Design of Laser Doppler Velocimeter based on self mixing-effect in VCSEL

Student: Daniel Lee

Supervisor: Aleksandar Rakic

Category: Engineering Thesis Project - Communications

Semiconductor laser has been the objective of studies for optical engineers for many years. In particular self-mixing effect in VCSEL (Vertical Cavity Surface Emitting Laser) has matured over these years, with an increasing interest being generated over the many uses of VCSEL. With more knowledge in this area, applications can be made to velocity and distance measurements, medical instruments, computer processors, telecommunication, the list is endless. The picture below shows the architecture of VCSEL.

The purpose of this thesis work is to understand and explore the Doppler effect of a signal reflected off a spinning target using self-mixing in VCSEL. Self-mixing is a phenomenon which happens when transmitted and reflected laser beam interacts at the laser cavity and creates little power fluctuations. These power fluctuations are amplified, converted to digital signals, and send to computer for signal processing. VCSEL are chosen for their simplicity and ease of use. Readings are taken before the object spins and when it starts spinning. A reference signal is obtained when the object is stationary. Another signal will be picked up when the object spins. The concept of Doppler is applied using the difference in frequency of these two signals. The result is that the velocity as well as the distance of the object can be obtained.

The prototype built; typical known as Laser Doppler Velocimeter (LDV), has the following features:

a) Up to 99% accuracy in velocity measurement.

b) Up to 99% accuracy in distance measurement

c) The use of VCSEL allows for more compact prototypes to be made (compared to conevntional edge emitting laser).

Thesis Document (PDF)

Poster Presentation (PDF)