Real-time acquisition and enhancement of remote acoustic signals by a free-space monostatic homodyne laser Doppler vibrometer.

This paper systematically presents the design and performance of an extremely sensitive 1.55-µm free-space monostatic laser Doppler vibrometer (LDV) using optical homodyne detection for real-time acquisition and enhancement of the remote acoustic signals. The phase shifts produced by laser light scattered off a remote target carries the extremely tiny vibration displacement information of the target' surface motivated by the acoustic source around and is demodulated using the optical in-phase/quadrature demodulator. The real-time acquisitions of the remote acoustic signals, including the sinusoidal signal and the speech signal at the target distance of 100 m, is performed between two buildings. The real-time speech enhancement of remote speech signals is also carried out by the different algorithms based on the short-time spectral magnitude, and the comprehensible speech signals can be reconstructed. The results demonstrate that the designed free-space monostatic homodyne LDV has a low system background noise and can offer high precision for the uncooperative targets in the real-time acquisition of the remote acoustic signal.