JP2716556B2 - Optical head for V-groove optical disk and signal detection method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for writing and reading information on a V-groove optical disk.

[Conventional technology]

 FIG. 3 shows the structure of the V-groove type optical disk.

In FIG. 3, reference numeral 301 denotes an optical disk, and the motor shaft 3
06 is set via a chucking hub 307. Reference numeral 302 denotes a recording surface (track surface) of information.

Irradiation light 305 emitted from a laser light source 303 and passing through an objective lens 304 is applied to the track surface 302 to write and read information.

A feature of the V-groove type optical disk is that adjacent track surfaces 302 are formed at symmetrical angles with respect to the disk surface normal.

By adopting such a structure, mixing of signals from adjacent tracks, that is, so-called crosstalk, can be eliminated during signal writing / reading.

As a result, the track width can be narrowed as compared with a general disk, so that the storage capacity can be increased.

The biggest problem with the V-groove type optical disk is that the structure of the optical head for writing and reading information becomes very complicated.

As a conventional technique, a mechanism in which two laser diodes or a point light emitting laser diode are used to separately write and read on two inclined surfaces, or one beam is divided into a plurality of beams using a hologram or the like. There are several ways to use it.

[Problems to be solved by the invention]

The mechanism of an optical head using a multi-laser becomes complicated, which hinders reduction in size, weight, and cost of the optical head.

In the method of dividing a beam using a hologram or the like, there is a problem that power for writing information is insufficient.

[Means for solving the problem]

In order to solve the above problems, the present invention is different from the incident optical path in that a laser beam incident perpendicularly to a disk surface through an objective lens is reflected by a track surface of a V-groove disk having an inclination. An optical head having the following configuration is constructed by utilizing the return to the objective lens through the optical path.

That is, the return light is separated by arranging an optical member at a position where the incident light and the return light are shifted, and a signal is detected by a photodetector focused on the return light. Two optical members for separating the return light are arranged symmetrically in the radial direction of the disk around the optical axis of the objective lens so as to be able to respond to the return light from each surface of the V-groove, and signal detection is performed at two positions corresponding to each. A photodetector for It is characterized by including a circuit for obtaining a focus servo signal and a tracking servo signal as data signals and servo signals from output signals from these optical systems and photodetectors.

〔Example〕

 FIG. 1 shows the basic structure of the present invention.

In FIG. 1, reference numeral 101 denotes a track surface of a V-groove type optical disk, 103 denotes an objective lens, and 105 denotes an optical member 1 for returning light separation.
107, a photodetector 1, 109, a laser diode, 111, a photodetector 2, and 113, a return light separating optical member 2, respectively.

The laser light incident from the direction perpendicular to the disk surface is reflected by the track surface 101 of the V-groove, and passes through a light furnace different from the incident light according to the inclination of the normal 117 of the track surface of the V-groove. Return light returning to the laser diode 109 is generated.

An optical member such as a mirror or a prism is separated at the position of the reciprocation of the optical path, and photodetectors 107 and 111 for signal detection are arranged at the focal point of the separated return light, thereby providing a servo for data signal and lens position control. Detect signal.

Optical members 105 and 113 for beam separation and photodetector 10
Reference numerals 7 and 111 arrange two sets of the optical axis 115 of the objective lens symmetrically with respect to the radial direction of the disk so that return light from either surface of the V-groove can be detected. Note that an aspheric lens in which astigmatism and field curvature are corrected is used as the objective lens 103.

The method of detecting a servo signal in the optical system of the present invention
This is shown using the figure.

In this embodiment, a two-divided photodetector is used as a photodetector, and FIG. 2 shows one of two two-divided photodetectors and a signal detection circuit connected thereto.

In FIG. 2, 201 is the return light separated by the optical member, 203 is the light detection element 1, 205 is the light detection element 2,
Reference numeral 207 denotes a two-part photodetector substrate, 209 denotes a subtraction amplifier for the outputs of the photodetectors 1 and 2, and 211 denotes the photodetectors 1 and 2.
Are shown, respectively.

In the optical system according to the present invention, the focal point of the return light moves in a two-dimensional trajectory such as 213 in response to a displacement in a vertical direction with respect to the disk surface, that is, a displacement in a focus direction.

The two-segment photodetector substrate 207 is arranged along the tangential direction 215 of the focal point movement due to the displacement in the focusing direction with the focus of the return light at the time of on-focus as the center. Although not shown, the other two-segment photodetector is similarly arranged.

In this optical system, a focus servo signal can be obtained by detecting the output of the subtraction amplifier 209 of the two-segment photodetector on the side where the return light is large.

The tracking servo signal is detected by taking the output of the addition amplifier 211 of each of the two-divided photodetectors and comparing the outputs. When the difference between the detection signals becomes maximum, the spot is most ideally on one surface of the V groove.

Then, it is possible to select which surface is to be on-track by the sign of the difference.

The data signal is detected by the output from the addition amplifier 211 of the two-segment photodetector on the side corresponding to the on-track surface.

〔The invention's effect〕

According to the present invention, it is possible to write and read information to and from a V-groove optical disk by using an optical head having a simple structure and a small number of components without using a plurality of laser diodes and an objective lens.

Further, in the present invention, by devising the arrangement of the optical member for separating the return light, the light use efficiency becomes extremely high, and the output power from the objective lens can be increased.

[Brief description of the drawings]

FIG. 1 shows the basic structure of the optical head of the present invention, FIG. 2 shows the signal detecting mechanism in the embodiment of the present invention, and FIG. 3 shows the structure of the V-groove optical disk. 101, 302: Information recording (track) surface, 103: Objective lens, 105: Return light separating optical member 1, 107 ... Photodetector 1, 109 ... Laser diode, 111 ... Photodetector 2, 113 ... Return light separating optical member 2, 201 ... Return light, 203 ... Photodetector 1, 205 ... Photodetector 2, 207 ... Two-divided photodetector board, 209 ... Subtractor amplifier, 211 ... Adder amplifier, 301 V-groove optical disk.

Claims (2)

(57) [Claims] 1. A V-groove type optical disk optical head for irradiating a laser beam to each surface of a V-groove of an V-groove type optical disk through an objective lens and detecting a data signal and a servo signal from return light thereof, a set of lasers. A diode and an objective lens, and two optical members provided symmetrically in the radial direction of the disk about the optical axis of the objective lens, for separating return light corresponding to each of the two surfaces of the V-groove. ,
A V-groove comprising: two photodetectors arranged corresponding to the respective optical members and receiving the separated return light; and a circuit for detecting a data signal and a servo signal from the outputs of the photodetectors. Type optical head for optical disks. 2. The method according to claim 2, wherein each of said two photodetectors has two photodetectors.
Using a split photodetector, the center of the two split photodetector is placed at the focal point of the return light at the time of on-focus, and the split photodetector is arranged along the tangential direction of the locus of the focus movement due to the displacement of the focus direction of the optical disk, so as to correspond to the on-track surface. The focus servo signal, which is one of the servo signals, is detected by taking the difference between the two outputs from the two-part photodetector, and the two outputs from each two-part photodetector are summed and the sums are compared. A tracking servo signal, which is one of the servo signals, is detected, and a data signal is detected by taking the sum of two outputs from the two-segment photodetector on the side corresponding to the on-track surface. Item (1): A signal detection method in an optical head for a V-groove optical disk according to Item (1).