JPH0973654A - Optical head device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical head device capable of reproducing two kinds of digital video disks with different substrate thickness and all compact disks containing a DRAW type disk. SOLUTION: A semiconductor laser and a detection optical system for light receiving reflected light from the disks 17, 18 with different substrate thickness are incorporated in modules 11 and 12. The wavelengths of the semiconductor laser in the modules 11, 12 are 635nm, 785nm. A hologram part having a spherical aberration canceling the sum between the spherical aberration occurring when the outgoing light from an objective lens 16 transmits through the substrate of the disk 17 and the spherical aberration provided in the objective lens 16 is formed on a hologram optical element 15 with aperture limit for fist-order diffracted light of 635nm. Further, an aperture limit part transmitting through for all incident light of 635nm and transmitting through only a central part of a luminous flux section for the incident light of 785nm is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device, and more particularly to an optical head device for reproducing from three types of optical recording media having different substrate thicknesses and recording densities.

[0002]

2. Description of the Related Art In recent years, standardization of large-capacity optical disks such as digital video disks having a larger capacity than compact disks has been advanced. The standards for digital video discs include those using a disc having a substrate thickness of 0.6 mm and those using a disc having a substrate thickness of 1.2 mm. On the other hand, in the standard such as the conventional compact disc, a disc having a substrate thickness of 1.2 mm is used. Therefore, an optical head device capable of reproducing all two types of digital video discs and compact discs is desired. However, in a normal optical head device, the objective lens is designed to cancel spherical aberration for a disc having a certain substrate thickness, and therefore spherical aberration remains for a disc having another substrate thickness. , Can not be played correctly.

As a conventional optical head device capable of reproducing all two types of digital video discs and compact discs, there is an example described on pages 27 to 29 of Optical Review Vol. 1, No. 1. FIG. 20 is a block diagram showing an example of this conventional optical head. In the figure, a hologram optical element 192 is provided with an objective lens 16 and a collimator lens 14.
And the transmitted light (0th order light) is provided between the
Used for reproduction of the digital video disk and the + 1st order diffracted light is used for reproduction of a digital video disk and a compact disk having a substrate thickness of 1.2 mm.

In this conventional optical head device, approximately half of the emitted light from the semiconductor laser 190 is reflected by the half mirror 191, is collimated by the collimator lens 14, and is incident on the hologram optical element 192. The transmitted light of the hologram optical element 192 enters the objective lens 16 as parallel light and is condensed on the disk 17 having a substrate thickness of 0.6 mm. The reflected light from the disk 17 passes through the objective lens 16 in the opposite direction, and is again divided into the transmitted light and the + 1st order diffracted light by the hologram optical element 192.

On the other hand, the + 1st order diffracted light of the hologram optical element 192 enters the objective lens 16 as divergent light and is condensed on the disk 18 having a substrate thickness of 1.2 mm. The reflected light from the disk 18 passes through the objective lens 16 in the opposite direction,
The hologram optical element 192 again separates the transmitted light and the + 1st order diffracted light.

Of the reflected light from the disk 17, the transmitted light of the hologram optical element 192 and the reflected light from the disk 18 of the + 1st order diffracted light of the hologram optical element 192 both enter the collimator lens 14 as parallel light. The transmitted light of the collimator lens 14 is a half mirror 19
Approximately half of 1 is transmitted, the concave lens 193 is transmitted, and the light is received by the photodetector 194. The photodetector 194 has a four-divided light receiving section, and the focus error signal is detected by the astigmatism method using the astigmatism generated in the half mirror 191, and the track error signal is detected by the push-pull method. Also, the reproduction signal is detected from the sum of the outputs of the four-division light receiving section of the photodetector 194.

The objective lens 16 has a spherical aberration that cancels the spherical aberration generated when the light emitted from the objective lens 16 passes through a substrate having a thickness of 0.6 mm, and the hologram optical element 192 corresponds to the hologram optical element 192. The + 1st-order diffracted light has a spherical aberration that cancels the sum of the spherical aberration that occurs when the light emitted from the objective lens 16 passes through a substrate having a thickness of 1.2 mm and the spherical aberration that the objective lens 16 has. Therefore, the transmitted light of the hologram optical element 192 is the objective lens 1
6, the light is condensed on the disk 17 without aberration, and the + 1st order diffracted light of the hologram optical element 192 is condensed on the disk 18 by the objective lens 16 without aberration.

FIG. 21 is a plan view of the hologram optical element 192. In the figure, the hologram optical element 192 has a pattern of concentric interference fringes, and functions as a concave lens for the + 1st order diffracted light together with the above-mentioned spherical aberration correction. Therefore, with respect to the objective lens 16, the focus position of the + 1st order diffracted light on the disk 18 is changed to the disk 1 of the transmitted light.
The objective lens 1 can be moved away from the focus position on 7.
The distance from 6 to the surface of the disks 17, 18 can be made substantially equal.

FIG. 22 is a sectional view of the hologram optical element 192. FIG. 22A shows a hologram optical element 192 having a rectangular cross section, which produces unnecessary −1st-order diffracted light with the same efficiency as + 1st-order diffracted light. FIG. 22B shows a hologram optical element 192 having a sawtooth cross section, in which the efficiency of the + 1st-order diffracted light increases and the efficiency of the unnecessary −1st-order diffracted light decreases. At this time, when the height of the sawtooth region is 2 h, the refractive index is n, and the wavelength of incident light is λ, the transmittance η ₀ and the + 1st-order diffraction efficiency η ₊₁ are given by the following equations.

Η₀ = Sin²φ / φ² (1) η₊₁= Sin²φ / (φ −π)² (2) However, φ = 2π (n−1) h / λ (3) From Equation (1) and (2), the transmittance η when φ = π / 2.₀
And + 1st-order diffraction efficiency η₊₁Are equal, η₀= Η₊₁= 0.
It becomes 405.

[0011]

By the way, according to the standard of the digital video disk, the wavelength is 635 nm to 655 n.
While a semiconductor laser that emits a laser beam of m is used, the standard of the conventional compact disk has a wavelength of 785.
A semiconductor laser that emits a laser beam of nm is used. FIG.
The conventional optical head device shown in FIG. 0 reproduces a high density digital video disc as compared with a compact disc, and thus emits a laser beam having a wavelength of 635 nm to 655 nm that can reduce the diameter of a focused spot as compared with a wavelength of 785 nm. It is necessary to use a semiconductor laser.

On the other hand, as a kind of compact disc,
A write-once compact disc called a CD-R is known. This write-once compact disc uses an organic dye as a recording medium and has a wavelength of 785 nm.
A high reflectance of 0% or more can be obtained, but a wavelength of 635 nm to
At 655 nm, only a very low reflectance of about 10% can be obtained. Therefore, the conventional optical head device shown in FIG. 20 cannot reproduce a write-once compact disc.

Further, in order to reproduce the digital video disc, it is necessary to make the diameter of the focused spot on the disc surface smaller than that of the compact disc in correspondence with the narrow track pitch. Therefore, since the diameter of the focused spot is inversely proportional to the numerical aperture of the objective lens 16, the numerical aperture of the objective lens 16 must be increased to about "0.52-0.6". On the other hand, in order to reproduce a compact disc, the compact disc has a loose standard with respect to the inclination of the disc, and it is necessary to suppress the occurrence of coma aberration due to the inclination of the disc. Therefore, the numerical aperture of the objective lens 16 is about “0.45”. Must be low.

In the conventional optical head device shown in FIG. 20,
By changing the diffraction efficiency between the central portion and the peripheral portion of the hologram optical element 192, it is possible to change the effective numerical aperture for the transmitted light and the + 1st order diffracted light. However, for example, the effective numerical aperture for transmitted light is "0.
6 ”, the effective numerical aperture for the + 1st order diffracted light is“ 0.4
5 ”, it is possible to reproduce a digital video disc with a substrate thickness of 0.6 mm by transmitted light and a compact disc with + 1st order diffracted light, but a digital video disc with a substrate thickness of 1.2mm by + 1st order diffracted light. Regeneration is not possible due to the small effective numerical aperture.

If, for example, the effective numerical aperture for transmitted light is "0.6" and the effective numerical aperture for + 1st order diffracted light is "0.52", the substrate thickness of transmitted light is 0.6 mm.
Although it is possible to reproduce a digital video disc of 1.2 mm thick with a + 1st-order diffracted light, a compact video disc with a + 1st-order diffracted light has a large effective numerical aperture. It is difficult because a tilt margin cannot be secured.

As described above, two types of digital video discs having different substrate thicknesses and compact discs including write-once discs have different wavelengths of the emitted light of the semiconductor laser and the numerical aperture of the objective lens which are optimum for reproducing the respective types. Therefore, the conventional optical head device shown in FIG. 20 cannot reproduce all of these plural types of disks.

The present invention has been made in view of the above points,
An object of the present invention is to provide an optical head device capable of reproducing all of two types of digital video discs having different substrate thicknesses and compact discs including write-once discs.

[0018]

In order to achieve the above object, the present invention provides a first light source for emitting a first light of a first wavelength and a second light source of a second wavelength different from the first wavelength. A second light source for emitting a second light, a first light from the first light source and a second light source
Optical multiplexing / demultiplexing means for multiplexing the second light from the light source to guide the light to the optical recording medium having the first or second substrate thickness, and for splitting the reflected light from the optical recording medium. , The light multiplexed by the optical multiplexing / demultiplexing means is condensed on the optical recording medium, reflected on the optical recording medium, the reflected light is transmitted, and the emitted light of itself is the light of the first substrate thickness. An objective lens having a first spherical aberration that cancels a spherical aberration generated when transmitting through a substrate of a recording medium, a hologram optical element with an aperture limit provided between the optical multiplexing / demultiplexing means and the objective lens, A first photodetection optical system for receiving the reflected light of the first wavelength demultiplexed by the wave / demultiplexing means, and a reflected light of the second wavelength demultiplexed by the optical multiplexing / demultiplexing means. An optical head device having a second photodetection optical system, comprising a hologram optical element having an aperture limit as described below. One in which the.

That is, the hologram optical element with aperture restriction generates at least 0th-order light and + 1st-order diffracted light that are transmitted light, and for the + 1st-order diffracted light of the first wavelength, the light emitted from the objective lens is the second light. A hologram portion having a third spherical aberration that cancels the sum of the second spherical aberration that occurs when transmitting through the substrate of the optical recording medium having the substrate thickness of 1 and the first spherical aberration that the objective lens has is formed. At the same time, an aperture limiting portion is formed which allows all the incident light of the first wavelength to pass therethrough and allows only the central portion of the cross section of the light flux to pass the incident light of the second wavelength.

Thus, in the present invention, the first substrate on which the information is recorded at the first recording density by using the first light emitted from the first light source and transmitted through the hologram optical element with aperture restriction. The recorded information of the optical recording medium of the second substrate thickness is reproduced by using the + 1st order diffracted light which reproduces the recorded information of the optical recording medium of the thickness, is emitted from the first light source, and is diffracted by the hologram optical element with aperture restriction. Of the optical recording medium of the first substrate thickness on which information is recorded at the second recording density by using the second light emitted from the second light source and transmitted through the hologram optical element with aperture restriction. The recorded information is reproduced.

Further, the hologram portion of the hologram optical element with aperture restriction according to the present invention comprises a hologram having a concentric circular pattern provided on the substrate, and the hologram has a circular cross section whose diameter is smaller than the effective diameter of the objective lens. It is characterized in that it has a rectangular shape outside the area and has a shape different from the rectangular shape inside the circular area.

Further, the aperture limiting portion of the hologram optical element with aperture limiting according to the present invention is outside the circular region having a diameter smaller than the effective diameter of the objective lens and on the surface on which the hologram portion is formed on the substrate. It consists of a wavelength filter film provided on the opposite surface and a phase compensation film provided on the wavelength filter film. Outside the circular region, the first light of the first wavelength is almost completely transmitted, and The second light having the wavelength of 2 reflects almost completely, and the light incident on the circular region has the first and second lights.
It is characterized in that it completely transmits both of the light.

Further, in the aperture limiting portion of the hologram optical element with aperture limiting according to the present invention, the diffraction grating and the wavelength filter film are provided outside the circular area having a diameter smaller than the effective diameter of the objective lens on the surface of the first substrate. A phase compensation film is provided outside the circular area on the back surface of the first substrate, and the back surface of the second substrate having the hologram portion formed on the front surface is bonded to the front surface of the first substrate with an adhesive. The first light of the first wavelength is almost completely transmitted outside the circular region, the second light of the second wavelength is almost completely reflected and diffracted, and the light incident on the circular region is received. Is characterized in that the first and second lights are completely transmitted.

The optical head device of the present invention combines the first light from the first light source and the second light from the second light source and guides them to the optical recording medium, while A hologram optical element with an aperture restriction is provided between the optical multiplexing / demultiplexing means for demultiplexing the reflected light and the objective lens, and the hologram part of this hologram optical element with an aperture restriction has a diameter smaller than the effective diameter of the objective lens. Since the diffraction efficiency is changed between the central portion of the region and the peripheral portion outside the circular region, the effective numerical aperture for the transmitted light of the first wavelength and the + 1st order diffracted light in the hologram optical element with aperture restriction is changed. be able to.

Further, in the present invention, the aperture limiting portion of the hologram optical element with aperture limiting allows all the incident light to pass through the first wavelength without aperture limiting, and allows the incident light to pass through the second wavelength. Since the central portion of the cross section of the light flux of the incident light (the circular region having a diameter smaller than the effective diameter of the objective lens) is transmitted, the effective numerical aperture for the transmitted light of the second wavelength in the hologram optical element with aperture restriction is First
It can be set independently of the wavelength of.

That is, the optical head device of the present invention has the optimum wavelength and objective lens for two types of optical recording media having different substrate thicknesses and two types of optical recording media having the same substrate thickness and different recording densities. The numerical aperture can be selected.

[0027]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a block diagram of a first embodiment of an optical head device according to the present invention. In the figure, the module 11 and the module 12 have a built-in semiconductor laser and a detection optical system for receiving the reflected light from the disk 17 or 18. The wavelength of the emitted light of the semiconductor laser in the module 11 is 635 nm, and the wavelength of the emitted light of the semiconductor laser in the module 12 is 785 nm.

The disks 17 and 18 are optical recording media having different substrate thicknesses. The disk 17 has a substrate thickness of 0.
A 6 mm digital video disc, the disc 18 is a digital video disc or a compact disc having a substrate thickness of 1.2 mm. At the time of reproduction, only one of the disks 17 and 18 is set in a rotation mechanism (not shown) and rotated at high speed.

The wavelength filter 13 multiplexes the first light from the module 11 and the second light from the module 12 and guides them to the collimator lens 14, while demultiplexing the reflected light from the disk 17 or 18. It composes the optical multiplexing / demultiplexing means, and transmits the light of wavelength 635 nm almost completely,
It functions to almost completely reflect light having a wavelength of 785 nm. Therefore, the emitted light from the semiconductor laser in the module 11 passes through the wavelength filter 13 with almost no loss, and the emitted light from the semiconductor laser in the module 12 is reflected with almost no loss by the wavelength filter 13.

The collimator lens 14 collimates the incident light. The objective lens 16 collects the light incident from the collimator lens 14 on the disk 17 or 18 and then reflects the light, transmits the reflected light, and suppresses the spherical aberration generated when the emitted light of itself passes through the substrate of the disk 18. It has a first spherical aberration that cancels. The aperture-limited hologram optical element 15 is provided between the collimator lens 14 and the objective lens 16 and has a configuration in which a hologram portion and an aperture limiting portion are respectively formed as will be described later, and the transmitted light having a wavelength of 635 nm and the + 1st order diffracted light are provided. By changing the effective numerical aperture for
In addition, the effective numerical aperture of transmitted light with a wavelength of 785 nm is 6
Set independently for that of 35 nm.

Next, the operation of this embodiment will be described. The light emitted from the semiconductor laser in the module 11 that has passed through the wavelength filter 13 with almost no loss is collimated by the collimator lens 14 and is incident on the hologram optical element 15 with an aperture limit having a configuration described later. It is divided into Origami. Holographic optical element with aperture restriction 15
The transmitted light of the forward path is condensed as parallel light by the objective lens 16 onto the disk 18 (in this case, a digital video disk) having a substrate thickness of 1.2 mm and a first recording density, and is reflected after forming a spot. The reflected light from the disk 18 passes through the objective lens 16 in the opposite direction, enters the hologram optical element with aperture restriction 15 again, and is divided into transmitted light and + 1st order diffracted light.

Further, the hologram optical element 15 with aperture restriction is provided.
The + 1st order diffracted light on the outward path of
Incident on the disk 1 with a substrate thickness of 0.6 mm
7 (digital video disk) is focused and formed into a spot and then reflected. The reflected light from the disk 17 passes through the objective lens 16 in the opposite direction, enters the hologram optical element with aperture restriction 15 again, and is separated into transmitted light and + 1st order diffracted light.

Of the reflected light from the disk 18, the transmitted light on the return path of the hologram optical element with aperture restriction 15 and the reflected light from the disk 17 on the return path of the hologram optical element 15 with aperture restriction are both parallel. The light passes through the collimator lens 14 in the opposite direction, and the wavelength filter 13
After being transmitted, the light is received by the detection optical system in the module 11.

On the other hand, the light emitted from the semiconductor laser in the module 12 which is reflected by the wavelength filter 13 with almost no loss is collimated by the collimator lens 14 and only the central portion of the cross section of the light beam has a hologram optical element 15 with aperture restriction.
After being transmitted, the light is condensed by the objective lens 16 on the disk (the compact disk in this case) 18 having the substrate thickness of 1.2 mm and the second recording density, and after forming a spot, it is reflected.

The light reflected from the disk 18 is the objective lens 1
The light passes through 6 in the opposite direction and is incident on the hologram optical element 15 with a limited aperture again. A part of the reflected light is a hologram optical element with aperture restriction 15 and a collimator lens 14.
In the opposite direction, and after being reflected by the wavelength filter 13,
The light is received by the detection optical system in the module 12. Since the wavelength of the emitted light of the semiconductor laser in the module 12 is 785 nm, reproduction is possible even when the disk 18 is a write-once compact disk. Note that the hologram optical element with aperture restriction 15 and the objective lens 16 are integrally driven by an actuator.

The objective lens 16 has a first spherical aberration that cancels the spherical aberration generated when the light emitted from the objective lens 16 passes through the substrate of the disk 18 having a substrate thickness of 1.2 mm. Further, the hologram optical element with aperture restriction 15 has a wavelength of 6 in the hologram optical element with aperture restriction 15.
With respect to the + 1st-order diffracted light of 35 nm, the second spherical aberration generated when the light emitted from the objective lens 6 passes through the substrate of the disk 17 having the substrate thickness of 0.6 mm, and the above-mentioned objective lens 1
A hologram portion having a third spherical aberration as shown in FIG. 2A to be described later is formed for canceling the sum of the first spherical aberrations 6 has.

Therefore, the hologram optical element 1 with aperture restriction
The transmitted light of No. 5 is converged onto the disk 18 without aberration by the objective lens 16 in both cases of the wavelengths of 635 nm and 785 nm, and the + 1st order diffracted light of the hologram optical element with aperture restriction 635 nm of wavelength 635 nm is transmitted by the objective lens 16. It is focused on the disk 17 without aberration.

FIG. 2 shows a hologram optical element 15 with a limited aperture.
FIG. FIG. 2A is a plan view seen from the front side,
FIG. 3B is a plan view seen from the back surface side. Also, FIG.
Shows a sectional view of the hologram optical element 15 with aperture restriction.
As shown in FIG.
As shown in (a), a hologram 20 having a pattern of concentric interference fringes is formed similarly to the hologram optical element 192 shown in FIG. Acts as a convex lens.

Therefore, with respect to the objective lens 16 shown in FIG. 1, the hologram optical element with aperture restriction 15 should bring the focus position of the + 1st order diffracted light on the disk 17 closer than the focus position of the transmitted light on the disk 18. Objective lens 16
From the surfaces of the disks 17, 18 can be substantially equal.

A hologram portion having a hologram 20 as shown in FIG. 2A is formed on the front surface of the hologram optical element with aperture restriction 15, and the back surface of the hologram optical element with aperture restriction 15 is shown in FIG. As shown in (), an opening limiting portion 23 having a circular opening is formed at the center. As shown in FIG. 3, the hologram portion is formed on the glass substrate 1
This is a structure in which the hologram 20 is formed on the surface of 9.
When the effective diameter of the objective lens 16 is 2a, the hologram 20 has a sawtooth shape in a region of a diameter 2b smaller than this, and has a rectangular cross-sectional shape outside the region of the diameter 2b. By making the cross-sectional shape of the area of the diameter 2b at the center of the hologram 20 into a sawtooth shape instead of a rectangular shape, the efficiency of the + 1st order diffracted light can be increased and the efficiency of the unnecessary −1st order diffracted light can be reduced.

Here, the height of the hologram 20 in a sawtooth-shaped cross-sectional area (hereinafter abbreviated as a sawtooth area) having a diameter 2b of the hologram 20 and the hologram in a rectangular cross-sectional area (hereinafter abbreviated as a rectangular area) outside the diameter 2b. When the heights of both 20 are 2h, the refractive index is n, and the wavelength of incident light is λ, the transmittance η _S0 and the + 1st order diffraction efficiency η _{S + 1} in the sawtooth region are given by the following equations.

Η _S0 = sin ² φ _S / φ ² _S (4) η _{S + 1} = sin ² φ _S / (φ _S −π) ² (5) where φ _S = 2π (n−1) h / λ (6) For example, when h = 345 nm and n = 1.46, λ = 6
For 35 nm, since φ _S = π / 2 from the equation (6), η _S0 = η _{S + 1} = 0.4 from the equations (4) and (5).
It will be 05. For λ = 785 nm, (6)
Since φ _S = 0.404π from the equation, η from the equation (4)
_S0 = 0.566.

On the other hand, the transmittance η _R0 of the rectangular area, +1
The next diffraction efficiency η _{R + 1} is given by the following equation.

Η_R0 = Cos²(Φ_R/ 2) (7) η_{R + 1}= (4 / π²) Sin²(Φ _R/ 2)  (8) However, φ_R= 4π (n-1) h / λ (9) For example, when h = 345 nm and n = 1.46, λ = 6
For 35 nm, from equation (9), φ_RIs π
From equations (7) and (8)_R0= 0, η_{R + 1}= 0.
It becomes 405.

That is, as can be seen from the above calculation results, in the hologram part of the aperture-limited hologram optical element 15, the light of wavelength 635 nm passes through only the sawtooth region of diameter 2b at 40.5% and the diameter of 2a. 40.5% is diffracted as + 1st order diffracted light over the entire region. In addition, the light having a wavelength of 785 nm is equivalent to the diameter 2 of the hologram portion.
56.6% is transmitted through the sawtooth region of b.

On the other hand, the aperture limiting portion 23 of the hologram optical element with aperture limiting 15 shown in FIG. 2B has a wavelength filter film 21 and a phase compensation film 22 on the back surface of the glass substrate 19, as shown in FIG. Is a laminated structure. The wavelength filter film 21 and the phase compensation film 22 are formed only outside the circular region having a diameter 2c smaller than the diameter 2b.

The wavelength filter film 21 functions to almost completely transmit light having a wavelength of 635 nm and almost completely reflect light having a wavelength of 785 nm. Further, the phase compensation film 22 is
For a wavelength of 635 nm, the phase difference between the light passing through the wavelength filter film 21 and the phase compensation film 22 and the light passing through the air is 2π.
[Rad. ] To adjust. That is, the aperture limiting portion 23 of the hologram optical element with aperture limitation 15 completely transmits the light having the wavelength of 635 nm over the entire area of the diameter 2a, and completely transmits the light having the wavelength of 785 nm within the circular area of the diameter 2c, The light is completely reflected outside the circular area.

The wavelength filter film 21 has, for example, a structure in which a high refractive index layer and a low refractive index layer are alternately deposited on the glass substrate 19 in an odd number. In order to provide the above wavelength selection characteristics, when the high refractive index layer and the low refractive index layer have refractive indices n ₁ and n ₂ and thicknesses d ₁ and d ₂ , n ₁ · d ₁ = n ₂ · d ₂ = λ / 4 (λ =
785 [nm]). Ti as high refractive index layer
If O ₂ and SiO ₂ are used as the low refractive index layer, n ₁ = 2.
Since 30 and n ₂ = 1.46, d ₁ = 85 from the above formula.
[Nm] and d ₂ = 134 [nm]. On the other hand, the phase compensation film 22 can be produced by depositing SiO ₂ on the wavelength filter film 21, for example.

In the second embodiment of the optical head device of the present invention, the hologram optical element with aperture restriction 15 shown in FIG. 2 is replaced by the hologram with aperture restriction shown in FIGS. In this configuration, the optical element 25 is replaced. FIG. 4 shows a plan view of the hologram optical element 25 with aperture restriction. FIG.
(A) is a plan view seen from the front side, and (b) is a plan view seen from the back side. Further, FIG. 5 shows a sectional view of the hologram optical element 25 with aperture restriction.

A hologram portion having a hologram 27 as shown in FIG. 4A is formed on the front surface of the hologram optical element with aperture restriction 25, and the back surface of the hologram optical element with aperture restriction 25 is shown in FIG. As shown in (), an opening limiting portion 32 having a circular opening is formed at the center. As shown in FIG. 5, the hologram portion is formed on the glass substrate 2
This is a structure in which the hologram 27 is formed on the surface of 6.
When the effective diameter of the objective lens 16 is 2a, the hologram 27 has a stepwise structure of four levels in a region of a diameter 2b smaller than this, and has a rectangular cross-sectional shape outside the region of the diameter 2b. By making the cross-sectional shape of the region of the diameter 2b at the center of the hologram 27 not a rectangular shape but a stepped shape of four levels, the efficiency of the + 1st-order diffracted light is increased and the efficiency of the unnecessary -1st-order diffracted light is reduced. it can.

Here, the height of each step in the four-level stepwise cross-sectional area (hereinafter abbreviated as stepwise area) of the diameter 2b of the hologram 27 is h / 2, and the rectangular cross-sectional area outside the diameter 2b (hereinafter, If the height of the hologram 27 in the rectangular area is 3h / 2, the refractive index is n, and the wavelength of incident light is λ, the transmittance η _F0 and the + 1st-order diffraction efficiency η _{F + 1} in the staircase region are It is given by the following formula.

Η_F0 = Cos²(Φ_F/ 2) cos²(Φ _F/ 4) (10) η_{F + 1}= (8 / π²) sin²(φ_F/ 2) cos² [(φ _F−π) / 4] (11 1) where φ_F= 2π (n-1) h / λ (12) For example, when h = 345 nm and n = 1.46, λ = 6
For 35 nm, φ from equation (12)_F= Π / 2
Therefore, from equations (10) and (11), η_F0= 0.42
7, η_{F + 1}= 0.346. Also, λ = 785 nm
For, from equation (12), φ_F= 0.404π
From equation (10), η_F0= 0.585.

On the other hand, the transmittance in the rectangular area η _R0 , +1
The next diffraction efficiency η _{R + 1} is given by the following equation.

Η_R0 = Cos²(Φ_R/ 2) (13) η_{R + 1}= (4 / π²) Sin²(Φ _R/ 2)  (14) However, φ_R= 3π (n-1) h / λ (15) For example, when h = 345 nm and n = 1.46, λ = 6
For 35 nm, from equation (15) φ_R= 3π / 4
Therefore, from equations (13) and (14), η_R0= 0.1
46, η_{R + 1}= 0.346.

That is, as can be seen from the above calculation results, in the hologram portion of the aperture-limited hologram optical element 25, the light having a wavelength of 635 nm is 42.7% inside the staircase region with a diameter 2b, and 14% outside the staircase region. 6% is transmitted, and as the + 1st order diffracted light over the entire area of the diameter 2a, 34.
6% is diffracted. The round-trip efficiency of transmitted light is 18.2% inside the staircase region with a diameter of 2b and 2.1% outside the staircase region, and the latter is at a level that can be ignored compared to the former. In addition, the light having a wavelength of 785 nm is equivalent to the diameter 2 of the hologram portion.
58.5% is transmitted through the staircase region of b.

On the other hand, as shown in FIG. 5, the aperture limiting portion 32 of the hologram optical element with aperture limiting 25 shown in FIG. 4B has a diffraction grating 29 and a wavelength filter film 30 on the front surface, and the back surface. In this structure, the surface of the glass substrate 28 on which the phase compensation film 31 is formed is attached to the back surface of the glass substrate 26 with an adhesive 33. The diffraction grating 29, the wavelength filter film 30, and the phase compensation film 31 are formed only outside the circular region having the diameter 2c smaller than the diameter 2b.

The wavelength filter film 30 has a function of almost completely transmitting light having a wavelength of 635 nm and almost completely reflecting light having a wavelength of 785 nm. In addition, the phase compensation film 31 is
For a wavelength of 635 nm, the phase difference between the light passing through the diffraction grating 29, the wavelength filter film 30, and the phase compensation film 31 and the light passing through the adhesive 33 and the air is 2π [rad. ] To adjust.

The diffraction grating 29 is made of Si on the glass substrate 28.
It is formed by depositing O ₂ , etching the glass substrate 28, and the like. The diffraction grating 29 does not work as a diffraction grating with respect to the transmitted light of the wavelength filter film 30, and cos ² (φ / 2) (where φ = 4) with respect to the reflected light of the wavelength filter film 30.
Reflects or diffracts light with a reflectance represented by πnh / λ). Here, h is the thickness of the diffraction grating 29, n is the refractive index, and λ
Is the wavelength of the incident light. Therefore, for example, the diffraction grating 29
Assuming that the thickness h is 134 nm and the refractive index n is 1.46,
When the wavelength λ of the incident light is 785 nm, φ = π, so the reflectance is 0%.

That is, the aperture limiting section 32 of the hologram optical element with aperture limitation 25 transmits light with a wavelength of 635 nm to a diameter of 2
A wavelength of 785
nm light is completely transmitted within the circular area of diameter 2c,
Outside the circular area, the light is completely reflected and diffracted.

The wavelength filter film 30 has, for example, a structure in which a high refractive index layer and a low refractive index layer are alternately deposited on the glass substrate 28 in odd layers. In order to provide the above wavelength selection characteristics, when the high refractive index layer and the low refractive index layer have refractive indices n ₁ and n ₂ and thicknesses d ₁ and d ₂ , n ₁ · d ₁ = n ₂ · d ₂ = λ / 4 (λ =
785 [nm]). Ti as high refractive index layer
If O ₂ and SiO ₂ are used as the low refractive index layer, n ₁ = 2.
Since 30 and n ₂ = 1.46, d ₁ = 85 from the above formula.
[Nm] and d ₂ = 134 [nm].

On the other hand, the phase compensation film 31 can be produced by depositing SiO ₂ on the back surface of the glass substrate 28, for example. As the adhesive 33, a material having substantially the same refractive index as that of the diffraction grating 29 is used. The pattern of the diffraction grating 29 is
Instead of the linear shape shown in FIG. 4B, other shapes such as concentric circles may be used.

FIG. 6 shows a hologram optical element 25 with a limited aperture.
3 is an enlarged view of a cross section of the hologram portion of FIG. FIG. 6A shows a cross section of a hologram portion formed by depositing SiO ₂ 35 on the glass substrate 26, and FIG. 6B shows a cross section of a hologram portion formed by etching the glass substrate 36. In both cases, two photomasks are used for creation. Figure 6
In the manufacturing method of (a), the first photomask is used to deposit SiO ₂ in the region F1 in the staircase region and the region R1 in the rectangular region by the height h, and then the second photomask. To the regions F2 and F3 in the staircase region and the region R2 above the region R1 in the rectangular region.
_2. Deposit ₂ at height h / 2.

On the other hand, in the creating method of FIG. 6B,
Using the first photomask, the area F1 in the staircase area
1 and the region R11 in the rectangular region are respectively etched to the depth h, and then the regions F12 and F13 in the staircase region and the region R11 in the rectangular region are etched using the second photomask.
Etching is performed to a depth h / 2 in each of the lower regions R12.

The wavelength of 635n in the hologram optical elements with aperture restrictions 15 and 25 whose cross sections are shown in FIGS.
The effective numerical apertures for the transmitted light of m, the + 1st order diffracted light, and the transmitted light of wavelength 785 nm are given by b / f, a / f, and c / f, respectively, where f is the focal length of the objective lens 16. Therefore, for example, f = 3 [mm] and a = 1.8 [m
m], b = 1.56 [mm], and c = 1.35 [mm], a / f = 0.6, b / f = 0.52, c / f =
It becomes 0.45.

Therefore, according to the embodiment of the present invention having the hologram optical element with aperture restriction 15 or 25 whose cross section is shown in FIGS. 3 and 5, and having the configuration as shown in FIG.
With a combination of 5 nm and a numerical aperture of 0.6, a digital video disc with a substrate thickness of 0.6 mm can be reproduced, and a wavelength of 63 mm can be reproduced.
Substrate thickness 1.2 mm with combination of 5 nm and numerical aperture 0.52
It is possible to reproduce a digital video disc having a first recording density by using a combination of a wavelength of 785 nm and a numerical aperture of 0.45, and a compact disc including a write-once disc having a second recording density of 1.2 mm with a substrate thickness. it can. The present invention can be applied not only to the read-only type and the write-once type but also to the rewritable type phase change disk and the magneto-optical disk.

It should be noted that the hologram optical element with aperture restriction 15
It is also possible to fabricate 25 and 25 by integral molding with plastic or glass. Further, by forming the hologram portion directly on the objective lens 16, it is possible to integrate the hologram optical elements 15 and 25 with aperture restrictions with the objective lens 16.

Next, the structure of the wavelength filter used in the embodiment of the optical head device of the present invention will be described. FIG. 7 shows a configuration diagram of each example of the wavelength filter shown at 13 in FIG. The wavelength filter 13 shown in FIG. 7A is formed by bonding two glass blocks 41 and 42 with a dielectric multilayer film 43 interposed therebetween. As shown in FIG. 7A, the incident light 44 having a wavelength of 635 nm is incident on the dielectric multilayer film 43 at an incident angle of 45 degrees, is almost completely transmitted, and travels straight. On the other hand, the incident light 45 having a wavelength of 785 nm is generated by the dielectric multilayer film 43.
Is incident at an incident angle of 45 degrees, is almost completely reflected, and the traveling direction is bent by 90 degrees.

In the wavelength filter 47 shown in FIG. 7B, the blocks 48 and 49 of the three glass blocks 48, 49 and 50 are bonded together via the dielectric multilayer film 51, and the blocks 49 and 50 are combined. The dielectric multilayer film 52 is used for bonding. As shown in FIG. 7B, the incident light 44 having a wavelength of 635 nm is incident on the dielectric multilayer film 52 through the block 50 at an incident angle of 22.5 degrees, is almost completely transmitted, and is transmitted through the block 49. Go straight. On the other hand, as shown in FIG. 7B, the incident light 45 having a wavelength of 785 nm enters the dielectric multilayer film 51 through the block 49 at an incident angle of 22.5 degrees, and after being reflected almost completely here. , Is incident on the dielectric multilayer film 52 at an incident angle of 22.5 degrees, and is reflected almost completely also here, the traveling direction is 9
It is bent at 0 ° and emitted through the block 49. Generally, the wavelength filter is easier to design as the incident angle to the dielectric multilayer film is smaller.

The wavelength filter 1 shown in FIGS. 7 (a) and 7 (b)
Dielectric multilayer films 43, 51 and 52 used in 3, 47
Is designed to almost completely transmit the incident light 44 having a wavelength of 635 nm and almost completely reflect the incident light 45 having a wavelength of 785 nm. However, it transmits almost completely the light having a wavelength of 785 nm and transmits the light having a wavelength of 635 nm. Can also be designed to reflect almost completely. in this case,
The wavelength of the semiconductor laser in the module 11 of FIG.
nm, the wavelength of the semiconductor laser in the module 12 is 635
nm may be changed respectively.

If the polarization direction of the emitted light from the semiconductor laser and the polarization direction of the reflected light from the disk are the same, a polarization beam splitter can be used instead of the wavelength filter. For example, wavelengths of 635 nm and 785 nm
By making the light of (1) enter the polarization beam splitter as P-polarized light and S-polarized light, respectively, the former is almost completely transmitted and the latter is almost completely reflected.

Next, a module when the optical head device of the present invention is applied to an optical head device for a read-only type disk will be described. FIG. 8 shows a block diagram of an example of the module in this case. As shown in the figure, in this module, a spacer 59 is sandwiched between a package 56 accommodating a semiconductor laser 54 and a photodetector 55 and a window portion of the package 56 in the optical path of laser light emitted from the semiconductor laser 54. Diffraction grating 57 and hologram optical element 58 provided
It is composed of The diffraction grating 57 and the hologram optical element 58 have a structure in which a pattern is formed of SiO ₂ on a glass substrate, and have a function of transmitting a part of incident light and diffracting a part thereof.

Next, to explain the operation of this module, the laser light emitted from the semiconductor laser 54 travels straight and is divided by the diffraction grating 57 into three lights, that is, the transmitted light and the ± first-order diffracted lights, each of which is hologram optical. About 50% of element 58
Permeate through to the disc (not shown). The three lights reflected by the disc are respectively holographic optical elements 58.
Is incident on the photodetector 55 and is then diffracted by about 40% as ± first-order diffracted light, transmitted through the diffraction grating 57 and received by the photodetector 55.

FIG. 9 shows each example of the mounting form of the semiconductor laser 54 on the photodetector 55 in the module of FIG. FIG. 9A shows the case where a glass mirror is used. The semiconductor laser 54 is installed on the photodetector 55 via a heat sink 61. The light emitted laterally from the semiconductor laser 54 is reflected by the inclined surface of the glass mirror 62 and travels upward in the drawing.

Further, FIG. 9B shows the case where a mirror formed by etching is used for the photodetector 55. The photodetector 55 has a concave portion 63 and a mirror 64 with an inclined surface formed by etching in the upper portion, and the semiconductor laser 54 is installed in the concave portion 63 formed by etching in the photodetector 55. As a result, the light emitted laterally from the semiconductor laser 54 is reflected by the mirror 64 formed by etching in the photodetector 55 and travels upward in the drawing.

FIG. 10A shows an interference fringe pattern of the diffraction grating 57 in the module of FIG. 8, and FIG. 10B shows an interference fringe pattern of the hologram optical element 58 in the module of FIG. The diffraction grating 57 has a region 66 near the center.
Only has a pattern. The light emitted from the semiconductor laser 54 passes through the inside of the region 66, and the reflected light from the disk passes through the outside of the region 66.

The hologram optical element 58 is shown in FIG.
As shown in (b), it has an off-axis concentric circular pattern, and functions as a convex lens for + 1st-order diffracted light and as a concave lens for -1st-order diffracted light.

FIG. 11 shows the photodetector 5 in the module of FIG.
5 shows an example of the pattern of the light receiving part of No. 5 and the arrangement of the light spots on the light receiving part. In FIG. 11, a semiconductor laser 54 is provided at a position slightly below the center of the photodetector 55, and a mirror 70 for reflecting the emitted light of the semiconductor laser 54 is provided. Further, in the figure, the light receiving portions 71, 72 and 73 are arranged on the left side and the light receiving portions 74, 75 and 76 are arranged on the right side of the installation position of the mirror 70. Further, the light receiving portions 7 are provided above the light receiving portions 71 and 74, respectively.
7, 78 are provided, and light receiving portions 79, 80 are provided on the lower side of the light receiving portions 73, 76 in the figure, respectively. Light receiving part 7
1, 72 and 73 total light receiving area and light receiving portions 74 and 75
And the total light-receiving area of 76 is the same,
The light receiving areas of 8, 79 and 80 are almost the same.

Of the transmitted light on the outward path of the diffraction grating 57 shown in FIG. 8, the + 1st order diffracted light of the hologram optical element 58 on the return path forms a light spot 81 on the three-divided light receiving portions 71 to 73 shown in FIG. Form and return hologram optical element 58
The -1st-order diffracted light forms a light spot 82 on the three-divided light receiving portions 74 to 76. Further, of the + 1st order diffracted light on the outward path of the diffraction grating 57, the hologram optical element 58 on the backward path is used.
The ± 1st-order diffracted light of the above forms light spots 83 and 84 on the light receiving portions 77 and 78, respectively, and the outward −1 of the diffraction grating 57
Of the diffracted light of the next order, ± 1 of the return hologram optical element 58
The secondary diffracted light forms light spots 85 and 86 on the light receiving portions 79 and 80, respectively.

The light receiving parts 71 to 73, 77 and 79 are located behind the converging point, and the light receiving parts 74 to 76, 78 and 80 are located in front of the converging point. When the levels of the electric signals obtained by photoelectric conversion by the light receiving units 71 to 80 are represented by V71 to V80, the focus error signal is {(V71 + V73 +) by the known spot size method.
V75)-(V72 + V74 + V76)}, and the track error signal is obtained by the known 3-beam method.
It is obtained from the calculation of {(V77 + V78)-(V79 + V80)}. The reproduction signal of the disc is (V71 +
V72 + V73 + V74 + V75 + V76).

Next, a module when the optical head device of the present invention is applied to an optical head device of a write-once disc or a rewritable phase change disc will be described. FIG. 12 shows a block diagram of an example of the module in this case. As shown in the figure, this module includes a semiconductor laser 90, a package 92 accommodating a photodetector 91, and a semiconductor laser 90.
The polarizing hologram optical element 93 and the quarter-wave plate 94 provided in the window portion of the package 92 in the optical path of the emitted laser light.

The polarizing hologram optical element 93 is shown in FIG.
As shown in FIG. 3, a pattern is formed on the lithium niobate substrate 96 having birefringence by the proton exchange region 97 and the phase compensation film 98, and all the ordinary light of the incident light is transmitted and all the extraordinary light is transmitted. It works to diffract.

Next, the operation of the module shown in FIG. 12 will be described. The emitted light from the semiconductor laser 90 is incident on the polarizing hologram optical element 93 as ordinary light and is transmitted therethrough. The polarized light is converted into circularly polarized light and goes to a disk (not shown). The reflected light from the disc is incident on the quarter-wave plate 94 and converted from circularly polarized light to linearly polarized light, and then is incident on the polarizing hologram optical element 93 as extraordinary light. The light is diffracted and received by the photodetector 91. The mounting form of the semiconductor laser 90 on the photodetector 91 is similar to that shown in FIG.

FIG. 14 shows a pattern of interference fringes of the polarization hologram optical element 93. As shown in the figure, the polarization hologram optical element 93 is divided into four regions 101 to 104. The optical axis 105 of the polarization hologram optical element 93 is set in the direction perpendicular to the polarization direction of the light emitted from the semiconductor laser 90.

FIG. 15 shows an example of the pattern of the light receiving portion of the photodetector 91 of the module shown in FIG. 12 and the arrangement of the light spots on the light receiving portion. In FIG. 15, the semiconductor laser 90 is provided at a position slightly below the center of the photodetector 91, and
Mirror 10 for reflecting emitted light of semiconductor laser 90
7 are provided. Further, in the figure, the light receiving portions 109 and 11 divided into two parts on the left side of the installation position of the mirror 107.
0 is also divided into two light receiving portions 111 and 112 on the right side.
Are arranged respectively. Further, the light receiving units 109 and 11
1, the light receiving portions 113 and 114 are provided on the upper side in the drawing, and the light receiving portions 115 and 116 are provided on the lower side in the drawing of the light receiving portions 110 and 112, respectively.

The + 1st order diffracted light from the region 103 of the polarizing hologram optical element 93 shown in FIGS. 12 and 14 forms a light spot 118 on the dividing line of the two light receiving portions 109 and 110 as shown in FIG. The −1st-order diffracted light from the region 103 forms a light spot 122 on the light receiving portion 116. The + 1st-order diffracted light from the region 104 of the polarizing hologram optical element 93 in FIG.
A light spot 119 is formed on the dividing line of the divided light receiving portions 111 and 112, and the −1st order diffracted light from the region 104 forms a light spot 123 on the light receiving portion 115.

Further, the ± first-order diffracted light from the region 102 of the polarizing hologram optical element 93 shown in FIG.
14A and 14B, light spots 120 and 124 are formed on the light receiving portions 113 and 116, respectively, and the area 1 shown in FIG.
The ± 1st-order diffracted lights from 01 are light spots 121 and 12 on the light receiving portions 114 and 115, respectively, as shown in FIG.
5 is formed.

When the levels of the electric signals obtained by photoelectric conversion by all the light receiving sections 109 to 116 are represented by V109 to V116, the focus error signal is {(V109 + V112) by the known Foucault method.
The track error signal obtained from the calculation of − (V110 + V111)} is (V113
It is obtained from the calculation of −V114). The reproduction signal of the disc is obtained from the calculation of (V115 + V116).

Next, a module when the optical head device of the present invention is applied to an optical head device of a rewritable type magneto-optical disk will be described. FIG. 16 shows a block diagram of an example of the module in this case. As shown in the figure, this module includes a package 130 containing a semiconductor laser 126, a photodetector 127, and microprisms 128 and 129.
And the polarizing diffraction grating 131 and the hologram optical element 13 provided on the window of the package 130 in the optical path of the laser light emitted from the semiconductor laser 126 with the spacer 133 interposed therebetween.
It consists of two. The polarizing diffraction grating 131 is shown in FIG.
It has a structure similar to that of the polarization hologram optical element 93 shown in FIG. 3, and functions to pass a part of the ordinary light of the incident light, diffract a part thereof, and diffract all the abnormal light.

Next, the operation of the module shown in FIG. 16 will be described. In FIG. 16, the laser light emitted from the semiconductor laser 126 passes through the hologram optical element 132 by about 80%.
Is transmitted and enters the polarizing diffraction grating 131 as ordinary light,
About 90% of the light is transmitted to the disc (not shown). On the other hand, of the reflected light from the disc, about 8% of the ordinary light component and about 80% of the extraordinary light component are diffracted by the polarizing diffraction grating 131 as ± first-order diffracted light, of which the + 1st-order diffracted light passes through the micro prism 128. The −1st-order diffracted light is received by the photodetector 127 via the microprism 129. Further, about 90% of the ordinary light component passes through the polarization diffraction grating 131 and enters the hologram optical element 132, and about 16% of ± first-order diffracted light is diffracted and received by the photodetector 127. The mounting form of the semiconductor laser 126 on the photodetector 127 is the same as in FIG.

FIG. 17 (a) is a pattern of interference fringes of the polarization diffraction grating 131 in the module of FIG. 16, FIG. 17 (b).
Shows respective interference fringe patterns of the hologram optical element 132 in the module of FIG. Polarizing diffraction grating 13
The first optical axis 135 is set in the direction perpendicular to the polarization direction of the light emitted from the semiconductor laser 126. The hologram optical element 132 has a pattern divided into four regions 136 to 139 only near the center as shown in FIG. 17B.

Of the reflected light from the disc, the transmitted light of the polarizing diffraction grating 131 passes through the inside of the regions 136 to 139, and the ± 1st order diffracted light of the polarizing diffraction grating 131 is the castle 136.
Pass through the exterior of ~ 139. The regions 136 and 137 of the hologram optical element 132 have an off-axis concentric circular pattern, and function as a convex lens for + 1st order diffracted light and a concave lens for −1st order diffracted light.

FIG. 18 shows the structure of the micro prism 128 in the module of FIG. Micro prism 128
Are three glass blocks 141, 142 and 143.
Blocks 141 and 142 of the dielectric multilayer film 145
The blocks 142 and 143 are bonded together via the dielectric multilayer film 146.

According to the micro-prism 128 having this structure, the P-polarized component of the incident light 147 is almost completely transmitted through the block 142, the dielectric multilayer film 146 and the block 143 to become the transmitted light 148. On the other hand, the S-polarized component of the incident light 147 is almost completely reflected twice by the dielectric multilayer films 146 and 145, and further passes through the block 142 to become reflected light 149. The structure of the micro prism 129 is similar to that shown in FIG.

FIG. 19 shows an example of the pattern of the light receiving portion of the photodetector 127 in the module shown in FIG. 16 and the arrangement of the light spots on the light receiving portion. In FIG. 19, the photodetector 1
A semiconductor laser 126 is provided at a position slightly below the center of 27, and a mirror 150 for reflecting the emitted light of the semiconductor laser 126 is provided. Further, in the figure, light receiving portions 151 and 152 are provided on the upper left side and light receiving portions 153 and 154 are provided on the lower right side.

Further, in the figure, the light receiving parts 155, 156, and 15 divided into three parts on the left side of the installation position of the mirror 150.
7, and light receiving portions 158, 159 and 160 divided into three parts are arranged on the right side. Further, the light receiving unit 15
5, light receiving parts 161 and 162 are provided on the upper side of FIG.
Are provided, and the light receiving portions 163 and 164 are provided on the lower side of the light receiving portions 157 and 160 in the figure, respectively.

In the photodetector 127, the + 1st order diffracted light from the polarizing diffraction grating 131 shown in FIG. 16 is separated into the transmitted light and the reflected light as shown in FIG. 18 using the microprism 128 as an analyzer. The transmitted light forms a light spot 171 on the light receiving portion 151 as shown in FIG. 19, and the reflected light forms a light spot 172 on the light receiving portion 152. The −1st-order diffracted light from the polarization diffraction grating 131 is separated into transmitted light and reflected light by using the microprism 129 as an analyzer, and the transmitted light forms a light spot 173 on the light receiving portion 153 as shown in FIG. Then, the reflected light forms a light spot 174 on the light receiving portion 154.

On the other hand, the hologram optical element 132 shown in FIG.
The + 1st order diffracted light from the regions 136 and 137 shown in (b) is divided into three light receiving portions 155 to 1 as shown in FIG.
57 light spots 175 and 176 are formed on 57,
The −1st-order diffracted light from the regions 136 and 137 is formed into a light spot 1 on each of the three light receiving portions 158 to 160.
77 and 178 are formed. The light receiving units 155 to 157 are located behind the converging point, and the light receiving units 158 to 160 are located in front of the converging point.

Further, the hologram optical element 132 shown in FIG.
The ± first-order diffracted light from the region 138 shown in FIG.
As shown in FIG. 9, light spots 179 and 181 are formed on the light receiving portions 161 and 164, respectively. Further, the ± first-order diffracted light from the region 139 shown in FIG. 17B of the hologram optical element 132 forms light spots 180 and 182 on the light receiving portions 162 and 163, respectively, as shown in FIG.

When the levels of the electric signals obtained by photoelectric conversion by all the light receiving sections 151 to 164 in the photodetector 127 are represented by V151 to V164, respectively, the focus error signal is represented by the well-known spot size method. (V155 + V157 + V159)-(V1
56 + V158 + V160)}, and the track error signal is {(V1
61 + V164)-(V162 + V163)}. Also, the reproduction signal of the disc is {(V15
1 + V153)-(V152 + V154)}.

Although the embodiment of the optical head device of the present invention shown in FIG. 1 has a configuration using two modules 11 and 12 each having a semiconductor laser and a detection optical system built therein for downsizing. However, the present invention is not limited to this, and a configuration using two sets of blocks in which a semiconductor laser and a detection optical system are separately provided is also possible. Further, the cross-sectional shape in a circular area having a diameter smaller than the effective diameter of the objective lens of the hologram portion of the hologram optical element with aperture restriction 25 may be a step shape having four or more steps.

[0101]

As described above, according to the present invention,
Optical multiplexing / demultiplexing for multiplexing the first light from the first light source and the second light from the second light source to guide them to the optical recording medium, while demultiplexing the reflected light from the optical recording medium A hologram optical element with aperture restriction is provided between the means and the objective lens, and the central portion of a circular area having a diameter smaller than the effective diameter of the objective lens and the outside of the circular area of the hologram portion of the hologram optical element with aperture restriction are provided. Since the diffraction efficiency is changed between the peripheral portion and the peripheral portion, the effective numerical aperture of the transmitted light of the first wavelength and the + 1st order diffracted light in the hologram optical element with aperture restriction can be changed.

Further, in the present invention, the aperture limiting section of the hologram optical element with aperture limiting allows all incident light to pass through the first wavelength without aperture limiting, and allows the incident light to pass through the second wavelength. Since the central portion of the cross section of the light flux of the incident light (the circular region having a diameter smaller than the effective diameter of the objective lens) is transmitted, the effective numerical aperture for the transmitted light of the second wavelength in the hologram optical element with aperture restriction is First
It can be set independently of the wavelength of.

Therefore, according to the present invention, the optimum wavelength and the effective of the objective lens are effective for two kinds of optical recording media having different substrate thicknesses and two kinds of optical recording media having the same substrate thickness and different recording densities. The optical recording medium having the first substrate thickness in which the information is recorded at the first recording density by using the light of the first wavelength transmitted through the hologram optical element with the aperture restriction. Recorded information of the optical recording medium of the second substrate thickness can be reproduced by using the + 1st-order diffracted light of the first wavelength, and the transmitted light of the hologram optical element with aperture restriction of the second wavelength can be reproduced. Can be used to reproduce the recorded information on the optical recording medium having the first substrate thickness on which the information is recorded at the second recording density.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of an optical head device of the present invention.

FIG. 2 is a plan view of a hologram optical element with aperture restriction used in the first embodiment of the optical head device of the present invention.

3 is a sectional view of the hologram optical element with aperture restriction shown in FIG.

FIG. 4 is a plan view of a hologram optical element with aperture restriction used in the second embodiment of the optical head device of the present invention.

5 is a sectional view of the hologram optical element with aperture restriction shown in FIG.

6 is an enlarged cross-sectional view of a hologram portion of the hologram optical element with aperture restriction shown in FIG.

FIG. 7 is a diagram showing a configuration of a wavelength filter used in the embodiment of the optical head device of the present invention.

FIG. 8 is a diagram showing a module configuration when the embodiment of FIG. 1 is applied to a read-only disc.

9 is a diagram showing a mounting mode of a semiconductor laser on a photodetector in the module of FIG. 8;

10 is a diagram showing a pattern of interference fringes of a diffraction grating and a hologram optical element in the module of FIG.

11 is a diagram showing an example of a pattern of a light receiving part of a photodetector and an arrangement of light spots on the light receiving part in the module of FIG.

FIG. 12 is a diagram showing a configuration of a module when the embodiment of the optical head device of the present invention is applied to a write-once disc or a rewritable phase change disc.

13 is a diagram showing a structure of an example of a polarization hologram optical element in the module of FIG.

14 is a diagram showing a pattern of interference fringes of the polarization hologram optical element in the module of FIG.

FIG. 15 is a diagram showing a pattern of a light receiving part of a photodetector and an arrangement of light spots on the light receiving part in the module of FIG. 12;

FIG. 16 is a diagram showing the configuration of a module when the embodiment of the optical head device of the present invention is applied to a rewritable magneto-optical disk.

17 is a diagram showing a pattern of interference fringes of a polarization diffraction grating and a hologram optical element in the module of FIG.

18 is a diagram showing a configuration of a micro prism in the module of FIG.

FIG. 19 is a diagram showing a pattern of a light receiving part of a photodetector and an arrangement of light spots on the light receiving part in the module of FIG. 16;

FIG. 20 is a diagram showing a configuration of an example of a conventional optical head device.

21 is a plan view of a hologram optical element used in the apparatus of FIG.

22 is a cross-sectional view of a hologram optical element used in the apparatus of FIG.

[Explanation of symbols]

11, 12 Module 13, 47 Wavelength Filter 14 Collimator Lens 15, 25 Hologram Optical Element with Aperture Limit 16 Objective Lens 17 Substrate Thickness of 0.6 mm Disc 18 Substrate Thickness of 1.2 Disc 19, 26, 28, 36 Glass Substrate 20, 27 Hologram 21, 30 Wavelength filter film 22, 31, 98 Phase compensation film 23, 32 Aperture limiting part 29, 57 Diffraction grating 33 Adhesive 35 SiO ₂ 41, 42, 48-50, 141-143 Block 43, 51, 52, 145, 146 Dielectric multilayer film 44, 45, 147 Incident light 54, 90, 126 Semiconductor laser 55, 91, 127 Photodetector 56, 92, 130 Package 58, 132 Hologram optical element 59, 133 Spacer 61 Heat sink 62, 64, 70, 107, 15 Mirror 63 Recesses 66, 101-104, 136-139 Regions 71-80, 109-116, 151-164 Light receiving parts 81-86, 118-125, 171-282 Light spots 93 Polarizing hologram optical element 94 1/4 wavelength Plate 96 Lithium niobate substrate 97 Proton exchange region 105, 135 Optical axis 128, 129 Micro prism 131 Polarizing diffraction grating 148 Transmitted light 149 Reflected light

Claims (6)

[Claims] 1. A first light source for emitting a first light of a first wavelength, a second light source for emitting a second light of a second wavelength different from the first wavelength, and While the first light from the first light source and the second light from the second light source are multiplexed and guided to an optical recording medium having a first or second substrate thickness, the light An optical multiplexing / demultiplexing means for demultiplexing the reflected light from the recording medium, and the light multiplexed by the optical multiplexing / demultiplexing means is condensed on the optical recording medium and then reflected on the optical recording medium, An objective lens having a first spherical aberration that allows reflected light to pass therethrough and cancels spherical aberration that occurs when its own outgoing light passes through the substrate of the optical recording medium having the first substrate thickness; A hologram optical element with aperture restriction provided between the demultiplexing means and the objective lens, and demultiplexed by the optical multiplexing / demultiplexing means. A first photodetection optical system for receiving the reflected light of the first wavelength, and a second photodetection optical system for receiving the reflected light of the second wavelength demultiplexed by the optical multiplexing / demultiplexing means. The hologram optical element with aperture restriction generates at least 0th-order light and + 1st-order diffracted light that are transmitted light, and the objective lens for the + 1st-order diffracted light of the first wavelength. A third spherical surface that cancels the sum of the second spherical aberration generated when the light emitted from the lens passes through the substrate of the optical recording medium having the second substrate thickness and the first spherical aberration of the objective lens. A hologram portion having aberration is formed, and the first portion
An opening limiting portion is formed to transmit all incident light of the wavelength of 2 and to transmit only the central portion of the light flux cross section to the incident light of the second wavelength, and to emit from the first light source. The recorded information of the optical recording medium having the first substrate thickness on which information is recorded at the first recording density is reproduced by using the first light transmitted through the hologram optical element with aperture restriction. , The + 1st-order diffracted light emitted from the first light source and diffracted by the aperture-limited hologram optical element is used to reproduce recorded information on the optical recording medium having the second substrate thickness, and Of the optical recording medium having the first substrate thickness in which information is recorded at a second recording density by using the second light emitted from the second light source and transmitted through the hologram optical element with aperture restriction. Optical head characterized by reproducing recorded information apparatus. 2. The hologram portion of the hologram optical element with aperture restriction is composed of a hologram having a concentric circular pattern provided on a substrate, and the hologram has a cross-sectional shape with a diameter smaller than the effective diameter of the objective lens. 2. The optical head device according to claim 1, wherein the optical head device has a rectangular shape outside the circular area and a shape different from the rectangular shape inside the circular area. 3. The optical head device according to claim 2, wherein the hologram forming the hologram portion of the aperture-limited hologram optical element has a sawtooth shape or a step shape in the circular region. 4. The aperture limiting portion of the hologram optical element with aperture limiting is outside a circular area having a diameter smaller than the effective diameter of the objective lens and on the surface of the substrate on which the hologram portion is formed. And a phase compensation film provided on the wavelength filter film, and the first light of the first wavelength is almost completely outside the circular region. The second wavelength of the second wavelength
2. The optical head device according to claim 1, wherein the light is reflected almost completely, and the light incident on the circular area is completely transmitted by both the first and second lights. 5. A diffraction grating and a wavelength filter film are provided outside the circular region having a diameter smaller than the effective diameter of the objective lens on the surface of the first substrate in the aperture restriction portion of the hologram optical element with aperture restriction. A phase compensation film is provided outside the circular region on the back surface of the first substrate, and the back surface of the second substrate having the hologram portion formed on the front surface and the front surface of the first substrate are bonded with an adhesive. Outside of the circular region, the first light of the first wavelength is almost completely transmitted, and the second light of the second wavelength is almost completely reflected and diffracted. 2. The optical head device according to claim 1, wherein the light incident on the circular area is configured to completely transmit both the first light and the second light. 6. The hologram section of the hologram optical element with aperture restriction is composed of a hologram provided concentrically on a substrate, and the hologram has a circular cross section whose diameter is smaller than the effective diameter of the objective lens. A rectangular shape outside the area, and a shape different from the rectangular shape within the circular area,
6. The optical head device according to claim 4, wherein the diameter of the circular area of the aperture limiting portion of the hologram optical element with aperture limitation is smaller than the diameter of the circular area of the hologram portion.