fringe disappearance

The fringes disappearance phenomenon in the self-mixing interferometry occurs whenever the external round-trip phase at free-running state is modulated by either external modulation such as external cavity length changes or internal modulation when the laser injection current is modulated with a high back-scattered light power. This phenomenon has been observed by many authors for harmonic motion or vibration application, and more recently in the case of the absolute distance measurement scheme when the laser injection current is modulated in the triangle waveform.