Holographic recording medium, method for manufacturing the same, and holographic recording-reproducing system

A holographic recording medium comprising:

• a recording layer having an interference pattern recorded thereon using object light and reference light emitted from a laser light source;
• and
• a servo layer formed above the recording layer so as to face a direction of incident light, the servo layer having one of wavelength selectivity and incident angle selectivity, each of the wavelength selectivity and the incident angle selectivity allowing the object light and the reference light to pass through the servo layer before incident onto the recording layer,
• wherein the servo layer reflects servo light having a wavelength different from a wavelength of the object light and a wavelength of the reference light or the servo layer reflects servo light having an incident angle different from an incident angle of the object light and an incident angle of the reference light,
• one of servo information and address information is recorded on the servo layer, and
• the servo layer is formed of a diffraction grating having a multilayer spheric shape and a constant grating space.

A holographic recording-reproducing optical system, comprising:

• a holographic recording medium including:
• a recording layer having an interference pattern recorded thereon using object light and reference light emitted from a laser light source;
• and
• a servo layer formed above the recording layer so as to face a direction of incident light, the servo layer having one of wavelength selectivity and incident angle selectivity, each of the wavelength selectivity and the incident angle selectivity allowing the object light and the reference light to pass through the servo layer before incident onto the recording layer,
• wherein the servo layer reflects servo light having a wavelength different from a wavelength of the object light and a wavelength of the reference light or the servo layer reflects servo light having an incident angle different from an incident angle of the object light and an incident angle of the reference light,
• one of servo information and address information is recorded on the servo layer, and
• the servo layer is constituted by any of a phase type reflection hologram, a dielectric multilayer film, and a dichroic mirror;
• the holographic recording-reproducing optical system further comprising:
• a servo optical system including a beam splitter that branches off a portion of light to form servo light incident on the holographic recording medium at nearly right angles to the servo layer;
• a polarizing beam splitter which splits the light branched off in a direction different from that of the servo light by the beam splitter into two linearly polarized light beams having orthogonal vibration planes;
• a reference optical system which allows one of the linearly polarized light beams split by the polarizing beam splitter to be incident on the holographic recording medium as reference light from a direction different from that of the servo light;
• an object optical system which allows the other of the linearly polarized light beams split by the polarizing beam splitter to be incident on the holographic recording medium as object light from a direction different from that of the servo light and the reference light;
• and
• a photodetector which detects the reflection of the servo light from the servo layer, wherein:
• the reference optical system comprises, in order from a polarizing beam splitter side, a ½ wave plate and a Fourier lens;
• the object optical system comprises, in order from the polarizing beam splitter side, a spatial light modulator for modulating the linearly polarized light beam according to information to be recorded and a Fourier lens;
• the servo optical system comprises, in order from a beam splitter side, a second polarizing beam splitter, a ¼ wave plate, and a condensing lens;
• the second polarizing beam splitter allows one of two linearly polarized light beams having orthogonal vibration planes to pass through and reflects the other;
• and
• the photodetector is provided on a reflection optical path which is formed when the reflection of the servo light from the servo layer is incident on the second polarizing beam splitter, the servo light being incident on the servo layer after passing through the second polarizing beam splitter.