Quadrature detection of a Doppler signal

We have employed a quadrature detection technique to measure the Doppler signal from a moving target. We mix a circularly polarized reference with a linearly polarized signal to produce an output that contains the real and the imaginary parts of the interference field in the two output polarizations. We are thus able to measure the in-phase and the quadrature components of an interferometric signal simultaneously by splitting the output with a polarizing beam splitter. We present data that demonstrate our ability through this technique to obtain both the amplitude and the frequency of vibration of an audio speaker. We also demonstrate the technique's ability to give one access to the direction of motion and instantaneous position of the target. (C) 1998 Optical Society of America.