JPS59177748A - Optomagnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To increase the sensitivity of a reproducing signal and a servo signal by using a beam splitter in stead of a half mirror to separate signal reproducing light from servo signal light. CONSTITUTION:Reflected light from an optomagnetic medium 5 is separated by a beam splitter 16 and sent to the 2nd beam splitter 17 to be separated into signal reproducing light 18 and servo signal light 19. If the matrix displays of the beam splitters 16, 17 are defined as A and B, formulas I and II are applied to the transmitted light and reflected light respectively. If the polarized state on a photodetector 13 is E+M when the magnetization of the medium is ascending and E-M at the time of descending magnetization, Ps=¦(E+M)<2>-(E-M)<2>¦ is detected as a signal component, so that the beam splitter 16 having 66% and 0% transmissivility of P and S components is optimum. In the servo signal light, the beam splitter 17 having 100% reflection factor of the S component is required. In respect of the (p) component, an optimum value is selected in accordance with the servo system or the like.

Description

Detailed Description of the Invention Technical Field of the Invention The present invention relates to a magneto-optical recording and reproducing device, particularly a magneto-optical recording and reproducing device that irradiates a magneto-optical medium on which information is recorded with a laser beam and reproduces information using the magneto-optic effect. The present invention relates to a recording/reproducing device.

(Bl Technical Background and Problems Figure 1 shows a conventional magneto-optical recording and reproducing device of this type. In Figure 1, a light beam emitted from a laser light source (1) is polarized by a polarizer (2). Half mirror after becoming linearly polarized light
In (3), 50% of the incident light α passes through the objective lens (4) and irradiates the magneto-optical medium (5). The reflected light from here passes through the objective lens (4) again and is separated by a half mirror (3) to a photodetection system.

The reflected light from the separated magneto-optical medium is transmitted to the second No.-7
It is divided into two by a mirror (6), passes through an analyzer (7, 8),
One is after passing through the cylindrical lens (9).

Each of the signals is converted into a signal by a photodetector (10, 11). Also, servo signals such as focus and tracking are sent to the photodetector αυ.
Obtained from the force of the skewer.

In the case of the conventional apparatus described above, since the incident linearly polarized beam α9 is divided into two by the first half mirror (3), there arises a drawback that the amount of light cannot be used effectively, especially during recording. Also, during reproduction, the change in the polarization plane as information on the magneto-optical medium (5) also goes toward the laser light source (1), and the change
There is a drawback that only 0chi can be used for playback. Furthermore, in FIG. 1, since the servo signal is detected by the same photodetector 0υ as the reproduced signal, it is necessary to insert an analyzer (8) between them.

Analyzers in general.

Since it is used near the extinction position and rotated, it has the disadvantage that a servo signal cannot be obtained in a sufficient form. Considering the use of an avalanche photodiode or the like as a detector, it becomes extremely difficult to obtain a servo signal with the device shown in FIG.

(Cl Object and structure of the invention In order to eliminate the drawbacks shown above, the present invention
Instead of the half mirrors (3, 6) shown in the figure, a beam splitter is used to separate the signals for signal reproduction and servo signals. The object of the present invention is to provide a device capable of performing the ascent. Therefore, the magneto-optical recording/reproducing apparatus of the present invention focuses a linearly polarized light beam onto a magneto-optical medium.

In a magneto-optical recording and reproducing device that reads information on the medium based on light reflected from the magneto-optical medium, substantially 66% of the linearly polarized incident light is directed onto the magneto-optical medium; A first beam splitter that separates substantially 100% of the polarized light component perpendicular to the incident light from the reflected light from the incident light, and a magneto-optical component that is separated by the first beam splitter. Equipped with a second beam splitter to further split the reflected light from the medium into two parts.

The second beam splitter is characterized in that it separates 100% of the component perpendicular to the incident light. This will be explained in detail below.

(Di Embodiment of the Invention FIG. 2 shows an embodiment of the present invention. In FIG. 2, a light beam emitted from a laser light source (1) becomes linearly polarized by a polarizer (2) and enters a beam splitter αG.

In this state, the vibration plane of the input source 9 is horizontal to the plane of the paper. The light beam that has passed through the beam splitter αe enters the magneto-optical medium (5), and the reflected light from there is separated again by the beam splitter tiQ and heads toward the second beam splitter←η, where it is sent to the signal reproducing source. and servo light (11).

Let us now assume that the matrix representation of the beam splitter is ``Person'', and the matrix representation of the beam splitter a'0 is ``B''.

For transmitted light, for reflected light, the p component is a polarized light component with a plane of vibration parallel to the plane of incidence, and the S component is a polarized light component with a plane of vibration perpendicular to the plane of incidence. It is.

Next, if we simply consider the magneto-optical medium as an optical rotator, It is expressed as

± depends on the direction of rotation of the plane of polarization due to the direction of magnetization.

It is also called the ψ ore Kerr rotation angle.

Furthermore, since the analyzer (7) is expressed as the position o' where the extinction occurs for polarized light orthogonal to the incident light and the rotation angle from there as θ, the light on the photodetector α4 is The polarization state of is expressed as when the magnetization of the medium is upward.

Here JRp = rp + JRB = 'B + V'T
If g='5+v"r,""'p, then E+Myu(rpB@rpl"tpA'CO9θ+ψarSB"aA"'FA"'θ).

Also, when the direction of magnetization is opposite, B-' = ('pH''FA''PA-LXl'
θ−ψ” ”+111 ”aA ” tPA・Town).

What is detected as a signal component is Ps=l (E")" - (E-')'1, so P8=2ψ""n"'8B"4" rPA
” fill ・ain2θ where r: +t2P= 1, so P8=2ψ@rpn ” rsa ” ”: A V'1
-... (1) From equation (1), regarding the beam splitter αQ, TP! ”1'Aw5t
R@=r@1 P8 becomes maximum when the amount is 1. A beam splitter with a transmittance of 66% for the P component and 0% for the S component is optimal.

Next, the state of the light incident on the servo signal photodetector (2) is determined in the same way as +w, , (b+i+ "rpA" bh+ψ
'tsos'rltpi)g-1(tPB”
rPA″tPA−ψ” t8B ” raa tPA
) Here, the Kerr rotation angle is very small, and from 2 rph = 茗, the above equation yields El-E-1 (?pB ``rpl'' jp person).

The amount of light is P. ” ('pm'tpA"rph)"=Z
"t"pB9 °°°°°゛°゛°°゛°
(2) becomes.

From the formula il+, +21, it is desired that for the beam splitter αD, r3B = 1, that is, the reflectance of the S component is 100%. On the other hand, regarding the p component, the optimum value may be selected depending on the servo system, the power during reproduction, etc. Assuming that, P8=0.51X (2ψ8in2θ)...River...(3). For comparison, in the case of the half mirror shown in Figure 1, the differential output is Ps = 0.25 X (2ψam2θ) ・
・・・・・・・・・・・・・・・ (4)

As explained above, in the case shown in FIG.

The sensitivity of the reproduced signal is increased by 25 inches compared to the one shown in Figure 1, and the transmittance of the beam splitter is 66%, so the amount of light can be used effectively during recording, and an analyzer is also included for the servo signal. There will be no shortage of light or undesirable changes in the amount of light.

FIG. 3 shows another embodiment of the invention, using the same parts as in FIG. 2, and like parts being numbered the same.

It goes without saying that there is a difference in arrangement between the one shown in Figure 3 and the one shown in Figure 2, but the incident light α9
The polarization plane of is perpendicular to the plane of the paper, and the beam splitter (lG)% characteristics are TP=1, R8=-g
, the characteristics of the beam sinter aη are chosen to be T, day 1.

(El) As described in detail, according to the present invention, the sensitivity of the reproduced signal is increased, the amount of light can be used effectively even during recording, and there is no problem such as insufficient light amount for the servo signal. there is no problem.

[Brief explanation of the drawing]

FIG. 1 shows an example of a conventional magneto-optical recording/reproducing device, FIG. 2 shows an embodiment of the present invention, and FIG. 6 shows another embodiment of the present invention. In the figure, (1) is a laser light source, (2) is a polarizer, and (4)
is an objective lens, (5) is a magneto-optical medium, (7) is an analyzer,
C11 represents a photodetector, and fiti and αη each represent a beam splitter. Patent applicant Fujitsu Limited

Claims (1)

[Claims] focusing a linearly polarized light beam onto a magneto-optical medium;
In a magneto-optical recording and reproducing apparatus that reads information on the medium based on light reflected from the magneto-optical medium, substantially 66 out of the linearly polarized incident light is directed onto the magneto-optical medium; A first beam splitter that separates the polarized light component orthogonal to the incident light out of the reflected light from the incident light by substantially 100 beams, and a magneto-optical component that is separated by the first beam splitter. a second beam splitter for further splitting the reflected light from the medium into two;
A magneto-optical recording and reproducing apparatus characterized in that the second beam splitter separates a component perpendicular to the incident light by 100 beams.