JPH0271442A - optical head - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the structure of an optical head used in a magneto-optical recording/reproducing device.

[Prior Art] As a conventional optical head for a magneto-optical recording/reproducing device, there is one in which a diffraction grating is used as a beam splitter to make the optical system compact, as disclosed in Japanese Patent Laid-Open No. 63-32743.

[Problems to be Solved by the Invention] However, in the conventional optical head described above, since the collimator lens and the diffraction grating are assembled in the disk word,
There is a problem that the cylinder becomes complicated and large due to positioning. The present invention is intended to solve these problems, and its purpose is to further reduce the number of parts by increasing the integration of elements, and to provide a small and thin optical head.

[t! I! Means for Solving the Problem] A first optical head of the present invention includes a semiconductor laser, an objective lens that focuses light from the semiconductor laser onto a recording medium,
A light-receiving element with an analyzer disposed on the front surface, and a diverging light having an elliptical far-field pattern from the semiconductor laser, which is formed on one surface of a transparent substrate in the optical path from the semiconductor laser to the objective lens. an elliptical Fresnel lens that converts light into parallel light; a diffraction grating lens formed on the other surface of the transparent substrate that branches reflected light from the recording medium toward the light receiving element; It is characterized by comprising a diffraction grating mirror that reflects light and makes it incident on the objective lens.

In the second optical head of the present invention, a semiconductor laser and a light receiving element with an analyzer placed on the front are in the same package, and a transparent substrate on which a Fresnel lens and a diffraction grating lens are formed serves as a window of the package. It is characterized by the presence of

The third optical head of the present invention is characterized in that the cross-sectional shape of the package in the direction perpendicular to the optical axis is not circular.

The fourth optical head of the present invention is characterized in that only the housing containing the diffraction grating mirror objective lens is movable.

In a fifth optical head of the present invention, the semiconductor laser has a structure in which the emitted light from the semiconductor laser is emitted in a direction perpendicular to the substrate, and the semiconductor laser is formed on the substrate on which the light receiving element is formed. It is characterized by the presence of

[Operation] The diverging light emitted from the semiconductor laser enters the diffraction grating lens formed on one surface of the transparent substrate, and the 0th order light of the grating lens is used as a collimator lens formed on the other surface of the transparent substrate. enters the Fresnel lens. The far-field pattern of light emitted from a semiconductor laser is elliptical, and if a Fresnel lens is constructed with a pattern that converts this elliptical far-field pattern into parallel light, the vignetting of the light beam that occurs with a circular Fresnel lens can be avoided. In addition, by arranging the long axis of the ellipse parallel to the recording medium, the light beam can be flattened in the thickness direction of the optical head, making it possible to effectively utilize the power of the light from the semiconductor laser. Enables thinner heads.

The light that has been made parallel by the Fresnel lens is bounced up by a mirror, enters the objective lens, and is focused on the recording medium, but in order to make the light that has been made parallel by the elliptical Fresnel lens enter the circular objective lens. To do this, it is necessary to convert an elliptical beam into a circular beam, and for this purpose a mirror consisting of a diffraction grating that utilizes Bragg reflection is used.

The reflected light from the recording medium passes through the objective lens, the diffraction grating mirror, and the Fresnel lens, and then returns to the diffraction grating lens.

A light-receiving element is arranged in the direction of the first-order diffracted light and -1st-order diffracted light by the diffraction grating lens, and an analyzer is arranged in front of each light-receiving element. The direction is 45°, and the direction of rotation of the polarization plane based on information on the recording medium is detected.

If the grating lens is designed to generate astigmatism depending on the distance of the recording medium relative to the objective lens, a focusing error signal can be obtained by dividing one of the light receiving elements into four parts. Tracking error signals can also be detected using the push-pull method.

If a semiconductor laser and a light receiving element with an analyzer placed on the front are placed in the same package, and a transparent substrate on which a Freil lens and a diffraction grating lens are formed is used as the window of the package, the optical system of the optical head can be integrated into this package. This means that it can be constructed using only a diffraction grating mirror and an objective lens.

Furthermore, by forming a semiconductor laser on a substrate such as Si on which the light receiving element is formed and emitting light from the semiconductor laser perpendicularly to the substrate, it is possible to integrate the charge conversion element as well. I can do it.

Hereinafter, the details of the present invention will be shown by examples.

[Example] Example 1 FIG. 1 is a diagram showing a first example of the optical head of the present invention. FIG. ) shows a main cross section including the disk substrate on which the recording medium is formed.

A semiconductor laser 101 is attached to a heat sink 102, and analyzers 1, which are sheet-shaped polarizing plates, are mounted on both sides of the semiconductor laser 101.
Photodiodes 103a and 103b with 04a and 104b bonded to the front surface are arranged.

A semiconductor laser 1 is mounted on a glass substrate 105 which is a transparent substrate.
A diffraction grating lens 106 is formed on the surface on the 01 side, and a Fresnel lens 107 as a collimator lens is formed on the other surface, forming a window of the package 119.

As will be described later, the Fresnel lens 107 has an elliptical shape with a length ratio of major axis to minor axis of approximately 3:1, so the cross-sectional shape of the package in the direction perpendicular to the optical axis is rectangular. It has become. Note that the cross-sectional shape of the package is not limited to a rectangle, and may be any flat shape.

As shown in FIG.
It has a pattern that causes astigmatism 201 and 202 due to the distance of 12. FIG. 2 shows a semiconductor laser 10
1. This is a diagram of photodiodes 103a and 103b viewed from the glass substrate 105 side, and analyzers 104a and 104b.
is omitted. When the recording medium 112 is at the focused position of the objective lens, the image of the returned light on the photodiode becomes a circle of least confusion. The photodiode 113a is divided into four parts as shown in Fig. 2, and the output voltages of each division A, B, C, and D are set to V(A), V(B), V(C), and v(D). (A) +V (C) -V (B) -V (
A focus error signal can be obtained from D).

On the other hand, when detecting a tracking error signal, it is obtained from V(A)-V(C) at the photodiode 103a, or from the other photodiode 10.
3b may be divided into two as shown by the broken line in FIG. 2, and detection may be made from the difference signal.

The objective lens 109 is driven by the lens actuator 116 based on the error signal obtained in this way, and the focused spot 120 is controlled so as to be always on the desired track and on the surface of the recording medium. In this embodiment, it has been described that the focus error signal is obtained by the astigmatism method, but it may be obtained by other methods such as the Foucault method by changing the pattern of the diffraction grating lens.

Now, the divergent light 110 from the semiconductor laser 101 that has passed through the diffraction grating lens 106 is converted into parallel light by the Fresnel lens 107. The far-field image of the emitted light from the junction type semiconductor laser is elliptical with its long axis in the direction perpendicular to the junction surface.
The Fresnel lens 107 is placed with its cemented surface perpendicular to the plane of the paper.
is an elliptical pattern as shown in FIG. 3, and its long axis direction is arranged parallel to the recording medium 112.

The diffraction grating lens 106 can be formed by coating one surface of the glass substrate 105 with photoresist, exposing it to ultraviolet light through a photomask on which a grating pattern is drawn, and etching the glass after development. On the other hand, the Fresnel lens 107 calculates an interference pattern that converts the diverging light from the semiconductor laser 101 into parallel light, and draws it on the resist coated on the glass substrate 105 with an electron beam or laser beam, and increases efficiency. For this reason, it can be formed by blazing and etching the glass using this resist as a mask. In addition, a master of the diffraction grating lens and Fresnel lens is made by the above method, a stamper is made by copying the shape by electroforming, etc., and a stamper is pressed onto the resin coated on the glass substrate 105 to form the diffraction grating lens 106 and Fresnel lens. The shape of 107 may be transferred.

Note that a Fresnel lens may be formed on the semiconductor laser side surface of the glass substrate 105, and a diffraction grating lens may be formed on the other surface. Further, the transparent substrate is not limited to a glass substrate.

The cross section of the light beam made parallel by the Fresnel lens 107 is elliptical as shown in FIG. 4 402, and the ratio of the long axis to the short axis is about 3:1, corresponding to the far-field pattern of the semiconductor laser. In the diffraction grating mirror 401 whose cross section is shown in FIG.
In order to make this elliptical light beam incident on the pair of lenses 109, it is necessary to bend the optical path at right angles and make it into a circular light beam 403, and the blazed linear diffraction grating has an inclination θ of approximately 19 It is formed on a slope of °. This slope is
It may be one surface of a prism polished into a wedge shape, or a diffraction grating may be formed on a parallel plate and the parallel plate may be arranged at an angle. The period of the diffraction grating is about 1.3 μm, and the blaze angle θB is about 266.

A1 is deposited on the surface of the diffraction grating.

The light reflected by the diffraction grating mirror 108 is transferred to the objective lens 1
09, the light is focused on the recording medium 112 made of a magnetic film through the disk substrate 113, and information is recorded by reversing the direction of the magnetic field applied to the recording medium by the magnetic field applying means 114.

On the other hand, when reproducing information, it is detected that the polarization plane of reflected light from the recording medium rotates in different directions depending on the direction of recorded magnetization.

The light that has returned from the objective lens 109, the diffraction grating mirror 108, and the Fresnel lens 107 is incident on the diffraction grating lens 106, and the first-order diffracted light and the first-order diffracted light are incident on photodiodes 103a and 103b, respectively.

An analyzer 104a is installed in front of each photodiode.
, 104b are attached. As shown in FIG. 5 when the semiconductor laser 101 and the analyzers 104a and 104b are viewed from the glass substrate 105 side, the transmission axes 502 of the analyzers 104a and 104b are orthogonal to each other, and the semiconductor laser 101
45'' with respect to the polarization plane 501 of the emitted light.

Therefore, the total sum signal V (A) +v (B) +V (C) + of the photodiode 103a divided into four.
By obtaining the difference signal between V(D) and the signal from the photodiode 103b, the polarization plane 501 by the recording medium is
The direction of 0 rotation can be detected. Photodiode 103b
If the total sum signal is divided, the total sum signal may be subtracted from the total sum signal of the photodiode 103a.

The above-mentioned elements are arranged in the housing 118, and when moving to a desired track, the entire cylinder is moved (121) by a voice coil motor or the like (not shown).

Although the embodiment has been described above, the light flux running inside the optical head is
The thickness of the optical head is approximately one-third that of the conventional one, allowing the optical system to be made thinner, and a semiconductor laser, a photodiode with an analyzer placed on the front, a diffraction grating lens, and a Fresnel lens are formed. The glass substrate is housed in one package, making it easy to assemble the optical head.

Embodiment 2 FIG. 6 is a main sectional view showing a second embodiment of the optical head of the present invention. The same elements as in the first embodiment are given the same numbers.

A diffraction sacrificial mirror 108, an objective lens 109, and a lens actuator 116 are arranged in a housing 601. The housing 601 is separated from a package 119 that includes a semiconductor laser, a photodiode, and the like. Since parallel light from the Fresnel lens 107 enters the diffraction grating mirror 108, in order to move the focused spot 120 to a desired track, the package 119 should be fixed and only the casing 601 (not shown) may be moved (602) using a voice coil motor or the like. In this case, the weight to be moved is lighter than in the first embodiment by the weight included in the package 119 and the casing 118, so high-speed access is possible.

Since the optical functions are the same as those in Example 1, the explanation will be omitted.

Embodiment 3 FIG. 7 shows a third embodiment of the optical head of the present invention, in which FIG. 7(a) shows a planar configuration seen from the recording medium side, and FIG. 7(b) shows a recording head. A main cross section is shown that also includes the disk substrate on which the media is formed.

The only difference from Example 1 is the configuration of the semiconductor laser and photodiode, so only that part will be explained, and the functions of the diffraction grating lens, Fresnel lens, diffraction grating mirror, objective lens, etc. are the same, so the explanation will be omitted. . Elements similar to those in Example 1 are numbered the same as in Example 1.

A semiconductor laser 70 is mounted on a Si substrate 701 on which photodiodes 703a and 703b are formed by pin junction.
The element on which 2 is directly formed is housed in a package 119. This element will be explained in detail with reference to FIG.

Photodiodes 703a and 703b are formed on the Si substrate 701 by pin junction, and the photodiode 703a is divided into four regions. This is to obtain a focus error signal and a tracking error signal, as described in the first embodiment. In order to obtain a tracking error signal, a photodiode 703b
may be divided into two.

A semiconductor laser 702 is formed by forming a T11 layer of a compound semiconductor film on a Si substrate 701 and then etching it. A mirror 801 having an angle of 450 is formed by taper etching, and reflects the light emitted from the semiconductor laser in a direction perpendicular to the substrate.

At this time, the direction of the polarization plane of the light emitted from the semiconductor laser is 5
01 direction.

Surface 80 of semiconductor laser 702 opposite to mirror 801 side
A total reflection mirror is formed in 2, and a photodiode 703
Make sure that no light leaks into b. Note that the photodiodes 703a and 703b are arranged offset from the extension line of the resonator of the semiconductor laser 702 so that they will not be affected by light from the end face of the semiconductor laser, and The grating pattern of the diffraction grating lens 106 may be designed.

On the surfaces of the photodiodes 703a and 703b, an eighth
Although shown in broken lines in the figure, analyzers 704a and 704b are attached, and their respective transmission axes 502 are perpendicular to each other, and the direction 50 of the polarization plane of the light emitted from the semiconductor laser 702 is
1 and each form an angle of 450. The method of detecting a signal from a recording medium using this configuration is described in the first embodiment.

As described above, by forming a semiconductor laser and a photodiode on the same substrate, the elements included in the package 119 include a photoelectric conversion element that integrates a semiconductor laser and a photodiode, a diffraction grating lens 106, and a Fresnel lens 107. There are only two integrated lens elements.

Note that the substrate on which the semiconductor laser is integrated is not limited to Si, and may be a compound semiconductor substrate. Also,
The structure of the semiconductor laser is not limited to the structure of this embodiment, and any structure may be used as long as it emits light whose far-field pattern is close to an ellipse in a direction perpendicular to the substrate. At this time, if the polarization ratio of the light emitted from the semiconductor laser is small, a polarization element may be inserted in front of the semiconductor laser to increase the polarization ratio of the light irradiated onto the recording medium. Furthermore, as the analyzer disposed in front of the photodiode, one in which a dielectric multilayer film is laminated on the surface of the photodiode may be used.

Embodiment 4 FIG. 9 is a main sectional view showing a fourth embodiment of the optical head of the present invention.

The functions are the same as in the second embodiment except that the semiconductor laser and the photodiode are integrated as described in the third embodiment using FIG. 8, and the diffraction grating mirror 108
, only the gator body 601 including the objective lens 109 and the lens actuator 116 is moved by the voice coil motor (602
), the access time can be shortened.

Although the embodiments have been described above, the present invention can also be applied to optical heads of devices that perform recording or reproduction using light, other than magneto-optical recording and reproducing devices, by removing the analyzer and changing the arrangement of the photodiodes. It is possible.

[Effects of the Invention] As described above, according to the present invention, an elliptical Fresnel lens is used as a collimator lens, and a diffraction grating separates reflected light from a recording medium from an optical axis from a semiconductor laser and guides it to a photodiode. Effectively utilizes the power of light from a semiconductor laser by forming lenses on both sides of a single transparent substrate and collimating the light using a collimator lens and making it incident on the objective lens using a diffraction grating mirror that utilizes Bragg reflection. At the same time, the light flux running inside the optical head becomes flat in an elliptical shape, making the thickness of the optical head 3 times smaller than that of the conventional one.
It has the effect that it can be reduced to about one-fold.

In addition, by putting a semiconductor laser and a photodiode with an analyzer on the front in the same package, and using the transparent substrate on which the Fresnel lens and the diffraction grating lens are formed as the window of the package, it becomes easier to assemble the optical head. By keeping the package fixed and moving only the two components, including the diffraction grating mirror, objective lens, and lens actuator, using a voice coil motor, etc., the weight to be moved is reduced, and access time can be shortened. have

Furthermore, by forming the semiconductor laser on the same substrate as the photodiode, there is also the effect that there is no need to mount the semiconductor laser and photodiode separately.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a first embodiment of the optical head of the present invention. FIG. ) is a main sectional view including the disk substrate on which the recording medium is formed. FIG. 2 is a diagram illustrating a method for dividing a photodiode and detecting an error signal in the first embodiment of the optical head of the present invention. FIG. 3 is a diagram showing a planar pattern of a Fresnel lens used in the optical head of the present invention. FIG. 4 is a sectional view of a diffraction grating mirror used in the optical head of the present invention. FIG. 5 is a diagram showing the arrangement of analyzers in the optical head of the present invention. FIG. 6 is a diagram showing a second embodiment of the optical head of the present invention, and is a main sectional view including a disk substrate on which a recording medium is formed. FIG. 7 is a diagram showing a third embodiment of the optical head of the present invention, and FIG. 7(a)
7(b) is a main configuration diagram as seen from the recording medium side, and FIG. 7(b) is a main sectional view including the disk substrate on which the recording medium is formed. FIG. 8 is a perspective view of an integrated element of a semiconductor laser and a photodiode used in the third and fourth embodiments of the optical head of the present invention. FIG. 9 is a diagram showing a fourth embodiment of the optical head of the present invention, and the main cross section 101...102...103a also includes the disk substrate on which the recording medium is formed. 1 0 4 a. 105 ... 106 ... 107 ... 108 river 109 ... 110 ... 1 1 1 a. 112 ... 113 ... 114 ... 115 ... 116 ... 117 ... 118 ... 119 ... Semiconductor laser heat sink 103b ... 104b ... Analyzer glass substrate diffraction grating lens Fresnel lens Diffraction grating mirror Objective lens Semiconductor laser emitted light 111b ... Diffractive optical recording medium disk substrate Magnetic field applying means Spindle Lens actuator Terminal housing package Photodiode 120 ... Focusing slot 121 ... Housing moving direction 201. 202...Light amount distribution A, B, C, D...Photodiode dividing element 401.402...Light beam cross-sectional shape 501...Semiconductor laser output light polarization plane 502...
-Analyzer transmission axis 601...Housing 602...Housing moving direction 701...Si substrate 702...Semiconductor lasers 703a, 703b...Photodiode 70
4a, 704b...Analyzer 801...Mirror 802...End face or above Applicant Seiko Epson Co., Ltd. Agent Patent attorney Kizobe Suzuki and one other person Figure 5 Figure 8

Claims (5)

[Claims] (1) A semiconductor laser, an objective lens that focuses light from the semiconductor laser onto a recording medium, a light-receiving element with an analyzer placed on the front surface, and a transparent element in the optical path from the semiconductor laser to the objective lens. an elliptical Fresnel lens formed on one surface of the substrate for converting diverging light having an elliptical far-field pattern from the semiconductor laser into parallel light; and an elliptical Fresnel lens formed on the other surface of the transparent substrate for converting the diverging light having an elliptical far-field pattern from the semiconductor laser into parallel light. An optical head comprising: a diffraction grating lens that branches reflected light from a medium toward the light receiving element; and a diffraction grating mirror that reflects parallel light from the Fresnel lens and causes it to enter the objective lens. . (2) A claim characterized in that a semiconductor laser and a light receiving element with an analyzer arranged on the front are in the same package, and a transparent substrate on which a Fresnel lens and a diffraction grating lens are formed is a window of the package. Item 1. The optical head according to item 1. (3) The optical head according to claim 2, wherein the cross-sectional shape of the package in the direction perpendicular to the optical axis is not circular. (4) The optical head according to claim 1, 2, or 3, wherein only the housing including the diffraction grating mirror and the objective lens is movable. (5) A claim characterized in that the semiconductor laser has a structure in which light emitted from the semiconductor laser exits in a direction perpendicular to the substrate, and is formed on the substrate on which a light receiving element is formed. An optical head according to claim 1, claim 2, claim 3, or claim 4.