This paper presents a new demodulation method for the removal of cochannel interference found in a laser Doppler vibrometer sensing system. Since the sensitivity of such an optical system is impaired by interference arising from spurious scattering along the propagation path, an amplitude locked loop (ALL) was combined with a phase locked loop (PLL) in the system demodulator to improve the signal to noise ratio. The ALL is the mathematical dual of the PLL and is a unique circuit which operates on amplitude rather than phase. Experimental and mathematical research demonstrate that the incorporation of the ALL technology in the circuit demodulator of the optical system gave an improvement of over 10dB compared to current technology.

Date Published: 1 June 1998
PDF: 12 pages
Proc. SPIE 3411, Third International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (1 June 1998); doi: 10.1117/12.307683

Published in SPIE Proceedings Vol. 3411:
Third International Conference on Vibration Measurements by Laser Techniques: Advances and Applications
Enrico Primo Tomasini, Editor(s)