Design of Laser Doppler Velocimeter based on Self-Mixing Effect in VCSEL

Student: Khai Weng Ho

Supervisor: Aleksandar Rakic

Category: Engineering Thesis Project - Communications

Non-contact measurement of distance and velocity using laser has been required and studied in many application fields. In addition to distance or velocity measurement this device is used in application such as for the precision alignment, non-destructive testing, 3-D vision and so on.

In this thesis we proposed a small and simple range finder and velocimeter using self-mixing effect inside a Vertical Cavity Surface Emitting Laser (VSCEL) diode. Self-mixing effect in a laser is a process whereby a portion of light is reflected back by an external reflector, causing an intensity modulation of the laser output. The signal is then processed to obtain the target distance. Subsequently due to Doppler effect light that is scattered by the moving reflector has a frequency that is different from the stationary reflector. With this signal the velocity of the reflector is measured.

To illustration the performance of the range finder and velocimeter. Distance measurements of a stationary disc and velocity measurements of a rotating disc covered with white paper are documented. Also a novel method based on the Fast Fourier Transform (FFT) was proposed and implemented. With this method, more accurate and robust behavior of the range finder and velocimeter is obtained compared to traditional processing methods.

To the best of our knowledge this is the first range finding and velocimeter implemented with a VCSEL using the self-mixing effect. It is also the first time that FFT is used to measure distance and velocity for this type of laser velocimetry and range-finding applications.

Thesis Document (PDF)

Poster Presentation (PDF)