JP2006010499A - Wavelength determination device and wavelength determination method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength determination device and a wavelength determination method capable of determining a wavelength of a laser beam emitted from an external resonator type semiconductor laser, over a wide range. <P>SOLUTION: The laser beam emitted from the external resonator type semiconductor laser 50 is determined in two steps by two detectors 202, 203. The detector 202 is provided with an optical wedge 204, and light intensity of a reflected beam thereof is detected by a two-divided detector 206. The detector 203 is provided with an optical wedge 205, and light intensity of a reflected beam thereof is detected by a two-divided detector 207. Wedge angles and plate thicknesses of the two optical wedges 204, 205 are regulated to generate the substantially same interference fringe even when receiving respectively different wavelength ranges of laser beams. A rough wavelength range of the laser beam is determined thereby using a differential value from the two-divided detector 206, and a detail level of wavelength is determined thereafter using a differential value from the two-divided detector 207. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a laser system including an external resonator type semiconductor laser, and more particularly to a wavelength determination device and a wavelength determination method for detecting the wavelength of laser light emitted from an external resonator type semiconductor laser.

  In recent years, laser systems have been 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 stored 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), which 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 / reproduction. It is.

  Here, a configuration of a Littrow type laser system including a conventional typical external cavity semiconductor laser will be described with reference to FIG. FIG. 23 is a plan view of the laser system 300. The configuration of the laser system 300 is the same as the configuration of the laser system described in Non-Patent Document 1.

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

  In the laser system 300, longitudinal multimode laser light (oscillation light) emitted from a semiconductor laser element such as a laser diode 301 is collected in parallel by a lens 302 and is incident on a grating (diffraction grating) 303. The grating 303 outputs first-order diffracted light of incident light. First-order diffracted light having a specific wavelength according to the arrangement angle of the grating 303 is back-injected into the laser diode 301 through the lens 302. As a result, the laser diode 301 resonates with the injected first-order diffracted light and emits single-mode light (0th-order light represented by the arrow F). The wavelength of the light is from the grating 303. It becomes the same as the wavelength of the returned light.

  In this example, the delicate angle of the grating 303 is adjusted by combining the screw 305 with the piezo element.

  Next, with reference to the graph of FIG. 24, the relationship between the laser power and the wavelength of the laser light output from the external resonator type laser system as described in FIG. 23 will be described. The horizontal axis of the graph shown in FIG. 24 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. 24, as the laser power of the laser light increases, the wavelength of the laser light generally shows a saw-like change.

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

  Also, for example, when the laser power is around 30 mW, a single wavelength laser beam is emitted and becomes a complete single mode, but when the laser power is around 32 mW, light of three modes (three modes) is generated. ing. Further, when the laser power in the vicinity of the mode hop by the laser chip in the semiconductor laser is about 35 mW, three-mode light is generated in the vicinity of a wavelength of 409.75 nm, and further, three-mode light is generated in the vicinity of a wavelength of 409.715 nm. As a whole, 6-mode light is emitted.

  When these laser lights are used for HDS, the three-mode light and the two-mode light that are generated when the laser power is around 32 mW exhibit the same recording / reproduction characteristics as the single-mode light. Can be used in the same way as 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, in a 6-mode state in which the laser power is generated in the vicinity of 35 mW, two sets of 3 modes are separated from each other by about 40 pm (0.04 nm), so that excellent hologram recording can be realized. Can not. Here, such a mode is referred to as an unusable mode. For example, when recording is performed using a laser beam in an unusable mode on a hologram medium having an M / # of 6.5 in the usable mode, M / # deteriorates to 2.5.

  The region where the usable mode laser light can be obtained substantially corresponds to the above-mentioned external cavity mode hop region, and the region where the unusable mode laser light can be obtained is the mode described above by the laser chip in the semiconductor laser. Almost corresponds to the hop area. As can be seen from the graph of FIG. 24, in general, the region in which the usable mode laser light is obtained is much wider than the region in which the unusable mode laser light is obtained. If this can be effectively eliminated, it is sufficiently possible to use an external cavity semiconductor laser for HDS.

  Also, as shown in FIG. 24, the relationship between the laser power and the wavelength of the laser light varies depending on the temperature in the external cavity semiconductor laser. For example, if the temperature of the semiconductor laser of the external resonator type semiconductor laser is not constant, the position of the laser power at which the unusable mode is changed. Therefore, conventionally, the temperature in the external cavity semiconductor laser is kept almost constant (for example, suppressed within 10 mK), and the region where the laser beam in the unusable mode can be 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 system 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.

  Furthermore, in the external resonator type semiconductor laser, the wavelength of the emitted laser light can be changed, for example, several nm by changing the installation angle of the grating, and in the laser light having such a wavelength changed, A minute change in wavelength (for example, a change in the range of 0.04 nm) due to a change in laser power appears. Therefore, there is a need for a laser system that can determine unusable mode laser light and usable mode laser light over a wavelength in the range of several nanometers. Currently, a laser system having such a function is proposed.・ Not developed.

  Accordingly, an object of the present invention is to provide a wavelength determination device that detects and determines the wavelength of a laser beam emitted from an external cavity semiconductor laser using a simple structure over a relatively wide range of several nm, and a wavelength. It is to provide a determination method.

  A further object of the present invention is to control the laser power to a predetermined level based on the detection result of the wavelength as described above, and thus to avoid the use of the laser beam in the unusable mode, and the wavelength It is to provide a determination method.

  According to a first embodiment of the present invention, a first reflection that receives at least a part of a laser beam emitted from an external cavity semiconductor laser and emits a first reflected light having a different light intensity distribution with respect to a first direction. Means, first light detecting means for detecting the light intensity of the first reflected light from the first reflecting means at at least two light receiving positions, and at least part of the laser light emitted from the external resonator type semiconductor laser. A second reflecting means for receiving and emitting a second reflected light having a different light intensity distribution with respect to the second direction; and a second reflecting means for detecting the light intensity of the second reflected light from the second reflecting means at at least two light receiving positions. The difference value of the detection signal at the at least two light receiving positions of the two light detection means and the first light detection means is obtained as the first difference value, and the difference value of the detection signal at the at least two light reception positions of the second light detection means. The Two difference values, and wavelength determining means for determining the wavelength of the laser light based on the first difference value and the second difference value, and the first light detecting means and the second light detecting means are respectively The wavelength determination device is configured to detect light intensities with different sensitivities according to the difference in light intensity distribution between the first reflected light and the second reflected light.

  According to a second embodiment of the present invention, a first reflected light having at least a part of a laser beam emitted from an external cavity semiconductor laser and receiving a different light intensity distribution with respect to the first direction is emitted. A first light detecting step for detecting the light intensity of the first reflected light from one reflecting means at at least two light receiving positions; and at least a part of the laser light emitted from the external resonator type semiconductor laser; A second light detecting step for detecting the light intensity of the second reflected light from the second reflecting means for emitting the second reflected light having different light intensity distributions in the two directions at at least two light receiving positions; The difference value of the detection signal at the at least two light receiving positions detected in the step is obtained as the first difference value, and the detection signal at the at least two light receiving positions detected in the second light detection step A wavelength determination step of determining a difference value as a second difference value and determining a wavelength of the laser beam based on the first difference value and the second difference value, and a first light detection step and a second light detection step. Is a wavelength determination method configured to detect light intensities with different sensitivities according to the difference in light intensity distribution between the first reflected light and the second reflected light.

  The wavelength determination apparatus and the wavelength determination method according to the present invention can detect and determine the wavelength of laser light emitted from an external cavity semiconductor laser using a simple structure over a relatively wide range of several nm. it can. Further, based on such a detection result, the laser power of the semiconductor laser can be controlled so that the laser beam can be prevented from having an unusable mode wavelength.

  The present invention uses a plurality of reflecting means such as an optical wedge to detect and determine the wavelength of laser light emitted from an external cavity semiconductor laser over a relatively wide range such as several nm, and if necessary Based on the detection result, the power of the semiconductor laser is to be controlled.

  Before describing specific embodiments of the present invention, a laser system having a simple structure for detecting the wavelength of laser light emitted from an external cavity semiconductor laser will be described.

  First, the optical wedge used in the laser system and the wavelength determination device of the present invention will be described. An optical wedge is a glass plate whose angle between both surfaces is about several tens of minutes. When laser light 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.

  FIG. 1 is a schematic diagram showing a state in which a laser beam 3 is incident on an 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. 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 perpendicular to the x-axis and the z-axis.

  FIG. 2 is a schematic diagram showing an example of interference fringes that can be observed with the frosted glass 2 in the situation shown in FIG. 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. 2 is generated. In FIG. 2, each interference fringe 10 is shown to be generated in a direction substantially perpendicular to the z-axis, but is not necessarily generated in such a direction. Due to the influence of aberration or the like, the interference fringes 10 may be generated at a considerably different angle from the direction perpendicular to the z-axis.

  As will be described later, in the above laser system, since it is not necessary for the human eye to see the interference fringes 10 shown in FIG. 2, the frosted glass 2 is not an essential component of the present invention. In the laser system, at least two detectors are used to detect the interference fringes 10.

  Here, the optical wedge will be described in more detail. Consider a case in which 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. 1, and is formed such that the thickness d of the optical wedge 1 decreases 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 a light beam C, and the light beam B is reflected by the back surface 1 b of the optical wedge 1 and is also converted to 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 (Expression 1)
On the other hand, the length of Lg is expressed by the following formula 2.
Lg = 2d * tan θ ′ * sin θ (Expression 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 ′ (Expression 3)

Here, when Lp ′ is an optical distance of Lp, Lp ′ is expressed by the following Expression 4.
Lp ′ = 2nd / cos θ ′ (Formula 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 ′) (Formula 5)
The phase difference Δδ due to ΔL is expressed by the following Equation 6.
Δδ = 2π * ΔL / λ + π (Formula 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 = 2 (1 + cosΔδ) (Expression 7)
Here, the light intensity I can be approximated to “1 + cos Δδ”, except for an unimportant factor “2”.

When the optical wedge 1 shown in FIG. 3 is viewed along the x-axis, the tip 15 has a wedge shape having an angle (wedge angle) α, and this state is shown in FIG. 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. As shown in FIG. 4, 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 * tan α (Expression 8)

  The optical wedge 1 has different interference depending on the wavelength of the incident light, the position of the optical wedge 1 on which the light is incident (distance (z) in the z-axis direction from the tip 15 of the optical wedge 1 shown in FIG. 4), and the like. Generate streaks.

  Here, the light incident on the optical wedge 1 is laser light from an external resonator type semiconductor laser, and, as shown in FIG. 5, changes in a sawtooth wavelength according to a change in laser power. . This schematically represents a change in wavelength similar to that of the graph shown in FIG. That is, as the laser power increases, the wavelength changes from about 410.00 nm to about 410.04 nm, but when the laser power becomes, for example, around 23 mW or 35 mW, the wavelength changes abruptly and returns to 410.00 nm. This change is repeated periodically. 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.

  FIG. 6 is a graph showing how the intensity of the reflected light changes according to the position of the optical wedge 1 where the light of wavelength λ1 and the light of wavelength λ2 are incident, and the vertical axis indicates relative light. The horizontal axis represents the distance from the tip 15 of the optical wedge 1, that is, the distance (z) in the z-axis direction from the tip 15 of the optical wedge 1 shown in FIG.

  In this example, for the optical wedge 1, the refractive index n = 1.5, the incident angle θ = 45 degrees, the wedge angle α of the optical wedge 1 = 0.01 degrees, the wavelength λ1 is 410.00 nm, and the wavelength λ2 is 41.04 nm.

  FIG. 6 shows a change in the intensity of reflected light when the light of wavelength λ1 and the light of wavelength λ2 are irradiated between the tip 15 of the optical wedge 1 and about 3 mm. In this case, since the two wavelengths λ1 and λ2 are very close to each other, and the light is irradiated on the portion close to the tip 15 of the optical wedge 1, the optical path difference is also extremely small. Therefore, 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 periodically changing curves, and the interference fringes are clearly visible. become.

  FIG. 7 shows how the intensity of the reflected light of the light incident on the optical wedge 1 changes in the same way as in FIG. 6. The position where the light enters is the tip 15 of the optical wedge 1. 1 to 1000 mm (1 m). 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. However, since the phase difference is small, the striped pattern observed in each case hardly changes.

  This is the result of experimenting by individually irradiating light of wavelength λ1 and light of wavelength λ2, and based on this result, light that repeats a sawtooth wavelength change as shown in FIG. It is assumed that the optical wedge 1 is irradiated. 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 by the reflected light of the light having the wavelength λ1 is obtained. Thereafter, as the laser power increases, the above-described interference fringe change (that is, light intensity distribution) is periodically observed.

  Further, when the wedge angle α is increased in the state shown in FIG. 7, both the periods of the curve 21 and the curve 22 are reduced, and the number of fringes at the same distance becomes larger than that shown in FIG. 7. In this way, by adjusting the position of the optical wedge that irradiates light, the wedge angle α, and the like, it is possible to control the interval of interference fringes (period of light intensity distribution) and the like.

  Next, with reference to FIG. 8, a case will be considered where interference fringes generated when the optical wedge 1 is irradiated with the laser light from the external cavity semiconductor laser described above are received by the two-divided detector 32. FIG. 8 shows the interference fringes when the light incident position is around 3000 mm (3 m) from the tip 15 of the optical wedge 1. The upper part of FIG. 8 is a graph showing a curve 30 corresponding to the light reflected by the front and back surfaces of the optical wedge 1. The horizontal axis of the graph corresponds to the z-axis shown in FIG. 3, and the vertical axis shows the amount of light (light intensity) constituting the interference fringes. This curve 30 is an example of a laser beam having 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 the curve changes accordingly. The phase of 30 changes. In the lower part of FIG. 8, a detector 32A and a detector 32B in the two-divided detector 32 are shown, and the amount of light indicated by the curve 30 is detected at that position.

  Of the light indicated by the curve 30, a portion with a small amount of light is shown as a region 31, and this portion corresponds to a portion of the interference fringe (striped pattern) that appears dark. Here, the curve 30 shown in FIG. 8 is obtained when a laser beam having a wavelength of, for example, 410.02 nm is incident, and the detector 32A and the detector 32B receive the maximum light amount in total at this time. The position has been adjusted to As described above, when the wavelength of light incident on the optical wedge 1 changes from 410.00 nm to 410.04 nm, the phase of the light indicated by the curve 30 changes accordingly, and is set at the above position. The amount of light received by the detector 32A and the detector 32B also changes gradually.

  Here, the push-pull value is obtained by obtaining the difference between the detection results of the detector 32A and the detector 32B, which is shown in FIG.

  However, FIG. 9 is a case where the light of each wavelength is irradiated to the predetermined position z of the optical wedge 1 independently. However, for example, as shown in FIG. 5, when a sudden change in wavelength occurs, light having a wavelength (λ1) of approximately 410.00 nm and light having a wavelength (λ2) of approximately 410.04 nm are mixed. When the light corresponding to each wavelength is almost in reverse phase, no interference fringe appears and the push-pull value is close to zero.

  Note that the push-pull value is usually used for tracking control of an optical disc, and the pickup is pushed or pulled based on a push-pull signal indicating the push-pull value. In this laser system, a predetermined component is not pushed or pulled based on the push-pull signal, but this term is used for convenience because of the commonality as a difference signal.

  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 thus normalized and the wavelength is shown in FIG.

  As described above, in the above-described laser system, by calculating the push-pull value, the corresponding wavelength, that is, the wavelength of the laser light emitted from the external resonator type semiconductor laser can be grasped.

  Further, as described above, in a state where almost opposite phase laser beams are mixed, the change in the amount of light with respect to the z axis is small, and interference fringes do not appear clearly. In the above example, when the wavelength is 410.02 nm and when the wavelength 410.00 nm and the wavelength 410.04 nm are mixed, the difference between the detection results of the two detectors is almost zero. However, it is possible to detect and determine the wavelength of the laser light emitted from the external resonator type semiconductor laser by grasping such a transition of the push-pull value and making a determination with a predetermined threshold.

  Next, the configuration of this laser system will be described. A laser system 51 shown in FIG. 11 includes a beam splitter 52, an optical wedge 53, a two-divided detector 54, and a laser control unit 55. The beam splitter 52 of the laser system 51 receives the laser light from the external resonator type semiconductor laser 50. The external cavity semiconductor laser 50 is, for example, a Littrow blue laser. The light 56 that has passed through the beam splitter 52 is used for HDS, for example.

  The light 57 reflected by the beam splitter 52 is preferably 10% or less of the laser light from the external resonator type semiconductor laser 50, and is used for monitoring the oscillation mode. Conversely, the light reflected by the beam splitter 52 may be used as HDS, and the light passing through the beam splitter 52 may be used for monitoring. However, even in this case, the light used for monitoring is desirably 10% or less of the laser light from the external resonator type semiconductor laser 50. This is simply to allocate more power to the original purpose of the laser light, such as HDS.

  The optical wedge 53 is arranged so that the light 57 reflected by the beam splitter 52 enters at an angle of about 45 degrees. The direction in which the thickness d of the optical wedge 53 gradually decreases is the z-axis direction shown in the figure. The z-axis direction is a direction from the front side of the drawing surface or the display surface to the back side. The light 58 reflected by the front and back surfaces of the optical wedge 53 is received by the two-divided detector 54. The two-divided detector 54 has two adjacent independent detectors. Two detectors in the two-divided detector 54 for monitoring the interference fringes are arranged side by side in a direction substantially perpendicular to the generated interference fringes. Since the interference fringes are not always generated in the direction perpendicular to the z-axis, the two detectors are not necessarily arranged side by side in the z-axis direction.

  The laser controller 55 grasps the wavelength of the laser beam from the external resonator type semiconductor laser 50 based on the output of the two-divided detector 54, and prevents the laser beam in the unusable mode from being emitted. The laser power supplied to the semiconductor laser of the laser 50 is determined. The laser control unit 55 will be described in detail later.

  In the example shown in FIG. 11, the laser system 51 is arranged outside the external resonator type semiconductor laser 50, but the laser system 51 can also be incorporated in the external resonator type semiconductor laser 50.

  Next, how the light 56 that has passed through the beam splitter 52 is used for HDS will be briefly described with reference to FIG. FIG. 12 shows a configuration of a hologram recording / reproducing system 60 that performs hologram recording / reproduction using a single-mode laser light source.

  Hologram recording and reproduction are performed by irradiating the hologram recording medium with reference light and signal light using a light source of a single mode laser.

  Here, the laser light source 61 corresponds to the one including the external cavity semiconductor laser 50 and the laser system 51 shown in FIG. 11, and the laser light 70 emitted from the laser light source 61 is the light shown in FIG. 56. In hologram recording, it is necessary to irradiate the hologram recording medium with laser light having a predetermined power for a predetermined optimum time. Such control is provided to the semiconductor laser in the external resonator type semiconductor laser 50. This is made possible by controlling the current (voltage) to be generated. Further, a shutter may be provided next to the laser light source 61, and the timing of irradiating the laser beam with the shutter may be controlled.

  The laser beam 70 emitted from the laser light source 61 is emitted toward the beam expander 62, where it becomes a laser beam 71 having an enlarged beam diameter. Next, the laser beam 71 enters the beam splitter 63 and is divided into two laser beams.

  The straightly traveling laser beam 72 is reflected by the mirror 64, further collected by the lens 65, and applied to the hologram recording medium 69 as reference light. The other laser beam 73 becomes signal light 74 modulated by a spatial modulator 66 composed of a liquid crystal element or the like. The signal light 74 is reflected by the mirror 67, collected by the recording lens 68, and irradiated on the hologram recording medium 69. At this time, the signal light 74 is applied to the same place as the place where the reference light 72 is applied onto the hologram recording medium 69, whereby a hologram pattern is recorded on the hologram recording medium 69.

  In such a hologram recording / reproducing system 60, multiplex recording / reproduction can be performed using the same area of the hologram recording medium 69. If holograms are recorded on the hologram recording medium 69 using reference light having different incident angles, the respective holograms are reproduced by reference light having the same incident angle as at the time of recording. In the spatial modulator 66, a liquid crystal element having a plurality of pixels is used. By preparing pixels with different transmission / shielding patterns for each signal light 74, desired data is multiplexed and recorded on the hologram recording medium 69. Can be (angle multiplexed).

  Next, the configuration of the laser controller 55 of the laser system 51 will be described with reference to FIG. The laser control unit 55 is connected to the two-divided detector 54 and the semiconductor laser 94 in the external resonator type semiconductor laser 50. The laser control unit 55 includes an NS determination circuit 91, a laser power correction circuit 92, and a semiconductor laser drive circuit 93.

The NS determination circuit 91 of the laser control unit 55 is provided with respective currents output from the detector 54A and the detector 54B of the two-divided detector 54 according to the laser power of the incident light. Therefore, the NS determination circuit 91 obtains a difference (difference signal) and a sum (sum signal) between the output of the detector 54A and the output of the detector 54B. Next, a normalized difference signal (hereinafter referred to as NS) is obtained. NS can be obtained by Equation 9 below.
NS = difference signal / sum signal (Equation 9)

  Thereafter, the NS value is compared with a preset range, and if the NS value is within the range, the digital value 1 is output, and if the NS value is out of the range, the digital value 0 is output. The setting range is, for example, between −0.4 and 0.4. In the example of FIG. 10 described above, it is recognized that when the value of NS (normalized push-pull value) approaches 0.5, it becomes an unstable unusable mode and a sudden change in wavelength occurs. It is. However, the threshold value as described above can be appropriately adjusted according to the position of the detector and the change characteristic of the reflected light from the optical wedge. By using such a threshold value, light having a wavelength generated in the external resonator mode hop region has a wavelength generated in the mode hop region by the laser chip in the semiconductor laser included in the external resonator semiconductor laser. The boundary of transition to light can be determined, and as a result, the emission of laser light in the unusable mode can be avoided.

  When the output of the NS determination circuit 91 is 0, the laser power correction circuit 92 instructs the semiconductor laser drive circuit 93 to change the laser power of the semiconductor laser 94. For example, first, the laser power of the semiconductor laser 94 is set to 33 mW, and each time 0 is output from the NS determination circuit 91, the control for lowering the laser power by 3 mW and the control for increasing the laser power by 3 mW are alternately repeated. To.

  The semiconductor laser drive circuit 93 is known as a circuit that performs APC (Auto Power Control), and can be used here.

  By such feedback control regarding the semiconductor laser 94, the laser power of the semiconductor laser 94 can be controlled so as to dynamically enter the usable mode. This is because, for example, the temperature control of the external resonator type semiconductor laser 50 and the semiconductor laser 94 is not performed (or the strict temperature control is not performed), so that the temperature of the semiconductor laser 94 changes and the unusable mode is set. Even when the laser power approaches, the return to the usable mode is automatically realized.

  In the above example, the laser power correction circuit 92 performs control to change the laser power by about 10% according to the output of the NS determination circuit 91 (for example, 33 mW is changed to 30 mW or 30 mW is changed to 33 mW). However, this change in laser power is not a problem for HDS applications. In HDS, not the irradiation power to the hologram recording medium but the irradiation energy (laser power × recording time) becomes a problem. Therefore, when the laser power is reduced by 10%, the recording time is about 11% (1 / 0.9). = 1.111) It should be increased. The change width may be made smaller by changing the specifications of the laser power correction circuit 92.

  Further, in the case where hologram recording is performed by gradually increasing the laser power, when the output of the NS determination circuit 91 becomes 0, the laser power correction circuit 92 sends a normal regularity to the semiconductor laser driving circuit 93. Independent of the laser power increase routine, the laser power of the semiconductor laser 94 can be instructed to be increased by several mW (for example, about 1 to 3 mW), and the unusable mode in which the wavelength becomes unstable can be controlled to be skipped. .

  For example, assuming that the laser light from an external cavity semiconductor laser changes as shown in FIG. 5 due to an increase in laser power (assuming that there is no change in wavelength due to temperature change of the semiconductor laser). By providing a laser power of about 18 mW, a 410.02 nm laser beam is emitted, which increases with increasing laser power and approaches 400.04 nm. Then, it is determined that NS calculated from the detection results of the two detectors is −0.4 or less and the region where the wavelength becomes unstable is approaching, and the laser power correction circuit 92 is a semiconductor laser driving circuit. 93 is instructed to increase the laser power of the semiconductor laser 94 several mW at a stroke. As a result, the region near 24 mW is skipped, and the laser light has a stable wavelength slightly exceeding 410.00 nm.

  After that, when the laser power gradually increases and approaches 35 mW, the NS calculated from the detection results of the two detectors becomes −0.4 or less, and the region where the wavelength becomes unstable is approaching. The laser power correction circuit 92 instructs the semiconductor laser drive circuit 93 to increase the laser power of the semiconductor laser 94 by several mW at a stroke. As a result, the region near 35 mW is skipped, and the laser light has a stable wavelength slightly exceeding 410.00 nm, and thereafter the same control is repeated.

  Each circuit in the laser control unit 55 described above can also be realized by control by a microcomputer including a CPU and a memory. In this case, the operation of each circuit is controlled by a program loaded in the memory. The program can be changed as necessary, and can be recorded in a recording device or memory in the microcomputer via a portable recording medium such as a CD-ROM or a network.

  Next, a modified example of the laser system 51 will be described. A laser system 101 shown in FIG. 14 includes a beam splitter 102, an optical wedge 103, a two-divided detector 104, a laser control unit 105, and a detector 106.

  Compared to the laser system 51, a detector 106 is added. The direction in which the thickness d of the optical wedge 103 decreases is the same as that of the laser system 51. In this example, the light 110 transmitted through the optical wedge 103 can be used instead of the total light amount. For example, the result detected by the detector 106 can be used as a sum signal, which is the denominator of the above-described equation 9, or as a signal when APC is performed by the semiconductor laser driving circuit 93.

  Here, a specific configuration of the optical wedge will be described with reference to FIG. For the push-pull values as shown in FIGS. 9 and 10, the optical wedge 120 shown in FIG. 15 is used. At this time, the widths of the two detectors are each 0.2 mm. Here, the x-axis, y-axis, and z-axis directions shown in FIG. 15 correspond to, for example, the x-axis, y-axis, and z-axis directions shown in FIG. The wedge angle α of the optical wedge 120 is 0.01 degrees, and the length in the z-axis direction is 10.0 mm. The length (thickness) of the optical wedge 120 in the y-axis direction gradually decreases from one end toward the other (along the z-axis direction), and the length in the y-axis direction at the smallest end ( (Plate thickness) is 0.5 mm. The wedge angle α is an angle formed by a plane obtained by extending the two reflecting surfaces 121 and 122 of the optical wedge 120, respectively.

  The wavelength variation range of the external cavity semiconductor laser 50 shown in FIG. 11 described above was 0.04 nm (410.00 nm to 410.04 nm) as shown in FIG. If it is 12 nm, the push-pull value (difference signal) at 410.00 nm is the same as the push-pull value at 410.12 nm, and the two cannot be distinguished. This is because the interference fringes have periodicity. However, even in such a case, by changing the wedge angle α and the plate thickness of the optical wedge, it is possible to adjust so as to have different push-pull values in the range of 410.00 nm to 410.12 nm.

  By the way, normally, HDS uses a single wavelength, but there is a method of performing wavelength multiplexing using a plurality of wavelengths (in contrast, the aforementioned multiplexing method is angle multiplexing). For example, recording is performed at a certain location of the hologram material at a wavelength of 410.00 nm, then at 410.10 nm, and in other words, multiplex recording is performed every 0.10 nm up to 414.00 nm. In this case, 41 times of wavelength multiplex recording is possible at the same location of the hologram material. However, this method has not been put into practical use yet.

  One of the main reasons why this method has not been put to practical use is that there is no semiconductor laser that can easily change the wavelength, but development of a semiconductor laser that can change the wavelength (tunable laser) is also progressing. The day when the wavelength multiplexing as described above is realized is also near.

  The wavelength changing method in the semiconductor laser capable of changing the wavelength in this way is performed by changing the angle of the grating, which is a component of the external resonator type semiconductor laser. This aspect will be described with reference to FIG.

  FIG. 16 shows a grating 130, a lens 131, and a semiconductor laser 132, which are components of an external cavity semiconductor laser. When the grating 130 receives the laser beam 133 from the semiconductor laser 132, it emits primary light 134 (134A, 134B, 134C, etc.) of various wavelengths, and becomes single mode at the wavelength of the primary light just returning to the semiconductor laser 132. , 0th-order light 135 is emitted from the grating 130 to the outside.

  Here, for example, when the angle at which the grating 130 receives laser light from the semiconductor laser 132 is changed by rotating the grating 130 around the rotation axis 136 in the direction of the arrow (dynamically), the light enters the semiconductor laser 132. The wavelength of the primary light 134 to be changed changes, and the oscillation wavelength of the laser light 135 emitted from the grating 130 to the outside can be changed. Further, even after such a wavelength change, the minute wavelength fluctuation as shown in FIG. 5 occurs. For example, when the laser beam is changed by rotating the grating 130 about the rotation axis 136 so that a laser beam of 411.00 nm is emitted, a wavelength of 0.04 nm including the wavelength is changed. Within the width, the wavelength of the laser light varies.

  Therefore, in such a laser system having an external cavity semiconductor laser capable of dynamically changing the wavelength by rotating the grating, the wavelength of the laser beam can be varied with a relatively large fluctuation range, for example, 4 nm. Can do. Even in this case, the laser system described above can be configured to detect the wavelength over these wavelength widths by changing the wedge angle α or the plate thickness of the optical wedge. However, the laser system having such a configuration is not suitable for an application in which the wavelength detection accuracy is too coarse and it is determined whether the emitted laser light is in a usable mode or an unusable mode. Absent.

  Therefore, in the present invention, two photodetectors are provided to have a two-stage configuration, one of which performs wavelength detection on the order of nm, and the other performs wavelength detection on the order of 0.01 nm. In other words, the two photodetectors detect the light intensity with different sensitivities, thereby performing highly accurate wavelength detection over a wide wavelength range. FIG. 17 shows the configuration of a laser system including the wavelength determination device of the present invention.

  A laser system 200 shown in FIG. 17 includes an external resonator type semiconductor laser 50 similar to that shown in FIG. The wavelength determination device 201 includes a first detector 202 and a second detector 203, and the first detector 202 includes an optical wedge 204 and a two-divided detector 206. The second detector 203 has the same configuration as the first detector 202, and includes an optical wedge 205 and a two-divided detector 207. The wavelength determination apparatus 201 further includes a laser control unit 208, and receives the output of the first detector 202 and the output of the second detector 203. Here, the z-axis direction is a direction from the front side of the description surface or the display surface of FIG. 17 toward the back side. The x-axis direction is a direction parallel to the reflecting surface of each optical wedge and perpendicular to the y-axis, and the y-axis direction is a direction perpendicular to the x-axis and the z-axis (optical along the y-axis). The thickness of the wedge is the plate thickness).

  The first detector 202 can measure the wavelength of the laser beam from the external resonator type semiconductor laser 50 in the order of nm, but it is difficult to detect with high accuracy (for example, in the order of 0.01 nm). The usable mode and the unusable mode that change according to the order cannot be determined. On the other hand, the second detector 203 can measure the wavelength of the laser light from the external cavity semiconductor laser 50 on the order of 0.01 nm, but distinguishes laser light having a wavelength different by 0.12 nm as described above. I can't.

  In the second detector 203, an optical wedge 205 similar to the structure shown in FIG. 15 is used, and the two-divided detector 207 is also the same as the two-divided detector 54 shown in FIG. Here, the width of each detector is 0.2 mm, for example. By adopting such a configuration, as described above, wavelength detection can be performed on the order of 0.01 nm.

  On the other hand, in the first detector 202, the change in the stripe pattern when the wavelength of the laser light from the external resonator type semiconductor laser 50 is changed by 4 nm is detected in the second detector 203 from the external resonator type semiconductor laser 50. The wedge angle α, the plate thickness, etc. of the optical wedge 204 are adjusted so as to be the same as when the wavelength of the laser beam changes by 0.04 nm.

  Specifically, the wedge angle α of the optical wedge 204 is set to 0.01 degrees as in the optical wedge 120 of FIG. Further, the amount of movement of the interference fringes when the wavelength of the incident light changes by 4 nm is substantially the same as the amount of movement of the interference fringes when the optical wedge 205 of the second detector 203 changes by 0.04 nm. The plate thickness of the wedge 204 is set to 1/100 of the plate thickness of the optical wedge 205. This is due to the ratio of 0.04 nm / 4 nm = 1/100.

  In this example, the movement amount of the interference fringe when the optical wedge 204 is changed by 4 nm is adjusted to be substantially the same as the movement amount of the interference fringe when the optical wedge 205 is changed by 0.04 nm. However, this indicates that the period of the light intensity distribution of the light reflected by each optical wedge is almost the same. However, the amount of movement (that is, the period of the light intensity distribution) does not have to be exactly the same. As long as the push-pull values can be appropriately detected by the corresponding two-divided detectors, they may be adjusted to have different periods. Therefore, a certain range of difference is allowed for the period of the reflected light of the two optical wedges. Further, in this example, the two optical wedges are adjusted to have the same interference fringe movement mode in the wavelength range (4 nm and 0.04 nm) having a difference of 100 times. In view of the wavelength range and the necessity of detection, the two optical wedges and the like can be adjusted so as to generate similar interference fringes in any difference wavelength range. For example, a wavelength range having a difference of several times to 10 times or several tens of times can be targeted.

  The thickness of the optical wedge 204 (thickness of the smaller thickness) is 0.5 mm / 100 = 5 μm from the ratio of 1/100 described above. As can be seen from FIGS. 6 to 8, when a laser beam is incident on a portion where the optical wedge has a small plate thickness, a stripe pattern corresponding to a change in the wavelength of the laser beam compared to a case where the plate thickness is large. This utilizes the phenomenon that the degree of displacement is small. In this case, the adjustment of the plate thickness is actually an adjustment of how far the laser light is received from the tip portion of the wedge angle α of the optical wedge. The tip portion is a portion where a plane obtained by extending the two reflecting surfaces of the optical wedge intersects (virtually).

  However, if the optical wedge 204 has such a thin structure, there is a risk that durability will be reduced. Therefore, in one embodiment of the present invention, an optical wedge 204 as shown in FIG. 18 is used. Here, the reflecting means having the structure as shown in FIG. 18 is also called an optical wedge for convenience.

  The optical wedge 204 shown in FIG. 18 is obtained by arranging two pieces of glass 220 at an angle of 0.01 degrees so that the distance between the inner sides 222 of the glass is 7.5 μm at the narrowest position. The inner side 222 of this glass corresponds to the two reflecting surfaces of the optical wedge. A gap 223 is formed between the two glasses 220. The interval between the two glasses 220 corresponds to the aforementioned plate thickness of 5 μm. In this example, the gap is set to 7.5 μm. In the optical wedge 120 as shown in FIG. 15, the gap 223 is made of glass. Whereas the refractive index is 1.5, the gap 223 of the optical wedge 204 in FIG. 18 is air, so that the plate thickness is adjusted to be a little thicker in consideration of this point. The outer surface 221 of the two glasses 220 is coated with an anti-reflective coating so that unnecessary reflection does not occur.

  With such a configuration of the optical wedge 204, a phase difference is generated between the light reflected on one inner side 222 of the two sheets of glass and the light reflected on the other inner side 222, and interference fringes are generated.

  In this way, since the optical wedge 204 of FIG. 18 is comprised with comparatively thick glass, fixed durability can be ensured and the risk at the time of use can be reduced. In addition, an object (not shown) made of any material as appropriate spacers is provided between the two glasses 220 (for example, two portions of a portion having the narrowest interval (a portion having a 7.5 μm interval) and a portion having the widest interval). ) Can be inserted and fixed so that the distance between the glasses 220 is kept constant.

  When the optical wedge 204 in FIG. 18 receives laser light having a wavelength of about 410 nm, the two-divided detector 206 of the first detector 202 described above emits light having a light intensity distribution as shown in FIG. Observed. Here, the width of each detector of the two-divided detector 206 is 0.2 mm, and the two-divided detector 206 is disposed at a position where the distance from the tip portion of the wedge angle α of the optical wedge 204 is about 32 mm. However, the tip portion of the wedge angle α of the optical wedge 204 is a virtual tip as described above.

  For example, when the wavelength of the laser beam from the tunable laser is changed to 409 nm, the two-divided detector 206 is arranged at a position where the light amounts detected by the respective detectors are equal. The value is 0. In this way, by arranging the two-divided detector 206 at a position relatively close to the tip of the wedge angle α of the optical wedge 204, the push-pull value change by the two-divided detector 206 can be associated with a large wavelength change. it can. For example, the push-pull value 0.58 corresponds to the wavelength 407 nm, the push-pull value 0 corresponds to the wavelength 409 nm, and the push-pull value −0.58 corresponds to the wavelength 411 nm.

  Next, an example in which a laser beam having a wavelength of about 410 nm is received by another optical wedge 204 'will be described. In this case, the two-divided detector 206 of the first detector 202 observes a striped pattern as shown in FIG. Here, the wedge angle α of the optical wedge 204 ′ is 0.02 degrees, and the distance between the inner sides 222 of the glass is set to 7.5 μm at the narrowest position as shown in FIG. 18. The width of each detector of the two-divided detector 206 is 0.2 mm, and the two-divided detector 206 is disposed at a position where the distance from the tip of the wedge angle α of the optical wedge 204 ′ is about 16 mm. Due to the increased wedge angle α, the fringe spacing is narrower than when the wedge angle α is 0.01 degrees (ie, the period is shorter), but the wavelength of the light is still reduced by the 0.2 mm wide detector. Can be distinguished.

  For example, when the wavelength of the laser beam from the tunable laser is changed to 409 nm, the two-divided detector 206 is arranged at a position where the light amounts detected by the respective detectors are equal. The value is 0. In this way, by arranging the two-divided detector 206 at a position relatively close to the tip of the wedge angle α of the optical wedge 204 ′, the push-pull value change by the two-divided detector 206 is associated with a large wavelength change. Can do. For example, the push-pull value 0.58 corresponds to the wavelength 407 nm, the push-pull value 0 corresponds to the wavelength 409 nm, and the push-pull value −0.58 corresponds to the wavelength 411 nm.

  Next, an example in which a laser beam having a wavelength of about 410 nm is received by another optical wedge 204 ″ will be described. In this case, a striped pattern as shown in FIG. 21 is observed with the two-divided detector of the first detector 202. Here, the wedge angle α of the optical wedge 204 ″ is 0.03 degrees, and the distance between the inner sides 222 of the glass is 12.0 μm at the narrowest place. The width of each detector of the two-divided detector is 0.1 mm (hereinafter, referred to as “two-divided detector 206 ′”). It is arranged at a position of about. Since the wedge angle α is increased, the interval between the fringes is further narrowed, and a detector having a width of 0.2 mm cannot detect the wavelength due to the influence of the adjacent interference fringes. Therefore, if the two-divided detector 206 'is configured to include a detector having a width of 0.1 mm, an appropriate wavelength can be detected.

  For example, when the wavelength of the laser beam from the tunable laser is changed to 409 nm, the two-divided detector 206 ′ is arranged at a position where the amount of light detected by each detector is equal. The pull value is 0. In this way, by arranging the two-divided detector 206 ′ at a position relatively close to the tip of the wedge angle α of the optical wedge 204 ″, the change of the push-pull value by the two-divided detector 206 ′ is changed by a large wavelength change. Can be associated. For example, push-pull value 0.72 corresponds to wavelength 407 nm, push-pull value 0 corresponds to wavelength 409 nm, and push-pull value −0.72 corresponds to wavelength 411 nm.

  Next, details of the laser control unit 208 shown in FIG. 17 will be described with reference to FIG. The laser control unit 208 is connected to the two split detectors 206 and 207 and the semiconductor laser 214 in the external resonator type semiconductor laser 50. The laser control unit 208 includes an NS determination circuit 210, a laser power correction circuit 211, and a semiconductor laser drive circuit 212.

  The NS determination circuit 210 acquires the light quantity detection results from the two detectors in the two-divided detector 206 of the first detector 202, and calculates NS from the difference signal and the sum signal. The method for obtaining NS is the same as that described above. As described above, in the first detector 202, for example, when a laser beam having a wavelength of 414 nm is received from a laser beam having a wavelength of 410 nm, the position of the striped pattern is displaced, and the amount of light obtained by the two detectors changes. Therefore, in principle, the 1's place of the wavelength can be obtained from the NS value obtained from these detectors. Further, when the incident wavelength changes from, for example, 418 nm to 422 nm, the first and tenth positions of the wavelength are required.

  In addition, the NS determination circuit 210 acquires the light quantity detection results from the two detectors in the two-divided detector 207 of the second detector 203, and calculates NS from the difference signal and the sum signal. Thereafter, the NS value is compared with a preset range, and if the NS value is within the range, the digital value 1 is output, and if the NS value is out of the range, the digital value 0 is output. The setting range is, for example, between −0.4 and 0.4, and these processes are the same as those of the NS determination circuit 91 shown in FIG.

  Further, the NS determination circuit 210 calculates the number of the first decimal place of the wavelength of the incident laser beam from the NS obtained from the two detectors in the two-divided detector 207 of the second detector 203, and the decimal places. Find the 2nd place number. In this example, as described above, the number of 1's and 10's of the wavelength are obtained from the detection result of the two-divided detector 206 of the first detector 202, and the number of decimal places is the second detector. Although it is calculated | required from the detection result in the 2 division | segmentation detector 207 of 203, the process calculated | required for every digit is not essential in this way.

  The approximate value (range) of the wavelength may be obtained based on the detection result of the first detector 202, and then the approximate value may be specified in more detail based on the detection result of the second detector 203. . For example, the wavelength of the laser beam that can be incident is divided into a plurality of groups in increments of 0.04 nm, and from the detection result of the two-divided detector 206 of the first detector 202, the group belonging to the plurality of groups is determined. After that, from the detection result of the two-divided detector 207 of the second detector 203, which wavelength in the determined group (0.04 nm wide group) corresponds to the order of 0.01 nm is determined. You can also take the following steps:

  The laser power correction circuit 211 acquires information about each digit of the number representing the wavelength from the NS determination circuit 210 and specifies the wavelength of the laser light from the information. Next, the laser power correction circuit 211 instructs the semiconductor laser drive circuit 212 to perform predetermined control based on the specified wavelength information, and the semiconductor laser drive circuit 212 performs semiconductor control based on the instruction. Control such as changing the laser power of the laser 214 is executed.

  Further, when the digital value 0 is received from the NS determination circuit 210, the laser power correction circuit 211 instructs the semiconductor laser drive circuit 212 to change the laser power of the semiconductor laser 214. For example, first, the laser power of the semiconductor laser 214 is set to 33 mW, and every time 0 is output from the NS determination circuit 210, the control for decreasing the laser power by 3 mW and the control for increasing the laser power by 3 mW are alternately repeated. To. These processes are the same as those described with reference to FIG.

  The semiconductor laser drive circuit 212 is known as a circuit for performing APC (Auto Power Control), and can be used here. Each circuit in the laser control unit 208 described above can also be realized by control by a microcomputer including a CPU and a memory. In this case, the operation of each circuit is controlled by a program loaded in the memory. The program can be changed as necessary, and can be recorded in a recording device or memory in the microcomputer via a portable recording medium such as a CD-ROM or a network.

  In the wavelength determination apparatus of the present invention, the blue laser has been described as an example of the semiconductor laser. However, it can be applied to other lasers by further changing the wedge angle α and the plate thickness of the optical wedge. is there. In the above example, the optical wedge 204 is configured by combining two glasses, but such a structure is not necessarily required. If the intensity is practical, an optical wedge having a normal configuration may be used, or a predetermined stripe pattern may be generated from incident light by various other methods.

  The wedge angle α of the optical wedge used in the present invention is, for example, 0.01 degrees, and each detector in the two-divided detector is 0.2 mm wide. However, the wavelength determination device of the present invention is limited to such conditions. Various variations are not conceivable. Further, the wedge angle α may be set to be different between the two optical wedges 204 and 205. In the embodiment, the first detector 202 receives the laser beam and then the second detector 203 receives the laser beam. However, the first detector 202 and the second detector The order of the detectors 203 can be switched, and the first detector 202 and the second detector 203 can be configured to individually receive the laser light.

  In the description of the present invention, the laser beam reflected by the optical wedge is received by the two-divided detector and the amount of light is detected. However, the present invention can be realized using a detector other than the two-divided detector. For example, the amount of light at two locations can be detected by two independent detectors. In addition, the wavelength of the laser light reflected by the optical wedge can be determined by detecting three or more light quantities.

  In this example, the wavelength is determined using the push-pull value, which is an application of a push-pull circuit for controlling the tracking of the optical disk. Therefore, it is possible to divert the tracking circuit of another optical disc that realizes the three-spot tracking method and other tracking methods.

  The detector used in the present invention is a photodetector such as a photodiode. However, the interference fringes may be received by a one-dimensional or two-dimensional detector array such as a CCD (Charge Coupled Device). Since interference fringes are generated in the z-axis direction, when using a one-dimensional detector, the detector is arranged in the z-axis direction. For example, the amount of light at a plurality of locations can be detected using a one-dimensional CCD array.

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

  Further, in the present invention, the embodiment has been described on the premise that a part of the optical wedge is used, but other optical components that can obtain the same effect as the optical wedge can also be used. It should not be construed as necessarily including an optical wedge.

  For example, when glass with flat surfaces is used instead of the optical wedge, the striped pattern changes with the change of the wavelength, as with the optical wedge, even if the laser light is slightly diffused light or convergent light. Depending on the angle of the incident laser beam and the glass whose both surfaces are flat, each striped stripe has a substantially linear shape or a curved shape.

  When diffused or convergent laser light is incident, the wavefront is not flat, so if glass with flat surfaces receives incident light at a predetermined angle (for example, for frosted glass that receives reflected light), it is concentric. The striped pattern appears. 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 (for example, in the frosted glass at the same position), and in this case, the striped pattern becomes 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, and in this case, each strip becomes a substantially straight striped pattern.

It is a basic diagram for demonstrating an optical wedge. It is a basic diagram which shows the aspect of the interference fringe produced | generated 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. In an external resonator type semiconductor laser, it is an approximate line figure showing roughly a wavelength of laser light which changes with change of laser power. It is a basic diagram which shows the light quantity when two laser beams of a predetermined wavelength enter into the predetermined position of an optical wedge. It is a basic diagram which shows the light quantity when two laser beams of a predetermined wavelength enter into the predetermined position of an optical wedge. It is a basic diagram explaining the positional relationship of two detectors and interference fringes. It is a basic diagram which shows the transition of the push pull value calculated based on the detected value from two detectors. It is a basic diagram which shows the value which normalized the push pull value shown in FIG. It is a basic diagram which shows the structure of an example of a laser system. It is a basic diagram which shows the structure of the hologram recording / reproducing system using the laser system shown in FIG. It is a block diagram which shows the structure of the laser control part of the laser system shown in FIG. It is a block diagram which shows the structure of the modification of the laser system shown in FIG. It is a basic diagram which shows the structural example of an optical wedge. It is a basic diagram for demonstrating the principle in which the wavelength of a laser beam changes with rotation of a grating. It is a block diagram which shows the structure of the wavelength determination apparatus which concerns on one Embodiment of this invention. It is a basic diagram which shows the other structural example of an optical wedge. It is a basic diagram which shows distribution of the light intensity at the time of receiving the reflected light by an optical wedge with a 2 division detector. It is a basic diagram which shows distribution of the light intensity at the time of receiving the reflected light by the optical wedge of another form with a 2 division detector. It is a basic diagram which shows distribution of the light intensity at the time of receiving the reflected light by the optical wedge of another form with a 2 division detector. It is a block diagram which shows the structure of the laser control part of the wavelength determination apparatus shown in FIG. It is a basic diagram which shows the structure of a Littrow type external resonator type semiconductor laser. It is the basic diagram which showed the wavelength of the laser beam inject | emitted from an external resonator type semiconductor laser according to the change of laser power.

Explanation of symbols

DESCRIPTION OF SYMBOLS 50 ... External cavity type semiconductor laser, 200 ... Laser system, 201 ... Wavelength determination apparatus, 202 ... First detector, 203 ... Second detector, 204, 205 ... Optical wedge, 206, 207, 2-divided detector, 208, laser control unit, 210, NS determination circuit, 211, laser power correction circuit, 212, semiconductor laser drive circuit, 214 ..Semiconductor laser

Claims (28)

First reflecting means for receiving at least a part of laser light emitted from an external cavity semiconductor laser and emitting first reflected light having a different light intensity distribution with respect to the first direction;
First light detection means for detecting light intensity of the first reflected light from the first reflection means at at least two light receiving positions;
Second reflecting means for receiving at least a part of the laser light emitted from the external cavity semiconductor laser and emitting second reflected light having a different light intensity distribution with respect to the second direction;
Second light detection means for detecting light intensity of the second reflected light from the second reflection means at at least two light receiving positions;
The difference value of the detection signal at the at least two light receiving positions of the first light detection means is obtained as a first difference value, and the difference value of the detection signal at the at least two light reception positions of the second light detection means is calculated as a first difference value. 2 as a difference value, and based on the first difference value and the second difference value, and having a wavelength determination means for determining the wavelength of the laser beam,
The first light detection means and the second light detection means detect light intensities with different sensitivities according to the difference in light intensity distribution between the first reflected light and the second reflected light, respectively. Wavelength determination device. In the wavelength determination apparatus of Claim 1,
The first reflecting means is configured such that the light intensity distribution of the first reflected light changes periodically along the first direction over a first wavelength range,
The second reflecting means is configured such that the light intensity distribution of the second reflected light changes periodically along the second direction over a second wavelength range narrower than the first wavelength range,
A wavelength determination apparatus, wherein a difference between a change period of the first reflected light and a change period of the second reflected light is within a predetermined range. In the wavelength determination apparatus according to claim 2,
The width of the first wavelength range is at least 10 times greater than the width of the second wavelength range. In the wavelength determination apparatus of Claim 1,
The wavelength determination means specifies the wavelength of the laser light as a rough value by the first difference value, and specifies the wavelength of the laser light as a more detailed value by the second difference value. A wavelength determination device characterized by the above. In the wavelength determination apparatus of Claim 1,
Each of the first reflecting means and the second reflecting means has two reflecting surfaces, each extending plane of the two reflecting surfaces is formed at a predetermined angle, and each extending plane intersects. Arranged to receive the laser beam at a position away from the portion to be a predetermined distance,
The predetermined angle and the predetermined distance of the first reflecting means and the second reflecting means are individually adjusted so that the wavelength of the laser light can be specified. Judgment device. In the wavelength determination apparatus according to claim 5,
The wavelength determining apparatus according to claim 1, wherein the predetermined distance of the first reflecting means is smaller than the predetermined distance of the second reflecting means. In the wavelength judgment device according to claim 6,
At least one of the first reflecting means and the second reflecting means is an optical wedge. In the wavelength determination apparatus of Claim 1,
The wavelength determination apparatus according to claim 1, wherein the first difference value and the second difference value are normalized by corresponding total values of detection signals obtained at the at least two light receiving positions, respectively. In the wavelength determination apparatus of Claim 1,
Each of the first light detection means and the second light detection means has one or more light detectors,
The wavelength determination device, wherein the detection signal is obtained by the one or more photodetectors. In the wavelength judgment device according to claim 9,
The wavelength determination device, wherein the photodetector is a photodiode or a CCD. In the wavelength determination apparatus of Claim 1,
The wavelength determination apparatus further comprising a control unit that increases or decreases a current value provided to the semiconductor laser in the external cavity semiconductor laser by a predetermined value based on the second difference value. In the wavelength determination apparatus of Claim 1,
The first reflecting means is configured to receive the laser light transmitted through the second reflecting means, or
The wavelength determining apparatus, wherein the second reflecting means is configured to receive the laser light transmitted through the first reflecting means. In the wavelength determination apparatus of Claim 1,
The at least two light receiving positions of the first light detection means are set along a direction parallel to the first direction,
The wavelength determination device according to claim 1, wherein the at least two light receiving positions of the second light detection means are set along a direction parallel to the second direction. The wavelength determination device according to claim 13,
An interval between the at least two light receiving positions is adjusted so that an effective first difference value and second difference value are obtained according to a light intensity distribution of the first reflected light and the second reflected light. A wavelength determination device characterized by the above. The light of the first reflected light from the first reflecting means that receives at least part of the laser light emitted from the external cavity semiconductor laser and emits the first reflected light having a different light intensity distribution with respect to the first direction. A first light detection step for detecting the intensity at at least two light receiving positions;
The second reflected light from the second reflecting means that receives at least a part of the laser light emitted from the external cavity semiconductor laser and emits second reflected light having a different light intensity distribution in the second direction. A second light detection step of detecting the light intensity at at least two light receiving positions;
A difference value between detection signals at the at least two light receiving positions detected at the first light detection step is obtained as a first difference value, and detection at the at least two light reception positions detected at the second light detection step. Obtaining a signal difference value as a second difference value, and determining a wavelength of the laser beam based on the first difference value and the second difference value; and
The first light detection step and the second light detection step detect light intensities with different sensitivities according to the difference in light intensity distribution between the first reflected light and the second reflected light, respectively. Wavelength determination method to be performed. The wavelength determination method according to claim 15,
The first reflecting means is configured such that the light intensity distribution of the first reflected light changes periodically along the first direction over a first wavelength range,
The second reflecting means is configured such that the light intensity distribution of the second reflected light changes periodically along the second direction over a second wavelength range narrower than the first wavelength range,
A wavelength determination method, wherein a difference between a change period of the first reflected light and a change period of the second reflected light is within a predetermined range. The wavelength determination method according to claim 16, wherein
The wavelength determination method, wherein the width of the first wavelength range is at least 10 times the width of the second wavelength range. The wavelength determination method according to claim 15,
The wavelength determination step specifies the wavelength of the laser light as a rough value by the first difference value, and specifies the wavelength of the laser light as a more detailed value by the second difference value. A wavelength determination method characterized by the above. The wavelength determination method according to claim 15,
Each of the first reflecting means and the second reflecting means has two reflecting surfaces, each extending plane of the two reflecting surfaces is formed at a predetermined angle, and each extending plane intersects. Arranged to receive the laser beam at a position away from the portion to be a predetermined distance,
The predetermined angle and the predetermined distance of the first reflecting means and the second reflecting means are individually adjusted so that the wavelength of the laser light can be specified. Judgment method. The wavelength determination method according to claim 19,
The wavelength determination method according to claim 1, wherein the predetermined distance of the first reflecting means is smaller than the predetermined distance of the second reflecting means. The wavelength determination method according to claim 20,
At least one of the first reflecting means and the second reflecting means is an optical wedge. The wavelength determination method according to claim 15,
The wavelength determination method, wherein the first difference value and the second difference value are normalized by a total value of detection signals obtained at the at least two light receiving positions corresponding to each other. The wavelength determination method according to claim 15,
In the wavelength determination method, the first light detection step and the second light detection step each perform light detection using one or a plurality of light detectors. The wavelength determination method according to claim 23, wherein
The wavelength determination method, wherein the photodetector is a photodiode or a CCD. The wavelength determination method according to claim 15,
The wavelength determination method further comprising a control step of increasing or decreasing a current value provided to the semiconductor laser in the external cavity semiconductor laser by a predetermined value based on the second difference value. The wavelength determination method according to claim 15,
The first reflecting means is configured to receive the laser light transmitted through the second reflecting means, or
The wavelength determining method, wherein the second reflecting means is configured to receive the laser light transmitted through the first reflecting means. The wavelength determination method according to claim 15,
The at least two light receiving positions of the first light detection step are set along a direction parallel to the first direction,
The wavelength determination method according to claim 2, wherein the at least two light receiving positions of the second light detection step are set along a direction parallel to the second direction. The wavelength determination method according to claim 27,
An interval between the at least two light receiving positions is adjusted so that an effective first difference value and second difference value are obtained according to a light intensity distribution of the first reflected light and the second reflected light. A wavelength determination method characterized by the above.

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