JPS6255222B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reproducing a recording medium using a magneto-optical material capable of recording, reproducing, and erasing.
This is an attempt to simplify the reproduction optical system that has been proposed in the past.

Recently, magneto-optical recording materials that are capable of recording, reproducing, and erasing have been attracting attention. The reproduction of magneto-optic signals is
This is usually done in the following way. A linearly polarized light source is used as a reproduction light source, and the light is focused onto the recording medium using an objective lens. The light reflected by this magnetic recording medium is guided by a half mirror to an optical path different from the outgoing path, and after passing through an analyzer such as a Glan-Thompson prism or a Wollaston prism, it enters a detector. However, in this reproduction method, the optical system becomes complicated due to the use of Grand-Mausson prisms, Wollaston prisms, etc.

The present invention aims to solve these problems and provide an optical system capable of reproducing a magneto-optical recording medium capable of recording, reproducing, and erasing with a good S/N ratio.
Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows the configuration of an optical system according to the present invention. For example, a light beam emitted from a He--Ne laser 1 having P polarization passes through a polarizing beam splitter 2 which has a characteristic of transmitting P polarized light and reflecting S polarized light.
Thereafter, the light flux becomes circularly polarized light through the quarter-wave plate 3. The circularly polarized light beam is irradiated onto the magnetic recording carrier 5 by a condensing lens 4 as a minute spot converged to the diffraction limit. The record carrier 5 is, for example, the second
As shown in the figure. It consists of a reflective layer B formed on a glass substrate A by Al vapor deposition, a magneto-optic thin film C made of EuS, and an anti-reflection film D for preventing reflections on the surface of the magneto-optic thin film C.
Therefore, as shown by the arrow line in the figure, the light incident on the record carrier 5 enters the D layer, and then the D layer and the C layer.
No reflection occurs at the interface between the layers, and the light is incident on the C layer.
After entering the C layer, it is reflected by the reflective layer B, and then enters the C layer D again.
A phase delay occurs due to birefringence until the interface between the layers is reached. At this time, the electric field E of the circularly polarized light at the time of emission from the C layer depends on the direction of magnetization of the magneto-optic thin film C. It is expressed as Here, C is the speed of light, d is the thin thickness of the C layer, n is the complex refractive index of the C layer, and n(+M) represents the complex refractive index when the magnetization is +M. C is the speed of light. Therefore, when the direction of magnetization is +M and when the direction of magnetization is -
The phase difference Δ of the reflected wave from the time of M is the light source wavelength λ
It becomes as follows.

That is, when the complex refractive index n(+M) is expressed by dividing it into a real part and an imaginary part, it becomes n(+M)=R _e n (+M)+jI _n n (+M). R _e and I _n indicate the real part and the imaginary part, respectively. Substituting this into the first equation above, we get The phase of this complex number arg(E _+M ) is arg(E _+M )=W/C2dR _e n (+M). Similarly, for a complex refractive index n(-M), the phase arg(E _-M ) becomes arg(E _-M )=W/C2dR _e n(-M).

Therefore, the phase difference Δ between the two becomes Δ=arg(E _+M )−arg(E _−M )=W/C·2d{ _Ren (+M) _−Ren (−M)}. Here, from W/C=2π/λ, Δ=4πd/ _λRe {n(+M)−n(−M)}.

Here, by determining d so that Δ=π,
Phase difference detection using birefringence can be easily performed. In the above equation, the value of Δ/2d, or 2π/λ・Re[n(+M)-n(-M)], is usually known as the Faraday rotation angle _θF of the magnetic material, and has been measured with various materials. There is. For example, taking EuS as an example, θ _F near λ = 6328 Å is 10 ⁷ degres/cm, so from θ _F = Δ/2d = 10 ⁷ degree/cm, in order to make Δ = π, the EuS The thickness d may be set to d〓900 Å.

Now, as mentioned above, signals are recorded on the magneto-optical recording medium in a state where the signal portion is n(+M) and the non-signal portion is n(-M).

Let us now consider, as an example, the reproduction of a signal recorded in dots along a spiral track on a disc-shaped recording medium that is rotationally driven as a signal. An enlarged view of the recorded signal is shown in FIG.

In FIG. 3, 10 indicates a signal region having a refractive index of n(+M), 11 indicates a condensing spot, and 12
is a no-signal region and has a refractive index of n(-M). Now, number 11 is shown as the reproduction light spot, but even if a signal is actually recorded at the same light collection spot, the magneto-optical recording material has a recording threshold level, so it will be smaller than the reproduction light spot like 10. I get used to it. Therefore, the dimensional relationship as shown in FIG. 3 naturally occurs when recording and reproducing are performed using the same device, which has been much studied recently. Therefore, the reflected light is from area 10 and area 12.
It is the sum of the reflected light from the
There is only one.

In this way, the two circularly polarized lights having a phase difference of Δ pass through the quarter-wave plate 3 again and appear as linearly polarized light, and the plane of polarization becomes S-polarized light that is orthogonal to the P-polarized light emitted from the laser light source. Therefore, it is then reflected by the polarizing beam splitter 2,
The optical path is separated and reaches the photoreceiver 6.

In this way, the method of applying monochromatic polarized light to a magneto-optical recording medium to generate a phase difference and detecting the interference is a completely new attempt. This is very different from the method of detection using photons.

In addition, for detection of magneto-optical signals using conventional methods,
Although it was necessary to use a light spot smaller than the recording pit, the method according to the present invention uses a larger light spot than the recording pit, so the amount of light can be increased compared to the same reproduction light energy density. Furthermore, since an analyzer such as a half mirror, Glan-Thompson prism, or Wollaston prism is not used, there is no power loss due to such an analyzer, and the reproduction apparatus can be simplified and lowered in price.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an optical system according to an embodiment of the present invention, Fig. 2 is a sectional view showing an example of a magneto-optical recording medium, and Fig. 3 shows a signal area and a reproduction spot on a disk during signal reproduction. FIG. 1... Laser light source, 2... Polarizing beam splitter, 3... 1/4 wavelength plate, 4... Condensing lens, 5
...Magneto-optical recording medium, 6... Light receiver.

Claims (1)

[Claims] 1. Linearly polarized light as a reproduction light source for reproducing recorded signals from a magneto-optical recording medium in which magnetization is recorded in a magneto-optic thin film such that the magnetization directions are opposite in the non-signal area and the signal image area. Using a light source, a polarizing beam splitter and a quarter-wave plate are arranged in this order from the light source toward the magneto-optical recording medium on this optical path, and the quarter-wave plate converts the linearly polarized light into circularly polarized light, and converts the linearly polarized light into circularly polarized light. The reflected light that is irradiated onto the optical recording medium and reflected through the magnetic thin film of the magneto-optical recording medium is emitted from the light source by the quarter-wave plate.The plane of polarization that is emitted from the light source is a straight line with a plane of polarization that is direct light. The polarized light is converted into polarized light and separated from the outgoing path by the polarizing beam splitter, and a photodetector is arranged on the separated optical path. An optical reproducing device characterized by detecting a signal by generating a diffraction image using reflected light. 2. The magneto-optical recording medium is a disk, and during playback, this disk rotates, and the recorded signals exist in a spiral shape, and are in two states: full exposure and final exposure. Between the spiral signals, there is a final exposure state. The optical reproducing device according to claim 1, characterized in that there is a location.