and the laser is used to pump a Ho:LLF crystal. In this scheme, an additional 1000nm narrowband filter (17) is needed to filter out the 795nm pump light.

[0112] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0113] Although this application has been described above with reference to specific embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of this application. In particular, as long as there is no structural conflict, the features in the specific embodiments disclosed in this application can be combined with each other in any way. The lack of an exhaustive description of these combinations in this specification is merely for the sake of brevity and resource conservation. Therefore, this application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A tunable spatially multiplexed multiwavelength laser based on Ho:LLF, characterized in that, It includes a 1940nm pump source (1), an optical fiber (2), an optical fiber coupling lens group (3), a microlens array (4), a polarizer group (5), an input plane mirror (6), a c-axis cut Ho:LLF crystal (7), an output plane mirror (8), a 1900nm narrowband filter (9), and a set of polarizing beam splitters (10). The 1940nm pump source (1) is connected to the fiber-coupled lens group (3) via the optical fiber (2). The fiber-coupled lens group (3) is arranged in sequence along the optical path on the right side with a microlens array (4), a polarizer group (5), an input plane mirror (6), a c-axis cut Ho:LLF crystal (7), an output plane mirror (8), a 1900nm narrowband filter (9), and a set of polarizing beam splitters (10). The rotation angle of the polarizer group is set to vary from 0 to 90°.

2. A tunable spatially multiplexed multiwavelength laser based on Ho:LLF according to claim 1, characterized in that, The surface of the input plane mirror (6) is coated with a 2050nm narrowband reflective film, the surface of the output plane mirror (8) is coated with a 2050nm 5% transmission film, and the c-axis cut Ho:LLF crystal (7) is in the shape of a cuboid.

3. A tunable spatially multiplexed multiwavelength laser based on Ho:LLF according to claim 1 or 2, characterized in that, The microlens array (4) is composed of microconvex lenses, and the focal length of the convex lens corresponds to the position of the front end face of the c-axis cut Ho:LLF crystal (7).

4. A tunable spatially multiplexed multiwavelength laser based on Ho:LLF according to claim 3, characterized in that, The microlens array (4) is replaced by a set of beam mirrors (11) and an optical path compensation plate (12).

5. A tunable spatially multiplexed multiwavelength laser based on Ho:LLF according to claim 4, characterized in that, In a beam splitter (11), the n beam paths are numbered from bottom to top. The transmittance of the first beam splitter is 1 / n and the reflectance is (n-1) / n. The transmittance of the second beam splitter is (n-2) / (n-1) and the reflectance is 1 / (n-1). The transmittance of the third beam splitter is (n-3) / (n-2) and the reflectance is 1 / (n-2). The transmittance of the i-th beam splitter is (ni) / (n-i+1) and the reflectance is 1 / (n-i+1).

6. A tunable spatially multiplexed multiwavelength laser based on Ho:LLF according to claim 5, characterized in that, The optical path compensation plate (12) is set as a glass plate placed at a 45° angle to the horizontal plane. The thickness of the glass plate is determined by the distance s between the beam splitters. The thickness difference between each pair of adjacent optical paths is 0.58×s. No optical path compensation plate is placed in the uppermost optical path. In order from top to bottom, the thickness of the first optical path compensation plate is 0.58×s, the thickness of the second optical path compensation plate is 0.58×2s, and so on. The thickness of the nth optical path compensation plate is 0.58×ns.

7. A wavelength tuning method for a tunable spatially multiplexed multi-wavelength laser based on Ho:LLF, implemented using the tunable spatially multiplexed multi-wavelength laser based on Ho:LLF as described in any one of claims 1-6, characterized in that... Includes the following steps: A 1940nm pump source outputs pump light, which is transmitted through an optical fiber and coupled into an optical fiber coupling lens group to output parallel light. After being split by a microlens array, the parallel light passes through a polarizer group to adjust the polarization direction of the pump light, and then is input into a plane mirror to obtain 1940nm wavelength light focused on the front end of a c-axis cut Ho:LLF crystal. After the c-axis cut Ho:LLF crystal absorbs the input light in the 1940nm band, it undergoes stimulated absorption and stimulated transition in the resonant cavity and continuously gains gain. After passing through the output plane mirror and the 1900nm narrowband filter, it outputs multi-wavelength laser light. Then, a set of polarization beam splitters is used to separate the σ polarization and π polarization of the orthogonally polarized dual-wavelength lasers generated by each branch, thereby achieving multi-wavelength laser output in the horizontal and vertical directions of 2052-2056.3nm and 2063.1-2065.7nm, respectively.

8. The wavelength tuning method for a tunable spatially multiplexed multi-wavelength laser based on Ho:LLF according to claim 7, characterized in that Ho When an LLF absorbs a 1940nm laser, it undergoes… 5 I8 and 5 The energy level transition between I7 and the multi-wavelength laser output by this laser system is actually... 5 I8 and 5 The result of the numerous fine energy levels generated by the energy level splitting in I7, and the transitions from upper to lower energy levels, can be simplified by analyzing the rate equations during these transitions, yielding the following expression: Where N1 is 5 The number of particles in the I8 level, N2 is 5 The number of particles in the I7 level, W 12 For a 1940nm laser pump rate, W 21 For the output laser rate, σ 12 and σ 21 W represents the emission or absorption cross-sectional area, and the output laser wavelength varies. 21 and σ 12 Different values ​​correspond to different fine energy levels; P is the total power absorbed during the energy level transition, h is Planck's constant, A is the cross-sectional area of ​​the beam, and υ P It is the center frequency of the pump light, υ L It is the center frequency of the emitted laser, τ ij It is the relaxation time between energy levels, τ ij sp It is the spontaneous emission time, τ ij nr It is the non-radiative transition time; Formulas (1) and (2) are based on 5 I8 energy level, 5 The rate equations for the increase and decrease of the number of particles in the I7 energy level are (3) and (4), which respectively represent the expressions for the pump rate and output laser rate of the 1940nm laser. (5) represents the relationship between the relaxation time, spontaneous emission time and non-radiative transition time of the particles in the energy level.

9. A wavelength tuning method for a tunable spatially multiplexed multi-wavelength laser based on Ho:LLF according to claim 8, characterized in that, When the polarization direction of the incident light changes by an angle α with the principal axis of the crystal, the wavelengths of the σ-polarization and π-polarization states output by the Ho:LLF crystal change, resulting in the expression: l σ (θ1)=λ σ (θ0)+Δλ σ (a)(6) l π (θ1)=λ π (θ0)+Δλ π (a)(7) Where θ0 is defined as the initial angle between the polarization direction of the input light and the principal axis of the crystal, and the angle becomes θ1 after rotation α. σ (θ0) and λ σ (θ1) is defined as the center wavelength of the output of the σ polarization state at angles θ0 and θ1, respectively. π (θ0) and λ π (θ1) is defined as the center wavelength of the π-polarized state output at angles θ0 and θ1, respectively, and Δλ is the center wavelength of the output of the π-polarized state. σ (α) and Δλ π (α) represents the change in the center wavelength of the σ polarization state and the change in the center wavelength of the π polarization state after rotation α; The expression for the refractive index relationship between the a-axis and c-axis planes of Ho:LLF crystal is: Where, n a and n c These are the refractive indices along the a-axis and c-axis, respectively, and n c (θ) is the refractive index when the polarization direction of the input light is at an angle θ with the principal axis of the crystal; Based on the constraint of the output light on the standing wave condition of the resonant cavity between the input and output mirrors, the expression is obtained as follows: 2kL'=2mπ(9) L'=n0L1+n c (θ)L2(10) Where k is the mode of the wave vector, L' is the total optical path, and n0L1 and n c (θ)L2 represents the optical path lengths outside and inside the crystal in the resonant cavity, respectively, where m is the first positive integer; L1 and L2 represent the propagation paths of light during oscillation in the resonant cavity outside and inside the crystal, respectively. Combining equations (8), (9), and (10), we obtain: When the angle θ changes by α, equation (6) changes to: Where k' is the magnitude of the transformed wave vector, and m' is the second positive integer; Introducing wavelength λ into equation (12), we obtain the following expression: Where m1' and m2' are the third positive integer and the fourth positive integer, respectively, and θ π0 and θ σ0 Let σ and π represent the angles between the output σ polarization and the crystal principal axis, respectively; based on equations (8) and (9), the variable Δλ is obtained after introducing α. π (α) / Δλ σ (α) and m1' / m2' also change synergistically; when the polarizer is rotated, the refractive index n changes with θ. c When (θ) changes, the optical path L' changes, and the mode k of the wave vector changes accordingly, that is, the wavelength λ changes.

10. A tunable spatially multiplexed multiwavelength laser based on Ho:LLF, characterized in that, Includes a 795nm LD pump source (13), an optical fiber (2), an optical fiber coupling lens group (3), a second input plane mirror (14), a b-axis cut Tm:YAP crystal (15), a second output plane mirror (16), a beam splitter (11), an optical path compensation plate (12), a polarizer group (5), an input plane mirror (6), a c-axis cut Ho:LLF crystal (7), an output plane mirror (8), a 1000nm narrowband filter (17), a 1900nm narrowband filter (9), and a set of polarizing beam splitters (10); The 795nm LD pump source (13) is connected to the fiber-coupled lens group (3) via the optical fiber (2). The fiber-coupled lens group (3) is arranged in sequence along the optical path on the right side with the following components: a second input plane mirror (14), a b-axis cut Tm:YAP crystal (15), a second output plane mirror (16), a set of beam splitters (11), an optical path compensation plate (12), a polarizer group (5), an input plane mirror (6), a c-axis cut Ho:LLF crystal (7), an output plane mirror (8), a 1000nm narrowband filter (17), a 1900nm narrowband filter (9), and a set of polarizing beam splitters (10). The surface of the second input plane mirror (14) is coated with a 1950nm narrowband reflective film, and the surface of the second output plane mirror (16) is coated with a 1950nm narrowband reflective film; the c-axis cut Ho:LLF crystal (7) is in the shape of a cuboid. In a beam splitter (11), the n beam splitting paths are numbered from bottom to top. The transmittance of the first beam splitter is 1 / n and the reflectance is (n-1) / n. The transmittance of the second beam splitter is (n-2) / (n-1) and the reflectance is 1 / (n-1). The transmittance of the third beam splitter is (n-3) / (n-2) and the reflectance is 1 / (n-2). The transmittance of the i-th beam splitter is (ni) / (n-i+1) and the reflectance is 1 / (n-i+1). The optical path compensation plate (12) is set as a glass plate placed at a 45° angle to the horizontal plane. The thickness of the glass plate is determined by the distance s between the beam splitters. The thickness difference between each pair of adjacent optical paths is 0.58×s. No optical path compensation plate is placed in the uppermost optical path. In order from top to bottom, the thickness of the first optical path compensation plate is 0.58×s, the thickness of the second optical path compensation plate is 0.58×2s, and so on. The thickness of the nth optical path compensation plate is 0.58×ns.

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