JPH03116453A - Optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To increase the number of reproduction beams well with a small sized and simple structure and to effectively perform a data reading by forming a diffraction grating pattern in an optical pass at reproduction time with the use of an electro-optical element. CONSTITUTION:An electro-optical element 14 is arranged in the optical path of an optical beam, for instance between a collimator lens 12 and polarized beam splitter 16 and a diffraction grating pattern can be generated by the electric signal transmitted from the external part provided this electrooptical element 14 is made in a proper structure. At the data reading time fed from an optical disk 22, an incident beam is divided into plural beams by the diffraction grating pattern of the electrooptical element 14 and the data reading is performed by these plural beams. Thus the number of reproduction beams can be increased with a small sized and simple structure and the data reading can be performed effectively.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to recording on an optical record carrier such as an optical disc,
The present invention relates to an optical recording and reproducing apparatus that performs reproduction, and particularly relates to an optical recording and reproducing apparatus that performs reproduction using a larger number of beams than during recording.

[Prior Art] Recording and reproducing information on an optical disk by irradiating a single light beam onto an information bit string results in a low data transfer rate, and it is not possible to perform reproduction immediately after recording. A multi-beam method has been proposed in which recording and playback are performed using a multi-beam system.

FIG. 7 (Al) shows an outline of the first conventional example of an optical disk device using the multi-beam recording/reproducing method. .

In the figure, a large number of laser beams are output from a laser array 100.

These laser beams are incident on an optical disk 104 through an optical head optical system 102 that includes a collimator lens, a polarizing beam splitter, a quarter-wave plate, an objective lens, and the like. Each laser beam reflected by the optical disk 104 enters the detector array 106 via the optical head optical system 102, where it is converted into an electrical signal.

According to this first conventional example, the speed of recording and reproduction is improved by the number of light sources of the laser array 100, that is, the number of beams, compared to the case of using an l-beam light beam.

Next, FIG. fB) schematically shows a second conventional example. This is rOPTIcAL ENGINEERI
N.G.J.

July/ August 1983/ Vol.
22 No. 4, P464-472. In the figure, first, at the time of writing, a single laser beam outputted from a writing laser 110 is applied to an optical disk by an optical head optical system 112.
14, and writing is performed using one beam. On the contrary.

During reading, the laser beam output from the reading laser 11B is converted into a multi-beam by a diffraction grating 118 provided in the optical head optical system 112, and the optical disc 114 is irradiated with a plurality of laser beams. In either case, the reflected beam from optical disk 114 is converted into an electrical signal by detector array 120.

According to this second conventional example, recording is performed using an l-beam, but
Since reproduction is performed using multiple beams, the speed increases by the number of beams used for reproduction.

[Problems to be Solved by the Invention] However, the above-mentioned conventional techniques have the following five disadvantages. First, in the first conventional example fAl in FIG. 1, there is a problem with the lifespan of the laser array 100 due to problems such as thermal interference between laser emission points. Furthermore, it is necessary to space the light emitting points apart by a certain distance or more, which inconveniently limits the number of beams that can be accurately focused onto the optical disk.

Next, in the second conventional example (f8) in the same figure, since two laser beams are wavelength-combined, there are disadvantages in that the number of parts is large (and the optical pickup becomes large as a whole).

Furthermore, although the data transfer rate increases with an increase in the number of beams, in the case of multi-beams with fixed beam spacing,
The transfer speed is not necessarily multiplied by the number of beams. For example, if the data length you want to read is recorded on a track that spans three revolutions of an optical disk, and the track is spiral-shaped and the radial position of the data is known. Consider the following case: 0 If normal reproduction is performed using one beam, it will take a readout time equivalent to three rotations of the optical disk. However, if three beams are used, data reading is completed in one rotation, as shown by arrows FA and FB in FIG. 8 tA). In this case, the data transfer rate has increased three times.

Next, as shown in FIG.
Consider the case of rotation. First, in normal one-beam reproduction, it takes 6 rotations to read out the 0th order.
When the number of beams is three.

The following two methods are possible. One method is to read data without using track jumps. In this method, data for 3 tracks can be obtained in the first rotation shown by arrows FC and FD, but the remaining data cannot be obtained until the next 3 rotations.Therefore, the data transfer rate is lower than that of the l-beam. This is only 6/4 times the case.

Next, another method is to use a track jump and perform a three-track jump after capturing data for one rotation. By performing a track jump, data for six tracks can be read out in two revolutions of the optical disc. However, since data cannot be read during a track jump, one more rotation of the disk is required to read the missing data.

In the end, it takes three rotations to read out all the data on six tracks, and the data transfer rate is 6/3 times that of the one-beam case.

As described above, the data transfer rate does not necessarily increase in proportion to the increase in the number of beams.

The present invention has been made in view of the above points, and an object of the present invention is to provide an optical recording/reproducing device that can satisfactorily increase the number of reproducing beams with a small and simple configuration and can read data efficiently. This is the purpose.

[Means for Solving the Problems] The present invention provides an optical recording and reproducing device that uses a light beam to record and reproduce information on tracks of an optical disk, in which a diffraction grating pattern is formed during reproduction based on an external electric signal. The present invention is characterized in that an electro-optical element is provided in the optical path of the light beam.

According to a main aspect of the present invention, the electro-optical element is configured such that the grating spacing of its diffraction grating pattern changes in accordance with the track spacing of the optical disc as necessary.

[Operation] According to the present invention, an electro-optical element is arranged in the optical path of a light beam, for example, between a conometer lens and a polarizing beam splitter. If this electro-optical element is configured appropriately,
A diffraction grating pattern can be generated by an external electrical signal. When reading data from an optical disk, an incident beam is split into a plurality of beams by the diffraction grating pattern of the electro-optic element, and data is read out using these plural beams.

[Examples] Examples of the present invention will be described below with reference to the accompanying drawings.

<First Embodiment> First, a first embodiment of the present invention will be described with reference to FIGS. 1 to 5. First, the main configuration of the first embodiment will be explained with reference to FIG.

In the figure, an electro-optical element 14 is arranged on the laser beam output side of the laser diode 10 via a collimating lens 12, and a polarizing beam splitter 16 is arranged on the multi-beam output side of the electro-optical element 14. It is located. This electro-optical element 14 divides the output beam of the laser diode 10 into three beams and outputs them, as will be described in detail later.

Next, on one beam output side of the polarizing beam splitter 16, a 1/4 wavelength plate 18. Objective lenses or condensing lenses 20 are arranged in order, and a laser beam output from the objective lenses 20 is irradiated onto the optical disc 22. Further, on the other beam output side of the polarizing beam splitter 16, a concave lens 24. Cylindrical lenses 26 are arranged in order, and a photodetector 28.3 is placed on the beam output side of the cylindrical lenses 26.
0.32 are arranged respectively. The signal output side of these photodetectors 28, 30, and 32 includes a reproduction signal processing circuit, a tracking servo circuit, and a focus servo circuit (
(not shown), and signal reproduction processing and servo control are performed using a general method.

Next, the electro-optical element 14 described above is configured as shown in FIG. 2, for example. As the electro-optical element, liquid crystal, translucent electro-optic ceramics (PLZT), etc. can be considered, and in this example, PLZT is used. In the figure, a grid-like transparent electrode 42 is formed on one surface of PLZT 40, and a layered transparent electrode 42 is formed on the other surface.
4 is formed. A polarizing plate 46 is provided on the grid-shaped transparent electrode 42.

Here, when the switch 48 is turned "ON" and a voltage is applied between the transparent electrodes 42 and 44 with the power supply 50, the PLZT40
(7) Only the portion sandwiched between the transparent electrodes 42 and 44 becomes a polarization plane, and only the light that passes through this is polarized. On the other hand, only light of the same polarization is transmitted through the polarizing plate 46, and light having a different plane of polarization is blocked by the polarizing plate 46.

Therefore, when viewed from the direction in which light travels as indicated by the arrow Fl, a diffraction grating pattern corresponding to the pattern of the transparent electrode 42 appears.

There are two types of diffraction gratings: the light-dark type, in which a light and dark pattern is provided to diffract light, and the phase type, in which parts with different refractive indexes or thicknesses are provided in a grating pattern, and the resulting diffraction is utilized due to the phase difference in light. It can be broadly divided into As the electro-optical element 14, any type of diffraction grating pattern may be used as long as its disappearance and appearance or grating pattern control can be electrically controlled.The one in FIG. 2 is an example of a bright and dark type. It is.

Further, in a configuration using such PLZT, it is easy to achieve a contrast with respect to incident light of 100:1 or more, and the polarization switching speed is also 0.1 ms or less.

It is also fully possible to set the grating pattern width to about 100 μm.

The light transmittance of this PLZT 40 is 60 to 70%, and considering that a part of the incident light is blocked, the utilization rate of the output light of the electro-optical element 14 is considerably reduced. However, since the diffraction grating pattern formed by the electro-optical element 14 is used only during reproduction, as will be described later, the beam power obtained on the optical disk 22 is sufficiently within the practical range.

Next, the operation of the first embodiment as described above will be explained. First, recording on the optical disk 22 is performed as shown in FIG.
As shown in the figure, this is done in the same way as before. That is,
This is performed in a state where no drive signal is applied to the electro-optical element 14 and no diffraction grating pattern is formed. The laser beam output from the laser diode 10 is collimated by a collimator lens 12, and is further collimated by an electro-optical element 1.
4 and enters the polarized beam brick 16. Further, the beam is passed through the l/4 wavelength plate 18° objective lens 20.
The light beams are transmitted through each of the light beams and irradiated onto the information tracks 34 of the optical disk 22. This causes the information contained in the laser beam to be recorded on the information track 34 of the optical disc 22.

Next, the operation in the case of reproduction will be explained. In this case, a drive signal is applied to the electro-optical element 14, and a diffraction grating pattern is formed on the electro-optical element 14 as described above. Therefore, three laser beams are formed by the diffraction grating pattern, and these beams are incident on the optical disk 22. These laser beams are
As shown in Figure 1 (FB), each different information track 3
4.

The three laser beams, each reflected from a different information track 34 of the optical disk 22, are transmitted through an objective lens 20.1/4.
Wave plate 18. Polarizing beam splitter 16. concave lens 24
．． The light enters the photodetector 28°30.32 through the cylindrical lens 26, respectively. These photodetectors 28, 30, and 32 perform photoelectric conversion on the input laser beam, and perform signal reproduction and servo control based on each electric signal. As a result, three information tracks on the optical disk 22 can be read simultaneously, and the data transfer rate during reproduction is three times that during recording.

By the way, each of the three laser beams formed by the diffraction grating pattern of the electro-optic element 14.

The beam spot formed on the optical disk 22 is extracted and shown as shown in FIG. 3 (Al).

Here, the opening angle of the beam divided by the diffraction grating pattern of the electro-optical element 14 is θ.

The distance f between the objective lens 20 and the optical disk 22.

Then, when the beam is incident on the objective lens 20 at an angle θ, the amount of deviation of the spot from the center point or the spot interval Δ is as follows: Δ=fo・tanθ・−・・・・・・・・・・・・・...
(11) On the other hand, the opening angle θ of the diffraction grating pattern of the electro-optical element 14 is expressed as θ=sin-'(n /P)・・・－・・・・・・・・・・・・
... is expressed as (2). Determining Δ from these formulas, Δ=fo-tan (s i n-' (λ/P))
・・・・・・・・・・・・・・・(3)

For example, as shown in FIG. 3+8), the interval Δ between the spots SP on the optical disk 22 is set to about 15 μm in consideration of ease of alignment by rotation. Assuming that the distance uf0 between the objective lens 20 and the optical disk 22 is 4 mm, which is a standard value, θ=0.215 from the above equation (1).

Furthermore, if the laser beam wavelength λ=0.78 μm, then P=208 μm.

Here, P=208 μm, P=104 μm.

When P=69.3 μm, the above (1) to (3)
From the relationship in the formula, the beam spacing is 15 μm.

It spreads to 30 μm and 45 μm, that is, the spots at both ends of the three beam spots SP move to tracks one track away and two tracks apart, respectively. According to the electro-optical element 14, the display pattern can be variously changed by external electrical control. Therefore, change the beam spacing depending on the situation.

Beam spots can be placed on different tracks.

Next, such a beam spacing change is performed as shown in FIG. 8 (
A case where the method is applied to example B) will be explained with reference to FIG. It is assumed that the data to be read is recorded in spiral tracks t1 to t7. first,
As shown in the same figure (Al), beam spot SP1.S
P2.5 Track t5. which is one track away from P3. t
When the optical disk rotates once, as shown by arrow F2 in the same figure (B), the beam spot SP1
．． SP2.5P3 is track t6°t4. It will be located on t2.

Here, by making one more rotation, all the data for six tracks t1 to t7 can be read out, and data reading for six tracks can be completed in two rotations without track jump. The data transfer rate in this case is 6/2 times.

Figure 5 shows the data read time (vertical axis, both expressed in terms of rotational speed on the disk) for various data lengths (horizontal axis) for each method shown in Figures 8 and 4, respectively. relationship is shown. In this figure, when comparing the graphs LA, LB, and LC showing the conventional method with the graph LD showing this example, it is clear that when the beam spacing is made variable, the longer the data length, the longer the data readout time will be. It can be shorter than the method. Specifically, data can be read within (1/3 of the data read time in the case of l beam) x (time for one rotation of the disk).

In reality, there is a limit to the effective field of view of the objective lens 20 of the optical system, so the beam interval cannot be expanded infinitely.The effective field of view of the objective lens 20 is generally 10
It is 0 to 200 μm, and it is necessary to keep the beam spacing within this range. Further, due to restrictions on the arrangement spacing of the light receiving elements or photodetectors 28°30.32, it is appropriate that the beam spacing be at least about 5 μm or more.

Assuming that the effective field of the objective lens 20 is 150 μm, if the basic beam spacing Δ (see Fig. 3 fAI I) is 15 μm, the beam spacing at both ends allowed within the effective field of view is a maximum of 10 tracks. It will be a minute. At this time, the beams on both sides of the central beam can be focused on a track separated by a maximum of four tracks. The basic spacing Δ can be made smaller (if designed, the same objective lens 20
It is also possible to focus the beams on both sides onto tracks further apart within the effective field of view. In order to efficiently improve the data transfer rate, it is sufficient to predict the data length (number of tracks) of the data to be read and control the beam spacing accordingly.

As described above, according to the first embodiment, the data read speed during reproduction of an optical disc can be reduced to within (multiple the number of beams + time required for one revolution of the disc).

<Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIG. Note that the same reference numerals are used for the same components as in the first embodiment described above.

In this second embodiment as well, a diffraction grating pattern is formed by the electro-optical element 60 during reproduction, and data is read out using three beams. The polarizing plate of the electro-optical element 60 is also used as the polarizing beam splitter 16, and in reality, it is often configured like this.

However, in this second embodiment, the electro-optical element 60 is provided with a rotary actuator 62, so that the electro-optical element 60 is configured to be rotatable in the direction of arrow F5. Either or both of the photodetectors 28 and 32 are configured as a two-split detector, and the photodetector 30 is configured as a four-split detector for tracking and focus servo.

One split side of the photodetectors 28 and 32 are each connected to the non-inverting input side of the differential amplifier 64, and the other split side is connected to the inverting input side of the differential amplifier 64. The output side of the differential amplifier 64 is connected to the input side of a phase compensation circuit 66, and the output side of the phase compensation circuit 66 is connected to the input side of the rotary actuator 62 via an amplifier 68.

Next, the operation of the second embodiment configured as above will be explained. First, the electro-optical element 60 is driven by an appropriate drive signal, and a diffraction grating pattern is formed during reproduction as in the first embodiment.

An optical pickup is directed radially of the optical disk 22 to read the information track 34.

At this time, if the feed deviates from the reference line toward the center of the optical disk 22 or if the radial position changes and the curvature of the track changes, the position of the beam spot with respect to the information track 34 will shift. In this case, an output difference corresponding to the amount of shift occurs between the divided outputs of the photodetectors 28 and 32. This amount of deviation is detected by a differential amplifier 64 and supplied to the rotary actuator 62 through a negative feedback circuit including a phase compensation circuit 66 and an amplifier 68.

The rotary actuator 62 rotates the electro-optical element 60 in the direction of arrow F5 according to human power so that the detected value of the differential amplifier 64 is minimized. Then, the beam spots on the optical disk 22 move in the direction of arrow F6 to correct the amount of deviation, and as a result, the three beam spots are properly positioned on different information tracks 34.

As described above, according to the second embodiment, the slit direction of the diffraction grating pattern formed by the electro-optical element 60 is rotated with respect to the optical axis during reproduction, so that the positional deviation of the beam spot can be well corrected. can be done.

<Other Examples> Note that the present invention is not limited to the above embodiments. For example, in the above embodiments, the diffraction grating pattern has three
Although we have shown the case where two laser beams are generated, the number of beams may be set as needed, and instead of using all the beams generated by the diffraction grating pattern, an appropriate number can be selected. Just use it.

Furthermore, +11 Use a laser diode array as a light source.

(2) Two diffraction grating patterns formed by electro-optical elements
It shall have a repeating pattern in the direction.

(3) Using another mechanism as a means for micro-rotating the electro-optical element.

(4) As an electro-optical element, use one whose transmittance or refractive index changes in addition to one whose polarization angle changes.

(5) Applicable to optical discs on which data can be repeatedly recorded, reproduced, and erased. Various design changes are possible within the scope of the present invention.

[Effects of the Invention] As explained above, according to the present invention, since a diffraction grating pattern is generated in the optical path during reproduction using an electro-optic element, the number of reproduction beams can be effectively controlled with a small and simple configuration. This has the effect of making it possible to read out data efficiently.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention, FIG. 2 is a block diagram showing main parts of the first embodiment, and FIGS.
The figure is an explanatory diagram showing the operation of the first embodiment, FIG. 5 is a graph comparing the data read times of the first embodiment and the prior art, and FIG. 6 is a diagram showing the third embodiment of the present invention. FIG. 7 is an explanatory diagram showing a conventional device, and FIG. 8 is an explanatory diagram showing data reading by the conventional device. lO...Laser diode, 12...-Collimating lens, 14.60...Electro-optical element, 16...Polarizing beam splitter, 18...l/4 wavelength plate, 20...
- Objective lens, 22... Optical disk, 24... Concave lens, 26... Cylindrical lens, 2B, 30° 32... Photo detector, 34... - Information track, 40... PLZT, 42. 44...Transparent electrode, 4
6-... Polarizing plate, 62... Rotating actuator, 64
...Differential amplifier, 66...Phase compensation circuit. Houmi 6 Figure (A) (8) b rotation data bit

Claims (1)

[Claims] In an optical recording and reproducing device that records and reproduces information on and from tracks of an optical disk using a light beam, an electro-optical element that forms a diffraction grating pattern during reproduction based on an external electrical signal is provided. An optical recording/reproducing device, characterized in that it is provided in the optical path of the light beam.