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This paper presents an experimental technique for two-dimensional imaging of dynamic acoustic pressure changes that is applied to visualize a stationary acoustic wave. This technique uses the optical feedback interferometry sensing scheme with a near-infrared laser diode and a two-axis scanning system. The stationary acoustic wave is generated by using a 40 kHz piezoelectric transducer pointing toward a concave acoustic reflector. The acoustic pressure dynamic changes are measured due to its impact on the propagating medium refractive index, which variation is integrated along the laser optical path from the laser diode to a distant mirror and back. The imaging system records a 100×50 pixels image of the acoustic pressure in 66 min.
This work proposes to measure the topography of microstructure surfaces using a self-mixing interference (SMI) configuration. The theoretical measurement model is built using beam-expanded plane wave method and considering SMI effect. The interference patterns for different objects are obtained based on the presented model. In addition, an algorithm for reconstructing the three-dimensional surface is implemented and applied onto an object with spherical surface. The presented work shows the potential application for topography measurement using a compact SMI configuration.
An enhanced laser self-mixing Doppler velocimeter by fiber Bragg grating (FBG) is proposed. In fiber sensing, FBG is often used as an optical filter to select the wavelength of the light using the narrow reflection spectrum. The Doppler frequency shift from the rotating target can be parsed in the self-mixing interferometry (SMI) signal. The frequency-fluctuant self-mixing signal is transformed into intensity variations by a FBG when the laser wavelength is set to the edge of the FBG steep transmission profile. An experimental comparison between the enhanced and the traditional SMI approaches is made. The magnitude of obtained FBG-enhanced SMI signal is about 40 times stronger than that from traditional SMI. The result of the experiments indicates that enhanced self-mixing Doppler velocimetry by FBG can be applied to velocity sensing. This method has potential application in the engineering industry because the FBG is easy to fabricate and connect to a SMI system and the wavelength of FBG can be changed to match the different lasers for an enhanced SMI signal.
We proposed an all-fiber tunable distributed Bragg reflector (DBR) laser rangefinder, which realized high-accuracy measurement of the absolute distance in the range of 1.88 to 3.33 m based on the self-mixing effect. The theoretical analysis of the all-fiber tunable DBR laser shows that wavelength tuning range and frequency of the laser can influence the measurement range and resolution. In addition, the experimental results indicate that the influence factors of measurement accuracy and sensitivity in absolute distance measurement are modulation response linearity, experimental equipment, and circuit bandwidth, which is in good agreement with theory analysis. Moreover, increasing the linear wavelength tuning range of the tunable DBR laser is an essential method to improve the measurement accuracy and sensitivity of the absolute distance measurement system.
We present an overview of the applications of self-mixing interferometer (SMI) to tasks of interest for mechanical engineering, namely high-resolution measurement of linear displacements, measurements of angles (tilt, yaw, and roll), measurements of subnanometer vibrations, and absolute distance, all on a remote target—representative of the tool-carrying turret of a tool-machine. Along with the advantages of SMI—compactness, low cost, minimum invasiveness, ease of use, and good accuracy, we illustrate the typical performance achieved by the basic SMI sensors, that is, the versions requiring a minimum of signal processing and discuss special features and problems of each approach.
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.
We present a self-mixing interferometer (SMI) vibrometer developed around a laser diode with a simple and compact analog processing of the fringe signal, and show that this instrument can readily detect ambient vibrations—which adversely affect mechanical material-working lathes. In addition, we find out that the vibrometer is an excellent intrusion detector, capable of discovering a man stepping several meters away from the sensor, thus hinting at an SMI application as an antithief sensor.