Abstract:
Self-Mixing Signals are used for measurement of target’s distance/displacement
and vibrations. SMI theory [1] is based on change in Laser’s characteristics due
to optical feedback from a remote target. These changes including the change in
Laser power can be recorded at receiver end (at the receiver photo diode). Fringe
corresponds to the portion of SMI signal corresponding to half of wavelength
change in the external cavity length. By analyzing the detected fringes, target’s
movement can be estimated. Thus, fringe detection is the fundamental step in
SMI processing. Conventional methods proposed lay foundation for SMI signal
detection from targets with smooth surface and efforts have been invested to
avoid speckle, mostly by tracking the strong signal by means of electro mechanical actuators. However, in case of irregular surface of the target, speckle
is introduced in the signal. Techniques have been proposed in literature for
fringe detection for speckle affected signal e.g. [2] Proposes fringe detection
matched filter, [3] by three envelope method etc. This thesis proposes a
methodology of fringe detection for speckle affected SMI signal by using
envelope tracking based on Hilbert transform. Results obtained by the proposed
technique indicate an improvement over conventional fringe detection method
for both simulated SMI signal as well as experimentally acquired signal
