JPS5814333A - Recording method for optical disc - Google Patents

Abstract

PURPOSE:To record information stably without the influence of dirt, by detecting the reflected light of a laser for recording to correct the reduction of the laser intensity due to dirt. CONSTITUTION:The light radiated from a semiconductor laser 9 is irradiated to a disc 14 through an optical system and is reflected partially by a recording film and is returned to the optical system, and this light is bent at right angles during this returning by a half mirror 11 and is measured through an object lens 15 by a photodetector 16. When the current detected by the detector 16 is denoted as (i), the light of the laser 9 is transmitted through the dirt on the surface of the disc in going the returning paths and is attenuated twice by the dirt. The current (i) satisfies i=alpha<2>i0 when the photocurrent for no dirt is denoted as i0, and this attenuation coefficient alpha is obtained, and a feedback circuit which increases the laser output by component of this reduction is provided on make always i=i0 true, thereby recording information stably.

Description

DETAILED DESCRIPTION OF THE INVENTION In a recordable optical disc, if the disc surface is dirty, the intensity of the recording laser beam decreases and recording becomes impossible. The objective is to provide a method for stably recording with a constant amount of light.

In contrast to playback-only video discs, optical discs that can also record video signals and the like are being developed. in general,
Optical video discs have a thick resin layer formed on the surface that contains signals as small as 1μ to protect the signal surface, and if dust or the like adheres to the surface of this protective resin layer. However, the laser beam is out of focus on this surface, resulting in a light spot of about 200 to 500 μm, so the design is such that the influence of foreign matter smaller than this size is small. However, if a large stain such as a fingerprint is about the size of a light spot on the surface, this will absorb or scatter the laser beam, weakening its intensity. However, in a playback-only video disc, even if there is some variation in the optical signal intensity, the signal amplitude will only change slightly, and since the FM modulation method or PCM modulation method is normally used, it does not have a big effect.

However, in a recordable optical disc, the light intensity decreases due to this dirt, and the light intensity at the recording film surface decreases, which impedes the recording operation.

The present invention provides an optical recording method that eliminates such problems and makes stable recording possible by keeping the amount of recording light constant. The details of the method according to the present invention will be explained below.

FIG. 1 is a diagram illustrating a disk on which recording and reproduction is performed using a semiconductor laser and its recording operation.

In the figure, 1 is a semiconductor laser beam, 2 is an objective lens that converges the beam, 3 is a transparent resin plate with a thickness of about 1 m, 4 is a recording film, and is a belt-shaped guide track formed in a concentric circle. It is formed on top of the Reference numeral 5 indicates a resin layer for preserving eel, 6 indicates dirt adhering to the surface of the transparent resin plate 3, and 7 indicates a light spot on the surface of the transparent resin plate 3. The semiconductor laser beam #1 is converged by the objective lens 2, and is generally converged to a size of about 0.8 μ on the recording surface. This recording surface is manufactured in a dust-free room, and dust particles of about 0.3 μm are controlled and completely covered, so contamination in this area is not a problem in practice. Although it varies depending on the NA of the transparent resin plates and the thickness of the transparent resin plate, the diameter is 200 to 500 μm. Generally speaking, dust is 100μ in size, so even if such small dust is present, it will not have a big impact.

The problem is, as shown in 6 in Figure 1, if there is dirt as big as or bigger than the light spot or door, the laser light intensity will be weaker. If the light intensity irradiated onto the recording film 4 is I, and the attenuation coefficient at which the light is attenuated due to dirt is α, then the irradiation light intensity when there is no dirt is 1! .

Against! =α■. Shouting... (1) holds true. If there is a way to detect this α, then I=
I. It turns out that all you have to do is adjust the laser output so that .

Next, a method for detecting α will be described. FIG. 2 is a diagram illustrating a recordable optical disc and its optical system. In the figure, 8 is a drive port 1 path of a semiconductor radar, 9 is a semiconductor laser, 10 is a condensing lens for condensing the light from this semiconductor, 11 is a half mirror, and 112 is a reflecting mirror, which is minutely driven. 13 is an objective lens, and 14 is a recording disk. The light emitted from the semiconductor laser 9 passes through the above-mentioned optical system and is irradiated onto the disk 14. A portion of the light is reflected by the recording film and returns through the same optical system, but on the way it is turned at a right angle by the nof mirror 11. It is measured by a photodetector 16 through an objective lens 15. If the photocurrent received by the photodetector 16 is i, then 0, the light from the semiconductor radar 9 passes through dirt on the disk surface on its way out and on its way back, and is attenuated twice. When there is no dirt, the photocurrent of i. Then i=α2i,...
・・・・・・・・・The relationship in (2) is established, αhaΔf〒 ・・・・・・・・・・・・(3)
is guided. That is, α is determined as the square root of the ratio of photocurrents at the photodetector. The amount of absorption due to dirt is small and αχ
1, approximately.

A feedback circuit may be provided to increase the output of the semiconductor laser by the decrease determined as described above.

Perform circuit design.

FIG. 3 shows an example of a received light current signal of the recording light reflected on the recording film surface. This is an example of i4rus recording, and the height of this no4rus is io. If there is dirt on the disk surface, this peak value decreases to i.

FIG. 4 is a diagram showing drive current versus output light intensity of a semiconductor laser. Since this varies depending on the type of semiconductor laser, it is necessary to take this characteristic into consideration when designing the correction circuit.

By using a simple design as described above, that is, using the reflected light of the Q laser, it is possible to compensate for the decrease in laser intensity due to dirt, and to achieve stable recording without the influence of dirt. It became possible to do so.

[Brief explanation of drawings]

゛Figure 1 is a diagram for explaining a recording/reproducing disk and its recording function. Figure 2 is a diagram showing a recording type optical disk and its optical system. Figure 3 is a diagram showing the optical disc reflected on the recording film surface. FIG. 4 is a diagram showing an example of a received light current signal of recording light. FIG. 4 is a diagram showing driving current versus output light intensity of a semiconductor laser. 1... Semiconductor laser beam, 2... Objective lens, 3
... Transparent resin plate, 4... Recording film, 5... Protective resin layer, 6... Dirt, 7... Light spot, 8... Laser drive circuit, 9... Semiconductor laser , 10...
Condensing lens, 11...Half mirror, 112...Reflecting mirror, 13...Objective lens, 14...Recording disk, 16...Photodetector. 4F! J$I −m @ya mi body ya ε

Claims (2)

[Claims] (1) In optical discs that use laser light to record and reproduce video and other signals, the recording laser light that is irradiated onto the recording film surface is reflected by the film surface, and this is received by a photodetector to measure its fluctuations. , an optical disc recording method characterized by controlling the laser light output to be increased when the received light signal becomes weak, and controlling the irradiation intensity on the film surface to always be constant. (2) The received light signal intensity when there is no dirt on the disk surface is i. The method for recording an optical disc according to claim (1), characterized in that when the optical disc is closed, the radar light output is increased in inverse proportion to the square root J of the ratio between io and the received light signal intensity i. .