JPH03238632A - Device for evaluating tracking characteristic of optical recording medium - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for evaluating tracking characteristics of an optical recording medium.

[Conventional technology]

In developing and manufacturing optical recording media equipped with guide grooves (pre-groups), a tracking evaluation device that can accurately measure the tracking characteristics of the optical recording medium is required.

Conventionally, this type of tracking characteristic evaluation device has been used to evaluate optical recording media, for example, as described in "Optical Pickup Design and Evaluation Technology" (Triketbus, published March 1984, page 64, Figure 4). A beam spot with a diameter larger than the zero width of the guide groove is irradiated onto the guide groove formed in the guide groove, and the tracking error signal amplitude, which is the intensity ratio of the diffracted light generated on the left and right sides of the guide groove, is measured to determine the tracking characteristics of the optical recording medium. Devices for evaluating are known.

FIG. 7 shows an example of this type of apparatus applied to evaluating the tracking characteristics of an optical disc.

Reference numeral 1 denotes an optical disk as an object to be inspected, on the surface of a substrate 4 on which guide grooves 2 and pre-pit rows 3 are formed in an uneven shape.
A reflective recording M5 is applied. The guide groove 2 is formed spirally or concentrically with respect to the rotation center of the optical disk, and the pre-pit row 3 is formed on this guide groove 2 or between two adjacent guide grooves 2. The pre-pit row 3 includes, for example, sector mark bits indicating the division of each sector, address bits indicating the address of the sector,
It also consists of a set of synchronization bits that generate synchronization signals necessary for recording/reproducing signals, and is formed along the guide groove 2 at predetermined intervals and over a predetermined length. The area where the pre-pit rows 3 are formed is called a pre-format area, and the area where only the guide grooves 2 are formed and no pre-pit rows are formed is an area where data can be additionally written and is called a data area.

Each prepit constituting the prepit row 3 is formed at a depth such that the intensity of reflected light from the recording film 5 is the lowest when irradiated with a light beam spot for signal reproduction. On the other hand, in the guide groove 2, the intensity of the reflected light from the recording film 5 is the intensity of the reflected light from the pre-pit portion, and the intensity of the reflected light from the portion (so-called land portion) where neither the guide groove 2 nor the pre-pit row 3 are formed. It is formed at a depth between the

Therefore, the guide groove 2 and the pre-pit row 3 can be optically distinguished.

6 is an optical head, which includes a light source 7 such as a semiconductor laser.
, an objective lens 9 that images the light beam 8 emitted from the light source 7 onto the recording film 5 , a beam splitter 10 and a mirror 11 that guide the light beam 8 to the objective lens 9 , and primary diffraction that occurs on the left and right sides of the guide groove 2 The light is passed through the objective lens 9 and the mirror 11.
, and a two-part photodetector 12 that receives light via a beam splitter 10 and performs photoelectric conversion.

Reference numeral 13 denotes a differential amplifier, which calculates a difference signal between the output signals of each photoelectric converter constituting the two-split photodetector 12, that is, a tracking signal amplitude.

14 is an A/D converter that converts the tracking signal amplitude, which is an analog signal, into a digital signal; 15 is a memory unit that stores the digitally converted tracking signal amplitude; 16
is a calculation unit that calculates the tracking error signal amplitude, which is the intensity ratio of the diffracted light generated on the left and right sides of the guide groove 2, from the tracking signal amplitude, and evaluates the tracking characteristics of the optical recording medium.

The tracking signal amplitude varies depending on the irradiation position of the light beam spot with respect to the guide groove 2. That is, when the center of the light beam spot coincides with the center of the guide groove 2, and when the light beam spot is located between the two guide grooves 2, the tracking signal amplitude becomes zero, and the light beam spot If the center of the guide groove 2 is offset from the center of the guide groove 2, the amplitude will correspond to the amount of the offset. Further, the direction of the bias can be determined by the sign of the output signal of the differential amplifier 13.

Therefore, in the above device, the tracking signal amplitude is continuously detected by scanning the optical beam spot along the guide groove 2 and applying tracking servo in the direction in which the output signal of the differential amplifier 13 becomes zero. From this signal, it is possible to determine the tracking error signal amplitude, which serves as an evaluation standard for the tracking characteristics of the optical disc.

In this way, no problem arises in detecting the tracking error signal amplitude in the data area. However, when the light beam spot falls on the preformat area, the amount of reflected light incident on the two-split photodetector 12 decreases, so that a low-level signal 22 is mixed into the tracking signal 21, as shown in FIG. The tracking characteristics of an optical recording medium are evaluated based on the tracking error signal calculated from the amplitude S of this tracking signal, so unless the second low level signal 22 is removed, accurate evaluation of the tracking characteristics will not be possible. can't do it.

As a means to solve this inconvenience, for example,
As described in Publication No. 3-153111, when the amount of light incident on the detector decreases below a preset value, the tracking signal is changed to the value before the amount of light incident on the detector decreased below the preset value. A sample hold method has been proposed.

[Problem N to be solved by the invention] However, according to the above method, even when the amount of reflected light from the optical disk decreases due to a defect in the recording film, for example, the tracking signal read from the relevant portion is ignored. Therefore, there is a problem in that it is not possible to accurately evaluate tracking characteristics in a minute area.

The present invention has been made in order to eliminate the deficiencies of the prior art, and is an optical recording medium that does not cause errors due to signal leakage from the preformat area and can detect defective parts. An object of the present invention is to provide a tracking characteristic evaluation device.

[Means to solve the problem]

Claims (3)

[Claims] (1) The optical recording medium and the light beam spot are relatively driven so that the light beam spot crosses a guide groove formed in the optical recording medium, and the light reflected and diffracted by the optical recording medium is directed to the track center. Optical recording in which light is received by two light receiving sections on a two-part photodetector arranged symmetrically with respect to the guide groove, and the output difference between the two light receiving sections when a light beam spot crosses a guide groove is detected as a tracking characteristic evaluation signal. An apparatus for evaluating tracking characteristics of an optical recording medium, which evaluates tracking characteristics of an optical recording medium in which a recording area is divided by a preformat area formed on the guide groove or between two adjacent guide grooves. , a signal generating unit that outputs a preformat area signal for a period corresponding to the preformat area even when the tracking of the light beam spot is removed; and a signal generating unit that outputs the preformat area signal for a period corresponding to the preformat area; A signal holding section is provided to hold the signal in a state before the preformat area signal is generated, and a signal component generated by the light beam spot passing through the preformat area during tracking characteristic measurement is removed. Tracking characteristic evaluation device for optical recording media. (2) Drive the optical recording medium and the optical beam spot relatively so that the optical beam spot crosses a guide groove formed in the optical recording medium, and direct the light reflected and diffracted by the optical recording medium to the center of the track. Optical recording in which light is received by two light receiving sections on a two-part photodetector arranged symmetrically with respect to the guide groove, and the output difference between the two light receiving sections when a light beam spot crosses a guide groove is detected as a tracking characteristic evaluation signal. An apparatus for evaluating tracking characteristics of an optical recording medium, which evaluates tracking characteristics of an optical recording medium in which a recording area is divided by a preformat area formed on the guide groove or between two adjacent guide grooves. , a signal generating section that detects a predetermined signal from the preformat area and outputs a synchronization signal; and a signal generation section that measures the generation cycle of the synchronization signal and generates a trigger signal for each predetermined specific sector. a trigger generating section for storing data using the trigger signal as a storage start signal; a memory section for storing data using the trigger signal as a storage start signal; A tracking characteristic evaluation device for an optical recording medium, comprising: a calculation section for calculating a tracking error signal, and removing a signal component caused by a light beam spot passing through a preformat area when measuring tracking characteristics. . (3) Drive the optical recording medium and the optical beam spot relatively so that the optical beam spot crosses the guide groove formed on the optical recording medium, and direct the light reflected and diffracted by the optical recording medium to the track center. Optical recording in which light is received by two light receiving sections on a two-part photodetector arranged symmetrically with respect to the guide groove, and the output difference between the two light receiving sections when a light beam spot crosses a guide groove is detected as a tracking characteristic evaluation signal. An apparatus for evaluating tracking characteristics of an optical recording medium, which evaluates tracking characteristics of an optical recording medium in which a recording area is divided by a preformat area formed on the guide groove or between two adjacent guide grooves. , a high-frequency signal removal circuit whose set frequency is set to a value higher than the frequency of the tracking characteristic evaluation signal and lower than a frequency of a signal component generated by the light beam spot passing through the preformat area; A tracking characteristic evaluation device for an optical recording medium, characterized in that a signal component generated by the light beam spot passing through a preformat area is removed from a tracking characteristic evaluation signal read from the recording medium.