JP2005175049A - External resonator semiconductor laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an external resonator semiconductor laser of a smaller size while achieving single mode operation by arranging a grating in closer proximity to the semiconductor laser. <P>SOLUTION: The external resonator semiconductor laser 1 is a Littrow type semiconductor laser comprising a semiconductor laser 2, a lens 3, a supporting part 4, and a grating 5. The semiconductor laser 2 employs a semiconductor laser element, e.g. a blue laser diode. The grating 5 is of a transmission type and most of laser beams emitted from the semiconductor laser 2 penetrate the grating 5 to be provided to the outside as 0th order transparent light. The grating 5 is supported while inclining at an angle larger than 45°, e.g. at about 60°, with respect to laser light from the semiconductor laser 2. Consequently, the external resonator semiconductor laser 2 where the grating 5 is arranged in closer proximity to the semiconductor laser can be reduced in size. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an external resonator type semiconductor laser including a laser diode (LD).

  Recording in the holographic memory is performed using laser light. More specifically, the laser light once divided into two is superimposed again on the hologram (recording medium), and the diffraction grating is recorded on the hologram by utilizing the coherence. Data is recorded by recording the diffraction grating. However, when the laser beam is in a multimode, the coherence is low and it is difficult to form the diffraction grating.

  Therefore, the laser beam used for the holographic memory is required to have a single mode. For this reason, conventionally, a 532 nm solid-state laser (second harmonic of YAG) has often been used.

  However, the individual laser has a drawback that it is difficult to control, for example, when the power setting value is changed, it takes time for the actual power to reach the setting value. Therefore, attempts have been actively made to apply a blue laser diode, which is relatively easy to control power and the like, and has a short wavelength and capable of higher density recording, to the field of holography memory.

  However, this blue laser diode is inherently multimode and has low coherence, so it is difficult to use it alone for holographic memory. Therefore, the blue laser diode is realized as a single mode by being configured as an external resonator type semiconductor laser combined with an external resonator. The external resonator type semiconductor laser stabilizes the wavelength of the oscillation light of the semiconductor laser (single mode) by inputting light of a predetermined wavelength from the outside.

  Here, a Littrow semiconductor laser, which is a typical example of an external cavity semiconductor laser, will be described with reference to FIG. For example, longitudinal multimode laser light (oscillation light) emitted from a semiconductor laser 51 including a semiconductor laser element such as a laser diode is collimated by a lens (collimating lens) 52 and incident on a grating (diffraction grating) 54. Is done. The grating 54 outputs first-order diffracted light of each mode, and specific first-order diffracted light is reversely injected into the semiconductor laser 51 through the lens 52 according to the arrangement angle. As a result, the semiconductor laser 51 resonates with the injected first-order diffracted light and emits single-mode light, and the wavelength of the light is the same as the wavelength of the first-order diffracted light returned from the grating 54. . Furthermore, the remainder of the laser light (zero-order light) incident on the grating 54 is reflected at the same angle as the incident angle and emitted to the outside.

  The wavelength of light incident on the semiconductor laser 51 can be adjusted by changing the arrangement angle of the grating 54. For example, the grating 54 is held by a leaf spring supported by a predetermined support portion, and when a screw in contact with the grating 54 is rotated, the grating 54 moves in the direction of the lens 52 or in the opposite direction. This movement approximates a movement in which the grating 54 rotates about a place where the plate spring is supported by a predetermined support portion, and the rotation angle changes the arrangement angle of the grating 54.

  The grating 54 is usually a reflection type and is arranged at an angle of about 45 ° with respect to the laser light emitted from the semiconductor laser 51. Therefore, the laser light emitted from the semiconductor laser 51 is reflected by the grating 54 with a bend of about 90 °. Since the adjustment of the arrangement angle of the grating 54 is about 2 °, the emission direction of the laser beam bent by 90 ° (that is, the zero-order light) also changes by about 2 °.

  There are two main reasons why the arrangement angle of the grating 54 is about 45 ° as described above. One is that if the grating 54 is arranged at an angle smaller than 45 ° with respect to the laser beam emitted from the semiconductor laser 51, a long grating is required to receive all the laser beam, resulting in an external resonator type. The semiconductor laser becomes large. Another reason is that when the grating 54 is disposed at an angle larger than 45 ° with respect to the laser light emitted from the semiconductor laser 51, the reflected light (zero-order light) proceeds in the direction close to the semiconductor laser 51, and the In this case, the reflected light hits the edge of the lens 52 and the laser light cannot be extracted to the outside.

  However, if the grating 54 is arranged at an angle of about 45 ° with respect to the laser beam emitted from the semiconductor laser as described above, a large size as shown by D in FIG. It is not possible to produce an external cavity type semiconductor laser of the size. FIG. 4 shows a Littrow type external resonator type semiconductor laser. Since the Littman type external resonator type semiconductor laser further includes a mirror or a prism, the size can be reduced. More difficult.

  Accordingly, an object of the present invention is to provide an external cavity semiconductor laser that can be configured in a smaller size.

  Furthermore, an object of the present invention is to incline the grating with respect to the laser beam emitted from the semiconductor laser at an angle larger than 45 °, so that even if the grating is arranged closer to the semiconductor laser, the single mode An object of the present invention is to provide an external resonator type semiconductor laser from which laser light can be extracted.

  Furthermore, an object of the present invention is to provide an external resonator type semiconductor laser that can provide externally emitted light in the same direction regardless of the wavelength by using a transmission type grating.

  The present invention includes a semiconductor laser that emits laser light, a collimating lens that emits laser light received from the semiconductor laser as substantially parallel light, and a transmission type grating that receives the laser light via the collimating lens. The grating that receives the laser light emits reflected primary light and transmitted zero-order light, and the reflected primary light is light having a predetermined frequency, and the reflected primary light passes through the collimator lens to the semiconductor laser. By being incident, the laser beam emitted from the semiconductor laser is made into a single mode, and the grating is disposed at an angle larger than at least 45 ° with respect to the direction of the laser beam emitted from the semiconductor laser toward the grating. This is an external cavity semiconductor laser.

  According to the present invention, the grating can be disposed close to the semiconductor laser, and as a result, an external cavity semiconductor laser having a smaller size can be realized. Further, since the direction of the optical path of the transmitted zero-order light is constant, the optical adjustment of the extracted laser light becomes easy.

  First, the configuration of the external cavity semiconductor laser according to the first embodiment of the present invention will be described with reference to FIG. An external resonator type semiconductor laser 1 shown in FIG. 1 includes a semiconductor laser 2, a lens (collimating lens) 3, a support portion 4, and a grating 5. The semiconductor laser 2 uses a semiconductor laser element such as a blue laser diode, for example, and is supported at a predetermined position by the support portion 4 together with the lens 3.

  The grating 5 is of a transmissive type, and most of the laser light emitted from the semiconductor laser 2 passes through the grating 5 and is provided to the outside. FIG. 1 shows a state in which laser light passes through the grating 5 from the semiconductor laser 2 through the lens 3. Here, in order to simplify the drawing, the reflected light from the grating 5 is omitted. Further, in this embodiment, the grating 5 is arranged in an inclined state with respect to the laser beam from the semiconductor laser 2 at an angle larger than 45 °, for example, about 60 °, for example, 2500 / mm is used. It is done.

  Strictly speaking, the inclination angle of the semiconductor laser 2 is 60 ° with respect to the direction of the laser beam from the semiconductor laser 2 toward the grating 5. Here, it should be noted that the direction of the optical path of the laser beam between the semiconductor laser 2 and the grating 5 is used as a reference (the optical path refracted by the grating 5 is not considered). Further, since the laser beam direction (a line extending in the direction) intersects the grating 5, there are two angles formed by the laser beam direction and the grating 5. However, here, the smaller of these angles is used to represent the positional relationship between them. Therefore, when the tilt angle is 60 °, the grating 5 may be tilted by 60 ° in the direction of lowering the right end of the grating 5 shown in FIG. 1, for example, or tilted by 60 ° in the direction of lowering the left end. Also good.

  With such a configuration shown in FIG. 1, the maximum distance from the semiconductor laser 2 to the grating 5 is D ′, and accordingly, the size of the external cavity semiconductor laser 1 can be further reduced. Compared to the maximum distance D from the semiconductor laser 51 to the grating 54 shown in FIG. 4, it can be seen that the size of the external cavity semiconductor laser 1 can be made considerably smaller than that of the conventional one. The grating 54 in FIG. 4 is arranged in a state inclined by about 45 ° with respect to the laser light from the semiconductor laser 51.

  Next, how the laser light received by the grating 5 in the external cavity semiconductor laser 1 according to the first embodiment shown in FIG. 1 will be described with reference to FIG. The same components as those in the external cavity semiconductor laser 1 in FIG. Further, the laser beam from the semiconductor laser 2 to the grating 5 shown in FIG. 1 is omitted.

  When the laser light emitted from the semiconductor laser 2 enters the grating 5 through the lens 3, a part of the light is reflected and becomes reflected light, and the remaining light is transmitted through the grating 5 and becomes transmitted light. Of the reflected light, the reflected primary light 9 returns to the semiconductor laser 2 and resonates, thereby realizing a single mode. Of the transmitted light, the transmitted 0th-order light 6 is laser light extracted to the outside, and recording to the holography memory is performed using this. The transmitted zero-order light 6 travels in the same direction as the direction in which the laser light emitted from the semiconductor laser 2 travels toward the grating 5. That is, the line extending in the direction in which the laser light emitted from the semiconductor laser 2 is directed toward the grating 5 is parallel to the line extending in the direction in which the transmitted zero-order light 6 is advanced. This relationship is maintained even when the arrangement angle of the grating 5 is changed in order to adjust the wavelength.

  The reflected zero-order light 10 and the transmitted primary light 7 are not used here. In this embodiment, the output power of the transmitted 0 order light 6 taken out to the outside is made as strong as possible, and the reflected primary light 9 is reduced to the total output power in order to make the semiconductor laser 2 have a good single mode. Assuming the requirement of 5% or more (more preferably 10% or more), the output power of the reflected primary light when a completely transparent grating is used is 4% or less of the total, and does not satisfy the above requirement.

  Therefore, it is desirable to form a layer that reflects laser light to some extent on the reflecting surface of the grating 5. In the present embodiment, the output power of the reflected zero-order light 10 may be weak, so that the grating 5 is a blazed diffraction grating in order to reduce it and increase the output power of the reflected primary light 9. The output power of the transmitted primary light 7 was about 15% of the whole. The grating 5 is produced, for example, by transferring a lattice shape to an epoxy resin coated on a glass substrate and then applying a thin aluminum coat on the surface thereof. Further, an antireflection coating can be applied to the opposite surface so that unnecessary reflected light from the back surface of the grating 5 can be reduced.

  With such a configuration of the external cavity semiconductor laser 1, the grating 5 can be disposed close to the semiconductor laser 2, and as a result, a smaller-sized external cavity semiconductor laser 1 can be realized. In addition, since the direction of the optical path of the transmitted zero-order light 6 is constant, optical adjustment of the extracted laser light is facilitated.

  Next, an external resonator type semiconductor laser according to a second embodiment of the present invention will be described with reference to FIG. The external cavity semiconductor laser 21 in FIG. 3 has a configuration in which a detector, a wavelength monitor, and an optical fiber are added to the external cavity semiconductor laser 1 in FIG. Similarly to FIG. 2, the laser beam from the semiconductor laser to the grating is omitted. Also in this embodiment, the grating 25 is arranged in an inclined state of about 60 ° with respect to the laser beam from the semiconductor laser 22, and for example, one having 2500 lines / mm is used.

  In the external cavity semiconductor laser 1 according to the first embodiment shown in FIG. 2, the transmitted primary light and the reflected zero-order light are not used, but in the second embodiment, the transmitted primary light 27 is The reflected zero-order light 30 is used for monitoring the output power of the laser light emitted from the semiconductor laser 22 and for confirming the wavelength of the laser light emitted from the semiconductor laser 22.

  First, the transmitted primary light 27 is received by the detector 31 and the value of the output power (light quantity) is obtained, and the value and the value of the output power of the transmitted zero-order light 26 that is laser light extracted outside A ratio is required. Thereafter, if the detector 31 detects the output power of the transmitted primary light 27 at a predetermined interval, the output power of the transmitted 0th-order light 26 can be grasped from the detected value and the ratio.

  Further, using the value of the output power of the transmitted primary light 27 detected by the detector 31, the drive current of the semiconductor laser 22 is feedback-controlled so that the output power of the transmitted 0th-order light 26 is always a desired power. You can also

  On the other hand, the reflected zero-order light 30 is incident on a wavelength monitor (optical spectrum analyzer) 32 via an optical fiber 33, where the wavelength of the reflected zero-order light 30 is checked. Further, since the optical fiber 33 is interposed, the power of the light received by the wavelength monitor 32 is about one thousandth of the output power of the reflected zero-order light 30.

  Similarly to the external resonator type semiconductor laser 1 of the first embodiment, the output power of the transmitted zero-order light 26 extracted to the outside is made as strong as possible and the semiconductor laser 22 exhibits a good single mode. desirable. Therefore, also in this case, the grating 25 having the same structure as that of the first embodiment is used.

  In the second embodiment, as described above, the transmitted primary light 27 is used for monitoring the output power, and the reflected zero-order light 30 is used for confirming the wavelength of the laser light. The reflected zero-order light 30 need not be limited to these applications, and can be used for various other applications.

  With such a configuration of the external cavity semiconductor laser 21, the grating 25 can be disposed close to the semiconductor laser 22, and as a result, a smaller-sized external cavity semiconductor laser 21 can be realized.

1 is a schematic diagram illustrating an external resonator type semiconductor laser according to a first embodiment of the present invention. FIG. 2 is a schematic diagram showing grading reflected light and transmitted light with respect to the external cavity semiconductor laser of FIG. 1. It is a basic diagram showing the external resonator type semiconductor laser of 2nd Embodiment of this invention. It is a basic diagram which shows the structure of the conventional external resonator type semiconductor laser.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,21 ... External cavity type semiconductor laser, 2,22 ... Semiconductor laser, 3,23 ... Lens, 4,24 ... Supporting part, 5,25 ... Grating, 6,26 ... 0th order transmitted light, 7, 27 ... 1st transmitted light, 9, 29 ... 1st reflected light, 10, 30 ... 0th reflected light, 31 ... Detector, 32 ...・ Wavelength monitor, 33 ... Optical fiber

Claims (11)

A semiconductor laser that emits laser light;
A collimating lens that emits laser light received from the semiconductor laser as substantially parallel light;
A transmission type grating that receives the laser light via the collimating lens,
The grating that receives the laser beam emits reflected primary light and transmitted zero-order light,
The reflected primary light is light having a predetermined frequency, and the reflected primary light is incident on the semiconductor laser through the collimating lens, so that the laser light emitted from the semiconductor laser is in a single mode. And
2. An external resonator type semiconductor laser, wherein the grating is disposed at an angle larger than at least 45 ° with respect to a direction in which laser light emitted from the semiconductor laser is directed toward the grating. The external cavity semiconductor laser according to claim 1,
The external-cavity semiconductor laser characterized in that the transmitted zero-order light travels in the same direction as the direction of the laser light emitted from the semiconductor laser toward the grating. The external cavity semiconductor laser according to claim 1,
2. The external cavity semiconductor laser according to claim 1, wherein a reflection film is formed on a side of the grating that receives a laser beam emitted from the semiconductor laser. The external cavity semiconductor laser according to claim 3,
An external cavity semiconductor laser, wherein the reflective film is an aluminum coat. The external cavity semiconductor laser according to claim 3,
2. The external cavity semiconductor laser according to claim 1, wherein the grating is provided with a non-reflective coating on the side opposite to the side receiving the laser light emitted from the semiconductor laser. The external cavity semiconductor laser according to claim 1,
2. The external cavity semiconductor laser according to claim 1, wherein the grating is a blazed diffraction grating. The external cavity semiconductor laser according to claim 1,
The grating that has received the laser light further emits transmitted primary light,
The external resonator type semiconductor characterized in that the transmitted primary light is used for feedback control of output power of laser light emitted from the semiconductor laser, or for checking the wavelength of laser light emitted from the semiconductor laser. laser. The external cavity semiconductor laser according to claim 1,
The grating that has received the laser light further emits reflected zeroth-order light,
The external resonator type semiconductor, wherein the reflected zero-order light is used for feedback control of output power of laser light emitted from the semiconductor laser or for checking the wavelength of laser light emitted from the semiconductor laser. laser. The external cavity semiconductor laser according to claim 1,
2. An external resonator type semiconductor laser, wherein the grating is arranged at an angle of approximately 60 ° with respect to a direction in which laser light emitted from the semiconductor laser is directed toward the grating. The external cavity semiconductor laser according to claim 5,
An external cavity semiconductor laser, wherein the grating is configured to reflect at least 10% of the output power of incident laser light as reflected primary light. The external cavity semiconductor laser according to claim 6, wherein
An external cavity semiconductor laser, wherein the grating is configured to transmit approximately 15% of the output power of incident laser light as transmitted primary light.

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