We present the optical feedback characteristics of a single-mode Nd:YAG laser with a wave plate in the external cavity. The laser intensities of the two orthogonal directions, which are both modulated by the change of external cavity length, have a phase difference due to the birefringence effect of the wave plate. When threshold intensity is introduced, a period of intensity fringe can be divided into four equal zones. Each zone corresponds to
displacement of the external feedback reflector. The direction of displacement can be discriminated by the sequence of these four zones.
This phenomenon provides a potential displacement sensor with directional discrimination and high resolution of eighth wavelength compared with the traditional optical feedback.
© 2007 Optical Society of America
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