CN106684702A - Apparatus for realizing semiconductor laser spectrum beam combination by utilizing double gratings - Google Patents

Abstract

A device for combining semiconductor laser beams by using double gratings, comprising: a semiconductor laser light source, a conversion lens, a first diffraction grating, a second diffraction grating, and an output coupling mirror; The diffraction effect performs secondary dispersion on the beam. After the feedback of the output coupling mirror, the lasers of each unit are locked at different wavelengths, so that the beams overlap to achieve a single beam of high-power and high-brightness laser output. The present invention uses two gratings as diffractive elements, which doubles the dispersion ability. When applied to the spectrum combining of semiconductor lasers, the spectral broadening can be reduced, and more beam combining units are added in the gain curve of the semiconductor laser gain material. The output power is increased while the length of the resonant cavity is compressed, so that the laser has a compact structure and improves stability.

Description

A Device Using Double Gratings to Realize Spectral Beam Combination of Semiconductor Lasers

technical field

The present invention relates to the technical field of semiconductor lasers, and in particular to a semiconductor laser spectral beam combining method that utilizes double gratings to realize beam combining of multiple semiconductor laser units into high-power and high-brightness laser output through external cavity feedback. device.

Background technique

Semiconductor lasers have the advantages of low cost, long life, small size, and high reliability. They have broad application prospects in industrial processing, pumping, medical treatment, and communications. Whether the brightness of semiconductor lasers can be further improved is an important factor restricting the future development of semiconductor lasers. The brightness of the laser beam is determined by the output power and beam quality. The higher the power, the better the beam quality and the higher the brightness. The application fields of semiconductor lasers are also wider.

Beam combining technology is currently a common method for realizing high-brightness semiconductor lasers. Conventional beam combining technologies include beam shaping, polarization combining, and wavelength combining. Beam shaping improves the beam quality by balancing the optical parameter product in the fast and slow axis directions, but the laser brightness does not increase; polarization beam combining can only double the brightness by combining light from two polarization directions into one beam; wavelength combining is affected by Due to the limitation of coating technology, the number of beam combining units generally does not exceed 5, and the improvement of power and brightness is also limited.

Spectral beam combining is a novel beam combining technology. Daneu V et al. proposed this method and discussed its principle in detail (Daneu V, Sanchez A, Fan T Y, et al. Spectral beam combining of a broad-stripe diode laser array in an external cavity. [J]. Optics Letters, 2000, 25(6): 405-7.). Through the feedback effect of the external cavity and the dispersion effect of the grating, each light-emitting unit is locked at different wavelengths, so as to obtain the same diffraction angle to realize beam combining. The advantages of spectral beam combining are as follows: First, the output light of multiple single-tube semiconductor lasers is combined to achieve power superposition, while the beam quality can be maintained at the high beam quality of a single light-emitting unit, which greatly improves the brightness of the semiconductor laser ; Second, several light-emitting units can share beam-combining elements, and the feature of not limiting the number of beam-combining units can greatly reduce costs and have greater advantages in application. Therefore, spectral beam combining technology has become an important topic in the field of high-power semiconductor lasers.

The current spectral beam combining technology uses a single grating as a diffractive element, such as the domestic patent with the announcement number CN102868089A and the title "A device and method for realizing multi-semiconductor laser beam combining with single grating external cavity feedback"; in addition, the announcement number is CN204156286U In the domestic patent titled "A Diode Laser Spectrum Synthesis Device Based on Double Grating External Cavity Feedback", although two gratings are used, the function of the first grating is similar to that of a transformation lens, which is used to converge multiple beams at one point , only the second grating plays the role of diffraction beam combining, and this method does not have the function of compressing the spectrum broadening. The diffraction ability of a single grating is limited, so that the spectral broadening after beam combining is relatively large, and the spectral broadening of laser beams after beam combining is compressed as much as possible, so adding more beam combining units within a certain gain bandwidth is the key to increasing the spectral beam combining power and brightness key. In the traditional spectral beam combining technology, there are two ways to compress the spectral broadening: first, reduce the period of the grating, but in order to ensure the diffraction effect of the grating, the minimum period of the grating must be greater than one-half of the light wavelength, which improves the compressed spectrum Limited; second, increase the focal length of the positive lens, but increasing the focal length of the positive lens will increase the cavity length of the beam combining system, multiply the adjustment accuracy and difficulty, and at the same time, the structural size is too large and the stability of the system will be reduced. The current two methods are limited in practical application, but the double grating structure proposed by the present invention can effectively solve this problem.

Contents of the invention

In order to solve the problem of limiting the number of beam combining units after the spectrum is broadened so that the spectrum broadens beyond the optimal gain range of the laser during the process of spectral beam combining, the present invention proposes a semiconductor laser beam combining method using double gratings The device uses two gratings to compress the spectral broadening of the output beam by double the dispersion capability of the single grating.

The technical solution adopted by the present invention to solve the technical problems is as follows:

A device for combining semiconductor laser beams by using double gratings, comprising: a semiconductor laser light source, a conversion lens, a first diffraction grating, a second diffraction grating and an output coupling mirror;

The semiconductor laser light source is located on the front focal point of the conversion lens, and the first diffraction grating is located in front of the rear focal point of the conversion lens. The semiconductor laser light source is a parallel beam of light emitting points, and the parallel beam After being converged by the conversion lens, the central beam of the diffracted beam is incident on the first diffraction grating at the Littrow angle and diffracted by the first diffraction grating, and the central beam of the diffracted beam is incident on the first diffraction grating at the Littrow angle. The second diffraction grating is to adjust the position of the second diffraction grating to minimize the light spot on the second diffraction grating; the light beam diffracted by the second diffraction grating is vertically incident on the output coupling mirror and combined for output.

After being diffracted on the first diffraction grating, the angle difference of each beam is reduced by half, and overlapped on the second diffraction grating to form a small spot, and after being diffracted by the second diffraction grating, the angle difference of each beam is reduced to zero, that is, the same The diffraction angle is , the laser output is obtained after the output coupling mirror is incident vertically, and the beams are superimposed in the near field and the far field to realize beam combining.

The semiconductor laser light source includes a semiconductor laser array and a beam collimation system. A laser resonant cavity is formed between the semiconductor laser array and the output coupling mirror, and the beam oscillates back in the laser resonant cavity.

The beam collimating system includes fast axis collimating mirrors and slow axis collimating mirrors placed front and back; The light in the fast axis direction of the laser array is collimated by the first cylindrical lens, and the light in the slow axis direction is collimated by the second cylindrical lens after being rotated by the 45° oblique cylindrical lens array.

The front surface of the semiconductor laser array is coated with an anti-reflection film with a reflectivity of <1%, and the back cavity is coated with a high-reflection film with a reflectivity of >95%.

The first diffraction grating and the second diffraction grating are transmissive or reflective gratings, the grating periods are equal, the wavelength of the highest diffraction efficiency matches the wavelength of the semiconductor laser light source, and the diffraction efficiency of the first order or -1 order greater than 90%, and the first diffraction grating and the second diffraction grating are polarization-independent gratings or gratings whose polarization direction is the same as that of the semiconductor laser light source.

The output coupling mirror is a partial reflection mirror with a reflectivity of 5% to 30%, and is perpendicular to the diffracted light direction of the second diffraction grating.

The advantages of the present invention are: using the double grating as the beam combining element, under the condition that the laser cavity length is constant, the laser spectral broadening can be shortened to half of the original, within the gain curve of the semiconductor laser, and in the high diffraction efficiency of the grating In the wavelength range, the number of beam combining units can be doubled, and the power and brightness can be doubled; on the other hand, the compression spectrum broadening can make the monochromaticity of laser output better, reduce chromatic aberration, and increase beam combining efficiency.

Description of drawings

Fig. 1 is a schematic structural diagram of a device for realizing semiconductor laser spectral beam combining by using double gratings in the present invention.

Fig. 2 is a schematic diagram of the optical path of the double grating.

Fig. 3 is a schematic diagram of a semiconductor laser array and a fast-slow axis collimating lens.

Fig. 4 is a spectrum diagram of the output beam of the present invention.

Fig. 5 is a spectrum diagram of output light using a traditional spectrum combining structure.

In the figure, 1 is the semiconductor laser light source; 2 is the conversion lens; 3 is the first diffraction grating; 4 is the second diffraction grating; 5 is the output coupling mirror; 6 is the laser output after beam combining; Unit beams; 11', 12', 13' are beams diffracted by the first grating 3; 14 is a semiconductor laser array; 15 is a fast axis collimator; 16 is a slow axis collimator.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

As shown in Fig. 1 to Fig. 2, a kind of device that utilizes double grating to realize semiconductor laser spectral beam combining comprises: semiconductor laser light source 1, transformation lens 2, first diffraction grating 3, second diffraction grating 4, output coupling mirror 5; The laser light source 1 is placed at the front focal length of the conversion lens 2 , and the first diffraction grating 3 is placed in front of the back focus of the conversion lens 2 . The semiconductor laser light source 1 emits multiple beams of parallel light. After being focused by the conversion lens 2, the beams of each light emitting unit enter the first diffraction grating 3 at different angles, and the central beam enters at the Littrow angle. After being diffracted by the first diffraction grating 3, the angle difference of each light beam is reduced by half, and is diffracted onto the second diffraction grating 4. The central beam is also incident at the Littrow angle, and the position of the second diffraction grating 4 is moved back and forth, so that each beam emits light. The light beams of the units completely overlap on the second diffraction grating 4 with the smallest light spot. After the diffraction of the second diffraction grating 4, the angle difference of each light beam is reduced to zero, that is, the same diffraction angle is arranged, and the output coupling mirror 5 is vertically incident. Due to the feedback effect of the output coupling mirror 5, the rear cavity surface of the semiconductor laser light source 1 A laser cavity is formed between the output coupling mirror 5, and the light beam oscillates back in the laser cavity to obtain laser output. Each light beam emitted by the semiconductor laser light source 1 is incident on the first diffraction grating 3 and the second diffraction grating 4 at a monotonically changing angle, and at the same time is feedback-locked by the external cavity at a monotonically changing wavelength, so that it is possible to achieve different incident angles. Obtain the same output angle and achieve beam combining. While maintaining the beam quality of a single light-emitting point, the power is the sum of the power of each unit. As shown in Figure 2, the angle between two adjacent beams of incident beams 11, 12, and 13 is twice the angle between two adjacent beams of incident beams 11', 12', and 13', that is, the diffraction effect originally completed by a grating Evenly distributed to the two gratings, the diffraction ability is doubled, and the spectral broadening is compressed to half compared with the traditional solution.

As shown in FIG. 3, the semiconductor laser light source 1 includes a semiconductor laser array 14, a fast-axis collimator mirror 15 and a slow-axis collimator mirror 16. The semiconductor laser array 14 includes several light-emitting units, and each light-emitting unit is arranged at equal intervals. The front cavity surface of the semiconductor laser array 14 is coated with an anti-reflection film, and the reflectivity of the cavity surface is less than 1%, and the back cavity surface is coated with a high-reflection film, and the cavity surface reflectivity is greater than 95%; The axis collimating mirror 16 is a microcylindrical lens array, and the two constitute a beam collimating system. After the beam passes through the collimating system, the divergence angle is compressed, and the fast axis collimating mirror 15 and the slow axis collimating mirror 16 are glued together, and Bonded on the light-emitting end face of the semiconductor laser array 14.

The above-mentioned semiconductor laser light source 1 can be replaced by a plurality of collimated laser units, or a plurality of collimated laser arrays, or a combination of a plurality of collimated laser arrays consisting of a laser line array or stacked array.

The above-mentioned first diffraction grating 3 and second diffraction grating 4 are transmissive gratings or reflective gratings, the grating periods are equal, and the first-order or -first-order diffraction efficiency is greater than 90%, and the wavelength of the highest diffraction efficiency is the same as that of the semiconductor laser light source 1. The appearance is matched; the grating is polarization-independent, or the grating whose polarization direction is the same as the laser polarization direction, and has a high damage threshold.

The above-mentioned output coupling mirror 5 is a partial reflection mirror, which is perpendicular to the incident direction of the light beam, and has a reflectivity of 5%-30% at the time of normal incidence, and has low loss at the wavelength of the semiconductor laser light source 1 .

In the beam combining scheme above, the semiconductor laser array can be extended to multiple semiconductor laser arrays, or multiple semiconductor laser modules, and the power of the output light can be increased by several times of the participating beam combining units.

Example:

The specific implementation process of the double grating-based external cavity feedback semiconductor spectral beam combining system of the present invention is as follows:

The center wavelength of semiconductor laser light source 1 is 945nm, including 19 light-emitting units, the fast-axis divergence angle of a single light-emitting point beam is 35°, the slow-axis divergence angle is 7°, and the beam is collimated by a 45° oblique cylindrical lens array and a cylindrical lens After the beam, the divergence angle of the fast axis is compressed to 0.5°, and the divergence angle of the slow axis is compressed to 4°. The front cavity of the laser array is coated with an anti-reflection film, and the reflectivity is less than 0.5%, and the rear cavity is coated with a high-reflection film, and the reflectivity is greater than 99%.

Assuming that the diffraction order of the first diffraction grating 3 and the second diffraction grating 4 is 1st order, the diffraction efficiency is greater than 90%, the grating period is d, and the incident angles of the unit light beams on the first diffraction grating 3 are respectively θ ₁ , θ ₂ ... θ ₁₉ , the diffraction angles are θ _d1 , θ _d2 ... θ _d19 , due to the dispersion effect of the double grating and the feedback of the external cavity, the wavelength of each unit changes monotonously with the incident angle, respectively λ ₁ , λ ₂ ... λ ₁₉ , have the following relationship:

λ ₁ =d(sinθ ₁ +sinθ _d1 );

λ ₂ =d(sinθ ₂ +sinθ _d2 );

...

λ ₁₉ =d(sinθ ₁₉ +sinθ _d19 ).

Wherein, the difference between the incident angles of any two adjacent unit beams can be regarded as a fixed value Δθ.

The second diffraction grating 4 is placed behind the first diffraction grating 3 to minimize the light spot on the second diffraction grating. The incident angles of each unit light beam on the second diffraction _grating 4 are _{θ i1} , _{θ i2 .} is a fixed value Δθ ₁ , and Δθ ₁ = Δθ/2, there is the following relationship:

λ ₁ =d(sinθ _i1 +sinθ _di1 );

λ ₂ =d(sinθ _i2 +sinθ _di2 );

...

λ ₁₉ =d(sinθ _i19 +sinθ _di19 ).

Since the light-emitting points are locked at different wavelengths, θ _di1 =θ _di2 = . . . = θ _di19 . The spectral diagram of the output laser after beam combining is shown in Figure 4, and the spectral broadening is about 7.0nm. If the structure of single grating spectral beam combining is adopted, the spectral diagram of the output laser is shown in Figure 5, and the spectral broadening is 13.7nm. Compared with the single-grating beam combining structure, the double-grating beam combining in the present invention can compress the output light spectrum to approximately half of the original.

Claims (8)

1. a kind of utilization double grating realizes that lasing spectrum of semiconductor lasers closes the device of beam, it is characterised in that including：Semiconductor laser Light source (1), transform lenses (2), the first diffraction grating (3), the second diffraction grating (4) and output coupling mirror (5)；

Described semiconductor laser light source (1) in the front focus of described transform lenses (2), the first described diffraction light Before the rear focus of described transform lenses (2), described semiconductor laser light source (1) is multiple luminous points to grid (3) Collimated light beam, after the transformed lens of collimated light beam (2) is converged, its central light beam incides described first with Littrow angle Diffraction grating (3), and through the first diffraction grating (3) diffraction, the central light beam of its diffracted beam incides institute with Littrow angle The second diffraction grating (4) stated, the position of the second diffraction grating of adjustment (4) makes the hot spot on the second diffraction grating (4) minimum； Incided after described output coupling mirror (5) closes beam through the beam orthogonal after the second diffraction grating (4) diffraction and exported.

2. utilization double grating according to claim 1 realizes that lasing spectrum of semiconductor lasers closes the device of beam, it is characterised in that The differential seat angle of each light beam reduces half after diffraction on first diffraction grating (3), is overlapped as one small on the second diffraction grating (4) Hot spot, zero is decreased to by the differential seat angle of each light beam after the diffraction of the second diffraction grating (4), that is, have the identical angle of diffraction, vertically Laser output is obtained after incident output coupling mirror (5), each light beam is superimposed near field and far field, realizes closing beam.

3. utilization double grating according to claim 1 realizes that lasing spectrum of semiconductor lasers closes the device of beam, it is characterised in that institute The semiconductor laser light source (1) stated includes semiconductor laser array (14) and passing through a collimating system, and described semiconductor swashs Laserresonator, light beam feedback oscillation in laserresonator are formed between light device array (14) and output coupling mirror (5).

4. utilization double grating according to claim 3 realizes that lasing spectrum of semiconductor lasers closes the device of beam, it is characterised in that institute Fast axis collimation mirror (15) and slow axis collimating mirror (16) that the passing through a collimating system stated is placed before and after including.

5. utilization double grating according to claim 3 realizes that lasing spectrum of semiconductor lasers closes the device of beam, it is characterised in that institute The first post lens, 45 ° of batter post lens arrays and the second post lens that the passing through a collimating system stated is placed before and after including, described half The light of conductor laser array (14) quick shaft direction is by the first post collimated, the slow axis after 45 ° of batter post lens arrays rotate The light in direction is by the second post collimated.

6. utilization double grating according to claim 3 realizes that lasing spectrum of semiconductor lasers closes the device of beam, it is characterised in that：Institute The front end face plating anti-reflection film of the semiconductor laser array (14) stated, reflectivity<1%, rear facet plating high-reflecting film, reflectivity> 95%.

7. realize that lasing spectrum of semiconductor lasers closes the device of beam, its feature according to any described utilization double gratings of claim 1-6 It is：Described the first diffraction grating (3) and the second diffraction grating (4) is transmission-type or reflective gratings, and screen periods are equal, The wavelength of its maximum diffraction efficiency matches with the wavelength of semiconductor laser light source (1), in 1 grade or the diffraction efficiency of -1 level More than 90% and described the first diffraction grating (3) and the second diffraction grating (4) are to polarize unrelated grating or be polarization direction With the polarization direction identical grating of semiconductor laser light source (1).

8. realize that lasing spectrum of semiconductor lasers closes the device of beam, its feature according to any described utilization double gratings of claim 1-6 It is：Described output coupling mirror (5) is partially reflecting mirror, and reflectivity is 5%~30%, with spreading out for the second diffraction grating (4) Penetrate light direction vertical.