A rotary actuator data recording disk file is provided with a retro-reflective diffraction grating for use in measuring the angular position of the rotary actuator arm. The diffraction grating has a diffraction pattern whose pitch varies along the length of the diffraction grating. The variation in pitch is arranged such that, as the rotary actuator arm swings about its pivot axis and the diffraction grating moves across an incident light beam and simultaneously rotates with respect to it, the diffracted beam travels back along the incident path. Thus, the source and detector of a laser position measurement system can remain fixed while measuring the position of a rotary actuator arm to which the diffraction grating is affixed. Due to its low mass and low cost, the diffraction grating can be attached to a rotary actuator arm, sealed into a disk file, used to servo-write the disk file, and left in the disk file when shipped, thus obviating the need for a clean room environment in which to perform the servo-write process.

When a diffraction grating having a grating period of d and a diffraction order of m for an incident light having a wavelength interval .DELTA..lambda..sub.i between i'th and (i+1)'th channels is used, an optical path length between the diffraction grating and the photodetector is represented by L and a mean output angle is represented by .theta..sub.o, a pitch p.sub.i between the i'th and (i+1)'th photodetectors in the photodetector array satisfies the equation of p.sub.i =m.DELTA..lambda..sub.i L/d cos .theta..sub.o.

A micro spectrophotometer is monolithically constructed on a silicon substrate. The spectrophotometer includes a concave grating, which is used for dispersing optical waves as well as focusing reflected light onto a photodiode array sited on a silicon bridge. The silicon bridge is bent 90.degree. from the surface of the silicon substrate in order to orthogonally intersect the output light from the grating. A precision notch is defined in the silicon substrate for coupling to an optical input fiber. Signal processing circuitry is etched on the substrate using conventional CMOS processes for initial processing of information received from the photodiode array.

The solid-state imaging device is applicable to a high sensitivity color camera although its structure is as simple as that of a monochromatic camera, and comprises a semiconductor chip in which a large number of pixels are arranged in a matrix form on one surface of a semiconductor substrate, and an optical grating body for separating an incident light into rays of light to allow them to be incident to the pixel trains in one direction on the chip. The optical grating body includes optical gratings arranged at a pitch corresponding to two or three pixels of a pixel train in a direction perpendicular to the above-mentioned one direction, having a fixed inclination relative to the substrate surface, and juxtaposed provided in the above-mentioned one direction, and a supporting surface for supporting the gratings so that they have the above-mentioned fixed inclination.

A micro spectrophotometer is monolithically constructed on a silicon substrate. The spectrophotometer includes a concave grating, which is used for dispersing optical waves as well as focusing reflected light onto a photodiode array sited on a silicon bridge. The silicon bridge is bent 90.degree. from the surface of the silicon substrate in order to orthogonally intersect the output light from the grating. A precision notch is defined in the silicon substrate for coupling to an optical input fiber. Signal processing circuitry is etched on the substrate using conventional CMOS processes for initial processing of information received from the photodiode array.