New monostatic balanced Doppler velocimeter using a high birefringence fiber

A novel fiber-optic Doppler velocimeter is presented. By suitably controlling the polarization state of the local oscillator, illuminating beam, and signal light, balanced mixing with a noise reduction of 30 dB as compared to unbalanced mixing can be realized. The remaining noise level is predominantly due to shot noise. Allowing for losses in the receiving optics and for nonperfect mixing efficiency, the minimum detectable signal power is estimated to be 10/sup -18/ W-Hz/sup -1/. The high sensitivity of the system is demonstrated by the detection of light scattered from a distant moving object. >