JPH06302010A - Optical information detector - Google Patents

Abstract

PURPOSE:To easilly assemble and adjust the decice by using incident angle depending transmission plates laminated on flat transparent members. CONSTITUTION:The beam-waist positions of convergent lights converged to a diffraction limits by condenser lenses 3, 4 and incident planes of incident angle depending transmission plates 5, 6 are arranged so as to be separated with distances more than lambda/pi(f/a)X(f/a) when defined as, f are focussing distances of lenses 3 and 4 and (a) is the diameter of lenses each other. The magneto-optical signal detection of high resolution is performed to luminous fluxes transmitting transmission plates 5, 6 through preamplifiers and differential amplifiers after luminous fluxes are converted into photoelectric currents by photo-diodes 7, 8. The magneto-optical signal detection of high resolution is enabled by only the adjustment in a light axis by combining incident angle depending transmission plates made by laminating dielectric mulrilayer films functioning so as to decresse a transmitivity as common focussing optocal systems and the incident angle of the luminous flux become large on the flat transparent members and an optical information detection device whose assembling and adjustment are easy, is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for recording and reproducing information on an optical recording medium, and more particularly to an apparatus for detecting information recorded at high density with high quality.

[0002]

2. Description of the Related Art In order to detect information recorded on an optical recording medium with a high density, it is most common to use a laser beam having a short wavelength. In addition, confocal optical systems and high resolution detection combining apodization and confocal optical systems are also known.

FIG. 5 shows a confocal optical system in magneto-optical recording and an optical system configuration of a conventional optical information detecting device for performing high resolution detection by a pinhole. The reflected light from the magneto-optical recording medium passes through the half-wave plate 26, is converted into converged light by the condenser lens 27, passes through the pinhole 28, and interference between the recording pits is removed. Two
After passing through 9, the polarization beam splitter 30 converts the light into reflected light and transmitted light according to polarization components, and the photodetector 3 is converted by a condenser lens 31 and a condenser lens 32, respectively.
3 and the photodetector 34 and are differentially detected by the differential amplifier.

[0004]

In the conventional method of combining the confocal optical system and the pinhole, the pinhole must be adjusted in three dimensions. In particular, it is very difficult to match the center of the pinhole with the center of the beam waist of the converged light. Further, if the diameter of the pinhole and the diameter of the beam waist of the convergent light are increased to facilitate the adjustment, the focal length of the condenser lens becomes long, which is not suitable for downsizing.

[0005]

In order to solve the above-mentioned problems, the present inventor diligently studied a method in which a conventional confocal optical system and a pinhole are combined, and instead of the pinhole, the transmittance of incident light is changed. The present invention was found by using an incident-angle-dependent transmission plate formed by laminating a dielectric multilayer film, which largely depends on the incident angle, on a flat transparent member.

That is, in order to solve the above-mentioned problems, the present invention provides a first means for converging a light beam emitted from a light source onto an optical information recording medium and a reflected light which receives optical information from the optical information recording medium. In the optical information detecting device, which comprises a second means for guiding the light to a detection optical system, converting the light into convergent light, and detecting the light information, and forming a confocal optical system by the first and second means, On the optical axis including the focal plane,
Provided is an optical information detection device characterized in that an incident angle dependent transmission plate having a dielectric multilayer film whose transmittance greatly depends on the incident angle of a light beam is arranged.

[0007]

[Function] By using an incident-angle-dependent transmission plate, which is formed by laminating a dielectric multilayer film whose transmittance greatly depends on the incident angle of an incident ray on a flat transparent member, instead of a pinhole, Since the optical relationship between the light flux and the incident-angle-dependent transmission plate is relatively immovable on the surface, alignment in the surface perpendicular to the optical axis becomes unnecessary.

Since the light beam on the signal detection side focal plane of the confocal optical system is a plane wave, when the dielectric multilayer film surface of the incident angle dependent transmission plate coincides with the signal detection side focal plane of the confocal optical system, There is no incident angle dependence of the transmittance. So, at a position slightly away from the focal plane, it is no longer a plane wave,
It approaches a spherical wave as it moves away.

In the area of the shadow of the convergent light in the geometrical optics, diffracted light exists even at a place away from the focal plane,
The diffracted light also approaches a spherical wave instead of a plane wave.

Therefore, the incident angle dependent transmission plate has a higher reflection effect as the incident angle of the diffracted light increases, and the amount of transmission of the diffracted light decreases as the distance from the optical axis increases. Therefore, an effect similar to that of the confocal optical system appears, and pit interference and track interference are suppressed, and high-resolution signal detection is achieved.

[0011]

The present invention will be described in detail below with reference to the drawings according to the embodiments of the present invention.

(Embodiment 1) FIG. 1 is a block diagram showing a main part of an embodiment of the present invention. The light flux narrowed to the diffraction limit is reflected from the magneto-optical information recording medium, and the further branched light flux is guided to the optical system shown in FIG.
The crystal axis of the half-wave plate 1 is adjusted so that the electric vector of the light beam is 45 degrees on average with respect to the incident surface of the separation layer of the polarization beam splitter 2. The light fluxes magneto-optically detected by the polarization beam splitter 2, reflected and transmitted are converted into convergent light by condenser lenses 3 and 4, respectively, and are incident on incident angle dependent transmission plates 5 and 6.

At this time, the beam waist position of the convergent light narrowed down to the diffraction limit by the condenser lenses 3 and 4 and the incident surface of the incident angle dependent transmission plates 5 and 6 are the focal points of the condenser lenses 3 and 4. When the distance is f and the lens radius is a, they are arranged so as to be separated by λ / π (f / a) (f / a) or more. The light flux transmitted through the incident angle dependent transmission plates 5 and 6 is converted into a photocurrent by the photodiodes 7 and 8, and then a high resolution magneto-optical signal is detected through a preamplifier and a differential amplifier.

FIG. 2 is a schematic cross-sectional view of an incident angle dependent transmission plate which is the element that is used in the present invention and forms the basis of the present invention.
The incident angle dependent transmission plate is formed by stacking, for example, magnesium fluoride, silicon oxide, or glass as a material forming the dielectric multilayer film 9 on the flat transparent member 10 by a technique such as vapor deposition, and thus, FIG. It satisfies the relationship between the incident angle of incident light and the transmittance in the incident angle-dependent transmission plate shown in FIG. The relationship between the incident angle and the transmittance shown in FIG. 6 is when the set wavelength is 780 nm ± 10 nm, and the transmittance on the vertical axis is the relative transmittance when vertical incidence is 100%. As can be seen from FIG. 6, the incident angle dependence of the transmittance is
Since it behaves almost the same as the wavelength dependence of transmittance,
When the wavelength is fixed, the transmittance decreases as the incident angle increases. Also, if the dielectric multilayer film 9 satisfies the condition of the above expression in relation to the beam waist position of the convergent light, the same effect can be obtained even if it is located on the light emitting side of the light flux.
This also applies to the following examples.

(Embodiment 2) Next, another embodiment of the present invention will be described. FIG. 3 shows a block diagram of the main part. The light flux reflected from the magneto-optical information recording medium is
The light passes through the half-wave plate 11, is converted into convergent light by the condenser lens 14, enters the incident angle dependent transmission plate 13 under the same conditions as in Example 1, and is converted again into a plane wave by the condenser lens 14. It is incident on the polarization beam splitter 15. The reflected and transmitted light fluxes magneto-optically detected by the polarization beam splitter 15 become convergent light by the condenser lenses 16 and 17, respectively, and enter the photodiodes 18 and 19 to be converted into photocurrents, and then are converted into a preamplifier and a differential amplifier. High-resolution magneto-optical signal detection is performed via.

(Embodiment 3) Further, another embodiment of the present invention will be described. FIG. 4 shows a block diagram of the main part. The light flux reflected from the magneto-optical information recording medium passes through the half-wave plate 20 and is then subjected to magneto-optical detection to obtain 2
The light enters the Wollaston prism 21 which splits the light into a light beam. The light fluxes branched into two light fluxes are converted into convergent light by the condenser lens 22, and the respective light fluxes are incident on the incident angle dependent transmission plate 23 under the same conditions as those shown in the first embodiment.
The emitted light is further converted into convergent light by the condenser lens 24, each of the two light fluxes is incident on each light receiving surface of the two-divided photodiode 25, converted into a photocurrent, and then transmitted through a preamplifier and a differential amplifier. Resolution magneto-optical signal detection is performed.

[0017]

In the optical information detecting device having the confocal optical system, the beam spot narrowed down to the diffraction limit by the objective lens is irradiated onto the recording surface of the recorded magneto-optical information recording medium and reflected from the recording surface. When the light flux containing the magneto-optical information is narrowed down to the diffraction limit by the condenser lens,
Each point of the diffraction image near the beam waist position is at each point in the plane perpendicular to the optical axis at the beam waist position immediately after the beam spot narrowed to the diffraction limit is irradiated on the recorded surface. There is almost a one-to-one correspondence, and the polarization state at each point is also preserved.

Therefore, in the case of magneto-optical information recorded at a high density, a plurality of magnetic domains will exist in the beam spot irradiated on the recording surface. Since the diffraction images at the beam waist position correspond one-to-one, the incident angle dependent transmission plate whose transmittance greatly depends on the incident angle of the light flux as shown in the present invention is almost diffraction limited by the condenser lens. Λ / π (f / a) (f
/ A) The spherical waves can be made incident by arranging them at a position more than a distance apart, and since the peripheral part with a large incident angle is difficult to transmit, the central part of the beam is relatively emphasized, resulting in high resolution. Signal detection is achieved.

That is, in the optical information detecting device, the confocal optical system and an incident angle formed by laminating a dielectric multilayer film that functions so that the transmittance decreases as the incident angle of the light beam increases on a flat transparent member. By combining the dependent transmission plate, the conventional pinhole method requires a three-dimensional adjustment of the pinhole in the plane perpendicular to the optical axis and in the optical axis direction. A magneto-optical signal of an image can be detected, and an optical information detecting device that is extremely easy to assemble and adjust can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram of an essential part of the present invention shown in a first embodiment.

FIG. 2 is a schematic sectional view of an incident angle dependent transmission plate used in the present invention.

FIG. 3 is a block diagram of an essential part of the present invention shown in a second embodiment.

FIG. 4 is a block diagram of an essential part of the present invention shown in a third embodiment.

FIG. 5 is a block diagram showing an optical system configuration of a conventional optical information detection device.

FIG. 6 is a chart showing the relationship between the incident angle of incident light and the transmittance in the incident angle-dependent transmission plate used in the present invention.

[Explanation of symbols]

 1 1/2 Wave Plate 2 Polarization Beam Splitter 3 Condenser Lens 4 Condenser Lens 5 Incident Angle Dependent Transmission Plate 6 Incident Angle Dependent Transmission Plate 7 Photodiode 8 Photodiode 9 Dielectric Multilayer Film 10 Transparent Member 11 1/2 Wavelength Plate 12 Condenser lens 13 Incident angle dependent transmission plate 14 Condenser lens 15 Polarization beam splitter 16 Condenser lens 17 Condenser lens 18 Photodiode 19 Photodiode 20 1/2 Wave plate 21 Wollaston prism 22 Condenser lens 23 Incident angle Dependent transmission plate 24 Condensing lens 25 2-division photodiode 26 1/2 wavelength plate 27 Condensing lens 28 Pinhole 29 Condensing lens 30 Polarizing beam splitter 31 Condensing lens 32 Condensing lens 33 Photodiode 34 Photodiode

Claims (1)

[Claims] 1. A first means for converging a light beam emitted from a light source onto an optical information recording medium, and a reflected light having received optical information from the optical information recording medium to a detection optical system for conversion into converged light. A second means for detecting the optical information,
In the optical information detection device that constitutes the confocal optical system by the first and second means, a dielectric multilayer film whose transmittance greatly depends on the incident angle of a light ray is provided on the optical axis including the focal plane on the detection side. An optical information detecting device characterized in that an incident angle dependent transmission plate is arranged.