JPH117635A - Optical head for optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the cost required for lead wires without adversely affecting tracking performance by mutually connecting at least one output with another output, connecting the other output with a detected signal processing circuit, selectively connecting inputs to light emitting elements of each optical system with a light emitting signal source, and synthesizing and separating luminous fluxes of each optical system. SOLUTION: In a first and a second light emitting and receiving elements 1, 2, cathodes of each PD d11-d15; d21-d25 composing light receiving elements 1c, 2c are mutually connected with common input terminals 23, 24 and are connected with a system controller 19 via switches SW3, SW4 which are selectively brought into conduction. Further, concerning anodes of each PD d11-d15; d21-d25, corresponding elements are mutually connected with common lines L1-L5 in parallel. From each PD of light receiving elements of unselected side, the corresponding laser diode LD1, etc., are turned off, and therefore, output which may cause disturbance is not derived.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk optical head having a plurality of optical systems for recording / reproducing or reproducing a plurality of optical disks having different specifications and standards.

[0002]

2. Description of the Related Art A technique for irradiating an optical disk with a light beam and detecting the reflected light thereof to reproduce information recorded on the optical disk is a CD (Compact Disc) or an LD (Laser Discharge).
c) It is widely put to practical use. Such an optical disk reproducing apparatus converges and irradiates a light beam emitted from a light source such as a semiconductor laser onto an optical disk signal surface with an objective lens, and detects reflected light from the optical disk with a photodetector, thereby recording on the optical disk. Play the information that is being played.

In such an optical disk, the recording density has been increased, and an optical disk having a different standard from the conventional optical disk has been used. For example, the size of a pit, which is a unit for recording information, is 0.83 μm for a CD, but is 0.4 μm for a newly proposed DVD (Digital Video Disc). The track pitch, which is the interval between the rows of pits on which information is recorded, is 1.6 μm for CDs and is reduced to 0.74 μm for DVDs.

[0004] The minute pits for recording information formed on the optical disk are read by an optical head. The recording density of the optical disc is determined by the size of the recording / reproducing light spot irradiated on the optical disc by the optical head.

The diameter of the light spot is determined by the wavelength of the laser to be used and the numerical aperture (NA) of the objective lens.
re), and is expressed by (light spot diameter) = k × (laser wavelength) / NA. Note that k is a constant.

From the above relationship, in order to read a higher density optical disk using a small light spot, it is necessary to use a laser with a short laser wavelength or a lens with a large NA.

However, when a high-density optical head provided with an objective lens having a large NA is used, if the optical disk is tilted with respect to the objective lens, the turbulence of the light spot becomes large, and information can be read accurately. become unable.

[0008] Such disturbance of the light spot due to the tilt of the optical disk is greatly affected by the thickness of the disk.
A thin disk has less disturbance of the light spot even if the disk is tilted. Therefore, a thin disk is often used for a substrate of a high-density optical disk.

For the above reasons, reading an optical disk having a lower density and a larger thickness by using an optical head having an optical system having an objective lens corresponding to a high-density optical disk having a smaller thickness. Can not.

Therefore, for example, a 1.2 mm thick C
To record and reproduce D and a high-density optical disk represented by a DVD having a thickness of 0.6 mm with the same apparatus, the optical head needs to have two types of optical systems.

Conventionally, as disclosed in, for example, JP-A-6-259804, an apparatus having two types of optical systems for recording and reproducing two types of optical disks has been proposed. These devices include a semiconductor laser and a photodetector corresponding to each optical disk.
The signals output from these photodetectors are to be extracted independently.

[0012]

However, in the above-mentioned conventional technique, a large number of conductors are required to independently extract signals output from the photodetectors. The large number of conductors impedes the movement of the optical head when the optical head accesses the tracks of the disk at a high speed, resulting in a large load. As a result, there is a problem that the tracking performance is adversely affected.

[0013] In addition, since many conductors are required,
There is a problem that the cost is increased.

[0014]

In order to solve the above-mentioned problems, an optical head for an optical disk according to the present invention is adapted to record and reproduce a plurality of optical disks of different types from each other. In the optical head for an optical disk having an optical system, at least one output of the outputs from the plurality of photodetectors in each optical system is mutually parallel to the output from the photodetectors in the other optical systems. The output connected in parallel from the photodetector and the other output are connected to a detection signal processing circuit, and the input to the light emitting element in each optical system is selectively supplied to the light emitting signal source. First to connect
, And an optical element for synthesizing and separating a light beam in each optical system.

With the above configuration, the light emitting element in the unused optical system is turned off by the first switching element, and is incident on the detecting element of the photodetector in the unused optical system by the optical element. Since the stray light can be eliminated, and the detection signal processing circuit can perform processing corresponding to the output signal from the light detection element of the optical system used, the outputs from the light detection elements can be parallelized as described above. Can be eliminated. Therefore, it is possible to reduce the number of conductors for extracting an output signal from the optical head. This allows the optical head to access the tracks on the disc at high speed,
It is possible to reduce a load caused by tension, inertia, and the like caused by a conductive wire that hinders movement of the optical head.

Further, the cost can be reduced by reducing the number of conductors.

According to a second aspect of the present invention, in order to solve the above-mentioned problems, in addition to the configuration of the first aspect, the same parts as those of the photodetector in each optical system are provided. Yes, corresponding outputs are connected in parallel.

According to the above configuration, the number of conductors for extracting an output signal from the optical head can be further reduced. Thus, when the optical head accesses the track of the disk at a high speed, the load caused by the wire, such as tension or inertia, which hinders the movement of the optical head can be further reduced.

Further, since the number of conductors can be further reduced, the cost can be further reduced.

According to a third aspect of the present invention, in order to solve the above-mentioned problem, in addition to the configuration of the first and second aspects, the optical head for the optical disc selects an input to each light detecting element in each optical system. And a second switching element connected to the detection signal processing circuit.

With the above configuration, when one photodetector is operating, the connection of a circuit for extracting an output signal from another photodetector can be disconnected by the switch. This makes it possible to completely block noise from the photodetector that is not operating, so that a more accurate output signal from the photodetector can be extracted.

According to a fourth aspect of the present invention, in order to solve the above-mentioned problem, in addition to the configuration of the third aspect, the second switching element is connected to a common input terminal of each photodetector. It is characterized by being connected.

According to the above configuration, it is possible to minimize the number of conductors for input to each photodetector in each optical system and the number of the second switching elements. Therefore, the cost for the conductor and the switching element can be minimized.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

FIG. 2 is a side view schematically showing an optical disk optical head according to an embodiment of the present invention. The light beam (light beam) 9a from the first light emitting and receiving unit 1 passes through the polarizing beam splitter (optical element) 3 and is converted into a parallel light beam 9b by the collimating lens 4. This light beam 9b is focused on the first disk 11 by the objective lens 5 through the first opening 7. First disk 11
Reflected light 9c passes through the polarizing beam splitter 3 through the objective lens 5, the first opening 7, and the collimating lens 4, and returns to the first light emitting and receiving unit 1. In the light emitting and receiving unit 1, the reflected light 9 c is transmitted to the hologram optical element 1.
b guides the light to the light receiving element 1c.

The light beam 10a from the second light emitting and receiving unit 2 passes through the aberration compensating element 6, the second opening 8 having a smaller diameter than the first opening 7, is reflected by the polarizing beam splitter 3, and is collimated. 4 results in a parallel light beam 10b. This light beam 10 b is focused by the objective lens 5 on a second disk 12 having a thickness different from that of the first disk 11. The reflected light 10 c from the second disk 12 passes through the objective lens 5, the first opening 7, and the collimating lens 4, is reflected by the polarization beam splitter 3, passes through the second opening 8 and the aberration compensating element 6, Return to the light emitting and receiving unit 2 of FIG. In the light emitting and receiving unit 2,
The reflected light 10c is guided to the light receiving element 2c by the hologram optical element 2b.

The separation surface 3a of the polarization beam splitter 3 is coated with a polarizing film that transmits or reflects depending on the polarization direction. The light beam 9a emitted from the first light emitting and receiving unit 1 and the light beam 10a emitted from the second light emitting and receiving unit 2 are set so that their polarization directions are orthogonal to each other. This allows
In the polarization beam splitter 3, the light beams 9a and 9
c is transmitted, and the light beams 10a and 10c are set to be reflected.

FIG. 3 is a perspective view showing the structure of an optical head using the hologram optical elements 1b and 2b. The light beam emitted from the laser diode (light emitting element) LD is
The tracking beam generating diffraction grating 14 formed on the back surfaces of the hologram optical elements 1b and 2b divides the light beam into three light beams, two sub-beams for detecting a tracking error and a main beam for reading an information signal.

Then, these light beams pass through the hologram optical elements 1b and 2b as zero-order light, are converted into parallel light by the collimator lens 4, and are then focused on the disk 13 by the objective lens 5.

The reflected light modulated by the pits on the disk 13 is transmitted through the objective lens 5 and the collimating lens 4 and then diffracted by the hologram optical elements 1b and 2b, and converted into a first-order diffracted light into a five-division PD (Photo Diode). )
(Light detecting elements) are guided onto the light receiving elements 1c and 2c provided with (light detecting elements).

The hologram optical elements 1b and 2b are composed of two regions having different grating periods, and the reflected light of the main beam is
The light incident on one area is on the divided areas D ₂ and D ₃ of the 5-split PD, and the light incident on the other area is
The light is focused on the divided areas D ₁ and D _{5 of} D.

These condensed beams change as shown in FIG. 4 according to the convergence state on the disk. FIG. 4 (a)
(B) is a state in which the disk is in focus, (c) is a state in which the disk is closer to the focal point, and (c) is a state in which the disk is closer to the focal point.
5 is shown.

Here, each of the divided areas D _{1 to} D of the five-divided PD
When the output signal from the ₅ respectively and S1-S5, the focus error signal (FES: Focusing Error Signal) is given by the following equation. FES = S2-S3 On the other hand, a tracking error is detected by a so-called three-beam method. Since the tracking sub-beams are respectively focused on the divided areas D ₁ and D _{5 of the} 5-split PD, a tracking error signal (TES) is given by the following equation. TES = S1-S5 Further, the reproduction RF (Radio Frequency) signal is given by the following equation. RF = S2 + S3 + S4 FIG. 1 is a circuit diagram schematically showing the input / output relationship of signals in the optical head according to one embodiment of the present invention.

The optical head section 18 includes two sets of light emitting and receiving units 1 and 2 and an actuator coil (not shown) for focusing and tracking. An optical head unit 18 that can be displaced in the radial direction of the optical disk by a guide member (not shown) includes a system control unit 19 provided at a fixed position and an FPC (Flexible Printed).
Circuits) 20. The system control unit 19 includes a detection signal processing circuit and a light emission signal source. The FPC 20 is configured such that lines L1 to L9 made of mutually parallel conducting wires are formed on the surface of a flexible substrate.

The first light emitting and receiving unit 1 includes the light receiving element 1c, the APC IC 21, and the laser diode L.
D1 and a monitoring diode MD1. The APC IC 21 detects the amount of light emitted from the laser diode LD1 by the monitor diode MD1, and controls the drive current of the laser diode LD1 in accordance with the detection result, thereby making the laser diode LD1 a desired constant. Drive with the amount of light emitted. The second light emitting and receiving unit 2 includes a light receiving element 2c and an APC IC similarly to the first light emitting and receiving unit 1.
22, a laser diode LD2, and a monitoring diode MD2, and perform the same operation as described above.

The APC ICs 21 and 22 are connected to the system control unit 19 from the lines L8 and L9 via the switches (first switching elements) SW1 and SW2, respectively, and the switches SW1 and SW2 are turned on. It is selectively activated.

First and second light emitting and receiving units 1 and 2
In each of the PDd11 constituting the light receiving elements 1c and 2c,
To d15; the cathodes of d21 to d25 are mutually connected by common input terminals 23 and 24, and are connected to the system control unit 19 via lines L6 and L7 and switches (second switching elements) SW3 and SW4. In addition, each PDd
In the anodes of 11 to d15; d21 to d25, corresponding elements are mutually connected in parallel to common lines L1 to L5.

Therefore, the light receiving element 1 on the side selected by the switch SW3 or SW4 which is selectively turned on.
PDs d11 to d15 of c or 2c; d21 to d25
Thus, output signals S1 to S5 are output to the system control unit 19. At this time, each of the PDs d11 to d15; d21 to d2 of the light receiving element 1c or 2c on the non-selected side.
5, the corresponding laser diode LD1 or L
Since D2 is turned off, these PDs d11 to d1
5: An output that causes a disturbance is not derived from d21 to d25. Thereby, the light receiving element 1c or 2c
Can be sent to the system control unit 19 in a clear state without noise.

As shown in FIG. 1, each light receiving element 1
By connecting the circuits for extracting the output signals S1 to S5 from c and 2c in parallel, the respective light receiving elements 1c and 2c are connected.
From c, the number of conductors required would be reduced as compared to independently extracting these output signals. Therefore, the FPC 2 connecting the optical head unit 18 and the system control unit 19
As the width of the zeros is reduced and the weight is reduced, the flexibility of the FPC is improved and the inertial weight is reduced. Therefore, it is possible to reduce the load due to the tension or inertia of the FPC at the time of tracking access of the optical head. Further, the cost can be reduced by reducing the number of conductors.

[0040]

As described above, the optical disk optical head according to the first aspect of the present invention has an optical system corresponding to each optical disk for recording and reproducing a plurality of optical disks of different types. In the optical head for an optical disk, at least one of outputs from a plurality of photodetectors in each optical system is connected in parallel with an output from a photodetector in another optical system. A first switching circuit for connecting the output connected in parallel from the elements and other outputs to a detection signal processing circuit, and selectively connecting an input to the light emitting element in each optical system to a light emitting signal source; Element and
An optical element for synthesizing and separating a light beam in each optical system is provided.

This eliminates the inconvenience of connecting the circuits for extracting the output signals from the photodetectors in parallel, thereby reducing the number of conductors for extracting the output signals from the optical head. This makes it possible to reduce the load caused by the pulling or inertia of the conductor when the optical head accesses the track of the disk at high speed. Also, there is an effect that the cost of the conductor can be reduced.

In the optical head for an optical disk according to the second aspect of the present invention, as described above, the configurations of the photodetectors in the respective optical systems are identical to each other, and the corresponding outputs are connected in parallel. The configuration is characterized by that.

In addition to the effects of the first aspect, the number of conductors for extracting an output signal from the optical head is further reduced, so that the optical head can access the track of the disk at high speed. The effect of being able to further reduce the load due to the tension or inertia of the conductor is obtained. Also, there is an effect that the cost of the conductor can be further reduced.

In the optical head for an optical disk according to the third aspect of the present invention, as described above, the second switching element selectively connects the input to each photodetector in each optical system to the detection signal processing circuit. This is a configuration characterized by comprising:

Thus, in addition to the effects of the first and second aspects, the noise from the non-operating photodetector can be completely cut off, so that a more accurate output signal from the photodetector can be obtained. Can be taken out.

The optical head for an optical disk according to a fourth aspect of the present invention has a configuration in which the second switching element is connected to a common input terminal of each photodetector as described above.

Thus, in addition to the effect of the configuration of the third aspect, the number of conducting wires for input to each photodetector in each optical system and the number of the second switching elements are minimized. And the cost of the conductor and the switching element can be minimized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram schematically showing a signal input / output relationship in an optical disk optical head according to an embodiment of the present invention.

FIG. 2 is a side view schematically showing the optical disk optical head.

FIG. 3 is a perspective view showing a configuration of an optical head using a hologram optical element in the optical disk optical head.

FIG. 4 is a plan view showing a state of a light spot on a light receiving element in the optical head for an optical disk, wherein FIG. 4A is a state where the disk is far from a focal position, and FIG. (C) shows a state in which the disk is closer to the focal position than the disk.

[Explanation of symbols]

1.2 Light emitting / receiving unit 1b / 2b Hologram optical element 1c / 2c Light receiving element 3 Polarizing beam splitter (optical element) LD1 / LD2 Laser diode (light emitting element) d11-d15; d21-d25 PD (light detecting element) SW1 / SW2 Switch (first switching element) SW3 / SW4 Switch (second switching element)

Claims (4)

[Claims] An optical head for an optical disk having an optical system corresponding to each optical disk for recording and reproducing a plurality of optical disks of different types from each other. Out of the outputs, at least one output is connected in parallel with an output from a photodetector in another optical system, and the output connected in parallel from the photodetector and the other output are A first switching element that is connected to the detection signal processing circuit and selectively connects an input to a light emitting element in each optical system to a light emitting signal source; and an optical element that combines and separates a light beam in each optical system. An optical head for an optical disk, comprising: 2. The optical head for an optical disk according to claim 1, wherein the structure of the photodetector in each optical system includes the same part, and the corresponding outputs are connected in parallel. 3. The apparatus according to claim 1, further comprising a second switching element for selectively connecting an input to each light detection element in each optical system to a detection signal processing circuit. Optical head for optical disks. 4. An optical head for an optical disk according to claim 3, wherein said second switching element is connected to a common input terminal of each light detecting element.