JPH05334760A - Optical head - Google Patents

Abstract

PURPOSE:To constitute a small-sized optical head for reproducing an MO signal by the smallest number of optical parts. CONSTITUTION:A laser beam from a semiconductor laser 20 is reflected by a polarizing film 15, reflected by the total reflection film 14 of a first prism 12, condensed by an objective lens 16 and radiates a disk D. A returning light from the disk D is given with a Kerr rotation angle by a Kerr effect, and it is emphasized by passing through the polarizing film 15. The light is separated into a normal light component alpha and an abnormal light component beta due to the difference of a refractive index of a second prism 13 of an anisotropic crystalline material, and received by photodetecting parts 22, 23, respectively. By taking the difference of these reception outputs, an MO signal is regenerated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head provided in a magneto-optical disk device or the like, for separating return light whose polarization direction is rotated by the Kerr effect into two different polarization components and detecting the respective lights.

[0002]

2. Description of the Related Art In a magneto-optical disk device, polarized light is separated in order to obtain a reproduction output, and the return light from a disk whose polarization direction is rotated by the Kerr effect is detected by two Kerr rotation angles. It is separated into polarized components. Figure 9
FIG. 10 shows a configuration of an optical system for a magneto-optical disk device using a conventional polarization separating means, and FIG. 10 shows polarization states in the paths of (a) and (b) of FIG. The laser light emitted from the semiconductor laser 1 becomes parallel light by the collimator lens 2, enters the beam splitter 3 as an S wave component, is reflected, is further reflected by the total reflection prism 4, and is reflected by the objective lens 5 of the disc D. It is focused on the recording surface.

The reflected return light from the recording surface of the disk D is
Although it returns through the objective lens 5 and the total reflection prism 4, the Kerr rotation angle (± θk) due to the Kerr effect as shown in FIG. 10A is given to the return light due to the recording pattern on the magneto-optical recording surface of the disk D. Be done. The return light passes through the beam splitter 3 and the half-wave plate 9, and the polarization direction is rotated by 45 degrees by passing through the half-wave plate 9 as shown in FIG. Further, the returned light is separated into two polarized components by the Wollaston prism 6, passes through the light receiving lenses 7a and 7b, and is received by the pin photodiode 8.

The two light beams Ba and Bb separated into the P-wave component and the S-wave component which are orthogonal components by the Wollaston prism 6 are two light receiving portions 8a and 8a of the pin photodiode 8, respectively.
The light is received by b. The light receiving amounts of the P wave component and the S wave component received by the light receiving units 8a and 8b are as shown by Pd and Sd in FIG. 10B. The Kerr rotation angle (+ θk or −θk) of the returning light is obtained by obtaining the difference between the light receiving amounts Pd and Sd at the light receiving portions 8a and 8b.
Is detected and becomes the MO reproduction signal. In addition, the two light receiving units 8
By dividing either one of a and 8b into four, a focus and tracking error signal is obtained.

[0005]

The above-mentioned conventional optical system has the following problems. (1) In the conventional optical system, 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, which limits the miniaturization.

(2) In the conventional optical system described above, a separate half-wave plate 9 is used to detect the polarization component given the Kerr rotation angle in the light receiving portions 8a and 8b. 10 (b)
As shown in, the polarization direction of the returning light is rotated by 45 degrees. Therefore, the number of optical components is increased by the provision of the half-wave plate 9, and a structure for positioning and fixing the half-wave plate 9 is required.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide an optical head which can be made compact with a minimum number of parts.

[0008]

In an optical head according to the present invention, a first prism on which light from a light emitting portion is incident, a second prism joined to the first prism, and a joint portion of both prisms are provided. A polarizing film formed on the recording medium, a condenser lens that collects the light reflected by the polarizing film and passed through the first prism on the recording medium, the first prism reflected by the recording medium, the polarizing film, and the second film. And a light receiving section for detecting the returning light passing through the prism, and the polarizing film reflects the linearly polarized component of the incident light into the first prism and the polarization direction is rotated by the Kerr effect. Light is transmitted through the second prism, and the second prism is formed of an anisotropic optical material for separating the return light whose polarization direction is rotated into an ordinary light component and an extraordinary light component. And the light receiving section It is characterized in that the detector for detecting the second normal light component and an extraordinary light component separated by the prism are respectively provided.

[0009]

In the above means, the light from the light emitting portion is reflected by the polarizing film formed at the junction of the two prisms, is condensed by the condenser lens through the first prism, and is applied to the recording medium. The return light whose polarization direction is rotated by the Kerr effect of the recording medium passes through the first prism and the polarizing film to reach the second prism. In the second prism, since the ordinary light component and the extraordinary light component have different refractive indices, the return light whose polarization direction is rotated is separated into ordinary light and extraordinary light, travels different paths, and is detected by different detection units of the light receiving unit. Is received. A reproduction output can be obtained by detecting the difference between these components.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.
1 is a front view showing a component structure of a first embodiment of an optical head according to the present invention, FIG. 2 is a front view showing only a second prism,
FIG. 3 is a right side view of FIG. Optical head 10 shown in FIG.
Each optical element is mounted on a chassis 11, and the chassis 11 is supported by an elastic support member (not shown) and is supported so as to be finely movable in the focus correction and tracking correction directions. Further, a magnetic drive circuit is provided between the chassis 11 and a fixing portion that supports the chassis 11 through the elastic support member, and the magnetic drive circuit causes the optical head 10 to operate.
Is finely driven in the respective correction directions of focus and tracking.

A first prism 12 and a second prism 13 joined to each other are fixed to the chassis 11. The first prism 12 is an isotropic optical material such as BK-.
It is formed of a glass material such as 7. A total reflection film 14 is formed on the reflection surface on the exit side of the first prism 12. The second prism 13 is formed of an anisotropic crystal material such as quartz. The junction between the first prism 12 and the second prism 13 forms an angle of 45 degrees with respect to the incident light, and the polarization film 15 is formed at this junction. The polarizing film 15 transmits 100% of the P wave component, transmits 20% of the S wave component, and reflects 80% of the S wave component. The exit surface 13a of the second prism 13 forms an angle γ of 90 degrees or less with the lower surface 13b in the figure.
That is, in FIG. 1, an imaginary vertical surface perpendicular to the lower surface 13b is indicated by f, but the emission surface 13a is a surface inclined with respect to the imaginary vertical surface f (and the y axis).

The light reflected by the total reflection film 14 formed on the reflecting surface of the first prism 12 is the objective lens 1
It is condensed on the recording surface of the disk D by 6. Chassis 1
The divergent light from the semiconductor laser 20 provided at No. 1 is condensed by the objective lens 16 and is applied to the disk D, and the objective lens 16 forms a finite system condensing path.

The ordinary light component α and the extraordinary light component β emitted from the second prism 13 are received and detected by the two light receiving portions 22 and 23 provided on the light receiving substrate 21. Figure 8 (a)
As shown in FIG. 5, the light receiving units 22 and 23 each have four-divided light receiving detection units A1 to D1. Here, the first prism 12 is formed of an isotropic optical material. For example, in the case of a BK-7 glass material, the refractive index is n = 1.51.
Is. Further, as shown in FIG. 3, the optical axis of the second prism 13 is inclined by 45 degrees with respect to the Cartesian coordinates xy.
When the second prism 13 is made of an anisotropic optical material such as quartz, the refractive index for the ordinary component α is nα = 1.
54, and the refractive index for the extraordinary light component β is nβ = 1.
55.

Next, the operation of the above optical head will be described. 4 (a) and 4 (b) are for explaining the polarization state of the return light M from the disk D, and FIGS. 4 (a) and 4 (b) are respectively (a) and (b) of the optical head 10 of FIG. Shows the polarization state of light at the position. The divergent laser light emitted from the semiconductor laser 20 enters the first prism 12 and enters the polarizing film 15 as an S wave component. Polarizing film 15
Then, 80% of the S wave component is reflected, so this 80%
The reflected light of is reflected by the total reflection film 14 after passing through the inside of the first prism 12, focused by the objective lens 16, and applied to the disk D. Information is recorded on the disk D by, for example, magneto-optical, and the return light M reflected from the recording surface has a Kerr rotation angle (+ θk) due to the Kerr effect corresponding to the record information, as shown in FIG. 4A. Or (-θk) is given.

The return light M returns from the objective lens 16 into the first prism 12 and is reflected by the total reflection film 14.
It is incident on the polarizing film 15. In the polarizing film 15, the P wave component is 10
Since 0% is transmitted and S wave component is transmitted by 20%,
The return light M1 that has entered the prism 13 is emphasized in the Kerr rotation angle (± θk) due to the Kerr effect, as shown in FIG.

Further, as shown in FIG. 3, the second prism 1
3, the optical axis rotates 45 degrees with respect to the polarization direction (x direction), so the ordinary light component α of the return light M1 becomes the component in the α direction of FIG. 3, and the extraordinary light component β becomes β of FIG. It becomes the direction component. Here, in the second prism 13, the ordinary light component α
Since the extraordinary light component β has a different refractive index, the light incident on the second prism 13 from the first prism 12 is separated into the paths indicated by α and β in FIG. 1 due to the difference in the refractive index. It Since the emission surface 13a of the second prism 13 is inclined with respect to the y axis, this inclination further emphasizes the separation angle between the ordinary light component α and the extraordinary light component β, and the respective components are received by the light receiving portions 22 and 23. Is received by. The separation angle of the emitted light may be further expanded by a concave lens.

As shown in FIG. 8A, assuming that the total amount of received light of the ordinary light component α by the light receiving unit 22 is E1 and the total amount of received light of the abnormal light component β by the light receiving unit 23 is E2, the information reproduction signal (M
The O signal) is obtained by MO = E1-E2. Further, since the emission surface 13a of the second prism 13 is inclined with respect to the y-axis, the light emitted from this emission surface 13a has astigmatism. Therefore, in the light receiving section 22, the focus error signal FE = (A1 + C1) − (B1 + D) is obtained by the astigmatism method.
1) is obtained, and the tracking error signal is obtained by TE = (A1 + B1)-(C1 + D1) by the push-pull method. Further, as shown in FIG. 8B, the light receiving portion is divided into eight, and the focus error signal is sent from the light receiving portion 22 to FE1 =
(A1 + C1)-(B1 + D1), FE from the light receiving unit 23
2 = (A2 + C2)-(B2 + D2), and FE1 +
It is also possible to obtain the focus error signal by FE2. Similarly, the tracking error signal is TE1 =
(A1 + B1)-(C1-D1), TE2 = (A2 + B
2)-(C2-D2) is calculated by TE1 + TE2.

The focus error signal can be detected by the astigmatism method using a cylindrical lens, and the tracking error signal can also be detected by the three-beam method by adding a diffraction grating. The shapes of the first prism 12 and the second prism 13 are not limited to those in the embodiment of FIG. 1, and may be the shapes shown in FIG. 5, for example. In the embodiment shown in FIG. 5, the semiconductor laser 2
The light from 0 enters the first prism 12 from the side surface, is reflected by the polarizing film 15 as an S wave component, is reflected by the total reflection film 14, and is sent to the objective lens. The return light from the disk passes through the polarizing film 15, is separated from the emission surface 13a of the second prism 13 into the ordinary light component α and the extraordinary light component β, and is emitted.

In the embodiment shown in FIG. 6, the semiconductor laser 20 is used.
The light that is emitted from the laser beam, is reflected by the polarizing film 15, passes through the first prism 12, and is collimated by the collimator lens 31. Further, the objective lens 1 is reflected by the prism 33.
It is condensed on the disk D by 6. The return light from the disk passes through the polarizing film 15, is separated into the ordinary light component α and the extraordinary light component β by the second prism 13, and is further concave lens 3.
The separation angle is emphasized by 2 and the light receiving portions 22 and 23 are respectively
Is received by. In this case, the component on the (a) side is a fixed optical system, and the prism 33 and the objective lens 16 on the (b) side are
May be a moving optical system, and only this moving optical system may be moved along the disk D in the left-right direction in the drawing. Furthermore, FIG.
As shown in, the first prism 12 and the second prism 1
3, the semiconductor laser 20, the light receiving substrate 21, etc.
It may be housed inside and packaged.

[0020]

As described above, according to the present invention, by joining the first prism and the second prism, the function as the beam splitter and the function as the light separating prism can be exhibited, and the minimum. A small optical head can be configured by the optical parts.

[Brief description of drawings]

FIG. 1 is a front view showing a component structure of a first embodiment of an optical head according to the present invention,

FIG. 2 is a front view showing a second prism,

3 is a right side view of the prism shown in FIG.

4 (a) and 4 (b) are explanatory views showing a polarization state of return light in each part of the optical head shown in FIG.

FIG. 5 is a partial perspective view showing a second embodiment of the optical head according to the present invention,

FIG. 6 is a front view showing a third embodiment of the optical head of the present invention,

FIG. 7 is a front view showing a fourth embodiment of the optical head of the present invention,

FIG. 8 is a side view showing the structure of the light receiving section,

FIG. 9 is a component configuration diagram showing a conventional optical head,

10A and 10B are explanatory views showing the polarization state of each optical path portion of the conventional optical head with the S wave component and the P wave component as orthogonal coordinates;

[Explanation of symbols]

 10 optical head 11 chassis 12 first prism 13 second prism 14 total reflection film 15 polarizing film 16 objective lens 21 light receiving substrate 22, 23 light receiving section D disk M, M1 return light α ordinary light component β extraordinary light component β

Claims (1)

[Claims] 1. A first prism on which light from a light emitting portion is incident, a second prism joined to the first prism, a polarizing film formed at a joining portion of both prisms, and the polarizing film. A condenser lens for condensing the light reflected by the first prism and passing through the first prism on the recording medium, and a light receiving unit for detecting the return light reflected by the recording medium and passing through the first prism and the polarizing film and the second prism. The polarizing film reflects the linearly polarized component of the incident light into the first prism and transmits the return light whose polarization direction is rotated by the Kerr effect into the second prism. And the second
Is formed of an anisotropic optical material for separating the return light whose polarization direction is rotated into an ordinary light component and an extraordinary light component, and the light receiving portion is separated by the second prism. An optical head characterized in that a detector is provided for detecting an ordinary light component and an abnormal light component, respectively.