JPH0316693B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus adjustment mechanism for an optical information recording device.

For example, a disk recorder such as an optical video disk recorder that forms pits on the disk surface using a laser beam requires highly accurate focus adjustment at the initial stage of forming the pits. Fig. 1 shows a schematic configuration of a conventional focus control mechanism, in which pits are formed by modulating an argon laser beam emitted from a laser light source 1 with an optical modulator 2, and converting the beam focused by a collimator lens 3 into half. The pits are melted and formed by the reflected light from the beam splitter 4, which allows mirrors, to enter the surface of the disk 7 via the dichroic mirror 5 and the objective lens 6, and the focus is controlled by a laser light source 8 for focus control. The helium neon laser beam emitted from the helium neon laser beam is focused by the collimator lens 9, and is irradiated onto the disk 7 via the polarizing beam splitter 10 1/4 input wavelength plate 11 dichroic mirror 5 and objective lens 6, and the reflected light is is incident on the light receiving element 12 through a slightly different optical path from the incident light, and the light receiving element 1
This is achieved by displacing the objective lens 6 in the optical axis direction according to the incident position of the lens 2. Figure number 1 in the diagram
3 is a variation detection circuit that compares the outputs obtained from each of the divided light receiving elements 12 and derives only the time axis variation; 14 is an electromagnetic circuit that receives the variation detection output and drives the moving coil 15 attached to the objective lens 6; A drive circuit 16 is a DC component variable circuit 17 that changes the position of the objective lens 6 by varying the DC current to the moving coil 15 through adjustment operations.
represent eyepiece lenses for observing the focused state.

To adjust the focus with this conventional device, the disc 7 is irradiated with a weak beam with significantly reduced beam energy from the recording laser light source 1, and the beam irradiation pattern is observed through the eyepiece 17. The objective lens 6 is adjusted by operating the DC variable circuit 16.
had to be moved to the in-focus position. This irradiation pattern must have a diameter of 0.5 μm in the focused state, which not only makes it difficult to observe the pattern, but also makes it technically difficult to align the focal point within a focal depth of about 0.5 μm. accompanied by.

Therefore, the present invention aims to propose a new and effective focus adjustment mechanism that automatically performs this initial adjustment.

First, the basic principle of the present invention will be explained below.
Fig. 2 shows the state of reflection of the beam on the disk surface, Fig. 2a shows the state of reflection when the beam is irradiated on the disk surface, and Fig. 2b shows the state of reflection when the beam is irradiated on the pit forming part. This shows the reflection state when As is clear from both figures, if a beam is irradiated onto the disk surface, it will be reflected as is, but if a beam is irradiated onto a pit P, the beam will be diffracted at the edge of the pit, and the reflectance in the optical path will decrease. The relationship between beam power and reflectance is shown in FIG. 3, and it has been confirmed that when the beam power exceeds a certain value, the beam forms grooves and the reflectance decreases significantly due to diffraction. Furthermore, as shown in FIG. 3, the relationship between the objective lens 6 and the reflectance is such that the closer the objective lens 6 is to the in-focus position, the more the beam is concentrated and forms a groove, so the reflectance decreases and the in-focus point The change in reflectance in the vicinity of the position is more significant in b ₂ for a weak beam than in b ₁ for a strong beam.

Therefore, in order to adjust the focal point, the recording laser beam needs to be strong enough to form a groove, but it is desirable that the intensity be as weak as possible.

Therefore, in the present invention, the reflectance change is detected while the disk is rotated at a constant speed, the beam power is adjusted to the optimum value, and then the objective lens is brought to the in-focus position while being moved at a constant speed. It automatically adjusts to

The operation of one embodiment of the circuit shown in FIG. 5 will be explained below. Components in the figure that are the same as those in FIG. 1 are designated by the same reference numbers and their explanations will be omitted.
In this embodiment, first, the beam power control circuit 18 is activated and a control output is applied to the recording laser light source 1 to increase the laser beam intensity at a constant rate of change. a photoelectric conversion output of a light receiving element 19 that photoelectrically converts the reflected beam passing through the beam splitter 4;
The reflectance calculation circuit 20 which receives the control output as an input derives the ratio of both outputs as a calculation output. The perforation detection circuit 21, which detects the decrease in the calculation output, that is, the decrease in the reflectance, keeps the control output of the power control circuit 18 constant to keep the beam power at the minimum required level, and at the same time puts the DC control circuit 22 into operation. The DC control circuit 22 increases or decreases the output at a constant rate, and displaces the objective lens 6 in the optical axis direction at a constant speed. The focus detection circuit 23 which inputs the calculation output outputs an output when the reflectance becomes minimum, fixes the output level of the DC control circuit 22, and the objective lens 6 is brought to the in-focus position. Thereafter, the apparatus increases the output of the recording laser light source 1 by a necessary amount to form a pit and operates the focus control laser light source 8 to perform focus control.

As described above, according to the present invention, since the focus adjustment is automatically performed with high precision, no special adjustment technique is required and the effect is great.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the conventional device, Figure 2 is a schematic diagram of the beam irradiation state, Figure 3 is a characteristic diagram showing the relationship between the laser beam power and reflectance, and Figure 4 is the lens position and reflection. A characteristic diagram showing the relationship between the ratios and FIG. 5 is an explanatory diagram of an apparatus according to an embodiment of the present invention. Explanation of main figure numbers, 18... Beam power control circuit, 20... Reflectance calculation circuit, 21... Perforation detection circuit, 23... Focus detection circuit, 15... Focus control coil.

Claims (1)

[Claims] 1. In a video disk recorder that forms a beam spot with a recording laser beam and performs focus control by following the surface runout of a rotating disk with a focus control laser beam, a beam power control circuit that gradually increases the intensity of the recording laser beam that irradiates the disk; a reflectance calculation circuit that calculates the reflectance of the recording laser beam; a perforation detection circuit that detects a decrease in reflectance and prohibits the power increasing operation of the beam power control circuit; and a perforation detection circuit that detects a decrease in reflectance and prohibits the power increasing operation of the beam power control circuit, and a perforation detection circuit that minimizes the reflectance of the recording laser beam after prohibiting the power increasing operation of the beam power control circuit. and a focus detection circuit that adjusts the DC voltage level applied to the focus control coil.