JPS6278755A - Pickup for photomagnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a highly efficient pickup for photomagnetic recording medium by transmitting approximately all of the laser light made incident on a half mirror through a lambda/2 plate in a record mode and moving this lambda/2 plate to avoid transmission of the laser light in a reproduction mode respectively. CONSTITUTION:The half of the light passed through a beam shaping prism 7 is made incident on a PBS 26. While the other half of said light passes through a lambda/2 plate 28 and is made incident on an HM 27 which reflects and transmits by half both S and P polarized waves respectively. The laser light passed through the PBS 26 and the HM 27 is focused by an objective lens 2 and irradiated on a disk 1 for heating. The laser light deliver from a laser device is all sent toward a photomagnetic recording medium and focused with maximum efficiency. In a reproduction mode, the plate 28 is removed. Then a semiconductor laser device 9 emits light by a laser drive circuit 10 and focuses the laser light 3 passed through a collimator lens 8, the prism 7, the PBS 26 and the HM 27 onto the surface of the disk 1 through the lens 2. The laser light is made incident on the recording surface in the form of a linear polarized wave as it is. Thus the photomagnetic recording medium has no trouble with its reproduction of signals.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical pickup for a magneto-optical recording medium used in a recording/reproducing apparatus for erasable magneto-optical recording media.

Conventional magneto-optical recording media include disk-type media and f-card type media, but the following explanation will be made using disks as a representative example.

There are three types of optical disc players: read-only type, write-once type, and erasing type. The present invention relates to a pickup used for magneto-optical discs and the like belonging to the erasing type.

A magneto-optical disk has a magnetic thin film formed on the disk base. During recording, the coercive force of that area is lowered by local heating with laser light, and at the same time, the direction of magnetization is reversed by applying an external magnetic field. be. During playback, a directly polarized laser beam is irradiated onto the signal surface of the disc, and the Kerr effect of the reflected light is used to separate the rotation of the polarization angle of the reflected light with an analyzer and read with a photodetector. be. .

A conventional recording pickup for recording signals on a magneto-optical disk will be explained with reference to FIG. 5, and a conventional reproduction pickup for reproducing signals from a disk on which signals have been recorded will be explained using FIG. 6.

In Fig. 5, 1 is a disk, 2 is an objective lens, 3 is a radar beam, 4 is a coil, 5 is a λ/4 plate, 6 is a polarizing beam splitter (hereinafter referred to as rPBsJ), 7 is a beam shaping prism, and 8 is a A collimating lens, 9 a semiconductor radar device, 10 a laser drive circuit, 11 a modulation circuit, 12 a lens, 13 a dividing mirror, and 14.15 a photodetector. A signal to be recorded is modulated by a modulation circuit 11, and a laser drive circuit 10 causes the semiconductor laser device 9 to emit light. The laser light emitted from the semiconductor laser device 9 is shaped from an elliptical diffused light to a circular parallel light by the collimating lens 8 and the beam shaping prism 7, passes through P8S6, becomes circularly polarized light by the λ/4 plate 5, The light is focused onto the disk 1 by the objective lens 2. The signal surface of the disk 1 is heated by the laser beam 3 focused on the disk 1, and at the same time an external magnetic field is applied by the coil 4, causing a reversal of the magnetization direction. The laser beam reflected by the disk 1 passes through the objective lens 2 and the λ/4 plate 5 again, is reflected by P2S5, becomes a focused beam by the lens 12,
The light that has passed through and reflected from the split mirror 13 enters two split photodetectors 14 and 15, respectively, and a focusing error signal and a tracking error signal are obtained.

In Fig. 6, 16 is a half mirror (hereinafter referred to as "HM"), 17 is a laser drive circuit, 18.19 is a beam splitter (hereinafter referred to as rBsJ), 20.21 is an analyzer, and 22.23 is a photodetector. 24 is a differential amplifier, and 25 is an output terminal. The laser drive circuit 17 causes the semiconductor laser device 9 to emit light with the laser output necessary for reproduction, and the collimator lens 8 and beam shaping prism 7 convert the light into circular parallel light. focus on. The laser beam reflected by the disk 1 and having its linearly polarized plane of polarization rotated by the Kerr effect passes through the objective lens 2 again, is reflected by the 8M16, and is reflected by the 8S
18, and is separated into transmitted light and reflected light at another [3319]. Each light is separated into a specific plane of polarization by an analyzer 20.21, and then directed to a photodetector 22.23. The outputs of both photodetectors 22 and 23 are detected by the differential amplifier 24 as a signal for disk 1, and are sent to the output terminal 25.
is output to.

In this way, the big difference between recording and reproducing is that during recording, the polarized light is not linearly polarized (which is better, but it is necessary to remove heat by 1-J to change the direction of magnetization, so a large output is required, but during reproducing, it is not linearly polarized light). Quite to the contrary, although the laser output may be small, the Kerr effect peculiar to magneto-optics cannot be detected unless the laser beam 3 directed to the surface of the disk is linearly polarized.

Therefore, during recording, the light is circularly polarized by a λ/4 plate using P8S6, and is quickly reflected by disk 1. When it enters PBS6 again, it is perpendicular to the plane of polarization at the time of output and is completely reflected by PBS6, maximizing efficiency. That's what I do. The transmission efficiency of the optical path is set to 50%, and the laser power required for one disk surface is 8 m.
Assuming W, the output of the semiconductor laser device 9 only needs to be 16 mW.

During playback, 1 mW on one side of the disc is sufficient, so
Similarly to the above, if the transmission efficiency of the optical path is 50%, the output of the semiconductor laser device 9 is halved at 8M16, so 4 mW is required.

There is another conventional device that performs recording and reproduction with a configuration similar to that shown in FIG. Modulate. However, with this method, P
Since 8M16 is used instead of the BS 6 and the λ/4 plate 5, the radar light from the semiconductor device ZAg@9 is 8M16, which is 172.

Therefore, assuming that the transmission efficiency of the optical path is 50% and the required laser power on one surface of the disk during recording is 8 mW, the output of the semiconductor laser device 9 must be 32 mW. The price of the semiconductor laser device 9 increases at an accelerating rate as the laser output increases, and the lifetime also decreases as the output increases. From another perspective, compared to low-output laser devices for reproduction, high-output radar devices for recording are shipped in fewer units, so they are inevitably more expensive.

Problems to be Solved by the Invention Conventionally, due to the cost, lifespan, and efficiency of the semiconductor laser device, recording and reproducing pickups have been completely separate from each other to record and reproduce information on magneto-optical disks. However, using a completely different pickup has problems in terms of efficiency, cost, and lifespan, and when the pickup is incorporated into a recording/playback device, there are major problems in terms of the size and price of the device. occurs.

The present invention solves the above conventional problems, and provides an efficient pickup for magneto-optical recording media that can perform both recording and reproduction without using an unnecessary high-output semiconductor laser device. The purpose is to

Means for Solving the Problems In order to solve the above problems, the pickup for a magneto-optical recording medium of the present invention includes a laser device for recording and reproducing images on a magneto-optical recording medium, and a laser device for recording and reproducing images on a magneto-optical recording medium. A collimating lens that covers the laser beam from the device into parallel light; an objective lens that focuses the laser beam that has passed through the collimating lens onto the magneto-optical recording medium; a photodetector for detecting the position of the track, a detection device for detecting the plane of polarization rotated by the Kerr effect during reproduction, and the collimating lens and the objective lens so that the laser beams are incident on each other with the same width. Polarizing beam splitter and half mirror installed in parallel
and a λ/2 plate that is removably inserted between the collimating lens and the half mirror, and the laser beam is directed toward the polarizing beam splitter after being reflected by the half mirror; The reflected laser beam is directed toward the magneto-optical recording medium, and during recording, almost the entire amount of the laser beam incident on the half mirror passes through the λ/2 plate, and during reproduction, the λ/2 plate is moved to direct the laser beam. The structure is such that it does not allow the passage of.

Effects According to the above configuration, half of the laser light is incident on the polarizing beam splitter and half of the half mirror, and the λ/2 plate is inserted into the half mirror side only during recording, so that only half of the laser light emitted from the laser beam is incident on the half mirror. The light that has passed through the half mirror side is reflected by the magneto-optical recording medium and then directed toward the polarizing beam splitter, and the light that has passed through the polarizing beam splitter side is reflected by the magneto-optical recording medium and then directed toward the half mirror.

If the polarization plane of the laser beam is set at an angle that allows it to pass through the polarizing beam splitter, the light incident on the half mirror will be λ/2
After passing through the plate, the plane of polarization becomes perpendicular to the light incident on the λ/2 plate, reflected by the half mirror, and all the light directed toward the polarizing beam splitter is directed toward the magneto-optical recording medium, so it is ultimately emitted from the laser device. All of the emitted laser light is directed toward the magneto-optical recording medium, and the laser light is focused on the magneto-optical recording medium with maximum efficiency.

During reproduction, by removing the λ/2 plate, the recording surface of the magneto-optical recording medium is directly exposed to I! Since the laser beam is incident as J-polarized, there is no problem in signal reproduction from the magneto-optical recording medium. In the method of replacing the beam splitter during recording and playback, the precision and angle of mounting the beam splitter are problems, and an accuracy of 1 μm or less is required, which is actually impossible. When a parallel plate is moved in and out through parallel light, viscosity is not required much.

EXAMPLE Hereinafter, an example of the present invention will be described based on FIGS. 1 to 4.

FIG. 1 is a configuration diagram of a pickup for a magneto-optical recording medium according to an embodiment of the present invention, and the same components as those shown in FIGS. 5 and 6 are given the same reference numerals and explanations thereof are given. Omitted. In FIG. 1, 26 is a polarizing beam splitter (hereinafter referred to as rP8sJ), 27 is a half mirror (
Hereinafter referred to as rHMJ ("F"), 28 is a λ/2 plate.

First, the operation during recording will be explained. Modulation circuit 11
The laser driving circuit 10 modulates the semiconductor laser device 9 using the signal from the laser beam, and the collimating lens 8 and beam shaping prism 7 convert the elliptical diffused light into circular parallel light. Half of the light passing through the beam shaping prism 7 is PBS
The other half passes through the λ/2 plate 28 and enters the 8M 27, which reflects and transmits half of both the S and P polarizations. The laser beams that have passed through the PBS 26 and l-(M27) are focused by the objective lens 2, and are irradiated onto the disk 1 to heat it. A current is applied to a certain coil 4 to generate an external magnetic field to cause magnetization reversal in the disk 1.The light reflected by the disk 1 enters the objective lens 2 again, and after being reflected by the PBS 26 and )1M27,
318, passes through the lens 12, and is reflected by the mirror 1
3 and are incident on photodetectors 15 and 14, respectively, to obtain a tracking error signal and a focusing error signal.

At the time of reproduction, the λ/2 plate 28 is removed. The laser drive circuit 10 causes the semiconductor laser device 9 to emit light, and the collimator lens 8, beam shaping prism 7, PBS 26 and 8M2
The laser beam 3 that has passed through
Focus on a surface. The light reflected by the disk 1 passes through the objective lens 2, and then is reflected by the PBS 26 and 8M27.
It passes through B 3 is, passes through B519, and is reflected, and each passes through an analyzer 20.21 and heads toward a photodetector 22.23. The light received by the photodetectors 22 and 23 is converted into an electrical signal, enters the differential amplifier 24, and outputs an output signal to the output terminal 25.

In this embodiment, error detection in scanning and tracking is carried out by a lens 12, a splitting mirror 13, and a photodetector 14, 15, which is called the Knifezi method.

Next, the path of the laser beam until it reaches the disk 1 will be explained.

First, in the case of recording shown in FIG. 2, the plane of polarization of the laser beam 29 from the semiconductor laser device 9 is set horizontally in the paper as shown by the arrow 30, and the laser beam 29 is divided into two at the center.
Assuming that the left side is A and the right side is B, 8 is P-polarized when viewed from the P B S 26, so almost the entire amount of light is directed toward the disk 1, and B is transmitted through the λ/2 plate 28 and the polarization plane is The direction changes to the direction perpendicular to the plane of the paper, and 172 is transmitted at 8M27 and is directed toward disk 1, while the remaining 172 is reflected and is directed toward P[3326. P
The light heading toward B S 2G is S-polarized when viewed from the PB 326, and almost the entire amount of light is directed toward the disk 1. In the end, all the light from the semiconductor laser device 9 is directed toward the disk 1, so there is no loss.If the optical path transmission efficiency is 50% and the laser power required for one disk surface is (3rnW), the semiconductor laser output should be 16mW. .The light reflected by disk 1 is
A is NM27 and 172 is on the photodetector side (right side in the figure),
1/2 of B reflected by P B S 26 is 1 at 8M27
/4 goes to the photodetector side, 17 of B transmitted through l-1M27
2 is totally reflected by P[3S26, 1/2 is transmitted by IM27, 1/4 is directed toward the photodetector, and in the end, 1/2 of the amount of light is directed toward the photodetector.

During reproduction, as shown in Fig. 3, the semiconductor laser device M9
If the plane of polarization of the laser beam 31 from 2000 is set horizontally in the plane of the paper as shown by the arrow 32, and the laser beam 31 is divided into two at the center, and the left and right sides of the drawing are respectively C and [), then C is P B
The entire amount of light passes through S 26 and reaches the first surface of the disc, and D is 1/
2 goes to the first side of the disc, the remaining 172 go to P B S 26
However, it passes through PBS 26 as it is. In the end, 3/4 of the amount of light is directed toward the disk 1.

Of the laser beams reflected by disk 1, C is IM27.
1/2 goes to the photodetector side, and D goes to the PBS 26, but since the polarization plane of D is P polarization when viewed from the P8S 26, almost the entire amount of light is transmitted. In the end, the amount of light directed toward the photodetector becomes 1/4. In other words, the amount of laser light that is effectively used during reproduction is 1/4.

FIG. 4 shows another embodiment, in which P B
A diamond-shaped prism 33 composed of three prisms 33a to 33c is used instead of S26 and l-1M27.
may also be used. The bonding surface 34 of this prism 33 transmits almost the entire amount of P polarized light and reflects almost all of S polarized light. Furthermore, the bonding surface 35 transmits and reflects approximately half of both the P-polarized wave and the S-polarized wave.

In the above embodiment, a magneto-optical disk is used as the magneto-optical recording medium, but it goes without saying that a magneto-optical card may also be used.

Effects of the Invention As described above, according to the present invention, recording and reproduction are possible with one pickup, and the laser beam can be directed from the laser device to the magneto-optical recording medium with maximum efficiency. The optical output of K[l15' can be small, and not only the price of the magneto-optical recording/reproducing device can be significantly reduced, but also the size of the device can be reduced.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a pickup for a magneto-optical recording medium according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of the optical path during recording in the same pickup, and FIG. 3 is an illustration of the optical path during reproduction in the same pickup. FIG. 4 is a front view of a prism that integrates a polarizing beam splitter and a half mirror in another embodiment, FIG. 5 is a configuration diagram of a conventional recording pickup, and FIG. 6 is a diagram of a conventional recording pickup. FIG. 3 is a configuration diagram of a pickup for reproduction. DESCRIPTION OF SYMBOLS 1... Disk, 2... Objective lens, 8... Collimating lens, 9... Semiconductor laser device, 14, 15
, 22.23... Photodetector, 20.21... Analyzer, 26... Polarizing beam splitter, 27... Half mirror 128... λ/2 plate, 33... Prism agent Yoshihiro MorimotoFigure 2Figure 3Figure 4, 33# Figure 5Figure 4!

Claims (1)

[Claims] 1. A laser device for recording and reproducing signals on a magneto-optical recording medium, a collimating lens that converts the laser beam from the laser device into parallel light, and a collimating lens that converts the laser beam that has passed through the collimating lens into parallel light. an objective lens for focusing on the magneto-optical recording medium; a photodetector for detecting the position of the recording surface of the magneto-optical recording medium and the track formed on the magneto-optical recording medium;
a detection device for detecting a plane of polarization rotated by the Kerr effect during reproduction; a polarizing beam splitter and a half mirror arranged in parallel between the collimating lens and the objective lens so that equal amounts of laser light are incident on each other; A λ/2 plate is provided between a collimating lens and a half mirror so as to be freely inserted and removed, the laser beam is reflected by the half mirror and then directed toward the polarizing beam splitter, and the laser reflected by the polarizing beam splitter Light is directed toward the magneto-optical recording medium, and during recording, almost the entire amount of laser light incident on the half mirror passes through the λ/2 plate, and during reproduction, the λ/2 plate is moved to prevent the laser light from passing through. A pickup for magneto-optical recording media. 2. The pickup for a magneto-optical recording medium according to claim 1, wherein the polarizing beam splitter and the half mirror are integrally constituted as a rhombic prism consisting of three prisms.