Abstract: A compound capable of satisfying both high refractive index and high light resistance, and a photocurable composition containing it, are provided. Further, an optical element having good light resistance against blue laser light, and an optical head device using it, are provided. A polymerizable compound represented by SiA1A2A3A4 wherein silicon and four cyclic groups are bonded directly or via oxygen. each of A1, A2, A3 and A4 which are independent of one another, is —(O)m—X; and each of four m's which are independent of one another, is 0 or 1. X is preferably a phenyl group. From 0 to 3 hydrogen atoms in the phenyl group are substituted by a polymerizable substituent represented by CH2?CR—COO—Y—, and some or all of remaining hydrogen atoms in the phenyl group may be substituted by a methyl group or a fluorine atom.

Abstract: A liquid crystal optical modulation element to modulate a laser beam having a wavelength of at most 500 nm, which contains a layer of a liquid crystal composition sandwiched between a pair of transparent substrates facing each other, wherein each transparent substrate has an electrode and an alignment film having a polyimide on the surface which faces the other transparent substrate, the alignment film and the liquid crystal composition are in contact with each other, and the liquid crystal composition contains at least one antioxidant.

Abstract: To provide optical elements such as a phase plate suitably used in a broadband range and a polarizing diffraction element excellent in diffraction efficiency, a polymerizable liquid crystal composition to be used for them, and an optical head device using them.

Abstract: To provide optical elements such as a phase plate suitably used in a broadband range and a polarizing diffraction element excellent in diffraction efficiency, a polymerizable liquid crystal composition to be used for them, and an optical head device using them.

Abstract: To provide a liquid crystal optical modulation element capable of stably modulating a laser beam having a wavelength of at most 500 nm for a long period of time. A liquid crystal optical modulation element to modulate a laser beam having a wavelength of at most 500 nm, which comprises a layer of a liquid crystal composition sandwiched between a pair of transparent substrates facing each other, characterized in that each of the pair of transparent substrates has an electrode and an alignment film comprising a polyimide on the surface which faces the other transparent substrate, the alignment film and the liquid crystal composition are in contact with each other, and the liquid crystal composition contains an antioxidant.

Abstract: An optical head device having an optical element capable of transmitting without diffracting light having a wavelength emitted from a two-wavelength semiconductor laser and capable of diffracting light having another wavelength, to provide high utilization efficiency of light in a stable manner.

Abstract: An optical head device having an optical element capable of transmitting without diffracting light having a wavelength emitted from a two-wavelength semiconductor laser and capable of diffracting light having another wavelength, to provide high utilization efficiency of light in a stable manner.

Abstract: An optically anisotropic diffraction grating for an optical read/write head, comprising optically isotropic polymer liquid crystal held between two transparent base plates. Gratings of different refractive indexes are formed by periodically changing the orientation of the polymer liquid crystal of the diffraction grating. This enables a high light-utilization efficiency and a high reliability to be obtained.

Abstract: As an optically anisotropic diffraction grating in an optical head for reading and/or writing of an optically recording medium, optically anisotropic diffraction grating which comprises an optically anisotropic polymer liquid crystal sandwiched between two transparent substrates are used. The optically anisotropic polymer liquid crystal can have an alignment direction periodically changed to form a grating of different refractive indices, obtaining a high-utilization efficiency by light ray and a high degree of reliability.

Abstract: An object is to provide an optical head device whereby the light utilization efficiency can be increased and which can be produced at a low cost. A glass substrate 1 having projections and recesses 2 formed by patterning a SiON type transparent thin film on its inner surface by dry etching, and a second glass substrate 3 having a polyimide film 4 formed as an alignment film on its inner surface, are laminated with a space, the periphery is sealed by a sealing material made of an epoxy resin 5, and liquid crystal 6 is injected under vacuum into the interior to form an optically anisotropic diffraction grating. On the outer surface of this second glass substrate 3, a quarter-wave film 7 is laminated, and a third glass substrate 9 is bonded by a photopolymer 8 to obtain a diffracting element 10. This diffracting element 10 is disposed between a light source and an optical recording medium to obtain an optical head device.

Abstract: High molecular liquid crystal obtained by photopolymerizing a liquid crystal composition which comprises CH2═CHCOO—X—OC6H4—C6H4CN (X is an alkylene group) and CH2═CHCOOC6H4—C6H4CN. An optical element which is a polarized hologram element made by using the high molecular liquid crystal and an optical head having the polarized hologram element as a beam splitter.

Abstract: An object is to provide an optical head device whereby the light utilization efficiency can be increased and which can be produced at a low cost. A glass substrate 1 having projections and recesses 2 formed by patterning a SiON type transparent thin film on its inner surface by dry etching, and a second glass substrate 3 having a polyimide film 4 formed as an alignment film on its inner surface, are laminated with a space, the periphery is sealed by a sealing material made of an epoxy resin 5, and liquid crystal 6 is injected under vacuum into the interior to form an optically anisotropic diffraction grating. On the outer surface of this second glass substrate 3, a quarter-wave film 7 is laminated, and a third glass substrate 9 is bonded by a photopolymer 8 to obtain a diffracting element 10. This diffracting element 10 is disposed between a light source and an optical recording medium to obtain an optical head device.