| 摘要 |
A system is described for determining the phase relationship between two coherent beams and, if the beams are not in phase, providing a correction signal to bring them into phase. The system combines the beams to create an interference fringe pattern, the pattern exhibiting, if the beams are in phase, a central peak (zero order) irradiance fringe bounded on either side by lesser peak (higher order) irradiance fringes. The fringe pattern responds to a change in the relative phase of the beams by the fringes walking to the left or right under the stationary modulation envelope depending upon the direction of phase change between the beams. A pair of side fringe detectors are positioned to detect the lesser peak irradiance fringes but not the central peak irradiance fringe and to provide signals indicative of the power in each lesser peak irradiance fringe. A processor responsive to those signals, provides a correction output when the signals indicate unequal powers. A preferred embodiment OPD correction system is described and additionally includes a center fringe detector for detecting the central peak irradiance fringe as well as detectors for the lesser peak irradiance fringes. The central fringe output signal is applied to the processor which, in combination with the lesser peak irradiance fringe signals, is used by the processor to derive the correction output.
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