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| Objective lens for recording and reproducing for use in an optical information recording medium |
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| Optical pickup used with both DVD and CD |
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| Objective lens for optical pick-up head of optical disk drive |
| It is therefore the principle object of the present invention to provide an objective lens for ... |
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| Optical head |
| For solving the problem of the prior art, an optical head of the present invention comprises, light ... |
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| Compound objective lens having two focal points |
| A first object of the present invention is to provide, with due consideration to the drawbacks of ... |
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Grating lens and focusing grating coupler
| Details |
Inventors: Aoyama, Shigeru; Tada, Masami; Hosokawa, Hayami; Horie, Noriyoshi; Yamashita, Tukasa;
Assignee: Omron Corporation (Kyoto, JP)
Primary Examiner: Bovernick; Rodney B.
Assistant Examiner: Ryan; J. P.
Attorney, Agent or Firm: Dickstein, Shapiro & Morin
A grating lens is disclosed in which diffraction efficiency varies in the focusing direction of light on a surface of the lens. Also disclosed is a focusing grating coupler in which the diffraction efficiency of a grating formed on an optical waveguide, which is formed on a substrate, varies in the focusing direction of light. |
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DETAILED DESCRIPTION An object of the present invention is to provide a grating lens in which the spot diameter of a light beam can be made small without using a super-resolution filter.
Another object of the present invention is to provide a focusing grating coupler in which focused spot diameter can be made small without necessarily making the grating period very small.
A grating lens in accordance with the present invention is characterized in that diffraction efficiency varies in a focusing direction of light on a surface of the lens.
A focusing grating coupler according to the present invention is characterized in that diffraction efficiency of a grating formed on an optical waveguide formed on a substrate varies in a focusing direction of light.
Gratings can be classified roughly into those of an index modulation type in which the refractive index of a medium is varied periodically, and those of a relief type provided periodically with ridges and grooves.
The present invention is applicable to lenses having both types of gratings.
The variation in diffraction efficiency can be realized by changing the thicknesses of the grating elements, changing the refractive index, or by some other method.
The grating element refers to one period of a variation in refractive index, or one period of ridges and grooves.
A grating pattern can take on any form, such as that of a circle, ellipse, circular arc or straight line, depending upon the application.
In accordance with an embodiment of the invention, diffraction efficiency is set high at the peripheral portion and low at the central portion of the grating in the grating lens or focusing grating coupler.
With such a construction, focused spot diameter can be made smaller, by means of the super-resolution phenomenon, than the diffraction limit decided by the wavelength of light and NA.
Accordingly, a super-resolution filter need not be used in order to obtain a small light-beam spot diameter, and therefore the optic axis alignment operation is unnecessary
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