Integrated microlaser Doppler velocimeter

We have developed a microlaser Doppler velocimeter in which the laser diode, photodiode, and optical waveguide are monolithically integrated on a GaAs substrate. This integration eliminates the difficult optical alignment and susceptibility to environmental disturbances which are disadvantages of the conventional laser Doppler velocimeter. Our velocimeter showed good linearity between relative velocity and output frequency, and it can detect very low velocities of less than 5 μm/s. It can also measure the flow speed of a liquid containing particles. Moreover, the addition of a step at the end of the waveguide and one more photodiode enables the phase difference to be used for directional discrimination.