JP2009021488A - Laser light source device and information recording / reproducing device - Google Patents

Abstract

A laser light source device capable of correcting an optical axis shift in a Littrow ECDL inexpensively and accurately and an information recording / reproducing device using the laser light source device are provided.
A Littrow ECDL 10A includes a semiconductor laser 1 that emits a light beam 7P, a diffraction grating 4 that receives the light beam 7P, returns a first-order diffracted light 7R to the semiconductor laser 1, and emits a zero-order diffracted light 8. , A square prism 3A that has a right angle between the a plane and the b plane and a right angle between the c plane and the d plane, and totally reflects the 0th-order diffracted light 8 on the d plane and emits it as reflected light 9. Prepare. The Littrow ECDL 10A varies the wavelength of the light beam 7P by rotating the prism 3A around the apex where the c-plane and d-plane intersect.
[Selection] Figure 1

Description

  The present invention relates to a laser light source device and an information recording / reproducing device, and more particularly to a laser light source device including an external resonator type semiconductor laser (ECDL) and an information recording / reproducing device using the same.

  2. Description of the Related Art Conventionally, a hologram recording method for recording information on an optical disk recording medium with a hologram at a very high density is known. In this hologram recording method, an interference fringe pattern is generated by superimposing information light carrying image information and recording reference light inside an optical disc recording medium, and this interference fringe pattern is recorded in the optical disc recording medium. The image information is written by. When reproducing information from the recorded interference fringe pattern, the interference fringe pattern recorded in the optical disc recording medium is irradiated with reproduction reference light similar to that at the time of writing, and diffraction is generated by the interference fringe pattern. To play back image information.

  In recent years, attention has been focused on the development of a volume hologram that further increases the recording density by three-dimensionally writing an interference fringe pattern using the thickness direction of the recording layer of the optical disk recording medium. By utilizing this volume hologram recording method and further performing multiple recording, the information recording capacity can be dramatically increased.

  As a hologram recording medium, a photopolymer is attracting attention because it is inexpensive to manufacture, has excellent durability, and has high sensitivity. However, in hologram recording media using such photopolymers, the angle and spacing of the diffraction grating, etc., due to dimensional changes such as shrinkage due to the change of monomer to polymer during recording and shrinkage / expansion of the polymer due to temperature change, etc. Appears to change. Due to such a change in the shape of the diffraction grating, the wavelength at which the peak of diffraction efficiency reaches is shifted between recording and reproduction, which may reduce the reliability of reproduction.

  As a countermeasure against the above-described wavelength shift, for example, the hologram recording device employs an oscillation wavelength tunable laser, records the temperature information detected during recording on the hologram recording medium, and acquires the temperature information from the hologram recording medium during reproduction. is doing. Based on the difference between the acquired recording temperature and the reproducing temperature, the hologram recording apparatus calculates a wavelength shift amount for canceling the influence of the dimension change between the recording time and the reproducing time of the hologram recording medium. Calculate to vary the oscillation wavelength of the light source.

  The wavelength tunable laser is usually an external cavity semiconductor laser (ECDL). There are mainly two types of external cavity semiconductor lasers, a Littrow type and a Littman type.

  FIG. 13 is a schematic diagram showing a schematic configuration of a conventional Littrow ECDL 100A. Referring to FIG. 13, a conventional Littrow ECDL 100 </ b> A includes a semiconductor laser (LD) 1, a collimating lens 2, and a diffraction member 5 having a diffraction grating 4.

  The light beam 7P emitted from the semiconductor laser 1 is converted into parallel light by the collimating lens 2 which is a convex lens. The diffraction grating 4 receives the parallel light and generates 0th-order diffracted light 8 and 1st-order diffracted light 7R. The 0th-order diffracted light 8 is emitted from the Littrow ECDL 100A as output light. The first-order diffracted light 7 </ b> R returns to the semiconductor laser 1, and a resonator is formed between the rear end face R <b> 1 of the semiconductor laser 1 and the diffraction grating 4.

  In the Littrow ECDL 100A, by rotating the diffractive member 5 about the rotation axis RX, the optical wavelength is changed by changing the resonator length. At this time, the incident angle of the light beam 7P with respect to the diffraction grating 4 and the emission angle of the 0th-order diffracted light 8 are equal. Therefore, the direction of the 0th-order diffracted light 8 changes as the diffractive member 5 rotates. That is, the optical axis of the 0th-order diffracted light 8 that is output light varies depending on the light wavelength of the light beam 7P.

  As described above, the Littrow ECDL 100A has a simpler configuration than the Littman type, and has high performance with respect to output power and the like. However, the Littrow ECDL 100A has a drawback in that the optical axis of the output light varies as the wavelength changes.

  FIG. 14 is a schematic diagram showing a schematic configuration of a conventional Littman ECDL 100B. Referring to FIG. 14, a conventional Littman ECDL 100B includes a semiconductor laser (LD) 1, a collimating lens 2, a diffractive member 5 having a diffraction grating 4, and a mirror 20.

  The light beam 7 emitted from the semiconductor laser 1 is converted into parallel light by the collimating lens 2 which is a convex lens. The diffraction grating 4 receives the parallel light at a larger incident angle than that of the Littrow type, and generates 0th-order diffracted light 9 and first-order diffracted light 8P. The 0th-order diffracted light 9 is emitted from the Littman ECDL 100B as output light. The first-order diffracted light 8P does not return directly to the semiconductor laser 1, but travels in the direction of the mirror 20 and is reflected vertically. The diffraction grating 4 receives the reflected light 8R from the mirror 20 and generates 0th-order diffracted light 9A and first-order diffracted light 9B.

  The first-order diffracted light 9 </ b> B returns to the semiconductor laser 1, and a resonator is formed between the rear end face R <b> 1 of the semiconductor laser 1 and the diffraction grating 4. In the Littman ECDL 100B, the optical wavelength is changed by changing the resonator length by rotating the mirror 20 around the rotation axis RY. Therefore, the optical axis of the 0th-order diffracted light 9 that is the output light is constant even when the light wavelength of the light beam 7 changes.

  As described above, the Littman ECDL 100B has a more complicated configuration than the Littrow ECDL 100A of FIG. Further, since the 0th-order diffracted light 9A of the reflected light 8R from the mirror 20 becomes a loss, the power of the output light becomes smaller than that of the Littrow type. Further, since the first-order diffracted light 9B returns to the semiconductor laser 1 through two degrees of diffraction, the feedback efficiency is reduced. As a result, the variable range of wavelength is narrowed.

  In the Littrow ECDL 100A, if the change of the optical axis of the output light due to the rotation of the diffraction member 5 can be eliminated, the Littrow ECDL has higher performance than the Littmann ECDL. Therefore, a configuration for correcting the deviation of the optical axis in the Littrow ECDL is examined (for example, see Patent Document 1).

  FIG. 15 is a schematic diagram showing a schematic configuration of an improved conventional Littrow ECDL 100C.

  Referring to FIG. 15, an improved conventional Littrow type ECDL 100C includes a semiconductor laser (LD) 1, a collimating lens 2, a diffractive member 5 having a diffraction grating 4, a jig 26, and a bottom surface having a right-angled isosceles side. And a prismatic prism 27 having a triangular shape. The jig 26 is used to fix the diffraction member 5 and the prism 27 in a predetermined arrangement. Here, the predetermined arrangement is an arrangement in which the grating surface of the diffraction grating 4 and the surface b7 corresponding to the hypotenuse of the isosceles right triangle of the prism 27 are parallel to each other.

  The light beam 7P emitted from the semiconductor laser 1 is converted into parallel light by the collimating lens 2 which is a convex lens. The parallel light passes through the jig 26 and is diffracted by the diffraction grating 4 into zero-order diffracted light 8 and first-order diffracted light 7R. The jig 26 is, for example, a cavity with respect to the path portions of the light beam 7P and the 0th-order diffracted light 8. The first-order diffracted light 7 </ b> R returns to the semiconductor laser 1, and a resonator is formed between the rear end face R <b> 1 of the semiconductor laser 1 and the diffraction grating 4.

In the Littrow ECDL 100C, the diffraction member 5, the jig 26, and the prism 27 are rotated together around the rotation axis RX, thereby changing the above-described resonator length and changing the light wavelength. The 0th-order diffracted light 8 enters the prism 27 through the jig 26, and the reflected light 9 reflected by the surface b7 is emitted from the Littrow ECDL 100C as output light.
JP-A-2005-322813

  In the improved conventional Littrow ECDL 100C, the optical axis from the light beam 7P through the 0th-order diffracted light 8 to the output as the reflected light 9 is centered on the rotation member RX with respect to the diffraction member 5, the jig 26 and the prism 27. Even if it is integrally rotated arbitrarily, it is constant.

  However, in the conventional Littrow ECDL 100C, the optical axis may actually be shifted by the above rotation unless the diffraction member 5, the jig 26 and the prism 27 are assembled and adjusted with high accuracy. Further, the rotation axis RX needs to be set accurately at a position away from the jig 26. Therefore, the conventional Littrow-type ECDL 100C is actually difficult to construct and costly.

  SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a laser light source device capable of correcting an optical axis shift in Littrow type ECDL inexpensively and accurately, and an information recording / reproducing device using the same.

  The present invention is a Littrow-type laser light source device, a laser light source that emits a light beam, a diffraction grating that receives the light beam, returns first-order diffracted light to the laser light source, and emits zero-order diffracted light; A polygonal prism having a right angle on the side where the 0th-order diffracted light is diffracted on the surface on which the grating is disposed, and a diagonal angle thereof.

  Preferably, the wavelength of the light beam is varied by rotating the polygonal prism around the vertex of the side where the diffraction grating is installed on the side where the 0th-order diffracted light is diffracted.

Preferably, an air layer is formed between the polygonal prism and the diffraction grating.
Preferably, a matching liquid is filled between the polygonal prism and the diffraction grating.

Preferably, the diffraction grating is formed on one surface of the polygonal prism.
According to another aspect of the present invention, there is provided an information recording / reproducing apparatus including a Littrow-type laser light source device, the laser light source device receiving a light beam and a first-order diffracted light upon receiving the light beam. Is returned to the laser light source and emits the 0th-order diffracted light, and a polygonal prism whose angle on the side where the 0th-order diffracted light is diffracted on the surface where the diffraction grating is installed and its diagonal is a right angle .

  Preferably, the information is recorded in units of books in which pages including wavelength detection information are recorded in a multiplexed manner.

  Preferably, among the wavelength detection information, a difference component between the first wavelength detection information and the second wavelength detection information is standardized to calculate a wavelength error signal indicating a deviation amount from the optimum reproduction wavelength.

  According to the present invention, the optical axis shift in the Littrow ECDL can be corrected inexpensively and accurately.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

[Embodiment 1]
FIG. 1 is a schematic diagram showing a schematic configuration of a Littrow ECDL 10A according to Embodiment 1 of the present invention. Referring to FIG. 1, a Littrow ECDL 10A according to the first embodiment includes a semiconductor laser (LD) 1, a collimator lens 2, and a columnar prism 3A having a bottom surface of a quadrangle whose both diagonals are right angles. The diffraction member 5 having the diffraction grating 4 and members 11m and 11n for fixing the diffraction member 5 to the prism 3A are included.

  As shown in FIG. 1, the four surfaces of the prism 3A are referred to as a-plane, b-plane, c-plane, and d-plane for convenience. The diffractive member 5 is affixed to the c-plane of the prism 3A with the members 11m and 11n interposed therebetween. The a-plane to d-plane are set as follows.

  First, the a-plane is set to be substantially perpendicular to the light beam 7P emitted from the semiconductor laser 1. The b-plane is set to be substantially parallel to the light beam 7P. As a result, the angle between the a-plane and the b-plane becomes a right angle. In addition, the angle formed by the c-plane and the d-plane is also set to a right angle. By setting both right angles of the prism 3A as described above, an effect that the optical axis of the light beam 7P does not tilt can be obtained.

FIG. 2 is an enlarged view of the diffraction member 5 of the Littrow ECDL 10A of FIG.
In FIG. 2, the angle α formed between the b-plane and the c-plane of the prism 3A is an incident angle to the diffraction grating 4 that is necessary for the light beam 7P parallel to the b-plane to externally resonate at the center wavelength λ of the wavelength variable range. Associated with θ1. When the number of grooves per unit length of the diffraction grating 4 is N (lines / mm), the relationship between the center wavelength λ and the incident angle θ1 is generally expressed by the following equation.

λ = 2 / N · Sinθ1 (1)
For example, when the center wavelength λ = 405 (nm) and the number of grooves N = 3600 (lines / mm), the incident angle θ1 = 46.8 (degrees) can be calculated from the above equation (1).

  In the first embodiment, the diffractive member 5 is attached to the c surface of the prism 3A with the members 11m and 11n interposed therebetween. Therefore, strictly speaking, it is necessary to consider that the light beam 7P in the prism 3A is once refracted on the c-plane and emitted to the air layer, and enters the diffraction grating 4 from the air layer at an incident angle θ1. That is, when the incident angle from the prism 3A to the c-plane is θ2, and the refractive index of the prism 3A is n, the following relational expression is established.

α = 90 ° + θ2 (2)
n · Sinθ2 = Sinθ1 (3)
From the above formulas (1) to (3), when the refractive index n = 1.53 and the incident angle θ1 = 46.8 (degrees), the incident angle θ2 = 28.45 (degrees), the b-plane and the c-plane The angle α is calculated as 118.45 (degrees).

  In the above case, since there is an air layer between the prism 3A and the diffractive member 5, the light beam 7P is refracted and enters the diffraction grating 4 when it exits from the prism 3A to the air layer. Therefore, in the diffraction grating 4, generation of unnecessary higher-order diffracted light exceeding the critical angle can be suppressed, and only necessary first-order diffracted light 7 </ b> R can be fed back in the direction of the semiconductor laser 1.

  Further, when the incident angle θ1 to the diffraction grating 4 is changed to change the wavelength, when the prism 3A is rotated by Δm around the vertex Q, the incident angle θ1 changes by Δθ1. At this time, the relationship between Δm and Δθ1 is Δθ1> Δm.

  That is, in the Littrow ECDL 10A according to the first embodiment, the rotation amount of the prism necessary for the same wavelength change is compared with that in the Littrow ECDL 10A according to the first embodiment as compared with the conventional Littrow ECDL 100A in FIG. Is as small as Δm. Therefore, the drive amount of the drive system used for rotationally driving the prism 3A can be reduced. As the drive system, it is generally considered to employ a piezoelectric element capable of precisely managing the amount of displacement. The smaller the required driving amount of the piezoelectric element, the more advantageous in terms of volume, cost, and driving power consumption.

  FIG. 3 is a schematic diagram showing a schematic configuration of a Littrow ECDL 10B according to a modification of the first embodiment of the present invention.

  The Littrow ECDL 10B of the modification shown in FIG. 3 is different in that the prism 3A is replaced with the prism 3B, and the matching liquid 12 is filled between the g-plane of the prism 3B and the diffractive member 5 instead of the air layer. 1 different from the Littrow ECDL 10A. The matching liquid 12 has substantially the same refractive index as that of the prism 3B.

  As shown in FIG. 3, the five surfaces of the prism 3B are referred to as e-plane, f-plane, g-plane, h-plane, and i-plane for convenience. The diffractive member 5 is affixed to the g-plane of the prism 3B with the members 11m and 11n interposed therebetween. As described above, the matching liquid 12 is filled between the g-plane and the diffractive member 5. The e-plane to i-plane are set as follows.

  First, the e plane is set to be substantially perpendicular to the light beam 7P emitted from the semiconductor laser 1. The f plane is set so as to be substantially parallel to the light beam 7P. As a result, the angle formed by the e-plane and the f-plane is a right angle. Further, the angle formed by the g-plane and the h-plane is also set at a right angle. By setting both right angles of the prism 3B as described above, an effect that the optical axis of the light beam 7P does not tilt can be obtained. The i plane is arbitrary.

  FIG. 4 is a schematic diagram showing a schematic configuration of a Littrow ECDL 10C according to another modification of the first embodiment of the present invention.

  The Littrow type ECDL 10C of another modification shown in FIG. 4 is the same as that of FIG. 3 except that the diffraction member 5, the members 11m and 11n, and the matching liquid 12 are removed and the diffraction grating 4 is directly formed on the g-plane of the prism 3B. Different from type ECDL10B.

  In the case of the Littrow ECDLs 10B and 10C of FIGS. 3 and 4, the incident angle from the prism 3B to the g-plane is θ2 = 46.8 (degrees), and the angle α formed between the f-plane and the g-plane is 136.8 (degrees). It can be. In this case, since the required effective area of the h surface of the prism 3B can be reduced to about the g surface, the prism 3B can be downsized.

  Next, returning to FIG. 1, the operation of the Littrow ECDL 10A will be described. This operation is also applied to the Littrow ECDLs 10B and 10C shown in FIGS.

  The light beam 7P emitted from the semiconductor laser 1 is converted into parallel light by the collimating lens 2 which is a convex lens. The parallel light enters from the a-plane of the prism 3A, and is diffracted by the diffraction grating 4 into the 0th-order diffracted light 8 and the first-order diffracted light 7R. The first-order diffracted light 7 </ b> R returns to the semiconductor laser 1, and a resonator is formed between the rear end face R <b> 1 of the semiconductor laser 1 and the diffraction grating 4.

  The Littrow ECDL 10A has a mechanism that rotates around a vertex Q that is an intersection of the c-plane and d-plane of the prism 3A. By rotating the prism 3A, the members 11m and 11n, and the diffractive member 5 integrally around the vertex Q, the light wavelength is changed by changing the resonator length. In the 0th-order diffracted light 8, the reflected light 9 totally reflected by the d-plane of the prism 3A is emitted again through the a-plane of the prism 3A as output light.

  With respect to the diffraction grating 4, the incident angle of the light beam 7 </ b> P is equal to the emission angle of the 0th-order diffracted light 8. For this reason, the emission direction of the reflected light 9 does not change regardless of the rotation of the diffraction member 5 or the like. For convenience, this can be explained as follows by considering the light reflection surface as a transmission surface by geometrically converting it into plane symmetry.

  FIG. 5 is a diagram for explaining the emission direction of the reflected light 9 in the Littrow ECDL 10A of FIG.

  As shown in FIG. 5, the light beam 7P enters from the a-plane of the prism 3A and is reflected by the c-plane. By converting the a-plane, b-plane, and d-plane into a1-plane, b1-plane, and d1-plane, respectively, with the c-plane as a symmetric plane, the c-plane can be considered as a transmission plane for convenience. Similarly, the d1 plane converted from the d plane is regarded as a symmetry plane, and the a1 plane, b1 plane, and c plane are converted into the a2, b2, and c1 planes, respectively, so that the d plane can be considered as a transmission plane for convenience. it can.

  By the above conversion, the reflected light 9 incident from the a-plane, reflected by the c-plane and d-plane, and emitted from the a-plane again enters the a-plane, passes through the c-plane and d1 plane, and from the a2 plane. It can be considered that the transmitted light 9Z is equivalent. As shown in FIG. 5, since the a-plane and the a2-plane are parallel, it can be seen that the reflected light 9 is always parallel to the light beam 7P regardless of the incident angle of the light beam 7P.

  Further, the phenomenon that the prism 3A rotates around the vertex Q corresponds to the fact that the virtual parallel prism LML1N1L2M1QN in FIG. 5 rotates around the vertex Q. Therefore, according to the same theory as described above, it is understood that the outgoing optical axis of the reflected light 9 does not change even when the prism 3A is rotated around the vertex Q.

  As described above, the outgoing optical axis of the reflected light 9 has an effect that does not depend on the change in the optical wavelength caused by rotating the prism 3A. Further, since the incident angle of the light beam 7P incident on the a-plane of the prism 3A is near 0 degrees, the shift of the outgoing optical axis of the reflected light 9 is sufficiently small so that there is no practical problem compared to the conventional example. There is an effect to be suppressed.

  As described above, according to the first embodiment, a diffraction grating is disposed on one surface of a polygonal prism whose predetermined diagonals are right angles to constitute a Littrow type ECDL, thereby rotating a diffraction member or the like. Regardless, the outgoing direction and outgoing optical axis of the output reflected light can be kept stable.

  A laser light source device according to an embodiment of the present invention is a Littrow external resonance semiconductor laser device, which receives a diffraction grating, a polygonal prism having two sides sandwiching a right angle, and zero-order diffracted light from the diffraction grating. A prism that reflects light in a second direction.

  The laser light source device is mounted on a hologram recording device, temperature information detected during recording is recorded on the hologram recording medium, and temperature information is acquired from the hologram recording medium during reproduction. Based on the temperature difference between the time of recording and the time of reproduction, a wavelength shift amount for canceling the influence of the dimension change between the time of recording and the time of reproduction of the hologram recording medium is calculated. As a result, a low-cost and small-sized light source that can vary the oscillation wavelength of the light source can be provided.

  Preferably, in the above-described polygonal prism, an angle formed by a surface having the diffraction grating and an adjacent surface is a right angle. Thereby, it is possible to realize a light source in which the optical axis of the output light does not change regardless of the change of the light wavelength. As a result, it is possible to prevent signal quality deterioration due to optical axis changes during hologram recording and reproduction.

  As an example, the diffraction grating is attached to one surface of a polygonal prism via an air layer. As a result, a plate-type grating that has been commercially available or can be manufactured at a low cost can be used, and the cost of the laser light source device can be reduced. In addition, the rotational drive amount when the wavelength is variable is small, and the size of the rotational drive system can be reduced, the cost can be reduced, and the power consumption can be reduced. Furthermore, unnecessary high-order diffracted light generated in the diffraction grating is cut.

  As another example, the diffraction grating is attached to one surface of the polygonal prism via a matching agent having a refractive index close to that of the polygonal prism. This makes it possible to reduce the size of the prism while using a plate-type grating that has been commercially available or can be manufactured at low cost.

  Preferably, the diffraction grating is formed on one surface of the polygonal prism. Thereby, the prism can be miniaturized and the number of parts can be reduced.

  Preferably, the polygonal prism is rotated about a vertex that is an intersection of an adjacent surface at an angle perpendicular to the surface on which the diffraction grating is located. Thereby, it is possible to realize a light source in which the optical axis of the output light does not change regardless of the change of the light wavelength. Further, it is possible to prevent signal quality from being deteriorated due to a change in the optical axis at the time of hologram recording and reproduction.

[Embodiment 2]
FIG. 6 is a diagram showing the configuration of the optical unit of the hologram recording / reproducing apparatus 30 according to the second embodiment of the present invention.

  Referring to FIG. 6, a hologram recording / reproducing apparatus 30 according to the second embodiment includes a laser light source device 31, a collimator lens 32, an isolator 33, half-wave plates 34 and 36, and polarization beam splitters 35 and 37. A reflective liquid crystal spatial light modulator 38, relay lenses 39 and 315, a pinhole 310, an objective lens 311, an aperture 313, a galvano mirror 314, a CMOS (Complementary Metal Oxide Semiconductor) sensor 317, A quarter-wave plate 318 and a reflection mirror 319 are provided. The CMOS sensor 317 includes detectors 317a and 317b.

  The laser light source device 31 is, for example, the Littrow ECDLs 10A to 10C described in the first embodiment. The hologram recording / reproducing apparatus 30 records and / or reproduces information with respect to the hologram recording medium 312 by an angle multiplexing method. The hologram recording / reproducing apparatus 30 can be separated into a hologram recording apparatus and a hologram reproducing apparatus. Hereinafter, the operation during recording will be described first.

  The light beam LP emitted from the laser light source device 31 is converted into parallel light by the collimator lens 32 and passed through an isolator 33 to prevent return light to the laser light source device 31. The ratio of P-polarized light and S-polarized light is adjusted by the half-wave plate 34 of the light beam LP passed through the isolator 33. The adjusted light beam LP is split by the polarization beam splitter 35 into P-wave signal light LS and S-wave reference light LR.

  The intensity of the signal light LS is adjusted by the half-wave plate 36, and only the P-polarized component transmitted through the polarization beam splitter 37 is incident on the spatial light modulator 38. The signal light LS modulated by the reflective liquid crystal of the spatial light modulator 38 is reflected by the polarization beam splitter 37 because the polarization is rotated by 90 degrees. From the signal light LS reflected by the polarization beam splitter 37, higher-order diffracted light from the reflective liquid crystal is cut by the pinhole 310 in the relay lens 39. The signal light LS that has passed through the relay lens 39 is condensed in the hologram recording medium 312 by the objective lens 311.

  The beam diameter of the reference light LR is adjusted by the aperture 313 and the angle is modulated by the galvanometer mirror 314. The reference light LR whose angle is modulated is incident on the same portion of the hologram recording medium 312 by the relay lens 315 so as to interfere with the signal light SL. As a result, interference fringes between the signal light LS and the reference light LR are formed in the hologram recording medium 312. At this time, information modulated by the spatial light modulator 38 is recorded as a hologram in the hologram recording medium 312.

  By changing the angle of the galvanometer mirror 314 in the hologram recording described above, the incident angle to the hologram recording medium 312 changes, and angle multiplex recording can be performed. When performing this multiple recording, data recorded at one angle is referred to as one page, and a plurality of pages recorded at multiple angles in the same area are collectively referred to as one book.

  FIG. 7 is a schematic diagram conceptually showing pages and books recorded on the hologram recording medium 312.

  As shown in FIG. 7, on the hologram recording medium 312, a book BK1 in which pages Pg0, Pg1, Pg2, Pg3,. In the first page Pg0 of the book BK1, wavelength detection information Ad and Bd indicating the irradiation wavelength of the reference light LR of each page Pg0, Pg1,. The pages Pg0, Pg1,... Are collectively referred to as an information data page Pg.

  The wavelength detection information of the hologram recording medium 312 is configured by a combination of the wavelength detection information Ad and the wavelength detection information Bd. The wavelength detection information of the hologram recording medium 312 is recorded at one or a plurality of predetermined positions in the outer peripheral portion or the inner peripheral portion of the recording area I of the information data page Pg recorded in multiple recording, or in the recording area. Recording is performed by changing the wavelength of the light beam LP of the laser light source device 31 (with wavelength dispersion). Thereby, even when any part is not detected, the wavelength of the reference light LR corresponding to the information data page Pg can be calculated using the read wavelength detection information of the plurality of parts.

  FIG. 8 is a diagram showing the relationship between the light amount and wavelength of the wavelength detection information recorded on the hologram recording medium 312.

  In FIG. 8A, the wavelength of the reference beam LR for recording information data is multiplexed with a plurality of wavelengths λ1 to λ4 at intervals shorter by a predetermined wavelength by changing the wavelength of the light beam LP of the laser light source device 31. The recorded wavelength detection information Ad is shown. In FIG. 8B, the wavelength of the reference beam LR for recording the information data is multiplexed with a plurality of wavelengths λ5 to λ8 that are longer by a predetermined wavelength by changing the wavelength of the light beam LP of the laser light source device 31. The recorded wavelength detection information Bd is shown. The wavelength detection information can also be referred to as angle detection information.

  FIG. 8C shows detection intensity SAd on which wavelength detection information Ad of wavelengths λ1 to λ4 is superimposed, and detection intensity SBd on which wavelength detection information Bd of wavelengths λ5 to λ8 is superimposed, centering on wavelength λ0. Yes. The wavelength interval is preferably determined by the wavelength selectivity of the hologram recording medium 312 and is preferably in the wavelength range until the diffraction efficiency is reduced to 50%. Desired wavelength detection information can be obtained by combining the wavelength detection information Ad and Bd.

  FIG. 9 is a diagram illustrating an example of the diffraction efficiency with respect to the wavelength change of the light beam PL. FIG. 9 shows a case where the wavelength detection range of the hologram recording medium 312 is 1.2 nm and the wavelength detection range until the diffraction efficiency is reduced to 50% is 0.6 nm.

  In the case of the conditions as shown in FIG. 9, in FIG. 8, it is desirable that the multiplexing interval is 0.6 nm centering on the wavelength λ1 or λ5 shifted by 0.3 nm from the wavelength λ0 of the reference light LR for recording information data. Further, the number of wavelength multiplexing is determined by how much wavelength deviation is detected. For example, when detecting a wavelength error up to ± 3 nm under the conditions as shown in FIG. 9, it can be realized by multiplexing each of the wavelength detection information Ad and Bd at intervals of 0.6 nm.

  When multiple recording is performed with different wavelengths as described above, it is important that the optical axis of the reference light LR or the like incident on the hologram recording medium 312 does not change, and it is effective to use the laser light source device 31 of the present invention. Become.

  Further, depending on the performance of the hologram recording medium 312, if the wavelength multiplexing recording is increased, unnecessary light is likely to be generated at the time of reproduction, which may be a noise signal. In this case, in order to widen the wavelength detection range as described above, if many wavelength multiplexing is repeated for the same region of the wavelength detection information Ad and Bd, unnecessary light is generated during reproduction at the wavelength λ0, and the wavelength The detection accuracy may be reduced.

  FIG. 10 is a schematic diagram conceptually showing another example of pages and books recorded on the hologram recording medium 312.

  As shown in FIG. 10, the hologram recording medium 312 records a book BK2 in which pages Pg0, Pg1, Pg2, Pg3,. Wavelength detection information Ae to De is recorded on the first page Pg0 of the book BK2. The pages Pg0, Pg1,... Are collectively referred to as an information data page Pg.

  FIG. 11 is a diagram illustrating another relationship between the light amount and wavelength of wavelength detection information recorded on the hologram recording medium 312.

  FIG. 11A shows wavelength detection information Ae recorded at a wavelength λ1 shorter by a predetermined wavelength than the wavelength of the reference light LR that records information data without wavelength multiplexing. FIG. 11B shows wavelength detection information Be recorded at a wavelength λ5 that is longer by a predetermined wavelength than the wavelength of the reference light LR that records information data without wavelength multiplexing. (C) and (d) of FIG. 11 show wavelength detection information Ce and De newly set in order to secure a range for detecting a wavelength error.

  The wavelength detection information Ce in FIG. 11C is information that is multiplexed and recorded at a plurality of wavelengths λ2 to λ4 that are shorter by a predetermined wavelength. The wavelength detection information De in FIG. 11D is information that is multiplexed and recorded at a plurality of wavelengths λ6 to λ8 that are long by a predetermined wavelength. That is, the wavelength detection information Ce and De may be any configuration that can obtain recording information that can determine whether the reproduction wavelength is longer or shorter than the recording wavelength. The wavelength detection information can also be referred to as angle detection information.

  Next, with reference to FIG. 6, the operation | movement at the time of reproduction | regeneration of the hologram recording / reproducing apparatus 30 of Embodiment 2 is demonstrated.

  At the time of reproduction, the laser light source device 31 reproduces the disc information area and outputs a light beam LP set at a recording wavelength or a predetermined wavelength read. At this time, the signal light LS is blocked by adjusting the ratio of polarization in the half-wave plate 34 and only the reference light LR is incident on the hologram recording medium 312.

  The S-polarized reference light LR separated by the polarization beam splitter 35 is then adjusted in beam diameter by an aperture 313. The angle of the reference light LR whose beam diameter has been adjusted is modulated by the galvanometer mirror 314 and passes through the hologram recording medium 312 via the relay lens 315. The transmitted reference light LR is converted into circularly polarized light by the quarter wavelength plate 318 and reflected by the reflection mirror 319. The reflected reference light RL is incident on the hologram recording medium 312 as P-polarized light from the surface opposite to that during recording.

  When the reference light LR enters the hologram recording medium 312 as described above, diffracted light (reproduced light) is generated from the hologram recorded on the hologram recording medium 312. The reproduction light follows an optical path opposite to that of the signal light LS and passes through the objective lens 311 and the relay lens 39. In the middle of passing through the relay lens 39, noise is cut by the pinhole 310.

  The noise-reduced P-polarized reproduction light passes through the polarization beam splitter 37 and is converted into an electrical signal corresponding to spatial two-dimensional data in the reflective liquid crystal of the spatial light modulator 38 by the CMOS sensor 317. . The output from the CMOS sensor 317 is converted into binarized data by a signal processing unit (not shown).

  In the above, the incident angle of the reference light LR to the hologram recording medium 312 can be made substantially the same as that during recording. However, the optimum wavelength at the time of reproduction differs from the wavelength used at the time of recording due to shrinkage or temperature change during recording of the hologram recording medium 312. Therefore, the signal recorded on the hologram recording medium 312 cannot be accurately reproduced at the same wavelength as that at the time of recording.

  Therefore, the hologram recording / reproducing apparatus 30 according to the second embodiment detects the wavelength detection information described above during the reproduction process of information data from the hologram recording medium 312, and detects the wavelength of the page on which the information data is recorded. Thereby, the wavelength of the laser light source device 31 used for reading is determined, and the wavelength can be easily controlled. In this case as well, it is important that the optical axis incident on the hologram recording medium 312 does not change when reproducing with the wavelength changed. For this reason, it is effective to use the laser light source device 31 of the present invention.

  Next, the flow of processing for detecting the wavelength of the reference light LR corresponding to the book from the above-described wavelength detection information will be described with reference to FIGS. As described with reference to FIG. 8, the detectors 317a and 317b in FIG. 6 detect the wavelength detection information Ad and Bd at different intensity peaks corresponding to the wavelength change of the reference light LR during reproduction.

  FIG. 12 is a diagram showing how the wavelength error signal WES is calculated from the detection intensities SAd and SBd of the wavelength detection information Ad and Bd.

  As shown in FIG. 12, the wavelength error signal WES (Wave-length Error Signal) includes the detection intensity SAd of the wavelength detection information Ad detected by the detector 317a and the detection intensity SBd of the wavelength detection information Bd detected by the detector 317b. Is calculated as follows by normalizing the difference component.

WES = (SAd−SBd) / (SAd + SBd) (4)
By calculating the wavelength error signal WES as described above, even if the detection intensities (reproduction intensities) SAd and SBd of the wavelength detection information Ad and Bd change in book units due to some condition, the wavelength error signal WES is stably generated. Can be calculated.

  The wavelength error signal WES is a numerical value indicating the amount of deviation of the book to be reproduced from the optimum reproduction wavelength λ0. In the negative slope portion of the wavelength error signal WES, a point ZX that becomes a zero (0) cross is the optimum reproduction wavelength of the reference light LR at the time of reading information data in each book. The wavelength of the reference light LR at the time of reading corresponds to the wavelength of the reference light LR at the time of writing the information data page of each book. At the wavelength of the reference light LR at the time of reading, the reproduction intensity (diffraction efficiency) of the recorded information data in the detectors 317a and 317b is maximized.

  When reading the information data recorded in each book for the calculation of the wavelength error signal WES, the information data page is accessed. The wavelength of the reference light LR at the time of reading can be used for wavelength servo control for adjusting by changing the wavelength of the emitted light of the laser light source device 31.

  When wavelength detection information is recorded at a plurality of locations, the wavelength error signal WES calculates the sum of the detection intensity SAd of the wavelength detection information Ad and the detection intensity SBd of the wavelength detection information Bd as shown below. Is calculated.

WES = (ΣSAd−ΣSBd) / (ΣSAd + ΣSBd) (5)
As described above, the wavelength of the reference light LR at the time of reading can be used for wavelength servo control for adjusting by changing the wavelength of the emitted light of the laser light source device 31.

  As described above, the hologram recording / reproducing apparatus according to the second embodiment records the wavelength detection information for each book and varies the wavelength of the laser light source device. Thereby, even when the optimum wavelength at the time of reproduction differs from the wavelength at the time of recording due to shrinkage or temperature change at the time of recording of the hologram recording medium, the optimum wavelength of the reference light at the time of reading the information data can be detected. As a result, information data can be reproduced continuously at high speed in the holographic reproduction process.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and is intended to include meanings equivalent to the scope of claims for patent and all modifications within the scope.

1 is a schematic diagram showing a schematic configuration of a Littrow ECDL 10A according to Embodiment 1 of the present invention. It is an enlarged view of the diffraction member 5 part of the Littrow type ECDL 10A of FIG. It is the schematic diagram which showed schematic structure of Littrow type | mold ECDL10B by the modification of Embodiment 1 of this invention. It is the schematic diagram which showed schematic structure of the Littrow type | mold ECDL10C by the other modification of Embodiment 1 of this invention. It is a figure for demonstrating the emission direction of the reflected light 9 in Littrow type | mold ECDL10A of FIG. It is the figure which showed the structure of the optical unit of the hologram recording / reproducing apparatus 30 by Embodiment 2 of this invention. 3 is a schematic diagram conceptually showing pages and books recorded on a hologram recording medium 312. FIG. FIG. 6 is a diagram illustrating a relationship between a light amount and wavelength of wavelength detection information recorded on a hologram recording medium 312. It is a figure showing an example of the diffraction efficiency with respect to the wavelength change part of the light beam PL. 10 is a schematic diagram conceptually showing another example of a page and a book recorded on a hologram recording medium 312. FIG. 6 is a diagram illustrating another relationship between the light amount and wavelength of wavelength detection information recorded on the hologram recording medium 312. FIG. It is a figure showing how wavelength error signal WES is computed from detection intensity SAd and SBd of wavelength detection information Ad and Bd. It is the schematic diagram which showed the schematic structure of the conventional Littrow type | mold ECDL100A. It is the schematic diagram which showed the schematic structure of the conventional Littman type | mold ECDL100B. It is the schematic diagram which showed the schematic structure of the improved conventional Littrow type | mold ECDL100C.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Semiconductor laser, 2,32 Collimate lens, 3A, 3B, 27 Prism, 4 Diffraction grating, 5 Diffraction member, 10A-10C, 100A-100C Littrow type ECDL, 11m, 11n Member, 12 Matching liquid, 20 Mirror, 26 30 Hologram recording / reproducing device, 31 Laser light source device, 33 Isolator, 34, 36 1/2 wavelength plate, 35, 37 Polarizing beam splitter, 38 Spatial light modulator, 39, 315 Relay lens, 310 Pinhole, 311 Objective Lens, 313 aperture, 314 galvanometer mirror, 317 CMOS sensor, 317a, 317b detector, 318 quarter wave plate, 319 reflection mirror.

Claims (8)

A Littrow type laser light source device,
A laser light source that emits a light beam;
Receiving the light beam, returning first-order diffracted light to the laser light source and emitting zero-order diffracted light;
A laser light source device comprising: a polygon prism having a right angle on the side where the diffraction grating is installed and a side on which the zero-order diffracted light is diffracted and a diagonal of the angle.   2. The wavelength of the light beam according to claim 1, wherein the wavelength of the light beam is varied by rotating the polygonal prism around the vertex of the surface where the diffraction grating is installed on the side where the 0th-order diffracted light is diffracted. Laser light source device.   The laser light source device according to claim 1, wherein an air layer is formed between the polygonal prism and the diffraction grating.   The laser light source device according to claim 1 or 2, wherein a matching liquid is filled between the polygonal prism and the diffraction grating.   The laser light source device according to claim 1, wherein the diffraction grating is formed on one surface of the polygonal prism.   An information recording / reproducing apparatus comprising the laser light source device according to claim 1.   The information recording / reproducing apparatus according to claim 6, wherein information is recorded in units of a book in which pages including wavelength detection information are multiplexed and recorded.   The wavelength error signal indicating a deviation amount from the optimum reproduction wavelength is calculated by normalizing a difference component between the first wavelength detection information and the second wavelength detection information in the wavelength detection information. The information recording / reproducing apparatus described in 1.

Images