CN114994934A - Spectrum beam combining device and method - Google Patents
Spectrum beam combining device and method Download PDFInfo
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- CN114994934A CN114994934A CN202210844972.3A CN202210844972A CN114994934A CN 114994934 A CN114994934 A CN 114994934A CN 202210844972 A CN202210844972 A CN 202210844972A CN 114994934 A CN114994934 A CN 114994934A
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- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/10—Beam splitting or combining systems
- G02B27/1006—Beam splitting or combining systems for splitting or combining different wavelengths
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- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
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- G02B27/1086—Beam splitting or combining systems operating by diffraction only
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- G02B27/4272—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having plural diffractive elements positioned sequentially along the optical path
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- H—ELECTRICITY
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Abstract
The invention relates to the technical field of laser, and particularly provides a spectrum beam combining device and a method, wherein the spectrum beam combining device comprises a laser unit, a transform lens, a reflection grating and an external cavity mirror; the front cavity surface and the external cavity mirror of the laser unit are both positioned on the front focal plane of the conversion lens, and the reflection grating is positioned on the rear focal plane of the conversion lens; the spectrum beam combining device takes the littrow angle of the normal line of the transmission grating as an optical axis, and the external cavity mirror is perpendicular to the optical axis. The spectrum beam combining device enables the laser unit to be directly imaged on the external cavity mirror through the cooperation of the spectrum beam combining direction and the non-spectrum beam combining direction, and high-stability external cavity feedback can be realized through light path compensation even if pointing deviation caused by smile packaging or adjustment occurs; and the beam combining light path and the laser unit emergent light path are overlapped in the spectrum beam combining direction, and the whole spectrum beam combining device can be used in occasions with high requirements on stability and reliability.
Description
Technical Field
The invention relates to the technical field of laser, in particular to a spectrum beam combining device and method.
Background
The spectral beam combining technology is one of the most feasible technologies for realizing high-power and high-beam-quality combined laser at present. From the 1999 report, the technology has been successfully applied to all-solid-state lasers, fiber lasers and semiconductor lasers, and the performance of the lasers is greatly improved.
The spectrum that uses at present in the semiconductor laser field closes and restraints the structure mainly for closed-loop type spectrum closes and restraints the structure, and its realization structure is: the rear cavity surface of the laser unit and the external cavity mirror form a resonant cavity, the front cavity surface of the laser unit is plated with an antireflection film, the laser units are arranged in the spectrum beam combining direction and are emitted along the same direction, the light is jointly incident on the grating under the action of the conversion lens and is output to the external cavity mirror through the diffraction of the grating, and only the light which is vertically incident on the external cavity mirror and can be reflected back to the original laser unit can resonate. Due to the effects of the grating, the external cavity feedback and the like, the laser unit resonates to different laser wavelengths, the laser power after the spectrum combination is multiplied, the beam quality is consistent with that of the laser unit, and the whole spectrum is widened.
In order to realize a good spectrum beam combination effect, the light-emitting end face of the laser chip and the grating are respectively positioned on the front focal plane and the rear focal plane of the conversion lens, namely the distance from the laser chip to the grating is at least twice the focal length of the conversion lens. In addition, no matter the spectrum beam combining structure based on the reflection grating or the spectrum beam combining structure based on the transmission grating, the output light path is not overlapped with the incident light path after the diffraction of the grating, so that the output laser needs to occupy extra space, and the size of the spectrum beam combining structure is further enlarged. And the external cavity mirror is typically located at the periphery or edge of the spectrally combined light source.
In order to realize effective spectrum beam combination in a proper spectrum range, the grating dispersion capacity is limited, the focal length of a conversion lens adopted by a spectrum beam combination light source of a near infrared waveband generally reported in the current literature is as long as hundreds of millimeters, and the focal length of the conversion lens is even up to a meter level in order to compress the bandwidth in some cases, so that the resonant cavity of an external cavity spectrum light source generally reaches hundreds of millimeters or even meters, and the volume size of the whole spectrum beam combination light source is larger.
In addition, the rear cavity mirror serving as the resonant cavity mirror is always positioned at the periphery or edge of the light source, so that the structural stability of the rear cavity mirror is difficult to guarantee, great hidden dangers are brought to the structural stability and long-term reliability of the whole spectrum beam combining light source, and the rear cavity mirror is particularly applied to occasions with high requirements on environmental adaptability, such as national defense and the like.
Disclosure of Invention
The invention provides a spectrum beam combining device and method folded at a small angle to solve the problems.
The invention provides a spectrum beam combining device, which comprises a laser unit, a transformation lens, a reflection grating and an external cavity mirror, wherein the laser unit is used for emitting laser beams; the front cavity surface of the laser unit and the external cavity mirror are both positioned on the front focal plane of the conversion lens, and the reflection grating is positioned on the back focal plane of the conversion lens; the spectrum beam combining device takes a littrow angle of a normal line of the reflection grating as an optical axis, and the external cavity mirror is vertical to the optical axis;
the light path of the spectrum beam combining device comprises a spectrum beam combining direction and a non-spectrum beam combining direction;
in the spectrum beam combination direction, the laser unit outputs laser beams, and the laser beams are incident to the reflection grating at different angles under the action of the transformation lens; the laser beams output by the laser unit are superposed on the reflection grating, and are incident to the external cavity mirror after being incident to the conversion lens again;
in the non-spectral beam combining direction, the laser beam output by the laser unit is acted by the transformation lens and then forms an angle theta y Incident on the reflection grating and passing through the reflection grating at the same included angle theta y After reflection, the light returns to the transformation lens and is collimated by the transformation lens and then enters the external cavity mirror.
Preferably, the conversion lens is a rotationally symmetric lens.
Preferably, the spectrum beam combining device further comprises a compensation mirror, the compensation mirror and the conversion lens are combined to form an imaging mirror, and the front cavity surface of the laser unit is imaged to the external cavity mirror.
Preferably, the compensation mirror is a rotationally symmetric lens.
Preferably, the laser units include a central laser unit and an edge laser unit, and each of the laser units respectively outputs laser beams with different wavelengths.
Preferably, the incident angle and the diffraction angle of the laser beam output by the central laser unit and the reflection grating are both littrow angles in the spectrum beam combining direction.
Preferably, an angle between the incident angle of the laser beam output by the central laser unit and the incident angle of the reflection grating in the non-spectral beam combining direction is smaller than 10 °.
Preferably, the laser unit includes a laser device and an optical element, the optical element performs at least one of collimation, shaping and polarization direction adjustment on a laser beam output by the laser device, and an antireflection film is plated on an end face of the laser device, where the laser beam is output by the laser device.
Preferably, the laser device is a semiconductor laser, a fiber laser or an all-solid-state laser.
Preferably, the reflection grating is a first-order diffraction grating, the first-order diffraction efficiency of the reflection grating is greater than 90%, and the diffraction polarization direction of the reflection grating is matched with the polarization direction of the laser beam.
The invention also provides a spectrum beam combining method, which is realized by the spectrum beam combining device and comprises the following steps:
s1, in the spectrum beam combination direction, the laser unit outputs laser beams, and the laser beams are acted by the conversion lens and enter the reflection grating at different angles; the laser beams output by the laser unit are superposed on the reflection grating, and are incident to the external cavity mirror after being incident to the conversion lens again;
s2, in the non-spectrum beam combination direction,the laser beam output by the laser unit is acted by the conversion lens and then forms an angle theta y Incident on the reflection grating and passing through the reflection grating at the same included angle theta y After reflection, the light returns to the transformation lens and is collimated by the transformation lens and then enters the external cavity mirror.
The small-angle folding spectrum beam combining device and the method provided by the invention have the advantages that through the cooperation of the spectrum beam combining direction and the non-spectrum beam combining direction, the spectrum beam combining direction is diffracted through the littrow structure, and the diffraction efficiency is high; folding the light path in the non-spectral beam combination direction, and enabling the laser unit to be directly imaged on the external cavity mirror through an imaging relation, even if pointing deviation caused by packaging smile or adjustment occurs, high-stability external cavity feedback can be achieved through light path compensation; and the beam combining light path and the emergent light path of the laser unit are overlapped in the beam combining direction of the spectrum, and the external cavity mirror is positioned in the laser light path, so that the laser beam combining device has high stability and compact light source, and can be used in occasions with high requirements on stability and reliability.
Specifically, the spectrum beam combining device and method provided by the invention have the following outstanding effects:
(1) high spectral beam combining efficiency. In the spectrum beam combining device, the incident angle and the diffraction angle of the reflection grating are both littrow angles, and the highest diffraction efficiency is achieved, so that the whole spectrum beam combining device has high spectrum beam combining efficiency; meanwhile, the front cavity surface of the laser unit, the conversion lens, the reflection grating, the conversion lens and the external cavity mirror are positioned in a 4f system, namely the focal length of the conversion lens is f, the front cavity surface and the external cavity mirror of the laser unit are positioned on the front focal plane of the conversion lens, the distance is f, the reflection grating is positioned on the back focal plane of the conversion lens, and the distance is also f, so that the laser beam is output to the external cavity mirror from the laser chip and experiences 4 f.
(2) High structural stability. In the spectrum beam combining device, the position of the external cavity mirror is superposed with the central laser unit in the spectrum beam combining direction and is positioned in the middle of the light path, so that the spectrum beam combining device has very good structural stability; meanwhile, the external cavity mirror is positioned at the focal position of the conversion lens, and stable external cavity feedback can be realized by using the cat eye effect even if the external cavity mirror has a certain angle or position change, so that high stable resonance is realized.
(3) Compact structure and convenient miniaturization of the light source. In the spectrum beam combining device, the beam combining light path after passing through the reflection grating and the beam combining light path before passing through the reflection grating are overlapped in the spectrum beam combining direction, do not occupy other spaces in the spectrum beam combining direction, and have very good structure compactness.
Drawings
Fig. 1 is a schematic perspective view of a spectrum beam combining device according to an embodiment of the present invention.
Fig. 2 is a schematic structural diagram of a spectrum beam combining device according to an embodiment of the present invention in a spectrum beam combining direction.
Fig. 3 is a schematic structural diagram of a spectrum beam combining device in a non-spectrum beam combining direction according to an embodiment of the present invention.
Fig. 4 is a schematic structural diagram of a spectral beam combining device of a first comparative example in the prior art.
Fig. 5 is a schematic structural diagram of a spectral beam combining device of a second comparative example in the prior art.
Fig. 6 is a schematic diagram of the deviation of the optical axis of the spectral beam combining device in the prior art.
Reference numerals
oz, an optical axis, 10, a laser unit array, 110, a central laser unit, 111, a first laser unit, 112, a second laser unit, 1001, an output beam, 1002, a combined beam, 2001, a first-order diffraction direction, 20, a conversion lens, 30, a reflection grating, 40, an external cavity mirror, 50, a transmission grating, 70 and a collimating mirror.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not to be construed as limiting the invention.
In a specific embodiment, the present invention provides a spectrum beam combining device, which includes a laser unit, a transforming lens, a reflective grating and an external cavity mirror; the front cavity surface of the laser unit and the external cavity mirror are both positioned on the front focal plane of the conversion lens, and the reflection grating is positioned on the back focal plane of the conversion lens; the littrow angle of the normal line of the reflection grating is used as an optical axis by the spectrum beam combining device, and the external cavity mirror is vertical to the optical axis;
the light path of the spectrum beam combining device comprises a spectrum beam combining direction and a non-spectrum beam combining direction;
in the spectrum beam combination direction, the laser unit outputs laser beams, and the laser beams are incident to the reflection grating at different angles under the action of the transformation lens; the laser beams output by the laser unit are superposed on the reflection grating, and are incident to the external cavity mirror after being incident to the conversion lens again;
in the non-spectral beam combining direction, the laser beam output by the laser unit is acted by the transformation lens and then forms an angle theta y Incident on the reflection grating and passing through the reflection grating at the same included angle theta y After reflection, the light returns to the transformation lens and is collimated by the transformation lens and then enters the external cavity mirror.
Fig. 1 is a schematic perspective view of a spectral beam combining apparatus according to an embodiment of the present invention, which includes a laser unit, a transforming lens 20, a reflective grating 30, and an external cavity mirror 40; the reflection grating 30 is located within a focal length range of one time of the conversion lens 20, the front cavity surface of the laser unit and the external cavity mirror 40 are both located on the front focal plane of the conversion lens 20, and the reflection grating 30 is located on the back focal plane of the conversion lens 20; in this embodiment, the conversion lens 20 is a rotationally symmetric lens, and may specifically be a circular lens, and may convert the spectrum beam combining direction and the non-spectrum beam combining direction of the laser beam at the same time, so that a 4f system is formed in both the spectrum beam combining direction and the non-spectrum beam combining direction, and imaging is simultaneously achieved in both directions, which also solves the problem of difficult feedback caused by smile effect and the like.
In this embodiment, the laser unit specifically adopts a laser unit array 10 including a central laser unit 110 and an edge laser unit, where the edge laser unit includes a first laser unit 111 and a second laser unit 112, and the two edge laser units are respectively located at two sides of the optical axis oz; the littrow angle of the normal line of the reflective grating 30 is used as the optical axis oz by the spectral beam combiner, and it should be noted that the optical axis oz is introduced for better describing the solution of the present invention, but the optical axis oz does not actually exist, and is only a direction axis similar to a coordinate axis for illustration.
As shown in fig. 2, which is a schematic structural diagram of a spectrum beam combining apparatus in a spectrum beam combining direction according to an embodiment of the present invention, in this embodiment, a rear cavity surface of a laser unit and an external cavity mirror 40 form a resonant cavity, a front cavity surface of the laser unit and the external cavity mirror 40 are both located on a front focal plane of a transform lens 20, and a reflection grating 30 is located on a rear focal plane of the transform lens 20, specifically, on a rear focal point; the scribing direction of the reflection grating 30 is perpendicular to the spectral beam combining direction.
In the spectrum combining direction x (i.e., the x direction is the spectrum combining direction), the output beam 1001 of the center laser unit 110 coincides with the optical axis oz, the first laser unit 111 and the second laser unit 112 of the edge laser unit are symmetrically distributed on both sides of the center laser unit 110, and the laser light is output along the same direction z. An output light beam 1001 of the central laser unit 110 is a principal ray, and the output light beam 1001 is incident to the reflection grating 30 at different angles after being acted by the conversion lens 20, wherein the incident angle of the output light beam 1001 on the reflection grating 30 is the littrow angle of the reflection grating 30; the laser beams output from the center laser unit 110, the first laser unit 111, and the second laser unit 112 are all overlapped on the reflection grating 30, and are finally diffracted out in the same direction through the reflection grating 30, and the diffraction direction is overlapped with the optical axis oz, and is incident on the conversion lens 20 again, and is finally incident on the external cavity mirror 40 perpendicular to the optical axis oz. The feedback of the external cavity mirror 40 and the dispersion of the reflection grating 30 make each laser unit resonate to different wavelengths, the facula and the divergence angle output by the external cavity mirror 40 are consistent with the unit beam, and the power is the sum of the powers of all the laser units.
As shown in fig. 3, a schematic diagram of a spectrum beam combining device according to an embodiment of the present invention is shown in a non-spectrum beam combining direction, in which an optical axis oz coincides with an optical axis of the conversion lens 20 and also coincides with a normal line of the reflection grating 30 in the non-spectrum beam combining direction y. Spaced from the optical axis oz by d y The output beam 1001 of the laser unit array 10 of (2) is acted on by the conversion lens 20 and then passes through an angle theta y Incident on the reflection grating 30, the reflection grating 30 has no dispersion effect in the non-spectral beam combining direction and can only be used as a reflector, so that the reflection grating 30 passes through and then forms the same included angle theta y The reflected light is reflected and then enters the transformation lens 20, is collimated by the transformation lens 20 and then enters the external cavity mirror 40, a combined beam 1002 is output through the external cavity mirror 40, and the combined beam 1002 and the output beam 1001 generate 2d in the y direction y Wherein d is y The distance θ between the output beam 1001 of the laser unit and the optical axis oz in the y direction y The output beam 1001 is incident on the reflection grating 30 at an angle to the optical axis oz in the y-direction.
In other embodiments, the front cavity surface of the laser unit is located within one focal length range of the conversion lens 20, and the spectral beam combining device further includes a compensation mirror (not shown in the figure) which is combined with the conversion lens 20 to form an imaging mirror for imaging the front cavity surface of the laser unit to the external cavity mirror 40; the compensation mirror may be a positive lens or a negative lens, specifically, the compensation mirror is a rotationally symmetric lens, specifically, the compensation mirror may be a circular lens, that is, the shape of the compensation mirror is rotationally symmetric.
In a specific embodiment, the reflection grating 30 is a first-order diffraction grating, the first-order diffraction efficiencies of the reflection grating 30 are all greater than 90%, and the grating efficient diffraction polarization direction of the reflection grating 30 matches the polarization direction of the laser beam.
In a specific embodiment, the laser units include a central laser unit 110 and edge laser units, each of which is divided into two partsRespectively outputting laser beams with different wavelengths. The incident angle and the diffraction angle between the laser beam output by the central laser unit 110 and the reflection grating 30 are both littrow angles in the spectrum beam combining direction. The angle between the incident angle of the laser beam output by the central laser unit 110 and the reflection grating 30 is smaller than 10 ° in the non-spectral beam combining direction, so that the diffraction efficiency of the reflection grating 30 is not reduced while the diffraction performance of the reflection grating 30 is minimally affected. The angle of the laser beam output by other edge laser units is close to the littrow angle, but not equal to the littrow angle, and the resonant wavelength lambda of the laser beam is equal to the littrow angle i Angle of incidence theta i And diffraction angle theta d Satisfying the grating equation as follows;
λ i =Λ（sinθ i +sinθ d ) Where Λ is the grating constant.
The laser unit comprises a laser device and an optical element, the optical element is used for at least one of collimation, shaping or polarization direction adjustment of a laser beam output by the laser device, and an antireflection film is plated on the end face of the laser device, which outputs the laser beam; the laser device is a semiconductor laser, a fiber laser or an all-solid-state laser.
The invention also provides a spectrum beam combining method, which is realized by the spectrum beam combining device and comprises the following steps:
s1, in the spectrum beam combining direction, the laser unit outputs a laser beam, and the laser beam is acted by the transforming lens 20 and enters the reflection grating 30 at different angles; the laser beams output by the laser units are overlapped on the reflection grating 30, and are incident to the transformation lens 20 again and then finally to the external cavity mirror 40;
s2, in the non-spectrum beam combining direction, the laser beam output by the laser unit is acted by the transformation lens 20 and then forms an angle theta y Incident on the reflection grating 30 and passing through the reflection grating 30 at the same included angle theta y After reflection, the light returns to the conversion lens 20 and is collimated by the conversion lens 20And then incident on the external cavity mirror 40.
As shown in fig. 6, it is a schematic diagram of a situation that an optical axis of a spectrum beam combining device in the prior art may deviate due to packaging or adjustment, where each bright point in the diagram represents a laser unit, specifically, I in the diagram represents a schematic diagram in an ideal state, and ii in the diagram represents a schematic diagram in a smile state, that is, due to packaging or adjustment, the laser unit deviates from an ideal position and appears undulated in a y direction, which is seen as a smile shape.
The small-angle folding spectrum beam combining device and the method provided by the invention have the advantages that through the cooperation of the spectrum beam combining direction and the non-spectrum beam combining direction, the spectrum beam combining direction is diffracted through the littrow structure, and the diffraction efficiency is high; folding the light path in the non-spectral beam combination direction, and enabling the laser unit to be directly imaged on the external cavity mirror through an imaging relation, even if pointing deviation caused by packaging smile or adjustment occurs, high-stability external cavity feedback can be achieved through light path compensation; and the beam combining light path and the emergent light path of the laser unit are overlapped in the beam combining direction of the spectrum, and the external cavity mirror is positioned in the laser light path, so that the laser beam combining device has high stability and compact light source, and can be used in occasions with high requirements on stability and reliability.
The following is a further description with reference to specific comparative examples and examples.
Comparative example 1
A structure for performing spectral beam combination based on a reflection grating is reported in a reference (B, Chann, R.K. Huang, L.J. Missaggia, et al, Near-differential-limited diode laser arrays by wavelength beam combining [ J ]. optics drivers, 2005, 30(16):2104 and 2106), wherein an external cavity mirror 40 and a rear cavity surface of a laser unit array 10 form a resonant cavity, and a front cavity surface of the laser unit array 10 and a reflection grating 30 are respectively positioned on a front focal plane and a rear focal plane of a conversion lens 20. After the laser unit is acted by the conversion lens 20 with the focal length f, the laser unit is incident on the reflection grating 30 at different angles, and is diffracted by the reflection grating 30, a diffracted laser beam is output to the external cavity mirror 40, and only light which is vertically incident on the external cavity mirror 40 can return to the original laser unit to form resonance. The incident laser beam and the diffracted laser beam of the reflection grating 30 are separated, and in order to achieve high grating diffraction efficiency, the separation angle between the two is small (< 10 °), and each is close to the littrow angle of the grating. Through the feedback and grating dispersion of the external cavity mirror 40, each laser unit resonates to different wavelengths, the light spots and divergence angles output by the external cavity mirror 40 are consistent with unit beams, and the power is the sum of the powers of all the laser units. Specifically, as shown in fig. 4, a transforming lens 20 with a focal length of 200mm is used to transform beams of 100 915nm laser units with front cavity surface anti-reflection (R < 1%), a reflective grating 30 with a grating period of 1800 lines/mm is used to diffract, an external cavity mirror 40 with a reflectivity of 10% is used to perform feedback to realize spectrum combining, and the output spectrum after combining is 17 nm. As can be seen from the figure, the distance from the light emergent cavity surface of the laser chip to the grating is at least 400 mm. In the content of the document, "For best effort angle on the grating is limited to a few degrees, and specific values are not reported, and it is known from the text that the light transmission direction diffracted by the reflection grating 30 is not coincident with the incident light, the physical size is increased in the X direction, and the external cavity mirror 40 is not included in the inside of the spectrum beam combining structure.
Example 1
Based on the principle shown in fig. 4, with the structure of the spectral beam combining device of the present invention, and referring to the embodiments shown in fig. 1-3 in particular, a single-piece reflection grating 30 is adopted, the number of grating lines of the reflection grating 30 is still 1800 lines/mm, and in the direction of spectral beam combining, the incident angle and the diffraction angle of the output light beam 1001 on the reflection grating 30 are both littrow angle 55.44 °, so that high grating diffraction efficiency can be obtained. The focal length of the conversion lens 20 is still 200mm, in the non-spectral beam combining direction, d y Set to 10mm, the incident angle theta when the light enters the reflection grating 30 y 2.86 degrees, the reflection angle after the reflection of the reflection grating 30 is kept at 2.86 degrees, the light is emitted in parallel to the optical axis oz after the action of the conversion lens 20, the light is incident on an external cavity mirror 40 arranged at the upper end of the laser unit, partial reflection forms oscillation, partial direct output forms a combined beamThe beam 1002, the combined beam 1002 and the laser unit are spatially separated by 20 mm. In the whole spectrum beam combination structure, the light path before passing through the reflection grating 30 and the light path after passing through the reflection grating 30 are overlapped in the spectrum beam combination direction, so that the size of the spectrum beam combination direction is reduced, and the light path is separated by 20mm in the non-spectrum beam combination direction; in addition, the external cavity mirror 40 is contained in the light path, so that the structural stability of the whole spectrum beam combining device is enhanced.
Comparative example 2
Reference (Jun Zhang, Handyu Pen, Xihong Fu, et al CW 50W/M2 = 10.9 diode source by spectral beam combining on a transmission [ J]Optics express, 2013, 21(3): 3627-3632) reports a structure for spectral beam combining based on a transmission grating, the external cavity mirror 40 and the back cavity surface of the laser unit array 10 form a resonant cavity, and the front cavity surface of the laser unit array 10 and the transmission grating 50 are respectively located on the front and back focal planes of the conversion lens 20. The laser beam output from the laser unit array 10 passes through the focal length f f And f s Through the focal length f, of the collimating mirror 70 t After the action of the conversion lens 20, the laser beams are incident on the transmission grating 50 at different angles, wherein the incident angle of the laser beam output by the laser unit at the middle position of the laser unit array 10 is the same as the littrow angle of the transmission grating, as shown in the first-order diffraction direction 2001 in the figure, the laser beam is diffracted by the transmission grating 50, the diffracted beam is overlapped with the littrow angle direction of the transmission grating, the diffracted light is output to the external cavity mirror 40, and only the laser beam vertically incident on the external cavity mirror 40 can return to the original laser unit to form resonance. The incident laser beam and the diffracted laser beam of the transmission grating 50 are separated, and in order to achieve high grating diffraction efficiency, the incident angle and the diffraction angle of the transmission grating 50 are Littrow angles (θ Littrow) of the grating, so that the included angle between the incident laser beam and the diffracted laser beam is 180-2 × θ Littrow, and in the document, the θ Littrow is 50.6 °, so that the included angle between the incident laser beam and the diffracted laser beam reaches 78.8 °.
Specifically, as shown in fig. 5, a conversion lens 20 with a focal length of 150mm is used for performing beam conversion on 970nm laser units with the anti-reflection performance (R < 0.5%) of 19 front cavity surfaces, a transmission grating 50 with a grating period of 1600 lines/mm is used for diffraction, then an external cavity mirror 40 with a reflectivity of 20% is used for feedback to realize spectrum beam combination, and the output spectrum after the beam combination is 24.1 nm. As can be seen, the light exit facets of the laser chips are at least 300mm from the transmission grating 50. Although the angles between the incident laser beam and the diffracted laser beam and the transmission grating 50 are littrow angles, high diffraction efficiency can be obtained, but the included angle between the incident laser beam and the diffracted laser beam reaches 78.8 degrees and almost forms a right angle, so that the whole light source structure occupies a large space, if the distance from the external cavity mirror 40 to the transmission grating 50 is 100mm, the size of the external cavity mirror 40 is directly increased by nearly 100mm in the X direction, and the external cavity mirror 40 is completely positioned at the far end of the spectrum beam combining structure, so that the stable structure is not easy to realize.
Example 2
Based on the principle shown in fig. 5, by using the structure of the spectral beam combining device of the present invention, and by using the structure of the spectral beam combining device of the present invention, referring to the embodiments shown in fig. 1 to fig. 3 specifically, by using the single-chip reflection grating 30, the grating line number of the reflection grating 30 is still 1600 lines/mm, and in the direction of spectral beam combining, both the incident angle and the diffraction angle of the output light beam 1001 on the reflection grating 30 are littrow angle 50.60 °, and high diffraction efficiency is obtained. Meanwhile, by the structure of the spectrum beam combining device of the embodiment, the light path before passing through the reflection grating 30 and the light path after passing through the reflection grating 30 are overlapped in the spectrum beam combining direction, and the space is only increased in the non-spectrum beam combining direction. If the focal length f of the conversion lens 20 is still 150mm, d in the non-spectral beam combining direction y When the angle of incidence θ y is set to 5mm, the angle of incidence θ y upon incidence to the reflection grating 30 is 1.91 °, the angle of reflection after reflection by the reflection grating 30 is also 1.91 °, the beam is emitted parallel to the optical axis oz after being acted by the conversion lens 20, and then the beam is incident on the external cavity mirror 40 disposed at the upper end of the laser unit, and is partially reflected to oscillate, and is partially directly output to form a combined beam 1002, and the spatial interval between the combined beam 1002 and the laser unit is 10 mm. In the whole spectrum beam combination structure, the light path before passing through the reflection grating 30 and the light path after passing through the reflection grating 30 are overlapped in the spectrum beam combination direction, so that the size of the spectrum beam combination direction is reduced, and the light paths are separated by 10mm in the non-spectrum beam combination direction; in addition, an external cavity mirror 40 is included inside the optical pathAnd the structural stability of the whole spectrum beam combining device is enhanced. Meanwhile, the front cavity surface of the laser unit forms an imaging relationship with the external cavity mirror 40, and even if the optical axis orientation deviates due to packaging or adjustment, such as the Smile situation shown in fig. 6, resonance can be formed, and the resonance capability of the spectrum beam combination light source is improved.
While embodiments of the present invention have been shown and described above, it should be understood that the above embodiments are exemplary and should not be taken as limiting the invention. Variations, modifications, substitutions and alterations of the above-described embodiments may be made by those of ordinary skill in the art without departing from the scope of the present invention.
The above embodiments of the present invention should not be construed as limiting the scope of the present invention. Any other corresponding changes and modifications made according to the technical idea of the present invention should be included in the protection scope of the claims of the present invention.
Claims (10)
1. A spectrum beam combining device is characterized by comprising a laser unit, a conversion lens, a reflection grating and an external cavity mirror; the front cavity surface of the laser unit and the external cavity mirror are both positioned on the front focal plane of the conversion lens, and the reflection grating is positioned on the back focal plane of the conversion lens; the littrow angle of the normal line of the reflection grating is used as an optical axis by the spectrum beam combining device, and the external cavity mirror is vertical to the optical axis;
the light path of the spectrum beam combining device comprises a spectrum beam combining direction and a non-spectrum beam combining direction;
in the spectrum beam combination direction, the laser unit outputs laser beams, and the laser beams are incident to the reflection grating at different angles under the action of the transformation lens; the laser beams output by the laser unit are superposed on the reflection grating, and are incident to the external cavity mirror after being incident to the conversion lens again;
in the non-spectral beam combining direction, the laser beam output by the laser unit is acted by the transformation lens and then forms an angle theta y Incident on the reflection gratingPassing through the reflection grating at the same included angle theta y After reflection, the light returns to the transformation lens and is collimated by the transformation lens and then enters the external cavity mirror.
2. The spectral combining apparatus of claim 1 wherein the transform lens is a rotationally symmetric lens.
3. The spectral beam combining apparatus of claim 1 further comprising a compensator, said compensator in combination with said transformative lens forming an imaging mirror that images a front facet of said laser unit to said external cavity mirror.
4. The spectral combining apparatus of claim 3 wherein the compensating mirror is a rotationally symmetric lens.
5. The spectral beam combining device of claim 1 wherein said laser units comprise a center laser unit and an edge laser unit, each of said laser units outputting a laser beam of a different wavelength.
6. The spectral beam combining apparatus of claim 5 wherein the central laser unit outputs a laser beam having an angle of incidence and an angle of diffraction with respect to the reflective grating that are both littrow angles in the spectral beam combining direction.
7. The spectral beam combining apparatus of claim 5 wherein the angle of incidence of the laser beam output by the central laser unit with the reflective grating in the non-spectral beam combining direction is less than 10 °.
8. The spectral beam combining apparatus of claim 1, wherein the laser unit comprises a laser device and an optical element, the optical element at least one of collimates, shapes or adjusts a polarization direction of a laser beam output by the laser device, and the laser device is coated with an antireflection film on an end surface outputting the laser beam; the laser device is a semiconductor laser, a fiber laser or an all-solid-state laser.
9. The spectral beam combining device of claim 1 wherein the reflection grating is a first order diffraction grating, the first order diffraction efficiency of the reflection grating is greater than 90%, and the diffraction polarization direction of the reflection grating matches the polarization direction of the laser beam.
10. A spectral beam combining method implemented by the spectral beam combining device according to any one of claims 1 to 9, the spectral beam combining method comprising the steps of:
s1, in the spectrum beam combination direction, the laser unit outputs laser beams, and the laser beams are acted by the conversion lens and enter the reflection grating at different angles; the laser beams output by the laser unit are overlapped on the reflection grating, and are incident to the transformation lens again and then are finally incident to the external cavity mirror;
s2, in the non-spectrum beam combining direction, the laser beam output by the laser unit is acted by the conversion lens and then forms an angle theta y Incident on the reflection grating and passing through the reflection grating at the same included angle theta y After reflection, the light returns to the transformation lens and is collimated by the transformation lens and then enters the external cavity mirror.
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