JP3956101B2 - Optical unit for hologram and optical axis adjustment method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical unit for hologram and an optical axis adjusting method thereof.
[0002]
[Prior art]
Hologram recording, in which information is recorded on a recording medium using holography, is generally performed by superimposing information light having image information and reference light inside the recording medium, and forming interference fringes at that time on the recording medium. Done by writing. At the time of reproducing the recorded information, the image information is reproduced by diffraction by interference fringes by irradiating the recording medium with reference light.
[0003]
In recent years, volume holography, particularly digital volume holography, has been developed and attracted attention for practical use for ultra-high density optical recording. Volume holography is a method of writing interference fringes three-dimensionally by actively utilizing the thickness direction of the recording medium. The diffraction efficiency can be increased by increasing the thickness of the recording medium. There is a feature that the capacity can be increased. Digital volume holography is a computer-oriented hologram recording method in which image information to be recorded is limited to a binarized digital pattern while using the same recording medium and recording method as in volume holography.
[0004]
In this digital volume holography, for example, image information such as an analog picture is once digitized, developed into two-dimensional digital pattern information, and recorded as image information. At the time of reproduction, the digital pattern information is read and decoded so that the original image information is restored and displayed. As a result, even if the S / N ratio (signal to noise ratio) is somewhat poor at the time of reproduction, the original information is reproduced very faithfully by performing differential detection or encoding binary data and performing error correction. It becomes possible.
[0005]
Such a conventional recording / reproducing system in digital volume holography includes a spatial light modulator for generating information light based on two-dimensional digital pattern information, and condensing the information light from the spatial light modulator to form a hologram recording medium. A reference light irradiating means for irradiating the hologram recording medium with reference light from a direction substantially orthogonal to the information light, and a CCD (charge coupled device) for detecting reproduced two-dimensional digital pattern information An array and a lens that collects the reproduction light emitted from the hologram recording medium and irradiates the light onto the CCD array are provided. Note that the hologram recording medium includes LiNbO. _Three Hologram recording materials such as crystals and photopolymers are used.
[0006]
With the above configuration, information can be multiplexed and recorded on the same hologram recording medium. However, in order to record information at an extremely high density, positioning of information light and reference light with respect to the hologram recording medium is important. However, in the above configuration, since there is no information for positioning in the hologram recording medium itself, positioning of the information light and the reference light with respect to the hologram recording medium can only be performed mechanically, and positioning with high accuracy is difficult.
[0007]
Therefore, the removability (ease of moving the hologram recording medium from one recording / reproducing apparatus to another recording / reproducing apparatus and performing the same recording / reproducing) is difficult, and random access is difficult and high-density recording is difficult. There is a problem that it is. Furthermore, since the optical axes of the information light, the reference light, and the reproduction light are arranged at spatially different positions, the optical system for recording or reproduction is enlarged, and the information light, the reference light, and the reproduction light are increased. Therefore, there is a problem that it is difficult to adjust the optical axes.
[0008]
FIG. 4 is an explanatory diagram showing a configuration of a pickup in “optical information recording apparatus and method and optical information reproducing apparatus and method” disclosed in, for example, Japanese Patent Application Laid-Open No. 11-311937 as means for solving the above problems. It is. The pickup 111 in such a configuration is arranged in order from the light source device 112 side in the traveling direction of the light emitted from the light source device 112 and the light source device 112 that emits coherent linearly polarized laser light having a wavelength of, for example, 532 nm or 650 nm. Collimator lens 113, neutral density filter (hereinafter referred to as ND filter) 114, optical element 115 for optical rotation, polarization beam splitter (hereinafter abbreviated as PBS) 116, phase spatial light modulator 117, beam splitter ( (Hereinafter abbreviated as BS) 118 and a photo detector 119.
[0009]
The light source device 112 emits S-polarized light or P-polarized linearly polarized light, and the collimator lens 113 emits the light emitted from the light source device 112 as a parallel light beam. The ND filter 114 has a characteristic that makes the intensity distribution of the emitted light from the collimator lens 113 uniform.
[0010]
S-polarized light is linearly polarized light whose polarization direction (polarization plane) is perpendicular to the incident plane, and P-polarized light is linearly polarized light whose polarization direction is parallel to the incident plane. Also, linearly polarized light obtained by rotating S-polarized light by −45 ° or P-polarized light by + 45 ° is referred to as polarization state A, and linearly polarized light obtained by rotating S-polarized light by + 45 ° or P-polarized light by −45 ° is referred to as polarization state B. In the following, the same meaning is used. The polarization state A and the polarization state B are orthogonal to each other.
[0011]
The optical rotatory optical element 115 rotates the light emitted from the ND filter 114 and emits light including an S-polarized component and a P-polarized component. As the optical rotation optical element 115, for example, a half-wave plate or an optical rotation plate is used. The PBS 116 has a PBS surface 116a that reflects the S-polarized component and transmits the P-polarized component of the light emitted from the optical rotation optical element 115.
[0012]
The BS 118 has a beam splitter surface 118a. The beam splitter surface 118a transmits, for example, 20% of the P-polarized component and reflects 80% thereof. The photodetector 119 is used to monitor the light amount of the reference light and perform automatic light amount adjustment of the reference light.
[0013]
The pickup 111 further includes a PBS 120, a two-part optical rotation plate 121, and a rising mirror 122 arranged in order from the BS 118 side in the direction in which the light from the light source device 112 is reflected by the beam splitter surface 118a of the BS 118 and travels. Yes. The PBS 120 has a PBS surface 120a that reflects the S-polarized component and transmits the P-polarized component of the incident light.
[0014]
The two-divided optical rotatory plate 121 includes an optical rotatory plate 121R disposed in the right portion of the optical axis in FIG. 4 and an optical rotatory plate 121L disposed in the left portion of the optical axis. The optical rotation plate 121R constituting the two-part optical rotation plate 121 rotates the polarization direction by −45 °, and the optical rotation plate 121L rotates the polarization direction by + 45 °. The rising mirror 122 is tilted by 45 ° with respect to the optical axis of the light from the two-divided optical rotatory plate 121, and reflects the light from the two-divided optical rotatory plate 121 in a direction perpendicular to the paper surface in FIG. It has a reflective surface.
[0015]
The pickup 111 is further arranged in a direction in which the light from the two-part optical rotatory plate 121 is reflected by the reflecting surface of the rising mirror 122 and travels, and the optical information recording medium is fixed when the optical information recording medium is fixed to the spindle. An objective lens 123 facing the transparent substrate 2 side of the medium, and an actuator (not shown) that can move the objective lens 123 in the thickness direction and the track direction of the optical information recording medium are provided.
[0016]
The pickup 111 further includes a spatial light modulator 125, a convex lens 126, a BS 127, and a photodetector 128 that are arranged in order from the PBS 116 side in the direction in which the light from the light source device 112 is reflected by the PBS surface 116a of the PBS 116 and travels. Yes.
[0017]
The convex lens 126 has a function of forming an interference area between the recording reference light and the information light by converging the information light on the near side of the recording reference light in the optical information recording medium. Further, by adjusting the position of the convex lens 126, the size of the interference area between the recording reference light and the information light can be adjusted. The BS 127 has a beam splitter surface 127a.
[0018]
The beam splitter surface 127a transmits, for example, 20% of the S-polarized component and reflects 80%. The photo detector 128 is used for monitoring the light quantity of information light and performing automatic power control (Auto Power Control) APC of information light. In the photodetector 128, the light receiving unit may be divided into a plurality of regions so that the intensity distribution of the information light can be adjusted. Light that enters the BS 127 from the convex lens 126 side and is reflected by the beam splitter surface 127 a enters the PBS 120.
[0019]
The pickup 111 further includes a convex lens 129, a cylindrical lens 130, and a four-divided photodetector 131 arranged in this order from the BS 127 side on the side opposite to the PBS 120 in the BS 127. The cylindrical lens 130 is arranged such that the central axis of its cylindrical surface forms 45 ° with respect to the dividing line of the four-divided photodetector 131.
[0020]
A focus error signal FE, a tracking error signal TE, and a reproduction signal RF are generated based on the output of the quadrant photodetector 131. Based on these signals, focus servo and tracking servo are performed, and the basic clock Playback and address discrimination are performed.
[0021]
The pickup 111 further includes an imaging lens 132 and a CCD array 133 which are arranged in order from the BS 118 side on the opposite side of the BS 118 from the PBS 120. The pickup 111 further includes a collimator lens 134 and a fixing light source device 135 arranged in order from the PBS 116 side on the opposite side of the PBS 116 from the spatial light modulator 125. The fixing light source device 135 emits light for fixing information recorded on the hologram layer of the optical information recording medium, for example, ultraviolet light having a wavelength of 266 nm.
[0022]
As such a fixing light source device 135, a laser light source, a light source device that emits light after being wavelength-converted through a nonlinear optical medium, or the like is used. The collimator lens 134 converts the emitted light from the fixing light source device 135 into a parallel light beam, and the fixing light source device 135 emits S-polarized light.
[0023]
[Problems to be solved by the invention]
In the above invention, the information light and the reference light can be separated or coaxially separated by the PBS 116, PBS 120, BS 118 and BS 127, whereby the optical axes of the information light, the reference light and the reproduction light are spatially mutually separated. Since they are arranged at different positions, it contributes to miniaturization of the recording or reproducing optical system.
[0024]
However, this method uses two PBSs and two BSs. On the other hand, the light source includes a fixing light source device 135 that emits ultraviolet light having a wavelength of 266 nm, for example, and a light source device 112 that emits laser light having a wavelength of 532 nm or 650 nm. There are two different wavelengths. Accordingly, light of different wavelengths is transmitted and reflected on each PBS and BS.
[0025]
In such a case, reflected light is generated for the transmitted light or transmitted light is generated for the reflected light due to the difference in reflection and transmission performance with respect to the wavelengths of the PBSs and BSs. As a result, a loss of light occurs, for example, a problem that the light reaching the optical information recording medium, the photodetector 131, or the CCD array 133 decreases.
[0026]
Further, an optical path difference is generated due to the difference in wavelength between the two light sources, and when the optical path is adjusted so that the optical path matches one wavelength, there arises a problem that the optical path is shifted with respect to the other wavelength. In addition, the use of different parts of two PBSs and two BSs increases the cost of the optical unit and has the disadvantages of complicated product management.
[0027]
The present invention has been made for the purpose of solving such problems and providing a high-performance hologram optical unit and a simple optical axis adjustment method thereof.
[0028]
[Means for Solving the Problems]
In order to achieve the above object, in the hologram optical unit according to claim 1, information is recorded / reproduced in a plurality of information recording areas by an interference pattern due to interference between information light and reference light. A first optical system that generates information light and reference light on the same optical path, a second optical system that generates control light for performing the focus servo and tracking servo, the information light and reference light, and control A third light that irradiates the recording medium with light in the same optical path and separates the control light reflected from the recording medium and the information light included in the reference light into the second optical system and the first optical system, respectively. The optical system is provided.
[0029]
The first optical system includes first, second, third, and fourth polarizing beam splitters, respectively, and the first polarizing beam splitter separates laser light into information light and reference light, and second polarized light. The beam splitter reflects the separated information light out of the information light and the reference light separated by the first polarization beam splitter in a direction for coupling to the separated reference light.
[0030]
The third polarizing beam splitter reflects the reference light separated by the first polarizing beam splitter in a direction to be combined with the information light reflected by the second polarizing beam splitter, and causes the fourth polarizing beam splitter to The reflected light that is transmitted and reflected from the recording medium is transmitted.
[0031]
The fourth polarizing beam splitter reflects and transmits the information light and the reference light reflected by the second polarizing beam splitter and the third polarizing beam splitter, respectively, and the information light and the reference light are on the same optical axis. The reflected light reflected from the recording medium is transmitted and incident on the third polarizing beam splitter.
[0032]
3. The hologram optical unit according to claim 2, wherein the first optical system includes a first optical rotation optical element for converting laser light emitted from the first laser light source into S-polarized light and P-polarized light, and the optical for optical rotation. A first polarization beam splitter that separates the S-polarized light and the P-polarized light transmitted through the element, a second optical rotatory optical element that converts the P-polarized light transmitted through the first polarized beam splitter into S-polarized light, and A spatial modulator that spatially modulates the S-polarized light transmitted through the optical rotatory optical element, a second polarization beam splitter that reflects the S-polarized light modulated by the spatial modulator and converts the S-polarized light into the information light, and the first A third polarizing beam splitter that reflects the S-polarized light reflected by the polarizing beam splitter and transmits the light having the wavelength of the first laser light source reflected from the recording medium, and the third polarizing beam splitter. Reflection A third optical rotatory optical element that converts the S-polarized light into P-polarized light, and the S-polarized light that has been transmitted through the third optical rotatory optical element and is reflected by the second polarizing beam splitter. The fourth polarization beam splitter that reflects the light and makes the S-polarized light and the P-polarized light have the same optical axis, and the two-split optical rotation that rotates the polarization directions of the S-polarized light and the P-polarized light that are made the same optical axis by −45 ° and + 45 °. A plate is provided.
[0033]
The second optical system transmits the laser light emitted from the second laser light source and enters the third optical system, and is emitted from the third optical system and reflected from the recording medium. A beam splitter that reflects light having the wavelength of the second laser light source is provided.
[0034]
The third optical system reflects S-polarized light and P-polarized light emitted from the first optical system and having the same optical axis, and emits laser light from the second laser light source emitted from the second optical system. And a dichroic mirror that reflects the light having the wavelength of the first laser light source reflected from the recording medium and transmits the light having the wavelength of the second laser light source.
[0035]
4. The hologram optical unit adjustment method according to claim 3, wherein the optical unit generates information light and reference light on the same optical path from the laser light emitted from the first laser light source with respect to the recording medium. A first optical system each including a second, third, and fourth polarizing beam splitter; a second optical system that generates control light for performing the focus servo and tracking servo; and the information light. A third optical system for irradiating the recording medium with the reference light and the control light on the same optical path is provided.
[0036]
The first optical system includes an optical path through which the laser light emitted from the first laser light source on the base on which the optical unit is mounted is transmitted / reflected, and the first polarizing beam splitter A first adjustment pin is provided on the laser beam incident side, and a second, third, fourth, and fourth laser beam output sides of the first, second, third, and fourth polarization beam splitters, respectively. A fifth adjustment pin is provided, and the first adjustment pin is irradiated with the laser light emitted from the first laser light source, and the shadow generated by the first adjustment pin is the second, third, fourth, The optical axes of the first, second, third, and fourth polarizing beam splitters are adjusted so as to coincide with the fifth adjustment pin.
[0037]
The order of the optical axis adjustment is such that after the optical axis of the first polarizing beam splitter is adjusted, the second adjustment pin is removed, and the third and fourth adjustment pins are erected and the second and second adjustment pins are erected. 3 or the optical axis of the third and second polarizing beam splitters is adjusted, and then the third and fourth adjusting pins are removed and the fifth adjusting pin is erected to stand up the fourth polarized light. The optical axis of the beam splitter is adjusted, and then the first and fifth adjustment pins are removed.
[0038]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is an optical unit applied to a polarization collinear hologram, and FIG. 1 is a diagram showing a configuration of a hologram optical unit in an embodiment of the present invention. In FIG. 1, a recording medium that does not need to be fixed is used as the hologram recording medium, the formed hologram is described as a transmission hologram, and the base on which the optical unit is mounted, the driving device, etc. are not shown. It is.
[0039]
In FIG. 1, the optical unit transmits information light and reference light to the recording medium 11 on the same optical path so that information is recorded in a plurality of information recording areas by interference patterns due to interference between information light and reference light. The first optical system OP1 generated at the same time, the second optical system OP2 that generates control light for performing focus servo and tracking servo, the information light, the reference light, and the control light are irradiated on the recording medium through the same optical path. The third optical system OP3 is provided.
[0040]
The first optical system OP1 includes, for example, a single-mode first laser light source 1 (P-polarized light or S-polarized light source) having a wavelength of 532 nm, and the emitted light from the first laser light source 1 is illustrated. It is converted into parallel light by a collimator lens that is not. The parallel light passes through the first half-wave plate 31 whose optical axis is set at a predetermined angle in advance, so that the plane of polarization is rotated and converted into A-polarized light or B-polarized light.
[0041]
The first optical system OP1 includes first, second, third, and fourth polarizing beam splitters PBS1, PBS2, PBS3, and PBS4, respectively, and is incident on the PBS1, PBS2, PBS3, and PBS4. Of the light, PBS surfaces PBS1a, PBS2a, PBS3a, and PBS4a that reflect the S-polarized component and transmit the P-polarized component are respectively formed.
[0042]
A first half-wave plate 31 is provided on the incident light side of the first polarizing beam splitter PBS1. The first half-wave plate 31 generates the information light IP and the reference light RP together with the first polarizing beam splitter PBS1.
[0043]
Further, the side through which the incident light is transmitted through the first polarizing beam splitter PBS1 (the outgoing side of the P-polarized component, the side from which the information light IP is emitted) and the side that reflects the incident light (the side from which the S-polarized component is emitted, reference light) A second polarizing beam splitter PBS2 and a third polarizing beam splitter PBS3 are provided on the RP exit side), respectively. The optical axis on the reflecting side of the second polarizing beam splitter PBS2 is orthogonal to the optical axis on the reflecting side of the third polarizing beam splitter PBS3, and a fourth polarizing beam splitter PBS4 is provided at the intersection. It has been. The fourth polarization beam splitter PBS4 includes an optical axis on the reflection side of the S polarization component incident from the second polarization beam splitter PBS2 and an optical axis on the transmission side of the P polarization component incident from the third polarization beam splitter PBS3. Are configured to match.
[0044]
A second half-wave plate 32, a convex lens 25, and a spatial modulator SLM are provided on the side of the first polarizing beam splitter PBS1 that outputs the P-polarized light component. The convex lens 25 performs the same function as the convex lens 125 described in the related art, but the spatial modulator SLM can also have the function, and in this case, the convex lens 25 may be omitted. it can. A third half-wave plate 33 is provided on the side of the third polarizing beam splitter PBS3 that outputs the S-polarized component, and converts the S-polarized light into P-polarized light by a predetermined ratio (for example, 50%). The optical axis is set so as to. The reason why all of the S-polarized light is not converted to P-polarized light is to enable part of the reflected light from the recording medium 11 to be guided to the sensor 2.
[0045]
A two-divided optical rotatory plate 4 is provided on the side of the fourth polarizing beam splitter PBS4 that outputs the P-polarized component and the S-polarized component.
[0046]
A sensor 2 such as a CCD camera is provided on the opposite side of the third polarizing beam splitter PBS3 from the side on which the third half-wave plate 33 is provided.
[0047]
The second optical system OP2 includes, for example, a single-mode second laser light source 6 (P-polarized light or S-polarized light source, control light CP) having a wavelength of 650 nm or 780 nm. The light emitted from the laser light source 6 is emitted as a parallel light beam. The wavelength of the second laser light source 6 is a wavelength at which recording sensitivity to the hologram layer of the recording medium 11 is not present.
[0048]
That is, the second laser light source 6 is continuously oscillating, and the recording medium 11 is constantly irradiated. On the other hand, the first laser light source 1 stops oscillation in the servo region or switches light by an electro-optic modulator or the like so that the light from the first laser light source 1 is not irradiated onto the servo region. Such control is performed using information in the address area.
[0049]
A half of the laser light emitted from the second laser light source 6 is transmitted (reflects ½) and enters the third optical system OP3, and the reflecting surface 11a of the recording medium 11 (see FIG. 2). ) Is reflected by the second optical system OP3 (control light CP), and the beam splitter 7 is formed with a reflection film 7a that reflects (transmits ½) of the light. The laser light source 6 and the collimator lens 12 are provided.
[0050]
Further, a cylindrical lens 8 and a four-divided photodetector 9 are provided in the direction in which the control light CP incident from the third optical system OP3 is reflected by the reflection film 7a of the beam splitter 7.
[0051]
A focus error signal and a tracking error signal are generated on the basis of the output of the four-divided photodetector 9. Based on these signals, focus servo and tracking servo are performed, and the basic clock is reproduced and the address is discriminated. Done.
[0052]
The third optical system OP3 is provided with a dichroic mirror 5 having a characteristic of reflecting light having the wavelength of the first laser light source 1 and transmitting light having the wavelength of the second laser light source 6. .
[0053]
The dichroic mirror 5 uses the same S-polarized light and P-polarized light (reference light RP and information light IP) emitted from the first optical system OP1 and the laser light of the second laser light source 6 emitted from the second optical system OP2. The light is guided to the lens 10 along the optical path. Further, the light having the wavelength of the first laser light source 1 reflected from the recording medium 11 and transmitted through the objective lens 10 is reflected and guided to the two-divided optical rotatory plate 4, and the light having the wavelength of the second laser light source 6 is transmitted to the beam. The light is incident on the splitter 7.
[0054]
By the objective lens 10, the reference light RP and the control light CP are focused on the reflection surface of the recording medium 11, and the information light IP is focused on the front side of the reflection surface of the recording medium 11. Therefore, the information light IP is diffused greatly after reflection and is not converged by the objective lens 10.
[0055]
FIG. 2 is a cross-sectional view of the recording medium 11, and the laser beam is irradiated from the A direction. The irradiation surface is covered with a transparent glass substrate 11d, and a hologram layer 11c is formed below the transparent glass substrate 11d and 11b. Further, a reflective film 11a is formed under the transparent glass substrate 11b by aluminum vapor deposition or the like.
[0056]
1 will be described in the order of the first optical system OP1, the second optical system OP2, and the third optical system OP3.
[0057]
At the time of recording information in the first optical system OP1, the P-polarized or S-polarized laser light emitted from the first laser light source 1 is converted into a parallel light beam by a collimator lens (not shown). The parallel light is converted into B-polarized (or A-polarized) linearly polarized light by the first half-wave plate 31 and enters the first polarizing beam splitter PBS1.
[0058]
Of the B-polarized light incident on the first polarizing beam splitter PBS1, the S-polarized light is reflected by the reflecting surface PBS1a and enters the third polarizing beam splitter PBS3 as the reference light RP, and the P-polarized light is transmitted through the reflecting surface PBS1a. The light enters the second half-wave plate 32 as information light IP.
[0059]
The reference light RP (S-polarized light) is reflected by the reflecting surface PBS3a of the third polarizing beam splitter PBS3 and enters the third half-wave plate 33. The incident light passes through the third half-wave plate 33 whose optical axis is set to a predetermined angle in advance, so that a part of the S-polarized light incident at a ratio corresponding to the set angle becomes P-polarized light. Converted.
[0060]
The P-polarized component of the reference light RP that has passed through the third half-wave plate 33 enters the fourth polarizing beam splitter PBS4 and passes through the reflecting surface PBS4a of the fourth polarizing beam splitter PBS4 as it is.
[0061]
On the other hand, the information light IP (P-polarized light) incident on the second half-wave plate 32 becomes S-polarized light and enters the spatial modulator SLM. It is modulated according to predetermined information by the spatial modulator SLM to become information to be recorded on the recording medium 11, and enters the second polarization beam splitter PBS2. The information light IP (S-polarized light) incident on the second polarizing beam splitter PBS2 is reflected by the reflecting surface PBS2a and enters the fourth polarizing beam splitter PBS4.
[0062]
The information light IP (S-polarized light) is reflected by the reflecting surface PBS4a of the fourth polarizing beam splitter PBS4 and has the same optical axis as the reference light RP (P-polarized light) transmitted through the reflecting surface PBS4a. Is incident on a two-split optical rotatory plate 4 that rotates the polarization direction of the light.
[0063]
There are two types of light incident on the two-divided optical rotatory plate 4: information light IP (S-polarized light) and reference light RP (P-polarized light). Such S-polarized light and P-polarized light are incident on the left half 4L and the right half 4R of the two-divided optical rotatory plate 4, respectively.
[0064]
The polarization directions of the information light IP (S-polarized light) and the reference light RP (P-polarized light) incident on the right half 4R and the left half 4L are rotated by −45 ° and + 45 °, respectively. That is, the information light IP (S-polarized light) and the reference light RP (P-polarized light) transmitted through the right half 4R become A-polarized light and B-polarized light, respectively. The information light IP (S-polarized light) and the reference light RP (P-polarized light) transmitted through the left half 4L become B-polarized light and A-polarized light, respectively.
[0065]
Therefore, the information light IP transmitted through the right half 4R and the reference light RP transmitted through the left half 4L are A-polarized light, and the information light IP transmitted through the left half 4L and the reference light RP transmitted through the right half 4R are B-polarized light. It becomes.
[0066]
As a result, the information light IP transmitted through the right half 4R converged by the objective lens 10 and the reference light RP transmitted through the left half 4L are in the same polarization state (A-polarized light), and the recording medium 11 has a semicircular shape. Interference fringes are formed on the hologram layer 11c, and information is recorded on the hologram layer 11c.
[0067]
Similarly, the information light IP transmitted through the left half 4L converged by the objective lens 10 and the reference light RP transmitted through the right half 4R are in the same polarization state (B-polarized light), and the recording medium 11 receives the half light. Interference fringes are formed in a semicircular shape facing the circle, and information is recorded in the hologram layer 11c. The two semicircular holograms are combined into one circular hologram.
[0068]
At the time of reproducing information in the first optical system OP1, A-polarized light and B-polarized light as information light included in the reference light having the wavelength of the first laser light source 1 reflected by the recording medium 11 will be described later. In this way, the light is reflected by the dichroic mirror 5 of the third optical system OP3, returns to the first optical system OP1, and enters the two-divided optical rotation plate 4 from the opposite direction.
[0069]
When the reflected A-polarized light and B-polarized light are incident on the two-divided optical rotatory plate 4 from the opposite direction, they are rotated in the opposite directions and returned to the original polarization plane. As described above, in the reference light RP incident on the recording medium 11, the reference light RP transmitted through the left half 4L of the two-divided optical rotatory plate 4 becomes A-polarized light, and the reference light RP transmitted through the right half 4R becomes B-polarized light.
[0070]
Therefore, the A-polarized light and the B-polarized light that are reflected from the recording medium 11 and re-enter the left half 4L and the right half 4R of the two-divided optical rotatory plate 4 become S-polarized light and P-polarized light, respectively. , Enters the fourth polarization beam splitter PBS4.
[0071]
Of the reflected light incident on the fourth polarization beam splitter PBS4, S-polarized light is reflected by the reflective surface PBS4a, and P-polarized light is transmitted through the reflective surface PBS4a.
[0072]
The P-polarized light transmitted through the reflection surface PBS 4 a is incident on the third half-wave plate 33. The incident light passes through the third half-wave plate 33 whose optical axis is set at a predetermined angle in advance, so that the polarization plane is rotated and P-polarized light and S-polarized light are generated.
[0073]
The P-polarized light and S-polarized light emitted from the third half-wave plate 33 are incident on the third polarizing beam splitter PBS3. Of the incident light, S-polarized light is reflected by the reflecting surface PBS3a, and P-polarized light passes through the reflecting surface PBS3a and enters the sensor 2. Light incident by the sensor 2 is converted into an electrical signal by a known method, and information is extracted.
[0074]
Next, the second optical system OP2 will be described. The second optical system OP2 generates control light CP for performing focus servo and tracking servo. The laser light emitted from the second laser light source 6 enters the beam splitter 7. The beam splitter 7 is formed with a reflective film 7a that reflects ½ of the light having the wavelength of the second laser light source, and ½ of the laser light emitted from the second laser light source 6 is transmitted therethrough. The light enters the dichroic mirror 5 of the third optical system OP3 through the collimator lens 12 as control light CP for servo control.
[0075]
On the other hand, of the reflected light reflected by the reflective film 11a of the recording medium 11, the light having the wavelength of the second laser light source 6 (control light CP) passes through the dichroic mirror 5 and enters the second optical system OP2. Returning to the beam splitter 7 through the collimator lens 12.
[0076]
The control light CP is incident on the quadrant photodetector 9 through a cylindrical lens 8 that is reflected by the reflecting surface 7a of the beam splitter 7 and condenses the laser light, and generates a focus error signal and a tracking error signal by a known method. Based on these signals, focus servo and tracking servo are performed, and the basic clock is reproduced and the address is discriminated.
[0077]
In the third optical system OP3, the reference light RP and the information light IP emitted from the two-part rotatory rotation plate 4 and the control light CP transmitted through the collimator lens 12 are reflected or transmitted by the dichroic mirror 5, respectively. The same optical axis is collected on the recording medium 11 by the objective lens 10. Then, the reflected light reflected from the recording medium 11 returns to the objective lens 10 and enters the dichroic mirror 5.
[0078]
Of the reflected light incident on the dichroic mirror 5, the control light CP passes through the dichroic mirror 5 as it is, and the remaining reflected light is reflected by the dichroic mirror 5 and incident on the two-divided optical rotation plate 4. Information is reproduced in the system OP1.
[0079]
FIG. 3 is a diagram for explaining a method of adjusting the optical unit for hologram recording in the embodiment of the present invention. In the hologram recording optical unit, the first, second, and third laser light emitted from the first laser light source 1 to the recording medium 11 is generated on the same optical path with the information light IP and the reference light RP. A first optical system OP1 having a fourth polarization beam splitter PBS1, PBS2, PBS3, PBS4, a second optical system OP2 for generating control light CP for performing focus servo and tracking servo, A third optical system OP3 that irradiates the recording medium with the information light IP, the reference light RP, and the control light CP on the same optical path is provided.
[0080]
Adjustment pins P1, P2, P3, P4, and P5 provided in the first optical system are in the middle of an optical path of a base (not shown) through which the reference light RP and the information light IP pass in the first optical system OP1. They are arranged upright in advance. The adjusting pin is, for example, a thin rod-shaped pin having a circular diameter, and the diameter is thick enough to allow the shadow of the laser beam to be visually observed, and the height is good enough that the optical axis and the tip of the pin coincide. . By making the optical axis in the state where there is no optical component other than the laser light source 1 and the height of the tip of the pin coincide with each other, it is easy to adjust the optical axis in the height direction when the optical component is arranged.
[0081]
The position where the adjustment pin is erected is on the optical path through which the laser beam emitted from the first laser light source 1 is transmitted / reflected, and the laser beam from the first polarization beam splitter PBS1 is incident thereon. The first adjustment pin P1 is provided upright and in front of the first half-wave plate 31. An adjustment pin P2 is provided on the side of the first polarization beam splitter PBS1 where the P polarization component is output, and an adjustment pin P2 is provided on the side of the second and third polarization beam splitters PBS2 and PBS3 where the S polarization component is output. An adjustment pin P5 is provided on the side where the pins P3 and P4 output the P-polarized component and the S-polarized component of the fourth polarizing beam splitter PBS4.
[0082]
First, the first adjustment pin P <b> 1 and the adjustment pin P <b> 2 are erected and laser light is emitted from the first laser light source 1. Of the laser light irradiated to the first adjustment pin P1, when the laser light transmitted through the reflection surface PBS1a of the first polarization beam splitter PBS1 is irradiated to the adjustment pin P2, the shadow of the first adjustment pin P1 is shadowed. The rotation angle (installation angle) of the first polarization beam splitter PBS1 is adjusted so as to overlap the adjustment pin P2.
[0083]
Next, the first half-wave plate 31 and the spatial modulator SLM are disposed at predetermined positions, and the second adjustment pin P2 is removed and the third adjustment pin P3 and the fourth adjustment pin P4 are erected. To do. Of the laser light irradiated to the first adjustment pin P1, the laser light that has passed through the first polarization beam splitter PBS1 and is reflected by the reflection surface PBS2a of the second polarization beam splitter PBS2 is applied to the adjustment pin P3. The rotation angle of the second polarization beam splitter PBS2 is adjusted so that the shadow of the first adjustment pin P1 overlaps the adjustment pin P3.
[0084]
Similarly, of the laser light irradiated to the first adjustment pin P1, the laser light reflected by the reflecting surface PBS1a of the first polarizing beam splitter PBS1 is reflected by the reflecting surface PBS3a of the third polarizing beam splitter PBS3. When the adjustment pin P4 is irradiated, the rotation angle of the fourth polarizing beam splitter PBS4 is adjusted so that the shadow of the first adjustment pin P1 overlaps the adjustment pin P4. Note that the adjustment of the second polarizing beam splitter PBS2 and the third polarizing beam splitter PBS3 may be performed first.
[0085]
Next, the third and fourth adjustment pins P3 and P4 are removed, and the laser beam reflected by the reflection surface PBS2a of the second polarization beam splitter PBS2 among the laser beams irradiated on the first adjustment pin P1. And the laser beam reflected by the reflecting surface PBS3a of the third polarization beam splitter PBS3 is irradiated onto the adjustment pin P5, so that the shadow of the first adjustment pin P1 overlaps the adjustment pin P5. The rotation angle of the splitter PBS4 is adjusted. After all the polarization beam splitters have been adjusted, the adjustment pins P1 and P5 are removed.
[0086]
In the adjustment method of the optical system, the shadow of the first adjustment pin P1 is made to coincide with the other adjustment pins. Thus, the second, third, and fourth polarization beam splitters PBS2, PBS3, Each adjustment pin of the PBS 4 is separated from the first adjustment pin P1. Accordingly, large deviations in the second, third, and fourth polarizing beam splitters PBS2, PBS3, and PBS4 are observed, and as a result, adjustment errors of the respective polarizing beam splitters can be reduced.
[0087]
In addition to the above, the adjustment pins after adjustment may be used sequentially. That is, for example, when adjusting the rotation angle of the second polarizing beam splitter PBS2, the shadow of the adjustment pin P2 may be made to coincide with the adjustment pin P3. In such a case, there is an advantage that the optical component between the adjustment pin and the adjustment pin can be adjusted independently.
[0088]
In the above-described embodiments, the fixing light source device for fixing has been described as a hologram recording medium that is not necessary. However, the present invention can also be applied to hologram recording media that require fixing. In such a case, the light from the fixing light source device is coupled to the third optical system so as not to pass through the first and second optical systems.
[0089]
【The invention's effect】
According to the hologram optical unit of claim 1, the first optical system that generates the information light and the reference light on the same optical path, and the second that generates the control light for performing the focus servo and tracking servo. Irradiating the recording medium with the information light, the reference light, and the control light in the same optical path, and the control light reflected from the recording medium and the information light included in the reference light in the second optical system A third optical system that separates the system and the first optical system was provided.
[0090]
As a result, laser light having the same wavelength is transmitted and reflected in the first optical system, there is no difference in reflection and transmission performance with respect to the wavelength, and no light loss occurs. Therefore, for example, the problem that the light reaching the optical information recording medium 11 and the sensor 2 is reduced does not occur.
[0091]
Further, an optical path difference is caused by the difference in wavelength, and if the optical path is adjusted so that there is an optical path with respect to one wavelength, there is no problem that the optical path is shifted with respect to the other wavelength.
[0092]
Furthermore, by making all the polarizing beam splitters in the first optical system the same, the cost of the optical unit is reduced and product management is simplified.
[0093]
According to the hologram optical unit of claim 2, the wavelength of the laser light in the first optical system and that of the second optical system are made different, and the optical system is coupled and separated by the third optical system. It will be easy.
[0094]
According to the optical axis adjustment method of the optical unit for hologram according to claim 3, on the optical path through which the laser light emitted from the first laser light source on the base on which the optical unit is mounted is transmitted / reflected. Easy adjustment of the optical axis by adjusting the polarizing beam splitter so that the shadows produced by the adjusting pins are aligned before and after the plurality of polarizing beam splitters used in the first optical system. Can be done.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a hologram optical unit according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of a hologram recording medium.
FIG. 3 is a diagram illustrating a method for adjusting a hologram optical unit according to an embodiment of the present invention.
FIG. 4 is an explanatory diagram showing a configuration of a pickup in a conventional optical information recording apparatus and method and an optical information reproducing apparatus and method.
[Explanation of symbols]
1, 6 Laser light source
2 sensors
4 Divided optical rotation plate
5 Dichroic mirror
7 Beam splitter
9 Quadrant photo detector
10 Objective lens
11 Recording media
12 Collimator lens
31, 32, 33 half-wave plate
SLM spatial modulator
OP1 First optical system
OP2 Second optical system
OP3 Third optical system
PBS1, PBS2, PBS3, PBS4 Polarizing beam splitter
P1, P2, P3, P4, P5 Adjustment pin

Claims (3)

Information for generating a basic clock serving as a reference for various operation timings in the optical information recording / reproducing apparatus, information for performing focus servo by the sampled servo method, information for performing tracking servo by the sampled servo method, and A hologram optical unit for recording / reproducing information using holography in each of a plurality of information recording areas in a recording medium having an address / servo area composed of address information,
A first optical system for generating information light and reference light on the same optical path so that information is recorded / reproduced by an interference pattern due to interference between information light and reference light in the plurality of information recording areas; A second optical system that generates control light for performing the focus servo and tracking servo; and the information light, the reference light, and the control light are irradiated on the recording medium through the same optical path and reflected from the recording medium A third optical system for separating control light and information light included in the reference light into the second optical system and the first optical system, respectively;
The first optical system includes first, second, third, and fourth polarizing beam splitters, respectively, and the first polarizing beam splitter separates laser light into information light and reference light, and second polarized light. The beam splitter reflects the separated information light of the information light and the reference light separated by the first polarization beam splitter in a direction to combine with the separated reference light, and the third polarization beam splitter The reference light separated by the first polarizing beam splitter is reflected in a direction to be combined with the information light reflected by the second polarizing beam splitter, and is transmitted through the fourth polarizing beam splitter from the recording medium. The reflected light is transmitted, and the fourth polarizing beam splitter receives the information light and the reference light respectively reflected by the second polarizing beam splitter and the third polarizing beam splitter. A hologram that reflects and transmits each of the information light and the reference light on the same optical axis, transmits the reflected light reflected from the recording medium, and enters the third polarization beam splitter. Optical unit. The first optical system includes a first optical rotatory optical element that converts laser light emitted from the first laser light source into S-polarized light and P-polarized light, and the S-polarized light and P-polarized light transmitted through the optical rotatory element. A first polarizing beam splitter for separating;
A second optical rotatory optical element that converts P-polarized light transmitted through the first polarizing beam splitter into S-polarized light, a spatial modulator that spatially modulates S-polarized light transmitted through the second optical rotatory optical element, and A second polarization beam splitter that reflects the S-polarized light modulated by the spatial light modulator to produce the information light;
A third polarizing beam splitter that reflects S-polarized light reflected by the first polarizing beam splitter and transmits light having a wavelength of the first laser light source reflected from the recording medium; and the third polarized light A third optical element for optical rotation for converting the polarization plane of the S-polarized light reflected by the beam splitter;
Of the light transmitted through the third optical rotation optical element, P-polarized light is transmitted, and the S-polarized light reflected by the second polarization beam splitter is reflected so that the S-polarized light and the P-polarized light have the same optical axis. A second polarizing beam splitter, and a two-split optical rotator that rotates the polarization directions of the S-polarized light and the P-polarized light having the same optical axis as −45 ° and + 45 °,
The second optical system transmits the laser beam emitted from the second laser light source and enters the third optical system, and is reflected from the recording medium and emitted from the third optical system. A beam splitter that reflects light having the wavelength of the laser light source of
The third optical system reflects S-polarized light and P-polarized light emitted from the first optical system and having the same optical axis, and emits laser light from the second laser light source emitted from the second optical system. And a dichroic mirror that reflects the light having the wavelength of the first laser light source reflected from the recording medium and transmits the light having the wavelength of the second laser light source. Item 2. The hologram optical unit according to Item 1. Information for generating a basic clock serving as a reference for various operation timings in the optical information recording / reproducing apparatus, information for performing focus servo by the sampled servo method, information for performing tracking servo by the sampled servo method, and An optical axis adjustment method in an optical unit for hologram for recording information using holography in each of a plurality of information recording areas in a recording medium having an address / servo area composed of address information,
The optical unit separates the laser beam emitted from the first laser light source into the recording medium into the information beam and the reference beam, and then makes the same optical path again, the first, second, third, and fourth polarizations A first optical system each including a beam splitter; a second optical system that generates control light for performing the focus servo and tracking servo; and the information light, the reference light, and the control light in the same optical path. A third optical system for irradiating the recording medium;
The first optical system includes an optical path through which the laser light emitted from the first laser light source on the base on which the optical unit is mounted is transmitted / reflected, and the first polarizing beam splitter A first adjustment pin is provided on the laser beam incident side, and a second, third, fourth, and fourth laser beam output sides of the first, second, third, and fourth polarization beam splitters, respectively. A fifth adjustment pin is provided, and the first adjustment pin is irradiated with the laser light emitted from the first laser light source, and the shadow generated by the first adjustment pin is the second, third, fourth, Adjusting the optical axes of the first, second, third and fourth polarizing beam splitters so as to coincide with the fifth adjustment pin;
The order of the optical axis adjustment is to remove the second adjustment pin after adjusting the optical axis of the first polarization beam splitter, and to erect the third and fourth adjustment pins to provide the second and second adjustment pins. 3 or the optical axis of the third and second polarizing beam splitters is adjusted, and then the third and fourth adjusting pins are removed and the fifth adjusting pin is erected to stand up the fourth polarized light. An optical axis adjustment method for an optical unit for hologram, wherein the optical axis of the beam splitter is adjusted, and then the first and fifth adjustment pins are removed.

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