JP2878510B2 - Light head - Google Patents

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 drive and other optical disk drives, and more particularly to an optical head which is reduced in size and weight so that the whole can be corrected and driven together.

[0002]

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

FIG. 9 shows the configuration of an optical system for a magneto-optical disk drive using a conventional polarization splitting means. Laser light emitted from the semiconductor laser 1 is converted into parallel light by a collimator lens 2, reflected by a beam splitter 3, reflected by a total reflection prism 4, and focused on a recording surface of a disk D by an objective lens 5. The return light reflected from the recording surface of the disk D returns via 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. , And is received by the six-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 converted into two light receiving portions 8a of the pin photodiode 8.
And 8b, and the Kerr rotation direction is detected from the difference between the two received light amounts to become an MO signal. The light beam B3, which does not depend on the polarization, is received by the four-divided light receiving portion 8c, whereby an error signal for focusing and tracking is obtained.

[0004]

The above-mentioned conventional optical system has the following problems. (1) In the above-mentioned conventional optical system, since the optical components are provided independently of each other, the number of components increases, and the optical path length becomes longer as a whole. As described above, since the optical system is constituted by a large number of components and has a long optical path length, the entire optical system cannot be mounted on the movable system, and the optical components must be separated into a fixed system and a movable system. . For example, if the entire optical system shown in FIG. 9 is housed in the optical head and the entire optical head is moved along the recording surface of the disk, the overall weight becomes too large, and the entire optical head is moved in the focus correction direction or the like. 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 are deviated, the light receiving unit 8c is divided into four parts.
The spot of the return light connected above is deviated from the center of the light receiving section 8c, which generates a tracking error signal, and a state occurs in which a tracking error cannot be detected with high accuracy.

[0005] Further, for example, the optical component of the portion shown in (a) is mounted on an optical head and only this portion is moved along the disk, and the optical component of the portion shown in (b) is provided on the fixed side. It is conceivable to form an optical path in space between the beam splitter 3 and the total reflection prism 4. In this case as well, when the tracking correction operation of the objective lens 5 is performed, the optical axis of the objective lens 5 and (b) A) occurs between the optical axis of the fixed optical system and the same problem as described above.

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

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide an optical head which can be configured to be small and thin as a whole, and which can correct and drive all the elements together. I have.

[0008]

According to the present invention, there is provided an optical head comprising: a light emitting element; an objective lens facing a recording medium;
Reflects detection light from the light emitting element toward the objective lens
And reflected from the recording medium and passed through the objective lens
Partial reflection member for transmitting return light, and this partial reflection member
Reflective surface that reflects the return light transmitted through
The partial reflection member is provided and transmitted through the partial reflection member.
The return light is transmitted to the reflection surface and further reflected by the reflection surface.
The reflected light is incident again, and the partial reflection
The light passes through the member and the flat plate, is reflected by the reflection surface, and is
On the path of light incident on
A polarizing member for rotating the plane of polarization of light by a predetermined angle;
The light that is formed on the flat plate and re-enters the flat
Cartesian coordinate components sandwiching the plane of polarization rotated by the optical member
A light separating unit for separating the light into a
Each light component placed and separated by the light separation unit
And a light receiving element for receiving the light.
The substrate is disposed substantially parallel to the substrate.
Things.

[0009]

[0010] Alternatively, in the above means , the light emitting element, the objective lens, the flat plate member, and the substrate are corrected and driven together, and the correction driving corrects the irradiation state of the detection light sent to the recording medium. It is.

[0011]

According to the present invention , 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 the disk is transmitted through the partial reflection member, is reflected by the reflection surface, and is incident on the flat plate. Before returning to the flat plate, the polarization plane of the light is rotated by, for example, 45 degrees by the polarizing member, and the light whose polarization plane is rotated is separated into light having different coordinate components by the light separation unit of the flat plate. The Kerr rotation information of the polarization plane of the light is read by receiving the separated lights and calculating the difference between the received light outputs.

[0012] Then, in the above first means, provided parts amount reflecting member in the flat plate, also provided with a reflecting surface and the light-receiving elements on the same substrate, by providing a substrate and a flat plate in parallel, the entire head Can be configured to be thin, small, and lightweight. Further , according to the second means, the flat plate and the substrate can be corrected and driven together with the light emitting element and the objective lens 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 configuration view 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 used in the optical head of FIG. In FIG. 1, reference numeral 10 denotes a 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 main body 10 and a fixed portion supporting the main body 10 via the elastic support member. The magnetic drive circuit allows the main body 10 to be finely driven in the respective correction directions of focus and tracking. Has become.

Inside the main body 10, a flat plate 11 and a substrate 12 are provided.
Are provided in parallel. As shown in FIG. 2, the left portion of the flat plate 11 in the drawing is a return light processing unit 11 </ b> A,
The portion on the right side in the figure is the light separating section 11B. The center of the flat plate 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 to reflect, for example, 80% of an incoming S-polarized wave (the plane of polarization of which is indicated by the symbol S in FIG. 2), and hardly reflect a P-polarized wave. A half-wave plate (plate or film) 15 is formed on the back surface of the glass substrate 13 in the return light processing unit 11A. This one
The light transmitted through the half-wave plate 15 has its polarization direction rotated by 45 degrees.

In the light separating section 11B, a polarizing film 16 is coated on the back side of the glass substrate 13. A retardation plate 17 is attached to the surface of the glass substrate 13, and the surface is coated with a total reflection film 18. The phase difference plate 17 is λ / 4 (or 5λ / 4,
9λ / 4) (where λ is the wavelength of the incident light). Therefore, the light transmitted through the phase difference plate 17, reflected by the total reflection film 18, returned, and further transmitted through the phase difference plate 17 passes through the phase difference plate 17 twice, so that (λ / 2) × (1 + 2n) ) (Where n is 0,
1, 2,...), And the angle of the polarization plane is 90
Rotated by degrees. Therefore, by reciprocating through the phase plate 17, the P-wave component of the light becomes the S-wave component, and the S-wave component becomes the P-wave component. The phase difference plate 17 may be one that causes a phase difference such as λ / 2 in light only when light passes through one of the two times of the phase difference plate.

In FIG. 2, orthogonal coordinates of α-β are taken with the α-axis being the vertical direction on the paper surface and the β-axis being the direction perpendicular to the paper surface.
The component of light whose polarization plane is in the α direction is a P-wave component, and the polarization plane is β
The component of the light in the direction is defined as an S-wave component. Also, the flat plate material 11
The angle of incidence of the incident optical axis B on the optical axis is θ. Is substantially Brewster's angle, and is set to about 60 degrees when, for example, the refractive index of the flat glass 11 is 1.51. By the Brewster angle θ and the design of the polarizing film 16, the P-wave component transmits 100%, the S-wave component transmits 60%, and the S-wave component 40% is reflected by the polarizing film 16. It is set as follows. This ratio can be set arbitrarily.

As shown in FIG. 1, a semiconductor laser chip 21 is provided in the main body 10 so as to face the surface of the flat plate 11. The chip 21 is supported by a support base 22 and has a heat sink 23 attached thereto. The main body 10 includes an objective lens 24 facing the recording surface D1 of the magneto-optical disk D.
Has been fixed. The objective lens 24 is provided with a laser beam emitted from the semiconductor laser chip
The laser light emitted from the semiconductor laser chip 21 is reflected by the polarizing film 14 and condensed on the recording surface D1 of the disk D by the objective lens 24, so that a minute spot is formed. It is formed.

The substrate 12 is substantially parallel to the back side of the flat plate 11 with an air layer (a) therebetween. This substrate 1
2, a reflection surface 31 for reflecting the laser beam transmitted through the flat plate 11 and pin photodiodes 32a and 3 for receiving the light separated by the light separating unit 11B of the flat plate 11.
2b and 32c are provided. FIG. 5 is a plan view of the pin photodiodes 32a, 32b, and 32c as viewed from the flat plate 11 side. The pin photodiodes 32a and 32b are M
The light receiving output from each of the pin photodiodes 32a and 32b is for obtaining an O signal.
And a current / voltage conversion, 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 sections.

Next, 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 beam 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 and condensed by the objective lens 24 to form a minute spot 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
4 and is transmitted through the glass substrate 13 in a direction unrelated to the substrate 12. The return light (S-polarized wave) B01 that has been subjected to Kerr rotation by the recording surface D1 is
Through the glass substrate 13 and through the half-wave plate 15 to reach the air layer (a). By passing through the half-wave plate 15, the polarization plane of the return light B01 is rotated by 45 degrees.

That is, FIG. 3 is a sectional view taken along the line III-II in FIG.
Although it is an explanatory view as viewed in the direction of the arrow I, in the return light B01 from the recording surface D1 of the disk D, the Kerr rotation angle θK is given in a positive or negative direction with respect to the S-polarized wave (the Y-axis direction is a polarization plane). I have. When this return light B01 passes through the half-wave plate 15, the plane of polarization is rotated by 45 degrees and further reflected by the reflection surface 31 to become a light flux B. As shown in FIG. 4 (an explanatory view taken in the direction of arrows IV-IV in 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 It is represented by α-β coordinates parallel and orthogonal to the plane of FIG. 2 as orthogonal coordinates sandwiching the axis. The α-axis direction is the P of the light given the Kerr rotation of θK.
The β-axis direction is an S-wave component of light given Kerr rotation of θK. In the light separating section 11B, the flat plate 11
Is separated into a P-wave component and an S-wave component,
Each of these functions functions to be sent 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 enters the light separating portion 11B of the flat plate 11 will be described. In the incident light beam B incident at an incident angle θ, the S film component is reflected 40% by the polarizing film 16 and transmitted by 60%. The polarizing film 16 transmits 100% of the P-wave component. That is, the polarizing film 16 reflects only the S-wave component of 40% of the incident light. In FIG. 2, this reflected light is indicated by R1. The 60% S-wave component and the 100% P-wave component transmitted through the polarizing film 16 pass through the glass substrate 13 and pass through the phase difference plate 17, are further reflected by the total reflection film 18, and pass through the phase difference plate 17 again. Transparent back. The reflected light returning to the inside of the glass substrate 13 after going back and forth through the phase difference plate 17 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 the polarizing film 16 reflects 40% of the S-wave component and transmits 60%. However, the P-wave component is not reflected, and all of the P-wave component passes through the polarizing film 16. Therefore, the light transmitted through the polarizing film 16 is
In both cases, the 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 returned to the glass substrate 13 again passes through the phase difference plate 17, is reflected by the total reflection film 18, passes through the phase difference plate 17, and passes through the glass substrate 11. Proceed to. Here, since the phase plate 17 makes one reciprocation, the S wave component of 40% becomes the P wave component. All of the 40% P-wave components pass through the polarizing film 16. This transmitted light is indicated by R2 in FIG.

The light R1 of the S-wave component of 40% is detected by the pin photodiode 32b, and the light R2 of the P-wave component of 40% is detected by the pin photodiode 32a. Light-receiving outputs from the respective pin photodiodes 32 a and 32 b are input to a differential amplifier 34. Differential amplifier 3
In No. 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 becomes 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. You can do it.

Further, the pin photodiode 32c is divided into four parts.
Are located at the convergence point of the light R0 which does not depend on the polarization state and have the S-wave component and the P-wave component of 60%. The focus error signal and the focus error signal A tracking error signal can be obtained. The converged light R0 passes through the flat glass substrate 13 and is reflected, so that an astigmatic difference is generated. Using this astigmatism difference, a focus error signal based on the astigmatism method can be obtained by the four-divided light receiving unit. 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 receiving outputs of two of the four light receiving units in the pin photodiode 32c.

FIG. 6 shows another example of the configuration of the light separating portion 11B of the flat plate material 11. As shown in FIG. Light splitting unit 11 shown in this embodiment
B denotes two flat glass plates 13a and 13a having the same thickness t.
The phase difference plate 17 is interposed between b. The polarizing film 16 is coated on the incident surface of the flat glass 13a, and the total reflection film 18 is coated on the front surface of the flat glass 13b.
Is coated. As in the embodiment shown in FIG. 2, the phase difference plate 17 transmits λ / 2
Is generated, and the plane of polarization is rotated by 90 degrees.

In the light separating section 11B, the polarizing film 1
6 reflects 40% of the S-wave component to obtain a light component of R1. 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 make one round trip on the phase difference plate 17, thereby forming the 60% P-wave component and the 100% It becomes an S wave component. Then, a light R0 that does not depend on the polarization of the S wave component and the P wave component of 60% is obtained. Further, the S-wave component of 40% reflected by the polarizing film 16 is reflected by the total reflection film 18 and reciprocates through the phase difference plate 17 to generate 4
0% of the 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 glasses 13a and 13b do not necessarily have to have the same thickness, but by making them the same thickness, the manufacture becomes easy.

FIG. 7 shows a further simplified structure of the light separating section 11B. Light splitting unit 1 shown in this embodiment
1B is made of an anisotropic crystal such as quartz, and has a phase difference plate 17a having a thickness T capable of generating a phase difference of λ / 2 by one round trip (two passes) of transmitted light. in use. A polarizing film 16 is directly coated on the incident side surface of the phase difference plate 17a, and a total reflection film 18 is directly coated on the other surface. In this embodiment, the polarizing film 16 has 10
0% of the P wave component and 60% of the S wave component are transmitted. The transmitted light is transmitted through the phase difference plate 17a, is reflected by the total reflection film 18 and is again transmitted through the phase difference plate 17a, whereby the polarization plane is rotated by 90 degrees.
There are 00% S-wave components and 60% P-wave components. Then, 60% of the S-wave component and the P-wave component are transmitted through the polarizing film 16 to obtain light R0. Further, the 40% S-wave component reflected by the polarizing film 16 reciprocates through the phase difference plate 17a to become a P-wave component, which passes through the polarizing film 16 and becomes 40% P-wave component.
Wave component light R2 is obtained. Note that the present invention is not limited to the above embodiments. For example, in the embodiment of FIG. 2, the polarizing film 16, the phase difference plate 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.

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 unit 11A of the flat plate material 11, and instead, the reflection surface 31a of the substrate 12 has a reflection function and 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 separate from the flat plate 11 or the substrate 12, and the half-wave plate may be arranged in a portion where the light flux B02 or B passes in the air layer (a). Good. Further, in each of the above embodiments, the reflection surface 31 is provided on the substrate 12, but the reflection surface may be constituted by a coating layer covering the pin photodiodes 32a to 32c. In addition, 11A of the flat plate material 11 in the present invention
Part and 11B part may be separated, in which case,
The portions 11A and 11B need not be located on the same plane.

[0029]

According to the present invention described in detail above, a small and lightweight optical head can be obtained. Further, the optical head according to the present invention can cope with 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 smaller and lighter,
Since the entire optical system can be driven for correction, occurrence of an offset to an error signal is eliminated. In addition, since there is no need to consider the relative displacement between the objective lens and the light emitting element, not only the design of the objective lens is facilitated, but also the manufacturing tolerance can be widened.

[Brief description of the drawings]

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

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

FIG. 3 is an explanatory view taken in the direction of arrows III-III in FIG. 2;

FIG. 4 is an explanatory view taken in the direction of arrows IV-IV in FIG. 2;

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

FIG. 6 is a sectional view showing another embodiment of the flat plate member.

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

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

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

[Explanation of symbols]

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

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G11B 11/10

Claims (2)

(57) [Claims] 1. A light emitting element and an objective lens facing a recording medium.
Lens and detection light from the light emitting element to the objective lens.
Objective lens that reflects light in a direction and is reflected from a recording medium
A partially reflecting member for transmitting return light passing through
A reflective surface that reflects the return light transmitted through the
The partial reflection member is provided on a partial surface of the
And transmitting the return light transmitted through the reflective surface to the reflective surface.
A flat plate on which the light reflected by the reflecting surface is incident again,
The light passes through the partially reflecting member and the flat plate material and is reflected by the reflecting surface.
Is located on the path of the light that is
Polarizer that rotates the plane of polarization of light on the path by a predetermined angle
And formed on the flat material and re-entered the flat material
Directly interposes the polarization plane rotated by the polarizing member.
A light separation unit that separates the light into a cross coordinate component,
Each set on the substrate and separated by the light separation unit
And a light receiving element for receiving these light components.
The flat plate and the substrate are arranged substantially in parallel.
An optical head characterized in that: 2. A light emitting device, an objective lens, a flat plate,
The substrate and the substrate are driven together for correction, and the recording
Request for correcting the irradiation state of the detection light sent to the medium
Item 2. The optical head according to item 1.