| 摘要 |
An optical system for measuring relative lateral displacement or velocity relative to a surface above which the system is independently supported has a grating consisting of different bands that are adapted to impart to incident light received from the surface two different optically selective characteristics such as different polarizations or different wavelengths. Light transmitted by or reflected from the bands is focussed through filtering means onto photodetectors which produce signals proportional to the light received thereby. The filtering means (polarization selective or wavelength selective, as the case may be) associated with the respective photodetectors respectively separate light coming from bands having one of said characteristics from light from the bands having the other of said characteristics. The signals from the photodetectors are applied to a differential amplifier which produces an output signal representing the difference between the photodetector signals and which thus has a frequency representing the speed or movement of the system relative to the surface. This output signal may then be applied to known frequency counting devices for indicating velocity or distance travelled from a zero position.
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