JPS62159353A - Optical head device - Google Patents

Abstract

PURPOSE:To exert a light condensed state at the diffraction limit, by separating a plastic condenser lens from the outside air so that no moisture absorbing effect is produced in the lens. CONSTITUTION:A plastic condenser lens 8 is enclosed in a lens barrel 9 so that it can be separated from the outside air by parallel glass plates 10a and 10b provided in front and back of the lens 8 in the direction of its optical axis perpendicular to the optical axis. The plastic condenser lens 8 is designed in such a way that a sine condition is satisfied and aberration correction is performed as a whole light condensing optical system including the outside- optical-axis object point aberration produced by the glass plates 10a and 10b when a laser light source 1 is positioned outside the optical axis of the plastic condenser lens 8.

Description

[Detailed Description of the Invention] [Field of Application] The present invention relates to an optical head device, particularly an optical head having a condensing optical system for irradiating a light beam emitted from a laser light source onto a clear track of a record carrier. It is related to the device.

[Conventional technology]

FIG. 4 is a configuration diagram showing a conventional optical head mounting device. In FIG. 1, (1) is a laser light source.

(2) is the output light flux emitted from the laser light source (1),
(3) is a track formed on a disc-shaped record carrier, (4) is a lens that focuses the emitted light beam (2) onto the 1# information track (3), and (5) is an information track ( 3) A reflected light beam that is focused and reflected by K, (6) is a beam splitter that separates the output light beam (2) and the reflected light beam (5), and (7) is a photodetector that receives the reflected light beam (5). It is.

Let me briefly explain the operation. The emitted light beam (2) from the laser beam g(t) passes through the beam splitter (6) and is focused onto the dt signal rack 3) by the condenser lens (4)K.

l1lf# Track (3) is made up of bits and lands.

Information is obtained as the strength of the reflected light beam (5). These 1
# information is read and the reflected light beam (5) reflected from the information track is changed in direction by a beam splitter (6) and is received by a photodetector (7).

Light detection! (7) converts the optical signal into an electrical signal,
This output can be used as, for example, an audio signal, a video signal, or a digital data valve by means of an electric circuit (not shown).

This IA, - This optical head device is equipped with a known track deviation correction mechanism and focus deviation correction mechanism.
Since these mechanisms are not directly related to the present invention, they will be omitted.

In recent years, a high-performance aspherical plastic molded lens has been used as the condenser lens (4).

Conventional glass combination condensing lenses were made up of 3 to 5 optical elements and were very expensive, but thanks to improvements in aspherical molding technology, plastic lenses can now be made from a single lens with high performance and low cost. Now you can get great things.

However, plastic condensing lenses have the disadvantage that their optical performance varies from the designed value due to changes in atmospheric humidity and temperature. In the following, changes in the optical performance of plastic condensing lenses due to changes in humidity will be described in detail.

The section on "Refractive index of glass" in Optics Vol. 12, No. 6 (December 1983) states that if a plastic condenser lens is left in a high humidity condition, the refractive index will change by 1 dimensional change due to moisture absorption. It is being This means that the light condensing characteristics of the plastic condenser lens differ from the designed value.

In the above-mentioned optical head device, in order to increase the information score 1ffi stored on the recording medium as much as possible and to utilize the large-capacity information medium, the pit length and track spacing are determined by the laser light source (1). The size is small enough to read the signal when the condensing system leading to the condensing lens (4) is in the ideal state of the 17-1fli field.

That is, in order to irradiate the information track with a single-diffraction-limited focused spot, the focused light beam exiting the focusing lens (4) must be free of aberration. At this time, the standard AM of wavefront aberration that is allowed within the limit for one time 'fr is 0.07λ (Ma
rechal limit).

:g5 figure is a plastic pair of proboscis lenses (M A = 0.
4s, material PMMA) at 40℃, 90FFLH
This is an actual measurement showing the change in wavefront aberration for each aberration component when placed in constant temperature soda.

In FIG. 5, the vertical axis shows standard l1i1 ratio (Zernike 3rd order spherical aberration) only for wavefront aberration (8eidel 4th order aberration Peak - Varray direct) and spherical aberration, and the horizontal axis shows storage days. Symbol S in the diagram
.

A stands for spherical aberration, Com Kai stands for comatic aberration, and As stands for astigmatism.

As is clear from the drawings, the moisture absorption characteristics of the plastic condensing lens particularly affected the spherical aberration, and the actual full value deteriorated by as much as 0.05λ. This value is close to the above-mentioned Marechal-A field, and is a major factor in the deterioration of the recording/I data recording characteristics of the optical head device.

[Problems that the invention aims to address] Since the conventional optical head device is configured as described above, it is necessary to use a sophisticated optical system similar to that in the world of diffraction and technology. There was a problem in that the light focusing characteristics of the plastic focusing lens deteriorated due to changes in atmospheric humidity, and the recording/reproducing characteristics deteriorated accordingly.

This invention improves the above M6 problems by +4 <? This was done to isolate the plastic condensing lens from the outside air and prevent it from absorbing moisture.

The object of the present invention is to obtain an optical head device that can exhibit a diffraction-limited light condensing state.

[Means for solving problems]

The optical head device according to the present invention is designed to provide optical elements before and after a plastic condensing lens, to closely face the plastic condensing lens so as to be shielded from the outside air, and to correct wavefront aberration generated by the optical element. It is.

[Effect]

The plastic condensing lens in this invention can be used for i&l? As a result, it is completely unaffected by changes in the humidity of the outside air and maintains aberration-free light focusing characteristics.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, (8) is a plastic Toko lens installed in the lens barrel (9), and (10a)-(tab) is a parallel lens made of glass material attached to the lens barrel (9) so as to sandwich the plastic lens (8). It is a flat plate.

The plastic condenser lens (8) has a parallel flat glass (TOA) placed perpendicularly to the optical axis in front of it in the optical axis direction.
-(tob) <[Jt is placed inside the lens barrel (9) so as to be isolated from the outside air.

By mounting the condensing lens (8) having the above configuration in place of the condensing lens (4) shown in FIG. Characteristics can be maintained.

However, since the parallel flat glasses (LOa) and (LOb) are reflected in the emitted light beam, spherical aberration occurs as is well known.

Hereinafter, the occurrence of spherical aberration will be explained with reference to FIG.

In Fig. 3, (10a) is a parallel flat glass with a diameter of 4 d and a refractive index η, which is placed perpendicularly to the optical axis (11) in a condensed beam (12) with an aperture JiN, A, = sin θ. 4 has been done. At this time, the 5eidel fourth-order spherical aberration (p-v value) S, A that occurs is given by the following equation.

Therefore, the plastic condenser lens (8) shown in Figure 1 is designed to have negative spherical aberration in advance, taking into account the spherical aberration caused by the two parallel flat glasses (LOa) - (10b), so that they cancel each other out. Ai.

The condensing optical system as a whole is designed to be non-concentrating.

The above explanation applies when the laser light source (1) is ideally placed on the optical axis of the plastic condenser lens (8), but in a typical optical head device, the image height is several μm. It is also necessary to design the above-mentioned Marechal limit.

Therefore, in Fig. 1, when the V-zer light source (1) is placed off the optical axis of the plastic condenser lens (8), the off-axis force point generated by the parallel r plate glass (LOA) = (10b) The plastic condenser lens (
8) should be designed in advance.

In addition, in the first embodiment, the plastic condenser lens (8) is sealed inside the lens barrel (9).
As shown in Fig. 2, even if the lens barrel (9) is integrally molded with the plastic condenser lens (8) and parallel flat glasses (LOa) and (LOb) are attached to both sides 11111,
The same effect as the above-mentioned implementation row is achieved.

Further, in the above-described IT embodiment, parallel flat glass was used as the optical element, but an optical element with one curvature may be used.

〔Effect of the invention〕

As described above, according to the present invention, since the plastic condensing lens is constructed so that it can be analyzed from the outside air, it is possible to avoid changes in the refractive index or external shape due to changes in humidity, and Since the off-axis light condensing characteristic becomes inconvergent, it is possible to obtain an optical head device l that takes advantage of only the advantages of the plastic condenser lens, such as low cost and high performance. ,

[Brief explanation of drawings]

FIG. 1 is a sectional view of a condensing optical system applied to an optical head device according to one embodiment of the present invention, and FIG. 2 is a cross-sectional view of a condensing optical system applied to an optical head device according to another embodiment of the present invention. FIG. 3 is an explanatory diagram of the occurrence of spherical aberration, FIG. 4 is a configuration diagram of a conventional optical head mount, and FIG. 5 is an actual diagram of the moisture absorption characteristics of a plastic condenser lens. In the figure, (1) is a laser light source, (2) is an emitted light beam, (3) is a news track, (8) is a plastic optical lens, and (10a) = (LOb) is an optical element (parallel flat glass). be. In addition, in the figures, the same reference numerals indicate the same or corresponding parts. Agent: Patent Attorney Masuo Oiwa (and 2 others) Figure 1 Figure 2 Figure 8 Near Ufumiko/Nekki Shinsho 10a, Job: Parallel Thousand Reaction Forces Figure 3 Figure 5 Procedural Amendment ( Voluntary) 19861. 2 days.

Claims (4)

[Claims] (1) In an optical head device having a condensing optical system that irradiates an information track of a record carrier with a light beam emitted from a laser light source, the condensing optical system includes a plastic condensing lens and shielding the plastic condensing lens from the outside air. 1. An optical head device comprising optical elements arranged before and after the plastic condenser lens, wherein the plastic condenser lens is designed to correct wavefront aberration generated by the optical element. (2) The optical head device according to claim (1), wherein the optical element is made of parallel flat glass. (3) The optical element according to any one of claims (1) and (2), wherein the optical element is made of parallel flat glass and is arranged perpendicular to the optical axis of the plastic condenser lens. formula head device. (4) Claims (1) and (2) characterized in that the condensing optical system satisfies a sine condition in order to correct off-axis aberrations.
), the optical head device according to any one of (3).