JP2003228875A - Optical unit for hologram and method for adjusting its optical axis - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical unit for holograms and a simple method of adjusting its optical axis. <P>SOLUTION: The optical unit is furnished with a first optical system OP1 for forming the information light and reference light on the same optical path of a recording medium 11, a second optical system OP2 for forming the control light for performing focus servo and tracking servo and a third optical system OP3 for aligning the information light, the reference light and the control light to the same optical path and irradiating the recording medium with such light in such a manner that information is recorded by the interference patterns formed by the interference of the information light and the reference light to a plurality of information recording regions, in which the first optical system OP1 is furnished with a first, second, third, and fourth polarization beam splitter PBS1, PBS2, PBS3, and PBS4, respectively. The information light and the reference light are formed by the first optical system and the recording medium 11 is irradiated with the light together with the control light emitted from the second optical system through the third optical system. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hologram optical unit and an optical axis adjusting method thereof.

[0002]

2. Description of the Related Art Holographic recording, which records information on a recording medium by utilizing holography, generally causes an information beam having image information and a reference beam to overlap each other inside the recording medium and causes interference at that time. This is done by writing stripes on the recording medium. At the time of reproducing the recorded information, by irradiating the recording medium with the reference light, the image information is reproduced by the diffraction due to the interference fringes.

In recent years, volume holography, particularly digital volume holography, has been developed in the practical range and has attracted attention for ultra-high density optical recording. Volume holography is a method in which interference fringes are three-dimensionally written by positively utilizing the thickness direction of the recording medium, and the diffraction efficiency can be increased by increasing the thickness of the recording medium. There is a feature that the capacity can be increased. The digital volume holography is a computer-oriented hologram recording method in which the image information to be recorded is limited to a binarized digital pattern while using the same recording medium and recording method as the volume holography.

In this digital volume holography, image information such as an analog picture is once digitized and developed into two-dimensional digital pattern information.
This is recorded as image information. During playback, by reading and decoding this digital pattern information,
The original image information is restored and displayed. As a result, even if the SN ratio (signal-to-noise ratio) is a little bad at the time of reproduction, the original information can be reproduced extremely faithfully by performing differential detection or coding the binary data and performing error correction. It will be possible.

A recording / reproducing system in such a conventional digital volume holography is a hologram recording by recording a spatial light modulator for generating information light based on two-dimensional digital pattern information, and collecting the information light from this spatial light modulator. A lens for irradiating the medium, a reference light irradiating means for irradiating the hologram recording medium with the reference light in a direction substantially orthogonal to the information light, and a CCD (charge) for detecting the reproduced two-dimensional digital pattern information. A coupling element) array and a lens that collects the reproduction light emitted from the hologram recording medium and irradiates it onto the CCD array. A hologram recording material such as a crystal such as LiNbO ₃ or a photopolymer is used for the hologram recording medium.

With the above construction, information can be recorded in multiple layers on the same hologram recording medium. However, in order to record information at an extremely high density, positioning of the information beam and the reference beam with respect to the hologram recording medium is important. . However, in the above configuration, since the hologram recording medium itself has no information for positioning, the information light and the reference light are mechanically positioned with respect to the hologram recording medium, and it is difficult to perform highly accurate positioning.

Therefore, the removability (the ease of moving the hologram recording medium from one recording / reproducing device to another recording / reproducing device to perform the same recording / reproducing) is poor, and random access is difficult and the high density is high. There is a problem that recording is difficult. Further, since the optical axes of the information light, the reference light and the reproduction light are spatially arranged at mutually different positions, the size of the optical system for recording or reproduction increases, and the information light, the reference light and the reproduction light However, there is a problem that it is difficult to adjust the optical axis.

FIG. 4 shows, as a means for solving the above-mentioned problems, the structure of a pickup in the "optical information recording apparatus and method and the optical information reproducing apparatus and method" disclosed in Japanese Patent Laid-Open No. 11-311937, for example. It is an explanatory view shown. The pickup 111 in such a form has a wavelength of 532 nm or 65 of coherent linearly polarized light, for example.
The light source device 112 that emits 0 nm laser light and the light source device 1 that is in the traveling direction of the light emitted from the light source device 112
The collimator lens 113 and the neutral density filter (hereinafter referred to as ND), which are sequentially arranged from the 12th side.
Described as a filter. ) 114, an optical element 115 for optical rotation, a polarization beam splitter (hereinafter abbreviated as PBS) 116, a phase spatial light modulator 117, a beam splitter (hereinafter abbreviated as BS) 118, and a photodetector 119.

The light source device 112 emits linearly polarized light of S polarization or P polarization, and a collimator lens 113.
Emits light emitted from the light source device 112 into a parallel light flux. The ND filter 114 has a property of making the intensity distribution of the light emitted from the collimator lens 113 uniform.

The S-polarized light is linearly polarized light whose polarization direction (polarization plane) is perpendicular to the incident surface, and the P-polarized light is linearly polarized light whose polarization direction is parallel to the incident surface. Further, linearly polarized light obtained by rotating S-polarized light at -45 ° or P-polarized light at + 45 ° is referred to as polarization state A, and linearly polarized light at which S-polarized light is rotated at + 45 ° or P-polarized light is referred to as polarization state B. The same meaning will be used below. The polarization states A and B have their polarization directions orthogonal to each other.

The optical element 115 for optical rotation is the ND filter 1
The emitted light of 14 is rotated, and the light including the S-polarized component and the P-polarized component is emitted. As the optical element 115 for optical rotation, for example, a ½ wavelength plate or an optical rotation plate is used. PBS
Reference numeral 116 denotes a PBS surface 11 that reflects the S-polarized component and transmits the P-polarized component of the light emitted from the optical element 115 for optical rotation.
6a.

BS 118 is a beam splitter surface 118.
a. This beam splitter surface 118a is
For example, the P-polarized component is transmitted by 20% and reflected by 80%. The photo detector 119 is used to monitor the light amount of the reference light and perform automatic light amount adjustment of the reference light.

The pickup 111 further includes the light source device 1.
The light from 12 is the beam splitter surface 118 of the BS 118.
A PBS 120, a two-divided optical rotation plate 121, and a rising mirror 122, which are sequentially arranged from the BS 118 side, are provided in a direction in which the light is reflected by a and travels. The PBS 120 has a PBS surface 120a that reflects the S-polarized component and transmits the P-polarized component of the incident light.

The two-divided optical rotation plate 121 has an optical rotation plate 121R arranged on the right side of the optical axis in FIG. 4 and an optical rotation plate 121L arranged on the left side 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.
° Rotate. The raising mirror 122 is tilted at 45 ° with respect to the optical axis of the light from the two-part optical rotation plate 121,
It has a reflection surface that reflects the light from the split optical rotation plate 121 in a direction orthogonal to the paper surface of FIG.

The pickup 111 is further arranged in a direction in which the light from the two-divided optical rotation plate 121 is reflected by the reflection surface of the rising mirror 122 and travels, and when the optical information recording medium is fixed to the spindle, The optical information recording medium includes an objective lens 123 facing the transparent substrate 2 side, and an actuator (not shown) capable of moving the objective lens 123 in the thickness direction and the track direction of the optical information recording medium.

The pickup 111 further includes the light source device 1.
The light from 12 is reflected by the PBS surface 116a of the PBS 116 and travels in a direction in which the spatial light modulator 125, the convex lens 126, and the BS 127 are sequentially arranged from the PBS 116 side.
And a photo detector 128.

The convex lens 126 has a function of converging the information light on the front side of the recording reference light in the optical information recording medium to form an interference region between the recording reference light and the information light. Further, by adjusting the position of the convex lens 126, the size of the interference region between the recording reference light and the information light can be adjusted. The BS 127 has a beam splitter surface 127a.

The beam splitter surface 127a transmits, for example, 20% of the S-polarized component and reflects 80% thereof. The photo detector 128 monitors the light amount of the information light and automatically adjusts the light amount of the information light (Auto Power Control).
ol) used for performing APC. In this photo detector 128, the light receiving portion may be divided into a plurality of regions so that the intensity distribution of the information light can be adjusted. The light that enters the BS 127 from the convex lens 126 side and is reflected by the beam splitter surface 127 a is PBS 120.
Incident on.

The pickup 111 further includes a BS 127.
A convex lens 129, a cylindrical lens 130, and a four-division photodetector 131, which are sequentially arranged from the BS 127 side, are provided on the side opposite to the PBS 120 in FIG. In the cylindrical lens 130, the central axis of its cylindrical surface is 4 with respect to the dividing line of the photo detector 131.
It is arranged to form 5 °.

The four-division photo detector 13
The focus error signal FE, the tracking error signal TE and the reproduction signal RF are generated based on the output of 1, and the focus servo and the tracking servo are performed based on these signals, and the reproduction of the basic clock and the determination of the address are performed. Done.

The pickup 111 further includes a BS 118.
Of the imaging lens 132 and the CCD array 1 which are sequentially arranged from the BS 118 side on the side opposite to the PBS 120 in FIG.
33 is provided. The pickup 111 also has a PB
On the side opposite to the spatial light modulator 125 in S116, P
Collimator lens 13 arranged in order from the BS 116 side
4 and a fixing light source device 135. The fixing light source device 135 is light for fixing the information recorded on the hologram layer of the optical information recording medium, for example, a wavelength of 266 nm.
Emits the ultraviolet light.

As such a fixing light source device 135, a laser light source, a light source device for wavelength-converting the light emitted from the laser light source through a non-linear optical medium and emitting the light is used. The collimator lens 134 is used for the fixing light source device 13.
The emitted light of No. 5 is made into a parallel light flux, and the fixing light source device 135 emits S-polarized light.

[0023]

In the above invention, PBS116, PBS120, BS118 and BS1 are provided.
The information light and the reference light can be separated or made coaxial by 27, whereby the optical axes of the information light, the reference light, and the reproduction light are spatially arranged at mutually different positions. Contributes to miniaturization of the optical system.

However, in this method, two PBSs and two PBSs are used.
Individual BSs are used. On the other hand, as a light source, there are a fixing light source device 135 for emitting ultraviolet light having a wavelength of 266 nm for fixing, and a light source device 112 for emitting laser light having a wavelength of 532 nm or 650 nm. There are two different wavelengths. Therefore, each PB
Light of different wavelengths is transmitted and reflected by S and BS.

In such a case, due to the difference in the reflection and transmission performances with respect to the wavelengths of the PBSs and BSs, reflected light is generated for transmitted light or transmitted light is generated for reflected light. As a result, there is a problem that light loss occurs and, for example, the amount of light reaching the optical information recording medium, the photodetector 131, or the CCD array 133 decreases.

Further, a difference in wavelength between the two light sources causes an optical path difference, and if the optical path is adjusted so that one of the wavelengths matches the optical path, there is a problem that the optical path of the other wavelength shifts. . In addition, the cost of the optical unit is increased due to the use of different components such as two PBSs and two BSs, and product management is complicated.

The present invention has been made for the purpose of solving the above problems and providing a high-performance hologram optical unit and a simple optical axis adjusting method thereof.

[0028]

In order to achieve the above object, the present invention provides a hologram optical unit according to claim 1, wherein information is recorded in a plurality of information recording areas by an interference pattern due to interference between the information light and the reference light. A first optical system for generating information light and reference light on the same optical path so that recording / reproduction is performed, and a second optical system for generating control light for performing the focus servo and tracking servo. Irradiating the recording medium with the information beam, the reference beam, and the control beam in the same optical path, and controlling the information beam contained in the control beam and the reference beam reflected from the recording medium with the second optical system and the first beam. And a third optical system for separating the optical systems.

The first optical system includes first, second, third, and fourth polarization beam splitters, respectively. The first polarization beam splitter splits laser light into information light and reference light. The second polarization 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 be combined with the separated reference light.

The third polarization beam splitter reflects the reference light separated by the first polarization beam splitter in a direction in which the reference light is combined with the information light reflected by the second polarization beam splitter, and the fourth polarization beam splitter. The reflected light transmitted through the beam splitter and reflected from the recording medium is transmitted.

The fourth polarization beam splitter reflects and transmits the information light and the reference light reflected by the second polarization beam splitter and the third polarization beam splitter, respectively, and outputs the information light and the reference light. The optical axis is the same, and the reflected light reflected from the recording medium is transmitted to enter the third polarization beam splitter.

In the hologram optical unit according to a second aspect of the present invention, the first optical system includes a first optical element for optical rotation that converts the laser light emitted from the first laser light source into S-polarized light and P-polarized light, A first polarization beam splitter for separating the S-polarized light and the P-polarized light transmitted through the optical element for optical rotation;
Second optical element for optical rotation that converts P-polarized light that has passed through the polarization beam splitter into S-polarized light, a spatial modulator that spatially modulates S-polarized light that passes through the second optical element for optical rotation, and the spatial modulator A second polarization beam splitter that reflects the S-polarized light that has been modulated by the first polarization beam splitter into the information light; and a first polarization beam splitter that reflects the S-polarized light reflected by the first polarization beam splitter and that is reflected from the recording medium. A third polarization beam splitter that transmits light having a wavelength of a laser light source;
Third polarization optical element for converting the S-polarized light reflected by the polarization beam splitter into P-polarized light, and the P-polarized light transmitted through the third optical rotation element, and the second polarization beam splitter. The fourth polarization beam splitter that reflects the S-polarized light reflected by and makes the S-polarized light and the P-polarized light have the same optical axis, and the polarization directions of the S-polarized light and the P-polarized light having the same optical axis are −
It is equipped with a two-divided optical rotation plate that rotates by 45 ° and + 45 °.

The second optical system transmits the laser light emitted from the second laser light source, enters the third optical system, and emits the laser light from the third optical system. A beam splitter that reflects the light having the wavelength of the reflected second laser light source is provided.

The third optical system reflects the S-polarized light and the P-polarized light emitted from the first optical system and having the same optical axis, and emits the second laser light source emitted from the second optical system. And a dichroic mirror that transmits the laser beam of the first laser light source reflected from the recording medium and transmits the light having the wavelength of the second laser light source. And

In the method of adjusting a hologram optical unit according to a third aspect, the optical unit generates the laser light emitted from the first laser light source for the recording medium on the same optical path as the information light and the reference light. 1st, 2nd, 3rd, 4th
First optical system each having a polarizing beam splitter of the above, a second optical system generating control light for performing the focus servo and tracking servo, and the information light, reference light, and control light in the same optical path. And a third optical system for irradiating the recording medium.

The first optical system is on 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 polarization A first adjusting pin is provided on a side of the beam splitter where the laser beam is incident, and a second adjusting pin is provided on a side of the first, second, third, and fourth polarization beam splitters where the laser beam is emitted, respectively. Fourth and fifth adjustment pins are provided, 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, The optical axes of the first, second, third and fourth polarization beam splitters are adjusted so as to match the fourth and fifth adjustment pins.

The order of the optical axis adjustment is that the second adjustment pin is removed after the optical axis of the first polarization beam splitter is adjusted, and the third and fourth adjustment pins are erected to the above-mentioned order. The optical axes of the second and third or third and second polarization beam splitters are adjusted, and then the third and fourth adjustment pins are removed and the fifth adjustment pin is erected and the The optical axis of the polarization beam splitter of No. 4 is adjusted, and then the first and fifth adjustment pins are removed.

[0038]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is an optical unit applied to a polarized 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, and 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. I am doing it.

In FIG. 1, the optical unit records the information light and the reference light on the recording medium 11 so that the information is recorded in the plurality of information recording areas by the interference pattern due to the interference of the information light and the reference light. A first optical system OP1 for generating on the same optical path, and a second optical system OP2 for generating control light for performing focus servo and tracking servo,
A third optical system OP3 for irradiating the recording medium with the information light, the reference light and the control light in the same optical path is provided.

The first optical system OP1 includes, for example, a single mode first laser light source 1 (P
A polarized light source or an S-polarized light source is provided, and the emitted light from the first laser light source 1 is converted into parallel light by a collimator lens (not shown). In addition, the parallel light has a first half-wave plate 31 whose optical axis is set to a predetermined angle in advance.
, The plane of polarization is rotated and converted into A-polarized light or B-polarized light.

The first optical system OP1 includes first, second, third and fourth polarization beam splitters PBS1 and PB.
S2, PBS3, and PBS4 are provided respectively, and the PBS1, PBS2, PBS3, and PBS4 have PBS surfaces PBS1a, PBS2a, PBS3a, and PBS surfaces that reflect the S-polarized component and transmit the P-polarized component of the incident light.
4a are formed respectively.

The first polarization beam splitter PBS1
A first half-wave plate 31 is provided on the incident light side of. The first half-wave plate 31 produces the information light IP and the reference light RP together with the first polarization beam splitter PBS1.

Further, the side where the incident light passes through the first polarization beam splitter PBS1 (the side where the P-polarized component is emitted, the side where the information light IP is emitted) and the side where the incident light is reflected (the side where the S-polarized component is emitted) are provided. , A second polarization beam splitter PBS2 and a third polarization beam splitter PBS3 are respectively provided on the side from which the reference light RP is emitted. Further, the optical axis on the reflecting side of the second polarization beam splitter PBS2 and the optical axis on the reflecting side of the third polarization beam splitter PBS3 are orthogonal to each other, and a fourth polarization beam splitter PBS4 is provided at the intersection thereof. Has been. The fourth polarization beam splitter PBS4 includes a second polarization beam splitter PB.
The optical axis on the side where the S-polarized component incident from S2 is reflected and the third
The optical axis on the transmission side of the P-polarized component that is incident from the polarization beam splitter PBS3 is matched.

The first polarization beam splitter PBS1
Of the second half-wave plate 3 on the side where the P-polarized component of
2, a convex lens 25, and a spatial modulator SLM are provided. The convex lens 25 has a function similar to that of the convex lens 125 described in the related art, but the spatial modulator SLM can have the function. In that case, the convex lens 25 can be omitted. it can. A third half-wave plate 33 is provided on the side of the third polarization beam splitter PBS3 that outputs the S-polarized component,
The optical axis is set so as to convert the polarized light into P polarized light by a predetermined ratio (for example, 50%). The reason why not all the S-polarized light is converted into P-polarized light is that it is possible to guide a part of the reflected light from the recording medium 11 to the sensor 2.

The fourth polarization beam splitter PBS4
On the side where the P-polarized component and the S-polarized component are output, a two-divided optical rotation plate 4 is provided.

Further, the third polarization beam splitter PB
A sensor 2 such as a CCD camera is provided on the opposite side of S3 from the side where the third half-wave plate 33 is provided.

In the second optical system OP2, 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 is used.
The collimator lens 12 collimates the light emitted from the second laser light source 6 and emits the collimated light. The wavelength of the second laser light source 6 is a wavelength at which the hologram layer of the recording medium 11 has no recording sensitivity.

That is, the second laser light source 6 oscillates continuously, and the recording medium 11 is constantly irradiated. On the other hand, the first laser light source 1 stops oscillation in the servo area or switches light by an electro-optic modulator so that the light of the first laser light source 1 is not applied to the servo area. Such control is performed using the information in the address area.

A half of the laser beam emitted from the second laser light source 6 is transmitted (1/2 is reflected) to enter the third optical system OP3, and the reflecting surface 1 of the recording medium 11 is also transmitted.
A beam splitter 7 having a reflective film 7a that reflects (transmits 1/2) half of the light (control light CP) emitted from the third optical system OP3 that is reflected by 1a (see FIG. 2). Are provided between the second laser light source 6 and the collimator lens 12.

A cylindrical lens 8 and a quadrant 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.

Then, a focus error signal and a tracking error signal are generated based on the output of the four-division photodetector 9, and focus servo and tracking servo are performed based on these signals, and reproduction and address of the basic clock are performed. Is determined.

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. Has been.

The dichroic mirror 5 emits S-polarized light and P-polarized light (reference light RP and information light IP) emitted from the first optical system OP1 and a second light emitted from the second optical system OP2.
The laser light from the laser light source 6 is guided to the same optical path and the lens 10
Is incident on. Further, the light of 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 of the wavelength of the second laser light source 6 is transmitted and beamed. It is incident on the splitter 7.

By the objective lens 10, the reference light RP and the control light CP are focused on the reflecting surface of the recording medium 11, and the information light IP is focused on the front side of the reflecting surface of the recording medium 11.
Therefore, the information light IP is largely diffused after being reflected and is not converged by the objective lens 10.

FIG. 2 is a sectional view of the recording medium 11.
Laser light is emitted from the A direction. The irradiation surface is covered with a transparent glass substrate 11d, and a hologram layer 11c is formed below the irradiation surface between the transparent glass substrates 11d and 11b. Further, a reflective film 11a is formed under the transparent glass substrate 11b by vapor deposition of aluminum or the like.

The operation of each part of the hologram recording optical unit in FIG. 1 will be described below in the order of the first optical system OP1, the second optical system OP2, and the third optical system OP3.

During recording of information in the first optical system OP1, the P-polarized light or S-light emitted from the first laser light source 1 is recorded.
The polarized laser light is collimated 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 polarization beam splitter PBS1.

Of the B-polarized light that has entered the first polarization beam splitter PBS1, the S-polarized light is reflected by the reflection surface PBS1a and is used as the reference light RP by the third polarization beam splitter P.
The P-polarized light enters the BS 3 and passes through the reflecting surface PBS 1 a and enters the second ½ wavelength plate 32 as the information light IP.

The reference light RP (S polarized light) is reflected by the reflection surface PBS3a of the third polarization beam splitter PBS3,
It 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 to a predetermined angle in advance, so that a part of the S-polarized light that is incident at a ratio according to the set angle becomes P-polarized light. To be converted.

The P-polarized component of the reference light RP that has passed through the third half-wave plate 33 is the fourth polarization beam splitter PBS.
The light then enters the fourth polarization beam splitter PBS4a and passes through the reflection surface PBS4a of the fourth polarization beam splitter PBS4 as it is.

On the other hand, the information light IP (P-polarized light) incident on the second 1/2 wavelength plate 32 becomes S-polarized light and the spatial modulator S
It is incident on the LM. Information is recorded on the recording medium 11 by being modulated by the spatial modulator SLM in accordance with predetermined information, and enters the second polarization beam splitter PBS2.
The information light IP (S-polarized light) incident on the second polarization beam splitter PBS2 is reflected by the reflecting surface PBS2a and then the fourth information light IP (S-polarized light) is reflected.
And enters the polarization beam splitter PBS4.

The information light IP (S-polarized light) is reflected by the reflection surface PBS4a of the fourth polarization beam splitter PBS4, and the reference light RP (P-polarized light) transmitted through the reflection surface PBS4a.
It becomes the same optical axis as that of and enters the two-divided optical rotation plate 4 which rotates the polarization directions of S-polarized light and P-polarized light.

The light incident on the two-divided optical rotation plate 4 is of two types: information light IP (S polarized light) and reference light RP (P polarized light). The S-polarized light and the P-polarized light are incident on the left half 4L and the right half 4R of the two-divided optical rotation plate 4, respectively.

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 have their polarization directions rotated by -45 ° and + 45 °, respectively. That is, the information light IP (S polarization) and the reference light RP (P
Polarized light becomes A polarized light and B polarized light, respectively. Further, the information light IP (S-polarized light) and the reference light RP (P
Polarized light becomes B polarized light and A polarized light, respectively.

Therefore, the information light IP transmitted through the right half 4R
And the reference light RP transmitted through the left half 4L becomes A-polarized light,
The information light IP transmitted through the left half 4L and the reference light RP transmitted through the right half 4R are B-polarized.

As a result, the information light IP transmitted through the right half 4R and the reference light RP transmitted through the left half 4L, which are converged by the objective lens 10, have the same polarization state (A polarization), and the recording medium 11 has the same polarization state. Interference fringes are formed in a semicircular shape, and information is recorded on the hologram layer 11c.

Similarly, the information light IP transmitted through the left half 4L converged by the objective lens 10 and the right half 4R are transmitted.
Becomes the same polarization state (B polarized light) as that of the reference light RP that has passed through, and forms interference fringes on the recording medium 11 in a semicircular shape facing the semicircle, and information is recorded on the hologram layer 11c. The two semicircular holograms are combined into one circular hologram.

During reproduction of information in the first optical system OP1, A-polarized light and B-polarized light as information light contained in the reference light having the wavelength of the first laser light source 1 reflected by the recording medium 11 is reproduced. Is reflected by the dichroic mirror 5 of the third optical system OP3 as described later, returns to the first optical system OP1, and enters the two-divided optical rotation plate 4 from the opposite direction.

When the reflected A-polarized light and B-polarized light are incident on the two-divided optical rotation plate 4 in the opposite directions, they are rotated in the opposite directions and return to their original polarization planes. 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 rotation plate 4 becomes A-polarized light and the right half 4R.
The reference light RP transmitted through becomes the B polarized light.

Therefore, A reflected from the recording medium 11 and re-incident on the left half 4L and the right half 4R of the two-part optical rotation plate 4.
The polarized light and the B-polarized light become S-polarized light and P-polarized light, respectively, which are emitted from the two-divided optical rotation plate 4 and are output from the fourth polarization beam splitter P.
It is incident on BS4.

Of the reflected light that has entered the fourth polarization beam splitter PBS4, S-polarized light is reflected by the reflecting surface PBS4a and P-polarized light is transmitted through the reflecting surface PBS4a.

The P-polarized light transmitted through the reflecting surface PBS4a is incident on the third ½ wavelength plate 33. The incident light has a third half-wave plate 3 whose optical axis is set to a predetermined angle in advance.
By passing through 3, the plane of polarization is rotated and P-polarized light and S-polarized light are rotated.
Polarized light is generated.

The P-polarized light and S-polarized light emitted from the third half-wave plate 33 are converted into the third polarized beam splitter PB.
It is incident on S3. Of the incident light, the S-polarized light is the reflection surface PB.
The P-polarized light reflected by S3a passes through the reflection surface PBS3a and enters the sensor 2. The light incident by the sensor 2 is converted into an electric signal by a known method to extract information.

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 a reflection film 7 that reflects 1/2 of the light having the wavelength of the second laser light source.
a is formed, half of the laser light emitted from the second laser light source 6 is transmitted, and the control light CP for servo control is transmitted to the dichroic mirror 5 of the third optical system OP3 via the collimator lens 12. Incident as.

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 the second optical Return to system OP2, collimator lens 12
It is incident on the beam splitter 7 via.

The control light CP is reflected by the reflecting surface 7a of the beam splitter 7 and enters the four-division photodetector 9 through the cylindrical lens 8 which collects the laser light, and the focus error signal and the tracking error are generated by a known method. Signals are generated, and based on these signals, focus servo and tracking servo are performed, and the basic clock is reproduced and the address is determined.

In the third optical system OP3, the reference light RP and the information light IP emitted from the two-divided optical rotation plate 4 and the control light CP transmitted through the collimator lens 12 are reflected or transmitted by the dichroic mirror 5, respectively. Then, they have the same optical axis and are condensed 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.

Of the reflected light that has entered the dichroic mirror 5, the control light CP passes through the dichroic mirror 5 as it is, and the remaining reflected light is the dichroic mirror 5.
Is reflected by and is incident on the two-divided optical rotation plate 4, and information is reproduced in the first optical system OP1.

FIG. 3 is a diagram for explaining a method of adjusting the hologram recording optical unit according to 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 generate the information light IP and the reference light RP on the same optical path. , Fourth polarization beam splitter PBS
1, a first optical system OP1 including PBS2, PBS3, and PBS4, a second optical system OP2 generating a control light CP for performing focus servo and tracking servo, the information light IP and the reference light RP. And control light CP
Optical system OP for irradiating a recording medium with the same optical path
3 is provided.

Adjustment pin P provided in the first optical system
1, P2, P3, P4, and P5 are vertically arranged in advance in the 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. The adjustment pin is, for example, a rod-shaped pin having a thin circular diameter, the diameter thereof is thick enough to allow the shadow of the laser beam to be visually recognized, and the height thereof is preferably such that the optical axis and the tip of the pin coincide with each other. . By matching the optical axis with the height of the tip of the pin when there is no optical component other than the laser light source 1, it becomes easy to adjust the optical axis in the height direction when the optical component is arranged.

The position where the adjusting pin is erected is on the optical path through which the laser light emitted from the first laser light source 1 is transmitted / reflected, and the laser of the first polarization beam splitter PBS1 is used. A first adjusting pin P1 is provided upright on the light incident side and before the first half-wave plate 31. In addition, the adjustment pin P is provided on the side where the P-polarized component of the first polarization beam splitter PBS1 is output.
2 is the second and third polarization beam splitters PBS2, P
Adjustment pins P3 and P4 are provided on the side of BS3 where the S-polarized component is output, respectively, and are provided with a fourth polarization beam splitter PBS4.
Adjustment pin P on the side where the P-polarized component and S-polarized component of
5 are provided.

First, the first adjustment pin P1 and the adjustment pin P2
Is erected and laser light is emitted from the first laser light source 1. Of the laser light applied to the first adjustment pin P1,
Reflection surface PBS1 of the first polarization beam splitter PBS1
The rotation angle (installation angle) of the first polarization beam splitter PBS1 is adjusted so that the shadow of the first adjustment pin P1 overlaps the adjustment pin P2 when the laser light transmitted through a is applied to the adjustment pin P2.

Next, the first half-wave plate 31 and the spatial modulator SLM are arranged at predetermined positions, the second adjusting pin P2 is removed, and the third adjusting pin P3 and the fourth adjusting pin P are removed.
4 is set up. Of the laser light emitted to the first adjusting pin P1, the laser light that has passed through the first polarization beam splitter PBS1 and is further reflected by the reflection surface PBS2a of the second polarization beam splitter PBS2 is emitted to the adjustment pin P3. When this happens, 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.

Similarly, of the laser light emitted to the first adjusting pin P1, the first polarization beam splitter PB
When the laser light reflected by the reflection surface PBS1a of S1 is reflected by the reflection surface PBS3a of the third polarization beam splitter PBS3 and is applied to the adjustment pin P4, the shadow of the first adjustment pin P1 overlaps the adjustment pin P4. Then, the rotation angle of the fourth polarization beam splitter PBS4 is adjusted. Any of the second polarization beam splitter PBS2 and the third polarization beam splitter PBS3 may be adjusted first.

Next, the third and fourth adjustment pins P3, P
4 is removed, and of the laser light emitted to the first adjustment pin P1, the laser light reflected by the reflection surface PBS2a of the second polarization beam splitter PBS2 and the reflection surface PBS3a of the third polarization beam splitter PBS3 are reflected. When the adjusted laser beam is applied to the adjustment pin P5, the rotation angle of the fourth polarization beam splitter PBS4 is adjusted so that the shadow of the first adjustment pin P1 overlaps the adjustment pin P5. The adjustment pins P1 and P5 are removed after the adjustment of all the polarization beam splitters is completed.

In the adjustment method of the optical system described above, the shadow of the first adjustment pin P1 is made to coincide with the other adjustment pins, which allows the second, third, and fourth polarization beam splitters PBS2. , PBS3, and PBS4 have their respective adjustment pins separated from the first adjustment pin P1. Therefore, the second, third, and fourth polarization beam splitters PBS
2, a large deviation between PBS3 and PBS4 is observed, and as a result, the adjustment error of each polarization beam splitter can be reduced.

In addition to the above, the adjustment pins after adjustment may be used one after another. That is, for example, when adjusting the rotation angle of the second polarization beam splitter PBS2, the shadow of the adjusting pin P2 may be made to coincide with the adjusting pin P3. In such a case, there is an advantage that the optical components between the adjusting pins can be independently adjusted.

In the embodiments of the present invention, the fixing light source device for fixing is described as a hologram recording medium which is not necessary, but it is also applicable to a hologram recording medium which requires fixing. In such a case, the light from the fixing light source device is configured so as not to pass through the first and second optical systems and coupled to the third optical system.

[0089]

According to the hologram optical unit of the first aspect, the first optical system for generating the information light and the reference light on the same optical path, and the control light for performing the focus servo and the tracking servo. A second optical system for generating
The recording medium is irradiated 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 contained in the reference light are supplied to the second optical system and the first optical system.
A third optical system for separating each optical system is provided.

As a result, the laser light of 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.

Also, the difference in wavelength causes an optical path difference, and if the optical path is adjusted so that one wavelength matches the optical path, there is no problem that the optical path shifts for the other wavelength.

Furthermore, since all the polarization beam splitters in the first optical system are the same, the cost of the optical unit is reduced and the product management is simplified.

According to the hologram optical unit of the second aspect, the wavelengths of the laser beams in the first optical system and the second optical system are made different, and the third optical system is used for coupling and separation, whereby The optical system becomes simple.

According to the optical axis adjusting method of the hologram optical unit described in 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. The adjustment of the optical axis of the polarization beam splitter is accomplished by installing adjustment pins in front of and behind the plurality of polarization beam splitters used in the first optical system, and adjusting the polarization beam splitters so that the shadows produced by the adjustment pins match. Easy to adjust.

[Brief description of 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 sectional view of a hologram recording medium.

FIG. 3 is a diagram illustrating a method of adjusting the hologram optical unit according to the 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 Sensor 4 Two-division optical rotation plate 5 Dichroic mirror 7 Beam splitter 9 Four-division photodetector 10 Objective lens 11 Recording medium 12 Collimator lenses 31, 32, 33 1/2 wavelength plate SLM Spatial modulator OP1 First optical System OP2 Second optical system OP3 Third optical system PBS1, PBS2, PBS3, PBS4 Polarization beam splitters P1, P2, P3, P4, P5 Adjustment pin

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ identification code FI theme code (reference) G11B 7/22 G11B 7/22 5D789 (72) Inventor Kozo Matsumoto 1743 Asana-cho, Asaba-cho, Shizuoka Prefecture 1 Minebea Co., Ltd. Hamamatsu Plant (72) Inventor Hideki Kato 1743-1, Asana-cho, Iwata-gun, Shizuoka Prefecture Minebea Co., Ltd. Hamamatsu Plant (72) Inventor Hideyoshi Horimai 1-22- Ebisu, Shibuya-ku, Tokyo 23-405 Incorporated company Optware (72) Inventor Shoji Kinoshita 1-22 Ebisu, Shibuya-ku, Tokyo 23-22-405 Incorporated company Optware (72) Inventor 攀 mei Hayashi 1-22 Ebisu, Shibuya-ku, Tokyo -23-405 F-term in Optware Co., Ltd. (reference) 2H099 AA05 BA17 CA02 CA07 CA08 CA11 5D090 AA01 BB04 BB16 CC14 CC16 FF03 FF05 LL02 5D117 AA02 CC07 HH03 KK01 KK15 5D 118 AA06 AA15 BA01 BB05 BC12 BC13 CA26 CB01 CC07 CC08 CC12 CG03 CG15 CG16 CG26 CG32. EC33 EC40 EC47 FA08 GA02 HA36 JA12 JA25 JA27 JA31 KA09 KA11 LB01 LB05

Claims (3)

[Claims] 1. Information for generating a basic clock that serves as a reference for various operation timings in an optical information recording / reproducing apparatus, information for performing focus servo by a sampled servo system, and tracking servo by a sampled servo system. A hologram optical unit for recording / reproducing information by using holography in each of a plurality of information recording areas in a recording medium having an address / servo area including information for addressing and address information. A first optical system for generating the information light and the reference light on the same optical path so that information is recorded / reproduced in the information recording area of the information recording medium by the interference pattern due to the interference of the information light and the reference light; A second optical system for generating control light for performing servo and tracking servo, and the information light The reference light and the control light are irradiated onto the recording medium in the same optical path, and the control light reflected from the recording medium and the information light contained in the reference light are transmitted to the second optical system and the first optical system. A third optical system for separating each is provided, the first optical system is provided with first, second, third, and fourth polarization beam splitters, respectively, and the first polarization beam splitter is used for information of laser light. The light beam and the reference light beam are separated, and the second polarization beam splitter couples the separated information light beam of the information light beam and the reference light beam split by the first polarization beam splitter to the separated reference light beam. Direction, the third polarization beam splitter reflects the reference light split by the first polarization beam splitter in a direction that combines with the information light reflected by the second polarization beam splitter, and the fourth polarization beam splitter reflects the reference light. Polarized beams Information light and reference light reflected by the second polarization beam splitter and the third polarization beam splitter are transmitted through the reflected light reflected by the recording medium and transmitted through the splitter. Are reflected and transmitted, the information light and the reference light are made to have the same optical axis, and the reflected light reflected from the recording medium is transmitted and is incident on the third polarization beam splitter. Optical unit for hologram. 2. The first optical system includes a first optical element for optical rotation that converts laser light emitted from a first laser light source into S-polarized light and P-polarized light, and the S-optical element that passes through the optical element for optical rotation. A first polarization beam splitter that separates polarized light and P polarized light, and P polarized light that has passed through the first polarization beam splitter
A second optical element for optical rotation that converts the polarized light, a spatial modulator that spatially modulates the S polarized light that has passed through the second optical element for optical rotation, and the S polarized light that has been modulated by the spatial modulator is reflected to A second polarization beam splitter for converting the information light; a second polarization beam splitter for reflecting the S-polarized light reflected by the first polarization beam splitter and transmitting light having the wavelength of the first laser light source reflected from the recording medium. Of the light transmitted through the third polarization beam splitter, the third optical element for optical rotation that converts the polarization plane of the S-polarized light reflected by the third polarization beam splitter, and the light transmitted through the third optical element for optical rotation. The P-polarized light is transmitted and the S-polarized light reflected by the second polarization beam splitter is reflected to make the S-polarized light and the P-polarized light have the same optical axis. S
The second optical system includes a two-divided optical rotation plate that rotates the polarization directions of the polarized light and the P-polarized light by −45 ° and + 45 °, and the second optical system transmits the laser light emitted from the second laser light source and transmits the laser light emitted from the second laser light source. While entering the optical system,
A beam splitter that reflects the light having the wavelength of the second laser light source reflected from the recording medium and emitted from the third optical system, wherein the third optical system emits from the first optical system. A first laser which reflects S-polarized light and P-polarized light having the same optical axis, transmits the laser light of the second laser light source emitted from the second optical system, and is further reflected from the recording medium. The hologram optical unit according to claim 1, further comprising a dichroic mirror that reflects light having a wavelength of the light source and transmits light having a wavelength of the second laser light source. 3. Information for generating a basic clock that serves as a reference for various operation timings in an optical information recording / reproducing apparatus, information for performing focus servo by a sampled servo method, and tracking servo by a sampled servo method. A method for adjusting an optical axis in a hologram optical unit for recording information by utilizing holography, in each of a plurality of information recording areas in a recording medium having an address / servo area consisting of information and address information, The optical unit separates the laser light emitted from the first laser light source into the recording medium into the information light and the reference light, and then makes the same optical path again, and the first, second, third, and fourth polarizations are provided. A first optical system each having a beam splitter, the focus servo and the tracking server A first optical system for generating a control light for performing the blurring; and a third optical system for irradiating the recording light with the information light, the reference light, and the control light on the same optical path. The optical system is on 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 laser light of the first polarization beam splitter is A first adjusting pin is provided on the incident side, and a second adjusting pin is provided on the laser beam emitting side of the first, second, third, and fourth polarization beam splitters, respectively.
Third, fourth, and fifth adjustment pins are provided, 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, The first, so as to match the third, fourth, and fifth adjustment pins.
The optical axes of the second, third, and fourth polarization beam splitters are adjusted, and the order of the optical axis adjustments is to remove the second adjustment pin after adjusting the optical axis of the first polarization beam splitter. The third and fourth adjustment pins are erected to adjust the optical axes of the second and third or third and second polarization beam splitters, and then the third and fourth adjustment pins. And the fifth adjusting pin is erected to adjust the optical axis of the fourth polarization beam splitter, and then the first and second adjusting pins are installed.
A method for adjusting an optical axis of a hologram optical unit, characterized by removing a fifth adjusting pin.