JPH03167504A - Double image element - Google Patents

Abstract

PURPOSE:To constitute the optical system without using costly optical elements by inclining the optical axis of the crystal bodies on the incident surface side in the double image prism formed by joining the crystal bodies by 45 deg. with a horizontal reference plane and paralleling the joint boundary line of the two crystal bodies appearing when the prism is cut at the plane orthogonal with the incident optical axis with the horizontal reference plane. CONSTITUTION:The optical axis of the crystal body 20a on the incident surface side has a prescribed angle theta (theta=45 deg.) with the horizontal reference plane 22 and the 2nd crystal body is formed by joining the two crystal bodies so as to intersect with the plane inclusive of the optical axis of the 1st crystal body and the optical axis of the incident light intersect with each other. The joint boundary line 24 of the incident surface side crystal body 20a and exit surface side crystal body 20b having the optical axes orthogonal with each other is paralleled with the horizontal reference plane 22. The optical system is easily constituted without using costly optical parts or holders or without forming the reference plane on the double image prism.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a magneto-optical disk or an optical head for an optical disk, and in particular to the structure of an optical head using a double-image prism and the structure of a double-image element used in the optical head. Regarding the configuration. (Prior art) As is well known, optical disks and magneto-optical disks use the thermal effect of light to write magnetic domains and record information signals, and use the magneto-optic effect to reproduce data, and are capable of high-density, large-capacity recording. It can be performed without contact, and in recent years it has been used as a recording medium to replace magnetic tape and magnetic disks. FIG. 4 is a diagram showing an example of a recording/reproducing optical system of a magneto-optical disk device, which converts light emitted from a light source such as a semiconductor laser into linearly polarized light via a collimating lens 2 and a beam splitter 3, and also converts it into linearly polarized light. Objective lens 4 for linearly polarized light
The recording medium 5 having a perpendicular magnetization film is irradiated with the irradiation light through the perpendicularly magnetized film. The linearly polarized light irradiated onto the recording medium 5 is reflected on the surface of the recording medium 5 and enters the beam splitter 3 again via the objective lens 4, but is reflected at the joint surface 3a of the beam splitter 3 and is transmitted to the next stage. The beam is emitted to the beam splitter 6.

A part of the light beam incident on the beam splitter 6 is detected by a sensor 7 for anti-QfL and servo control on the dielectric film provided on the joint surface 6a, while the transmitted light that has passed through the beam splitter 6 is detected by the sensor 7 for servo control. It enters the 1/2 wavelength plate 9 through the lens 8 provided at the next stage, and the 172-wave plate 9
In this case, the plane of polarization is rotated so that the plane of polarization is tilted by 45 degrees with respect to the optical axis of the crystal on the incident surface side of the double-image prism lO provided in the next stage, and the light is emitted to the double-image prism lO in the next stage. The light beam incident on the double-image prism (1) is separated into two components, an ordinary ray O and an extraordinary ray E, whose polarization planes are perpendicular to each other, and then emitted, and then detected by photodiodes l1 and 11 arranged on the output surface. By determining the difference between the two outputs using the output difference detector 12, the information on the recording medium 5 can be read.

For example, the plane of polarization of the light beam reflected at the area where data is recorded is generally rotated by around 10 due to the Kerr effect compared to the reference plane of polarization of linearly polarized light before irradiation, so it enters the double-image prism. The polarization plane of optical binding is 45°±l
1, and as a result, the output of the ordinary ray and extraordinary ray emitted from the double-image prism fluctuates, and the output difference detector 12
An output based on the above fluctuation appears. In addition, the plane of polarization of the light beam reflected at the part where no data is recorded does not rotate, so the double-image prism I
Direct # incident on O! Since the polarization plane of the deflection is 45 degrees,
Equal outputs are detected on the photodiodes 11, so that no output appears on the output difference detector l2.

As described above, the differential type polarization plane rotation detection optical system is a generally widely used system because it can compensate for the influence of external noise.

However, as mentioned above, when configuring a differential optical system, in order to split the linearly polarized light incident on the double-image prism (1) into two with equal output, The polarization plane of the light beam is
It is necessary to irradiate at an angle of 45" with respect to the optical axis of the crystal on the incident surface side of the prism.
This requires an optical element such as a 72-wavelength plate, which has the problem of making the optical system expensive and large. In order to eliminate this problem, the optical axis of the crystal on the incident surface side of the double-image prism (1) is tilted at 45 degrees with respect to the polarization plane of the incident linearly polarized light, as shown in Figure 5 (al). Alternatively, instead of using the holder 12 as shown in FIG. 5(b), place the double-image prism (1) #1 on the holder l4, or instead of using the holder 12 as shown in FIG. A reference surface (1) a having an angle of .degree. is provided, and the reference surface (
1) By grounding a horizontally, the optical axis of the crystal on the incident surface side of the double-image prism can be tilted by 45 degrees with respect to the polarization plane of the incident linearly polarized light, similar to when placed on the holder. It becomes possible. However, when using the above-mentioned method, a holder is required to place the double-image prism, or a reference plane must be provided on the double-image prism, which increases the number of parts or increases the number of prisms. There is a problem that the number of man-hours for manufacturing increases and the cost increases, and the light beam exiting from the double-image prism is in the same plane as the plane containing the optical axis of the crystal on the side of incidence and the optical axis of the incident light. Therefore, there was a problem in that the sensor 11 had to be installed at an angle to match the emitted light.

(Object of the Invention) The present invention has been devised in view of the problems of the conventional art as described above, and it is possible to achieve an optical system without using expensive optical parts or holders, and without forming a reference surface on a double-image prism. The object of the present invention is to provide a double-image prism that can easily configure an optical system for an optical disk, a magneto-optical disk, etc., and an optical system for detecting the amount of rotation of the plane of polarization using the double-image prism. (Summary of the Invention) In order to achieve this object, a double-view prism according to the present invention has a double-view prism in which at least two crystal bodies are joined, and the optical axis of the crystal body on the incident surface side is aligned with a horizontal reference plane. In addition to tilting by θ (however, 0° minus θ<90°),
A plane containing the optical axis of one light beam and the optical axis of the crystal body on the side of the incident surface is perpendicular to a plane containing the optical axis and the optical axis of at least one other crystal body, and this prism is The polarization rotation amount detection optical system according to the present invention is characterized in that, when cut along a plane perpendicular to the incident optical axis, the bonding boundary line of both crystals that appears is parallel to the horizontal reference plane. The system is characterized by being constructed using the above-mentioned double-image prism. (Example) The present invention will be described in detail below based on the example shown in the drawings. FIG. 1 fat is a diagram showing a double-image prism according to the present invention, in which 20a is a crystal body on the side of the light incident surface;
0b is a crystal body on the exit surface side, and as shown in the same figure, the optical axis of the crystal body 20a with an incident plane structure has a predetermined angle θ (θ=45°) with respect to the horizontal reference plane 22, and , the second crystal body is obtained by joining two crystal bodies so as to be perpendicular to a plane containing the optical axis of the first crystal body and the optical axis of the incident light. The double-image prism configured in this way has an input q.
- It has a function of separating the t ray into ordinary light IIO and extraordinary light E.

That is, the light incident perpendicularly to the crystal on the side of incidence is the ordinary ray O
, extraordinary ray E travel in the same direction, but when they enter the crystal on the exit surface side, they are separated into ordinary ray O and extraordinary ray E and are emitted.

FIG. 1+bl is a cross-sectional view taken along a plane 2l perpendicular to the incident optical axis of the double-image prism shown in FIG. The junction boundary line 24 with the output surface side crystal body 20b is parallel to the horizontal reference plane 22. Fig. 2 shows an example in which the double-image prism shown in Fig. 1 is used in a recording/reproducing optical system of a magneto-optical disk device. The same reference numerals as those in FIG. 4 have the same meanings, and the explanation thereof will be omitted. That is, the difference from FIG. 4 is that the double-image prism 20 is By using a double-image prism as shown in Fig. 1, the l/2 wavelength plate that was conventionally required can be removed, and the optical axis of the crystal on the side of the entrance surface of the double-image prism can be set at 45 degrees with respect to the polarization plane of the incident light beam. The optical system is constructed without requiring a holder for tilting or a reference end face.

In the polarization plane rotation detecting optical system configured in this way,
The light beam, which is emitted from the beam splitter 6 and has a polarization plane parallel to the plane of the paper and perpendicular to the incident optical axis, is transmitted to the next stage double-image prism 20.
The individual wavefront of the incident light and the double image prism 2
Since the optical axis of the crystal body 20a on the incident surface side of O has a deviation of 45'', the ordinary ray O exiting the double-image prism
The two component light beams of the abnormal light ill E have equal output.

Moreover, since the two light beams exiting the double-image prism 20 are parallel to the end surface 20c of the double-image prism 20,
There is no need to tilt and install the sensor 11.11 that detects the emitted light. That is, in a conventional double-image prism, for example, a Wallaston prism, the optical axis of the crystal on the incident surface side is perpendicular to the horizontal reference plane, and the optical axis of the second crystal is parallel to the horizontal reference plane. In addition, since it was configured to be orthogonal to the incident optical axis, when the incident light beam is made to enter the prism, a 172-wave plate is used to change the plane of polarization of the incident light beam to the crystal body on the incident surface side of the double image element. By using the double-image prism of the present invention, an optical system that had to be rotated by 45 degrees with respect to the optical axis can be constructed without using the above-mentioned optical elements.

FIG. 3 (al is a diagram showing another embodiment of the double-image prism according to the present invention, and the points different from the above-mentioned FIG. 1 are inputs q; t;
The point is that a dielectric multilayer film 26 having the function of making the transmittance and reflectance equal for both the ordinary ray 0 and the extraordinary ray E is formed at the joint surface between the surface-side crystal body 20a and the output surface full crystal body 20b.

Therefore, the incident linearly polarized light includes the ordinary ray O and the extraordinary ray E component reflected by the dielectric multilayer 112 2 6, and the ordinary ray O and the extraordinary ray whose polarization planes are orthogonal to each other and exit from the output surface side crystal body 20b. Separate it into three components with E and roll.

Since the double-image prism configured in this way can reflect a portion of the incident light beam on the dielectric multilayer film 26, when configuring the wavefront rotation detection optical system as described above, the third As shown in Figure (bl), the output can be obtained without using an expensive beam splitter for servo control, and the optical system can be configured more simply.

In addition, in the embodiment of the present invention, the polarization plane of linearly polarized light is set to 45
Although the embodiment has been described in which an I/2 wavelength plate is used for the rotation, the present invention is not limited to this, and it is clear that a <45° optical rotator may be used.

(Effects of the Invention) Since the present invention is constructed and functions as described above, the optical system for detecting the amount of rotation of the polarization plane does not require the use of a 1/2 wavelength plate or a 45° optical rotator, and a double-image prism. There is no need for a holder to hold it or a new reference end surface for installing the double-image prism, and there is no need to tilt the sensor to detect the emitted light and install it, making the optical system inexpensive and compact. It is extremely effective in configuring the system.

[Brief explanation of the drawing]

FIG. 1 (al (bl) is a perspective view and a cross-sectional view showing the configuration of a double-image prism according to the present invention, and FIG. 2 is a polarization plane rotation detecting optical system constructed using the double-image prism according to the present invention. 1B) is a diagram showing another embodiment of the double-image prism according to the present invention, and FIG. 4 is a diagram showing an example of a recording/reproducing optical system of a magneto-optical disk device, and FIG. 5 is a diagram showing the configuration of a conventionally used double-image prism. 1... Light source, 2...Collimating lens, 3, 6...
・Beam splitter, 4... Objective lens, 5... Storage medium, 7... Sensor, 8... Lens, 9... l
/2 wavelength plate, (1)...double image prism, loa...
Reference plane, 11... Photodiode, l2... Output difference detector, 20... Double image prism, 20a... Input Q
{Face side crystal body, 20b... mocking emission. Surface side crystal body, 22... Horizontal reference plane, 24... Junction boundary cotton, 26... Dielectric multi-Ig film

Claims (2)

[Claims] (1) In a double-image prism in which at least two crystal bodies are joined, the optical axis of the crystal body on the incident surface side is tilted by θ (θ = 45°) with respect to the horizontal reference plane, and the optical axis of the incident light is aligned with the optical axis of the incident light. a plane containing the optical axis of the crystal on the side of incidence is perpendicular to a plane containing the optical axis and the optical axis of at least one other crystal, and the prism is perpendicular to the optical axis of incidence thereon; A Wollaston prism characterized in that, when cut along a plane where the prism is cut, a joining boundary line between both crystal bodies that appears is parallel to the horizontal reference plane. (2) An optical system for detecting the amount of rotation of the plane of polarization using the magneto-optical effect, characterized by using the Wollaston prism according to claim 1.