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.