JPH05144113A - Optical head - Google Patents

Abstract

PURPOSE:To constitute the optical head including a light separating function to a small size and thin type so that focusing and tracking correction are enabled over the entire part. CONSTITUTION:A flat plate material 11 essentially consisting of a glass substrate 13 and a substrate 12 are provided nearly in parallel as the constitution of the optical head. A luminous flux B0 emitted from a semiconductor laser is reflected by a polarizing film 14 and is sent to an objective lens. The return light B01 from the objective lens is transmitted through a wavelength plate 15, by which the plane of polarization is rotated 45 deg.. This light is reflected by a reflection surface 31 and is separated by a polarizing film 16, a phase difference plate 17 and a total reflection surface 18 to light R1 of an S wave component, light R2 of a P wave component and light R0 which does not depend on the polarization state. An MO signal is reproduced by taking the difference in the outputs between PIN photodiodes 32a and 32b. The error signal of focus, etc., is obtd. by the output of a PIN photodiode 32c.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head used in a magneto-optical disk device and other optical disk devices, and more particularly to a compact and lightweight optical head that can be driven together with correction.

[0002]

2. Description of the Related Art In a magneto-optical disk device, polarization separation is performed in order to obtain a reproduction output, and the return light from the disk has two light components for detecting a polarization component depending on the Kerr rotation angle and a focus and the like. And an optical signal for detecting an error signal for detecting the error signal of.

FIG. 9 shows a structure of an optical system for a magneto-optical disk device using a conventional polarization separation means. The laser light emitted from the semiconductor laser 1 is collimated by the collimator lens 2, is reflected by the beam splitter 3, is reflected by the total reflection prism 4, and is condensed on the recording surface of the disc D by the objective lens 5. Reflected return light from the recording surface of the disk D returns through the objective lens 5 and the total reflection prism 4, passes through the beam splitter 3, is separated into three light components by the Wollaston prism 6, and is received by the light receiving lenses 7a and 7b. Then, the light is received by the 6-divided pin photodiode 8. The two light beams B1 and B2 separated into different polarization components (P-wave component and S-wave component) by the Wollaston prism 6 are two light receiving portions 8a of the pin photodiode 8.
And 8b, and the Kerr rotation direction is detected from the difference between the amounts of the received light and the MO signal is obtained. Further, the light beam B3 which does not depend on the polarization is received by the four-divided light receiving portion 8c, whereby the focus and tracking error signals are obtained.

[0004]

The above-mentioned conventional optical system has the following problems. (1) In the conventional optical system described above, the number of parts is large because the optical parts are provided independently of each other, and the optical path length is long as a whole. Since the optical system is composed of a large number of parts and has a long optical path length, the entire optical system cannot be mounted on the movable system, and the optical parts have to be separated into a fixed system and a movable system. .. For example, if all of the optical system shown in FIG. 9 is housed in an optical head and the entire optical head is moved along the recording surface of the disk, the weight of the whole becomes too large, and the whole of the focus correction direction or It becomes impossible to drive in the tracking correction direction. Therefore, when the entire optical system is housed in the optical head, it is necessary to drive only the objective lens 5 in each of the focus and tracking correction directions in the optical head. However, in this case, when the objective lens 5 is driven in the tracking correction direction,
Since the optical axis of the light reflected by the total reflection prism 4 and the optical axis of the objective lens 5 deviate from each other, the light receiving portion 8c divided into four parts.
The spot of the returning light coupled to the top deviates from the center of the light receiving portion 8c, and this causes a tracking error signal, which causes a state in which highly accurate tracking error detection cannot be performed.

Further, for example, the optical component shown in (a) is mounted on the optical head and only this portion is moved along the disk, and the optical component shown in (b) is provided on the fixed side. It is conceivable to form an optical path in the space between the beam splitter 3 and the total reflection prism 4, but in this case as well, the optical axis of the objective lens 5 and (b There is a deviation between the optical axis of the fixed optical system and the optical axis of the fixed optical system, and the same problem as described above occurs.

(2) In the optical system shown in FIG. 9, the Wollaston prism 6 is used as an element for polarization separation. However, since the Wollaston prism 6 is manufactured by using two anisotropic crystals such as quartz and bonding them together, the manufacturing cost is high.

The present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide an optical head which can be made compact and thin as a whole and in which all elements can be corrected and driven together. There is.

[0008]

An optical head according to the present invention includes a light emitting element, an objective lens facing a recording medium, and detection light from the light emitting element reflected in the direction of the objective lens and reflected from the recording medium. The partial reflection member that transmits the return light that has passed through the objective lens, the reflection surface that reflects the return light that has passed through the partial reflection member, the flat plate member on which the light reflected by the reflection surface is incident, and the portion A polarizing member, which is located on the path of light that passes through the reflecting member and is reflected by the reflecting surface and is incident on the flat plate member, for rotating the polarization plane of the light on this path by a predetermined angle, A light splitting unit that splits the light incident on the flat plate member into orthogonal coordinate components sandwiching the plane of polarization rotated by the polarizing member, and a light receiving element that receives each light component split by this light splitting unit. What is kicked is characterized in.

In the above structure, the partial reflection member is formed on the flat plate member, and the reflection surface for reflecting the return light transmitted through the partial reflection member and the light receiving element for receiving the respective light components are on the same substrate. The flat plate material and the substrate are arranged substantially parallel to each other,

Further, the light emitting element, the objective lens, the flat plate material, and the substrate are driven together for correction, and the irradiation state of the detection light sent to the recording medium is corrected by this correction driving.

[0011]

In the above means, the detection light emitted from the light emitting element is reflected by the partial reflection member and condensed by the objective lens to form a spot on the disk recording surface. The return light from this disc passes through the partial reflection member, is reflected by the reflection surface, and enters the flat plate member. By the time of returning to this flat plate material, the plane of polarization of light is rotated by, for example, 45 degrees by the polarizing member,
The light whose plane of polarization has been rotated is separated into light having different coordinate components by the light separating portion of the flat plate material. The Kerr rotation information of the polarization plane of the light is read by receiving each of the separated lights and determining the difference between the received lights.

Further, the partial reflection member is provided on the flat plate member, the reflecting surface and each light receiving element are provided on the same substrate, and the substrate and the flat plate member are provided in parallel, so that the entire head can be made thin, small and lightweight. The flat plate material, the substrate, the light emitting element, and the objective lens can be corrected and driven together in the focusing and tracking directions.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a component diagram showing a basic embodiment of an optical head according to the present invention, and FIG. 2 is an enlarged sectional view of a flat plate material used in the optical head of FIG. In FIG. 1, reference numeral 10 is the main body of the optical head. The main body 10 is supported by an elastic support member (not shown) so as to be finely movable in the focus correction and tracking correction directions.
A magnetic drive circuit is provided between the magnetic drive circuit and a fixed portion supporting the elastic support member via the elastic support member, and the magnetic drive circuit finely drives the main body 10 in the respective correction directions of focus and tracking. Is becoming

Inside the main body 10, a flat plate material 11 and a substrate 12 are provided.
And are provided in parallel. As shown in FIG. 2, a portion on the left side of the flat plate material 11 in the drawing is a processing unit 11A for returning light,
The portion on the right side of the drawing is the light separating section 11B. The central portion of the flat plate material 11 is a glass substrate 13 having a predetermined thickness. In the return light processing unit 11A, a polarizing film 14 is formed on the surface of the glass substrate 13 as a partial reflection member. The polarizing film 14 is configured so as to reflect an incident S-polarized wave (the plane of polarization of which is indicated by symbol S in FIG. 2) by 80%, and the P-polarized wave is hardly reflected. A half-wave plate (plate-shaped or film-shaped) 15 is formed on the back surface of the glass substrate 13 in the return light processing unit 11A. This one
The polarization direction of the light transmitted through the / 2 wavelength plate 15 is rotated by 45 degrees.

In the light separating section 11B, the polarizing film 16 is coated on the back surface side of the glass substrate 13. A retardation plate 17 is attached to the surface of the glass substrate 13, and a total reflection film 18 is coated on the surface thereof. The retardation plate 17 has a λ / 4 (or 5λ / 4,
A phase difference of 9λ / 4 (where λ is the wavelength of incident light) is generated. Therefore, the light that passes through the retardation plate 17, is reflected by the total reflection film 18, returns, and further passes through the retardation plate 17 by passing through the retardation plate 17 twice ((λ / 2) × (1 + 2n ) (Where n is 0,
1, 2, ...) and a polarization plane angle of 90
Can be rotated once. Therefore, by reciprocating through the phase difference plate 17, the P wave component of light becomes an S wave component, and the S wave component becomes a P wave component. The phase difference plate 17 may be one that causes a phase difference of λ / 2 or the like in the light only when the light passes through the phase difference plate twice.

In FIG. 2, the α-β orthogonal coordinate is taken with the α-axis being the vertical direction of the paper and the β-axis being the direction orthogonal to the paper.
The component of light whose polarization plane is in the α direction is the P wave component, and the polarization plane is β
The component of the light that becomes the direction is the S wave component. In addition, flat plate material 11
The angle of incidence of the incident optical axis B on is θ. The incident angle θ is approximately Brewster's angle, and is set to about 60 degrees when the flat glass 11 has a refractive index of 1.51, for example. Due to the Brewster angle θ and the design of the polarization film 16, 100% of the P wave component is transmitted, 60% of the S wave component is transmitted, and 40% of the S wave component is reflected to the polarization film 16. Is set. This ratio can be set arbitrarily.

As shown in FIG. 1, a semiconductor laser chip 21 is provided inside the main body 10 so as to face the surface of the flat plate member 11. The chip 21 is supported by a support 22 and a heat dissipation plate 23 is attached. The main body 10 has an objective lens 24 facing the recording surface D1 of the magneto-optical disk D.
Is fixed. The objective lens 24 receives the laser light emitted from the semiconductor laser chip 21 from the polarizing film 14.
The laser light emitted from the semiconductor laser chip 21 is reflected by the polarizing film 14 and is focused on the recording surface D1 of the disc D by the objective lens 24 to form a minute spot. It is formed.

The substrate 12 faces the back side of the flat plate material 11 substantially in parallel with the air layer (a) in between. This board 1
On the surface of 2, the reflecting surface 31 for reflecting the laser light transmitted through the flat plate material 11, and the pin photodiodes 32a, 3 for receiving the light separated by the light separating section 11B of the flat plate material 11 are provided.
2b and 32c are provided. FIG. 5 is a plan view of the pin photodiodes 32a, 32b, 32c as viewed from the flat plate material 11 side. Pin photodiodes 32a and 32b are M
This is for obtaining the O signal, and the light receiving outputs from the pin photodiodes 32a and 32b are amplifiers 33a and 33b.
Is amplified and converted into a current / voltage, and a differential output (IJ output) is obtained by the differential amplifier 34. The central pin photodiode 32c is for obtaining a tracking error signal and a focus error signal, and is composed of four-divided light receiving portions.

The operation of the optical head in the above embodiment will be described. As shown in FIG. 2, the S-wave component of the laser light flux B0 emitted from the semiconductor laser chip 21 is used. 80% of this S-wave component is reflected by the polarizing film 14 of the flat plate material 11, is condensed by the objective lens 24, and a minute spot is formed on the recording surface D1 of the magneto-optical disk D. The P wave component of the laser beam B0 is the polarization film 1
The light is hardly reflected by 4, and passes through the glass substrate 13 to proceed in a direction unrelated to the substrate 12. The return light (S-polarized wave) B01 given the Kerr rotation by the recording surface D1 is the polarization film 14
Through the glass substrate 13 and the half-wave plate 15 to reach the air layer (a). The polarization plane of the return light B01 is rotated by 45 degrees by passing through the half-wave plate 15.

That is, FIG. 3 shows III-II in FIG.
It is an explanatory view seen from the direction of arrow I. In the return light B01 from the recording surface D1 of the disk D, the Kerr rotation angle θK is given in the positive direction or the negative direction with respect to the S polarized wave (the Y-axis direction is the polarization plane). There is. The return light B01 is transmitted through the half-wave plate 15 so that the plane of polarization is rotated by 45 degrees and further reflected by the reflection surface 31 to become a light beam B. As shown in FIG. 4 (IV-IV arrow explanatory view of FIG. 2), since the polarization plane (for example, the Y axis) of the light flux B is rotated by 45 degrees, the S wave component and the P wave component are Y It is represented by α-β coordinates parallel and orthogonal to the plane of the paper of FIG. 2 as orthogonal coordinates with the axis sandwiched therebetween. The P axis of the light given the Kerr rotation of θK in the α-axis direction
The wave component is the S wave component of the light given the Kerr rotation of θK in the β-axis direction. In the light separating section 11B, the flat plate material 11
The incident light flux B for is separated into a P wave component and an S wave component,
It functions to send each of these to the pin photodiodes 32a and 32b.

Here, the light separating function when the incident light beam B whose polarization plane is rotated by 45 degrees is incident on the light separating portion 11B of the flat plate material 11 will be described. In the incident light flux B incident at the incident angle θ, 40% of the S wave component is reflected by the polarizing film 16 and 60% thereof is transmitted. Further, 100% of the P wave component is transmitted through this polarizing film 16. That is, the polarizing film 16 reflects only 40% of the S-wave component of the incident light. In FIG. 2, this reflected light is indicated by R1. The S wave component of 60% and the P wave component of 100% transmitted through the polarizing film 16 are transmitted through the glass substrate 13 and the phase difference plate 17, and are further reflected by the total reflection film 18 to be reflected again by the phase difference plate 17. Return transparently. The reflected light that travels back and forth in the glass substrate 13 through the phase difference plate 17 once becomes a 100% S-wave component and a 60% P-wave component by rotating the polarization plane by 90 degrees.

This light reaches the polarizing film 16 again, but in the polarizing film 16, 40% of the S wave component is reflected and 60% is transmitted. However, the P wave component is not reflected and all of it passes through the polarizing film 16. Therefore, the light transmitted through the polarizing film 16 is
Both light has 60% P-wave component and S-wave component and does not depend on the polarization state. In FIG. 2, the light component that does not depend on the polarization state is indicated by R0. The 40% S-wave component reflected by the polarizing film 16 and returning to the inside of the glass substrate 13 is transmitted through the phase difference plate 17, reflected by the total reflection film 18, transmitted through the phase difference plate 17, and is transmitted through the glass substrate 11. Proceed to. Here, since the phase difference plate 17 is reciprocated once, 40% of the S wave component becomes a P wave component. The 40% P-wave component is entirely transmitted through the polarizing film 16. This transmitted light is indicated by R2 in FIG.

The 40% S-wave component light R1 is detected by the pin photodiode 32b, and the 40% P-wave component light R2 is detected by the pin photodiode 32a. The received light output from each of the pin photodiodes 32a and 32b is input to the differential amplifier 34. Differential amplifier 3
At 4, the difference between the light receiving outputs from the pin photodiodes 32a and 32b (the difference between the I output and the J output) is detected, and this is the reproduction output (MO signal) from the magneto-optical disk. That is, the difference between the received light output of the P wave component and the received light output of the S wave component in FIG. 4 is obtained by this differential output, and the direction of the Kerr rotation angle θK of the polarization plane of the return light from the disc is detected as the reproduction information. You can do it.

Further divided into four pin photodiodes 32c
Is located at the focal point of the light R0 which does not depend on the polarization state and has both S-wave component and P-wave component of 60%. A tracking error signal can be obtained. The focused light R0 passes through the flat glass substrate 13 and is reflected, so that an astigmatic difference occurs. By utilizing this astigmatic difference, it is possible to obtain the focus error signal by the astigmatism method by the four-division light receiving section. Further, the tracking error signal can be detected by a so-called push-pull method by obtaining a differential output of the sum of the light reception outputs of two light receiving portions of the four-divided light receiving portions in the pin photodiode 32c.

FIG. 6 shows another example of the structure of the light separating section 11B of the flat plate material 11. Light splitting portion 11 shown in this embodiment
B is two flat glass sheets 13a and 13 having the same thickness t.
The phase difference plate 17 is interposed between b. The plane of incidence of the flat glass 13a is coated with the polarizing film 16, and the plane of the flat glass 13b is covered with the total reflection film 18.
Is coated. Similar to the embodiment shown in FIG. 2, the phase difference plate 17 allows the light to pass through twice, resulting in λ / 2.
And a plane of polarization is rotated by 90 degrees.

Also in this light separating section 11B, the polarizing film 1
40% of the S wave component is reflected by 6, and the light component of R1 is obtained. Further, the 100% P wave component and the 60% S wave component transmitted through the polarizing film 16 are reflected by the total reflection film 18 and reciprocate the phase difference plate 17 once to make 60% P wave component and 100% of the P wave component. It becomes an S wave component. Then, the light R0 that does not depend on the polarization of the S wave component and the P wave component of 60% is obtained. Further, 40% of the S wave component reflected by the polarizing film 16 is reflected by the total reflection film 18 and reciprocates through the phase difference plate 17 to obtain 4
It becomes 0% P wave component, which passes through the polarizing film 16 and becomes R
2 is obtained. In the light separating section 11B, the two flat glass plates 13a and 13b do not necessarily have the same thickness dimension, but the same thickness dimension facilitates the manufacture.

FIG. 7 shows a further simplified structure of the light separating section 11B. Light splitting section 1 shown in this embodiment
1B uses an anisotropic crystal such as quartz crystal, and the retardation plate 17a has a thickness dimension T that can generate a phase difference of λ / 2 by passing the transmitted light back and forth (twice). It is used. The polarizing film 16 is directly coated on the incident side surface of the retardation plate 17a, and the total reflection film 18 is directly coated on the other surface. In this embodiment, the polarizing film 16 is 10
0% P wave component and 60% S wave component are transmitted. This transmitted light is transmitted through the phase difference plate 17a, reflected by the total reflection film 18 and again transmitted through the phase difference plate 17a, so that the plane of polarization is rotated by 90 degrees, and when it returns to the polarization film 16, it is 1
The S wave component is 00% and the P wave component is 60%. Then, 60% of the S wave component and the P wave component are both transmitted through the polarizing film 16 to obtain the light R0. Further, the 40% S-wave component reflected by the polarizing film 16 travels back and forth through the phase difference plate 17a to become a P-wave component, which passes through the polarizing film 16 and becomes 40% P-wave.
Wave component light R2 is obtained. The present invention is not limited to each of the above-described embodiments. For example, in the embodiment of FIG. 2, the polarizing film 16, the retardation film 17, the glass substrate 13, and the total reflection film 18 are sequentially arranged from the incident side of the light separating section 11B. You may comprise in order.

Further, FIG. 8 shows another embodiment.
In this embodiment, the half-wave plate 15 is not provided on the lower surface side of the return light processing portion 11A of the flat plate material 11, and instead the reflecting surface 31a of the substrate 12 has a reflecting function. It has a function of rotating the plane of polarization by 45 degrees.
The structure of the light separating section 11B is the same as that of the embodiment shown in FIG. The half-wave plate 15 may be provided separately from the flat plate material 11 or the substrate 12, and the half-wave plate 15 may be arranged in a portion of the air layer (a) where the light flux B02 or B passes. Good. Further, in each of the above embodiments, the reflecting surface 31 is provided on the substrate 12, but the reflecting surface may be formed of a coating layer that covers the pin photodiodes 32a to 32c. Note that 11A of the flat plate material 11 in the present invention
Part and 11B part may be separated, in that case,
11A and 11B do not have to be located in the same plane.

[0029]

According to the present invention described in detail above, a compact and lightweight optical head can be obtained. Further, the optical head according to the present invention can be applied to not only a magneto-optical disk but also a compact disk, a phase change disk and the like with the same head. Furthermore, because it can be made smaller and lighter,
Since the entire optical system can be corrected and driven, no offset occurs in the error signal. Further, since it is not necessary to consider the relative displacement between the objective lens and the light emitting element, not only the objective lens can be designed easily, but also the manufacturing tolerance can be widened.

[Brief description of drawings]

FIG. 1 is a component diagram showing a basic embodiment of an optical head according to the present invention.

FIG. 2 is an enlarged sectional view of the flat plate material shown in FIG.

FIG. 3 is an explanatory view taken along the line III-III of FIG.

4 is an explanatory view taken along the line IV-IV in FIG.

FIG. 5 is a plan view of a pin photodiode.

FIG. 6 is a cross-sectional view showing another embodiment of the flat plate material.

FIG. 7 is a cross-sectional view showing another embodiment of the flat plate material.

FIG. 8 is a cross-sectional view showing another embodiment of the flat plate material and the substrate.

FIG. 9 is a component layout view showing an optical device of a conventional magneto-optical disk device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Main body, 11 Flat plate material, 11A Return light processing part 11B Light separation part 12 Substrate 14 Polarizing film 15 1/4 wavelength plate 16 Polarizing film 17 Phase difference plate 18 Total reflection surface 31 Reflection surface 21 Semiconductor laser 24 Objective lens 32a, 32b, 32c pin photodiode

Claims (3)

[Claims] 1. A light-emitting element, an objective lens facing a recording medium, and detection light from the light-emitting element reflected in the direction of the objective lens, and return light transmitted from the recording medium and passing through the objective lens is transmitted. A partial reflection member, a reflection surface that reflects the return light transmitted through the partial reflection member, a flat plate member on which the light reflected by the reflection surface is incident, and a partial reflection member that is transmitted by the reflection surface and reflected by the reflection surface. And a polarizing member that is located on the path of the light incident on the flat plate material and rotates the plane of polarization of the light on this path by a predetermined angle; An optical head comprising: a light splitting unit that splits a rotated plane of polarization into orthogonal coordinate components and a light receiving element that receives each light component split by the light splitting unit. 2. The partial reflection member is formed on the flat plate member, and a reflection surface for reflecting return light transmitted through the partial reflection member and a light receiving element for receiving each light component are installed on a common substrate. 2. The optical head according to claim 1, wherein the flat plate material and the substrate are arranged substantially parallel to each other. 3. A light emitting element, an objective lens, a flat plate material,
The optical head according to claim 2, wherein the substrate and the substrate are correction-driven together and the irradiation state of the detection light sent to the recording medium is corrected by the correction driving.