JPS61216148A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To prevent the deterioration of C/N of a reproduction signal due to back talk as well as the unstable focusing and tracking servo control, by preventing the reflected light sent from a recording medium from returning to a laser. CONSTITUTION:The laser luminous flux delivered from a semiconductor laser 9 is turned into parallel luminous fluxes through a collimator lens system 10 and transmitted through a polarizer 11. Then the luminous flux whose polarizing surface is turned by pi/4 is made incident on a polarized beam splitter. The polarization axis of the splitter 13 is set coincident with the polarizing direction of the incident laser luminous flux. Then the polarized luminous flux is formed into a minute spot on a magnetic disk 15 via an objective lens system 14. The polarizing surface of the reflected light sent from the disk 15 is turned by an angle + or -thetak by the Kerr effect. This turned luminous flux is condenced to a photodetector 18 via a condenser lens 16 and a photodetector 17.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to an information recording/reproducing device that utilizes the magneto-optical effect, and in particular uses a laser as a light source and irradiates the recording medium with the light flux as a minute spot to record information. The present invention relates to an optical information recording and reproducing device that performs recording and reproducing.

[Prior art]

In recent years, there has been active research and development into the practical application of optical memory, which performs recording and playback using semiconductor laser light, as a high-density recording memory. However, optical disks, such as video disks that have already been commercialized, are only for playback, and the recorded content is Therefore, there is a strong demand for a magneto-optical disk that can be erased and rewritten. Magneto-optical disks magnetically record information by utilizing the local temperature -I rise of a magnetic thin film caused by laser spot irradiation.
The information is reproduced by Here, the Kerr effect refers to a phenomenon in which when light is reflected by a recording medium, the plane of polarization of the reflected light rotates.

Now, in optical information reproduction using the Kerr effect, a portion of the reflected light from the recording medium returns to the semiconductor laser, resulting in a decrease in the CAH of the reproduced signal, or instability in the focus or l/racking servo. Problems such as oxidation occur. In video disks and the like, such returning light is removed by a combination of a polarizer and a quarter wavelength plate, but when used in magneto-optical disks, signal detection becomes impossible and a similar method cannot be used.

FIG. 5 is a schematic diagram showing an example of a conventional optical information recording/reproducing device using a Faraday element. Here, the Faraday element utilizes a phenomenon (Faraday effect) in which the plane of polarization of light rotates when light passes through a substance placed in a magnetic field. In Fig. 5, 1 is a semiconductor laser, 2 is a collimator lens system, 3 is a polarizing beam splitter, 4 is a Faraday element, 5 is an objective lens system, 6 is a magneto-optical disk, 7 is a condensing lens system, and 8 is a photodetector. It is a vessel.

The laser beam emitted from the semiconductor laser is made into a parallel beam by the collimator lens system 2 and sent to the beam splitter 3.
incident on .

Figures 6 (A) to (D) show the polarization directions after passing through or reflecting each optical element, and Figure 6 (A) t:
ntag, v-fo':tjjrmeP(iis:t
The 'ji direction and the direction perpendicular to it will be called the S polarization direction. Here, if the transmittance of the P-polarized light component of the polarizing beam splitter 3 is tp, and the transmittance of the S-polarized light component is ts, then in order to increase the utilization efficiency of the laser light, tp~:゛°olfactory path°~° t63 is 5repa・21□: The light beam transmitted through the beam splitter 3 enters the Faraday element 4, where its polarization plane is as shown in Fig. 6 (
As shown in B), rotate by an angle ψ. This polarized light flux passes through an objective lens system 5 and is imaged as a minute spot on a magneto-optical disk 6.

Further, as shown in FIG. 6(C), the reflected light from the magneto-optical disk 6 has a polarization plane in the opposite direction at an angle of ±θ depending on the magnetization direction of the spot irradiation area due to the Kerr effect. Make a rotation. The reflected light whose plane of polarization has been rotated in this manner enters the objective lens 5 again and is returned to a parallel beam. The plane of polarization of this parallel light beam is again rotated by the angle ψ by the Faraday element 4, so that it becomes as shown in FIG. 6(D).

The polarization characteristic of the polarization beam splitter 3 is P polarization transmittance tp
= too%, since the S polarization reflectance is 100%,
The S-polarized component of the luminous flux in FIG.
incident on . On the other hand, the P-polarized light component reaches the semiconductor laser l as returned light. Here, if the amplitude of the semiconductor laser l is A, the intensity Ig of the signal light detected by the photodetector 8 is expressed by the following formula % Formula % On the other hand, the average intensity IB of the return light to the semiconductor laser l is expressed by the following formula is given by

In NA2tF”Rcos22(/1)
(2) However, tF is the transmittance of the Faraday element, R
is the Fresnel reflectance of the magneto-optical disk 6.

As can be easily seen from equations (1) and (2), the intensity of the signal light becomes O under the condition of r=π14, which minimizes the return light. Therefore, the apparatus shown in FIG. 5 is not suitable as an optical system for recording and reproducing information using the magneto-optical effect.

〔the purpose〕

SUMMARY OF THE INVENTION Therefore, the purpose of the present invention is to eliminate the two consecutive drawbacks, solve problems such as a reduction in the C/N of the reproduced signal due to the warped light on the semiconductor laser, and instability of the focus and tracking servos. An object of the present invention is to provide an information recording and reproducing device.

[Structure of the invention]

In order to achieve such an object, the present invention provides an optical information system that includes a laser light source, irradiates light from the laser light source onto a recording medium as a minute spot, and records and reproduces information using the magneto-optical effect of the recording medium. In a recording/reproducing device, light from a laser light source passes sequentially through a polarizer, a Faraday element, and a polarizing beam splitter, and is irradiated onto a recording medium, and the reflected light from the recording medium passes through a polarizing beam splitter and is sent to a photodetector. It is characterized in that it is configured so that the light is guided to the laser beam and detected as an information signal, and the return light to the laser laser light source is removed by using a Faraday element and a polarizer.

〔Example〕

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

Figure 1 shows an example of the configuration of the optical system of the present invention, and Figure 2 (
A) to (G) are transmitted through each optical element of the optical system of the present invention,
Alternatively, it shows the plane of polarization and amplitude after reflection.

First, in FIG. 3, 9 is a semiconductor laser, 10 is a collimator lens system, 11 is a polarizer, 12 is a Faraday element, 13 is a polarized beam spree 2, 14 is an objective lens system, 15 is a magneto-optical disk, and 16 is a A condensing lens system, 17 an analyzer, and 18 a photodetector.

The laser beam emitted from the semiconductor laser 9 is made into a parallel beam by a collimator lens system 10, and then passed through a polarizer 1.
In the present invention, the polarization direction of the semiconductor laser 9 and the polarization axis of the polarizer 11 are made to match.

In FIGS. 2A to 2G, the direction forming an angle of 45° with the polarization direction of the semiconductor laser 9 and the polarization axis direction of the polarizer 11 will be referred to as the P polarization direction for convenience.

Next, the polarization plane of the light beam transmitted through the Faraday element 12 is rotated, but in the present invention, this rotation angle is changed as shown in FIG.
As shown in B), it is set as π/4. The light beam whose polarization plane has been rotated in this manner is made incident on the polarizing beam splitter 13. Here, the polarization axis of the polarization beam splitter 13 is made to match the polarization direction of the incident laser beam. Regarding its polarization characteristics, the transmittance of P-polarized light is tp, and the reflectance is r
If p (rp = l - tp), the photodetector 18
When using a detector with a multiplication effect as the photodetector 18, select tp(rp) described in Japanese Patent Application No. 59-33848, and when using a detector without multiplication effect as the photodetector 18, select the It is sufficient to select tp(rp) described in No. 59-33849. For example, tp=
eo% (i.e., rp=2o%), although the efficiency of laser light use decreases slightly, the C of the reproduced signal
/N can be made maximum. Note that if the transmittance of S-polarized light is ts and the reflectance is rs (rs = 1-ts), then in the present invention, rs = 100% (tS = O%).

FIG. 2(C) shows the polarization direction and amplitude after passing through the polarization beam splitter 13. This polarized light beam passes through the objective lens system 14 and is imaged as a minute spot on the magnetic disk 15J. Due to the Kerr effect, the polarization plane of the reflected light from the magneto-optical disk 15 has an angle ± as shown in FIG. 2(D).
Rotates only in θ. Since the polarization characteristics of the polarizing beam splitter 13 are, for example, rp=20% and rs=100%, the light beam reflected by the polarizing beam splitter 13 has a smaller amplitude as shown in FIG. 2(E). As shown in , the apparent Kerr rotation angle increases to ±θk. This light flux passes through a condensing lens 16 and an analyzer 17 and is condensed onto a photodetector 18 as signal light. Since the polarization axis of the analyzer 17 is in the direction of the angle θ^ from the P polarization direction, the intensity of the signal light detected by the photodetector 18 is given by the following equation.

■s~2A2 tpow 11 tF t, i”, t
ANAXRsin2θksin2θA (3)
However, tpoL, tp, and tA are each polarizer 11.
The transmittance of the Faraday element 12 and the analyzer 17, R is the Fresnel reflectance of the magneto-optical disk 15. It is known that the C/N can be improved by selecting an appropriate angle for θA; for example, when a detector without multiplication is used as the photodetector 18, 0A=70'' to 80°.

Note that the present invention is also effective even if a half mirror is inserted after the condenser lens system 16 to achieve differential amplification. Further, focus and tracking servo are performed by known means, but since these have no direct relation to the present invention, detailed explanation thereof will be omitted here.

On the other hand, the polarization direction and amplitude of the light beam that passes through the polarizing beam splitter 13 and enters the Faraday element 12 are shown in Figure 2 (F
). The light beam transmitted through the Faraday element 12 undergoes rotation of the plane of polarization by π14 again, as shown in Fig. 2 (G
). The average intensity Ln of the return light to the semiconductor laser 9 is given by equation (4).

IE ~ηpoL11A2tBtp"tp'Rcos2
θA (4) where ηpOL is the extinction ratio of the polarizer 11. here.

Since the returned light has a polarization direction perpendicular to the optical axis of the polarizer 11, it is extinguished.

In FIG. 1, when detecting the transmitted light of the polarizing beam splitter, the polarization direction of the incident light may be set to the S polarization direction, and the optical system shown in FIG. 3 may be used. In FIG. 3, the semiconductor laser 9 emits light, and the collimator lens system l
The light that has passed through the O1 polarizer 11 and the Faraday element 12 is incident on the polarizing beam splitter 13, and the light reflected here is incident on the magneto-optical disk 15 via the objective lens system 14. The reflected light from the magneto-optical disk 15 passes through the polarizing beam splitter 13, passes through the condenser lens system 16, passes through the analyzer 17, and enters the photodetector 18.

FIGS. 4(A) to 4(G) show the polarization plane and amplitude after transmission or reflection through each optical element at this time.

FIG. 4(A) shows the polarization direction of the semiconductor laser 9 and the polarization axis direction of the polarizer 11, and FIG. 4(B) shows the Faraday element 12.
4(C) shows the polarization direction and amplitude after being reflected from the polarizing beam splitter 13, FIG. 4(D) shows the polarization direction and amplitude after reflecting from the magneto-optical disk 15, and FIG. 4(E) shows the polarization of the signal light. Beams “Transmits through splitter 13: Li! (71!ff111m,
! -41ii111! , 14[1< (F) l*@
'if.

The polarization direction and amplitude of the returning light to the semiconductor laser 9 reflected from the beam splitter 13 are shown in FIG. be.

1 [Effect] As explained above, according to the present invention, recording 1
Since reflected light from the medium does not return to the laser, problems such as a reduction in the C/H of the reproduced signal due to backtalk and instability of focus and tracking servo can be solved.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing the configuration of an optical system in an embodiment of the optical information recording/reproducing apparatus of the present invention, and FIGS. 2(A) to (G) are transmission or reflection through each optical element of the optical system shown in FIG. FIG. 3 is a configuration diagram showing the configuration of an optical system in another embodiment of the optical information recording/reproducing apparatus of the present invention, and FIGS. 4(A) to (G) are Fig. 3 is an explanatory diagram of the polarization direction and amplitude of the light beam after passing through or reflecting each optical element of the optical system shown in Fig. 5. Fig. 5 shows an example of the optical system of a conventional optical information recording/reproducing device using a Faraday element. The configuration diagram shown in Fig. 6 (A) ~
(D) is an explanatory diagram of the polarization direction and amplitude of the light beam after passing through or reflecting each optical element of the optical system shown in FIG. 9... Semiconductor laser, 10... Collimator lens system, 11... Polarizer, 12... Faraday element, 13... Polarizing beam splitter, 14... Objective lens system, 15... Light Magnetic disk, 1B... Condensing lens system, 17... Analyzer, 18... Photodetector. Figure 6 (A) (B) (C) (B)

Claims (1)

[Claims] 1) Optical information recording and reproducing that includes a laser light source, irradiates light from the laser light source as a minute spot onto a recording medium, and records and reproduces information using the magneto-optical effect of the recording medium. In the apparatus, the light from the laser light source sequentially passes through a polarizer, a Faraday element, and a polarizing beam splitter,
irradiating the recording medium onto the recording medium, guiding the reflected light from the recording medium to a photodetector through the polarizing beam splitter to detect it as an information signal, and returning it to the laser light source by the Faraday element and polarizer. An optical information recording/reproducing device characterized by being configured to remove light. 2) The optical information recording and reproducing apparatus according to claim 1, wherein the polarization axis of the polarizer is made to coincide with the polarization direction of the laser light source. 3) The optical information recording and reproducing apparatus according to claim 1, wherein the rotation of the plane of polarization by the Faraday element is π/4. 4) The polarization characteristic of the polarization bead splitter is determined by the optical detection for a polarization component of the light reflected from the recording medium in a direction perpendicular to the polarization plane of the light from the laser light source rotated by the Faraday element. 2. The optical information recording/reproducing device according to claim 1, wherein the light transmittance to the side of the device is approximately 100%. 5) The polarization characteristic of the polarizing beam splitter is determined by the optical detection with respect to the polarization component of the light reflected from the recording medium in a direction perpendicular to the polarization plane of the light from the laser light source rotated by the Faraday element. 2. The optical information recording and reproducing device according to claim 1, wherein the light reflectance toward the side of the device is approximately 100%.