JPH10247335A - Optical head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently use emitted luminous flux to miniaturize an optical head, by disposing a transparent member on a support substrate having a semiconductor laser and disposing a hologram having a light beam shaping function in this transparent member. SOLUTION: A parallel flat plate 4 attached to a support substrate 2 is disposed on the optical path of a light emitted from a semiconductor laser 3, a first hologram lens 6 having an astigmatic correction function is provided on the end surface of the semiconductor laser 3 side of this parallel flat plate 4 and a second hologram lens 7 having a collimator lens function for making a light emitted from the semiconductor laser 3 to be a parallel light is provided in the end surface of the opposite side. Also, a diffraction hologram 22 is formed in the inner end surface of the package of a protection plate 11. This diffraction hologram 22 has no objective lens functions and thus an objective lens 2 is provided outside the package. Then, a beam shaping function is provided to the first or second hologram lens 6 or 7.

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, in the above-mentioned prior art, a light beam emitted from a semiconductor laser is directed to a recording medium without shaping. In such an optical system without a beam shaping function, the use efficiency of the light of the semiconductor laser deteriorates, and the spot shape of the light condensed on the optical disk becomes elliptical, and the recording and reproducing capability of the signal deteriorates. have. Further, when the beam shaping function is provided outside the unit, there is a disadvantage that the apparatus becomes large.

[0004]

An optical head according to the present invention comprises:
A transparent member is disposed on a support substrate on which a semiconductor laser is disposed, and a hologram having a light beam shaping function is disposed on the transparent member.

[0005]

Embodiments of the present invention (hereinafter, referred to as "embodiments") will be described below with reference to the drawings.

FIG. 1 relates to a first embodiment of the present invention, and FIG. 1 is an explanatory view showing a configuration of an optical head. As shown in FIG. 1, the optical head 1 includes a support substrate 2. At one end of the support substrate 2, a step 2a protruding upward is formed, and the semiconductor laser 3 is provided on the step 2a. The semiconductor laser 3 is arranged to emit light in the horizontal direction. A parallel plane plate 4 mounted on the support substrate 2 is arranged on the optical path of the light emitted from the semiconductor laser 3. A first hologram lens 6 is provided on the end face of the parallel plane plate 4 on the semiconductor laser 3 side, and a second hologram lens 7 is provided on the opposite end face. The first hologram lens 6 has a function of correcting astigmatic difference. Further, the second hologram lens 7 has a function of a collimator lens that converts the light emitted from the semiconductor laser 3 into parallel light. A prism 8 is disposed on the support substrate 2. A semi-permeable film 21 is formed on the slope of the prism 8. Further, a diffraction hologram 22 is formed on an inner end surface of the package of the protective plate 11. The diffraction hologram 22 does not have the function of an objective lens unlike the first embodiment, and therefore, the objective lens 23 is provided outside the package.

The first hologram lens 6 or the second hologram lens
May have a beam shaping function.
The emitted light of the semiconductor laser 3 is the same as in the first embodiment,
Parallel light whose astigmatic difference has been corrected is emitted from the first hologram lens 6 and the second hologram lens 7 and enters the semi-permeable membrane 21. A front monitor photodetector 25 is provided on the support substrate 2 on the optical path of the light transmitted through the semi-permeable film 21.

The diffraction hologram 22 separates the light emitted from the semiconductor laser 3 into zero-order and ± 1st-order diffracted light,
Zero-order light is converged on the surface of the recording medium 15 by the objective lens 23, and ± 1st-order light is diffracted out of the objective lens 23,
It is not converged on the recording medium 15. Therefore, the diffraction hologram 22 is formed so that most of the light quantity goes to the recording medium 15 as zero-order light. The light reflected on the surface of the recording medium 15 passes through the objective lens 23, becomes parallel light, and enters the diffraction hologram 22 again. In this case, most of the light amount is diffracted and divided into three so that it can be obtained as ± first-order light. This light passes through the semi-permeable membrane 21, and ± 1st-order light is received by a photodetector 26 provided between the end face of the prism 8 and the support substrate 2. A focus error signal based on an astigmatism method, a spot size method, or the like, a tracking error signal based on a push bull method or the like,
And an information signal.

Next, the operation of this embodiment will be described.
The light beam emitted from the semiconductor laser 3 is corrected for astigmatism by the first hologram lens 6, converted into parallel light by the second hologram lens 7, and formed into a circular shape.
Incident on the semi-permeable membrane 21 of FIG. The light transmitted through the semi-permeable membrane 21 is obliquely incident on the prism 8 from the air and is refracted and received by the front monitor photodetector 25. And
The output of the monitoring photodetector 25 controls the output of the semiconductor laser 3 and the like. On the other hand, the light reflected by the semi-permeable film 21 is incident on the diffraction hologram 22, and the zero-order diffracted light is converged on the surface of the recording medium 15 by the objective lens 23. The light reflected by the recording medium 15 re-enters the diffraction hologram 22, is diffracted and divided into three so that most of the light quantity is obtained as ± first-order light, passes through the semi-permeable film 21, and ± 1 of them. The next light is received by the light detector 26. From the output of the photodetector 26, an information signal,
Focus and tracking error signals are obtained.

Conventionally, there has been proposed a means for converting an elliptical beam into a circular beam by obliquely entering light emitted from a semiconductor laser into a prism surface using a shaping prism. When the shaping prism is arranged on the support substrate 2, the semiconductor laser on the support substrate 2 is arranged obliquely with respect to the surface of the prism. For example, it is necessary to use a shaping method according to (1) or (2). On the other hand, in the present embodiment, the first hologram lens 6 or the second hologram lens 7 is provided with the astigmatic difference correction or the collimator function and the beam shaping function, so that the optical head 1 is further reduced in size. doing.

FIG. 2 is an explanatory view showing the structure of an optical head according to a second embodiment of the present invention. In the present embodiment, the configurations of the semiconductor laser 3, the first hologram lens 6, and the second hologram lens 7 are the same as those in the first or second example.

In the present embodiment, the S-polarized light (linearly polarized light vibrating in the direction perpendicular to the plane of the drawing) that has passed through the second hologram lens 7 is turned into parallel light by the prism 41 provided on the support substrate 2. The light is incident on a polarization hologram 42 of a diffraction hologram in which a dielectric multilayer film is deposited on the surface side formed on the slope. The S-polarized light is totally reflected by the polarization hologram 42, becomes a circularly polarized light by a quarter-wave plate 43 provided on the end face inside the package of the protective plate 11, and converges on the recording medium 15 by the objective lens 23. Is done. The position of the quarter-wave plate 43 may be between the objective lens 23 and the protection plate 11 as shown by a broken line in the figure.
The light reflected by the recording medium 15 becomes parallel light by the objective lens 23, passes through the 波長 wavelength plate 43, becomes P-polarized light (linearly polarized light oscillating in the direction of the paper), and becomes a polarization hologram 4.
2 is incident. The P-polarized light is applied to the polarization hologram 4.
The light is transmitted and refracted by the light source 2, is reflected by the prism surface 45 of the prism 41 on the support substrate 2, and is incident on a reflective third hologram lens 46 formed on the upper surface of the prism 41. The third hologram lens 46 divides and separates the light beam into three light beams for detecting a focus / tracking error signal,
Each light beam is received by a photodetector 47 provided on the support substrate 2. Then, from the output of the photodetector 47, an information signal and a focus tracking error signal are obtained.

The reflection type third hologram lens 46
Can be easily realized by coating a metal film. As described above, since the polarization hologram 42 is operatively a polarization beam splitter film, a conventional polarization beam splitter film may be used. However, when a simple polarization beam splitter is used, a part of the light passing through the polarization beam splitter easily enters the photodetector 47. That is, assuming that the refractive index in the air is n0, the refractive index of the prism is n, the incident angle is θ0, and the refractive angle is θ, nsinθ = n0sinθ0, that is, sinθ = (n0 / n) sinθ0, for example, n0 = 1, n = 1.5, θ0 =
Assuming 45 °, sin θ = 0.43, θ = 28.5 °
And the deflection angle becomes about 16.5 °, so that the light easily enters the photodetector 47. Therefore, in order to prevent this, a somewhat thick prism 41 is required. On the other hand, when the polarization hologram 42 is used, the diffraction angle can be increased for one of the polarization planes, so that the thickness of the prism 41 can be reduced, and the optical head 1 can be made smaller and flat. be able to.

In FIG. 2, the light is reflected once on the lower surface and once on the upper surface of the prism 41. However, the number of times of reflection can be set arbitrarily. Also, the polarization hologram 42
Thus, the third hologram lens 46 may be omitted so that the light beam is divided and separated into three light beams for error signal detection. In this case, each light beam split and separated by the polarization hologram 42 is reflected by the lower surface and the upper surface of the prism 41 and enters the photodetector 47. In this case, the upper surface of the prism 41 that reflects each light beam may be a metal reflecting surface.

Other structures, operations and effects are the same as those of the first embodiment. In the first and second embodiments described above, the functions of the first hologram lens and the second hologram lens are reversed, and the collimator lens that makes the light emitted from the semiconductor laser 3 parallel to the first hologram lens 6 is used. And the second hologram lens 7 may have a function of correcting the astigmatic difference.

FIG. 3 is an explanatory diagram showing a part of the optical head, FIG. 4 is an explanatory diagram for explaining correction of astigmatism, and FIG. 5 is an explanatory diagram showing a method of forming a hologram. In this embodiment, one hologram 51 is provided with a function of correcting astigmatism and a collimator function, and the first hologram lens 6 and the second hologram lens 7 shown in the first and second embodiments are replaced by This is replaced with one hologram 51. This hologram 51 is provided on one end face of the plane-parallel plate 4, as shown in FIG. Thus, by using one hologram, the diffraction efficiency is increased, and the loss of the emitted light amount is reduced.

Next, a method of forming the hologram 51 will be described. As shown in FIG. 4, the output spherical wave of the semiconductor laser 53 having astigmatism is transmitted through a parallel flat plate 54 arranged obliquely with respect to the output light of the semiconductor laser 53, thereby correcting the astigmatism. Is done. The corrected transmitted light becomes parallel light by the collimator lens 55.

Therefore, the hologram 51 can be created by a method as shown in FIG. That is, the light beam from the same light source is converted into parallel light by a collimator lens,
The light is split into two parts by a semi-permeable membrane, and one of the lights is irradiated to the hologram dry plate 56 as plane wave reference light. The other light is
After being reflected by the mirror 57, the light is converged by the single lens 58 and converted into a spherical wave through the diaphragm 59. The light beam is passed through a parallel plane plate 60 inclined at a predetermined angle to form a spherical wave with astigmatic difference The hologram dry plate 56 is radiated as the object light. The hologram 51 can be created by the double exposure of the reference light and the object light.
When the hologram 51 is irradiated with a spherical wave having an astigmatic difference from the semiconductor laser from the object light side, parallel light whose astigmatic difference is corrected is emitted. That is, the spherical wave of the semiconductor laser having the astigmatic difference interferes with the astigmatic component of the hologram surface, cancels it, and removes the astigmatic difference.

[0019]

According to the present invention, a light beam emitted from a semiconductor laser can be used efficiently and a small optical head can be realized.

[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 a second embodiment of the present invention, and is a diagram illustrating a configuration of an optical head.

FIG. 3 is a diagram showing a part of an optical head.

FIG. 4 is a diagram for explaining correction of astigmatic difference.

FIG. 5 is a diagram illustrating a method of creating a hologram.

[Explanation of symbols]

 Reference Signs List 1 optical head 3 semiconductor laser 4 parallel plane plate 6 first hologram lens 7 second hologram lens 8 prism 13 diffraction hologram 14 photodetector 15 recording medium

Claims (3)

[Claims] 1. An optical head comprising: a transparent member disposed on a support substrate on which a semiconductor laser is disposed; and a hologram having a light beam shaping function disposed on the transparent member. 2. The optical head according to claim 1, wherein a semiconductor laser is disposed on the upper surface of the supporting substrate in a projecting shape. 3. A beam splitter comprising a hologram having a light beam shaping function and a dielectric multilayer film and an analyzer are formed on a transparent substrate on the support substrate 2, and the transparent substrate is housed in the support substrate and a package. 2. The optical head according to claim 1, wherein the opening is sealed by sealing a transparent substrate with an adhesive.