JPH04362553A - Light separation element and light-receiving optical device using same - Google Patents

Abstract

PURPOSE:To obtain a light separation element and a light-receiving optical device using the element with simple constitution. CONSTITUTION:40% of the S-wave component of incident light is reflected by a polarization film 12a, and 60% of the S-wave component and 100% of a P-wave component are transmitted. The transmission light becomes 100% of the S-wave component and 60% of the P-wave component by a phase difference plate 60% of the S-wave component and 60% of the P-wave component transmit a polarization film 12b, and light is received by a pin photo diode 24 of four division. 40% of the S-wave component reflected by the polarization film 12b becomes 40% of the P-wave component by the phase difference plate 13, and it transmits the polarization film 12a. Light-receiving parts 21 and 22 receive 40% of the S-wave component and 40% of the P-wave component.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a light separation element used in a magneto-optical disk device, etc., which separates light having a polarization component of 90 degrees in the rotational direction into three light components, and a light separation element using this light separation element. The present invention relates to a light receiving optical device.

0002

[Prior Art] In order to obtain reproduction output in a magneto-optical disk device, polarization separation is performed, and the return light from the disk is divided into an output of the difference in polarization components due to the Kerr rotation angle (MO signal), a focusing signal, etc. It is necessary to separate the error signal into an error signal detection component and an error signal detection component for detecting the error signal.

FIG. 6 shows the configuration of an optical system of a magneto-optical disk device using a conventional polarization separation means. The laser light emitted from the semiconductor laser 1 passes through the collimating lens 2
The light becomes parallel light, is reflected by the beam splitter 3, is reflected by the total reflection prism 4, and is focused onto the recording surface of the disk D by the objective lens 5. The reflected return light from the recording surface of the disk D passes through the beam splitter 3,
The light is separated into three components by a Wollaston prism 6, passes through light receiving lenses 7a and 7b, and is received by a six-divided pin photodiode 8. The two light beams B1 and B2 separated into different polarization components by the Wollaston prism 6 are received by the two light receiving sections 8a and 8b of the pin photodiode 8, and an MO signal is detected from the difference in the amounts of the two received light beams. Furthermore, the light beam B3, which does not depend on the polarization state, is received by the four-divided light receiving section 8c, thereby obtaining focus and tracking error signals.

0004

SUMMARY OF THE INVENTION The conventional light-receiving optical device described above uses a Wollaston prism 6 as an element for polarization separation. However, since the Wollaston prism 6 is manufactured by using two anisotropic crystals such as quartz crystals and bonding them together, the manufacturing cost is high. Furthermore, in order to obtain a focus error signal in the four-divided light receiving section 8c of the focus photodiode 8, it is necessary to provide a cylindrical lens that produces an astigmatism difference as the light receiving lens 7b, which increases the number of optical components.

The present invention solves the above-mentioned conventional problems, and provides an optical separation element that can perform polarization separation of light with a simple configuration and also generate an astigmatism difference, and a light receiving optical device using the same. is intended to provide.

[0006]

Means for Solving the Problems The present invention provides a light separation element located in a path of light having first and second polarization components at 90 degrees in the direction of rotation with respect to the optical axis, the first polarization component being Polarizing films that transmit the second polarized light component at a predetermined rate and transmit the second polarized light component at a predetermined rate are arranged parallel to each other and at an angle to the optical axis, and the polarizing plane is set at 90° between the two polarizing films. It is characterized by disposing an optical member that can be rotated by a certain degree.

Further, in the light receiving optical device according to the present invention, the light separating element is disposed in the path of light having first and second polarized light components at 90 degrees in the rotation direction with respect to the optical axis, and both polarized light of the light separating element is arranged. It is provided with a light receiving section that receives light transmitted through the film, and a light receiving section that receives reflected components from both polarizing films.

[0008]

[Operation] In the above means, when return light whose polarization plane is given a Kerr rotation angle in a magneto-optical disk is incident on the light separation element, a part of the component is reflected by the polarizing film,
Other components pass through. Furthermore, the polarization plane located in the middle is 9
The polarized light component is rotated by 90 degrees by the optical member that rotates it by 0 degrees, and reaches the next polarizing film. In the next polarizing film, part of the light is reflected and other components are transmitted. By receiving the transmitted light at the light receiving section, error detection such as focusing is performed. Furthermore, since the light reflected from both polarizing films has components with different polarization directions, an MO signal or the like can be obtained by determining the difference in output.

[0009]

[Embodiments] Examples of the present invention will be explained below with reference to the drawings. FIG. 1 is a sectional view showing a first embodiment of a light separation element 10 according to the present invention. In FIG. 1, reference numerals 11a and 11b are flat glasses having the same thickness and dimension t. Both flat glass 11
The surfaces of a and 11b are coated with polarizing films 12a and 12b. A retardation plate 13 is interposed between the flat glasses 11a and 11b to generate a phase difference of λ/2 (where λ is the wavelength of the light) for the light passing therethrough.

[0010] In FIG. 1, α-β orthogonal coordinates are taken with the α axis in the vertical direction of the paper and the β axis in the direction perpendicular to the paper, and 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 light that corresponds to the direction is assumed to be the S-wave component. Further, the incident angle of the incident optical axis B with respect to the light separation element 10 is assumed to be θ.

The incident angle θ is approximately the Brewster angle,
For example, when the refractive index of the flat plates 11a and 11b is 1.51, the angle is set to about 60 degrees. Due to this Brewster angle θ and the design of the polarizing films 12a and 12b, 100% of P waves are transmitted through each polarizing film 12a and 12b, and 60% of S waves are transmitted through each polarizing film 12a and 12b.
It is set so that 40% of the S wave is transmitted and 40% of the S wave is reflected. Note that this ratio can be set arbitrarily.

[0012] Furthermore, since the polarization plane of the light passing through the retardation plate 13 that generates the phase difference of λ/2 is rotated by 90 degrees, the P-wave component becomes an S-wave component, and the S-wave component becomes a P-wave component. becomes.

The function of the light separation element 10 will be explained. The incident light incident at the incident angle θ is converted into S by the polarizing film 12a.
40% of the wave components are reflected and 60% are transmitted. Furthermore, 100% of the P wave component is transmitted through this polarizing film 12a. That is, the polarizing film 12a reflects only 40% of the S wave component of the incident light. In FIG. 1, this reflected light is indicated by R1.

The 60% S-wave component and the 100% P-wave component that have passed through the polarizing film 12a pass through the flat glass 11a and further pass through the retardation plate 13. Since the plane of polarization is rotated by 90 degrees by this retardation plate 13, the next flat glass 1
The light transmitted through 1b has 100% S-wave component and 60% P-wave component.
It is a wave component.

In the next polarizing film 12b, 4 of the S wave components
0% is reflected and 60% is transmitted. However, since the P wave component is not reflected, only 40% of the S wave component is reflected by the polarizing film 12b and returns within the flat glass 11b. Since this S-wave component passes through the retardation plate 13 again, the plane of polarization is rotated by 90 degrees, and the 40% S-wave component becomes a P-wave component. Since the P wave component is not reflected by the polarizing film 12a and all of it passes through, the component reflected by the polarizing film 12b becomes the P wave component, and the reflected light R
Output parallel to 1. This reflected light with 40% P wave component is R
Shown as 2.

Further, in the polarizing film 12b, 6 of the S wave component
0% is transmitted, and 60% of the P wave component is completely transmitted as is. Therefore, the transmitted light indicated by the symbol T has both 60% S-wave components and 60% P-wave components.

FIG. 1 shows a case where the optical separation element 10 is arranged in a path of return light (focused light) from a recording surface of a disk in a magneto-optical disk device. 40 mentioned above
Light receiving sections 21 and 22 of pin photodiodes are arranged in the path of the reflected light R1 of the S-wave component of % and the path of the reflected light R2 of the P-wave component of 40%, respectively. Both light receiving parts (I
By obtaining the difference in the amount of light received by the differential amplifier 23 (received light of the output and light received of the J output), it is possible to know the difference between the I output and the J output, that is, the difference in the light amount of the S wave component and the P wave component,
The MO signal of the magneto-optical disk can be obtained.

Furthermore, a four-divided pin photodiode 24 is arranged on the path (focusing point) of the transmitted light T. The transmitted light T is light that does not depend on the polarization state of the returned light, and it can be expressed as 4
A focus error signal and a tracking error signal can be obtained by detecting with the divided light receiving sections. In addition, since the optical separation element 10 has a flat plate structure as a whole,
The transmitted light (focused light) T that passes through this has an astigmatism difference. Therefore, it is possible to obtain a focus error signal using the four-divided light receiving section by utilizing this astigmatism difference, and there is no need to use a cylindrical lens like the conventional example shown in FIG. 6 as the light receiving lens 7b. Further, the tracking error signal can be detected by a so-called push-pull method using a four-divided light receiving section.

FIG. 4 shows in more detail the structure of the optical system of a magneto-optical disk device using the optical separation element 10 described above. Laser light emitted from the semiconductor laser 31 is made into parallel light by the collimator lens 32. A part of the laser beam (mainly the S wave component) is reflected by the polarizing beam splitter 33, reflected by a movable mirror 34 for tracking correction, further reflected by a total reflection prism 35, and then reflected by an objective lens 36 onto the recording surface of the disk. The light is focused on. The return light from the recording surface of the disk returns through the original path, passes through the polarizing beam splitter 33, is focused by the light receiving lens 37, and enters the light separation element 10.

FIG. 5 shows the arrangement angle of the light separation element 10 from the direction of incidence of the light separation element 10 (direction V in FIG. 4). In the apparatus of FIG. 4, if orthogonal coordinates are provided with X in the horizontal direction and Y in the vertical direction, the orthogonal coordinates of the α axis and β axis shown in FIG. around 4
It is arranged at an angle rotated by 5 degrees.

Assume that the return light from the magneto-optical disk is given a Kerr rotation angle, and the plane of polarization is rotated by θk in the plus or minus direction with respect to the Y axis, as shown in FIG. In the optical separation element 10 of FIG. 1, the component of the polarization plane rotated by θk is the P-wave component in the α-axis direction and the S-wave component in the β-axis direction.
The light is separated as wave components, and the difference between the S wave component and the P wave component is detected by the light receiving sections 21 and 22. Therefore, the differential amplifier 23
The rotation direction of the polarization plane of plus θk or minus θk shown in FIG. 5 is detected by the output from , and the MO signal is reproduced.

FIG. 2 shows a second embodiment of the optical separation element according to the present invention. In this embodiment, the two flat glasses used in FIG. 1 are reduced to one. In other words, Figure 2
The structure of the light separation element 10A includes, in order from the incident side, a polarizing film 12a, a flat glass 11, a retardation plate 13 that provides a phase difference of λ/2, and a polarizing film 12b. The function of this optical separation element 10A is the same as that of the optical separation element 10 shown in FIG. It is separated into transmitted light T having an S wave component and a P wave component.

The third embodiment shown in FIG. 3 has a further simplified structure. Light separation element 10 shown in this example
For B, an anisotropic crystal such as quartz is used, and the transmitted light has a wavelength of λ/2.
Polarizing films 12a and 12b are directly coated on both sides of a retardation plate 13a having a thickness t1 that can provide a retardation of . In this embodiment, 100% of the P wave component and 60% of the S wave component are transmitted through the polarizing film 12a on the front surface. The polarization plane of this transmitted light is rotated 90 degrees as it passes through the retardation plate 13a, and when it reaches the polarizing film 12b on the rear surface, it has 100% S-wave component and 60% S-wave component.
% P wave component. In the polarizing film 12b, both 60% of the S wave component and the P wave component are transmitted, and transmitted light T is obtained.
40% of the S wave component is reflected. As this S-wave component passes through the phase difference plate 13a, it becomes a P-wave component and passes through the polarizing film 12a. Therefore, both 40% P wave component and S
The wave components are obtained as reflected lights R1 and R2, respectively.

Note that the present invention is not limited to the above embodiments; for example, in the second embodiment shown in FIG. A membrane 12b may also be provided.

[0025]

According to the present invention described in detail above, it is possible to obtain a light separation element having a small size and a simple structure. Furthermore, by using this light separation element, a compact light receiving optical device can be formed. Furthermore, since the light separation element can be formed into a flat plate configuration, the light transmitted through it contains an astigmatism difference, making it possible to detect focus errors as is.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing a light separation element according to a first embodiment of the present invention;

FIG. 2 is a sectional view showing a light separation element according to a second embodiment of the present invention;

FIG. 3 is a sectional view showing a light separation element according to a third embodiment of the present invention;

FIG. 4 is a perspective view of the arrangement of an optical system of a magneto-optical disk device using the optical separation element of the present invention;

FIG. 5 is an explanatory diagram showing the arrangement angle of the light separation element in the apparatus of FIG. 4;

FIG. 6 is an arrangement side view showing a conventional light separation element and a light receiving optical device using the same;

[Explanation of symbols]

10, 10A, 10B Light separation element 11, 11a, 11b Flat glass 12a, 12b Polarizing film 13, 13a Retardation plate 21, 22 Pin photodiode 24 4-split pin photodiode 31 Semiconductor laser

Claims (2)

[Claims] Claim 1: A first angle of 90 degrees in the direction of rotation with respect to the optical axis.
and a second polarization component, the light separation element is located in a path of light having a second polarization component, and transmits the first polarization component at a predetermined ratio;
Optical films that transmit the second polarized light component at a predetermined rate are arranged parallel to each other and at an angle to the optical axis, and an optical member that rotates the plane of polarization by 90 degrees is arranged between both polarizing films. A light separation element characterized by: Claim 2: A first angle of 90 degrees in the direction of rotation with respect to the optical axis.
and a light-receiving section for receiving light transmitted through both polarizing films of the light-separating element, wherein the light-separating element according to claim 1 is disposed in a path of light having a second polarization component, and a light-receiving section that receives light transmitted through both polarizing films of the light-separating element, and components reflected from both polarizing films. 1. A light-receiving optical device comprising: a light-receiving section that receives each light.