Wavelength-selective light-shielding element and optical head using the same
View Patent ↗In order to provide a wavelength-selective light-shielding element capable of blocking circularly-polarized light beams rotating in a specific direction among light beams whose wavelengths falling in a specific range, a light-shielding region is provided in a portion of a transparent substrate, wherein the light-shielding region permits passage of first circularly-polarized light rotating in a first direction regardless of a wavelength of the first circularly-polarized light and blocks second circularly-polarized light beams whose wavelengths falling within a predetermined range, among second circularly-polarized light beams rotating in the second direction, to thus permit passage of the second circularly-polarized light beams falling outside the predetermined range.
1. A wavelength-selective light-shielding element, comprising:
a transparent substrate; and
a light-shielding region provided in a portion of the transparent substrate, the light-shielding region permitting passage of a first circularly-polarized light rotating in a first direction regardless of a wavelength, blocking a portion of a second circularly-polarized light whose wavelength falls within a predetermined range in the second circularly-polarized light rotating in a second direction opposite the first direction, and permitting passage of the second circularly-polarized light falling outside the predetermined range,
wherein the light-shielding region is a reflection region which reflects the portion of the second circularly-polarized light whose wavelength falls within the predetermined range.
2. The wavelength-selective light-shielding element according to claim 1 , wherein the reflection region is formed of a cholesteric phase liquid crystal material.
3. The wavelength-selective light-shielding element according to claim 2 , wherein the reflection region reflects light beams included in a reflection wavelength region having
a center frequency λ c ={(n o +n e )/2}×P
a wavelength bandwidth Δλ=(n e −n o )×P
where n o =an ordinary refractive index of cholesteric phase liquid crystal
n e =an extraordinary refractive index of cholesteric phase liquid crystal
P=a helical pitch of cholesteric phase liquid crystal.
4. A wavelength-selective light-shielding element comprising the wavelength-selective light-shielding element according to claim 1 in a plurality in a laminated fashion.
5. The wavelength-selective light-shielding element according to claim 1 , wherein the predetermined range of the wavelength includes 660 nm and excludes 785 nm.
6. An optical head comprising:
a light source;
a collimator lens which collimates a light-source light emitted from the light source;
an objective lens which converges a light to a recording layer of an optical disk;
a beam splitter which is positioned in an optical path for the light-source light between the light source and the collimator lens and which deflects and separates a light reflected by the recording layer to an optical path differing from an optical path along which the light-source light reaches the recording layer;
a photodetector which detects the light deflected and separated by the beam splitter; and
the wavelength-selective light-shielding element according to claim 1 , the wavelength-selective light-shielding element being positioned in an optical path between the collimator lens and the objective lens.
7. An optical head comprising:
a light source;
a collimator lens which collimates a light-source light emitted from the light source;
an objective lens which converges a light to a recording layer of an optical disk;
a beam splitter which is positioned in an optical path for the light-source light between the light source and the collimator lens and which deflects and separates a light reflected by the recording layer to an optical path differing from an optical path along which the light-source light reaches the recording layer;
a photodetector which detects the light deflected and separated by the beam splitter; and
a wavelength-selective light-shielding element comprising a transparent substrate and a light-shielding region provided in a portion of the transparent substrate,
wherein the light-shielding region permits passage of a first circularly-polarized light rotating in a first direction regardless of a wavelength, blocks a portion of a second circularly-polarized light whose wavelength falls within a predetermined range in the second circularly-polarized light rotating in a second direction opposite the first direction, and permits passage of the second circularly-polarized light falling outside the predetermined range, the light source is configured to emit a linearly-polarized light as the light-source light, and the optical head further comprises a phase modulation element positioned in an optical path between the beam splitter and the wavelength-selective light-shielding element and configured to convert the light-source light into a circularly-polarized light.
8. The optical head according to claim 7 , wherein the light-shielding region is a reflection region which reflects the portion of the second circularly-polarized light whose wavelength falls within the predetermined range.
9. The optical head according to claim 8 , wherein the reflection region is formed of a cholesteric phase liquid crystal material.
10. The optical head according to claim 9 , wherein the reflection region reflects light beams included in a reflection wavelength region having
a center frequency λ c ={(n o +n e )/2}×P
a wavelength bandwidth Δλ=(n e −n o )×P
where n o =an ordinary refractive index of cholesteric phase liquid crystal
n e =an extraordinary refractive index of cholesteric phase liquid crystal
P=a helical pitch of cholesteric phase liquid crystal.
11. The optical head according to claim 7 , wherein the predetermined range of the wavelength includes 660 nm and excludes 785 nm.