JP4670472B2 - Laser equipment - Google Patents

Description

  The present invention relates to a laser device having a configuration of an external cavity semiconductor laser.

  In recent years, laser devices have come to be widely used in information equipment because of their small size and low power consumption. For example, a single mode laser is used for holographic data storage (HDS). In the HDS, one laser beam is divided into two by a beam splitter and then recombined on a recording medium, and data is recorded by the interference.

  As such a light source for hologram recording / reproduction, a gas laser or SHG laser which is a single mode light source is often used. However, even a semiconductor laser such as a laser diode (LD) that is multimode oscillation can be made into a single mode by combining it with an external resonator, and can be used as a light source for hologram recording and reproduction. is there.

  Here, the configuration of a Littrow type laser device including a conventional typical external cavity semiconductor laser will be described with reference to FIG. FIG. 1 is a plan view of the laser device 200. The configuration of the laser device 200 is the same as the configuration of the laser device described in Non-Patent Document 1 below.

L. Ricci, et al .: "A compact grating-stabilized diode laser system for atomicphysics", Optics Communications, 117 1995, pp541-549

  In the laser device 200, longitudinal multimode laser beams emitted from the laser diode 201 are collected in parallel by a collimator lens 202 and are incident on a reflective diffraction grating (hereinafter referred to as a grating) 203. The grating 203 outputs first-order diffracted light of incident light. First-order diffracted light having a specific wavelength corresponding to the arrangement angle of the grating 203 is reversely injected into the laser diode 201 through the lens 202. As a result, the laser diode 201 resonates with the injected first-order diffracted light and emits single-mode light (0th-order light represented by the arrow F), and the wavelength of the light returns from the grating 203. It becomes the same as the wavelength of the incoming light.

  The grating 203 is held by the support unit 204. A groove 206 is provided in the support portion 204, and by rotating a screw 205 provided in the support portion 204, the interval between the grooves 206 is partially widened or narrowed, thereby the horizontal direction of the grating 203. The placement angle changes slightly. The reflection angle of the primary light reflected by the grating 203 differs depending on the wavelength. By setting the angle of the grating 203 so that the primary light corresponding to the desired wavelength returns to the laser diode 201, a laser having a desired wavelength is obtained. Can generate light.

  A similar mechanism is provided for adjusting the vertical angle of the grating 203. The support part 204 that holds the grating 203 is held by the support part 207. The support portion 207 is provided with a groove (not shown), and by rotating a screw 208 provided on the support portion 207, the interval between the grooves is partially expanded or narrowed, whereby the vertical direction of the grating 203 is increased. The orientation angle of the direction changes slightly.

  Here, for example, a blue laser diode is used as the laser diode 201. The external resonance type configured as described above can also be used for applications such as a holographic memory writer that requires a single mode single laser beam.

  Next, with reference to the graph of FIG. 2, the relationship between the laser power and the wavelength of the laser beam output from the external resonator type laser device as described in FIG. 1 will be described. The horizontal axis of the graph shown in FIG. 2 indicates the laser power, and the unit is mW. On the other hand, the vertical axis of the graph represents the wavelength, and the unit is nm. As can be seen from FIG. 2, as the laser power of the laser beam increases, the wavelength of the laser beam generally changes in a sawtooth waveform.

  In the external cavity type laser device, the laser beam emitted when the laser power increases, and the external cavity mode hop region where the wavelength of the emitted laser light gradually increases as the laser power increases. There is a mode hop region due to the laser chip in the semiconductor laser, where the wavelength of the laser diode decreases rapidly. The wavelength of the laser light changes discretely to some extent as the laser power increases.

  For example, when the laser power is around 30 mW, a single wavelength laser beam is emitted and becomes a complete single mode. However, when the laser power is around 32 mW, light of three modes (three modes) is generated. ing. Further, when the laser power is around 35 mW, which corresponds to the mode hop region of the laser chip in the semiconductor laser, three-mode light is generated near the wavelength of 409.75 nm, and further, the three-mode light is emitted near the wavelength of 409.715 nm. As a whole, 6-mode light is emitted.

  FIG. 3 shows the spectrum of several laser beams. As described above, in the external resonator mode hop region where the wavelength of the laser light gradually increases, the spectrum is as shown in FIGS. 3A, 3B, and 3C. On the other hand, for example, in a mode hop region by a laser chip in a semiconductor laser having a laser power of around 35 mW, the spectrum is as shown in FIG. 3D.

  When these laser lights are used for HDS, three-mode light or two-mode light (that is, light as shown in FIG. 3B) that is generated at a laser power around 32 mW (that is, as shown in FIG. 3A). Shows recording / reproduction characteristics equivalent to perfect single-mode light (spectrum light shown in FIG. 3C), and can be used in the same manner as single-mode light. Here, for example, a complete single mode in which the laser power is generated in the vicinity of 30 mW and a three mode or two mode in which the laser power is generated in the vicinity of 32 mW are collectively referred to as usable modes.

  On the other hand, for example, as shown in FIG. 3D, the 6-mode state in which the laser power is generated in the vicinity of 35 mW realizes good hologram recording because the two 3-mode sets are separated from each other by about 40 pm. I can't. Here, such a mode is referred to as an unusable mode.

  The region where the usable mode laser light is obtained almost corresponds to the external resonator mode hop region, and the region where the unusable mode laser light is obtained almost corresponds to the mode hop region by the laser chip in the semiconductor laser. To do. As can be seen from the graph of FIG. 2, in general, the region in which the laser beam in the usable mode is obtained is much wider than the region in which the laser beam in the unusable mode is obtained. If this can be effectively eliminated, it is sufficiently possible to use an external cavity semiconductor laser for HDS.

  Further, the characteristics of the laser power and the wavelength of the laser beam as shown in FIG. 2 vary depending on the temperature in the external resonator type semiconductor laser. For example, if the temperature of the semiconductor laser is not constant, the position of the laser power in the unusable mode changes. Therefore, conventionally, the temperature in the external resonator type semiconductor laser is kept almost constant (for example, suppressed to fluctuation within 10 mK), and the region where the laser beam in the unusable mode is obtained is not changed. The technique of avoiding the use of the laser power belonging to that region has been taken.

  However, in order to control the external resonator type semiconductor laser so that the unusable mode laser beam is not emitted by the conventional method described above, the temperature in the external resonator type semiconductor laser is kept substantially constant. Therefore, it is necessary to control the laser power, and the structure and control of the laser device become complicated.

  A method of controlling the laser power of the external cavity semiconductor laser using the wavelength detection result is also conceivable, but the conventional wavelength detection device is very large and expensive, and is used for applications such as HDS. Does not fit.

  In order to solve such problems, the inventor of the present application has previously proposed an apparatus and a method capable of determining the wavelength of laser light emitted from an external cavity semiconductor laser using a simple structure. ing. Specifically, it has been proposed to detect the wavelength of laser light emitted from an external cavity semiconductor laser using an optical wedge.

  When a laser device having the configuration of the external resonance semiconductor laser having the configuration shown in FIG. 1 is commercially available, the laser device is accommodated in a case. In order to prevent dust from entering the case, a window glass is attached to the laser beam exit. In order to improve the quality of the emitted laser light, it is necessary to use a window glass having a small aberration and having an antireflection coating. In addition to the need to make the optical wedge itself high quality, the need for the window glass has a problem of increasing the cost of the laser device.

  Accordingly, an object of the present invention is to provide a laser apparatus capable of reducing the cost by combining an optical wedge for wavelength detection with the function of a window glass.

In order to solve the above-described problems, the present invention provides a semiconductor laser,
A reflective diffraction grating that receives laser light from the semiconductor laser, emits zero-order light at a predetermined reflection angle, and diffracts the primary light at an angle corresponding to a predetermined wavelength and returns it to the semiconductor laser;
An optical element that receives zero-order light, emits zero-order light to the outside, and generates reflected light having a striped light intensity distribution;
A detection element that receives the reflected light from the optical element and detects the position of the light spot on the light receiving surface;
A case in which a semiconductor laser, a reflective diffraction grating, an optical element, and a detection device are housed, and an opening for emitting 0th-order light is formed;
The laser device is provided so that the optical element closes the opening of the case.

  In this invention, since the optical element for wavelength detection, such as an optical wedge, also has a function of closing the opening for laser emission, the window glass can be made unnecessary, the necessary parts can be reduced, and the cost can be reduced. .

  The present invention detects the wavelength of laser light emitted from an external resonator type semiconductor laser using an optical wedge.

  Here, first, an optical wedge that is an example of an optical element that generates interference fringes will be described. An optical wedge is a wedge-shaped glass plate having a cross-sectional angle of several tens of minutes. When laser light having a single wavelength is incident on this at an angle of about 45 degrees, the light reflected by the front and back surfaces of the glass plate forms interference fringes. That is, if the phases of the two reflected lights match, it becomes bright, and if the phases of the two reflected lights are opposite, it becomes dark. Since the phase difference changes depending on the thickness of the optical wedge, a bright and dark striped pattern image is obtained in the direction in which the thickness changes. Further, when the wavelength changes, the position of light and dark changes.

  FIG. 4 shows a state in which the laser beam 3 is incident on the optical wedge 1. The laser beam 3 is reflected by the optical wedge 1 and enters the frosted glass 2. The optical wedge 1 is formed so that the thickness d becomes smaller as it proceeds in the z-axis direction of the coordinates shown in FIG. The z-axis direction is a direction from the front side of the description surface or the display surface of FIG. 4 toward the back side. The x-axis direction is a direction parallel to the front surface 1a and the back surface 1b of the optical wedge 1 and perpendicular to the y-axis, and the y-axis direction is a direction orthogonal to the x-axis and the z-axis.

  The laser beam 3 is reflected by the front surface 1a of the optical wedge 1 and incident on the frosted glass 2 and is also reflected by the rear surface 1b of the optical wedge 1 and incident on the frosted glass 2. Therefore, an optical path difference occurs, and as a result, FIG. 5 is generated. Note that the direction in which the thickness d of the optical wedge 1 decreases may be the x-axis direction. In this case, the interference fringes 10 shown in FIG.

  As will be described later, in the present invention, since it is not necessary for the human eye to see the interference fringes 10 shown in FIG. 5, the frosted glass 2 is not an essential component of the present invention. In the present invention, a two-divided detector having at least two detectors is used for detecting the interference fringes 10.

  Here, the optical wedge will be described in more detail. Consider the case where light rays A and B in one laser are incident on the optical wedge 1 as shown in FIG. Here, the optical wedge 1 is the same as that shown in FIG. 4, and is formed so that the thickness d of the optical wedge 1 becomes smaller as it advances in the z-axis direction shown in the figure.

The light beam A is reflected by the front surface 1 a of the optical wedge 1 to become the light beam C, and the light beam B is reflected by the back surface 1 b of the optical wedge 1 and is also the light beam C. At this time, the optical path difference between the light beam A and the light beam B is obtained, and the phase difference at the light beam C is calculated using the difference. First, the relationship of the following formula | equation 1 is formed from Snell's law.
sin θ / sin θ ′ = n (1)
On the other hand, the length of Lg is expressed by the following formula 2.
Lg = 2d * tan θ ′ * sin θ (2)
Further, the distance Lp through which the light beam B passes through the optical wedge 1 is expressed by the following Expression 3.
Lp = 2 (Lp / 2) = 2 (d / cos θ ′) = 2 d / cos θ ′ (3)

Here, when Lp ′ is an optical distance of Lp, Lp ′ is expressed by the following Expression 4.
Lp ′ = 2nd / cos θ ′ (4)
The optical path difference ΔL between Lp ′ and Lg is expressed by the following Equation 5.
ΔL = Lp′−Lg = 2nd / cos θ′−2d * tan θ ′ * sin θ = 2d (n / cos θ′−sin θ * tan θ ′) (5)
The phase difference Δδ due to ΔL is expressed by the following Equation 6.
Δδ = ΔL / λ + π (6)
However, π is added for the phase change at the time of reflection.
Here, the light intensity I is expressed by Equation 7 below.
I = (cosΔδ) ² (7)

As shown in FIG. 7, when viewed along the x-axis, the optical wedge 1 has a wedge shape in which the distal end portion 15 is configured with an angle α (referred to as a wedge angle as appropriate) α. However, the optical wedge 1 does not need to have the tip portion 15 and is generally configured in an approximately trapezoidal shape that does not include a tapered tip portion. Further, as shown in FIG. 7, the thickness d of the optical wedge 1 is a function of the displacement z in the z-axis coordinates, and is expressed as the following Expression 8. Here, z is the distance from the tip 15 on the z-axis.
d = z * tanα (8)

  Next, what kind of interference fringes are generated by the light reflected by the optical wedge 1 is examined by paying attention to the intensity of light of two wavelengths. Here, it is assumed that light having a typical lower limit wavelength (λ1) and upper limit wavelength (λ2) that are found in the sawtooth wave-like wavelength change in the external cavity semiconductor laser is used. That is, λ1 is 410.00 nm and λ2 is 410.04 nm. Further, the refractive index n = 1.5, the incident angle θ = 45 degrees, and the wedge angle α of the optical wedge 1 = 0.02 degrees.

  FIG. 8 is a graph showing how the intensity of the reflected light of the optical wedge 1 changes according to the position of the optical wedge 1 where the light of the wavelength λ1 and the light of the wavelength λ2 are incident. The relative light intensity is represented, and the horizontal axis represents the distance from the tip 15 of the optical wedge 1, that is, the distance from the tip 15 of the optical wedge 1 shown in FIG. 7 in the z-axis direction. FIG. 8 shows a change in the intensity of the reflected light when the light with the wavelength λ1 and the light with the wavelength λ2 are irradiated from the tip 15 of the optical wedge 1 to about 3 mm.

  As described above, when an image by reflected light is generated, a position where the intensity is high becomes a bright band, a position where the intensity is low becomes a dark band, and interference fringes where bright bands and dark bands are alternately positioned appear. In this case, the two wavelengths λ1 and λ2 are very close to each other, and furthermore, since the light is irradiated on the portion close to the tip 15 of the optical wedge 1, the optical path difference is also very small. Accordingly, the curve 21 representing the intensity of the reflected light of the wavelength λ1 and the curve 22 representing the intensity of the reflected light of the wavelength λ2 are substantially the same curve, and the interference fringes appear to overlap.

  FIG. 9 shows how the intensity of the reflected light of the light incident on the optical wedge 1 changes as in FIG. FIG. 9 shows a case where the light incident position is about 1000 mm (1 m) from the distal end portion 15 of the optical wedge 1. Even if the distance from the tip 15 of the optical wedge 1 is about 1 m, an optical wedge having a length of 1 m is not necessarily required. As described above, since the portion near 1 m from the distal end portion 15 is cut out in a trapezoidal shape, the size of the optical wedge itself can be reduced.

  In this case, at a position of about 1 m from the tip 15 of the optical wedge 1, the thickness d of the optical wedge 1 is considerably large. As a result, a wavelength difference of 0.04 nm between λ1 and λ2 is accumulated. A slight phase difference occurs. Since the phase difference is small, the striped pattern observed in each case hardly changes.

  This is a result of an experiment in which light of wavelength λ1 and light of wavelength λ2 are individually irradiated at predetermined positions. It is assumed that the optical wedge 1 is irradiated with light having a sawtooth wave-like wavelength change as shown in FIG. Here, it is assumed that the lower limit of the wavelength in the wavelength change is λ1, and the upper limit is λ2. Then, first, a curve 21 due to the reflected light of the light having the wavelength λ1 appears. Thereafter, as the laser power of the semiconductor laser is increased, the wavelength gradually changes from λ1 to λ2 and approaches the curve 22. Thereafter, when the laser power is further increased, both the curve 21 and the curve 22 are present, and thereafter, only the curve 21 due to the reflected light of the light having the wavelength λ1 is obtained. Thereafter, as the laser power increases, such interference fringe changes are periodically observed.

  FIG. 10 shows how the light intensity of the reflected light of the light incident on the optical wedge 1 changes as in FIG. FIG. 10 shows a case where the light incident position is about 6000 mm (6 m) from the distal end portion 15 of the optical wedge 1. In this case, the curve 21 representing the intensity of the reflected light of the wavelength λ1 and the curve 22 representing the intensity of the reflected light of the wavelength λ2 are almost opposite in phase, and both lights simultaneously enter the optical wedge 1. When incident, interference fringes are difficult to observe.

  In addition, when the wedge angle α is changed from 0.02 degrees to 0.04 degrees in the state shown in FIG. 9, both the curves 21 and 22 have a shorter period, and the number of fringes at the same distance is shown in FIG. 9. More than what is shown. As described above, by adjusting the position where the light of the optical wedge is irradiated, the wedge angle α, and the like, the mode of the interference fringes can be freely adjusted.

  Next, the push-pull value obtained from the reflected light from the optical wedge 1 will be described with reference to FIG. In FIG. 11, in addition to the curve 21 based on the lower limit wavelength (λ1) and the curve 22 based on the upper limit wavelength (λ2), the wavelength λ3 (410.01 nm), the wavelength λ4 (410.02 nm), and the wavelength λ5 (410.03 nm). The light curves are represented as a curve 23, a curve 24, and a curve 25, respectively. Further, here, the shape of the optical wedge 1 and the conditions such as the wedge angle α are the same as those shown in FIG.

  Here, a two-divided detector in which the first detector 31 and the second detector 32 each having a width of 0.3 mm are arranged before and after the position where the distance (z) from the tip 15 of the optical wedge 1 is 6001.6 mm. To generate a difference signal (push-pull). Here, the difference signal indicates a difference in light intensity respectively detected by the detector 31 and the detector 32. The position of light detected by the detector 31 is indicated by an arrow D, and the position of light detected by the detector 32 is indicated by an arrow E. In addition, detectors 35 and 36 are provided at positions close to the detectors 31 and 32. The positions of the light detected by these detectors 35 and 36 are indicated by arrows F and G, respectively. In the following description, attention is paid to detection by the detectors 31 and 32.

  As a result of detection by the detector 31 and the detector 32, a push-pull value as shown in FIG. 12 is obtained for each wavelength. However, this is a signal when light of each wavelength is irradiated to the position z of the optical wedge 1 alone.

  Further, since the push-pull value obtained in this way also changes depending on the increase or decrease in the amount of light, it is desirable to normalize using the sum signal. The relationship between the push-pull value normalized in this way and the wavelength is shown in FIG.

  Next, the relationship between the wavelength change of the light of the external cavity semiconductor laser and the push-pull value will be described. Now, as shown in FIG. 14, it is assumed that there is an external cavity semiconductor laser that changes the wavelength of a sawtooth wave according to the laser power. This schematically represents the same wavelength change as the graph shown in FIG. That is, as the laser power increases, the wavelength changes from 410.00 nm to 410.04 nm. However, when the laser power becomes, for example, around 23 mW or 35 mW, the wavelength changes abruptly and returns to 410.00 nm. Repeat the change. In addition, when this sudden change occurs, light having a wavelength of about 410.00 nm and light having a wavelength of about 410.04 nm are mixed and are not suitable for hologram recording or the like (unusable mode light). It becomes.

  Therefore, when this abrupt change occurs, that is, when light having a wavelength of 410.00 nm (λ1) and light having a wavelength of 410.04 nm (λ2) coexist, the positional relationship described with reference to FIG. The push-pull value is acquired by the detector 31 and the detector 32. In FIG. 15, the amount of light obtained for the light of wavelength λ1 is represented by a curve 21, and the amount of light obtained for the light of wavelength λ2 is represented by a curve 22. Since the curves 21 and 22 are almost in reverse phase, the light intensity obtained as a whole by these lights does not change much even if the irradiation position on the optical wedge 1 changes. As a result of detection by the detector 31 and the detector 32, the amount of light detected by the detector 31 and the amount of light detected by the other detectors 32 are substantially equal, and the push-pull value is close to zero.

  On the other hand, when the wavelength of the laser light emitted from the external resonator type semiconductor laser increases monotonously in accordance with the increase in the laser power (usable mode), the single mode or two modes with very close wavelengths, or It becomes 3 mode light. Therefore, in this case, it is assumed that single mode light having a wavelength constituting a typical peak is emitted. When the wavelength is 410.01 nm (λ3), as shown in FIG. 16, the difference in the amount of light detected by the detector 31 and the detector 32 is small, and the push-pull value is small.

  FIG. 17 shows how the detector 31 and the detector 32 detect the amount of light for a wavelength of 410.02 nm (λ4). In this case, there is a difference in the amount of light detected by each detector, and a relatively large push-pull value is obtained. FIG. 18 shows how the detector 31 and the detector 32 detect the light amount at a wavelength of 410.03 nm (λ5). In this case, there is a large difference in the light amount detected by each detector. Yes, a large push-pull value can be obtained.

  When a two-divided detector comprising detectors 35 and 36 is used in place of detector 31 and detector 32, the push-pull value changes differently. Thus, the actual push-pull value obtained on the premise of the wavelength change of the external cavity semiconductor laser can be close to 0 near the wavelength of 410.02 nm. On the other hand, when the push-pull value obtained for each wavelength shown in FIGS. 12 and 13 is seen, it can be seen that the wavelength 410.00 nm and the wavelength 410.04 nm show a large push-pull value at that wavelength alone. Further, at least different push-pull values can be obtained for light of wavelengths generated in the external resonator mode hop region.

  Therefore, in the present invention, it is detected from the push-pull value obtained in the region of the external resonator mode hop that the wavelength of the laser light approaches 410.00 nm (or 410.04 nm), and in that case, the semiconductor laser The laser power is controlled so as to avoid a mode in which light of these wavelengths is mixed, that is, an unusable mode. Depending on the application, even in the case corresponding to FIG. 3A and FIG. 3B, it is possible to change the laser power so as to always be in the single mode.

  With this control, the wavelength of the laser light emitted from the external cavity semiconductor laser can be grasped, and the wavelength of the laser light can be maintained at an appropriate level without strictly controlling the temperature of the semiconductor laser or the like. It becomes possible to control to do. As described above, in the conventional external resonator type semiconductor laser, for example, the angle of the grating can be adjusted and the wavelength can be changed by combining a screw and a piezo element. The angle shall be kept constant. In addition, this wavelength control is effective for specifying a wavelength that fluctuates within a narrow range, such as a change in wavelength of laser light emitted from an external cavity semiconductor laser.

  Next, the positional relationship between the two detectors 31 and 32 of the two-divided detector and the interference fringes will be described with reference to FIG. In FIG. 19, reference numeral 40 indicates a curve corresponding to the brightness of light reflected by the front and back surfaces of the optical wedge. The horizontal axis corresponds to the z-axis, and the vertical axis represents the amount of light (light intensity). This curve 40 is an example of a certain wavelength. However, if the laser power provided to the semiconductor laser in the external resonator type semiconductor laser is changed, the wavelength changes, and accordingly, the curve 40 also has the phase. Also changes. In the lower part of FIG. 19, a detector 31 and a detector 32 in the two-divided detector are shown, and the light quantity of the curve 40 is detected at that position.

  Of the curve 40, a portion with a small amount of light is shown as a region 41, and this portion corresponds to a portion of the interference fringes that appears dark. In the state shown in FIG. 19, the detector 31 is arranged in a portion of the curve 40 where the amount of light is large, and consequently detects a large amount of light. On the other hand, the detector 32 is arranged in a portion of the curve 40 where the amount of light is small (partly overlaps the region 81), and detects the small amount of light. Here, the push-pull value is obtained by obtaining the difference between the detection signals of the detectors, and the corresponding wavelength can be grasped.

  20A and 20B show one configuration of the laser apparatus having the wavelength detection function described above. 20A is a view as seen from the reflection surface side of the grating 54 of the laser device, and FIG. 20B is a plan view of the laser device. In FIG. 20, reference numeral 51 indicates a laser diode. The laser diode 51 is housed in the holder 52 in an airtight manner. Laser light from the laser diode 51 is emitted through the collimator lens 53 attached to the holder 52 and is incident on the grating 54. The collimating lens 53 also serves as a window glass for accommodating the laser diode 51 in the holder 52 in an airtight manner.

  A grating 54 is attached to the grating attachment portion 55. The grating mounting portion 55 is held by the support column 57 via the leaf spring 56. The position of the grating mounting portion 4 away from the position where the plate spring 4 is mounted is displaced up and down in accordance with the rotation of the screw 58, whereby the angle of the grating 54 is varied. The screw 58 is inserted into the screw support 59.

  The laser light diffracted by the grating 54 is incident on the optical wedge 1. The inclination of the optical wedge 1 is not 45 ° but 30 °, for example. As will be described later, in the present invention, the optical wedge 1 also serves as a window glass for closing the laser emission port of the box cover. Therefore, when the angle is set to 45 °, the two-divided detector moves closer to the end of the laser device. Increases in size. For this purpose, the optical wedge 1 is installed at an angle of about 30 °.

  The optical wedge 1 has a reflectance of 5% or less, for example. In the case of 5%, approximately 10% of the reflection on the front surface and the reflection on the back surface is used for wavelength detection, and the laser beam emitted to the outside is reduced to 90%. In order to reduce this loss, the reflectance of the optical wedge 1 is preferably 3% or less. Specifically, low reflectance can be achieved by applying a low reflection coating. However, if the reflectance is too low, the wavelength detection is hindered, so it is necessary to ensure a reflectance of 0.5% or more.

  The optical wedge 1 is attached to a holding table 60 in which a window having a rectangular cross section is formed. The reflected light of the optical wedge 1 is incident on the two-divided detector 61, and the laser light transmitted through the optical wedge 1 is emitted to the outside. The two-divided detector 61 is supported by a detector support 62. As described above, the wavelength of the laser beam is detected from the value of the difference signal between the detection signals of the two detectors of the two-divided detector 61. Components of the laser device such as the laser diode 51 are mounted on the pedestal 64. In FIG. 20A, illustration of the leaf spring 55, the support 56, the two-divided detector 61, and the detector support 62 is omitted for the sake of simplicity.

  The entire laser device described above is accommodated in the box cover. In FIG. 21, reference numeral 70 indicates a box cover. FIG. 21A is a side view of the box cover 70, and FIG. 21B is a plan view of the box cover 70. The box cover 70 is attached on the pedestal 64 so as to cover the components of the laser device formed on the pedestal 64 from above.

  A circular opening 71 is formed at the laser beam emission position of the box cover 70. A rectangular tube-shaped light guide 72 having a width and height slightly larger than the diameter of the opening 71 is provided so as to extend inward from the opening 71 so that the holding table 60 of the optical wedge 1 can be fitted. Yes. The extended end of the light guide 72 is cut off obliquely. The angle of the extended end is set to coincide with the inclination of the optical wedge 1. In addition, you may provide a cylindrical light guide part instead of a rectangular tube shape.

  22A and 22B are a side view and a plan view showing a state in which the box cover 70 is attached. However, for the sake of simplicity, illustration of some of the components shown in FIG. 20 is omitted. As shown in FIG. 22B, the holding base 60 of the optical wedge 1 is fitted and attached to the end of the light guide 72 provided in the box cover 70. The optical wedge 1 is attached to the holding table 60. Therefore, the opening 71 of the box cover 70 is closed by the optical wedge 1, and the optical wedge 1 functions as a window glass, so that the window glass can be omitted.

The present invention is not limited to the above-described embodiments of the present invention, and various modifications and applications are possible without departing from the spirit of the present invention. For example, the detection element is not limited to the two-divided detector 21, but a one-dimensional PSD (Position Sensitive Detector) may be used. The PSD has a configuration in which a uniform resistance layer is formed on one surface or both surfaces of a high-resistance semiconductor substrate, and a pair of electrodes for signal extraction are provided on both ends of the resistance layer. The light receiving surface forms a PN junction simultaneously with the resistance layer, and a photocurrent is generated by the photovoltaic effect. Photocurrents A and B are generated from the electrodes at both ends in accordance with the position of the light spot LB on the light receiving surface. When the light spot is located at the center position of the light receiving surface, the photocurrents A and B have the same value. Further, a CCD (Charge Coupled Device) may be used as the detection element.

  Further, the external resonator type semiconductor laser of the present invention has been described as using the Littrow type, but other external resonator type semiconductor lasers such as the Littman type can also be used.

  Further, the present invention may use other optical components that can obtain the same effect as the optical wedge. For example, when glass having flat surfaces is used instead of the optical wedge, the striped pattern changes with the change of the wavelength as in the optical wedge, even if the laser light is slightly diffused light or convergent light. Depending on the angle of the incident laser light and the flat glass, each stripe in the stripe pattern has a substantially straight shape or a curved shape.

  When the diffused light or convergent light is incident, the wavefront is not flat, and concentric stripes appear when the flat glass receives incident light at a predetermined angle. At this time, when the wavelength changes, concentric stripes spread outward or gather inside. Therefore, when the angle of the flat glass is changed, a striped pattern away from the center of the concentric circle appears, and in this case, the striped pattern is a curved striped pattern. On the other hand, when the angle of the flat glass is further adjusted, a striped pattern further away from the center of the concentric circle appears. In this case, each strip becomes a substantially straight striped pattern.

It is a basic diagram which shows the structure of a Littrow type external resonator type semiconductor laser. It is a graph which shows the wavelength of the laser beam inject | emitted from an external resonator type semiconductor laser according to the change of laser power. It is a basic diagram which showed the pattern of the mode of the laser beam inject | emitted from an external resonator type semiconductor laser. It is a basic diagram for demonstrating the effect | action of an optical wedge. It is a basic diagram which shows the interference fringe which generate | occur | produces by reflecting with an optical wedge. It is a basic diagram for calculating the optical path difference of an optical wedge. It is the basic diagram which looked at the optical wedge along the x-axis direction. It is a graph which shows the intensity | strength of the reflected light when the light of wavelength (lambda) 1 and wavelength (lambda) 2 reflects in an optical wedge. It is another graph which shows the intensity | strength of the reflected light when the light of wavelength (lambda) 1 and wavelength (lambda) 2 reflects in an optical wedge. It is a graph which shows the intensity | strength of the reflected light when the light of wavelength (lambda) 1 and wavelength (lambda) 2 reflects in an optical wedge. It is a graph which shows the intensity | strength of the reflected light when the light of wavelength (lambda) 1-wavelength (lambda) 5 reflects in an optical wedge. It is a graph which shows the transition of the push pull value calculated based on the detected value from two detectors. It is a graph which shows the value which normalized the push pull value shown in FIG. In an external resonator type semiconductor laser, it is an approximate line figure showing typically a wavelength of a laser beam which changes with change of laser power. It is a graph which shows the intensity | strength of the reflected light when the upper limit wavelength and lower limit wavelength of the laser beam inject | emitted from an external resonator type semiconductor laser are reflected on the optical wedge simultaneously. It is a graph which shows the aspect of the detection of the intensity | strength of reflected light when the light of wavelength (lambda) 3 reflects in an optical wedge, and a detector. It is a graph which shows the intensity | strength of the reflected light when the light of wavelength (lambda) 4 reflects in an optical wedge, and the aspect of a detection by a detector. It is a graph which shows the intensity | strength of the reflected light when the light of wavelength (lambda) 5 reflects in an optical wedge, and the aspect of a detection by a detector. It is a basic diagram explaining the positional relationship of two detectors and interference fringes. It is the side view and top view which show an example of a structure of the laser apparatus which can apply this invention. It is the side view and top view of a box cover in one Embodiment of this invention. It is the side view and top view of the state which attached the box cover.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical wedge, 51 ... Semiconductor laser, 54 ... Grating, 60 ... Optical wedge holding stand, 61 ... 2-part detector, 70 ... Box cover, 71 ... Opening 72 light guide

Claims (6)

A semiconductor laser;
A reflective diffraction grating that receives laser light from the semiconductor laser, emits zero-order light at a predetermined reflection angle, and diffracts primary light at an angle corresponding to a predetermined wavelength and returns the first-order light to the semiconductor laser;
An optical element that receives the zero-order light, emits the zero-order light to the outside, and generates reflected light having a striped light intensity distribution;
A detection element that receives the reflected light from the optical element and detects the position of the light spot on the light receiving surface;
A case in which the semiconductor laser, the reflective diffraction grating, the optical element, and the detection device are housed, and an opening for emitting the zero-order light is formed;
The laser apparatus provided so that the said optical element might block | close the said opening of the said case. In claim 1,
A laser apparatus in which the reflectance of the optical element is set to 5% or less. In claim 1,
A cylindrical light guide is extended inward from the opening of the case,
A laser device to which the optical element is attached so as to cover an extended end portion of the light guide portion. In claim 1,
A laser device in which a difference signal that changes in accordance with a change in the position of the light spot is formed from an output signal of the detection element, and the wavelength of the zero-order light is detected from the difference signal. In claim 4,
A laser device for controlling the power of the semiconductor laser based on the detected wavelength so that the laser power of the zero-order light emitted to the outside does not become a power whose oscillation spectrum is disturbed. In claim 1,
A laser apparatus, wherein the optical element is an optical wedge.

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