Optical phase locked loop to make two diode lasers coherent

Thread Starter


Joined Mar 25, 2018
Hi, does anyone know how I might be able to approach locking the phases of two laser diodes? I know the frequency can be changed when more or less current is supplied to the diode allowing the phase to shift. I'd be expecting to use a PLL but I have no idea of how to implement an optical PLL. Any thoughts would be much appreciated.


Joined Oct 29, 2013
Disclaimer; I'm not a pro with PLL or lasers. That said, I believe your first task is figuring out how to get feedback from the lasers that indicates their phase, so that you have an input for your PLL.


Joined Feb 24, 2006
A prism will deflect different frequencies through different angles. You measure the angular displacement of the controlled beam until you get the desired deflection.

An interferometer might work also. The controlled beam moves along the path with a variable distance and when the beams are recombined the interference pattern will tell you if they are in phase.
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