JPH02214048A - Optical head - Google Patents

Abstract

PURPOSE:To simplify the constitution of an optical system and to miniaturize the entire part of the optical system by disposing a Faraday element in the optical path of collimated beams of light and splitting and detecting the reflected light from a recording medium by a photodetector which divides the light receiving surface to plural regions. CONSTITUTION:The light emitted from a semiconductor laser 1 is collimated by a collimator lens 2 to the collimated beams of light which arrive through a polarized beam splitter 7 and an optical member 5 for the Faraday element to an objective lens 3. The beams are converged in this lens and the magneto-optical information recording medium 4 are irradiated with the beams. The light irradiating the recording medium 4 is rotated in the linearly polarized light by 45 deg. forward and backward at the time when the light passes the Faraday element and the polarized beam splitter 7 reflects only the polarized light component in the direction perpendicular to the lane of the figure and, therefore, the light is made incident on the photodetector 8. The photodetector 8 detects the quantities of the received light respectively independently on the light receiving surfaces divided to the quadrisected regions A, B, C, D. The information signal and servo signal are computed from the quantities of the received light of the plural regions and are taken out.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an optical head in an information recording and reproducing apparatus that records and/or reproduces information on an optical or magneto-optical information recording medium. .

(Prior art) In order to ensure sufficient recording capacity, recording media used in information recording and reproducing devices include optical video discs, compact discs, and write-once optical discs using metal thin films or dye-based recording materials. Optical or magneto-optical information recording media have been developed. The optical spatula P used for recording on or reproducing from such a recording medium needs to be as lightweight as possible since access speed is required.

However, conventional optical heads have a large number of parts and are difficult to miniaturize. For example, as a conventional optical head for magneto-optical memory, the one shown in FIG. 5 is known. Here, the semiconductor radar 101 is used as a light source, and the diverging light from this is converted into a parallel beam via a collimator lens 102, and is applied to an objective lens 105 via a beam shaping prism l03&(i-light beam splitter 104).
Here, the light is condensed to form a spot on the surface of the recording medium 106, and the reflected light is returned to the beam sinter 104 through the objective lens 105, where a part of the reflected light is separated, and the control optical system is bringing it to. In the above-mentioned control optical system, a polarizing beam splitter 10 separately prepared for separating light beams is used.
7, and the - side is further separated by a 1/2 wavelength plate 108. It is delivered to a polarizing beam splitter 110 via a condensing lens 109, where it is further separated and supplied to photodetectors 111, 112, and the other is sent to a condensing lens 113. half prism 1
14 to a photodetector 115 and a knife 116
The signal is sent to the photodetector 117 via the signal, and the signal and the information signal are detected separately. In such a control optical system, condenser lenses 109 and 113 are used to ensure the sensitivity of the photodetector and the sensitivity of the servo signal.
is needed.

(Problems to be Solved by the Invention) As described above, since there are many optical system components, the weight of the optical head increases, and there is a situation in which the access speed cannot be increased.

Therefore, without using a condensing lens, the servo signal (
A method that can detect errors has been proposed. This is called the critical angle method, but in this method, the reflection characteristics near the critical angle change very rapidly, and the characteristics are discontinuous before and after the critical angle, so the critical angle prism The drawback is that fairly high precision is required for alignment adjustment.

To compensate for this drawback, for example, Japanese Patent Laid-Open No. 63-26
As described in Publication No. 1539, there is also a method of obtaining a seven-occurrence error signal using a beam splitter having a reflective surface made of a dielectric multilayer film whose reflectance changes continuously with respect to the incident angle. Although this method has been proposed, since the light beam is incident on the beam sinter as S-polarized light or P-polarized light, and another light splitting element is required, sufficient miniaturization cannot be achieved.

Incidentally, there is a component configuration of a semiconductor laser as shown in FIG. 6 or FIG. 7, and efforts are being made to miniaturize it. For example, in the semiconductor laser shown in FIG. 6, a semiconductor laser chip 7'l 19t- is disposed within a semiconductor laser matrix 118, a monitoring photodetector 120 is disposed behind it, and a micro-micrometer is provided as a collimator lens on the front surface. A Fresnel lens 121 is provided so that a parallel light beam 122 can be led directly from the semiconductor radar to another optical system. In addition, in the semiconductor radar in FIG. 7, the semiconductor radar package 127
A semiconductor radar noise 123 is disposed inside, a monitoring photodetector 126 is disposed behind it, a garnet film 124 is provided on the front side, and a magnet 125 is disposed around the garnet film 124. 111!124 and the magnet 125 constitute a Faraday element, which reduces radar noise caused by the returned light. However, although these methods reduce the size of a part of the optical system, this is not enough to reduce the size of the entire optical system.

(Object of the Invention) The present invention was made based on the above circumstances, and the information signal is directly detected from the parallel light flux itself, and optical systems such as intermediate condensing lenses are eliminated as much as possible. The present invention aims to provide an optical head that can record and/or reproduce information using an optical system with a single configuration.

([Measures to Solve the Problem]) Therefore, in the present invention, the diverging light from the semiconductor radar is converted into a parallel beam through a collimator lens, and the optical beam is converted into an optical beam through a polarizing beam snoritter and an objective lens. 9. In an optical head, in the optical path of the parallel light beam, the reflected light is applied to a sensor via an objective lens, a beam gooseberry, and a magnetic recording medium, and the reflected light is recorded and/or reproduced. A Faraday element that rotates the polarization angle of linearly polarized light by approximately 45 degrees during the round trip at the beam splitter is provided, or the linearly polarized light is changed into circularly polarized light in the optical path of the parallel light beam, and the polarized light is changed into circularly polarized light. A quarter wavelength plate is installed to convert the light into linearly polarized light, and
A part of the nine beams reflected from the recording medium through the objective lens is separated by the beam sinter, and the separated beam is divided and detected by a photodetector having a light-receiving surface divided into multiple areas. .

In this case, the beam splitter is preferably formed of a dielectric polarizing multilayer film whose reflectance changes continuously with respect to the incident angle.

(Function) In such a configuration, the parallel light beam is divided and detected directly from the beam by the photodetector, and information signals and serge signals can be extracted by calculating from the amount of light received in multiple areas. As an optical head, an optical system having a structure as compact as possible can be used, which can be useful for improving access speed.

(Example) Hereinafter, an example of the present invention will be specifically described with reference to the drawings.

In the first embodiment shown in FIG. 1, the diverging light from the semiconductor radar 1 is converted into a parallel light beam via the collimator lens 2).
The light reaches the objective lens 3 via the polarizing beam sinter 7 and the optical member 5 for the Faraday element, where it is focused and irradiated onto the magneto-optical information recording medium 4 . A magnet 6 is disposed on the outer periphery of the optical member 8.
Together, they constitute a 772-day element. In this case, the light from the semiconductor radar 1, which is turned into a parallel beam by the collimator lens 2, is linearly polarized (O), and the polarization direction of the parallel beam is parallel to the plane of the paper (P-polarized light). And the polarized beam currants,
It is assumed that the filter 7 transmits almost 100% of P-polarized light. Therefore, the parallel light beam is incident on the optical member 5. The optical member 5 may be a garnet film, for example, and rotates the polarization angle of linearly polarized light by approximately 22.5 degrees each time the light passes through the Faraday element.

As a result, the nine rays of light that are irradiated onto the recording medium 4 through the objective lens 3 are reflected.

Returning to the polarization beam smitter, the linearly polarized light is rotated an additional 22.5 degrees (45 degrees round trip) when passing through the Faraday element. Since the polarized beam Gooseberry 7 reflects only the polarized light component in the direction perpendicular to the plane of the paper (S polarized light),
Here it acts as an analyzer. And polarized beams
The light is incident on a photodetector 8 provided opposite to the side surface of the splitter 7. In reproducing a magneto-optical signal, linearly polarized light is rotated in opposite directions due to the difference between upward and downward perpendicular magnetization in the recording medium 4 (Kerr effect, etc.). This difference causes a difference in the amount of light reflected by the polarizing beam sinter 7 to the photodetector 8, so that information can be read. Now, in FIG. 1(a), T is a direction parallel to the tracks on the recording medium 4, R is a direction perpendicular to the tracks,
When the recording medium 4 is moved in the track direction, the photodetector 8 is divided into four areas A and B as shown in FIG. 1(b).
The light-receiving surfaces are divided into , C, and D, so that the amount of received light can be detected independently. Therefore, the above-mentioned information readout is given as the sum of the amount of light received by each of the divided areas A, B, C, and D. Also, error signal glue for sir?
+, )? In the Sangruser method, the tracking error signal is the sum of each area, and is obtained from the difference in light intensity from the so-called quadrupled bits, but in the continuous groove method, (for example, the Gutshusol method), (A10) - (B0D ) can be used to find the difference in light intensity.

Note that in the first embodiment, the collimator lens 2. Objective lens 3 is a GRIN lens (QRAD IENT-I
NDEX-LENS) and microphone four Fresnel lenses,
The entire optical head can be made smaller and lighter by using a microscopic optical element such as a bulb m-lens to form an image that is close to the same magnification. Therefore, it is also possible to provide the optical head with a spring mechanism for floating and use it as a floating optical head. Autofocus in this case can be controlled by the flying height of the optical head.

Figure 2(a) shows the characteristics of reflectance and angle of incidence, and Figure 2(b)
) indicates the extraction of the focus error signal in the embodiment of FIG. In this case, the polarizing beam splitter 7 constitutes a reflection space using a dielectric polarizing multilayer film. Then, 100% of P-polarized light is transmitted, and S-polarized light is highly reflected. However, it is assumed that the reflectance continuously changes around the incident angle of 45 degrees.

Now, when the spot is focused on the recording medium 4 and the reflected light enters the polarization beam sinter 7, then z+l
, parallel light is incident at 45 degrees. At this time, it is on the r side with the optical axis (-dotted chain line) as the center.

Since both sides are incident at the same 45 degrees, the signal of (A + B) - (C + D) at the photodetector 8 (for the sake of explanation, the photodetector 8 is drawn away from the polarization beam grid) is O. Become.

When the recording medium 4 approaches the objective lens 3 side from the in-focus position,
Like Cr*CL, the light to the photodetector 8 becomes diverging light.

The Cr light on the r side has an incident angle as large as 45 degrees, L
Conversely, the light from the CZ on the side has an incident angle smaller than 45 degrees.

Finally, (A+B)-(C+D)>0. In this way, if you use a nine-beam smudger with a reflective surface whose reflectance changes continuously before and after the 45-degree incident angle,
A seven-occasion error signal will also be obtained. This focus error signal may be used to perform conventional actuator focus control, but when configured as a floating optical head as described above, the focus error signal is used to control the control amount of the pressing force of the spring mechanism. may also be used.

In the above embodiment, the rotation angle of the 7 Alladay elements was set at 45 degrees for the round trip of the light, but since a differential system is not used for the detection system of the magneto-optical signal, the optimum detection system Considering the above, it is actually preferable to make the rotation angle smaller than 45 degrees in both directions.

Further, a Roche prism or a 9-ohm two-stroke prism may be used as a substitute for the polarizing beam sinter used here.

Furthermore, in the above embodiment, the direction of the linearly polarized light incident on the recording medium is not parallel or perpendicular to the track direction of the recording medium, but there is a gap between the optical member 5 for the Faraday element and the objective lens 3. A two-wavelength plate may be interposed so that the direction of linearly polarized light is parallel or perpendicular to the track direction.

In the embodiment shown in FIG. 3, the optical system of the optical head is housed in a motherboard cage 9 of a semiconductor radar. Here, the reference numeral 10 denotes a semiconductor laser depth 11, a nine transparent group provided as a connector between the micro 7 Lens lens (as a collimator lens) 11 and the semiconductor laser chip 10;
A plate, 13 is a polarized beam gooseberry, 14 is an optical member for a Faraday element, 15 is a magnet, 16 is an objective lens, 17
1 is a magneto-optical information recording medium, 18 is a photodetector having divided areas, and 19 is a monitoring detector.

In addition, in the case of optical recording media other than magneto-optical, or in the case of dichroism among magneto-optical recording media, linearly polarized light can be converted into circularly polarized light instead of the 7 Alladay element as shown in Figure 4. To,
Alternatively, a 174-wave plate 20 that converts circularly polarized light into linearly polarized light may be used. In this case, if the light exiting the semiconductor radar is P polarized light, the reflected light from the optical information recording medium 4' is S
The light enters the polarization beam splitter 7 as polarized light. Then, the information polarization becomes a difference in the amount of light (due to the difference in the shape and reflectance of the bits on the medium) and is incident on the photodetector having the above-mentioned divided areas, and is obtained as the sum of the light. (9) The error signal for the sensor material is obtained by calculating using a predetermined calculation formula, as in the above-described embodiment.

Note that a Faraday element may be used in place of the 1/4 wavelength plate (in place of the 1/4 wavelength plate) in the same way as the spinning speed, and in consideration of light efficiency, the rotation angle may be set to 90 degrees for the round trip of the light.

(Effects of the Invention) As described in detail above, the present invention uses a Faraday element or a quarter-wave plate, and further uses a photodetector with a light-receiving surface divided into a plurality of areas, thereby generating polarized light. Information signals and error signals can be detected by directly applying parallel light flux from the beam to the photodetector.Therefore, by using a single optical system as an optical head, it is possible to achieve sufficient size and weight reduction, and shorten access time. can be realized.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of the optical head for magneto-optical memory of the present invention, FIG. 2 is an explanatory diagram showing a mode of obtaining a focus error word, and FIG. FIG. 4 is a configuration diagram illustrating nine embodiments in which all optical systems are housed, and FIG. 4 is a configuration diagram illustrating another embodiment used in an optical head for optical memory. FIG. 5 is a configuration diagram showing a conventional magneto-optical optical head. FIG. 6 is a block diagram of a conventional semiconductor laser with a built-in collimator lens, and FIG. 7 is a block diagram of a conventional semiconductor laser with a built-in seven Allade elements. 1... Semiconductor laser, 2... Collimator lens, 3
...Objective lens, 4...Magneto-optical information recording medium, 5.
...Optical member for Faraday element, 6... Magnet for Faraday element, 7... Polarizing beam splitter, 8... Photodetector, 20... 174 wavelength plate agent, patent attorney Johei Yamashita ( a) Figure 1 Figure 2 (b) -T Figure Figure (E>-11-T

Claims (3)

[Claims] (1) The diverging light from the semiconductor laser is converted into a parallel beam of light through a collimator lens, and is irradiated onto an optical or magneto-optical recording medium through a polarizing beam splitter and an objective lens.The reflected light is sent to the objective lens and beam splitter. In the optical head, the optical head records and/or reproduces information by providing information to a sensor through a Faraday element that rotates the polarization angle of linearly polarized light in the optical path of the parallel light beam by approximately 45 degrees during a round trip through a beam splitter. In addition, a part of the light reflected from the recording medium through the objective lens is separated by the beam splitter, and the separated beam is divided and detected by a photodetector whose light receiving surface is divided into multiple areas. An optical head characterized by: (2) The diverging light from the semiconductor laser is converted into a parallel beam of light through a collimator lens, and is irradiated onto an optical or magneto-optical recording medium through a polarizing beam splitter and an objective lens.The reflected light is sent to the objective lens and beam splitter. In the optical head that records and/or reproduces information by applying it to the sensor through the optical head, a quarter-wave plate converts linearly polarized light into circularly polarized light or circularly polarized light into linearly polarized light in the optical path of the parallel light beam. At the same time, a part of the light reflected from the recording medium through the objective lens is separated by the beam splitter, and the separated beam is divided and detected by a photodetector whose light receiving surface is divided into multiple areas. An optical head characterized by comprising: (3) The optical head according to claim 1 or 2, wherein the beam splitter is formed of a dielectric polarizing multilayer film whose reflectance changes continuously with respect to the incident angle.