Laser self mixing and laser feedback interferometry and Fabry-Perot cavity precise position measurements

Thank you for sharing your research. – Richard

I try to follow all low cost interferometry methods. I started it because of my interest in gravitational imaging arrays and gravitational wave communication. Joe Weber at Univ Maryland College Park encouraged me to work on that back in the late 1970’s. Beside photon interferometry, there is a lot of good stuff on atom interferometry and electrochemical methods. The Bose Einstein groups are not really interested in applications.

You might find these videos interesting. You can search YouTube for “laser diode self mixing”. It offers the possibility of single diode, single path precise measurement. Great for embedded applications.

Laser diode self-mixing: Range-finding and sub-micron vibration measurement at

Yes, these are crude, but it is fairly easy to improve on, once the idea is started.

This one might seem really crude, but it shows that Ben Krasnow’s suggestion that the feedback to the laser drive current of a reflected beam can be used to solve for length of cavity. It is a type of cavity resonator then. Laser Diode Self-Mixing Interferometer with pocket laser style diode[No Photodiode] at

I have not read the Fabry-Perot equations lately, but I expect it is fairly straight-forward to estimate the signal level and put them into use. Arduinos I have been looking at recently are cheaper and faster and better. The amplifiers and ADCs are impressive. Roughly 24 bit at 10 Msps, 32 bit at 1 Msps, and 12 bits at 1 Gsps are cost effective now.

This guy has diagrammed it pretty well, but likes to make it more complicated than it needs to be. Laser/Self-mixing Interferometry

“laser self mixing” OR “laser feedback interferometry” has 14,700 entry points now, so it is growing very quickly as a workable method. A tiny bit of circuitry and very low cost diode laser. Multicolor methods, just like they use for GPS to remove atmospheric and ionospheric effects work even better. So buy three $2 laser diodes instead of one. LOL!

Thanks for your paper. I wish I could share all that is happening now. It is really exciting. I had to wait 45 years for the computers and sensors for things I wanted to do. Now they are 10 for $20.


Richard K Collins

About: Richard K Collins

Director, The Internet Foundation Studying formation and optimized collaboration of global communities. Applying the Internet to solve global problems and build sustainable communities. Internet policies, standards and best practices.

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