laser diode and the photodiode are feedback looped to maintain the optical output power of the laser diode constant independently of the working temperature a laser diode remote sensing technique described by thierry bosch in u201c an overview of self mixing sensing applications u201d can be used to measure displacement vibration velocity and distance by using the optical feedback interferometry ofi properties inside the active cavity of the laser diode 600 see fig5 fig5 a presents the self mixing u201c sm u201d technique that consists in injecting a triangular waveform modulated current 602 into the laser diode 600 to perform absolute distance 604 measurements of a stationary target 603 indeed by modulating the injected current the length of the equivalent laser diode cavity is modified while the complex refractive index of the active cavity is varying moreover both the optical frequency and power are also modulated the emitted wavelength x then presents a triangular shift ax therefore the wave number 2 u03c0 u03bb is shifted by the amount u2212 2 u03c0 u03b4 u03bb u03bb2 optical power swings occur while injecting the current with a triangular waveform modulation the absolute distance 604 measurement of a stationary target can be performed by counting the n number of optical power swings 605 during each modulation cycle detected with the integrated photodiode 601 in alternative embodiments absolute distance measurement may be performed by evaluation of time of flight based for example on avalanche photodiode triggered by single photons and time.