| 摘要 |
Monitor signals are produced which are qualitative or quantitative measures of the shape, size or position of a light spot on an optical head relative to fibre-optic receptors in the optical head. One pair or two pairs of receptors may be used. Production of the monitor signals involves modulating the incident light forming the light spot at a predetermined frequency, delaying the light signals in one or more of the fibre-optic receptors relative to the light signals in one or more of the other receptors by, say half a wavelength of the predetermined frequency, combining the outputs of the fibre-optic receptors to produce a compound light signal, producing an equivalent compound electrical signal by means of a photodiode, and processing the compound electrical signal in electronic processors to extract one or more of its components to act as the monitor signals. Use of the invention is particularly in the monitoring of relative displacements involving optical systems which image a light source on one object onto an optical head on another object, thereby forming the light spot whose shape, size, or position alters according to the relative displacement between the two objects and the type of optical system used.
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