Minimizing Specular Reflections in a Sagnac based Fiber Gyro

AI Thread Summary
The discussion focuses on building an airspeed flowmeter using a Sagnac fiber optic gyro, with the challenge of minimizing specular backreflections that obscure weak signals. The author notes that a previous group successfully achieved this using a commercial fiber gyroscope, likely due to their effective phase modulation techniques that isolate the desired signal from noise. They express concern about achieving sufficient backreflection reduction without misaligning the system, as their calculated signal levels are significantly weaker than the constructive signal. The author seeks insights into methods for sensing small signals and eliminating reflections from fiber components. Overall, the conversation emphasizes the technical challenges of DIY fiber optic gyroscope setups and the need for effective noise reduction strategies.
Diyon
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My project is to build an airspeed flowmeter using the design of a signac fiber optic based gyro. There is a group that has already accomplished this task (http://www.ncbi.nlm.nih.gov/pubmed/18301479), however they used a commercial fiber gyroscope whereas I am trying to build the entire setup myself.

The problem I'm encountering is the specular backreflections off my fiber optic components are washing out my inherently extremely weak signal. After a lot of reading, I have come to the conclusion that it must be their phase modulation that is somehow isolating the phase shifted signal through the DC noise of the reflections. All the other components (short coherance length source+Phase Shift) are to deal with separate problems (Rayleigh Scattering and Birefringence of the fiber).

Can anyone explain why they are able to sense such a small signal, or how they are able to eliminate the reflections off their fiber components? I found the most ideal case would be -70db of backreflection after using 8 degree cut fiber and misaligning it, both of which I am hesitant to do since it would misalign my system and my signal i calculated is -60-80db compared to my constructive signal.
 
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Bump, if anyone can point me in the right direction of a good resource that would be helpful as well.
 

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