Abstract
We present a Self-Mixing (SM) interferometric laser displacement sensor that is capable of providing correct target measurements in real time, even when it is subject to extraneous parasitic movements. The sensor achieves such robustness by using an embedded MEMS Solid -State Accelerometer (SSA) that has been coupled with the laser sensor. The SSA thus measures the extraneous movement acting on the laser s ensor and this information is used to provide correct sensing. The proposed SSA-SM sensing system uses Consecutive-Samples based Unwrapping (CSU) to process the SM interferometric signal while a Digital Signal Processor (DSP) takes care of band-pass filtering, double integration as well as phase and gain corrections needed for the acceleration signal. Hence, a compact, real-time, precise and self-aligned SSA-SM sensor has been designed that has a displacement measurement precision of approximately 100 nm with a parasitic movement elimination of 31dB for a laser diode emitting at 785 nm.
Highlights
SM effect occurs in a laser when a part of the beam backscattered by a target is coupled back into the laser cavity and causes interference with the emitted beam, modifying the spectral properties of the laser
The C parameter plays an important role in the SM interferometry as variations in C cause changes in the so called SM operating regimes varying from weak to moderate to strong feedback [12], where each regime would require specific signal processing for the sake of displacement retrieval [13]
As indicated in figure 1, the Solid-State Accelerometer (SSA)-SM sensor was mounted on a mechanical shaker that has been used to generate extraneous movement acting on the SSA-SM sensor
Summary
SM effect occurs in a laser when a part of the beam backscattered by a target is coupled back into the laser cavity and causes interference with the emitted beam, modifying the spectral properties of the laser. This provides the maximum measurable target speed of 2.45mm/s for the real-time SM signal based displacement retrieval method with the above-mentioned configuration [16].
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