JP2643595B2 - Optical head device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device, and more particularly, to an optical circuit for irradiating a recording medium with laser light to process return light and processing a detected signal thereof. The present invention relates to an optical head device having means.

[Conventional technology]

Generally, an optical information recording / reproducing apparatus converges a laser beam from an internal laser light source and irradiates the laser beam onto a minute area (spot) on a recording medium surface. Information is recorded, and at the time of reproduction, reading of recording and spot position control are performed by detecting laser light (return light) reflected and diffracted on the recording medium surface. This type of recording system has a very high information recording density because information is recorded in a minute area on the surface of a recording medium, and is attracting attention as a next-generation recording system.

The optical head of the optical information recording / reproducing apparatus is manufactured very precisely and has a basic configuration as shown in FIG. A laser diode 5 as a laser light source, a collimating lens 4 for converting the laser light emitted from the laser diode 5 into parallel rays, and a light transmitted through the collimating lens 4 toward the information recording medium 1 and a return light from the information recording medium 1. Recording signal detection system (such as two-segment detector 18) and spot position error detection system (such as beam splitter 20)
And an objective lens 2 for forming a laser beam spot on the information recording medium 1 with the light transmitted through the two beam splitters 14 and 15.

The recording signal detection system of the optical head includes a beam splitter 14
A converging lens 16 that converges the return light separated by the above, a Wollaston prism 17 that separates the return light converged by the converging lens 16 into two orthogonal polarization components, and two return lights that are separated by the Wollaston prism 17 And a two-segment detector 18 for independently detecting light.

The spot position error detection system of the optical head includes a converging lens 19 for converging the return light separated by the beam splitter 15 and a return light converged by the converging lens 19 for a light for focus error detection and a light for track error detection. A beam splitter 20 for separating the light into light, and detecting a track error detecting light separated by the beam splitter 20 2
A knife edge 22 for detecting the focus error detection light separated by the beam splitter 20 by the knife edge method; and a two-segment detector 23.

 Next, the optical operation of the optical head will be described.

The laser light emitted from the laser diode 5 is diffused light, and becomes parallel laser light by the collimating lens 4. The parallel laser beam passes through the beam splitter 15 and the beam splitter 14 and is converged by the objective lens 2 to form a spot on the surface of the information recording medium 1. The laser light is reflected and diffracted on the surface of the information recording medium 1 and returns to the objective lens 2. (Hereinafter, this light is referred to as return light.) The return light is converted into a parallel light by the objective lens 2 and is a beam splitter.
At 14, the light is separated into a recording signal detection system and light traveling to a beam splitter 15. The light returned to the beam splitter 15 is reflected by the beam splitter 15 and travels to a spot position error detection system.

The light traveling toward the recording signal detection system is converged by the converging lens 16 and separated by the Wollaston prism 17 into two mutually orthogonal polarized lights having different directions. These two lights are independently detected by the two-segment detector 18, converted into an electric signal, and output to a signal (not shown) for processing the electric signal.

The light heading for the spot position error detection system is converged by a converging lens 19 and is split by a beam splitter 20 into a two-part detector 21.
The light is separated into light traveling toward the two-way detector 23 and light traveling toward the two-division detector 23.

The light traveling to the two-division detector 21 is converted into an electric signal by the two-division detector 21 and output as a track error signal P2 to a device (not shown) for processing the electric signal.

The light traveling to the two-division detector 23 is detected by the knife edge 22 and the two-division detector 23 constituting the focus detector by the knife-edge method, and the electric signal is processed by the two-division detector 23 (see FIG. Not shown.) Focus error signal
Output as P1.

[Problems to be solved by the invention]

The optical head of the conventional optical information recording / reproducing apparatus has a configuration in which the recording signal detection system and the spot position error detection system are independent, so that the number of components of the optical circuit is large, so that adjustment is difficult, and the size is small. There was a problem that conversion was not easy.

Furthermore, since laser light and return light pass through many beam splitters and divide the light amount, if the laser light amount (emission efficiency) from the laser diode to the information recording medium is to be obtained, the reflected light amount of the beam splitter will be reduced. As a result, the amount of light returning to the recording signal detection system and the spot position error detection system becomes insufficient, and there is a problem that the emission light rate becomes low when trying to obtain a sufficient amount of light to these detection systems. .

[Object of the invention]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the disadvantages of the conventional example and to provide a small-sized optical head in which the number of components of an optical circuit is rationalized.

[Means for solving the problem]

According to the present invention, a collimating lens, a beam splitter, and an objective lens are sequentially arranged along an optical path from a laser light source to a recording medium, and a light converging lens for converging reflected return light separated by the beam splitter; And a Wollaston prism that separates the light into two polarizations having polarization planes perpendicular to each other, and separates the optical paths of those polarizations into different optical paths.

Further, a photodetector for independently detecting the polarized light separated by the Wollaston prism and converting it into an electric signal is provided. This photodetector detects a zero-order diffracted light of the reflected return light, and a detection portion of the reflected return light. It is divided into at least two detection portions, that is, a detection portion that detects interference light between the zero-order diffracted light and the first-order diffracted light.

Further, this photodetector is provided with two detection units including a four-division detection unit having four detection units and another detection unit having one detection unit. The four-division detection unit is configured such that two detection portions of the four-division detection unit are close to a straight line connecting the centers of the two detection units, and are symmetrical with respect to a straight line connecting the centers of the two detection portions and are perpendicular to the straight line. The remaining two detection portions of the four-segment detection unit on the equal line form a four-segment detection unit arranged close to each other.

This aims to achieve the above-mentioned object.

[Action]

The path of the reflected return light is changed toward the photodetector by one beam splitter on the optical path from the laser light source to the recording medium, and the reflected return light is converged by a converging lens.

The Wollaston prism separates the reflected return light into two polarized lights having polarization planes perpendicular to each other, and separates the optical paths of those polarized lights into different optical paths.

The photodetector independently detects the converged polarized light and converts it into an electric signal. In the divided detection part,
The 0th-order diffracted light of the reflected return light and the interference light of the 0th-order diffracted light and the 1st-order diffracted light of the reflected return light are detected independently.

〔Example〕

Next, an embodiment of the present invention will be described with reference to FIGS. Here, the same components as those in the conventional example described above are denoted by the same reference numerals.

The basic configuration of the optical head of the embodiment shown in FIG. 1 includes a laser diode 5 as a laser light source, a collimating lens 4 for converting the laser light emitted from the laser diode 5 into parallel rays, and information transmitted through the collimating lens 4 for information. A beam splitter 3 for turning the light traveling toward the recording medium 1 and the return light from the information recording medium 1 toward a detection system, and an objective lens 2 for forming a laser beam spot on the information recording medium 1 using the light transmitted therethrough. .

Further, the detection system includes a λ / 2 plate 6 for rotating the polarization plane of the return light whose path is bent by the beam splitter 3, and
A converging lens 7 for converging the return light whose polarization plane has been rotated by the λ / 2 plate 6, and a Wollaston prism 8 for separating the return light converged by the converging lens 7 into two orthogonal polarization components.
And a photodetector 9 for independently detecting the two return lights separated by the Wollaston prism 8.

Next, the operation of the optical circuit of the optical head will be described.

The laser light emitted from the laser diode 5 is diffused light, and becomes parallel laser light by the collimating lens 4. The parallel laser light passes through the beam splitter 3 and is converged by the objective lens 2 to form a spot on the surface of the information recording medium 1. The laser light is reflected and diffracted on the surface of the information recording medium 1 and returns to the objective lens 2. (Hereinafter, this light is referred to as return light.) The return light is converted into a parallel light by the objective lens 2, and its path is bent by the beam splitter 3 to the detection system. The return light toward the detection system is rotated in the polarization plane by the λ / 2 plate 6. The return light passing through the λ / 2 plate 6 is converged by the converging lens 7. As shown in FIG. 2, the cross section of the return light perpendicular to the optical axis is an interference pattern (ball shape pattern 10) between the 0th-order diffracted light and the 1st-order diffracted light due to diffraction on the surface of the information recording medium 1. .

The direction of the optical axis of the return light is defined as the z-axis, the direction of the first-order diffracted light is defined as the x-axis on a plane perpendicular to the z-axis, and the y-axis is defined perpendicular to the x-axis. The Wollaston prism 8 is arranged in the converging optical path of the return light so that the polarization separation direction is on the yz plane. Therefore, the return light that has passed through the Wollaston prism 8 is separated into two mutually orthogonal polarization components,
Proceeding in different directions symmetrically with respect to the axis, the light detector 9 makes two convergent spots. The light is detected by the light detector 9 and converted into an electric signal.

In the experiment, when a plano-convex lens having a glass material BK7, a curvature of 13 mm, and a thickness of 3 mm was used as a converging lens 7 by attaching it to a 5 mm square quartz Wollaston prism 8, it was separated from the rear end face of the Wollaston prism 8 by about 20 mm in the axial direction. At the position, two spots about 200 μm apart from the z-axis are obtained on the yz plane.

As shown in FIG. 3, the photodetector 9 has a quadrant detection unit 12 having four detection parts and a detection unit 13 having one detection part.
Are provided. Quadrant detector 12 and detector
13 is located symmetrically to the origin on the xy plane, and 4
The division detection unit 12 detects light separated by the Wollaston prism 8 and traveling in the positive y-axis direction, and the detection unit 13 detects light separated by the Wollaston prism 8 and traveling in the negative y-axis direction. .

A, C from the side farthest from the origin of the light-receiving surface on the y-axis in the light-receiving surface of the four-split detection unit 12; Is D, and the detection unit
The light receiving surface of 13 is denoted by E, and the detection signals detected from A, B, C, D and E are denoted by a, b, c, d and e.
At d, interference between the 0th-order diffracted light and the 1st-order diffracted light is detected. In the entire 4-split detection unit 12 and e, that is, in the detection unit 13, the total amount of the return light is detected by their sum, and the change in the polarization plane of the return light is detected by their difference. By processing these detection signals, various control signals and recording signals can be obtained.

Here, a method for reproducing various control signals and recording signals similar to those of the conventional example in order to connect to an apparatus (not shown) for processing an electric signal in an existing optical information recording / reproducing apparatus will be described.

Since the focus error signal P1 is obtained by the difference in light amount between the 0th-order diffracted light and the 1st-order diffracted light, the detection signals a, b, c, d, and e are obtained by performing signal processing of "(a + c)-(b + d)". .

Since the track error signal P2 is obtained as a light quantity difference due to diffraction of the 0th-order diffracted light and the 1st-order diffracted light, the detection signals b and d are obtained by performing signal processing of "bd".

Since the recording signal P3 reproduced from the fluctuation of the light amount in a phase change medium such as a compact disk or a hole-recording type write-once optical disk can be obtained with the total light amount, the detection signals a, b, c, d and e are calculated as "(a + b + c + d) + e It can be obtained by signal processing.

Since the recording signal P4 reproduced from the change in the polarization plane of the magneto-optical disk or the like is obtained from the difference in the polarization plane, the detection signal a,
b, c, d, e are obtained by performing signal processing of “(a + b + c + d) −e”.

An embodiment of this signal processing circuit 50 is shown in a block diagram in FIG.

FIG. 4 shows an example in which an analog computing unit is used.
The amplifier 51, the amplifier 52, the amplifier 53, the amplifier 54, and the amplifier 55 are amplifiers that amplify the detection signals a, b, c, d, and e to an appropriate level for the input of the next-stage arithmetic unit. The adder 56 calculates and outputs “a + c”. The adder 57 calculates and outputs “b + d”. The subtractor 58 calculates “b−d” and outputs a track error signal P2. The subtractor 59 includes an adder 56 and an adder 57
, That is, “(a + c) − (b + d)”, and outputs a focus error signal P1. The adder 60
The addition of the adder 56 and the adder 57, that is, "a + b + c +
d ”is calculated and output. The adder 61 is composed of the adder 60 and the amplifier.
An addition of 55, that is, "(a + b + c + d) + e" is calculated, and a recording signal P3 reproduced from the light quantity fluctuation is output. The subtractor 62 subtracts the adder 60 and the amplifier 55, that is, “(a
+ B + c + d) -e "to output a recording signal P4 reproduced from the change in the polarization plane. Various control signals and recording signals similar to those in the conventional example are output to a device (not shown) for processing electric signals.

When the embodiment shown here is compared with the above-mentioned conventional example, the number of optical circuit components requiring high precision of the optical head is greatly reduced, and the number of adjustment steps is reduced. Further, since only one return beam passes through the beam splitter, a sufficient amount of light can be obtained to the detection system.

〔The invention's effect〕

As described above, according to the present invention, the optical circuit components that require the accuracy constituting the optical head are streamlined,
Since the returning light does not pass through one beam splitter, a sufficient amount of light can be obtained to the detection system, and since there is only one photodetector, the man-hours for adjusting these optical circuits are reduced, and the device can be easily miniaturized. In addition, there is an effect that the mass productivity is further improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing how polarization is separated by a Wollaston prism, FIG. 3 is a block diagram of a photodetector, and FIG. 4 is a signal processing circuit. FIG. 5 is a block diagram showing a conventional example. DESCRIPTION OF SYMBOLS 1 ... Information recording medium, 2 ... Objective lens, 3 ... Beam splitter, 4 ... Collimating lens, 5 ... Laser diode, 7 ... Convergent lens, 8 ... Wollaston prism, 9 ... Photodetector , 12... 4 division detector, 13.
Detector, 50: Signal processing circuit, P1: Focus error signal, P2: Track error signal, P3: Recording signal reproduced from fluctuation in light amount, P4: Recording signal reproduced from fluctuation in polarization amount.

Claims (2)

(57) [Claims] A collimating lens, a beam splitter, and an objective lens are sequentially arranged along an optical path from a laser light source to a recording medium, and a light converging lens for converging reflected return light split by the beam splitter; A Wollaston prism that separates the light into two polarized lights having polarization planes perpendicular to each other and separates the optical paths of those polarized lights into different optical paths, and independently detects the polarized lights separated by the Wollaston prism. A photodetector for converting the reflected return light into 0th-order diffracted light and an interference light between the 0th-order diffracted light and the 1st-order diffracted light of the reflected return light. An optical head device having a portion divided into at least two detection portions including a detection portion, wherein the photodetector includes a four-division detection portion having four detection portions and one detection portion.
And two detection units each including another detection unit having one detection unit, wherein the four division detection units are arranged such that the two detection parts of the four division detection units are close to a straight line connecting the centers of the two detection units. And the other two detection parts of the four division detection part are symmetrically arranged on a straight line connecting the centers of these two detection parts and on the vertical bisector of the straight line, thereby forming a four division detection part arranged in close proximity. An optical head device characterized by the following. 2. The signal detected by the four-division light detection unit is defined as a, b, c, d clockwise with respect to a position where the distance from the center of the detector is the maximum. When the signal detected by the detection unit is e, a focus error signal: P1 = (a + c) − (b + d) a track error signal: P2 = b−d a recording signal reproduced by a change in light amount: P3 = (a + b +
c + d) + e Recorded signal reproduced by polarization fluctuation: P4 = (a + b)
2. The optical head device according to claim 1, further comprising means for calculating and outputting + c + d) -e.