CN115079426B - Spectrum beam combining device and method - Google Patents
Spectrum beam combining device and method Download PDFInfo
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Abstract
The invention relates to the technical field of laser, in particular to a spectrum beam combining device and a method, wherein the spectrum beam combining device comprises a laser unit, a conversion lens, a transmission grating, a translation prism and an external cavity mirror; the transmission grating is positioned in the focal length doubling range of the conversion lens, and the front cavity surface and the outer cavity mirror of the laser unit are positioned on the front 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 disclosed by the invention is matched with the spectrum beam combining direction and the non-spectrum beam combining direction, passes through the diffraction element for the second time, and enables the outer cavity mirror to coincide with the cavity surface of the central laser unit, so that the outer cavity feedback of the cat eye structure is realized, and the beam combining light path and the emergent light path of the laser unit are overlapped in the spectrum beam combining direction, so that the structure has the series advantages of high-efficiency spectrum beam combining, high-beam quality adjustment, high-stability outer cavity resonance, high-stability structure, high-dispersion capacity improvement, structure miniaturization and the like.
Description
Technical Field
The invention relates to the technical field of lasers, in particular to a spectrum beam combining device and method.
Background
Spectral beam combining technology is currently one of the most feasible techniques for achieving high-power, high beam quality beam combining lasers. From 1999 to date, this technology has been successfully applied to all solid state lasers, fiber lasers, and semiconductor lasers, greatly improving laser performance.
The spectrum beam combining structure currently applied to the field of semiconductor laser is mainly a closed-loop spectrum beam combining structure, and the implementation structure is as follows: the back cavity surface of the laser unit and the outer cavity mirror form a resonant cavity, the front cavity surface of the laser unit is plated with an antireflection film, the antireflection film is arranged in the spectrum beam combining direction and is emitted along the same direction, the laser unit and the outer cavity mirror are jointly incident on the grating under the action of the conversion lens, and then are output to the outer cavity mirror through grating diffraction, so that only light which vertically enters the outer cavity mirror and can be reflected back to the original laser unit can resonate. Due to the effects of grating and external cavity feedback, the laser unit resonates to different laser wavelengths, the laser power after spectrum beam combination is multiplied, the beam quality is consistent with that of the laser unit, but the whole spectrum is widened.
In order to achieve a good spectrum beam combination effect, the light emitting end face of the laser chip and the grating are respectively positioned on front and back focal planes 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 combination structure based on the reflection grating or the spectrum beam combination structure based on the transmission grating, the output light path is not overlapped with the incident light path after grating diffraction, so that the output laser needs to occupy additional space, and the size of the spectrum beam combination structure is further increased. 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 current literature generally reports that the focal length of a conversion lens adopted by a near infrared band spectrum beam combination light source is hundreds of millimeters, and in order to compress bandwidth, the focal length of the conversion lens even reaches the order of meters, so that the resonant cavity of an external cavity spectrum light source generally reaches hundreds of millimeters or even a plurality of 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 the edge of the light source, so that the structural stability of the rear cavity mirror is difficult to ensure, and great hidden danger is 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 aims to solve the problems and provide a spectrum beam combining device and a spectrum beam combining method which are more compact in structure and more stable in performance.
The invention provides a spectrum beam combining device, which comprises a laser unit, a conversion lens, a transmission grating, a translation prism and an external cavity mirror, wherein the conversion lens is arranged on the laser unit; the transmission grating is positioned in the focal length doubling range of the transformation lens, the front cavity surface of the laser unit is positioned on the front focal plane of the transformation lens, and the outer cavity mirror is positioned on the front focal plane of the transformation lens; the spectrum beam combining device takes a Littrow angle of a normal line of the transmission grating as an optical axis, and the external cavity mirror is perpendicular to the optical axis;
the optical path of the spectrum beam combining device comprises a spectrum beam combining direction and a non-spectrum beam combining direction;
in the spectrum beam combining direction, the laser unit outputs laser beams, the laser beams are acted by the transformation lens and are incident to the transmission grating at different angles, and the laser beams are diffracted by the transmission grating and then are incident to the translation prism; the laser beams output by the laser unit are overlapped on the transmission grating and finally enter the external cavity mirror after entering the conversion lens again;
in the non-spectrum beam combining direction, the laser beam output by the laser unit is incident to the translation prism after passing through the transformation lens and the transmission grating, translates in the y direction, returns to be incident to the transmission grating and the transformation lens, and then enters the external cavity mirror.
Preferably, the translation prism is an optical element with beam translation capability; the incident light of the translation prism and the emergent light of the translation prism are parallel to each other.
Preferably, the translation prism is a right-angle triangular prism or a plane reflecting mirror combination.
Preferably, the spectrum beam combining device further comprises a compensating mirror, wherein the compensating 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 outer cavity mirror.
Preferably, the transmission grating is a negative first-order transmission grating, the negative first-order diffraction efficiency of the transmission grating is greater than 90%, and the diffraction polarization direction of the transmission grating is matched with the polarization direction of the laser beam.
Preferably, the number of the transmission gratings is two or more, and adjacent transmission gratings are not parallel to each other.
Preferably, the laser unit includes a central laser unit and an edge laser unit, each of which outputs laser beams of different wavelengths, respectively.
Preferably, the incidence angle and the diffraction angle of the laser beam output by the central laser unit and the transmission grating are rittrow angles.
Preferably, the laser unit comprises a laser device and an optical element, the optical element performs at least one of collimation, shaping or polarization direction adjustment on a laser beam output by the laser device, and the laser device is coated with an antireflection film on the end face of the output 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 the spectrum beam combining method comprises the following steps:
s1, outputting laser beams by the laser unit in the spectrum beam combining direction, wherein the laser beams are incident to the transmission grating at different angles under the action of the conversion lens, and are diffracted by the transmission grating and then are incident to the translation prism; the laser beam is incident to the external cavity mirror after being acted by the transmission grating and the transformation prism;
s2, in the non-spectrum beam combining direction, the laser beam output by the laser unit is incident to the translation prism after passing through the transformation lens and the transmission grating, is translated in the y direction, then returns to be incident to the transmission grating and the transformation lens, and then is incident to the external cavity mirror.
According to the spectrum beam combining light source device and the spectrum beam combining light source method, through the cooperation of the spectrum beam combining direction and the non-spectrum beam combining direction, the light path is diffracted through the Littrow structure in the spectrum beam combining direction, the light path is folded in the non-spectrum beam combining direction, the light path passes through the diffraction element for the second time, the outer cavity mirror is enabled to be overlapped with the cavity surface of the central laser unit, the outer cavity feedback of the cat eye structure is achieved, the beam combining light path and the laser unit outgoing light path are overlapped in the spectrum beam combining direction, the quality of the laser beam of the high-quality combined beam of the translational lens is adjusted, and the like, so that the structure has the advantages of high-efficiency spectrum beam combining, high-beam quality adjustment, high-stability outer cavity resonance, high-stability structure, high-dispersion capacity improvement, structure miniaturization and the like.
Specifically, the spectrum beam combining device and the spectrum beam combining method provided by the invention have the following outstanding effects:
(1) High dispersion capability. In the spectrum beam combining device provided by the invention, the transmission grating is passed through at the Littrow angle twice, and compared with a conventional spectrum beam combining structure, the dispersion capacity multiple improvement can be realized by adopting only a single grating.
(2) High spectral beam combining efficiency. The spectrum beam combining efficiency is closely related to the diffraction efficiency of the grating, and the incidence angle and the diffraction angle of the transmission grating are all littrow angles in the invention, so that the highest diffraction efficiency is achieved, and the whole spectrum beam combining light source has high spectrum beam combining efficiency.
(3) High beam quality. According to the spectrum beam combining device structure, the coincidence ratio of light spots can be adjusted in real time through translating the position of the lens in the Z direction, so that the near field and the far field of light beams of all laser units coincide, wherein the far field coincidence realizes stable external cavity resonance through external cavity feedback and cat eye effect, and the coincidence ratio of the far field output directions of all laser units can be controlled; the near field is mainly realized through the light spot coincidence ratio of each laser unit in the last diffraction, so that the optimal near field coincidence effect is realized, and the optimal beam combination beam quality is realized.
(4) High structural stability. In the structure of the spectrum beam combining device, the position of the outer cavity mirror is overlapped with the central laser unit in the spectrum beam combining direction and is positioned in the middle of the light path, so that the structure has very good structural stability; meanwhile, the external cavity mirror is positioned at the focal position of the transformation lens, and stable external cavity feedback can be realized by utilizing the Cat eye effect even if the external cavity mirror has a certain angle or position change, so that high stable resonance is realized; the up-down folding structure in the y direction is realized by adjusting the twice-reflecting light path of the translation prism, and even if pitch offset occurs, the relative position of the light path in and out cannot be influenced, so that the structure has high structural stability.
(5) Compact structure, the miniaturization of light source of being convenient for. In the structure of the spectrum beam combining device, the beam combining light path after passing through the transmission grating and the beam combining light path before passing through the transmission grating are overlapped in the spectrum beam combining direction, and do not occupy other spaces in the spectrum beam combining direction, so that the structure has very good compactness.
(6) Low cost. In the spectrum beam combining device structure, the conversion lens and the transmission grating structure are directly multiplexed, so that the number of components is reduced, particularly the use of high-value gratings is reduced, and the cost of the spectrum beam combining light source can be greatly reduced.
Drawings
Fig. 1 is a schematic perspective view of a spectrum combining device according to a first embodiment of the present invention.
Fig. 2 is a schematic structural view of a spectrum combining device in a spectrum combining direction according to a first embodiment of the present invention.
Fig. 3 is a schematic structural view of a spectral beam combining device according to a first embodiment of the present invention in a non-spectral beam combining direction.
Fig. 4 is a schematic structural view of a spectrum combining device according to a second embodiment of the present invention.
Fig. 5 is a schematic diagram of a transmission grating structure in a spectral beam combining device according to an embodiment of the present invention.
Fig. 6 is a schematic structural diagram of a spectrum combining device of a first comparative example in the prior art.
Fig. 7 is a schematic structural diagram of a spectrum combining device of a second comparative example in the prior art.
Reference numerals
oz, optical axis, 10, laser unit array, 100, central laser unit, 101, first laser unit, 102, second laser unit, 1001, output beam, 1002, combined beam, 2001, first order diffraction direction, 20, conversion lens, 30, transmission grating, 40, translation prism, 301, first transmission grating, 302, second transmission grating, 303, third transmission grating, 30N, nth transmission grating, 50, external cavity mirror, 60, reflection grating, 70, and collimator mirror.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not to be construed as limiting the invention.
In a specific embodiment, the invention provides a spectrum beam combining device, which comprises a laser unit, a conversion lens, a transmission grating, a translation prism and an external cavity mirror; the transmission grating is positioned in the focal length doubling range of the transformation lens, the front cavity surface of the laser unit is positioned on the front focal plane of the transformation lens, and the outer cavity mirror is positioned on the front focal plane of the transformation lens; the spectrum beam combining device takes a Littrow angle of a normal line of the transmission grating as an optical axis, and the external cavity mirror is perpendicular to the optical axis;
the optical path of the spectrum beam combining device comprises a spectrum beam combining direction and a non-spectrum beam combining direction;
in the spectrum beam combining direction, the laser unit outputs laser beams, the laser beams are acted by the transformation lens and are incident to the transmission grating at different angles, and the laser beams are diffracted by the transmission grating and then are incident to the translation prism; the laser beams output by the laser unit are overlapped on the transmission grating and finally enter the external cavity mirror after entering the conversion lens again;
in the non-spectrum beam combining direction, the laser beam output by the laser unit is incident to the translation prism after passing through the transformation lens and the transmission grating, translates in the y direction, returns to be incident to the transmission grating and the transformation lens, and then enters the external cavity mirror.
Referring to fig. 1, a schematic perspective view of a spectrum combining device according to a first embodiment of the present invention is shown, where the spectrum combining device includes a laser unit, a conversion lens 20, a transmission grating 30, a translation prism 40, and an external cavity mirror 50; the spectrum beam combining device takes a littrow angle of a normal line of the transmission grating as an optical axis oz, and the laser units specifically adopt a laser unit array 10 comprising a central laser unit 100 and edge laser units, wherein the edge laser units comprise a first laser unit 101 and a second laser unit 102, and the two edge laser units are respectively positioned at two sides of the optical axis oz; it should be noted that, in order to better describe the solution of the present invention, the optical axis oz is introduced, but the optical axis oz is not actually present, but is just a schematic direction axis similar to a coordinate axis.
As shown in fig. 2, a schematic structural diagram of a spectrum combining device in a spectrum combining direction according to a first embodiment of the present invention is shown, in which a rear cavity surface of a laser unit and an external cavity mirror 50 form a resonant cavity, and a front cavity surface of the laser unit and the external cavity mirror 50 are both located on a front focal plane of a conversion lens 20.
In the spectrum combining direction x (i.e., the x direction is the spectrum combining direction), the output beam 1001 of the central laser unit 100 coincides with the optical axis oz, and the first laser unit 101 and the second laser unit 102 of the edge laser unit are symmetrically distributed on both sides of the central laser unit 100, and output laser along the same direction z. The output light beam 1001 of the central laser unit 100 is taken as a main light ray, the output light beam 1001 is incident to the transmission grating 30 at different angles after being acted by the conversion lens 20, wherein the incident angle of the output light beam 1001 at the transmission grating 30 is the littrow angle of the transmission grating 30, and the output light beam 1001 is further incident to the translation prism 40 at the littrow angle after being diffracted by the transmission grating 30, and returns to the transmission grating 30 at the littrow angle along the original path after being acted by the translation prism 40; the laser beams output from the central laser unit 100, the first laser unit 101, and the second laser unit 102 are all superimposed on the transmission grating 30, and finally diffracted in the same direction through the transmission grating 30, and the diffracted direction is superimposed on the optical axis oz, and then incident on the conversion lens 20 again, and finally incident on the external cavity mirror 50 perpendicular to the optical axis oz. Each laser unit resonates to different wavelengths through the feedback of the external cavity mirror 50 and the dispersion action of the transmission grating 30, the light spot and the divergence angle output by the external cavity mirror 50 are consistent with the unit light beam, and the power is the sum of the powers of all the laser units.
FIG. 3 is a schematic view showing a structure of a spectral beam combining device according to a first embodiment of the present invention in a non-spectral beam combining direction, wherein the spectral beam combining device is spaced from an optical axis oz by d in a non-spectral beam combining direction y y1 The output beam 1001 of the laser unit array 10 of (a) enters the translation prism 40 after passing through the conversion lens 20 and the transmission grating 30, and the combined beam 1002 is a combined beam after passing through the translation prism 40, and is generated in the y direction (d) y1 +d y2 ) Wherein the y-direction is the non-spectral beam combining direction, d y2 For d, the spacing of the combined beam 1002 from the optical axis oz in the y-direction y1 And d y2 The size of the two spaces is not particularly limited as long as the size of the translation prism 40 is satisfied, and at the same time, the minimum spot size of the second incident light on the transmission grating 30 can be satisfied; then, the laser beam is returned to the transmission grating 30 and the conversion lens 20, finally, the laser beam is finally incident to the external cavity mirror 50, only the laser beam which is vertically incident to the external cavity mirror 50 and reflected by the external cavity mirror 50 and can be returned to the laser unit can effectively resonate, and the light transmitted and output by the external cavity mirror 50 forms combined laser.
In a specific embodiment, the front cavity surface of the laser unit is located within the focal length doubling range of the transformation lens 20, and the spectrum beam combining device further comprises a compensating mirror (not shown in the figure), and the compensating mirror and the transformation lens 20 are combined to form an imaging mirror to image the front cavity surface of the laser unit to the external cavity mirror 50; the compensation lens can be a positive lens or a negative lens, and can be a cylindrical lens or a round lens.
In a specific embodiment, the translating prism 40 is an optical element with a beam translating capability; the incident light of the translation prism 40 and the outgoing light of the translation prism are parallel to each other. The translation prism 40 may be a right-angle triangular prism or a planar mirror combination, and the planar mirror combination specifically refers to a combination of two or more planar mirrors, so that the incident light and the outgoing light are parallel to each other through multiple reflections, and only a displacement is generated in the non-spectrum beam combining direction y.
In a specific embodiment, the transmission grating 30 is a negative first-order transmission grating, the negative first-order diffraction efficiency of the transmission grating 30 is greater than 90%, and the high-efficiency diffraction polarization direction of the transmission grating 30 is matched with the polarization direction of the laser beam. In a preferred embodiment, the number of the transmission gratings 30 is two or more, that is, a combination of multiple transmission gratings, as shown in fig. 5, and the number of the transmission gratings 30 is multiple, that is, a combination of multiple negative first-order transmission gratings, including a first transmission grating 301, a second transmission grating 302, a third transmission grating 303, …, and an nth transmission grating 30N, where the negative first-order diffraction efficiency of each transmission grating 30 is greater than 90% and the adjacent transmission gratings 30 are not parallel to each other. In the combination scheme of the multiple transmission gratings 30, each transmission grating 30 may have the same grating constant or different grating constants, when the grating constants are the same, the angles of the incident angle and the diffraction angle are the same, and when the grating constants are different, the incident angle and the diffraction angle of each transmission grating 30 are the same; each of the transmission gratings 30 is located within a focal length of one of the conversion lenses 20, and an included angle between the (N-1) -th transmission grating and the N-th transmission grating 30N is (θ L(N-1) +θ LN ) Wherein θ L(N-1) Littrow angle, θ, for the (N-1) -th sheet transmission grating LN Is the littrow angle of the nth sheet transmission grating 30N.
In a specific embodiment, the laser units include a central laser unit and an edge laser unit, and each laser unit outputs laser beams with different wavelengths. The incidence angle and the diffraction angle of the laser beam output by the central laser unit and the transmission grating are Littrow angles. The angles of the laser beams output by other edge laser units are close to the Littrow angle, but are not equal to the Littrow angle, and the resonance wavelength lambda of the laser beams is equal to the Littrow angle i Angle of incidence theta i And the diffraction angle θd satisfies 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, wherein the optical element performs at least one of collimation, shaping or polarization direction adjustment on a laser beam output by the laser device, and the end face of the laser device outputting the laser beam is plated with an antireflection film; the laser device is a semiconductor laser, a fiber laser or an all-solid-state laser.
Fig. 4 is a schematic structural diagram of a spectrum combining device according to a second embodiment of the present invention. With respect to the structure of the first embodiment shown in fig. 1 to 3, in this second embodiment, the transmission grating 30 may be placed directly against the conversion lens 20, and by adjusting the position Δz of the translation prism 40 in the transmission direction, all laser units may be overlapped on the transmission grating 30 during diffraction return, so as to achieve near field overlapping; specifically, the position is shifted back and forth in the Δz direction so that the spot size of the second incident on the transmission grating 30 is minimized. The overall size of the spectral combining package is more compact due to the folded optical path of the translating prism 40. Meanwhile, the lens 20 and the transmission grating 30 are changed to serve as light path secondary transmission elements, and the whole structure can be more stable due to the small relative distance. Meanwhile, in other embodiments, the conversion lens 20 and the transmission grating 30 may be assembled as a whole or directly manufactured as an integrated element, thereby improving reliability. By fully describing the embodiment, in the structure of the spectrum beam combining device of the invention, the position requirement on the transmission grating 30 is not strict, the adjustment difficulty can be fully reduced, and the structure can be changed according to the requirement, namely, the position of the transmission grating 30 can be adjusted in a large range according to the structure of the whole device, so long as the transmission grating 30 is ensured to be positioned within the range of one focal length of the change lens 20.
The invention also provides a spectrum beam combining method which is realized by the spectrum beam combining device, and the spectrum beam combining method comprises the following steps:
s1, outputting laser beams by the laser unit in the spectrum beam combining direction, wherein the laser beams are incident to the transmission grating at different angles under the action of the conversion lens, and are diffracted by the transmission grating and then are incident to the translation prism; the laser beam is incident to the external cavity mirror after passing through the transmission grating and the transformation lens;
s2, in the non-spectrum beam combining direction, the laser beam output by the laser unit is incident to the translation prism after passing through the transformation lens and the transmission grating, is translated in the y direction, then returns to be incident to the transmission grating and the transformation lens, and then is incident to the external cavity mirror.
According to the spectrum beam combining light source device and the spectrum beam combining light source method, through the cooperation of the spectrum beam combining direction and the non-spectrum beam combining direction, the light path is diffracted through the Littrow structure in the spectrum beam combining direction, the light path is folded in the non-spectrum beam combining direction, the light path passes through the diffraction element for the second time, the outer cavity mirror is enabled to be overlapped with the cavity surface of the central laser unit, the outer cavity feedback of the cat eye structure is achieved, the beam combining light path and the laser unit outgoing light path are overlapped in the spectrum beam combining direction, the quality of the laser beam of the high-quality combined beam of the translational lens is adjusted, and the like, so that the structure has the advantages of high-efficiency spectrum beam combining, high-beam quality adjustment, high-stability outer cavity resonance, high-stability structure, high-dispersion capacity improvement, structure miniaturization and the like.
Further description will be given below with reference to specific comparative examples and examples.
Comparative example 1
Reference (B.Chann, R.K.Huang, L.J.Missaggia, et al near-diffraction-limited diode laser arrays by wavelength beamcombining [ J ]. Optics letters,2005,30 (16): 2104-2106) reports a structure for spectral beam combining based on a reflection grating, an external cavity mirror 50 forming a resonant cavity with the back cavity surface of the laser unit array 10, and the front cavity surface of the laser unit array 100 and the reflection grating 60 being located on the front and back focal planes of the conversion lens 20, respectively. 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 60 at different angles, and then is diffracted by the reflection grating 60, the diffracted laser beam is output to the external cavity mirror 50, and only the light vertically incident on the external cavity mirror 50 can return to the original laser unit to form resonance. The incident laser beam and the diffracted laser beam of the reflection grating 60 are separated, and in order to achieve high grating diffraction efficiency, the separation angle of the two is small (< 10 °) and is close to the littrow angle of the grating, respectively. Each laser unit resonates to different wavelengths through the feedback of the external cavity mirror 50 and the grating dispersion, the light spot and the divergence angle output by the external cavity mirror 50 are consistent with the unit light beam, and the power is the sum of the powers of all the laser units. Specifically, as shown in fig. 6, a conversion lens 20 with a focal length of 200mm is used to perform beam conversion on 915nm laser units with an antireflection (R < 1%) of 100 front cavity surfaces, a reflection grating 60 with a grating period of 1800 lines/mm is used to perform diffraction, and then an external cavity mirror 50 with a reflectivity of 10% is used to perform feedback to realize spectrum beam combination, and the output spectrum after beam combination is 17nm. As can be seen from the figure, the light exit surface of the laser chip is at least 400mm from the grating. The document explicitly mentions "For best efficiency the incidence angle on the grating is limited to several degrees around the Littrow angle", i.e. that both the angle of incidence and the angle of diffraction of the reflection grating 60 deviate from the littrow angle of the grating, which is limited to a few degrees as much as possible for good efficiency, and the specific values are not reported, while it is known from the document that the direction of light transmission diffracted by the reflection grating 60 does not coincide with the incident light, that the physical dimension is increased in the X-direction, and that the external cavity mirror 50 is not included inside the spectral beam-combining structure.
Example 1
Based on the principle shown in fig. 6, the spectrum beam combining device structure of the present invention, specifically referring to the embodiment shown in fig. 1-3, adopts the combination of the monolithic transmission grating 30 and the translation prism 40, the number of grating lines of the transmission grating 30 is still 1800 lines/mm, the same 17nm combined beam spectrum bandwidth is maintained, the focal length f of the conversion lens 20 can be reduced to 100mm, the physical distance from the laser chip to the last transmission grating is directly reduced to 200mm without considering the folding effect of the transmission grating 30 on the light path, and the folding effect of the translation prism 40 is superimposed, and the physical distance is shorter, namely, the space dimension in the Z direction is at least changed to 1/2 of the original space dimension. Meanwhile, the diffracted optical path is superimposed with the incident laser light, and the translating prism 40 is placed next to the transmission grating 30 (refer to the embodiment shown in fig. 3), there is no need to consider the increase in space in the X direction, and thus the size of the entire spectral combining device becomes smaller regardless of the X or Z direction. If two transmissive gratings 30 are used in combination, the same linewidth can shorten the conversion lens focal length to 50nm, and the spatial dimension can be reduced to 1/4 of that in comparative example 1. In addition, in embodiment 1, the external cavity mirror 50 can be directly designed into the optical path, so that the structural stability of the whole spectrum beam combining device is enhanced.
Comparative example 2
Reference (Jun Zhang, hangyu Peng, xihong Fu, et al cw 50W/m2= 10.9diode laser source by spectral beam combining based on atransmission grating[J]Optics express,2013,21 (3): 3627-3632) reports a structure for spectral beam combination based on a transmission grating, the external cavity mirror 50 and the rear 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 30 are respectively located on front and rear focal planes of the conversion lens 20. The laser beam output by the laser cell array 10 passes through the focal length f f And f s Through a focal length f t After the transformation lens 20 of the above is applied, the laser beams are incident on the transmission grating 30 at different angles, wherein the incidence angle of the laser beams output by the laser units in the middle position of the laser unit array 10 is the same as the littrow angle of the transmission grating, specifically, as shown by the first-order diffraction direction 2001 in the figure, the laser beams are diffracted by the transmission grating 30, the diffracted beams coincide with the littrow angle direction of the transmission grating, the diffracted beams are output to the external cavity mirror 50, and only the laser beams vertically incident on the external cavity mirror 50 can return to the original laser units to form resonance. The incident laser beam and the diffracted laser beam of the transmission grating 30 are separated, and in order to achieve high grating diffraction efficiency, the incident angle and the diffraction angle of the transmission grating 30 are both Littrow angles (θlittrow) of the grating, and the included angle between the incident laser beam and the diffracted laser beam is 180-2×θlittrow, in this document, θlittrow is 50.6 °, and the included angle between the incident laser beam and the diffracted laser beam is 78.8 °.
Specifically, as shown in fig. 7, a conversion lens 20 with a focal length of 150mm is used to perform beam conversion on 970nm laser units with anti-reflection (R < 0.5%) on 19 front cavity surfaces, a transmission grating 30 with a grating period of 1600 lines/mm is used to perform diffraction, and then an external cavity mirror 50 with a reflectivity of 20% is used to perform feedback to realize spectrum beam combination, and the output spectrum after beam combination is 24.1nm. As can be seen from the figure, the light exit surface of the laser chip is at least 300mm from the transmission grating 30. Although the angles of the incident laser beam and the diffracted laser beam and the transmission grating 30 are littrow angles, high diffraction efficiency can be obtained, the included angle of the incident laser beam and the diffracted laser beam reaches 78.8 degrees, almost forms a right angle, so that the whole light source structure occupies a large space, if the distance between the external cavity mirror 50 and the transmission grating 30 is 100mm, the dimension of nearly 100mm is directly increased in the X direction, and the external cavity mirror 50 is completely positioned at the far end of the spectrum beam combining structure, so that a stable structure is not easy to realize.
Example 2
Based on the principle shown in fig. 6, the spectrum beam combining device structure of the present invention is adopted, and specifically referring to the embodiments shown in fig. 1-3, the single-chip transmission grating 30 and the translation prism 40 are adopted, the number of grating lines of the transmission grating 30 is still 1600 lines/mm, the same 24.1nm beam combining spectral bandwidth is maintained, the focal length of the conversion lens 20 can be reduced to 75mm, the folding effect of the transmission grating 30 on the light path is not considered, the physical distance from the laser chip to the last transmission grating 30 is directly reduced to 150mm, the folding effect of the transmission grating 30 is superimposed, and the physical distance is shorter, namely, the space dimension in the Z direction is at least changed to 1/2 in comparative example 2. Meanwhile, the diffracted light path and the incident laser light form a superposition, and the translating prism 40 and the transmission grating 30 are placed next to each other (refer to the embodiment shown in fig. 4), so that the size of the direction is greatly reduced without considering the increase in space in the X direction, and thus the size of the entire spectrum combining device becomes smaller regardless of the X or Z direction. The size may be further reduced if more transmission gratings 30 are used. In addition, in embodiment 2, the external cavity mirror 50 can be directly designed into the optical path of the laser beam, so that the stability is greatly improved compared with the structure shown in fig. 6, and the structural stability of the whole spectrum beam combining device is obviously enhanced.
While embodiments of the present invention have been illustrated and described above, it will be appreciated that the above described embodiments are illustrative and should not be construed as limiting the invention. Variations, modifications, alternatives and variations of the above-described embodiments may be made by those of ordinary skill in the art within the scope of the present invention.
The above embodiments of the present invention do not limit the scope of the present invention. Any other corresponding changes and modifications made in accordance with the technical idea of the present invention shall be included in the scope of the claims of the present invention.
Claims (7)
1. The spectrum beam combining device is characterized by comprising a laser unit, a conversion lens, a transmission grating, a translation prism and an external cavity mirror; the transmission grating is positioned in the focal length doubling range of the transformation lens, the front cavity surface of the laser unit is positioned on the front focal plane of the transformation lens, and the outer cavity mirror is positioned on the front focal plane of the transformation lens; the spectrum beam combining device takes a Littrow angle of a normal line of the transmission grating as an optical axis, and the external cavity mirror is perpendicular to the optical axis; the translation prism is an optical element with the light beam translation capability; the incident light of the translation prism and the emergent light of the translation prism are parallel to each other; the translation prism is a right-angle triangular prism or a plane reflecting mirror combination;
the optical path of the spectrum beam combining device comprises a spectrum beam combining direction and a non-spectrum beam combining direction;
in the spectrum beam combining direction, the laser unit outputs laser beams, the laser beams are acted by the transformation lens and are incident to the transmission grating at different angles, and the laser beams are diffracted by the transmission grating and then are incident to the translation prism; the laser beams output by the laser unit are overlapped on the transmission grating and finally enter the external cavity mirror after entering the conversion lens again;
in the non-spectrum beam combining direction, the laser beam output by the laser unit enters the translation prism after passing through the transformation lens and the transmission grating, translates in the y direction, returns to enter the transmission grating and the transformation lens, and enters the external cavity mirror;
the number of the transmission gratings is two or more, and adjacent transmission gratings are not parallel to each other.
2. The spectral beam combining apparatus of claim 1, further comprising a compensation mirror, the compensation mirror in combination with the conversion lens forming an imaging mirror, imaging the front facet of the laser unit to the external cavity mirror.
3. The spectral beam combining apparatus of claim 1, wherein the transmission grating is a negative first order transmission grating, the negative first order diffraction efficiency of the transmission grating is greater than 90%, and the diffraction polarization direction of the transmission grating matches the polarization direction of the laser beam.
4. The spectral beam combining apparatus of claim 1, wherein the laser units comprise a center laser unit and an edge laser unit, each of the laser units outputting a laser beam of a different wavelength, respectively.
5. The spectral beam combining apparatus of claim 4, wherein the incident angle and the diffraction angle of the laser beam outputted from the central laser unit and the transmission grating are ritrol angles.
6. The optical spectrum beam combining apparatus as claimed in claim 1, wherein the laser unit comprises a laser device and an optical element, the optical element performs at least one of collimation, shaping or polarization direction adjustment on the laser beam output by the laser device, and the laser device is coated with an antireflection film on an end face of the output laser beam; the laser device is a semiconductor laser, a fiber laser or an all-solid-state laser.
7. A method of spectral beam combination, characterized in that it is achieved by a spectral beam combination device according to any one of claims 1 to 6, comprising the steps of:
s1, outputting laser beams by the laser unit in the spectrum beam combining direction, wherein the laser beams are incident to the transmission grating at different angles under the action of the conversion lens, and are diffracted by the transmission grating and then are incident to the translation prism; the laser beam is incident to the external cavity mirror after passing through the transmission grating and the transformation lens;
s2, in the non-spectrum beam combining direction, the laser beam output by the laser unit is incident to the translation prism after passing through the transformation lens and the transmission grating, is translated in the y direction, then returns to be incident to the transmission grating and the transformation lens, and then is incident to the external cavity mirror.
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