JPH10247334A - Optical head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a small optical head, by arranging a beam splitter consisting of a hologram with a collimeter function and a dielectric multi-layered film on a supporting substrate with a semiconductor laser arranged thereon. SOLUTION: On the end face on the semiconductor laser 3 side of a 1st prism 61, a sheet of hologram having a corrective function of an astigmatic distance and a collimeter function is provided, and on a slope of the opposite side end face, a beam splitter 63 consisting of dielectric multi-layered film is provided. The beam splitter 63 reflects 50% of P-polarized light and transmits 100% of S-polarized light. On a slope of an end face of a 2nd prism on a 1st prism side, a surface-relief type hologram 64 is provided. This hologram 64 has a polarization ability, transmitting P-polarized light component, and diffracting S-polarized light component. Moreover, compared with a wavelength used, a grating pitch is formed smaller, and a diffraction angle larger. And on a top surface of the 2nd prism 62, a reflection-type hologram 65 is provided, and on a bottom surface, the 1st and 2nd optical detectors 66, 67 are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an improvement in an optical head for reading information recorded on a recording medium, for example.

[0002]

2. Description of the Related Art FIG. 1 of JP-A-64-10433 (A,
As shown in B), the semiconductor laser 1 is placed on the bottom 11a of the concave holding member 11 made of a heat conductive material such as A1.
2 and a transparent substrate 13 made of transparent glass, plastic, or the like is bonded and fixed to the holding member 11 with respect to the semiconductor laser 12 and the photodetector 20. Semitransparent mirrors 14 and 15 are provided on the transparent substrate 13, and hologram lenses 16 and 17 are provided on an upper surface 13b opposite to the lower surface 13a facing the semiconductor laser. FIG. 7 shows an optical reading apparatus using a hologram lens 16 for correcting astigmatism from the semiconductor laser 12, and FIG. Window glass 62 to protect the hologram lens 1
6 and 17 are formed integrally with the transparent substrate 13.

[0003]

However, the above-mentioned prior art employs a finite optical system having no collimator function. Such an optical system has a drawback that the distance between the objective lens and the unit in which the semiconductor laser or the photodetector is integrated is large. Further, if a collimator lens is provided, there is a disadvantage that the apparatus becomes large.

An object of the present invention is to provide an optical head which has solved the above-mentioned disadvantages.

[0005]

An optical head according to the present invention comprises:
A hologram having a collimator function and a beam splitter made of a dielectric multilayer film are arranged on a support substrate on which a semiconductor laser is arranged.

[0006]

1 to 4 relate to a first embodiment of the present invention (hereinafter referred to as "first embodiment"). FIG. 1 is an explanatory view showing the structure of an optical head, and FIG. FIG. 3 is an explanatory diagram showing an optical path of diffracted light in the second prism, FIG. 3 is an explanatory diagram showing a first photodetector, and FIG. 4 is an explanatory diagram showing a second photodetector.

This embodiment is an example of an optical head for magneto-optics. In the present embodiment, as shown in FIG. 1, a first prism 61 and a second prism 62 made of glass or the like are provided on the support substrate 2 in order from the semiconductor laser 3 side. In the present embodiment, the bonding surface of the semiconductor laser 3 is arranged in the vertical direction. Therefore, the output light of the semiconductor laser 3 is P-polarized light oscillating in the minor axis direction of the ellipse (FIG. 1).
(Linearly polarized light oscillating in the in-plane direction of the drawing). The end face of the first prism 61 on the side of the semiconductor laser 3 is perpendicular to the optical axis of the light emitted from the semiconductor laser 3, and a single hologram 51 having an astigmatic difference correction function and a collimator function is provided on this end face. Is provided. Further, the first prism 6
The one semiconductor laser 3 and the end surface on the reflection side are slopes facing downward, and a beam splitter 63 made of a dielectric multilayer film is provided on the slope. The beam splitter 63 reflects P-polarized light by 50% (transmits 50%) and transmits S-polarized light by 100%.

On the other hand, the end face of the second prism 62 on the side of the first prism 61 is a slope slightly inclined from a state parallel to the slope of the first prism 61.
A hologram 64 of a surface relief type is provided on this slope. This hologram 64 has a polarization property,
The P-polarized light component is transmitted and the S-polarized light component is diffracted. The hologram 64 has a smaller grating pitch and a larger diffraction angle than the wavelength used. The reflection hologram 6 is provided on the upper surface of the second prism 62.
5 are provided, and a first photodetector 66 and a second photodetector 67 are provided on the lower surface. At one end of the support substrate 2, a step 2a protruding upward is formed.
The semiconductor laser 3 is provided on a. The semiconductor laser 3 is arranged to emit light in the horizontal direction.

The support substrate 2 and the members on the substrate 2 are housed in a package 10, and the package 10
Is sealed by bonding a protective plate 11 made of a transparent glass material with an adhesive 19. The objective lens 23 is provided outside the package.

Next, the operation of this embodiment will be described. The emitted light of the semiconductor laser 3 shown in FIG. 1 has an elliptical shape, and is P-polarized light that vibrates in the minor axis direction of the ellipse. This semiconductor laser 3
Outgoing light is made parallel by the hologram 51 and the astigmatic difference is corrected. The P-polarized light is reflected 50% by the beam splitter 63, and the reflected light is transmitted through the protective plate 11 and provided in a driving device that can be driven in two-dimensional directions, that is, in the optical axis direction and the tracking direction. The objective lens 23 converges on the surface of the magneto-optical recording medium.
The return light reflected by the recording medium surface becomes linearly polarized light that has been subjected to one rotation according to the direction of magnetization of the recording medium surface, becomes parallel light again by the objective lens 23, and passes through the beam splitter 63. This beam splitter 63 converts P-polarized light by 50%
Since the light is transmitted and the S-polarized light is transmitted at 100%, the P-polarized light component of the light that has passed through the beam splitter 63 has a light amount of 、, and the apparent rotation angle per force increases. The light that has passed through the beam splitter 63 is incident on a surface relief type hologram 64 having polarization. Thereby, as shown in FIG. 2, the P-polarized light component is transmitted, and the S-polarized light component is diffracted. The O-order light transmitted through the hologram 64 is received by the first photodetector 66. On the other hand, the primary light diffracted by the hologram 64 is reflected by the reflective hologram 65, and the outgoing light of the −1st order light of the hologram 65 (hereinafter referred to as “1-1st order light”) is a second photodetector. Light is received at 67. Here, the hologram 64 is provided with a lens function, for example, the first
Is located in front of the focal point of the O-order light in the focused state, and the second photodetector 67 is 1-1 in the focused state.
When placed after the focus of the next light, the size of the beam on the photodetectors 66 and 67 decreases as one increases and the other decreases according to the defocus. As shown in FIGS. 3 and 4, the photodetectors 66 and 67 are respectively A11 and A11.
12, A13, B11, B12, and B13. Then, the information signal SRF and the focus error signal SFE can be obtained by the following equations. A11, A12, A13, C in the following equation
Reference numerals 11, C12, and C13 indicate the amounts of received light in the areas indicated by the symbols in FIGS. SRF = (A11 + A12 + A13)-(C11 + C1
2 + C13) SFE = (A11 + A13−A12) − (C11 + C1
3-C12) Further, the hologram 64 may not have a lens function, and a circular beam of parallel light may be incident on the photodetectors 66 and 67 in a focused state. In this case, when the recording medium moves away from the focal position of the objective lens 2, the light becomes circular convergent light on the photodetectors 66 and 67. Conversely, when the recording medium approaches, the light becomes circular divergent light. Therefore, a focus error signal can be obtained by setting the three divisions of the photodetectors 66 and 67 to an optimal division ratio with a circular beam at the time of focusing. However, in this case, there is a problem that the sensitivity is low. In order to solve this, in the present embodiment, the hologram 64 is provided with a prism effect, and the
The beam is shaped so as to form an elliptical beam on 6, 67 so that the major axis of the elliptical beam is parallel to the long side of the rectangle of the three-divided element of the photodetector. Then, a focus error signal is detected by the light beam of the 1-1 order light, and an information signal is obtained from the O order light.

[0011]

According to the present invention, there is an advantage that a small optical head can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a first embodiment of the present invention, and is a diagram illustrating a configuration of an optical head.

FIG. 2 is a diagram illustrating an optical path of diffracted light in a second prism.

FIG. 3 is a diagram showing a first photodetector.

FIG. 4 is a diagram showing a second photodetector.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 optical head 3 semiconductor laser 51 hologram 63 beam splitter 64 hologram 65 reflection hologram 66 first photodetector 67 second photodetector

Claims (6)

[Claims] 1. An optical head, comprising: a hologram having a collimator function and a beam splitter made of a dielectric multilayer film arranged on a supporting substrate on which a semiconductor laser is arranged. 2. The optical head according to claim 1, wherein the transparent substrate is housed in a package, and the opening is sealed by sealing the transparent substrate with an adhesive. 3. The optical head according to claim 1, wherein the hologram having the collimator function has an astigmatic difference function. 4. The optical head according to claim 1, wherein an analyzer is arranged between the beam splitter made of the dielectric multilayer film and the photodetector. 5. The optical head according to claim 4, wherein the analyzer is a hologram having polarization characteristics. 6. The supporting substrate is integrated with a protruding step, and has a flat surface area on the photodetector side disposed between the supporting substrate and the transparent substrate, as compared with the surface area of the step portion. The optical head according to claim 1.