JP3162842B2 - Optical information reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium reproducing apparatus capable of recording at high density.

[0002]

2. Description of the Related Art For example, Japanese Patent Publication No. 4-3575 discloses a reproducing apparatus for reproducing data from a magneto-optical recording medium at a larger signal level.

In a reproducing apparatus using a next-generation photon mode type optical recording medium, reproduction is performed with an extremely low reproducing power of the order of tens of nW in order to prevent signal deterioration during reproduction.
The present inventor has proposed a device for maintaining a sufficient SN ratio as Japanese Patent Application No. 4-224138.

[0004] These two conventional reproducing devices separate the light emitted from the same light source into two, irradiate one to a medium, and light-mix the other with light obtained by reflection on the medium. The characteristic feature is that detection is performed by a photodetector after interference with each other.

[0005] In these conventional devices, even if the reflected light obtained from the medium is weak, it is possible to amplify the reproduction signal intensity by setting the intensity of the other separated light to a moderately high level. .

[0006]

However, in the above-mentioned conventional apparatus, it is necessary to separately provide an optical element for separating the radiated light from the same light source and an optical element for synthesizing each separated beam. However, there is a problem in that the size becomes large and complicated.

The present invention has been made to solve such a problem of the conventional apparatus, and an object of the present invention is to provide a reproducing apparatus having a simple structure which can use the conventional reproducing method as it is.

[0008]

SUMMARY OF THE INVENTION The present invention provides an incoming polarized light beam having two mutually orthogonal polarization states:
A single polarizing optical element that combines the beams of the separated components that are separated and re-entered into a second beam component in such a manner that the planes of polarization are orthogonal to each other, and the first and second beams separated by the polarizing optical element To a circularly polarized light, a lens system for focusing the first beam on an optical recording medium and extracting reflected light reflected on the medium, and the second beam on the same optical path as an incident optical path. A reflecting mirror, a polarizer whose direction is inclined with respect to the two polarization directions of the beam itself, which passes through the beam recombined in a form in which the polarization plane is orthogonal by the polarizing optical element, and passes through the polarizer. And a photodetector for photoelectrically converting the converted beam.

Further, the polarization planes are orthogonal to each other by the polarization optical element .
And a polarizer that transmits a beam that has passed through the phaser, and a photodetector that performs photoelectric conversion of the beam that has passed through the polarizer. Good.

[0010]

Since a single optical element is used as an element for separating and reproducing and synthesizing the radiation emitted from the light source, the optical system is simplified, and the size and cost can be reduced. On the other hand, the signal can be amplified by light mixing (interference) by detecting the combined beam through an optical element having polarization characteristics and detecting the combined beam with a photodetector.

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a reproducing apparatus according to the present invention.

[First Embodiment] FIG. 1 shows the configuration of a reproducing apparatus according to a first embodiment. Reference numeral 1 denotes a λ / 2 plate that transmits a radiated light L1 from a light source, and 2 denotes a λ / 2 plate that transmits the λ / 2 plate. L
2, a beam splitter for splitting into two lights L3, 3 is a phase compensator that transmits the split light L2, 4 is a first λ / 4 plate that transmits the split light L2, and 5 is a reflector that reflects the split light L2. A mirror 6 for generating reflected light L4, and a second λ / 4 transmitting radiation light L1 passing through the beam splitter 2.
The plate 7 is an objective lens for condensing the radiation L1 transmitted through the second λ / 4 plate 6 on the medium 8. The reproduction light L5 radiated from the medium 8 is again transmitted to the objective lens 7, the second λ
The light passes through the / 4 plate 6 and enters the beam splitter 2.

On the other hand, the reflected light L4 is applied to the first λ / 4 plate 4
Then, the light enters the beam splitter 2 via the phase compensator plate 3 and is combined with the reproduction light L5 to form a combined light L3, passes through the polarizer 9 and the lens 10, and enters the photodetector 11.

In such a configuration, the light L1 emitted from the light source
Is a linearly polarized light, and has the following electric field intensity VE (hereinafter, V is a prefix meaning a vector) as a result of adjusting the polarization direction by the λ / 2 plate 1.

[0015]

(Equation 1)

The emitted light L1 is split by the polarizing beam splitter 2 into two lights according to its polarization components as follows.

[0017]

(Equation 2)

The split beam L2 (electric field intensity VE ₂ ) is reflected by the beam splitter 2 as an S-wave, and
And converted into circularly polarized light by the λ / 4 plate 4, reflected by the mirror 5, again passed through the λ / 4 plate 4 and the phase compensator plate 3,
This time, a P wave (electric field intensity V) is applied to the polarization beam splitter 2.
E ₂ ') and made to pass through.

On the other hand, the radiated light L1 (electric field intensity VE ₁ ) that has passed through the polarization beam splitter 2 as a P-wave is converted into circularly polarized light by the second λ / 4 plate 6, and
3 is collected. The reflected light that has undergone some change due to the information recorded on the medium 23, that is, the reproduced light L5, is again converted into an S-wave (electric field intensity VE ₁ ′) by the action of the λ / 4 plate 6, and the polarized light is split by the polarization beam splitter 2. Is reflected. After all, the beams having the _two electric field intensities VE ₁ ′ and VE ₂ ′ are combined by the polarization beam splitter 2 in a form where their polarization planes are orthogonal to each other, and the following combined light L3 (electric field intensity VE ′) is obtained. Become.

[0020]

(Equation 3)

Where φ is the luminous flux VE associated with separation / recombination.
₁ and VE ₂ , and here, it is assumed that E ₂ has changed from E ₂ to E _2S depending on the recording information of the medium.

Now, let us consider that the combined light L3 is detected by the detector 11 after passing through the polarizer 9 having the azimuth θ. Jones matrix MP generally corresponding to polarizer with orientation θ
θ (hereinafter, M is a prefix meaning a matrix) is as follows.

[0023]

(Equation 4)

Therefore, the beam VE ″ after passing through the polarizer 9 is

[0025]

(Equation 5)

## EQU1 ##

The light intensity I detected by the photodetector 11 is given by the square of the electric field intensity, that is, | VE "| ² .
For example, when θ = 45 °,

[0028]

(Equation 6)

## EQU1 ## Therefore, since the term E ₁ × E _2S exists, even if E _2S is small, it is possible to obtain a sufficient signal strength by appropriately increasing E ₁ .

[0030] In the reproducing apparatus of the second embodiment] Now the first embodiment undeniable that a relatively large laser noise for E ₁ ² term in the equations 6 remains occurs. Therefore, a reproducing apparatus which improves this point will be described as a second embodiment with reference to FIG. This apparatus is the same as the first embodiment up to the point where the two reflected beams L4 and L5 are combined by the polarizing beam splitter 2. Therefore, the combined light L3 has the electric field VE 'represented by the above equation (3).

The combined light L3 has a third λ as a phase shifter.
By the action of the / 4 plate, each orthogonal polarized light component is converted into circularly polarized light in the opposite direction. This λ / 4
Expressed using a Jones matrix corresponding to the plate 12,

[0032]

(Equation 7)

## EQU1 ## Then, the orthogonal polarization component is changed to L by the second polarization beam splitter 13 as a polarizer.
6 and L7, transmitted through the lenses 101 and 102, respectively, and independently detected by the two photodetectors 111 and 112. At this time, the detection outputs I ₁ and I ₂ of the respective detectors are expressed as follows.

[0034]

(Equation 8)

In the differential amplifier 14, the output I
_When subtracting between ₁ and I ₂ ,

[0036]

(Equation 9)

The next, is canceled E ₁ ² of terms involving relatively large laser noise, only term proportional to E ₁ × E _2S containing amplified signal E ₁ remains. The optical system according to the second embodiment can be applied not only to a reflectance changing type medium such as a photochromic optical recording medium but also to a magneto-optical recording medium.

That is, reproduction is performed by irradiating the magneto-optical recording medium with linearly polarized light and detecting the rotation (Kerr rotation) of the plane of polarization of the reflected light. However, when circularly polarized light is radiated as in the second embodiment, not the polarization state but the phase thereof is affected by the recorded information. Therefore, information to be reproduced is included in the phase term sinφ instead of the magnitude E _2S of the reflected light intensity from the medium. Since the phase change φ is very small as well as the Kerr rotation angle is usually very small, Equation 9 can be approximated as follows.

[0039]

(Equation 10)

From equation (10), it can be seen that φ in the magneto-optical recording medium is
It can be seen that it is possible to amplify the signal that increases the E ₁ be smaller.

[Third Embodiment] FIG. 3 is a block diagram showing a third embodiment of the present invention. Similar to the second embodiment, the combined beam L3 by the polarizing beam splitter 2 is also given by the following equation (3). And In this embodiment, the azimuth of the second polarization beam splitter 13 as a polarizer is simply inclined with respect to the first polarization beam splitter 2. Of course, a λ / 2 plate may be provided equivalently.

In particular, when the inclination angle of the second polarization beam splitter 13 is 45 °, the electric field of the incident beam based on the azimuth of the polarization beam splitter 13 is given as follows.

[0043]

[Equation 11]

Accordingly, the light detection is performed in the same manner as in the second embodiment.
Output I of output units 111 and 112₁ , I _Two Is

[0045]

(Equation 12)

The output of the differential amplifier 14 is

[0047]

(Equation 13)

Then, the signal is amplified by E ₁ and
₁ laser noise becomes possible to obtain a reproduced signal output is reduced.

[0049]

As described above, according to the present invention, an optical system and a medium having a very simple structure are compared with a conventional reproducing apparatus.
Since the reproduction signal output can be amplified and the laser noise can be reduced by the body configuration , a high SN ratio of the reproduction signal can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a reproducing apparatus of the present invention.

FIG. 2 is a configuration diagram showing a second embodiment of the reproducing apparatus of the present invention.

FIG. 3 is a configuration diagram showing a second embodiment of the reproducing apparatus of the present invention.

[Explanation of symbols]

 L1 to L7 Beam 2 Polarizing beam splitter 4, 6 Element for converting to circularly polarized light 7 Lens system 5 Mirror 9, 13 Polarizer 11, 111, 112 Photodetector 12 Phaser

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B ^7/ 12-7/22 G11B 11/105 551

Claims (2)

(57) [Claims] 1. An incident polarized beam is separated into first and second beam components having two mutually orthogonal polarization states, and a beam of each separated component that is re- entered is directly polarized.
A single polarizing optical element for combining in an intersecting manner, an element for converting each of the first and second beams separated by the polarizing optical element into circularly polarized light, and collecting the first beam on an optical recording medium. a lens system for taking out a reflected light reflected on the medium with light, wherein the mirror the second beam to anti <br/> morphism in the incident light path and the optical path, the polarization plane by the polarizing optical element is a straight
Optics having a polarizer whose direction is inclined with respect to the two polarization directions of the passing beam of the beam recombined in an intersecting manner, and a photodetector for photoelectrically converting the beam passing through the polarizer Information reproducing device. 2. An incident polarized beam is separated into first and second beam components having two orthogonal polarization states, and a beam of each separated component that is re- entered is directly polarized.
A single polarizing optical element for combining in an intersecting manner, an element for converting each of the first and second beams separated by the polarizing optical element into circularly polarized light, and collecting the first beam on an optical recording medium. a lens system for taking out a reflected light reflected on the medium with light, wherein the mirror the second beam to anti <br/> morphism in the incident light path and the optical path, the polarization plane by the polarizing optical element is a straight
Optical information having a phaser through which a beam recombined in an intersecting manner passes, a polarizer through which a beam exiting the phaser passes, and a photodetector which photoelectrically converts the beam passing through the polarizer. Playback device.