JPS58158049A - Optical information recorder - Google Patents

Abstract

PURPOSE:To enable focusing with good accuracy in the state of having no dark cruciforms even if a recording lens having high numerical aperture is used by recording the luminous flux from a recording laser light as circularly polarized light in the stage of monitoring the focusing state. CONSTITUTION:A lambda/4 plate 14 is inserted into the optical path between a wedge plate 7 and a recording lens 4 of an observing system for reflected light, and an incident luminous flux 1 is changed from linearly polarized light to circularly polarized light which is then made incident to the lens 4. then, the distribution in the inclination of the spacial polarization plane after passage through the lens 4 is eliminated, and the luminous flux 1 reflected by the plate 7 or a parallel flat plate has no longer spacial asymmetry and the spot observed by the observing system constituted of a convergent lens 8, and the objective lens 10 and eyepiece lens 11 of a microscope 9 is a distinct spot having no dark cruciforms.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention monitors the reflected light from the recording master when recording information such as video, PCM audio, etc. on the recording master with high density, and accurately directs a laser beam onto the recording master. Regarding an optical information recording device having a means for converging
It is an object of the present invention to provide an optical information recording device that can perform focusing with high accuracy even when a recording lens with a high numerical aperture is used.

In recent years, the information recording capacity of video disks and PCM audio disks has become much larger than that of conventional memories, but in order to achieve high-density recording, a high numerical aperture (N, A) is required. For example, if you use a recording lens with N, A = 0.98 and record with argon laser light (λ = 0.4579 μm), Depth of focus Δ is: Δ=λ/2, (N, A)”=±0.45?il/2
X(0,98)”2 ±0.26 prn, which is small (
In both cases, it is necessary to control the focal position within the depth of focus. However, with conventional optical information recording devices, there are cases where the precision is not sufficient even though the depth of focus is actually within the depth of focus, and when the recording master is rotated, surface wobbling always occurs. There is. By the way, in response to this deviation,
Using current servo technology, it is relatively easy to make the recording lens track with sufficient accuracy. However, the problem is how to precisely adjust the absolute position of the focus.

FIGS. 1 and 2 show the optical system of a conventional optical information recording device. Both use conventional focusing methods. Figure 1 shows the case of a parallel system, where the incident light flux (1
) is incident on the recording lens (4) via a parallel plate (2) and a reflecting mirror (3) inserted in the optical path,
The reflected light is focused on the recording master (6) by a recording lens (4), and the reflected light is passed through the same optical path again and reflected on both sides of the parallel plate (2) to perform shifening.
The two light beams are caused to interfere with each other on the interference pattern observation screen (6). The interference fringes are then observed, and the position where the interference fringe interval is maximized is determined as the optimal focal position. Note that if the parallelism of the incident light beam (1) is guaranteed, it can be said that the optimal focal position is when the reflected light beam also becomes parallel.

Figure 2 shows the case where an optical system for actually observing the spot is provided, and the incident light beam (1) is passed through the recording lens ( 4), passes through the same optical path through the recording lens (4), is reflected by the wedge plate (7), and enters the converging lens (8), where it is observed using a microscope (9). In such a case, the positional relationship between the converging lens (8) and the objective lens of the microscope (9) should be adjusted according to the converging lens (
8) When the parallel light is incident on the microscope (9), when it is observed through the eyepiece (b), the observed spot diameter is minimized. It is set using In such a configuration, if the focus s11 is performed so that the spot of the light beam reflected from the recording master disk (5) is minimized, the incident light beam (1) will be at the optimum focal position on the recording master disk (6). It is.

However, according to such a conventional optical information recording device, focusing can be performed effectively when the N and A of the recording lens (4) are low, but the N and A of the recording lens (4) become high. Especially when N and A>0.9, a phenomenon occurs in which the plane of polarization of the incident light beam (1) rotates depending on the radial position of the recording lens (4). Lasers with relatively high output power are generally external chain type, and the end face of the laser tube is a Brewster window. Therefore, it is linearly polarized. When this light flux is made incident on the recording lens (4) and the anti-oblique light from the recording master plate (5) is observed, even if the light is made incident with uniform intensity,
The angle of incidence on the lenses of each group constituting the recording lens (4), the parallel plate (2) in Figure 1, and the wedge plate (7) in Figure 2.
There is a difference in the reflectance of the perpendicular (S) and parallel C) components in the surface reflection of
Observation by
Only spots with a dark cross (isogyre) can be obtained. Therefore, interference by the parallel plate (2) reduces the visibility of interference fringes and makes accurate focusing impossible.

Figure 8 shows the polarization state of linearly polarized light (total) at the back focal plane (at 4 resistance) when linearly polarized light is incident on the recording lens (4) having high N and A. is the recording master (5
) shows the polarization state at the rear focal plane (4a) of the linearly polarized light (b) that has been reflected from the recording lens (4) and returned once again through the recording lens (4). As is clear from this figure, the linearly polarized light that has passed through the recording lens (4) becomes linearly polarized because the transmittance of S-polarized light and P-polarized light differs on the glass surface where the incident angle is large. Even if the recording lens (4) is incident on the recording lens (4)
) The plane of polarization of the linearly polarized light (b) rotates as shown in Figure 4, and the light reflected by the parallel plate (2) in Figure 1 or the wedge plate (n in Figure iI2) rotates the plane of polarization as shown in Figure 1. Depending on the amount,
The reflectance differs, and it functions just like an analyzer. Therefore, the observed spot reflected by the reflected light from the recording master (!1) has a dark cross, and when the light beam from the recording lens (4) is focused to the maximum on the recording master (6), The accuracy is insufficient to confirm the
It is nearly impossible to set the best focal position with good reproducibility.

The present invention aims to solve such problems, and includes a recording laser beam 1, a modulation means for modulating the recording laser beam according to an information signal, a recording lens for focusing the recording laser beam on a recording master, It includes a focal position control means for focusing the light emitted from the recording lens onto the recording master, and a means for optically monitoring the reflected light from the self-recording master. This objective is achieved by providing an optical information recording device configured to allow the luminous flux from a laser light source to enter as a circular light, so that even when a recording lens with a high numerical aperture is used, Good accuracy (focusing can be performed without dark crosses).

EMBODIMENT OF THE INVENTION Hereinafter, the structure of this invention will be described in detail based on the drawing which shows one Example. Components having the same functions as those in FIGS. 1 and 2 are given the same numbers and their explanations are omitted.

FIG. 6 shows an optical system of an optical information recording device according to the present invention. That is, in addition to the optical system shown in Fig. 2, a disk plate (b) is inserted in the optical path between the wedge plate (7) of the reflected light observation system and the recording lens (4), and It is configured to change the linearly polarized light into circularly polarized light and make it incident on the recording lens (4). The plate (b) itself may be inserted into the optical path only during focusing, or may be inserted all the time without any problem. Alternatively, it may be placed in the optical path in front of the wedge plate (7) other than between the two plates (b). As a result, since the circular tin light is incident on the λ/4 plate (b), the distribution of the slope of the spatial polarization plane after passing through the lens (4) is eliminated, and the wedge plate (7)
Alternatively, the light beam (1) reflected by the parallel plate no longer has spatial a asymmetry, and the converging lens (8) and the microscope m
The spot observed by the observation system consisting of the objective lens (to) and the eyepiece (b) in (9) is a clear spot without a dark cross, making it possible to determine the optimal focus position with high precision. becomes.

FIG. 6 shows an optical system in which the optical information device according to the present invention is used for a vHD format video disc. In the case of recording on optical video discs, PCM digital audio discs, etc., the recording laser beam is one beam and has one type of polarization plane, but as shown in Figure 6, there are two different polarization planes.
When using a luminous flux, the insertion position of the plate (b) is limited. To briefly explain the recording optical system of a VHD video disc, the light beam (λ = 0) emitted from an argon laser (
．． 4579 μm) is divided into a main signal recording beam (b) and a pilot signal (tracking bit) recording beam (to) by a reflecting mirror Q. The main signal recording power is FM-modulated through the optical modulator (2), and then enters the optical modulator (2) via the reflective mirror (2), where the required recording power, which varies depending on the disk radial direction, is controlled. It will be done. Next, the light beam (B) enters the cylindrical lens (C) through the reflective mirror 4, is narrowed down by the first slit (2) and its width is controlled, and then enters the lens (C) and becomes parallel light. The light then enters the polarizing beam splitter (2). On the other hand, the pilot beam for recording tracking bits passes through the optical modulator via the reflection mirror, then passes through the beam expansion optical system via the reflection mirror, and then passes through the reflection mirror (the optical modulator). ) to the polarizing beam splitter 4, where it is added to the main signal recording beam (b). The polarization directions of the main signal recording beam @ and the pilot signal recording beam (toward) entering the polarizing beam splitter (branch) are shown in (A) (
b) It is the direction of hail.

The beam exiting the polarizing beam splitter 4 is partially reflected by the wedge plate (7), enters the mirror, and after being reflected enters the spot observation optical system (8, 10, 11). Here, adjust and check the parallelism of the incident beam. The light exiting the wedge plate (7) passes through the reflecting mirror (3), and then the second slit limits the higher-order diffracted light generated at the first slit (2), thereby controlling the bit shape. The beam that passes through the recording lens (4) and is reflected on the surface of the recording master disk (5) passes through the same optical path again and enters the spot observation system (8, 10, 11) at the same time as the incident light. Incident light -
Since the light enters the spot observation optical system (8, 10, 11) before passing through the recording lens (4), it can be observed accurately without rotation of the plane of polarization. However, with this configuration, the recording master (
The reflected light from 5) still produces a dark cross. Therefore, in this embodiment, by inserting a wedge plate shaft between the wedge plate (7) of the reflected light observation system and the second slit, spots due to reflected light can be observed without the occurrence of dark crosses. The structure is as follows. In this case, since two beams with orthogonal polarization planes are incident, it is possible to make one of the beams look best, but it is not possible to make both of them look best at the same time. However, in reality, if only the main signal recording beam (b) is made the best, the pilot beam (to) will automatically become the best. In addition, the main beam (b) and pilot beam (
Since the positional relationship of (g) needs to be monitored from start to finish during recording, it is necessary to remove v4 (b) from the optical path except when focusing.

As described above, according to the present invention, when a conventional optical information recording device performs laser recording using a lens with high N and A, when linearly polarized light is incident on the recording lens, the curvature of the lens surface causes S The transmittance of polarized waves and P-polarized waves are different, and the accuracy was insufficient when optically monitoring the reflected light from the recording master (disc) to set the best focal position. Since the light beam from the recording laser light source is made to enter the recording lens as circularly polarized light, the dark cross (
This is a problem in that it is possible to achieve accurate focusing even when there is no isogyre.

[Brief explanation of drawings]

Figures 1 and 2 show a conventional example, with Figure 1 showing a recording optical system that performs focusing using a parallel plate;
The figure shows the recording optical system equipped with an optical system for actually observing the spot, Figure 8 shows the polarization state of the incident beam at the back focal plane of the recording lens, and Figure 4 shows the recording optical system from the recording master. Figures 186, 186, and wiG show an example of the present invention; Figure 2 shows the configuration of the recording optical system with a plate inserted.
FIG. 6 is a schematic diagram of the ■Φ type recording optical system with the insert plate inserted. (1)...Incoming light flux, (2)...Parallel plate, (4)
Recording lens, (5)...recording master, (7)...wedge plate, (8)...converging lens, (9)...microscope, (b)...plate, (to) ...Argon laser,
(6) @4... Optical modulator agent Yoshihiro Morimoto Figure 1 Figure 2 ψ-12 Figure S 3

Claims (1)

[Claims] 1. A recording laser light source, a modulation means that modulates the recording laser beam according to an information signal, a recording lens that focuses the recording laser beam onto the recording master, and a focal point that focuses the light emitted from the recording lens onto the recording master. position control means;
f! (a) an optical information recording device, comprising means for optically monitoring reflected light from the recording master disc, and configured to cause the light beam from the recording laser light source to enter the recording lens as circularly polarized light at least at the time of monitoring the focusing state; .