My project is basically dealing with phase shifts in a pulsing laser. I am going to pulse the intensity of the laser at a frequency of about 60 kHz in a sine wave. The laser then goes through a medium that slows it down, creating a phase shift. This phase shifted laser output then hits a photodiode which converts it back into an electrical signal. The phase shift detector will then recieve the original sine wave from the laser controller, and the shifted signal from the photodiode. I need the Phase Shift Detector to then translate the phase shift into some DC voltage that feeds into a micro controller.

Inputs:

A(t) = ACos(wt); Original wave form from laser controller

B(t) = BCos(wt - phi); Wave form from photodiode

My initial thinking was somehow multiplying these waves together, and then integrating them over 1 period of the wave. This way I can solve for phi, and use a simple function in the micro controller to convert the integration value into phi.

I am not really sure how to multiply the two signals together, is there some circuit I can use or some trick with the photodiode maybe? For the integrator, I was just going to use an op amp circuit.

Anyone got any suggestions on how to multiply the signals together? Or am I doing this phase shift detection in a complete wrong way? Is there a much simpler way to do this out there somewhere?