JP2725324B2 - Optical head for optical recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] Regarding an optical component acting as a phaser, a plurality of lights incident from different directions with one optical component are intended to act as phasers having different functions, respectively. An optical functional layer that provides a phase difference of a different wavelength corresponding to each of a plurality of lights from different directions that are not parallel to each other; and 2 that is sandwiched from both sides in close contact with the optical functional layer.
At least an optical component comprising two transparent media,
The optical component is disposed on an optical path of laser light and / or return light reflected by the recording medium from the recording medium, and the light is obliquely incident on the optical function layer from different directions that are not parallel to each other. By arranging them, an optical head for an optical recording medium is configured. Further, the optical component is configured such that the two transparent media are formed of a transparent flat plate, a prism, or a combination thereof. Also,
An optical head for an optical recording medium is configured by using it.

[Industrial applications]

 The present invention relates to an improvement in an optical component, in particular, a retarder.

In recent years, the introduction of optical technology into communication systems, information processing / OA devices, and the like has become increasingly active.

For example, the development of an optical disk device that records, reproduces, and erases information using a laser beam and an optical disk that is a recording medium for the optical disk device have been remarkable, and include a compact disk (CD) for consumer use and a CD-ROM as a ROM medium for a personal computer. ROM
Has become widespread.

In addition, expectations for optical disk devices are increasing more and more as large-capacity recording devices for OA equipment and other information-related equipment. In particular, a rewritable magneto-optical disk device is being developed as a favorite which covers an even larger capacity area of a magnetic disk device currently most frequently used as a file memory.

Various optical components are used in the above-described optical applied device, and a polarizer and a phaser are well known as typical ones.

Among the retarders, a linear retarder, for example, a half-wave plate or a quarter-wave plate is one of the basic optical components widely used for controlling the polarization of light.

[Conventional technology]

FIG. 4 is a cross-sectional view of a conventional retarder (wave plate).
Reference numeral 31 denotes a thin plate cut in parallel to the optical axis of an optically anisotropic crystal, for example, a uniaxial anisotropic crystal. 32 and 33
Is a transparent flat plate, for example, a flat plate made of optical glass. C-
C ′ is light that is perpendicularly incident on the optically anisotropic crystal thin plate 31.

Reference numeral 24 denotes a light-shielding cover made of an adhered film of aluminum or the like, and reference numeral 25 denotes an input / output light window.

At this time, the incident light is transmitted through the quartz plate and then split into ordinary light and extraordinary light. The phase difference δ between the two lights is expressed by the following equation, as is well known.

δ = 2π (d / λ) (n e -n o) ...... (1) Thisゝa, d is the thickness of the optically anisotropic crystal thin 31, lambda is the wavelength of light, n _e and n _o are It is the refractive index of ordinary light and extraordinary light.

Thus, d, lambda, the δ be determined to n _e and n _o can be produced 1/2 wavelength or 1/4 wavelength any other phase shifter (wavelength plate).

Next, an example of an optical device using these retarders (wave plates) will be described.

FIG. 5 is a configuration diagram of a conventional two-beam optical head for a magneto-optical disk. In FIG. 5, reference numeral 101 denotes a 1/4 wavelength plate, and 102 denotes a 1/2 wavelength plate.

The laser beam emitted from the reading laser diode 5 passes through a collimator lens 13, a beam shaping prism 12, a beam splitter 7, a dichroic mirror 22, and an objective lens 15, and enters the magneto-optical recording medium 100, where the medium information is stored. And is reflected by the beam splitter 7 to enter the half-wave plate 102. Here, the light is rotated by 45 ° about the optical axis so that the maximum signal amplitude is obtained at the time of differential detection, and then the polarization beam splitter 9
The photodetectors 19 and 20 detect the medium signal differentially.

On the other hand, the laser light emitted from the writing laser diode 6 also passes through the other collimator lens 14, the beam shaping prism 12, and the polarizing beam splitter 8, and
The wave plate 101 is entered.

Here, the light becomes circularly polarized light, is reflected by the mirror 10 and the dichroic mirror 22, and irradiates the magneto-optical recording medium 100 through the objective lens 15.

The writing laser light has a longer wavelength than the reading laser light,
In addition, although the medium is absorbed by the medium with high power and raises the temperature of the medium, some return light (circularly polarized light) follows the above-described path, enters the quarter-wave plate 101 again, and the transmitted light returns to linearly polarized light again. ,
The light is reflected by the polarization beam splitter 8 and detected by a photodetector 21 for tracking error detection.

That is, two phase shifters (wave plates) are used, and two
They are arranged to separate the two light paths. The portion indicated by the broken-line frame is the optical system of the two-beam optical head for a magneto-optical disk.

[Problems to be solved by the invention]

A conventional retarder, for example, a typical example of a wave plate,
As described above, it is an individual optical component that realizes one function with one component.

Therefore, when an optical system is configured using these retarders (wave plates), the number of components must be increased, and the optical system must be designed to inevitably separate the optical path.

Many recent optical application devices require miniaturization,
In particular, due to the demand for higher density and higher speed of optical disc devices, there is a strong demand for smaller and lighter optical heads, and the problem of increasing the functionality of retarders (wave plates), which are the optical components used in them. Was brought up and the solution was needed.

[Means for solving the problem]

FIG. 1 is a sectional view for explaining the configuration and principle of the optical component of the present invention.

In the figure, reference numeral 1 denotes an optical functional layer made of a thin film or a thin plate having a desired function. Reference numerals 2 and 3 are optically bonded to both sides of the optical function layer 1 with a transparent medium. Further, on the outer surfaces of the transparent media 2 and 3, a light-shielding cover 24 for providing at least two sets of input / output optical windows 25 is provided.

FIG. 1A shows the case where the transparent medium is a flat plate, and FIG. 2B shows the case where the transparent medium is a right-angle prism.

AA 'and BB' denote the optical paths of two lights entering from different directions that are not parallel to each other. Configure to function. For example, by designing a phase difference of 1/2 wavelength in the AA 'direction and a phase difference of 1/4 wavelength in the BB' direction, the function of two And the optical paths of the two lights can be crossed there.

That is, the above-mentioned problem is that the desired characteristics are respectively obtained for a plurality of lights obliquely incident from different directions that are not perpendicular to each other and are not parallel to the optical function layer sandwiched between the two transparent media. This problem can be solved by functioning as a retarder having the optical component so that the two transparent media are formed of a transparent flat plate, a prism, or a combination thereof.

[Action]

For example, in FIG. 1 (b), when the two transparent media are rectangular prisms, the optical functional layer 1 is cut parallel to the optical axis of an optically anisotropic crystal, for example, a crystal which is a uniaxial anisotropic crystal. It is assumed that light is incident from the direction of AA 'or BB' using a thin plate.

Light obliquely incident on the quartz plate undergoes birefringence and is split into two light waves. Now, when the angle of refraction of two light waves in the wave-normal vector and x ₁ and x _2, also the refractive index for the wave-normal vector for two light waves and n ₁ and n _2, both after passing through the optically functional layer 1 The phase difference δ ′ of the light wave is obtained by the following equation.

δ ′ = 2π (d / λ) [n ₂ Cos (x ₂ ) −n ₁ Cos (x ₁ )] (2) where d is the thickness of the optical functional layer 1 (quartz plate) and λ Is the wavelength of light.

Therefore, by determining x ₁ , x ₂ , n ₁ , and n ₂ in consideration of d, λ, the incident angle of light, the orientation of the refractive index ellipsoid of quartz, and the like, one optical component can be used from different directions. Oblique-incidence retarder (wave plate) that functions as a half-wave or quarter-wave, or any other wave retarder, for multiple incident lights
Can be produced.

〔Example〕

First, in FIG. 1 (b), when the two transparent media are rectangular prisms made of optical glass, the optical functional layer 1 is aligned with the optical axis of a crystal which is an optically anisotropic crystal, for example, a uniaxial anisotropic crystal. Using a thin plate cut in parallel, fabricate an optical component (phaser) that functions as a half-wave plate for light in the AA 'direction and a quarter-wave plate for light in the BB' direction. did.

FIG. 2 is a block diagram of a two-beam optical head for a magneto-optical disk using the above-described optical component of the present invention, which is applied to the conventional two-beam optical head shown in FIG. This is an example.

Reference numeral 4 denotes an oblique incidence type phase shifter according to the present invention using a right-angle prism for the transparent media 2 and 3, which emerges from the reading laser diode 5, and has a lens 13, a beam shaping prism 12, a beam splitter 7, a dichroic mirror 22, and a lens. The read laser beam which is reflected by the magneto-optical recording medium 100 and passes through 15 returns as a half-wave plate, exits from the write laser diode 6, passes through the lens 14, the beam shaping prism 1
2, the mirror 10, the dichroic mirror 22, the outgoing path through the polarizing beam splitter 8 and the mirror 10 after passing through the phaser 4 of the present invention.
It was designed to function as a quarter-wave plate with respect to the return write laser light reflected by the magneto-optical recording medium 100 through the lens 15 and returned.

Therefore, the number of components is reduced by one in comparison with the conventional example shown in FIG.
Thus, the optical path can be crossed, so that the optical head can be reduced in size and weight.

3 (a), 3 (b) and 3 (c) are views showing another embodiment of the present invention.

As the optical functional layer 1, a uniaxially anisotropic crystal, for example, a thin plate of quartz was used. The transparent media 2 and 3 are both right-angle prisms, and the two surfaces sandwiching the right angle and the optical functional layer 1 make an angle of 45 °.

All the incident light was set perpendicular to the prism surface, and the optical function layer 1 was configured to function as a 45 ° incident type retarder.

In the figure, 23 indicates the direction of the C axis of the quartz crystal, that is, the direction of the optical axis, and the crystal plane is cut so as to be parallel to the plane of the optically functional layer 1.

FIG. 3A shows one side (cd) of the optical functional layer 1 (abcd surface).
In the case where the angle θ between the optical axis 23 and the optical axis 23 is 30 °, FIG.
In the case of 55 °, FIG. 11C shows the case of θ = 74 °.

When the above angle θ is viewed from the light incident direction (for example, from right to left in the drawing), the projection angles of the optical axis 23 to the prism surface (a′b′cd surface) are π / 8 and π, respectively. / 4 and 3π / 8.

In this embodiment, each of them is designed as a half-wave retarder at 45 ° incidence.

Therefore, in FIG. 3A, the incident P wave or S wave is rotated by π / 4 with respect to the projection angle on the prism surface (a′b′cd surface), and is emitted. Light can be extracted as a P, S mixed wave.

On the other hand, in the case of FIG.
Since the light is emitted after receiving the rotation of π / 2 with respect to the projection angle, the S wave can be converted into the P wave and the P wave can be converted into the S wave and extracted.

It is easily understood that the case of FIG. 3C has exactly the same functions as those of FIG.

It goes without saying that the optical component of the present invention can be used as an oblique incidence type retarder (wave plate) having a desired function for light in one direction. In this case, if a thin plate cut so that the optical axis is perpendicular to the refracted light is used, design becomes easier.

〔The invention's effect〕

As described above, the optical component according to the present invention acts as a phase shifter having a desired function with respect to a plurality of lights incident from different directions that are not parallel with one component. This greatly contributes to the reduction in size and weight of the optical head for optical and optical recording media.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating the configuration and principle of an optical component (phaser) according to the present invention, and FIG. 2 is a magneto-optical disk 2 using the optical component according to the present invention.
FIG. 3 is a diagram showing another embodiment of the optical component of the present invention, FIG. 4 is a sectional view of a conventional retarder (wave plate), and FIG. 5 is a conventional magneto-optical device. FIG. 2 is a configuration diagram of a two-beam optical head for a disk. In the figure, 1 is an optical functional layer, 2 and 3 are transparent media, 4 is a retarder, 5 is a reading laser diode, 6 is a writing laser diode, 7 is a beam splitter, 8 and 9 are polarization beam splitters, 10 And 11 are mirrors, 12 is a beam shaping prism, 13 to 18 are lenses, 19 to 21 are photodetectors, 22 is a dichroic mirror, 23 is an optical axis, 24 is a cover, 25 is an input / output optical window, 100 is a magneto-optical recording medium, 101 is a 1/4 wavelength plate and 102 is a 1/2 wavelength plate.

Claims (3)

(57) [Claims] 1. An optical function layer for providing a phase difference of a different wavelength corresponding to each of a plurality of lights from different directions which are not parallel to each other, and two optical layers sandwiched from both sides in close contact with said optical function layer. At least an optical component comprising a transparent medium, wherein the optical component is disposed on an optical path of laser light or / and return light reflected from the recording medium, and the light is transmitted to the optical functional layer. An optical head for an optical recording medium, wherein the optical head is arranged so as to be obliquely incident from different directions that are not parallel to each other. 2. The optical head for an optical recording medium according to claim 1, wherein said two transparent media are made of a transparent flat plate, a prism, or a combination thereof. 3. The optical component according to claim 1, wherein the read laser light acts as a half-wavelength phase shifter on the return light reflected from the recording medium, and the forward light before the write laser light enters the recording medium. When,
3. An optical head for an optical recording medium according to claim 1, wherein said optical head acts as a quarter-wave retarder for return light reflected from said recording medium.