Optical proximity sensor based on self-mixing interferometry

A proximity detector based on self-mixing technique, well suited for different industrial applications, is demonstrated. Instead of using a light-source plus a detector, the proposed sensor is realized by a single laser source. Two different physical effects in the laser diode allow for a continuous detecting range, from 10 mm up to 80 mm. The main advantages of the sensor are target detection from just one point of view; multiple sensors configuration does not need optical filters; separation of source and detector is eliminated; and background rejection is intrinsically given by the self-mixing effect, which shows a sharp cut-off after the focus

Self-mixing instrument for simultaneous distance and speed measurement

A novel instrument based on Self-mixing interferometry is proposed to simultaneously measure absolute distance and velocity. The measurement method is designed for working directly on each kind of surface, in industrial environment, overcoming also problems due to speckle pattern effect. The laser pump current is modulated at quite high frequency (40 kHz) and the estimation of the induced fringes frequency allows an almost instantaneous measurement (measurement time equal to 25 µs). A real time digital elaboration processes the measurement data and discards unreliable measurements. The simultaneous measurement reaches a relative standard deviation of about 4·10â\u88\u924 in absolute distance, and 5·10â\u88\u923 in velocity measurement. Three different laser sources are tested and compared. The instrument shows good performances also in harsh environment, for example measuring the movement of an opaque iron tube rotating under a running water flow

Exploiting the FM-signal in a laser-diode SMI by means of a Mach-Zehnder filter

We develop a new method to read the frequency modulation (FM) of a laser diode (LD) self-mixing interferometer (SMI), based on using a Mach-Zehnder interferometer as an edge filter, and obtain improved performance respect to the normally used amplitude modulation (AM) signal. The converted FM signal is much larger and has a better SNR than the normally used AM signal. The minimum detectable signal of the SMI is improved by a factor 150 with our setup that uses an all-fiber technology to realize the compact Mach-Zehnder filter (MZF). The MZF has a record 19 (GHz)-1 conversion factor and is tuned at half-fringe on the laser wavelength with a feedback loop acting on the laser bias current. On small amplitude vibrations measured with the converted-FM signal, we attain a displacement (NED) of 1.3-pm/√ Hz, about two order of magnitude better than the AM channel or a normal SMI

Self-mixing digital closed-loop vibrometer for high accuracy vibration measurements

The novelty of Self-mixing interferometry is represented by the combination of high accuracy and contactless operation with compact, very-low-cost and user-friendly setup. This paper introduces state of the art techniques to monitor vibrations focusing on a novel digital feedback vibrometer. It exploits a control loop to delete interferometric signal distortion and improve measurement accuracy. A digital implementation is proposed to enhance system performances through a real-time elaboration

Development of a design tool for closed-loop digital vibrometer

The closed-loop technique has been demonstrated as a possible configuration to design a vibrometer based upon self-mixing interferometry. The electronic feedback loop allows a better linearity while extending the linearity range of a self-mixing interferometer. A deep analysis of the feedback loop is carried out in order to improve stability and performance through a digital approach. This work describes first the simulation of the closed-loop vibrometer, and then the performance obtained through its implementation on an FPGA based prototype

Drop Measurement System for Biomedical Application

This paper describes the realization of a sensor capable of measuring the volume of a drop in free fall. The sensor realized is made of a simple low-cost red laser and a photodiode and optics to focus the beam on the light sensor. In this way, when the drop is falling down, it is possible to estimate its volume from the signal generated on the photodiode while getting through the laser beam. This system may be very useful together with a drip chamber to have accurate and low-cost volume and flow rate measurements of the infused substances