JP2017204530A - External cavity diode laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an external cavity diode laser device capable of reducing the length of an external laser resonator.SOLUTION: An external cavity diode laser device 40 includes a plurality of external resonators configured between first wavelength dispersion elements 10a, 10b, 10c, 10d, 10e disposed on a side of a rear side end face of a semiconductor laser element 1 and front side end faces 2a, 2b, 2c, 2d, 2e of semiconductor laser elements 1a, 1b, 1c, 1d, 1e, respectively. In the external cavity diode laser device, a plurality of laser beams 100a, 100b, 100c, 100d, 100e emitted from the front side end faces 2a, 2b, 2c, 2d, 2e are superimposed on a second wavelength dispersion element 14 by passing through a coupling optical system 13.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an external resonant semiconductor laser device that outputs a beam of a plurality of wavelengths emitted from a plurality of front end faces by combining them with wavelength dispersion of a wavelength dispersion element.

  In a conventional external resonant semiconductor laser device, in order to improve the brightness of a semiconductor laser, beams from a plurality of light emitting points are superimposed on a wavelength dispersion element using a lens, and each wavelength dispersion property of a wavelength dispersion optical element is used for each. A technique is known in which an external laser resonator is formed by combining a beam from a light emitting point and installing a partial transmission mirror on the combined beam (see, for example, Patent Document 1).

US Pat. No. 6,192,062

  However, with the technique shown in Patent Document 1, since the length of the external laser resonator is increased, the resonator loss is increased, so that the oscillation efficiency is lowered, and the laser output or beam quality is a disturbance such as vibration. There was a problem of being greatly influenced by.

  The present invention has been made in view of the above, and an object thereof is to obtain an external resonant semiconductor laser device capable of shortening the length of an external laser resonator.

  In order to solve the above-described problems and achieve the object, the present invention is configured between the first wavelength dispersion element disposed on the rear end face side of the semiconductor laser element and the front end face of the semiconductor laser element. A plurality of external laser resonators are provided. In the present invention, a plurality of laser beams emitted from the front end face are superimposed on the second wavelength dispersion element through the coupling optical system.

  According to the present invention, it is possible to realize an external resonant semiconductor laser device capable of reducing the length of the external laser resonator.

  In addition, since the oscillation beam of the external laser resonator is emitted from the front end face of the semiconductor laser element, it is possible to arrange optical elements corresponding to each of the plurality of oscillation beams, and it is possible to reduce the size of the apparatus. .

  Furthermore, even if the oscillation wavelength is changed, the emission direction does not change, and a stable oscillator can be configured.

1 is a perspective view schematically showing an external resonant semiconductor laser device according to a first embodiment of the present invention. FIG. 2 is a top view schematically showing the external resonant semiconductor laser device according to the first embodiment. 1 is a side view schematically showing an external resonant semiconductor laser device according to a first embodiment. The figure which shows the measurement result of the reflectance of the rear side end face of the usual semiconductor laser which does not constitute the external laser resonator FIG. 2 is a top view schematically showing an external resonant semiconductor laser device used for comparison with the external resonant semiconductor laser device according to the first embodiment. The figure which shows the spectrum of the laser oscillation of the external resonance semiconductor laser apparatus used for description of contrast with the external resonance semiconductor laser apparatus concerning Embodiment 1 FIG. 3 is a top view schematically showing an external resonant semiconductor laser device according to a second embodiment of the present invention. FIG. 6 is a perspective view schematically showing an external resonant semiconductor laser device according to a third embodiment of the present invention. FIG. 4 is a top view schematically showing an external resonant semiconductor laser device according to a third embodiment. FIG. 5 is a side view schematically showing an external resonant semiconductor laser device according to a third embodiment. FIG. 6 is a top view schematically showing an external resonant semiconductor laser device according to a fourth embodiment of the present invention. Side view schematically showing an external resonant semiconductor laser device according to a fourth embodiment.

  Hereinafter, an external resonant semiconductor laser device according to an embodiment of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a perspective view schematically showing an external resonant semiconductor laser device 40 according to the first embodiment of the present invention. FIG. 1 also shows the directions of the X, Y, and Z axes. FIG. 2 is a top view schematically showing the external resonant semiconductor laser device 40 according to the first embodiment. FIG. 2 is a view of the external resonant semiconductor laser device 40 as viewed in the Y-axis direction. FIG. 3 is a side view schematically showing the external resonant semiconductor laser device 40 according to the first embodiment. FIG. 3 is a view of the external resonant semiconductor laser device 40 as viewed in the X-axis direction.

  The external resonant semiconductor laser device 40 includes a semiconductor laser element 1 (1a, 1b, 1c, 1d, and 1e), beam collimating elements 11 and 12 that are optical elements, and a first wavelength dispersion element 10 (10a, 10b, and 10c). , 10d, 10e), a coupling optical system 13, and a second wavelength dispersion element 14.

  The external resonant semiconductor laser device 40 includes front end surfaces 2a, 2b, 2c, 2d, and 2e of the plurality of semiconductor laser elements 1a, 1b, 1c, 1d, and 1e (hereinafter collectively referred to as the front end surface 2). This laser beam is superposed on one beam by using the wavelength dispersion effect of the second wavelength dispersion element 14. Note that the number of the plurality of semiconductor laser elements 1 may not be five as described above, and is not limited as long as it is plural.

  In the external resonance semiconductor laser device 40, an optical system including the front end face 2 of the semiconductor laser element 1, the beam collimating element 11, and the first wavelength dispersion element 10 is a laser resonator. In the external cavity semiconductor laser device 40, the front end face 2 (2a, 2b, 2c, 2d, 2e) is subjected to a partial reflection coating, and the rear end face 3 (3a, 3b, 3c, 3d, 3e). Anti-reflective coating is applied. Thus, a laser resonator is configured between the front end face 2 and the first wavelength dispersion element 10.

  In the following description, the laser resonator configured between the front end face 2 and the first wavelength dispersion element 10 as described above is referred to as an external laser resonator. Therefore, in the external resonant semiconductor laser device 40, there are a plurality of external laser resonators between the front end face 2 and the first wavelength dispersion element 10 corresponding to the semiconductor laser elements 1a, 1b, 1c, 1d, and 1e, respectively. Composed. Actually, the beam reciprocates in the external laser resonator. First, the propagation of the beam in the direction from the front end face 2 toward the first wavelength dispersion element 10 will be described.

  The beam propagating from the front end face 2 to the first wavelength dispersion element 10 first propagates through the semiconductor laser element 1 from the front end face 2 to the rear end face 3 and is emitted from the rear end face 3. At this time, the beam emitted from the semiconductor laser element 1 is emitted while diverging. If it is left as it is, the beam returning from the first wavelength dispersion element 10 will return as a much larger beam than the rear end face 3, and most of the beam will be lost and emitted out of the external laser resonator. As a result, an external resonator cannot be configured. Therefore, in order to couple with the mode of the external laser resonator, the beam generated from the rear end face 3 of the semiconductor laser element 1 is almost collimated by the beam collimating element 11. Here, the coupling with the mode means that the beam diameter emitted from the rear side end face 3 and the beam diameter returned to the rear side end face 3 are substantially equal.

  The beam collimating element 11 can be a spherical lens, an aspherical lens, a cylindrical lens, or a mirror having a curvature. The beam collimating element 11 is not limited to one each, and may be a combination thereof.

  The divergence angle of the beam generated from the semiconductor laser element 1 is generally anisotropic, and the divergence angle differs between the X-axis direction and the Y-axis direction. The X-axis direction of the semiconductor laser element 1 is called the fast axis direction, and diverges at a large angle of about 30 ° in half angle. The Y-axis direction is called the slow axis direction, and generally diverges at about 4 degrees in half-width if the width of the front side end face 2 is about 100 μm. The beam quality at this time is about 10 times the diffraction limit in the slow axis direction while the fast axis direction is almost the diffraction limit. Therefore, as the beam collimating element 11, it is desirable to use a combination of an aspheric lens and a cylindrical lens that is different in the X-axis direction and the Y-axis direction.

  The beams substantially collimated by the beam collimating element 11 are incident on the first wavelength dispersion element 10 at incident angles α1, α2, α3, α4, and α5 shown in FIG.

  The 1st wavelength dispersion element 10 is an element which has a wavelength dispersion effect as the name says, a diffraction grating, a prism, a grism, TFF (Thin Film Filter), VBG (Volume Bragg Grating), FBG (Fiber Bragg Grating), an etalon. Such elements are generally used.

  A diffraction grating is an element in which a large number of parallel grooves are cut at equal intervals on a flat or concave substrate, and includes a reflection type diffraction grating and a transmission type diffraction grating. Diffraction is a phenomenon in which light travels behind the obstacle. When light enters the diffraction grating, the light is strengthened at an angle determined for each wavelength, and the wavelength can be selected by taking out the strengthened light. .

  TFF is an element in which a dielectric multilayer film is laminated on a substrate. A dielectric multilayer film is a thin film made by stacking dielectrics having different refractive indexes in multiple layers. Reflection occurs at the interface of materials having different refractive indexes, and the magnitude thereof depends on the refractive index difference. The dielectric multilayer film can be designed to transmit only 100% of a certain wavelength and reflect 100% of other wavelengths by the effects of multiple reflection and multiple interference. In TFF, the transmission bandwidth can be reduced from about 0.1 nm to about 1 nm, and the transmission wavelength can be made variable between about 20 nm and about 40 nm by changing the incident angle of light.

  VBG and FBG are elements in which a periodic refractive index change is formed inside glass. The refractive index change works as a diffraction grating, and can reflect only light having a wavelength that satisfies the Bragg reflection condition created by the period of the diffraction grating.

  In the configuration of the external resonant semiconductor laser device 40 shown in FIGS. 1 to 3, it is assumed that a reflective diffraction grating is used as the first wavelength dispersion element 10. When a transmission type diffraction grating, TFF, VBG, or the like is used as the first wavelength dispersion element 10, the configuration is different from those shown in FIGS. 1 to 3, but the same effect as when a reflection type diffraction grating is used is obtained. Can do.

  The beam incident on the first wavelength dispersion element 10 has a wavelength width corresponding to the gain width of the semiconductor laser element 1 immediately after being emitted from the semiconductor laser element 1, but the wavelength dispersion effect is present in the external laser resonator. By arranging the first wavelength dispersion element 10 having the above, only a specific wavelength can be fed back to the semiconductor laser element 1, and only a specific wavelength is amplified by the semiconductor laser element 1. .

  At this time, as shown in FIG. 2, the incident angles from the semiconductor laser elements 1a, 1b, 1c, 1d, 1e to the first wavelength dispersion elements 10a, 10b, 10c, 10d, 10e are α1, α2, α3, respectively. Since they are different from α4 and α5, the wavelengths fed back from the first wavelength dispersion elements 10a, 10b, 10c, 10d, and 10e to the semiconductor laser elements 1a, 1b, 1c, 1d, and 1e are also different. Therefore, the laser beams 100a, 100b, 100c, 100d, and 100e emitted from the front end faces 2a, 2b, 2c, 2d, and 2e of the semiconductor laser elements 1a, 1b, 1c, 1d, and 1e (hereinafter collectively referred to as lasers). (Referred to as beam 100) are output at different wavelengths. In FIG. 2, the distance between the optical axes from the laser beam 100a to the laser beam 100e is indicated by d, and the required distance from the rear side end face 3 to the beam collimating element 11 is indicated by M.

  The laser beams 100 a, 100 b, 100 c, 100 d, and 100 e emitted from the semiconductor laser elements 1 a, 1 b, 1 c, 1 d, and 1 e and having passed through the beam collimating element 12 pass through the coupling optical system 13 and pass through the coupling optical system 13. It is spatially superimposed on the two-wavelength dispersion element 14.

  The beam collimating element 12 may be a spherical lens, an aspherical lens, a cylindrical lens, or a mirror having a curvature. The beam collimating element 12 is not limited to one each, and may be a combination thereof.

  The coupling optical system 13 is shown as a single lens in FIGS. 1 to 3, but anything that changes the direction of the optical axis, such as a mirror, a curvature mirror, a cylindrical lens, a prism, or a combination thereof, can be used. Good. However, an element having a chromatic dispersion effect, such as the second chromatic dispersion element 14, changes the characteristics of the chromatic dispersion effect depending on the incident angle of the beam. Therefore, in order to prevent the beam quality after superimposition from deteriorating, it is desirable that the laser beams 100a, 100b, 100c, 100d, and 100e are incident on the second wavelength dispersion element 14 after being collimated.

  The second wavelength dispersion element 14 is not limited as long as the first wavelength dispersion element 10 is an element having a wavelength dispersion effect, and is a diffraction grating such as a reflection diffraction grating or a transmission diffraction grating, a prism, a diffraction grating and a prism. A grism, a VBG, a TFF, a dichroic mirror, or the like, which is a combination of elements, can be used. However, when beams are combined using a VBG or dichroic mirror, the same number of types of VBGs or dichroic mirrors as the number of wavelengths is required. It is desirable from the viewpoint of ease of assembly. In addition, the larger the wavelength dispersion effect, that is, the larger the difference in the diffraction angle or the refraction angle when two beams having different wavelengths are incident, the more space-saving from the plurality of semiconductor laser elements 1a, 1b, 1c, 1d, and 1e. It is desirable to use a diffraction grating rather than a prism. In the configuration of the external resonant semiconductor laser device 40 shown in FIGS. 1 to 3, it is assumed that a reflective diffraction grating is used as the second wavelength dispersion element 14.

  Laser beams 100a, 100b, 100c, 100d, and 100e having different wavelengths, which are spatially superimposed on the second chromatic dispersion element 14, rotate depending on the chromatic dispersion effect of the second chromatic dispersion element 14, that is, the wavelength. The beams are combined as a single beam depending on the characteristic that the folding angle or the refraction angle changes, and output as a laser beam 101 after the combination.

  Next, the effect brought about by the external resonant semiconductor laser device 40 according to the first embodiment will be described in detail.

  Unlike the external resonance semiconductor laser device 40, when the laser output is performed by forming the laser resonator only with the semiconductor laser element without forming the external laser resonator, the reflectance of the rear end face is about 85% to 90%. is there. FIG. 4 is a diagram showing the measurement results of the reflectance of the rear end face of a normal semiconductor laser that does not constitute an external laser resonator. The semiconductor laser element of FIG. 4 oscillates near the wavelength of 980 nm. As shown in FIG. 4, it can be seen that the reflectance of the rear end face at the wavelength of 980 nm is 90% or less.

  Thus, in the external resonant semiconductor laser device 40, in order to achieve an oscillation efficiency equivalent to that of a normal semiconductor laser element alone while configuring an external laser resonator, the first wavelength dispersion element 10 is used. That is, the efficiency of 90% or more is sufficient.

  The oscillation efficiency here refers to a value obtained by dividing the output of the laser beam 100 from the semiconductor laser element 1 by the amount of electric power applied to the semiconductor laser element 1. The efficiency of the first wavelength dispersion element 10 refers to diffraction efficiency when the first wavelength dispersion element 10 is a diffraction grating, and reflection when the first wavelength dispersion element 10 is an element such as VBG. It refers to the rate (sometimes referred to as diffraction efficiency).

  In order to make the diffraction efficiency as close as possible to 100% in a reflective diffraction grating, there is a method of cutting a groove in a dielectric multilayer film laminated on a substrate. However, it is necessary to increase the number of laminated layers, so that the cost is high. Become. In the first wavelength dispersion element 10 of the external cavity semiconductor laser device 40 according to the first embodiment, since the diffraction efficiency only needs to be 90% or more, it is possible to reduce the cost by reducing the number of laminated dielectric multilayer films. Become. Further, as the first wavelength dispersion element 10, a cheap diffraction grating such as a metal reflection type diffraction grating, which is formed by cutting a groove in a metal film laminated on a substrate, is used instead of the dielectric multilayer reflection type diffraction grating. You can also

  Further, only a beam having an output of about 1/5 is propagated to the rear end face 3 side of the semiconductor laser element 1 as compared with the front end face 2 side. In the external resonant semiconductor laser device 40 according to the first embodiment, since the first wavelength dispersion element 10 is disposed on the rear end face 3 side, an inexpensive first wavelength dispersion element 10 for a low-power laser can be selected. And cost reduction can be realized. In addition, since the first wavelength dispersion element 10 is not always irradiated with the high-power beam, the deterioration of the first wavelength dispersion element 10 is small. Therefore, the reliability of the external resonant semiconductor laser device 40 can be improved.

  Further, when an external laser resonator is configured for the semiconductor laser element 1, the semiconductor is caused by causes such as reflection loss of the beam collimating element 11, which is an element disposed in the external laser resonator, and coupling loss due to aberration. There is a possibility that the oscillation efficiency is worse than that when the laser element 1 oscillates alone. However, in the external resonant semiconductor laser device 40 according to the first embodiment, the above-described loss can be compensated by increasing the efficiency of the first wavelength dispersion element 10 to more than 90%. Thereby, in the external resonant semiconductor laser device 40, an external laser resonator that realizes an oscillation efficiency equal to or higher than the oscillation efficiency of the semiconductor laser element 1 during single oscillation can be configured.

  FIG. 2 shows a state in which each of the first wavelength dispersion elements 10 (10a, 10b, 10c, 10d, 10e) is inclined with the Y axis as the central axis. In the case where a diffraction grating is used as the first wavelength dispersion element 10, in order to narrow the wavelength width of the laser beam 100, the number of grooves included in the irradiation region of the beam on the first wavelength dispersion element 10 is increased. There is a need to. Here, in FIG. 2, the grooves of the diffraction grating of the first wavelength dispersion element 10 are carved in parallel to the Y-axis direction. At this time, among the beams irradiated to the diffraction grating of the first wavelength dispersion element 10, if the beam quality in the direction perpendicular to the groove of the diffraction grating, that is, the X-axis direction is good, the narrow oscillation wavelength width It is possible to reduce the beam diameter necessary for obtaining the above, that is, the number of grooves.

Specifically, when comparing the irradiation with a beam whose beam quality is approximately diffraction limited and the irradiation with a beam having a diffraction limit of about 10 times, the beam on the diffraction grating necessary to obtain the same oscillation wavelength width. The diameter can be reduced by about 1/10 in the case of using a beam having a diffraction limit of about 10 times that in the case of using a beam having a diffraction limit of about 10 times. This is expressed by the following mathematical formula (1). Where λ is the center wavelength of the oscillation wavelength width Δλ, m is the diffraction order, N is the number of grooves per mm, W is the beam diameter on the diffraction grating, and M ² is the beam quality.

  As described above, the semiconductor laser device 1 generally has a beam quality better for a beam diverging in the X-axis direction, which is the fast axis direction, than for a beam diverging in the Y-axis direction, which is the slow axis direction. Therefore, as shown in FIG. 2, the first wavelength dispersion element 10 is tilted about the Y-axis center, and the beam is irradiated in the X-axis direction that is perpendicular to the grooves of the diffraction grating, that is, the fast axis direction. Then, the beam diameter for obtaining a required wavelength width can be reduced. As a result, the size of the first wavelength dispersion element 10 can be reduced, leading to cost reduction of the external resonant semiconductor laser device 40.

  Further, by arranging the first wavelength dispersion element 10 on the rear end face 3 side of the semiconductor laser element 1, even if the inclination angle of the first wavelength dispersion element 10 changes, the emission angle of the laser beam 100 does not change. Since the oscillation wavelength only changes, the position where the laser beam 100 is incident on the element arranged in the emission direction of the laser beam 100 from the front side end face 2 does not change, and is highly reliable against disturbances such as vibration. The external resonant semiconductor laser device 40 can be configured.

  The laser beam 100 of the external laser resonator according to the first embodiment is emitted from the front end face 2 having a very small area of 1 μm width in the X-axis direction and 100 μm width in the Y-axis direction, and as described above. The emission position of the laser beam 100 is fixed to the front end face 2, and the emission direction is always constant. Therefore, for example, even with the beam collimating element 12 having a small area having a width of 150 μm in the X-axis direction and a width of 200 μm in the Y-axis direction, alignment with the laser beam 100 can be easily performed. As a result, the assembly cost can be reduced, and the apparatus can be reduced in size and cost.

  Unlike the external resonant semiconductor laser device 40 according to the first embodiment, the first wavelength dispersion element 10 is disposed on the front end face 2 side of the semiconductor laser element 1, and the laser beam 100 is emitted from the first wavelength dispersion element 10. If the external laser resonator is configured as described above, the laser beam 100 is emitted with a beam diameter larger than the area of the front side end face 2, and after emitting the laser beam 100, the beam diameter is again reduced to the size of the area of the front side end face 2. Even if an attempt is made to narrow down, it is very difficult to realize due to the influence of aberration and the like. In addition, since the emission position or emission angle of the laser beam 100 varies greatly depending on the angle of the first wavelength dispersion element 10 or the position of the optical element in the external laser resonator, a width of 150 μm in the X-axis direction, Y It is very difficult to arrange the beam collimating element 12 with a width of 200 μm in the axial direction with respect to the laser beam 100.

  Further, advantages of the external resonant semiconductor laser device 40 according to the first embodiment will be described. FIG. 5 is a top view schematically showing the external resonant semiconductor laser device 40 ′ used for comparison with the external resonant semiconductor laser device 40 according to the first embodiment. In the external resonant semiconductor laser device 40 ′, which is a comparative example shown in FIG. 5, the front end face 2 ′ (2) of the semiconductor laser element 1 ′ (1′a, 1′b, 1′c, 1′d, 1′e). Laser beams 100 '(100'a, 100'b, 100'c, 100'd, 100'e) emitted from' a, 2'b, 2'c, 2'd, 2'e) respectively The beam reaches the partial reflection mirror 16 through the beam collimating element 12 ′, the coupling optical system 13, and the wavelength dispersion element 15. In the semiconductor laser device 40 ′, the rear end face 3 ′ (3′a, 3′b) of the semiconductor laser element 1 ′ (1′a, 1′b, 1′c, 1′d, 1′e) is formed. , 3′c, 3′d, 3′e) to the partial reflection mirror 16 including the wavelength dispersion element 15 are external laser resonators.

  In the external resonant semiconductor laser device 40 ′, the beams emitted from the semiconductor laser elements 1 ′ (1′a, 1′b, 1′c, 1′d, 1′e) are incident on the coupling optical system 13 differently. The light is incident on the wavelength dispersion element 15 at an angle. Since the beam diffracted from the wavelength dispersion element 15 is selectively amplified only at the wavelength perpendicularly incident on the partial reflection mirror 16, the beams emitted from the respective semiconductor laser elements 1 ′ oscillate at different wavelengths. . At this time, since each beam is spatially overlapped on the wavelength dispersion element 15 by the coupling optical system 13, as a result, a plurality of beams are combined and emitted as a single beam. It becomes.

  As described above, in the configuration of the external resonant semiconductor laser device 40 ′ shown in FIG. 5, the external laser resonator is configured between the rear end face 3 ′ and the partial reflection mirror 16, and the external laser resonator The length is several hundred mm.

  On the other hand, in the external resonant semiconductor laser device 40 according to the first embodiment, the external laser resonator is configured between the front end face 2 and the first wavelength dispersion element 10, and the length of the external laser resonator is increased. It can be several mm or less.

  In general, the longer the laser resonator is, the lower the oscillation efficiency is due to the influence of diffraction loss and the like. In addition, when the length of the laser resonator is increased, it becomes sensitive to a shift of an element disposed in the laser resonator, and there is a possibility that the laser output is greatly reduced by a slight shift. According to the external resonant semiconductor laser device 40 according to the first embodiment, the length of the external laser resonator is only a few hundredths compared with the external resonant semiconductor laser device 40 ′ shown in FIG. Efficient oscillation is possible, and the influence of element displacement due to disturbances such as vibration is reduced, so that a highly reliable laser device can be realized.

  In the following, a specific configuration is shown, and the external resonant semiconductor laser device 40 according to the first embodiment is compared with the external resonant semiconductor laser device 40 'shown in FIG.

First, the length of the external laser resonator in the configuration of the external resonant semiconductor laser device 40 ′ shown in FIG. 5 is obtained. The length of the optical axis interval d from the laser beam 100′a to the laser beam 100′e is 10 mm, the oscillation wavelength difference Δλ between the laser beams 100′a to 100′e is 4 nm, and the oscillation wavelength λ of the laser beam 100′c. ₀ is 980 nm, the diffraction angle B of the combined laser beam 101 ′ from the wavelength dispersion element 15 is 65 °, and the groove density N when the wavelength dispersion element 15 is a diffraction grating is 1850 lines / mm. Note that the diffraction order m = 1.

  The incident angle A of the laser beam 100′c to the wavelength dispersion element 15 under the above conditions can be obtained by the following formula (2), and the incident angle A to the wavelength dispersion element 15 is 65 °. .

  An arrangement in which the incident angle A and the diffraction angle B are equal is called a Littrow arrangement, and is generally known as an arrangement that can maximize the diffraction efficiency. FIGS. 1 to 3 and FIG. 5 show diagrams in the case where the second wavelength dispersion element 14 and the wavelength dispersion element 15 are reflective diffraction gratings. Therefore, under the condition that the incident angle A is equal to the diffraction angle B, the laser beam 100c and the combined laser beam 101 cannot be separated, and the laser beam 100′c and the combined laser beam 101 ′ cannot be separated. Separation is possible by tilting the two-wavelength dispersion element 14 and the wavelength dispersion element 15 in directions other than around the X-axis center. Further, the reflection type diffraction grating can be separated by changing to a transmission type diffraction grating.

  Here, the distance L from the coupling optical system 13 for satisfying the above condition to the second wavelength dispersion element 14 and the wavelength dispersion element 15 can be obtained by the following equation (3), and L = 571 mm.

  Here, the procedure for deriving Equation (3) will be described. First, when both sides of the grating equation represented by the following mathematical formula (4) are differentiated by the wavelength λ, the mathematical formula (5) is obtained. When formula (5) is transformed, formula (6) is obtained. Here, the diffraction order m = 1, and the diffraction angle B is constant.

  Subsequently, when the distance L from the coupling optical system 13 to the second wavelength dispersion element 14 and the wavelength dispersion element 15 is multiplied to both sides of the formula (6), the following formula (7) is obtained.

  Further, when the incident angle difference dA is a small angle, the following relational expression (8) is established between the distance L and the distance d.

  Further, by substituting the formula (8) into the formula (7) and expressing dλ in the formula (7) as Δλ, a relational expression such as the formula (3) is derived.

  Therefore, with the configuration of the external resonant semiconductor laser device 40 ′ shown in FIG. 5, it can be seen that the length of the external laser resonator that satisfies the above conditions is at least 571 mm.

  FIG. 6 is a diagram showing a laser oscillation spectrum of the external resonant semiconductor laser device 40 ′ used for comparison with the external resonant semiconductor laser device 40 according to the first embodiment. At this time, as shown in FIG. 6, the oscillation wavelength of the combined laser beam 101 ′ is the laser beam 100 emitted from each semiconductor laser element 1′a, 1′b, 1′c, 1′d, 1′e. Oscillation is performed at five wavelengths corresponding to 'a, 100'b, 100'c, 100'd, and 100'e, and each oscillation wavelength has an oscillation wavelength width δλ.

  The size of the oscillation wavelength width δλ is defined by the structure of the external laser resonator, and is obtained from the following formula (9). At this time, the narrower the oscillation wavelength width δλ, the more the number of beam combinations can be increased in principle, and the laser output can be increased while maintaining the beam quality.

Here, W is the beam diameter on the wavelength dispersion element 15. The beam collimating element 12 ′ is an element that corrects the divergence angle in the X-axis direction of the semiconductor laser element 1 ′, and the focal length is 0.3 mm. Further, assuming that the beam emission half-angle from the semiconductor laser element 1 ′ in the X-axis direction is 30 ° and the beam quality in the X-axis direction of the emitted beam from the semiconductor laser element 1 ′ is the diffraction limit, The beam diameter ω _G is obtained as follows.

First, the beam diameter ω ₀ on the beam collimating element 12 ′ is obtained by the following formula (10).

Further, the beam diameter ω _{L at} the position of the wavelength dispersion element 15 is obtained by the following formulas (11) and (12).

The beam diameter ω _G projected onto the wavelength dispersion element 15 is obtained by the following formula (13).

As described above, since the beam diameter ω _G on the wavelength dispersion element 15 is 5 mm, by setting W = ω _G in Equation (9), the oscillation wavelength width δλ = 0.1 nm.

  Next, the length of the external laser resonator in the external resonant semiconductor laser device 40 according to the first embodiment is obtained. In order to obtain the same characteristics as those of the external resonant semiconductor laser device 40 'shown in FIG. 5, an external laser resonator having an oscillation wavelength width δλ = 0.1 nm may be used. When the groove number density of the first wavelength dispersion element 10 is 1850 lines / mm and α3 = 65 °, it is necessary to achieve the oscillation wavelength width δλ = 0.1 nm as in the case of the external resonant semiconductor laser device 40 ′ described above. The beam diameter on the first wavelength dispersion element 10 becomes 5.0 mm. Now, since the divergence half-angle of the beam emitted from the semiconductor laser element 1 in the X-axis direction is 30 °, the beam diameter on the first wavelength dispersion element 10 is 5.0 mm. The required distance M to the control element 11 is expressed by the following formula (14).

  From the above, the length of the external laser resonator of the external resonant semiconductor laser device 40 according to the first embodiment can be about 3.6 mm when it is considered to be about twice the distance M, and the external resonance shown in FIG. Compared with the semiconductor laser device 40 ', the resonator length can be made shorter than 1/158. As a result, the external resonant semiconductor laser device 40 can oscillate with high efficiency and can obtain high reliability that is strong against disturbance.

  Further, according to the external resonant semiconductor laser device 40 according to the first embodiment, the oscillation wavelength width δλ is 0, which is half of 0.1 nm, by simply setting the external laser resonator length to 7.2 mm, which is twice 3.6 mm. .05 nm can be realized, and at this time, the oscillation wavelength difference Δλ of the laser beams 100 a to 100 e remains 4 nm. It is also possible to independently change the oscillation wavelength width δλ of each of the laser beams 100'a, 100'b, 100'c, 100'd, and 100'e.

  As described above, according to the external resonant semiconductor laser device 40 according to the first embodiment, the external laser resonator is configured between the front end face 2 and the first wavelength dispersion element 10, and the first wavelength dispersion element By arranging 10 on the rear end face 3 side of the semiconductor laser element 1, the length of the external laser resonator can be shortened, so that high-efficiency oscillation and reliability can be improved.

  Further, since the oscillation beam of the external laser resonator is emitted from the front end face 2 of the semiconductor laser element 1, it is possible to arrange optical elements corresponding to each of the plurality of oscillation beams, improving the light condensing property, and further oscillating. Even if the wavelength is changed, a remarkable effect is obtained that the emission direction does not change.

Embodiment 2. FIG.
FIG. 7 is a top view schematically showing the external resonant semiconductor laser device 41 according to the second embodiment of the present invention. The external resonant semiconductor laser device 41 according to the second embodiment includes, in addition to the configuration of the external resonant semiconductor laser device 40 of the first embodiment, laser beams 100a, 100b, 100c, 100d, and 100e emitted from the front end face 2, respectively. Waveguides 17a, 17b, 17c, 17d, and 17e (hereinafter collectively referred to as “waveguide 17”) are disposed at the incident destinations of the. That is, the laser beams 100 a, 100 b, 100 c, 100 d, and 100 e emitted from the front end face 2 are respectively incident on separate waveguides 17 (17 a, 17 b, 17 c, 17 d, and 17 e) and pass through the waveguide 17. Via the coupling optical system 13.

  Further, the beam collimating element 12 of the external resonant semiconductor laser device 40 is replaced with the beam coupling element 19 in the external resonant semiconductor laser device 41. The laser beams 100a, 100b, 100c, 100d, and 100e are coupled to the waveguide 17 by the beam coupling element 19.

  The configurations other than those described above for the external resonant semiconductor laser device 41 are the same as those of the external resonant semiconductor laser device 40 of the first embodiment.

  As the beam combining element 19, a spherical lens, an aspherical lens, a cylindrical lens, and a mirror having a curvature can be used, and the beam combining element 19 is not limited to one each, but may be a combination thereof.

  In order to couple the laser beam 100 to the waveguide 17, it is not always necessary to use the beam coupling element 19. A method of coupling the waveguide 17 directly to the front end face 2, and a condensing function on the incident surface of the waveguide 17. There is also a method of giving it.

  As the waveguide 17, an optical fiber, a planar lightwave circuit, or the like can be used.

  The planar lightwave circuit is also referred to as PLC (Planner Lightwave Circuit). By applying the flame direct deposition method, which is an application technology of optical fiber manufacturing technology, the lower clad layer and core layer are deposited on a quartz substrate and heated to melt and clear the glass film. Semiconductor integrated circuit manufacturing technology, photolithography and reactive ion etching It is made by forming a waveguide pattern and forming an upper clad by a flame direct deposition method.

  The arrangement of the laser beam 100 coupled to the waveguide 17 is changed by the waveguide 17, and the laser beam 100 is emitted from the waveguide 17 again at an optical axis interval e narrower than the optical axis interval d of the semiconductor laser element 1 before coupling. To do.

  According to the external resonant semiconductor laser device 41 according to the second embodiment, the optical axis interval can be narrowed by the waveguide 17. For this reason, in the external resonant semiconductor laser device 41, when compared with the optical axis interval d of the semiconductor laser element 1 being the same, compared with the external resonant semiconductor laser device 40 according to the first embodiment, The distance to the two-wavelength dispersion element 14 can be further shortened. In addition, since the optical path of the waveguide 17 can be set arbitrarily, the optical path from the semiconductor laser element 1 to the coupling optical system 13 can be bent very easily. The size of the laser device 41 can be further reduced.

Embodiment 3 FIG.
FIG. 8 is a perspective view schematically showing an external resonant semiconductor laser device 42 according to the third embodiment of the present invention. FIG. 8 also shows the directions of the X, Y, and Z axes. FIG. 9 is a top view schematically showing the external resonant semiconductor laser device 42 according to the third embodiment. FIG. 9 is a view of the external resonant semiconductor laser device 42 as viewed in the X-axis direction. FIG. 10 is a side view schematically showing the external resonant semiconductor laser device 42 according to the third embodiment. FIG. 10 is a view of the external resonant semiconductor laser device 42 as viewed in the Y-axis direction.

  In the external resonant semiconductor laser device 42 according to the third embodiment, a plurality of semiconductor lasers are used in place of the semiconductor laser element 1 (1a, 1b, 1c, 1d, 1e) in the external resonant semiconductor laser device 40 of the first embodiment. A semiconductor laser array 5 having elements is arranged. A beam collimating element 21 is provided on the side of the rear end face 3 of the semiconductor laser element of the semiconductor laser array 5. In the external resonant semiconductor laser device 42, a plurality of first wavelength dispersion elements 10 and a plurality of first wavelength dispersion elements 10 arranged on the rear end face 3 (3a, 3b, 3c, 3d, 3e) side of the plurality of semiconductor laser elements included in the semiconductor laser array 5 are provided. An external laser resonator is formed between the front end face 2 (2a, 2b, 2c, 2d, 2e) of the semiconductor laser element.

  The beam collimating element 21 is also used to collimate the laser beam that is emitted from the rear end face 3 of the semiconductor laser element of the semiconductor laser array 5 and spreads in the X-axis direction, thereby increasing the coupling efficiency of the external laser resonator. The beam collimating element 21 is disposed at a position away from the rear end face 3 by the focal length of the beam collimating element 21.

  Although the beam collimating element 21 is depicted as a cylindrical lens in FIG. 8, a spherical lens, an aspherical lens, and a mirror having a curvature can be used, and the beam collimating element 21 is not limited to one each. Alternatively, a combination of these may be used. On the side of the object-side telecentric optical element 22 (to be described later) of the beam collimating element 21, there is a generatrix 210 along the Y-axis direction along the apex of the curved surface.

  The parallel direction of the plurality of semiconductor laser elements of the semiconductor laser array 5 is aligned in the Y-axis direction before the tilt, and the parallel direction of the plurality of semiconductor laser elements of the semiconductor laser array 5 and the bus 210 of the beam collimating element 21. The directions are consistent. In the external resonant semiconductor laser device 42 according to the third embodiment, the parallel direction of the plurality of semiconductor laser elements of the semiconductor laser array 5 and the beam collimating element 21 are inclined by tilting the semiconductor laser array 5 about the Z axis. The direction of the bus 210 is shifted. Thereby, the heights of the beams emitted from the rear end face 3 of the semiconductor laser array 5 entering the beam collimating element 21 are different from each other.

  The beams incident on the beam collimating element 21 at different heights are incident on the first wavelength dispersion element 10 at different angles, and thus oscillate at different wavelengths.

  In the above description, the semiconductor laser array 5 is tilted. However, the same effect can be obtained by tilting the beam collimating element 21 without tilting the semiconductor laser array 5.

  The object-side telecentric optical element 22 and the image-side telecentric optical element 23 are configured to increase the coupling efficiency in the Y-axis direction of the external laser resonator, and the rear-side end face 3 of the semiconductor laser array 5 is subjected to the first wavelength dispersion. An image is formed on the element 10.

  The object-side telecentric optical element 22 and the image-side telecentric optical element 23 are depicted as cylindrical lenses in FIGS. 8 and 9, but a spherical lens, an aspherical lens, or a mirror having a curvature can be used. The configuration is not limited to one by one, but may be a combination of these.

  The laser beam 100 emitted from the front end face 2 of the semiconductor laser array 5 is collimated by the beam collimating optical system 24.

  The beam collimating optical system 24 can be a cylindrical lens, a spherical lens, an aspheric lens, a mirror having a curvature, or a combination thereof.

  At this time, the beam collimating optical system 24 may include a beam rotating optical system. Examples of the beam rotation optical system include a cylindrical lens array shown in a publicly known document (see Japanese Patent Laid-Open No. 2000-137139, FIG. 2), a reflector shown in a publicly known document (see WO98 / 08128, FIG. 2), and the like. Used.

  By passing the beam rotating optical system, the laser beam 100 having anisotropy emitted from each front side end face 2 is rotated about 90 degrees in a plane perpendicular to the optical axis.

  The configuration of the external resonant semiconductor laser device 42 other than that described above is the same as that of the semiconductor laser 40 of the first embodiment.

  According to the external resonant semiconductor laser device 42 according to the third embodiment, by using the semiconductor laser array 5, increasing the number of the laser beams 100 and increasing the output can be easily performed at low cost. it can.

Embodiment 4 FIG.
FIG. 11 is a top view schematically showing an external resonant semiconductor laser device 43 according to the fourth embodiment of the present invention. FIG. 12 is a side view schematically showing the external resonant semiconductor laser device 43 according to the fourth embodiment.

  In the external resonant semiconductor laser device 43 according to the fourth embodiment, semiconductor laser arrays 5a, 5b, and 5c each including a plurality of semiconductor laser elements are arranged. Each of the semiconductor laser arrays 5a, 5b, and 5c is the same as the semiconductor laser array 5 of the third embodiment, and each of the semiconductor laser arrays 5a, 5b, and 5c includes a plurality of front end faces 2 and a plurality of rear end faces 3. Prepare. And each of the some front side end surface 2 becomes a light emission point. The oscillation wavelength of the semiconductor laser array 5 is selected by the first wavelength dispersion elements 10a, 10b, and 10c arranged on the rear end face 3 side of the semiconductor laser array 5.

  Therefore, in the external resonant semiconductor laser device 43, there are a plurality of external laser resonators between the front end face 2 and the first wavelength dispersion elements 10a, 10b, 10c corresponding to the semiconductor laser arrays 5a, 5b, 5c, respectively. Composed.

  The beam collimating optical systems 24a, 24b, 24c provided on the front end face 2 side of the semiconductor laser arrays 5a, 5b, 5c are the same as the beam collimating optical system 24 of the third embodiment. The beam collimating elements 21a, 21b, 21c provided on the rear end face 3 side of the semiconductor laser arrays 5a, 5b, 5c are the same as the beam collimating elements 21 of the third embodiment.

  A plurality of beams emitted from the semiconductor laser array 5a are all incident on the first wavelength dispersion element 10a at the same incident angle α1. Therefore, the plurality of laser beams 100a emitted from the semiconductor laser array 5a all have the same oscillation wavelength λ1.

  A plurality of beams emitted from the semiconductor laser array 5b are all incident on the first wavelength dispersion element 10b at the same incident angle α2. Therefore, the plurality of laser beams 100b emitted from the semiconductor laser array 5b all have the same oscillation wavelength λ2.

  The plurality of beams emitted from the semiconductor laser array 5c are all incident on the first wavelength dispersion element 10c at the same incident angle α3. Therefore, the plurality of laser beams 100c emitted from the semiconductor laser array 5c all have the same oscillation wavelength λ3.

  Laser beams 100a, 100b, and 100c emitted from the semiconductor laser arrays 5a, 5b, and 5c are incident on separate waveguides 17a, 17b, and 17c by the waveguide coupling optical systems 18a, 18b, and 18c, respectively, and the waveguide 17a. , 17b and 17c are superimposed on the second wavelength dispersion element 14 by the coupling optical system 13 and output as a single combined laser beam 101.

  According to the external resonant semiconductor laser device 43 according to the fourth embodiment, by using the semiconductor laser array 5, it is possible to increase the number of laser beams 100a, 100b, and 100c and increase the output, thereby reducing the cost. It can be performed simply. Further, since the arrangement interval of the laser beams 100a, 100b, and 100c can be narrowed using the waveguide 17, the apparatus can be miniaturized.

  The configuration described in the above embodiment shows an example of the contents of the present invention, and can be combined with another known technique, and can be combined with other configurations without departing from the gist of the present invention. It is also possible to omit or change the part.

  1, 1a, 1b, 1c, 1d, 1e, 1 ', 1'a, 1'b, 1'c, 1'd, 1'e Semiconductor laser element, 2, 2a, 2b, 2c, 2d, 2e, 2 ', 2'a, 2'b, 2'c, 2'd, 2'e Front end face, 3, 3a, 3b, 3c, 3d, 3e, 3', 3'a, 3'b, 3 ' c, 3'd, 3'e Rear end face, 5, 5a, 5b, 5c Semiconductor laser array, 10, 10a, 10b, 10c, 10d, 10e First wavelength dispersion element, 11, 12 Beam collimating element, 13 Coupling optical system, 14 Second wavelength dispersion element, 15 Wavelength dispersion element, 16 Partial reflection mirror, 17 Waveguide, 18a, 18b, 18c Waveguide coupling optical system, 19 Beam coupling element, 21, 21a, 21b, 21c Beam parallel 22 element side telecentric optical element, 23 image side telephoto element 24, 24a, 24b, 24c Beam collimating optical system, 40, 40 ', 41, 42, 43 External cavity semiconductor laser device, 100, 100a, 100b, 100c, 100d, 100e, 100', 100 ' a, 100′b, 100′c, 100′d, 100′e Laser beam, 101 laser beam after coupling, 210 bus.

Claims (9)

A plurality of external laser resonators configured between the first wavelength dispersion element disposed on the rear end face side of the semiconductor laser element and the front end face of the semiconductor laser element;
The external resonant semiconductor laser device, wherein a plurality of laser beams emitted from the front end face are superimposed on the second wavelength dispersion element via a coupling optical system. An external laser resonator configured between a first wavelength dispersion element disposed on a rear end face side of a plurality of semiconductor laser elements included in the semiconductor laser array and a front end face of the semiconductor laser element;
The external resonant semiconductor laser device, wherein a plurality of laser beams emitted from the front end face are superimposed on the second wavelength dispersion element via a coupling optical system. A plurality of external laser resonators configured between a first wavelength dispersion element disposed on a rear end face side of a plurality of semiconductor laser elements included in the semiconductor laser array and a front end face of the semiconductor laser element;
The external resonant semiconductor laser device, wherein a plurality of laser beams emitted from the front end face are superimposed on the second wavelength dispersion element via a coupling optical system. The external resonant semiconductor laser device according to any one of claims 1 to 3, wherein the first and second wavelength dispersion elements are diffraction gratings. 4. The external resonant semiconductor laser device according to claim 1, wherein the first wavelength dispersion element includes a dielectric multilayer film. 5. 2. The external resonant semiconductor laser device according to claim 1, wherein each of the plurality of laser beams emitted from the front end face enters a separate waveguide and then passes through the coupling optical system. 3. Separate waveguides are provided corresponding to each of the plurality of semiconductor laser arrays, and the plurality of laser beams emitted from the semiconductor laser array are incident on the waveguides corresponding to the semiconductor laser array and then coupled. The external resonant semiconductor laser device according to claim 3, wherein the external resonant semiconductor laser device passes through an optical system. The external resonant semiconductor laser device according to claim 6, wherein the waveguide is an optical fiber. A beam collimating element for collimating a laser beam emitted from the rear end face;
3. The external resonant semiconductor laser device according to claim 2, wherein a direction of a bus line of the beam collimating element is shifted from a parallel direction of the plurality of semiconductor laser elements included in the semiconductor laser array.

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