Multi-wavelength solid laser based on Ho-doped crystal and operation method thereof

Abstract

The invention discloses a multi-wavelength solid laser based on a Ho-doped crystal and an operation method thereof, and belongs to the technical field of optoelectronic device manufacturing and optical engineering laser. In order to solve the problem of developing a multi-wavelength solid laser with a simpler operation process, the multi-wavelength solid laser comprises a 1940nm pumping source, the 1940nm pumping source is connected with an optical fiber coupling lens group through an optical fiber, and a micro-lens array, an input plane mirror, an Ho doped mixed crystal, an output plane mirror and a 1900nm narrow-band filter are sequentially arranged on the right side of the optical fiber coupling lens group along an optical path; the Ho-doped mixed crystal is formed by combining a cylindrical doped crystal at the central position, and a first fan-ring-shaped doped crystal, a second fan-ring-shaped doped crystal, a third fan-ring-shaped doped crystal and a fourth fan-ring-shaped doped crystal which surround the cylindrical doped crystal. According to the invention, one pumping source and one laser excite multi-wavelength laser, which is of great significance to wavelength division multiplexing scenes such as optical fiber communication, optical calculation and the like.

Description

Technical Field

[0001] The present invention belongs to the fields of optoelectronic device manufacturing and optical engineering laser technology, and particularly relates to a multi-wavelength solid-state laser based on Ho-doped crystals and an operation method thereof. Background Art

[0002] As a core technology in frontier fields such as optical fiber communication and optical computing, wavelength-division multiplexing (WDM) technology is rapidly expanding to multiple sectors of the information industry. Its demand for high-efficiency and high-integration laser output poses a major challenge to modern laser technology. However, due to the inherent absorption and emission spectral limitations of laser crystals, most traditional lasers are limited to single-wavelength operation. The ability to generate multi-wavelength signals is restricted by the number of lasers. Moreover, due to the complex tuning characteristics of independent lasers, it is difficult to achieve stable multi-wavelength output, which poses a severe challenge to fields widely applying WDM technology such as optoelectronic integration (such as on-chip computing and data interconnection) and optical fiber communication.

[0003] The "multi-wavelength laser" with the authorization announcement number CN203674555U uses a green laser module, a red laser module, and a blue laser module placed in parallel. The centers of the three modules form an equilateral triangle, and the emitted light of the three modules has the same divergence angle and spot size. By lighting the red, blue, and green laser modules in different combinations, different colors of laser can be obtained. However, it can only output lasers of red, green, and blue three colors.

[0004] The "multi-wavelength laser" with the authorization announcement number CN112928588B uses a resonant cavity with an imaging structure and a cavity mirror coating process, so that the distribution regions of lasers with different wavelengths in the gain medium are different, avoiding the competition of each wavelength. Films with different reflectivities for different wavelengths are coated, so that the losses of each wavelength in each coating region are different, satisfying that only one wavelength oscillates in each coating region, and realizing the simultaneous output of lasers with different wavelengths by the laser. However, the preparation process involves the coating processes of different gain media, and its actual application process is extremely complex. It also involves a series of problems such as whether there is a mature coating process for the corresponding gain medium, and different wavelength outputs require corresponding pump sources, etc. Summary of the Invention

[0005] The problem to be solved by the present invention is to develop a multi-wavelength solid-state laser with a simpler operation process and higher use value, and propose a multi-wavelength solid-state laser based on Ho-doped crystals and an operation method thereof.

[0006] To achieve the above object, the present invention is realized through the following technical solutions:

[0007] A multi-wavelength solid-state laser based on a Ho-doped crystal, comprising a 1940 nm pump source, an optical fiber, an optical fiber coupling lens group, a microlens array, an input plane mirror, a Ho-doped mixed crystal, an output plane mirror, and a 1900 nm narrowband filter;

[0008] The 1940 nm pump source is connected to the optical fiber coupling lens group through an optical fiber. On the right side of the optical fiber coupling lens group along the optical path, a microlens array, an input plane mirror, a Ho-doped mixed crystal, an output plane mirror, and a 1900 nm narrowband filter are arranged in sequence;

[0009] The Ho-doped mixed crystal is composed of a cylindrical doped crystal at the central position and a first sector-shaped ring doped crystal, a second sector-shaped ring doped crystal, a third sector-shaped ring doped crystal, and a fourth sector-shaped ring doped crystal surrounding the cylindrical doped crystal. The cylindrical doped crystal is one of Ho:YAP crystals cut in different axial directions, and the first sector-shaped ring doped crystal, the second sector-shaped ring doped crystal, the third sector-shaped ring doped crystal, and the fourth sector-shaped ring doped crystal are several combinations of Ho:LLF crystals, Ho:YAP crystals, and Ho:YLF crystals cut in different axial directions;

[0010] Or the Ho-doped mixed crystal is replaced by a combination of a first sector-shaped doped crystal, a second sector-shaped doped crystal, a third sector-shaped doped crystal, and a fourth sector-shaped doped crystal. The first sector-shaped doped crystal, the second sector-shaped doped crystal, the third sector-shaped doped crystal, and the fourth sector-shaped doped crystal are several combinations of Ho:LLF crystals, Ho:YAP crystals, and Ho:YLF crystals cut in different axial directions.

[0011] Further, the surface of the input plane mirror is coated with a 2050 nm narrowband reflection film, and the surface of the output plane mirror is coated with a 5% transmission film of 2050 nm.

[0012] Further, the cylindrical doped crystal in the Ho-doped mixed crystal is a Ho:YAP crystal cut along the a-axis, the first sector-shaped ring doped crystal is a Ho:LLF crystal cut along the c-axis, the second sector-shaped ring doped crystal is a Ho:YAP crystal cut along the c-axis, the third sector-shaped ring doped crystal is a Ho:YLF crystal cut along the c-axis, and the fourth sector-shaped ring doped crystal is a Ho:YAP crystal cut along the b-axis.

[0013] Further, the first sector-shaped doped crystal in the Ho-doped mixed crystal (6) is a Ho:LLF crystal cut along the c-axis, the second sector-shaped doped crystal is a Ho:YAP crystal cut along the c-axis, the third sector-shaped doped crystal is a Ho:YLF crystal cut along the c-axis, and the fourth sector-shaped doped crystal is a Ho:YLF crystal cut along the b-axis.

[0014] Further, the angular range of each doped crystal in the Ho-doped mixed crystal is 0-90°.

[0015] An operating method of a multi-wavelength solid laser based on a Ho-doped crystal, which is realized relying on the multi-wavelength solid laser based on a Ho-doped crystal described above, includes the following steps:

[0016] A pump source of 1940 nm outputs pump light. The pump light is transmitted through an optical fiber and then coupled by an optical fiber coupling lens group to output parallel light. The parallel light is split and focused by a microlens array and then passes through an input plane mirror, and the light in the 1940 nm band is converged on the front end face of the Ho-doped mixed crystal;

[0017] After different doped crystals in the Ho-doped mixed crystal absorb the input light in the 1940 nm band, light of different bands is output;

[0018] The light of different bands passes through an output plane mirror and then is filtered by a 1900 nm narrowband filter to obtain 2 μm band lasers with different frequency ranges.

[0019] Further, based on the crystal rotation angle of 0-90° in different doped crystals, the polarization direction of each input laser and the axis of the crystal with different rotation angles focused on are different. When the angle change amount α occurs between the polarization direction of the input laser and the crystal main axis, it causes the wavelength change of the σ polarization state and the π polarization state output by the doped crystal, and the obtained expression is:

[0020] λ σ (θ1) = λ σ (θ0) + Δλ σ (α) (1)

[0021] λ π (θ1) = λ π (θ0) + Δλ π (α) (2)

[0022] Among them, θ0 is defined as the initial included angle between the polarization direction of the input light and the crystal main axis. After rotating α, the included angle becomes θ1. λ σ (θ0) and λ σ (θ1) are respectively defined as the central wavelengths output by the σ polarization state at the included angles of θ0 and θ1. λ π (θ0) and λ π (θ1) are respectively defined as the central wavelengths output by the π polarization state at the included angles of θ0 and θ1. Δλ σ (α) and Δλ π (α) represent the central wavelength change amount of the σ polarization state and the central wavelength change amount of the π polarization state after rotating α;

[0023] The expression for the refractive index relationship between the a-axis and c-axis planes of the doped crystal is:

[0024]

[0025] Where, n a and n c are the refractive indices of the a-axis and c-axis respectively, and n c (θ) is the refractive index when the polarization direction of the input light makes an angle θ with the crystal principal axis;

[0026] Based on the fact that the output light is restricted by the standing wave condition of the resonator between the input mirror and the output mirror, the expression is obtained as:

[0027] 2kL' = 2mπ (4)

[0028] L' = n0L1 + n c (θ)L2 (5)

[0029] Where, k is the modulus of the wave vector, L’ is the total optical path, n0L1 and n c (θ)L2 represent the optical paths outside and inside the crystal in the resonator respectively, and m is the first positive integer; L1 and L2 represent the propagation distances of light outside and inside the crystal during oscillation in the resonator respectively;

[0030] Combining Equation (3), Equation (4) and Equation (5), we get:

[0031]

[0032] When the angle θ changes by α, Equation (6) changes to:

[0033]

[0034] Where, k' is the modulus of the changed wave vector, and m' is the second positive integer;

[0035] Introducing the wavelength λ into Equation (7), the expression is obtained as:

[0036]

[0037] Where, m1' and m2' are the third positive integer and the fourth positive integer respectively, and θ π0 and θ σ0 represent the angles between the output σ polarization and π polarization and the crystal principal axis respectively;

[0038] Based on Equation (8) and Equation (9), it is obtained that after introducing α, the variable Δλ π (α) / Δλ σ (α) and m1' / m2' will also change synergistically. When rotating the polarizer, with the change of θ, the refractive index n c(θ) changes, resulting in the change of the optical path L'. To satisfy the standing wave condition, the modulus k of the wave vector will change accordingly, that is, the wavelength λ changes; under the conditions satisfying equations (8) and (9), the multi-wavelength solid-state laser based on the Ho-doped crystal outputs lasers in the 2-μm band with different frequency ranges.

[0039] The above derivation is based on the c-axis cut Ho:LLF crystal, and this theoretical model is also applicable to Ho:YLF and Ho:YAP, with only the difference in outputting single-wavelength lasers and double-wavelength lasers.

[0040] A multi-wavelength solid-state laser based on Ho-doped crystal, comprising a 795-nm LD pump source, an optical fiber, an optical fiber coupling lens group, a microlens array, an input plane mirror, a Tm:YAP crystal, a Ho-doped mixed crystal, an output plane mirror, a 1000-nm narrowband filter, and a 2000-nm narrowband filter;

[0041] The 795-nm LD pump source is connected to the optical fiber coupling lens group through an optical fiber. On the right side of the optical fiber coupling lens group along the optical path, there are arranged in sequence a microlens array, an input plane mirror, a Tm:YAP crystal, a Ho-doped mixed crystal, an output plane mirror, a 1000-nm narrowband filter, and a 2000-nm narrowband filter;

[0042] The Ho-doped mixed crystal is composed of a cylindrical doped crystal at the central position and a first-sector annular doped crystal, a second-sector annular doped crystal, a third-sector annular doped crystal, and a fourth-sector annular doped crystal surrounding the cylindrical doped crystal. The cylindrical doped crystal is one of the Ho:YAP crystals cut in different axial directions, and the first-sector annular doped crystal, the second-sector annular doped crystal, the third-sector annular doped crystal, and the fourth-sector annular doped crystal are several combinations of Ho:LLF crystals, Ho:YAP crystals, and Ho:YLF crystals cut in different axial directions;

[0043] Or the Ho-doped mixed crystal is composed of a first-sector doped crystal, a second-sector doped crystal, a third-sector doped crystal, and a fourth-sector doped crystal. The first-sector doped crystal, the second-sector doped crystal, the third-sector doped crystal, and the fourth-sector doped crystal are several combinations of Ho:LLF crystals, Ho:YAP crystals, and Ho:YLF crystals cut in different axial directions.

[0044] Furthermore, the surface of the input plane mirror is coated with a 2050-nm narrowband reflection film, and the surface of the output plane mirror is coated with a 5% transmission film of 2050 nm.

[0045] Further, in the Ho-doped mixed crystal, the cylindrical doped crystal is a Ho:YAP crystal cut along the a-axis, the first sector-shaped annular doped crystal is a Ho:LLF crystal cut along the c-axis, the second sector-shaped annular doped crystal is a Ho:YAP crystal cut along the c-axis, the third sector-shaped annular doped crystal is a Ho:YLF crystal cut along the c-axis, and the fourth sector-shaped annular doped crystal is a Ho:YAP crystal cut along the b-axis; the angular range of each doped crystal in the Ho-doped mixed crystal is 0-90°.

[0046] Advantages of the present invention:

[0047] A multi-wavelength solid laser based on a Ho-doped crystal according to the present invention innovatively designs a special hybrid laser crystal, and uses one pump and one optical cavity to output lasers with extremely many different wavelengths, efficiently realizing the output of multiple wavelengths.

[0048] A multi-wavelength solid laser based on a Ho-doped crystal according to the present invention can realize the switching of wavelength output through derivation and analysis of angle tuning. An arc structure is innovatively designed, and by using different crystal compositions and different angular arrangements, multi-wavelength output is achieved within a wide wavelength band. By different tangential output wavelengths, multi-wavelength output can be achieved by combining different tangentials and different angle combinations.

[0049] A multi-wavelength solid laser based on a Ho-doped crystal according to the present invention utilizes the efficient absorption of all components of the Ho-doped mixed crystal for light in the 1940 nm band, and through the combination of Ho-doped crystals with different substrates, multi-wavelength output is achieved with one laser in a wide wavelength band.

[0050] A multi-wavelength solid laser based on a Ho-doped crystal according to the present invention. Since an orthogonally polarized dual-wavelength solid laser can emit two lasers with a fixed wavelength difference, it is very suitable as a basic unit of a wavelength division multiplexing light source. Moreover, the dual-wavelength laser has non-coherent characteristics, and each wavelength can efficiently carry different information, thus significantly improving the efficiency of complex information transmission and processing. Therefore, when integrating multiple orthogonally polarized dual-wavelength lasers with a strong absorption effect on the same pump, the light source of the system will simultaneously have extremely high efficiency and a highly integrated multi-wavelength output ability. By utilizing the strong absorption characteristics of different Ho-doped substrate materials for the same pump source (1940 nm) and frequency modulation methods such as angle tuning, a laser with the ability to output an extremely large number of wavelengths of laser is designed, solving the contradiction between multi-wavelength output and high integration of the laser. The characteristics of the present invention are that only one pump source and one laser are required, and lasers with multiple wavelengths can be excited, which is of great significance for wavelength division multiplexing scenarios such as optical fiber communication and optical computing, and greatly compresses the volume of the light source part.

[0051] A multi-wavelength solid laser based on Ho-doped crystal according to the present invention has verified its multi-wavelength output performance through theoretical analysis and experimental verification. The present invention not only provides a new idea to cope with the challenges of current multi-wavelength laser sources, but also lays a foundation for future innovations in related fields such as optical communication and optical computing. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 FIG. 6 is a schematic diagram of the first structure of a multi-wavelength solid laser based on Ho-doped crystal constructed according to the 1940 nm pump source of the present invention;

[0053] Figure 2 FIG. 10 is a schematic structure of the Ho-doped mixed crystal of the present invention Figure 1 , and an axial schematic diagram of small crystals at different rotation angles, where a is a schematic structure of the Ho-doped mixed crystal, and b is an axial schematic diagram of small crystals at different rotation angles;

[0054] Figure 3 FIG. 16 is a schematic diagram of a c-axis cut portion of the Ho-doped mixed crystal of the present invention;

[0055] Figure 4 FIG. 20 is a schematic diagram of an a-axis cut portion of the Ho-doped mixed crystal of the present invention;

[0056] Figure 5 FIG. 24 is a refractive index ellipse diagram of the c-axis cut Ho:LLF crystal of the present invention;

[0057] Figure 6 FIG. 28 is a schematic structure of the Ho-doped mixed crystal of the present invention Figure 2 ;

[0058] Figure 7 FIG. 34 is a schematic diagram of the structure of a multi-wavelength solid laser based on Ho-doped crystal constructed according to the 795 nm pump source of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0059] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the specific embodiments described are only a part of the embodiments of the present invention, rather than all of the specific embodiments. The components of the specific embodiments of the present invention usually described and shown in the drawings here can be arranged and designed in various different configurations, and the present invention can also have other embodiments.

[0060] Accordingly, the following detailed description of the specific embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected specific embodiments of the present invention. All other specific embodiments obtained by those skilled in the art based on the specific embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0061] To further understand the content, features and effects of the present invention, the following specific embodiments are exemplified and are accompanied by the attached Figure 1 - Attached Figure 7 The detailed description is as follows:

[0062] Example 1:

[0063] A multi-wavelength solid-state laser based on a Ho-doped crystal, comprising a 1940 nm pump source 1, an optical fiber 2, an optical fiber coupling lens group 3, a microlens array 4, an input plane mirror 5, a Ho-doped hybrid crystal 6, an output plane mirror 7, and a 1900 nm narrow-band filter 8;

[0064] The 1940 nm pump source 1 is connected to the optical fiber coupling lens group 3 through the optical fiber 2. On the right side of the optical fiber coupling lens group 3 along the optical path, there are arranged in sequence a microlens array 4, an input plane mirror 5, a Ho-doped hybrid crystal 6, an output plane mirror 7, and a 1900 nm narrow-band filter 8;

[0065] The Ho-doped hybrid crystal 6 is composed of a cylindrical doped crystal 16 at the central position and a first sector-shaped ring doped crystal 12, a second sector-shaped ring doped crystal 13, a third sector-shaped ring doped crystal 14, and a fourth sector-shaped ring doped crystal 15 surrounding the cylindrical doped crystal 16. The cylindrical doped crystal 16 is one of Ho:YAP crystals cut along different axes, and the first sector-shaped ring doped crystal 12, the second sector-shaped ring doped crystal 13, the third sector-shaped ring doped crystal 14, and the fourth sector-shaped ring doped crystal 15 are several combinations of Ho:LLF crystals, Ho:YAP crystals, and Ho:YLF crystals cut along different axes.

[0066] Furthermore, the surface of the input plane mirror 5 is coated with a 2050 nm narrow-band reflection film, and the surface of the output plane mirror 7 is coated with a 5% transmission film of 2050 nm.

[0067] Furthermore, in the Ho-doped hybrid crystal 6, the cylindrical doped crystal 16 is a Ho:YAP crystal cut along the a-axis, the first sector-shaped ring doped crystal 12 is a Ho:LLF crystal cut along the c-axis, the second sector-shaped ring doped crystal 13 is a Ho:YAP crystal cut along the c-axis, the third sector-shaped ring doped crystal 14 is a Ho:YLF crystal cut along the c-axis, and the fourth sector-shaped ring doped crystal 15 is a Ho:YAP crystal cut along the b-axis.

[0068] Furthermore, the angular range of each doped crystal in the Ho-doped mixed crystal 6 is 0 - 90°. Further, the Ho:LLF crystal, Ho:YLF crystal, and Ho:YAP crystal in the Ho-doped mixed crystal have high hardness, and conventional mechanical cutting or laser cutting can be used. When combining the Ho-doped mixed crystal, a heat sink with a customized required shape can be made, and the crystal is placed in the heat sink to complete the crystal production; one method of crystal cutting is to cut all along the c-axis and then splice and place them in the heat sink in the form of the left figure in Figure 2 the heat sink, and another method is not to cut along the c-axis, but directly cut small crystals on the large crystal cut along the c-axis at different angles with the c-axis. This cutting direction is defined as "c - 5° cutting", "c - 10° cutting"... "c - θ cutting", etc. After cutting, they can be directly spliced and placed in the heat sink.

[0069] Furthermore, the microlens array is composed of microlenses, and the positions of the convex lenses correspond to each small crystal in the Ho-doped mixed crystal, ensuring that each beam of split laser is focused on the end face of the small crystal. During operation, the placement position of the Ho-doped crystal should be adjusted according to the focal length of the microlens array.

[0070] Furthermore, the function of the fiber coupling lens group 3 is to couple the pump light in the fiber and output parallel light;

[0071] Furthermore, the reasons for the Ho-doped mixed crystal 6 to output multi-wavelength laser are as follows: First, all three Ho-doped crystals strongly absorb light in the 1940 nm band and output lasers in different bands. The Ho:LLF double-wavelength output band is near 2060 nm, the Ho:YAP output band is near 2130 nm, and the Ho:YLF output band is near 2050 nm. Therefore, due to different substrate materials, the four crystals output four bands of lasers. Second, for any one of the four crystals cut along the c-axis, taking the Ho:LLF crystal cut along the c-axis as an example, the polarization directions of each beam of pump light output by the microlens array are the same. According to the different rotation angles (0 - 90°) of each small crystal that makes up the Ho:LLF part, the polarization state of each beam of laser and the axial direction of the small crystal it is focused on are different.

[0072] To verify the influence of crystal rotation on wavelength change in the theory, taking the Ho:LLF crystal cut along the c-axis as an example, Table 1 shows the wavelength change of the output laser at an angular tuning of 13° - 80°, which is the same as the result of theoretical derivation. Among them, the wavelength change range of the π polarization output in the horizontal direction is 2053 - 2056.3 nm, and the wavelength change range of the σ polarization output in the vertical direction is 2063.1 - 2065.7 nm. The test results verify the feasibility of a multi-wavelength solid-state laser based on Ho-doped crystals.

[0073] Table 1:

[0074] Angle / Polarization π - polarized wavelength (nm) σ - polarized wavelength (nm) 13° 2052 2063.9 27° 2052.6 2064.2 45° 2055.3 2065 55° 2056.3 2065.7 69° 2053.4 2064.7 80° 2052.1 2063

[0075] A multi-wavelength solid laser based on Ho-doped crystal described in this embodiment innovatively makes a special design for the laser crystal. By using the high absorption of each part of the mixed crystal for the output beam of Tm:YAP, a series of 2-μm band lasers with different wavelengths are output according to different crystal substrates, different rotation angles, and different cutting directions.

[0076] Example 2:

[0077] An operating method of a multi-wavelength solid laser based on Ho-doped crystal is realized relying on the multi-wavelength solid laser based on Ho-doped crystal described in Example 1, and includes the following steps:

[0078] The pump source of 1940 nm outputs pump light. The pump light is transmitted through the optical fiber and coupled by the fiber coupling lens group to output parallel light. The parallel light is split and focused by the microlens array and then passes through the input flat mirror, and the light in the 1940-nm band is converged on the front end face of the Ho-doped mixed crystal.

[0079] After different doped crystals in the Ho-doped mixed crystal absorb the input light in the 1940-nm band, light in different bands is output.

[0080] The light in different bands passes through the output flat mirror and then is filtered by a 1900-nm narrowband filter to obtain 2-μm band lasers in different frequency ranges.

[0081] Furthermore, based on the crystal rotation angle of 0-90° in different doped crystals, the polarization direction of each input laser and the axis of the crystal with different rotation angles focused are different. When the angle change amount α occurs between the polarization direction of the input laser and the crystal main axis, the wavelength change of the σ polarization state and π polarization state output by the doped crystal is caused, and the expression is:

[0082] λ σ (θ1) = λ σ (θ0) + Δλ σ (α) (1)

[0083] λ π (θ1) = λ π (θ0) + Δλ π (α) (2)

[0084] Among them, θ0 is defined as the initial included angle between the polarization direction of the input light and the crystal main axis. After rotating α, the included angle becomes θ1, λ σ (θ0) and λ σλ(θ1) is defined as the central wavelength of the output of the σ polarization state at the angles θ0 and θ1 respectively, λ π λ(θ0) and λ π λ(θ1) are defined as the central wavelengths of the output of the π polarization state at the angles θ0 and θ1 respectively, Δλ σ Δλ(α) and Δλ π Δλ(α) represents the change in the central wavelength of the σ polarization state and the change in the central wavelength of the π polarization state after rotating by α;

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

[0086]

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

[0088] Based on the fact that the output light is restricted by the standing wave condition of the resonator between the input mirror and the output mirror, the expression is obtained as:

[0089] 2kL' = 2mπ (4)

[0090] L' = n0L1 + n c (θ)L2 (5)

[0091] Among them, k is the modulus of the wave vector, L’ is the total optical path, n0L1 and n c (θ)L2 represent the optical paths outside and inside the crystal in the resonator respectively, and m is the first positive integer; L1 and L2 represent the propagation distances of the light outside and inside the crystal during oscillation in the resonator respectively;

[0092] Combining Equation (3), Equation (4) and Equation (5), we get:

[0093]

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

[0095]

[0096] Among them, k' is the modulus of the changed wave vector, and m' is the second positive integer;

[0097] Introducing the wavelength λ into Equation (7), the expression is obtained as:

[0098]

[0099] Among them, m1' and m2' are the third positive integer and the fourth positive integer respectively, θπ0 and θ σ0 respectively represent the angles between the output σ polarization and π polarization and the crystal principal axis;

[0100] Based on Equations (8) and (9), after introducing α, the variable Δλ π (α) / Δλ σ (α) and m1' / m2' will also change synergistically. When rotating the polarizer, as θ changes, the refractive index n c (θ) changes, thus changing the optical path L'. In order to satisfy the standing wave condition, the modulus k of the wave vector will change accordingly, that is, the wavelength λ changes; The above derivation is based on the c-axis cut Ho:LLF crystal. This theoretical model is also applicable to Ho:YLF and Ho:YAP. There is only a difference in outputting single-wavelength laser and double-wavelength laser. Under the conditions of satisfying Equations (8) and (9), the multi-wavelength solid-state laser based on Ho-doped crystals outputs 2μm band lasers with different frequency ranges.

[0101] According to the above derivation, due to the special design of the Ho-doped mixed crystal, as θ changes, the refractive index n c (θ) changes, thus changing the optical path L'. In order to satisfy the standing wave condition, the modulus k of the wave vector will change accordingly, that is, the wavelength λ changes. This theoretical model is also applicable to doped crystals including Ho:YLF and Ho:YAP. There is only a difference in outputting single-wavelength laser and double-wavelength laser. That is to say, each part of the Ho-doped mixed crystal outputs lasers with different wavelengths due to the change of the polarization direction. Even for the same crystal, each part of the fan-shaped structure outputs lasers with different wavelengths due to different rotation angles.

[0102] Example 3:

[0103] The difference between this example and Example 1 is that in this example, the Ho-doped mixed crystal 6 is replaced by a combination of the first sector-doped crystal 18, the second sector-doped crystal 19, the third sector-doped crystal 20, and the fourth sector-doped crystal 21. The first sector-doped crystal 18, the second sector-doped crystal 19, the third sector-doped crystal 20, and the fourth sector-doped crystal 21 are several combinations of Ho:LLF crystals, Ho:YAP crystals, and Ho:YLF crystals cut along different axes.

[0104] Furthermore, in the Ho-doped mixed crystal 6, the first sector-doped crystal 18 is a c-axis cut Ho:LLF crystal, the second sector-doped crystal 19 is a c-axis cut Ho:YAP crystal, the third sector-doped crystal 20 is a c-axis cut Ho:YLF crystal, and the fourth sector-doped crystal 21 is an a-axis cut Ho:YLF crystal.

[0105] Example 4:

[0106] The difference between this embodiment and Embodiment 1 is that the 1940 nm pump source 1 in this embodiment is replaced by a 795 nm LD pump source 9. The 795 nm LD pump source 9 is connected to a fiber coupling lens group 3 through an optical fiber 2. On the right side of the fiber coupling lens group 3, a microlens array 4, an input plane mirror 5, a Tm:YAP crystal 17, a Ho-doped hybrid crystal 6, an output plane mirror 7, a 1000 nm narrowband filter 10, and a 2000 nm narrowband filter 11 are arranged in sequence along the optical path.

[0107] It should be noted that relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising one..." does not exclude the existence of additional identical elements in the process, method, article or device comprising the element.

[0108] Although the present application has been described above with reference to specific embodiments, various improvements can be made to it and components therein can be replaced with equivalents without departing from the scope of the present application. In particular, as long as there is no structural conflict, the various features in the specific embodiments disclosed in the present application can be combined with each other in any way. The fact that the combinations of these situations are not exhaustively described in this specification is only for the sake of saving space and resources. Therefore, the present 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 multi-wavelength solid-state laser based on Ho-doped crystal, characterized in that: It comprises a 1940 nm pump source (1), an optical fiber (2), an optical fiber coupling lens group (3), a microlens array (4), an input plane mirror (5), a Ho-doped mixed crystal (6), an output plane mirror (7), and a 1900 nm narrow-band filter (8); The 1940 nm pump source (1) is connected to a fiber coupling lens group (3) via an optical fiber (2); a micro lens array (4), an input plane mirror (5), a Ho-doped mixed crystal (6), an output plane mirror (7), and a 1900 nm narrowband filter (8) are sequentially arranged on the right side of the fiber coupling lens group (3) along the optical path; The Ho-doped mixed crystal (6) is composed of a cylindrical doped crystal (16) at a central position and a first fan-shaped doped crystal (12), a second fan-shaped doped crystal (13), a third fan-shaped doped crystal (14), and a fourth fan-shaped doped crystal (15) surrounding the cylindrical doped crystal (16); the cylindrical doped crystal (16) is one of Ho:YAP crystals cut in different axial directions; the first fan-shaped doped crystal (12), the second fan-shaped doped crystal (13), the third fan-shaped doped crystal (14), and the fourth fan-shaped doped crystal (15) are a combination of Ho:LLF crystals, Ho:YAP crystals, and Ho:YLF crystals cut in different axial directions; Alternatively, the Ho-doped mixed crystal (6) is composed of a first fan-shaped doped crystal (18), a second fan-shaped doped crystal (19), a third fan-shaped doped crystal (20), and a fourth fan-shaped doped crystal (21), wherein the first fan-shaped doped crystal (18), the second fan-shaped doped crystal (19), the third fan-shaped doped crystal (20), and the fourth fan-shaped doped crystal (21) are a combination of several of Ho:LLF crystals, Ho:YAP crystals, and Ho:YLF crystals cut in different axes.

2. A multi-wavelength solid-state laser based on Ho-doped crystal according to claim 1, characterized in that: The surface of the input plane mirror (5) is coated with a 2050nm narrow-band reflection film, and the surface of the output plane mirror (7) is coated with a 2050nm 5% transmission film.

3. A multi-wavelength solid-state laser based on Ho-doped crystal according to claim 2, characterized in that: The cylindrical doped crystal (16) in the Ho-doped mixed crystal (6) is an a-axis cut Ho:YAP crystal, the first sector ring-shaped doped crystal (12) is a c-axis cut Ho:LLF crystal, the second sector ring-shaped doped crystal (13) is a c-axis cut Ho:YAP crystal, the third sector ring-shaped doped crystal (14) is a c-axis cut Ho:YLF crystal, and the fourth sector ring-shaped doped crystal (15) is a b-axis cut Ho:YAP crystal.

4. The multi-wavelength solid-state laser based on Ho-doped crystal according to claim 3, characterized in that: In the Ho-doped mixed crystal (6), the first sector-shaped doped crystal (18) is a c-axis cut Ho:LLF crystal, the second sector-shaped doped crystal (19) is a c-axis cut Ho:YAP crystal, the third sector-shaped doped crystal (20) is a c-axis cut Ho:YLF crystal, and the fourth sector-shaped doped crystal (21) is a b-axis cut Ho:YLF crystal.

5. The multi-wavelength solid-state laser based on Ho-doped crystal according to claim 4, characterized in that: The angle range of each doped crystal in the Ho-doped mixed crystal (6) is 0-90°.

6. An operating method of a multi-wavelength solid-state laser based on a Ho-doped crystal, implemented by a multi-wavelength solid-state laser based on a Ho-doped crystal according to any one of claims 1 to 5, characterized in that: The steps include: The 1940nm pump source outputs pump light, which is transmitted through the optical fiber and then coupled into the optical fiber coupling lens group to output parallel light. The parallel light is split and focused by the microlens array and then passes through the input plane mirror to obtain the light in the 1940nm band, which is focused on the front end of the Ho-doped mixed crystal. Different doped crystals in the Ho-doped mixed crystal absorb the input light of 1940nm band and output light of different bands; Light of different wavelength bands passes through the output plane mirror and then is filtered by a 1900nm narrow-band filter to obtain 2μm-band lasers of different frequency ranges.

7. The method for operating a multi-wavelength solid-state laser based on a Ho-doped crystal according to claim 6, characterized in that: In different doped crystals, based on the crystal rotation angle of 0-90°, the polarization direction of each input laser beam and the axial direction of the crystal with different rotation angles are different. When the angle change α between the polarization direction of the input laser and the main axis of the crystal occurs, the wavelength of the σ polarization state and π polarization state output by the doped crystal changes, and the expression is: l σ (θ1)=λ σ (θ0)+Δλ σ (a)(1) l π (θ1)=λ π (θ0)+Δλ π (a)(2) Among them, θ0 is defined as the initial angle between the polarization direction of the input light and the main axis of the crystal. After rotating α, the angle becomes θ1, λ σ (θ0) and λ σ (θ1) are defined as the central wavelength of the σ polarization state when the angle is θ0 and θ1, λ π (θ0) and λ π (θ1) are defined as the central wavelength of the π polarization state when the angle is θ0 and θ1, Δλ σ (α) and Δλ π (α) represents the change in the central wavelength of the σ polarization state and the central wavelength of the π polarization state after a rotation of α; The expression for the refractive index relationship between the a-axis and c-axis planes of the doped crystal is: Among them, n a and n c are the refractive indices of the a-axis and c-axis, n c (θ) is the refractive index when the input light polarization direction and the crystal principal axis include an angle θ; Based on the fact that the output light is subject to the resonant cavity standing wave condition between the input mirror and the output mirror, the expression is obtained: 2kL'=2mπ(4) <h2 style=";text-align:left;direction:ltr">L'=n0L1+n<h2 style=";text-align:left;direction:ltr"> c <h2 style=";text-align:left;direction:ltr"> (θ)L2(5) Where k is the modulus of the wave vector, L' is the total optical path, n0L1 and n c (θ)L2 represent the optical path outside and inside the crystal in the resonant cavity, respectively, and m is a first positive integer; L1 and L2 represent the propagation path of light outside and inside the crystal when oscillating in the resonant cavity, respectively; Combining equation (3), equation (4) and equation (5), we get: When the angle θ changes by α, equation (6) changes to: Among them, k' is the modulus of the wave vector after the change, and m' is the second positive integer; Introducing wavelength λ into equation (7), we get the following expression: Where m1' and m2' are the third positive integer and the fourth positive integer respectively, θ π0 and θ σ0 Respectively represent the angles between the output σ polarization and π polarization and the principal axis of the crystal; Based on equations (8) and (9), we can get the variable Δλ after introducing α π (α) / Δλ σ (α) and m1' / m2' will also change in tandem. When the polarizer is rotated, the refractive index n c (θ) changes, thereby changing the optical path L', and the mode k of the wave vector will change accordingly, that is, the wavelength λ changes; under the conditions of satisfying equations (8) and (9), the multi-wavelength solid-state laser based on Ho-doped crystal outputs 2μm band lasers in different frequency ranges.

8. A multi-wavelength solid-state laser based on Ho-doped crystal, characterized in that: It includes a 795nm LD pump source (9), an optical fiber (2), an optical fiber coupling lens group (3), a microlens array (4), an input plane mirror (5), a Tm:YAP crystal (17), a Ho-doped mixed crystal (6), an output plane mirror (7), a 1000nm narrowband filter (10), and a 2000nm narrowband filter (11); The 795 nm LD pump source (9) is connected to a fiber coupling lens group (3) via an optical fiber (2); a micro lens array (4), an input plane mirror (5), a Tm:YAP crystal (17), a Ho-doped mixed crystal (6), an output plane mirror (7), a 1000 nm narrow-band filter (10), and a 2000 nm narrow-band filter (11) are sequentially arranged on the right side of the fiber coupling lens group (3) along the optical path; The Ho-doped mixed crystal (6) is composed of a cylindrical doped crystal (16) at a central position and a first fan-shaped doped crystal (12), a second fan-shaped doped crystal (13), a third fan-shaped doped crystal (14), and a fourth fan-shaped doped crystal (15) surrounding the cylindrical doped crystal (16); the cylindrical doped crystal (16) is one of Ho:YAP crystals cut in different axial directions; the first fan-shaped doped crystal (12), the second fan-shaped doped crystal (13), the third fan-shaped doped crystal (14), and the fourth fan-shaped doped crystal (15) are a combination of several of Ho:LLF crystals, Ho:YAP crystals, and Ho:YLF crystals cut in different axial directions; Alternatively, the Ho-doped mixed crystal (6) is composed of a first fan-shaped doped crystal (18), a second fan-shaped doped crystal (19), a third fan-shaped doped crystal (20), and a fourth fan-shaped doped crystal (21), wherein the first fan-shaped doped crystal (18), the second fan-shaped doped crystal (19), the third fan-shaped doped crystal (20), and the fourth fan-shaped doped crystal (21) are a combination of several of Ho:LLF crystals, Ho:YAP crystals, and Ho:YLF crystals cut in different axes.

9. The multi-wavelength solid-state laser based on Ho-doped crystal according to claim 8, characterized in that: The surface of the input plane mirror (5) is coated with a 2050nm narrow-band reflection film, and the surface of the output plane mirror (7) is coated with a 2050nm 5% transmission film.

10. The multi-wavelength solid-state laser based on Ho-doped crystal according to claim 9, characterized in that: The cylindrical doped crystal (16) in the Ho-doped mixed crystal (6) is an a-axis cut Ho:YAP crystal, the first sector ring-shaped doped crystal (12) is a c-axis cut Ho:LLF crystal, the second sector ring-shaped doped crystal (13) is a c-axis cut Ho:YAP crystal, the third sector ring-shaped doped crystal (14) is an a-axis cut Ho:YLF crystal, and the fourth sector ring-shaped doped crystal (15) is a b-axis cut Ho:YLF crystal; the angle range of each doped crystal in the Ho-doped mixed crystal (6) is 0-90°.

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