JPS6256582B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention has been made with the object of providing an optical recording method that enables efficient and high-density recording of information signals using linearly polarized light. be.

When attempting to optically record information signals at high density, it is necessary to project light whose intensity is modulated by the information signal onto a recording medium as a minute light spot. As a light source for obtaining the above-mentioned light, a laser light source that emits linearly polarized light is often used.

By the way, when light whose intensity is modulated by an information signal is focused or imaged on a recording medium using a lens or a concave mirror, the refractive index of the medium on the path of the incident light to the recording medium and the recording medium It is well known that reflection or refraction of light occurs on the recording medium surface due to the difference in the refractive index of the
It is also well known, based on the so-called Fresnel equation, that the polarization component S and the polarization component S in the plane perpendicular to the plane of incidence are set with different reflectances Rp and Rs, respectively.

Figure 1 shows the angle of incidence of light on the horizontal axis and the reflectance on the vertical axis.
When light enters glass with a refractive index of 1.5, the reflectance against the angle of incidence of light is calculated using Fresnel's equation and is shown by the solid curve. The reflectance for the angle of incidence of light is calculated using Fresnel's formula and is shown by the dotted curve in the figure.
For Rp and Rs, the reflectance for the polarized light component P in the plane of incidence is Rp, and the reflectance for the polarized light component S in the plane perpendicular to the plane of incidence is Rs.

Looking at Figure 1, when light enters the interface between two media with different refractive indexes, the reflectance of the interface is Rp for the polarized light component P in the incident plane.
The reflectance for the polarized light component S in the plane orthogonal to the plane of incidence is smaller than Rs up to a large angle of incidence, and the above relationship holds true from a medium with a small refractive index to a medium with a large refractive index. It can be seen that the same holds true even when light is incident, or when light is incident from a medium with a high refractive index to a medium with a low refractive index.

Now, light is focused or imaged by a lens or concave mirror (if there is an object plane on the focusing plane of the lens or concave mirror, the image will be focused on the object plane, and if the object plane is shifted in front of or behind the focusing plane of the lens or concave mirror) The angle of incidence of the incident light on the object (for example, a condensing spot appears on the object surface) ranges from zero to an angle θmax determined by the characteristics of the lens or concave mirror used. To explain the case where it is used (the same applies to the case of a concave mirror), the angle θmax mentioned above is the numerical aperture of the lens.

Lenses used for optical high-density recording have a large numerical aperture (NA) in order to form tiny spots of light on the recording medium. For example, if a lens with a numerical aperture N·A of about 0.95 is used, it can be seen that the angle θmax in that lens is approximately 72 degrees from the relationship sin θmax=0.95.

During high-density recording, in order to reduce the focal point diameter of the light focused on the recording medium or to increase the resolution of the image formed on the recording medium, it is necessary to , it goes without saying that it is also necessary to make the light at the incident angle θmax mentioned above enter, but as is clear from Figure 1, the reflectance of the light incident on the recording medium depends on the polarization in the plane of incidence. The reflectance Rp for the component P and the reflectance Rs for the polarized component S in the plane perpendicular to the plane of incidence are different values with respect to the angle of incidence, and the reflectance Rp for the polarized component P in the plane of incidence is different. Reflectance Rp
Compared to , the reflectance of the polarized light component S in the plane perpendicular to the plane of incidence is larger for Rs at a small angle of incidence, so if the light incident on the recording medium is perpendicular to the plane of incidence, In the case of in-plane polarization component S, even if the light is incident on the entire surface of the lens and the light at the incident angle θmax is also given to the recording medium, the light incident on the recording medium Light with a large incident angle will be reflected by the surface of the recording medium, and that light will not be used effectively for recording.

In other words, in order to perform high-density recording, a lens with a large numerical aperture is used, and light from the entire surface of the lens is focused or focused onto the recording medium as incident light, and a tiny spot of light is projected onto the recording medium. Even if an attempt is made to record an information signal with a
In this case, the light that is effective for recording will be the same as when the light is incident on the recording medium using a lens with a small numerical aperture, so it is necessary to use a lens with a large numerical aperture. Even if one attempts to perform high-density recording using the same method, high-density recording cannot be performed.

The present invention provides a method for focusing linearly polarized light onto a recording medium using a lens or a concave mirror, or when forming an image with a different minimum dimension depending on the direction. Among the planes of incidence of incident light, the plane of incidence that extends in the direction in which the dimensions of the cross-sectional shape of the condensed light should be minimized, or the direction in which the resolution of the formed image should be the highest By performing recording so that the plane of polarization of linearly polarized light approximately coincides with the incident plane extending across the plane, information signals can be recorded efficiently and with high density. The present invention provides an optical recording method.

Figure 2 shows a laser beam spot having a substantially rectangular cross-section that is focused or imaged to be projected onto a recording medium in the optical recording method disclosed in Japanese Patent Application Laid-open No. 55-146633. This is a perspective view of a recording medium, and in FIG. 2, D is a recording medium, and A is a rectangular light spot consisting of short sides a, c and long sides b, d.

By applying the optical recording method of the present invention, the light spot A as shown in FIG.
The optical recording method of the present invention will be explained as follows, taking as an example the case of recording on an image.

That is, the optical recording method of the present invention focuses on an incident surface including the short side a of the light spot A to be focused or imaged on the recording medium D, an incident surface including the short side c, and the above-mentioned short sides a and c. Within the plane of incidence of light incident on the recording medium D, such as an incident plane including parallel line segments, it extends in the direction that should minimize the cross-sectional shape of the condensed light. The plane of polarization of the linearly polarized light is made to approximately match the plane of incidence, or the plane of incidence that extends in the direction that should give the highest resolution in the formed image. This allows for optical recording.

When an information signal is recorded on the recording medium D according to the optical recording method of the present invention as described above, the condensed light will extend in the direction that should minimize its cross-sectional shape. Since the incident plane, or the incident plane extending in the direction that should give the highest resolution in the formed image, is a polarization plane, the linearly polarized light incident on the recording medium has a polarization component P, Therefore, among the light incident on the recording medium, even the light with a large incident angle is not reflected on the surface of the recording medium, the size of the light spot does not expand, and the incident light can be used effectively for recording. It is possible.

As described above, according to the optical recording method of the present invention, it is possible to efficiently perform high-density recording using linearly polarized light.

[Brief explanation of the drawing]

FIG. 1 is a curve diagram showing the relationship between the incident angle and the reflectance, and FIG. 2 is a perspective view of a portion of the recording medium. D...recording medium, A...spot of light.

Claims (1)

[Claims] 1. When linearly polarized light is focused onto a recording medium with a non-circular cross-section using a lens or concave mirror, or when an image with a minimum dimension that differs depending on the direction is formed, the light incident on the recording medium Within the plane of incidence, the plane of incidence extends in the direction that should minimize the dimensions of the cross-sectional shape of the condensed light, or extends in the direction that should maximize the resolution of the formed image. The plane of polarization of the linearly polarized light is approximately aligned with the plane of incidence, and the linearly polarized light is focused or imaged onto the recording medium using a lens or concave mirror. An optical recording method characterized by: