Agency of Industrial Science and Technology

Ministry of International Trade & Industry

Keisuke Kikuchi

Junichi Shimada

Kenjiro Sakurai

Takitaro Morikawa

Yoshinobu Mitsuhashi

A spherical recess is provided to one end wall of a first planar lens and the opposite end walls of a second planar lens, the first planar lens having a thicknesswise index distribution in the vicinity of the one end wall whereas the second planar lens has a thicknesswise index distribution in the vicinity of each of the opposite end walls. A high refractive index homogeneous sphere lens is sandwiched between the first planar lens and the second planar lens to be brought into contact with the spherical recesses. A homogeneous semi-sphere lens is held to contact the other spherical recess of the second planar lens. The homogeneous sphere lens side first planar lens and second planar lens of the first planar lens and second planer lens increase in refractive index toward the homogeneous sphere lens so that the sphere lens is corrected in spherical aberration, and so that distribution gradient of the refractive index is selected for correcting the sphere lens in coma. The homogeneous semi-sphere lens side heterogeneous portion of the second planar lens decreases in refractive index toward the homogeneous semi-sphere lens to correct the whole curvature of field, and the refractive index of the homogeneous semi-sphere lens is selected to be low for correcting the distribution.

Compound lens

A spherical lens of graded refractive index distribution comprises a core of uneven refractive index of the shape of a sphere or hemisphere and a clad of the shape of a spherical shell and a rod clad, with the two clads disposed on the periphery of the core. By the combination of the core showing negative aberration characteristic and the spherical-shell type clad and the rod clad both showing positive aberration characteristic, there can be formed a lens of corrected aberration. This lens suits combination or integration with other elements and permits easy manufacture of clads. It also provides effective convergence of beams of light desirable for use in an optical pickup, for example.

Spherical lens for spherically symmetrical graded refractive index

An optical memory playback apparatus is constructed so that a single longitudinal mode of laser beam emitted from a self-coupling semiconductor laser element is projected through an optical system onto an information recording medium and the laser beam reflected by the information recording medium is returned through the same optical system back to the semiconductor laser element. In addition, the apparatus interposes a spatially uneven phase plate in the optical system, whereby the longitudinal mode of emission of the semiconductor laser element is converted into a random multi-mode at all times and, consequently, the reproduction of information from the information recording medium is effected by detecting the variation in the intensity of output or terminal voltage of the semiconductor laser element which occurs in conformity with the variation in the intensity of the reflected laser beam.

Optical memory playback apparatus

A cladded lens having an uneven refractive index comprises a spherical core having a graded refractive index and producing negative lateral aberration and a cladding producing positive lateral aberration. The aberrations of the core and the cladding are canceled by each other to be considerably corrected. Such a cladded lens is especially effective for optical communication and optical recording-regenerating as in PCM technology.

Growing community of inventors

Ibaraki, Japan

Keisuke Kikuchi