Real-Time Self-Mixing Interferometer for Long Distances

Abstract

This work describes a novel instrument based on a self-mixing optical interferometer, able to reconstruct the target speed and direction, without heterodyne detection. The real-time elaboration employs the signal non-linearity in order to recover the speed sign in the frequency domain. The target speed is measured by the signal frequency, while the speed sign is evaluated by the phase of the harmonics in the frequency domain. The high-sensitivity of the elaboration allows the measurement over diffusive target with distances up to 10 m. The measurements results have been successfully compared with a very-high resolution a commercial calibrated instrument

Laser diode for flow-measurement

“…The back reflection of a diffusing target induces a modulation index m around 10 -3 for a collimated beam. With such a reflection level, the self-mixing signal is suitable for measuring displacement [13][14][15][16], absolute distances [17][18][19] or vibrations [20,21].…”

Nanoscale Displacement Sensing Based on Nonlinear Frequency Mixing in Quantum Cascade Lasers

“…The main drawback is that at least one fringe is needed to implement the signal analysis process for phase retrieval. Prototype systems featuring on-line nanometric resolution have been lately demonstrated in differential feedback interferometry referenced to a twin diode laser [11,12]. An open question is whether nanoscale resolution can in principle be achieved in laser feedback-based sensing systems working at longer wavelengths, including those using QCLs.…”

Edge filter enhanced self-mixing interferometry

“…The measurement principle presented here can be used at any wavelength if a narrow absorption profile is available. The demonstrated ESMI sensitivity improvement has potential impact on fields where SMI has already been established as sensing technique, i.e., velocity, contactless vibration measurements, distance, displacement, surface imaging, thickness measurements, and so on [1,2,[12][13][14][15]. Moreover, ESMI opens up possibilities to use the self-mixing technique in new applications where the sensitivity of the conventional SMI has not been adequate.…”

“…The ESMI signal can be recovered for attenuation up to two orders of magnitude far from the SMI limit, i.e., OD > 3. Additionally, we tested the performance of the ESMI technique at longer distances, e.g., increasing the laser power P T 400 mW, a reliable signal can be detected at distances up to 20 m. In the literature, SMI is usually limited to distances in the range of few cm up to few meters for applications involving diffusive targets [1,2] and up to tens of meters using reflective targets [12]. The distance range limitation is strongly related to the amount of backreflected light coupled into the cavity, e.g., the longer the distance the larger the power attenuation.…”