JPS61265746A - Optical pickup device - Google Patents

Abstract

PURPOSE:To facilitate the manufacture of a diffracting means and to attain thin profile and low cost by providing a reflecting type diffracting element represented by a special forming formula. CONSTITUTION:Let the optical length from a light source 1 generating a light of wavelength lambda be L1(x, y) and let the optical length of a conjugation point of the light source be L2(x, y), the reflection type diffracting element 11 expressed as a shape formula of L1(x, y)-L2(x, y)=mlambda is provided (where m=0, + or -1, + or -2, ...). One diffracting light diffracted and reflected by the diffracting means 11 is irradiated onto a disc 4 via an objective lens 3 and the other diffracted light diffracted and reflected by the diffracting means 11 is received by a photodetector 5. Thus, the depth of the groove of the diffracting means is made shallower more than that of the transmission type. Thus, the manufacture of the diffracting means is facilitated and thin profile and low cost are realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup device for recording and reproducing information on optical video discs, digital audio discs, and the like.

[Summary of the invention]

The present invention includes a light source that emits light with a wavelength of λ, an objective lens that converges incident light emitted from the light source and incident on the disk onto the disk, and receives at least a portion of the reflected light reflected by the disk. A light receiving element is placed in the optical path of the incident light and reflected light.

In an optical pickup device having a diffraction means for diffracting incident light into at least two diffracted lights, the diffraction means is provided with an optical path length from the light source L (X, y) - an optical path length from the military service point of the light source. to L2(x.

When y).

LX (Xp y) LX (X+ y)=
A reflective diffraction element expressed by the shape formula mλ is provided (
However, m=0. ±1. ±2. ), one diffracted light emitted from the light source, diffracted and reflected by the diffraction means is irradiated onto the disk through the objective lens, and the other diffracted light is reflected from the disk and diffracted and reflected by the diffraction means. The diffraction means is received by a light-receiving element, making it easy to manufacture the diffraction means, and realizing a reduction in thickness and cost.

[Conventional technology]

When optically recording and reproducing information on a disk, it is necessary to accurately focus recording and reproducing light such as a laser beam onto the disk, and various optical pickup devices have been proposed for this purpose. FIG. 3 is a schematic plan view of a conventional optical pickup device.

In the figure, reference numeral 1 denotes a light source such as a semiconductor laser or a gas laser that emits recording and reproducing light of a predetermined wavelength λ.

2 is a phase type diffraction plate (diffraction grating) that diffracts and transmits incident light. The phase type diffraction plate 2 has grooves (gratings) as shown in FIG. 4, for example, and the depth of the grooves is as follows.

The distribution state of the diffracted light is determined by the spacing and direction, and the depth (depth and thickness) is set to approximately 1/2 of the wavelength λ, so that approximately only the first-order diffracted light is derived. . , 3 are objective lenses, which are driven by a focus motor (not shown) or the like so as to converge light onto the disk 4. Reference numeral 5 denotes a light receiving element that receives the reflected light reflected by the disc 4 and outputs a focus error signal and a reproduction signal of information recorded on the disc 4. 6 is a conjugate point of the light source 1.

Light emitted from a light source 1 is diffracted by a phase type diffraction plate 2. The depth and thickness of the groove is approximately 1/2 of the wavelength λ of light.
Since it is set to , most of the results derived at this time are +
There are only the first-order diffracted light and the first-order diffracted light. Phase type diffraction plate 2
9 is designed to diffract, for example, only the −1st order diffracted light (or +1st order diffracted light) with almost no aberration, and this −1st order diffracted light is incident on the objective lens 3 as an incident light and converged on the disk 4. (+1st-order diffracted light is not shown). The light reflected by the disk 4 and incident on the objective lens 3 is further incident on the phase type diffraction plate 2, where it is diffracted again into +1st order diffraction light and 11th order diffraction light.

Then, the +1st order diffracted light (or -1st order diffracted light) which has almost no aberration is returned to the light source 1, and the 11st order diffracted light (or +1st order diffracted light) which has astigmatism is irradiated onto the light receiving element 5.

Therefore, by dividing the light-receiving element 5 into four parts, the focus error can be controlled by the so-called astigmatism method.6 [Problems to be Solved by the Invention] However, conventional devices do not perform phase-type diffraction as described above. Since the plate 2 is configured to transmit light, the relief of the first diffraction element (
The problem was that the grooves were deep (thick), making it difficult to manufacture. Furthermore, in order to make the device thinner, it is necessary to add other optical means such as a mirror to deflect the beam, which increases the number of parts.

This not only hinders miniaturization of the device, but also has the disadvantage of being expensive.

[Means for solving problems]

FIG. 1 shows a schematic plan view of the optical pickup device of the present invention. In this figure, parts corresponding to those in FIG. 3 are denoted by the same reference numerals, and detailed description thereof will be omitted. In the present invention, the surface of the phase type diffraction plate 11 is made of aluminum, laminate, etc., and is adapted to reflect light. Then, on the phase type diffraction plate 11
+ When taking the y coordinate, the optical path length between any point (x, y) and a light source l that generates light with wavelength λ is 1, and the optical path between any point (xty) and the conjugate point 6 of light source 1 is 1. When the length is LX, for the one-phase diffraction plate 11.

A reflective diffraction element is formed which is expressed by the shape formula: LL (xty) - LX (xty) = mλ (where m = 0.±1.±2. . . ).

That is, its shape is determined by phase matching between the wavefront emitted from the light source 1 and the wavefront emitted from the conjugate point 6.

In addition, the depth of the groove of the grating is such that the difference in optical path length of the light that is reflected and diffracted on the upper and lower surfaces of the groove is approximately λ/2 (or an odd number multiple thereof).
It can be configured as follows. In this way, it is possible to reduce the 0th-order diffracted light and increase the diffraction efficiency of the ±1st-order diffracted light. Furthermore, in order to increase the diffraction efficiency of the ±1st-order diffracted light, the cross-sectional shape of the groove can be blazed (made step-like (ideally curved)) with respect to the rectangular shape. One of the diffracted lights emitted from the light source 1 and diffracted and reflected by the 1-phase diffraction plate 11 is irradiated onto the disk 4 via the objective lens 3, and reflected by the disk 4.
One of the diffracted lights that has been diffracted and reflected by the phase type diffraction plate 11 is received by the light receiving element 5.

[Effect]

The effect will now be explained. Light emitted from the light source 1 is reflected and diffracted by the phase type diffraction plate 11. The phase type diffraction plate 11 is, for example, -1st order diffracted light (or +1st order diffracted light)
This aberration-free 1st-order diffracted light enters the objective lens 3 as incident light, and is converged and irradiated onto the disk 4 (the +1st-order diffracted light is not shown in the figure). ), reflected by disk 4,
The reflected light incident on the objective lens 3 is further incident on the phase type diffraction plate 11, where it is again reflected and diffracted (separated) into +1st-order diffracted light and 11th-order diffracted light.

The first-order diffracted light with almost no aberration is then returned to the light source 1.

The first-order diffracted light having astigmatism is incident on the light receiving element 5.

When the relative distance between the disk 4 and the objective lens 3 changes, the beam spot on the light receiving element 5 changes as shown in FIG. 2(a).
It changes as shown in (c).

That is, when the disk 4 is at the focused position, the spot becomes approximately circular as shown in FIG. 2(a).

If you get closer or further away, Figure 2 (b) or (c)
) as shown respectively in a vertically long or horizontally long oval shape. Therefore, the focus error signal can be generated by dividing the light receiving element 5 into four parts and obtaining the difference between the sums of the outputs from the diagonally located parts. This focus error signal is supplied to a focus motor (not shown) to control the relative distance between the objective lens 3 and the disk 4.

In cases where a semiconductor laser with considerable astigmatism is used as the light source 1, or where spherical aberration etc. remain in the objective lens 3, the shape of the phase type diffraction plate 11 should be determined by taking these aberrations into consideration. If this is determined, it is possible to irradiate the disc 4 with light that cancels out such aberrations.

Furthermore, since the direction of the light can be changed by tilting the phase type diffraction plate 11, the light source 1 can be adjusted to adjust the optical system.
What is necessary is to adjust the optical axis direction of the light receiving element 5, rotate the phase type diffraction plate 11 in the in-plane direction, and adjust the elevation angle.

In the above, the depth of the groove of the phase type diffraction plate 11 is set to λ/2.
As a result, substantially only the first-order diffracted light is obtained, and this first-order diffraction light is
Although the disk 4 is irradiated with the diffracted light of the next order, the phase type diffraction plate 11 is used so that the diffracted light of the 0th order and the diffracted light of the 1st order can be obtained.
It is also possible to configure the disc 4 to be irradiated with the 0th order diffracted light and to make the 1st order diffracted light having astigmatism enter the light receiving element 5 in order to generate a focus error signal.

Also, when generating a focus error signal using the astigmatism method,
It is also possible to arrange a cylindrical lens in the first-order diffraction optical path to the light-receiving element 5, or to arrange a plane-parallel plate inclined with respect to its tip axis. Of course, it is also possible to obtain the focus error signal by a method other than the astigmatism method, for example by arranging a wedge prism.

〔effect〕

As described above, the present invention includes a light source that emits light with a wavelength of λ, an objective lens that converges the incident light emitted from the light source and incident on the disk, and at least one of the reflected light reflected by the disk. In an optical pickup device, the optical pickup device includes a light-receiving element that receives a portion of the light, and a diffraction means that is disposed in the optical path of incident light and reflected light and that diffracts the incident light into at least two diffracted lights. When the optical path length from the conjugate point of the light source is Lx (xt y) - the optical path length from the conjugate point of the light source is L2 (xt y), the reflective type Provide a diffraction element (however, m =
Q, ±1. ±2. ), one of the diffracted lights emitted from the light source, diffracted and reflected by the diffraction means is irradiated onto the disc via the objective lens, and the one reflected from the disc is
Since one of the diffracted lights diffracted and reflected by the diffraction means is received by the light-receiving element, the depth of the groove of the first diffraction means can be made shallower than that of a transmission type, making it easier to manufacture the diffraction means. Thinness and cost reduction can be achieved.

[Brief explanation of drawings]

FIG. 1 is a schematic plan view of the optical pickup device of the present invention, FIG. 2 is a schematic plan view of a spot on the light receiving element, and FIG. 3 is a schematic plan view of a conventional optical pickup device. FIG. 4 is a plan view of the phase type diffraction plate. 1... Light source 2.11... Phase type diffraction plate 3...
Objective lens 4... Disk 5... Light receiving element
6...Conjugate point or more

Claims (1)

[Scope of Claims] A light source that emits light with a wavelength of λ, an objective lens that converges the incident light emitted from the light source and incident on the disk onto the disk, and a An optical pickup device comprising a light receiving element that receives at least a portion of light, and a diffraction means that is disposed in an optical path of the incident light and reflected light and that diffracts the incident light into at least two diffracted lights, the diffraction means , the optical path length from the light source is L_1(x,y)
, where the optical path length from the conjugate point of the light source is L_2(x,y), a reflective diffraction element is provided ( However, m=0, ±
1, ±2, ...), one of the diffracted lights emitted from the light source, diffracted and reflected by the diffraction means, is irradiated onto the disk via the objective lens, and is reflected from the disk,
An optical pickup device characterized in that one of the diffracted lights diffracted and reflected by the diffraction means is received by the light receiving element.