JPH02192031A - Polarized light separation type hologram head - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical head that detects an information signal of an optical disk and a servo signal such as focus or tracking, and particularly relates to an optical head that detects a signal using polarized light or a magneto-optical head that detects a signal using polarized light. It can be used in an optical head that records information signals in a shading pattern or a pit pattern.

2. Description of the Related Art As a method of detecting an information signal recorded on an information carrier using polarization of a light beam, a method using a polarizing beam splitter or a Volaston prism is conventionally known. A system for detecting signals on, for example, a magneto-optical disk using these techniques is disclosed in Japanese Patent Application Laid-open No. 78755/1983, and detailed explanation thereof will be omitted.

The technology to detect servo signals using polarization holograms is
For example, it is well known from Japanese Patent Application Laid-Open No. 62-97141.

However, even if such a polarizing hologram is used, multiple functions cannot be sufficiently achieved. In particular, in order to detect polarized light, it was necessary to combine it with a polarized light splitting element such as a polarized beam splitter or a Volaston prism.

Problems to be Solved by the Invention As is clear from the above-mentioned conventional example, the conventional polarization separation element is an element that only performs polarization separation, and it is usually not possible to combine it with other functions. It was difficult. - Function - Element-type optical heads have a large number of parts and are complex to adjust, and in order to make the optical head smaller and simpler, it is necessary to combine functions.

In view of this point, an object of the present invention is to provide a polarizing hologram head that can have multiple functions.

Another object of the present invention is that by utilizing polarization separation using a polarization hologram, it is possible to simplify the functions of a wavelength plate, Volaston prism, polarization beam splitter, etc., which were conventionally required, by integrating them into a single element, thereby reducing costs. The purpose is to reduce the number of parts and simplify the assembly process.

Means for Solving the Problems In order to achieve the above object, the present invention provides a beam splitter located between a radiation source and a radiation source, and a light beam that is reflected by an information phase body, split by the beam splitter, and transmitted. or a polarizing hologram to be reflected, and a plurality of photodetectors that receive the 0th-order light, the +1st-order diffracted light, and the -1st-order diffracted light whose polarization planes emitted from the polarizing hologram are orthogonal to each other; The configuration is equipped with the following.

Function: By having the above structure, the present invention utilizes polarization separation by a polarizing hologram to simplify the structure of the optical head.

Example Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a basic configuration example of a first embodiment of the present invention. An example is shown in which a semiconductor laser 1 is used as a radiation light source. The light beam emitted from the semiconductor laser 1 passes through the beam splitter 4 and enters the objective lens 2. The light beam that is converged by the objective lens 2 is incident on an optical disk 3 that is an information carrier. The light beam reflected by the disk 3 passes through the objective lens 2 again and is reflected by the beam splitter 4. In FIG. 1, the light emitted from the semiconductor laser 1 is first transmitted through the beam splitter 4, but depending on the optical system design, the light emitted from the semiconductor laser 1 may be reflected first at the beam splitter 4. You may also do so.

The light beam transmitted through the objective lens 2 and reflected by the beam splitter 4 is incident on the polarizing hologram 5.

Generally, in a polarizing hologram, P-polarized light polarized in a direction perpendicular to the grating direction of the diffraction element forming the hologram becomes 0th-order light, and S-polarized light polarized in a direction horizontal to the grating direction of the diffraction element forming the hologram becomes +1st-order light. The light is split into a diffracted light and a −1st-order diffracted light.

In this embodiment, a part of the zone plate as shown in FIG. 2 or 3 is used as the polarizing hologram 5. Therefore, in the polarizing hologram 5, the +1st-order diffracted light and the -
S-polarized light is split into first-order diffracted light, and P-polarized light is split into zero-order light.

Each of these light beams is detected by an optical signal detector 7.8.
I'll take it at 6.

Single lenses 51 and 52 are placed between the semiconductor laser 1 and the beam splitter 4 so that 9 vanes are incident thereon.

It may also be arranged between the beam splitter 4 and the polarizing hologram 5 as shown in FIG. 1(b). For example, the method for creating the polarization side grating is as shown in Fig. 2(a), (
b) A method of forming a relatively shallow groove-shaped grating in an anisotropic material as shown in a plan view and a cross-sectional view;
A well-known method is to form a relatively deep groove-shaped grating by etching or pressing, as shown in a plan view and a cross-sectional view in FIGS.

It is possible to form polarizing holograms using the same process.

If the optical disk records and reproduces magneto-optical signals, the polarizing hologram 6 has multiple branches of P.
The magneto-optical signal can be reproduced by detecting the difference signal between the polarized wave and the S-polarized wave.

In addition, since a part of the zone plate is used as the polarizing hologram 5, as shown in FIG. A focus error signal and a tracking error signal can be obtained from the diffracted light.

Next, the situation will be explained using FIG. In order to simplify the drawing, only the polarizing hologram 5 and the optical signal detector 7.8.6 are shown in FIG.

FIG. 4(a) shows the case where the disk 3 in FIG. 1 is in the direction away from the objective lens 2, and FIG. Figure (C) shows the case in which the disk 3 approaches the objective lens 2. Detector 7, 8. 6 are respectively (,), (b
), if the shape is as shown on the right side of (C),
The focus error signal is (7-2)-(8-2)...
・・・・・・ Equation (1) % expression %)) ・・・・・・・・・・・・ Can be obtained by calculating the detector output of Equation (2) (for example, Publication No. 1987-258339, Japanese Patent Publication No. 61-333
(See Japanese Patent Application Laid-Open No. 11/1988/60-59545, etc.).

Moreover, the information signal recorded magneto-optically is ((-r-1
)+(7-2)+(7-3))+((8-1)+(8-
2)+(8-3))-(e)・・・・・・・・・・・・
... Obtained from the calculation of the detector output in equation (3).

The information signal recorded in normal bit type or the information signal recorded in gray pattern is ((7--1)+(7-2)+(7-3))+((
8-1)+ (8-2)+ (8-3) )+(e)・
It can be obtained from the calculation of the detector output in equation (4).

In addition, when the three-thickness line of the detector and 8 is parallel to the track recorded on the disk 3, the far field tracking signal for tracking in FIG. )+(8-3))-((7-3)+(8-1
)1・・・・・・・・・・・・ Although it can be obtained from equation (6), it is also possible to divide the polarizing hologram and extract the far field signal separately.

Figure 5 shows such an example. Figure 5(a)
As shown in FIG. 1, a light beam 10 is irradiated onto multi-divided polarizing holograms 12 to 16. Further, within the light beam 10, the tracking signal 11 corresponding to the position of the track recorded on the disk 3 partially forms a bright part or a dark part (bright part or dark part depends on whether the track is concave or convex). )

With this polarizing hologram, polarizing signals such as magneto-optical signals and error signals of focus error and far-field tracking can be obtained simultaneously. That is, the polarizing holograms 12, 14.16 are the same polarizing holograms as shown in FIG.
are incident on the light beams 21 and 22 to form light beams 21 and 22. however,
The shaded portion of the light beam 21.22 undergoes diffraction 131 by the polarization hologram 13.15, as will be described later, and is therefore incident on another detector.

The light beam passing through the polarizing hologram 13 has +1st order and -
The first-order diffracted lights are incident on detectors 17 and 18, respectively. In the light beam passing through the polarizing hologram 15, the +1st order and -1st order diffracted lights are sent to the detectors 19 and 2o, respectively.
is incident on the Therefore, the focus error signal is obtained by calculating the output of each of the three-part detectors 7 and 8 based on equations (1), 2, and (2) as explained in FIG. The tracking error signal is ((17)+(1B))-((19)+(20))
...... It can be obtained by calculating the detector output of equation (6), and the magneto-optical signal is obtained by calculating the +1st order diffracted light and -1st order diffracted light based on equation (3). This can be obtained by adding up all the received detector outputs and taking the difference from the output of the detector 6 that receives the zero-order light.

In this way, the focus error signal is transmitted to the detectors 7 and 8.
It is obtained by calculating the output of light beam 2.
1.22, there is no light in the portion corresponding to the polarizing hologram 13.15 (shaded area) 14,.

However, this portion has almost no influence on the focus error signal, and in fact, the interference of the tracking error signal with the focus error signal is reduced, giving a favorable result.

The angle between the +1st and -1st order diffraction directions of the polarizing hologram to obtain the tracking error signal and the +1st and -1st order diffraction directions of the polarizing hologram to obtain the focus error signal should be designed to be as small as possible. is desirable. This is because, as shown in FIG. 5(b), the angle of analysis when obtaining the magneto-optical signal is 12. This is because j4°16, 13, and 15 are different.

One way to make this angle as small as possible is to change the carrier frequency of the polarizing holograms 13 and 14. By changing the carrier frequency of the polarizing hologram, the diffraction angle of the light beam diffracted by the polarizing hologram can be changed.

Although the angle is exaggerated in FIG. 6(b), the carrier frequencies of the polarizing holograms are almost the same in all polarizing holograms 12 to 16.

FIG. 6 on page 15 shows an example of changing the carrier frequency of a polarizing hologram. There are detectors 25, 26 corresponding to the polarizing hologram 23 and detectors 27, 28 corresponding to the polarizing hologram 24.

As shown in FIG. 6(b), the carrier frequency of both holograms 23, 24 is higher than that of the polarizing holograms 12, 14, 16 for focus error signals, and by arranging them as shown in the figure, the analyzer It is possible to reduce the difference in the ing angle.

Furthermore, by increasing the carrier frequency of one of the polarizing holograms, it is possible to completely match the analyzing angles. FIG. 7 shows detectors 29 and 30 corresponding to such a polarizing hologram. In this way, the magneto-optical signal can be detected without changing the analyzing angle using the multi-divided polarizing hologram.

Figures 1 to 7 show examples of the same focusing error detection method, but polarizing holograms 5' and 5'' as shown in Figures 8 (a) and (b) are used to eliminate astigmatism. It is also possible to use a detector 31 that generates light.

The polarizing hologram has the effect of a cylindrical lens that causes astigmatism. At this time ±1
Astigmatism occurs in the next diffracted light, and its circle of minimum confusion
oJIPcircle ) By inserting a detector in the vicinity, a non-depressing aberration type focusing operation can be performed.

In addition, a polarizing hologram 5' as shown in FIG. 6(C)
``Double knife detector 32 using
It is also possible to use (JP-A-61-120352
(see publication).

For example, as disclosed in Japanese Unexamined Patent Publication No. 120352/1982, semicircular beams with different focal states can be positioned on the detector. In this case, the polarizing hologram needs to be designed so that the upper and lower halves on the optical axis have different focal points and are blazed to +1st order light. At this time, the diffraction efficiency of the 0th-order light and the +1st-order light changes slightly, but this is due to the difference between the individual components connected to each detector.

You can achieve balance by adjusting the gain of the fur amplifier.

FIG. 9 shows a circuit configuration used in realizing the present invention. The numbers in parentheses at the left end are the numbers of the detectors in the drawings shown in FIGS. 2 and 3, and here indicate that the output is input from each detector. Buffer amplifiers 34 to 38 mainly convert the impedance of input signals. Buffer amplifier 34.35
The output of is subtracted by a differential amplifier 39 to obtain a focus error signal 43. Buffer amplifier 36. The output of 37 is subtracted by a differential amplifier 40 to obtain a far-field tracking error signal. Buffer amplifier 34-37
The outputs of are added by an adding amplifier 41 and subtracted from the output of the buffer amplifier 38 by a differential amplifier 42 to obtain a magneto-optical signal 45. If the information carrier is a normal phase pattern or a gray pattern, the outputs of the amplifier 41 and the output of the amplifier 38 can be added to obtain the information signal as in the conventional case.

18/<-A Effects of the Invention As described above, according to the polarizing hologram of the present invention, it is possible to easily detect magneto-optical signals and to combine functions that have been difficult with conventional methods.

In addition, in the present invention, by utilizing polarization separation using a hologram, functions such as a wavelength plate, a Glaston prism, a polarization beam splitter, etc. that were required in the past can be integrated into one element and simplified, reducing costs and assembly process. can be simplified.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic optical system configuration of a polarization separation type hologram head according to an embodiment of the present invention, and FIG.
Figure 3 is a plane a and cross-sectional view of the polarizing hologram, Figure 4 is a schematic diagram showing the basic detector configuration and operation for obtaining the focus error signal and magneto-optical signal, and Figure 5 is the multi-division polarizing hologram. A schematic diagram showing a configuration example of a polarizing hologram and a detector from which a focus error signal, a tracking error signal, and a magneto-optical signal are obtained.
7, 7 A schematic diagram showing an example of a polarizing hologram and detector configuration that reduces the difference in analyzing angles for obtaining magnetic signals, Figure 7 is a schematic diagram showing an example of the improved detector configuration, and Figure 8 shows its focus error. A schematic diagram showing an embodiment of a polarizing hologram and a detector configuration for obtaining a signal. FIG. 9 is a circuit diagram showing an example of the circuit configuration. 1... Semiconductor laser, 2... Objective race, 3... Disc, 4... Beam splitter, 5, 12° 13.14, 15, 16, 23.2
4...Hologram, 6, 7, 8, 17, 18, 1
9,20,25゜26 27 28 29 3
0 31 32...Detector, 34-38
......Amplifier, 39,40°42...Differential amplifier, 41.47...Adder. Name of agent: Patent attorney Shigetaka Awano and one other person

Claims (7)

[Claims] (1) a radiation light source; an optical means for receiving a light beam emitted from the radiation light source and converging the light beam onto an information recording carrier; a beam splitter located between the optical means and the radiation light source; and the information carrier. a polarization hologram that transmits or reflects the light beam reflected by the beam splitter and split by the beam splitter, and polarizes the transmitted or reflected 0th-order light and the +1st-order diffracted light so that they are orthogonal to each other, and the 0th-order light and the -1st-order diffracted light are orthogonal to each other; , polarized 0th order light, +1st order diffracted light and -
A polarization separation type hologram head including a plurality of photodetectors that receive first-order diffracted light. (2) Polarization holograms produce light beams of different sizes as +1st-order diffracted light and -1st-order diffracted light on a photodetector when the distance between the information carrier and the optical means for converging the light beam is inappropriate. If the distance between the information carrier and the optical means for converging the light beam is appropriate, the +1st-order diffracted light and the -1st-order diffracted light are made to have approximately the same size on the photodetector. The polarization separation type hologram head according to claim 1, wherein the polarization separation type hologram head is configured to input the beam as a beam. (3) Polarization holograms produce light beams of different shapes as +1st-order diffracted light and -1st-order diffracted light on a photodetector when the distance between the information carrier and the optical means for converging the light beam is inappropriate. When the distance between the information carrier and the optical means for converging the light beam is appropriate, the +1st-order diffracted light and the -1st-order diffracted light are formed into light beams of approximately the same shape on the photodetector. The polarization separation type hologram head according to claim 1, wherein the polarization separation type hologram head is configured to allow the light to enter. (4) A polarization hologram comprising a portion having at least three different patterns, and a photodetector into which the corresponding +1st-order diffracted light, −1st-order diffraction light, and 0th-order diffraction light are incident, and the polarization hologram has different patterns. 2 of them
One part receives a light beam containing mainly the diffracted signals due to the tracks on the information carrier, and the remaining part of the polarization hologram receives the light beam which mainly contains the diffracted signals due to the tracks on the information carrier, and the remaining part receives the light beam if the distance between the information carrier and the optical means for converging the light beam is unsuitable. +1st-order diffracted light and -1st-order diffracted light are incident on a photodetector as light beams of different sizes, and when the distance between the information carrier and the optical means for converging the light beams is appropriate, the light is + on the detector
2. The polarization separation type hologram head according to claim 1, wherein the first-order diffracted light and the -first-order diffracted light are made to enter as light beams of approximately the same size. (5) A polarization hologram consisting of a portion having at least three different patterns, and a photodetector into which the corresponding +1st-order diffracted light, -1st-order diffraction light, and 0th-order diffraction light are incident, and the polarization hologram has different patterns. 2 of them
one part receives a light beam containing mainly the diffracted signals due to the tracks on the information carrier, and the remaining part of the polarization hologram receives the light beam which mainly contains the diffracted signals due to the tracks on the information carrier, and the remaining part receives the light beam if the distance between the information carrier and the optical means for converging the light beam is unsuitable. The +1st-order diffracted light and the -1st-order diffracted light are incident on the photodetector as light beams of different shapes, and the photodetection is performed when the distance between the information carrier and the optical means for converging the light beams is appropriate. +1 on the vessel
2. The polarization separation type hologram head according to claim 1, wherein the second-order diffracted light and the -first-order diffracted light are made to enter as light beams having substantially the same shape. (6) Output of the photodetector into which the 0th-order diffracted light is incident, and +1
6. The polarization separation type hologram head according to claim 1, further comprising a circuit for creating a differential signal between the second order diffraction light and the sum of outputs of a photodetector into which the second order diffracted light is incident. (7) The polarization separation type hologram head according to claim 4 or 5, comprising a polarization hologram and a photodetector, each consisting of at least three different patterns having at least two different carrier frequencies.