JPH01179237A - Optical pickup device - Google Patents

Abstract

PURPOSE:To enable the high density recording and reproducing and to miniaturize a device with lighter weight by forming a hologram having an action of optical element on either an incident surface or an outgoing surface of a nonlinear optical element. CONSTITUTION:When a spherical wave is radiated as an object beam Q2 to a hologram recording medium 12a, it is passed through the medium 12a to focus at a point P2. On the other hand, a point light source is made at a point P corresponding to a laser position, and when a spherical wave generated herein is radiated as a reference beam R2 to the medium 12a simultaneously with the beam Q2, hyperbolic interference fringes are recorded to form a 2nd hologram 12. At the time of reproducing, a laser is disposed at the point P and its outgoing beam is projected to the hologram 12, so that the beam is diffracted by the hologram 12 to be converged at the point P2. Thus, by forming the hologram on either the incident surface or the reflected surface of the nonlinear optical element, the high density recording and reproducing can be performed, and the device is contrived for miniaturization and light weight.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup device capable of high-density recording using harmonics obtained by a nonlinear optical element.

[Background Art] In recent years, the progress of information-related industries has been remarkable, and the amount of information R handled is also increasing. For this reason, instead of recording or reproducing equipment that uses a conventional magnetic head to record or reproduce information, it is possible to record information at high density on a recording medium using a light beam (1). 2. Description of the Related Art Optical information recording and reproducing devices that can reproduce information recorded at high density on a recording medium at high speed are attracting attention.

The optical information recording/reproducing device is required to improve areal recording density, but the minimum detectable bit period is generally the spatial frequency r! It is determined by ifC=2NA/λ. Here, NΔ is the aperture ratio of the lens, and λ is the wavelength of light irradiated onto the optical disc. Therefore, the larger the numerical aperture of the lens and the shorter the wavelength of the laser, the higher density recording becomes possible. Here, there is a limit to increasing the lens opening number NA because the influence of the skew of the optical disk, the influence of the thickness unevenness of the optical disk, etc. becomes significant.

In addition, the wavelength λ of the laser light is argon, He-C
Gas lasers such as d can obtain wavelengths of 400 to 500 nm, but because gas lasers require large equipment, they are not suitable as light sources for general consumer equipment. Semiconductor lasers are widely used as light sources for small consumer equipment. It is used. However, with semiconductor lasers, it is very difficult to achieve short wavelengths like gas lasers.

Therefore, recently, it has been proposed to utilize the second harmonic generated by a nonlinear optical element, as disclosed in, for example, Japanese Patent Laid-Open No. 60-179949. The device shown in this conventional example emits light (860 nm) from a semiconductor laser.
This is a device that reads information by inputting a wavelength of 100 nm (nm wavelength) into a nonlinear optical element, and by irradiating an optical disk recording medium with a second harmonic wave emitted from the nonlinear optical element. In this device, in order to increase the output efficiency of the second harmonic, coupling lenses are placed on both sides (incidence side and output side) of the nonlinear optical element, and the light emitted from the semiconductor laser is
A collimator lens converts it into parallel light, a beam shaping prism spreads the short axis of the elliptical beam from the semiconductor laser, converting it into a circular beam, the coupling lens converges the beam, and the beam enters a nonlinear optical element. This light is converted into CI/2-wavelength (430 nm) light by the nonlinear optical element, diverges again inside the nonlinear optical element, is emitted from this nonlinear optical element, and is coupled to another coupling. It is made into parallel light by a lens, and is irradiated onto the recording medium by an objective lens.

[Problems to be Solved by the Invention] Incidentally, in the conventional example, the diameter of the beam is narrowed down within the nonlinear optical element using a coupling lens. As described in the above publication, this is done for the purpose of increasing wavelength conversion efficiency.

However, those that use a coupling lens use a lens frame to hold the lens (although this is not clearly stated in the above publication, it is assumed that a lens frame is used as a matter of course. ), and the lens is positioned with respect to this lens frame. Therefore, there is a problem in that the optical pickup becomes larger by the size of the lens frame.

[Object of the Invention] The present invention has been made in view of the above circumstances, and provides a compact, U-sized optical pickup capable of high-density recording and reproduction using harmonics obtained by a nonlinear optical element. The purpose is to provide equipment.

[Means for Solving the Problems] The optical pickup device of the present invention inputs light emitted from a semiconductor laser into a nonlinear optical element, and uses optical harmonics emitted from the nonlinear optical element to detect a recording medium. In an apparatus that performs at least one of recording, reproducing, and erasing information, a hologram having the effect of an optical element is formed on at least one of the entrance surface and the exit surface of the nonlinear optical element, and the nonlinear optical element At least one of the surface and the exit surface is used as a hologram holding member that functions as an optical element.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

Figures 1 to 6 relate to the first embodiment of the present invention.
The figure is an explanatory diagram showing the configuration of the optical pickup device.
The figure is an explanatory diagram showing how to create and use the second hologram, Figure 3 is an explanatory diagram showing how to create and use the first hologram, and Figure 4 is how to create and use the third and fourth holograms. An explanatory diagram showing the method, Figure 5 is the third
FIG. 6 is an explanatory diagram showing the effects of the hologram and the fourth bologram, and FIG. 6 is an explanatory diagram showing a method of creating a hologram that performs the beam shaping function.

As shown in FIG. 1, the optical pickup device 1 of this embodiment includes a semiconductor laser 2 as a light source, and a semiconductor laser 2 with -=1'
A first hologram 11, a second hologram 12, . Nonlinear optical element 5° fourth hologram 14. Third
It is reflected by the hologram 13 and the recording medium 3, and the third . Fourth hologram 13, 14. Nonlinear optical element5. Second. The photodetector 6 receives the light transmitted through the first hologram 12.11. The four holograms 11
．． 12, 13, and 14 are joined to the entrance end face and the exit end face of the nonlinear optical element 5. Further, the semiconductor laser 2 is arranged so that its emitted light enters the first hologram 11 from an oblique direction, and the photodetector 6 is arranged from the first hologram 11 to the semiconductor laser 2 side. are arranged so that light emitted in different oblique directions is incident thereon.

The semiconductor laser 2 emits infrared light of, for example, 830 nm or 780 nm, and this emitted light
The light passes through the hologram 11, is diffracted and focused by the second hologram 12, and enters the nonlinear optical element 5. The light passing through this nonlinear optical element 5 is
After converging within the hologram 14, the light is converged and then diverged, converted into a second harmonic of 415 nm or 390 nm, emitted, and incident on the fourth hologram 14. The fourth hologram 14 and the third hologram 13 act as objective lenses, and the light incident on the fourth hologram 14 is focused by the fourth hologram 14 and the third hologram 13, and is focused on the surface of the recording medium 3. Irradiated in the form of a spot.

The reflected light containing the information of the recording medium 3 enters the third hologram 13, is diffracted by the third hologram 13 and the fourth hologram 14, is converged and diverged by the nonlinear optical probe 5, and is transmitted to the second hologram. 12 and is diffracted by the first hologram 11.

The focused beam is received by a photodetector 6. The photodetector 6 generates a signal corresponding to the information recorded on the recording medium 3, focus,
Error signals such as tracking can be obtained.

A particularly important point in the pickup device 1 of the present embodiment is that the light emitted from the semiconductor laser 2 is transmitted through the first hologram 11 and diffracted by the second hologram 12, and the return light from the recording medium 3 is , second hologram 1
2 and diffracted by the first hologram 11, the beam can be split into a light source side and a photodetector side, which is what is called a beam splitter function.

Next, a method for preparing and using Moekki No. 1 to No. 4 1 Grams 11 to 14 will be explained.

First, a method for creating and using the second hologram 12 will be explained with reference to FIG.

The hologram recording medium 12a serving as the second hologram 12 is irradiated with a spherical wave that passes through the hologram recording medium 12a and is focused at 12 points as the object light Q2. Here, the distance f from the second hologram 12 to the 12 focal points
2 is the coupling action focal length. On the other hand, a microscope objective lens and an aperture (
A point light source is created using a shutter), and a spherical wave generated from this point light source is irradiated onto the hologram medium 12a as reference light R2 at the same time as the object light Q2. Then, hyperbolic interference fringes are recorded on the hologram medium 12a, and a second hologram 12 is formed.

During reproduction, the semiconductor laser 2 is placed at the point P, and the second
As shown by the broken line in the figure, the second hologram 12
By irradiating the emitted light onto the hologram, this irradiation beam is diffracted by the second hologram 12 and becomes a beam focused on 12 points.

Note that in an optical pickup, a shaping prism or the like is usually used to transform the elliptical beam of the semiconductor laser into a circular beam. In the present invention, this shaping prism may be used, but the hologram may also have the function of a shaping prism. An example of creating a hologram having such a beam shaping function is shown in FIG.

That is, the elliptical beam reference beam RO is applied to the hologram recording medium (dry plate) 15 using, for example, a mirror 16° half mirror.
17. At the same time, in order to convert the elliptical beam into a circular beam, the parallel elliptical beam is passed through a prism or a combination of a concave cylindrical lens 18 and a convex cylindrical lens 19 to form a circular beam as the object light QO. The light is irradiated through the half mirror 17. As a result, interference fringes are recorded on the dry plate 15 and a hologram is formed. By inserting this hologram between the semiconductor ray IJ'2 and the nonlinear optical probe 5, beam shaping becomes possible.

Next, a method for creating and using the first hologram 11 will be explained with reference to FIG.

The hologram recording medium 11a serving as the first hologram 11 is irradiated with a spherical wave as the object light Q1 that passes through the hologram recording medium 11a and is focused on 81 points. Here, the distance f from the first hologram 11 to the focal point 11
1 is the coupling action focal length. On the other hand, the reference light R
1, the hologram medium 11a is irradiated simultaneously with the object light Q1. Then, the hologram medium 11
Hyperbolic interference fringes are recorded in a, and the first hologram 1
1 is formed.

During playback, as shown by the broken line in FIG.
By irradiating the first hologram 11 with diverging light from the same point P1' as one point, this irradiation beam is diffracted by the first hologram 11 and becomes a beam focused on the P' point.

Next, referring to FIGS. 4 and 5, the third bologram 1
The method for creating and using the third and fourth holograms 14 will be explained.

FIG. 4 shows a method for creating the third hologram 13 and a method for creating the fourth hologram 14 in one diagram. As shown in this diagram, the hologram recording medium that becomes the third hologram 13 is The third hologram 1 is placed on the vologram recording medium i 4 a which becomes the fourth hologram 13a or the fourth hologram 14.
In the case of the third hologram 13, a spherical wave Q3 that is focused on 23 points is irradiated, and in the case of the fourth hologram 14, a spherical wave Q4 that is focused on 14 points is irradiated. The distance f3 from P to the focal point 13 is the coupling focal length of the third hologram 13, and the distance f3 from the fourth hologram 14 to the focal point P4 is
1f 4 is the coupling focal length of the fourth hologram 14. Further, the hologram recording medium 13a
Or, in 14a, the parallel wave R3 is used as a plane wave, and the spherical wave Q 3. Q: Irradiate at the same time as 4. And the hologram medium 13a.

Interference fringes are recorded on the convex portion 14a, and the third hologram 13 or the fourth hologram 14 is formed.

During reproduction, as shown in FIG.
It is diffracted by the hologram 14 and becomes parallel light, and this parallel light enters the third hologram 13, and this third hologram 1
3, it is diffracted and focused at 23 points corresponding to the recording medium 3. In addition, the above-mentioned 2 which is the return light from the recording medium 3
Divergent light generated from three points is diffracted by the third hologram 13 and becomes parallel light, and this parallel light is transmitted to the fourth hologram 14.
It is diffracted by the fourth hologram 14 and focused on the 14 points.

The third and fourth holograms 13 and 14 are holograms that generate a spherical wave from a plane wave, or a plane wave from a spherical wave, and when combined, act as a focusing lens. In addition, in Figure 5, the third
Although the hologram 13 and the fourth porogram 14 are placed apart, this is a diagram of the principle of conversion to show that each hologram 13 and 14 performs conversion between a plane wave and a spherical wave. Actually, both holograms 13.1
4 has a joint name.

Similarly, the first and second holograms 11°12 are
They may be joined.

The above four holograms 11.12, 13.14 are A
For example, it is bonded to the entrance end face and the exit end face of the linear optical element 5. There is also a method of directly transferring a photoresist as a master using a beam etching method or a photopolymer method using a photopolymer or the like.

As for the molding method of these holograms 11, 12, 13, and 14, when the transparent substrate is made of glass, for example, a mold is set on the glass substrate, a photopolymer is applied to the glass substrate, and then the photopolymer is exposed to ultraviolet light. After curing, the mold is peeled off and molded, or a photoresist WII film is recorded on a glass substrate by reactive ion etching, developed to form a pattern, and then ionized with CHF3 gas. There are methods such as etching, then removing the resist, and molding. In addition, when the transparent substrate is made of plastic, a photoresist is coated on the substrate, a pattern is recorded with a laser beam, and after this is developed,
It can be formed by plating a metal such as Ni on the resist pattern by electroforming to create a stamper.

Note that for the length 1 of the nonlinear optical element in the optical axis direction, jl=
There is a relationship of f2+f4. Moreover, it is f2-f4.

As described above, in this embodiment, the holograms 11, 12, 13, and 14 having the function of an optical element are formed on the incident end face and the exit end face of the nonlinear optical element 50. Therefore, the entrance end face and the exit end face of the nonlinear optical element 5 are connected to the hologram 1.
1, 12, 13, and 14, eliminating the need for a lens frame when using a conventional lens, reducing the number of parts of the optical pickup device 1, and making it lightweight and compact. It becomes possible.

Furthermore, positioning of the hologram as an optical element is easy. Furthermore, by directly forming a hologram on the input rJJ end face and the output end face of the nonlinear optical element 5, position adjustment becomes unnecessary.

7 to 9 relate to the second embodiment of the present invention, and FIG.
The figure shows the configuration of the optical pickup device! j explanatory diagram,
FIG. 8 is an explanatory diagram showing the vicinity of a nonlinear optical element in a modified example of this embodiment, and FIG. 9 is an explanatory diagram showing a method of creating and using a fifth hologram and a sixth hologram.

In this embodiment, the dimensions of a pickup device for, for example, a CD are shown.

As shown in FIG. 7, in the optical pickup device 21 of this embodiment, a fifth hologram 25. Nonlinear optical stringer5. Sixth hologram 261, diffraction grating 22, beam splitter 23, such as a half mirror. Objective lenses 24 are sequentially arranged. The diverging light emitted from the semiconductor laser 2 is focused by the fifth bog-o-gram 25, wavelength-converted into a second harmonic by the nonlinear optical element 5, and is emitted from the nonlinear optical element 5 as a diverging light. The beam is converted into parallel light by the sixth hologram 26, divided into three beams by the diffraction grating 22, transmitted through the beam splitter 23, focused by the objective lens 24, and irradiated onto the recording medium 3 in the form of a spot. It has become. The return light from the recording medium 3 passes through the objective lens 24 and enters the beam splitter 23, and the light reflected by the beam splitter 23 is reflected by the single lens 27,
The light passes through a cylindrical lens 28 and is received by a photodetector 29.

In this embodiment, the photodetector 29 can obtain a signal corresponding to information on the recording medium 3, a tracking error signal based on the three-beam method, and a focus error signal based on the astigmatism method.

Incidentally, by using a polarizing beam splitter as the beam splitter 23, and disposing a 1/4 wavelength plate between the polarizing beam splitter and the objective lens 24, and changing the polarization direction by 90a between the outgoing and returning paths, The returning light from the medium 3 may be separated by the polarizing beam splitter.

In FIG. 7, the fifth hologram 25 and the sixth hologram 26 are placed apart from the nonlinear optical element 5, but in reality, they are bonded to the entrance 0AGW surface and the output end surface of the nonlinear optical element 5. has been done.

Further, as shown in FIG. 8, the fifth hologram 25 and the sixth hologram 26 are directly transferred onto the incident end face and the outgoing end face of the nonlinear optical element 5 by beam etching or photopolymer transfer using a photopolymer or the like. I made it and it's 6 good.

Next, with reference to FIG. 9, the fifth bog 25 and the sixth bog
A method for creating the hologram 26 will be explained.

FIG. 9 shows a method for creating the fifth hologram 25 and a method for creating the sixth hologram 26 in one diagram. Hologram recording medium 25 that becomes the fifth bologram 25
A or the hologram recording medium 26a which becomes the sixth hologram 26 is irradiated with a diverging spherical wave obtained by condensing the object light Q5 with the aspherical lens 31 and passing through the aperture 32 disposed at the point P56 η' Ru. At the same time, when creating the fifth hologram 25, the hologram recording medium 25a or Is 26a is provided with a spherical wave reference beam diverging from 15 points on the side opposite to the surface irradiated with the object beam Q5. R
5, and when creating the sixth hologram 26, plane wave reference light R6 is irradiated. And the hologram recording medium 25a.

Interference fringes are recorded on 26a, forming the fifth hologram 25 or the sixth hologram 26.

During reproduction, the diverging lights emitted from 15 points corresponding to the positions of the semiconductor laser 2 are focused on a point P56 by the fifth hologram 25, and the lights diverging from this point P56 are further converted into parallel lights by the sixth hologram 26. be made into

In addition, the fifth bologram 25. ps from 6th hologram 26
Distance to point e 1111f 5. f 6 is the fifth hologram 25. This is the coupling focal length of the sixth hologram 26, and there is a relationship of f5-f6. Furthermore, if the length of the nonlinear optical element 5 in the optical axis direction is 12, then j
2-f5+f6.

Other functions and effects are similar to those of the first embodiment.

10 to 12 relate to the third embodiment of the present invention,
FIG. 10 is an explanatory diagram showing the configuration of the optical pickup device, FIG. 11 is an explanatory diagram showing the method for creating the tenth hologram, and FIG. 12 is an explanatory diagram showing the method for creating the ninth hologram.

As shown in FIG. 10, in the optical pickup 4 Uifi 41 of this embodiment, a semiconductor laser +f 2 is fixed to the bottom of the housing 42, and on the emission side of the semiconductor laser 2,
In order from the semiconductor laser 2 side, a seventh hologram 47.
8th bologram 48. Nonlinear optical element5. 10th hologram 50. A ninth hologram 49 is arranged, and these are
It is integrated and fixed to the upper part of the housing 42. Further, a glass block 53 fixed to the upper part of the housing 42 is bonded to the side of the nonlinear optical element 5. On this glass block 53 is a beam splitting zone plate 52. The eleventh holograms 51 are sequentially joined, and two photodetectors 54a and 54b fixed to the bottom of the housing 42 are disposed below the glass block 53.

The diverging light emitted from the semiconductor laser 2 is focused by a seventh hologram 47 and an eighth hologram 48,
The wavelength is converted into a second harmonic by the nonlinear optical element 5, and the light is emitted from the nonlinear optical element 5 as a diverging light, which is deflected in an oblique direction by the tenth hologram 50 and the ninth hologram 49, and is then focused. and irradiates the recording medium 3 in a spot shape.

The return light that is diagonally reflected by the recording medium 3 enters the eleventh hologram 51 and becomes parallel light, which is split into two by the beam splitting zone plate 52, and each
Through the glass block 53, the photodetectors 54a, 54
The light is received at b.

The method of creating the seventh hologram 47 and the eighth hologram 48 is the same as the method of creating the third hologram 13 and the fourth hologram 14.

A method for creating the tenth hologram 50 will be described with reference to FIG. 11.

Hologram recording medium 50a that becomes the tenth hologram 50
Then, a plane wave is emitted from an oblique direction as the object light Q10, and at the same time, a spherical wave diverging from 210 points is emitted as the reference light R10. Interference fringes are recorded on the hologram medium 50a, and a tenth hologram 50 is formed.

Furthermore, a method for creating the ninth hologram 49 will be explained with reference to FIG.

A spherical wave that passes through the hologram recording medium 49a and converges at P9r:λ is irradiated from an oblique direction as an object beam Q9 to the hologram recording medium 49a constituting the four ninth holograms, and at the same time, as a reference beam R9, A plane wave is irradiated from the same oblique direction as the object light QIO when the tenth hologram 50 was created. Interference fringes are recorded on the hologram medium 49a, and a ninth hologram 49 is formed.

During reproduction, 2 points corresponding to the focal point within the nonlinear optical element 5
The diverging light emitted from the 10 points is the 10th hologram 50
The light is made into parallel light by the 9th hologram 49, and is then made into a deflected and focused light by the ninth hologram 49.

In addition, the eighth hologram 48. The coupling action focal length of the tenth hologram 5O is f8. Assuming flo, there is a relationship of f8=f10. Furthermore, if the length of the nonlinear optical element 5 in the optical axis direction is 13, then 13=f8+f1
It becomes 0.

In addition, in this embodiment, the hologram is directly transferred onto the top or bottom surface of the bonded nonlinear optical element and the glass block 53 using a photoresist as a master and a beam etching method or a photopolymer method using a photopolymer. By doing so, the number of optical components can be reduced.

In this embodiment, the eleventh hologram 51 and the glass block 5
3 and a zone plate 52 of a 7-Co lens for detecting focus errors and tracking errors.
The light beam divided into two by the zone plate 52 is received by two photodetectors 54a and 54b, and based on their outputs, a focus error signal is detected, and an information signal and a tracking error signal are detected. It is designed to detect signals.

In addition, in the configuration shown in FIG. 10, conventional focusing error and tracking error detection techniques such as using a cylindrical lens zone plate instead of the Foucault lens zone plate 1.52 can be used, and recording In order to eliminate track offset due to optical axis deviation based on the inclination of the medium 3, it is also possible to configure so that only the ±1st-order diffracted light is used for detecting running errors.

Other functions and effects are similar to those of the first embodiment.

It should be noted that the present invention is not limited to the above embodiments, but includes, for example,
The hologram formed on at least one of the entrance surface and the exit surface of the nonlinear optical element may have the function of an aspheric lens.

In addition, the present invention is capable of recording a light beam by forming bits, changing the direction of magnetization, changing reflectance or transmittance by phase transition, and forming bubbles. It can be widely applied to things that are recorded, reproduced, or erased using this method.

[Effects of the Invention] As explained above, according to the present invention, it is possible to perform density recording and reproduction using harmonics obtained by a nonlinear optical element, and the optical pickup device can be made smaller and lighter. effective.

[Brief explanation of the drawing]

Figures 1 to 6 relate to the first embodiment of the present invention.
The figure is an explanatory diagram showing the configuration of the optical pickup device.
The figure is an explanatory diagram showing how to create and use the second hologram, Figure 3 is an explanatory diagram showing how to create and use the first hologram, and Figure 4 is an explanatory diagram showing how to create and use the third and fourth holograms. An explanatory diagram showing the method, Figure 5 is the third
FIG. 6 is an explanatory diagram showing the action of the hologram and the fourth hologram. FIG. 6 is an explanatory diagram showing a method of creating a hologram having a beam shaping function. FIGS. 7 to 9 relate to the second embodiment of the present invention. FIG. 7 is an explanatory diagram of the configuration of the optical pickup device, FIG. 8 is an explanatory diagram showing the vicinity of the nonlinear optical element in a modification of this embodiment, and FIG. 10 to 12 are explanatory diagrams showing how to use the invention, FIG. 10 is an explanatory diagram showing the configuration of the optical pickup device, and FIG. 11 is a diagram showing the creation of the 10th hologram. FIG. 12 is an explanatory diagram showing the method for creating the ninth hologram. 1... Optical pickup device 2... Semiconductor laser 3... Recording medium 5...
Nonlinear optical element 6... Photodetector 11.12.13
．． 14...Hologram Figure 1 Figure 2 Without hand Figure 2 Figure 3 P' Figure 4 Figure 12

Claims (1)

[Claims] An optical pickup device that inputs light emitted from a semiconductor laser into a nonlinear optical element and performs at least one of recording, reproducing, and erasing information on a recording medium using optical harmonics emitted from the nonlinear optical element. In at least one of the entrance surface and the exit surface of the nonlinear optical element,
An optical pickup device characterized by forming a hologram having the function of an optical element.