Suppression of backreflection noise in a resonator integrated optic gyro by hybrid phase-modulation technology

A method to suppress backreflection noise due to facet reflection in a resonator integrated optic gyro (RIOG) is demonstrated using hybrid phase-modulation technology (HPMT). First, calculations are carried out to evaluate the effect of the backreflection. Although its amplitude has been remarkably decreased by angle polishing, residual backreflection noise is still a severe factor in RIOGs. Next, a hybrid phase-modulation method to eliminate the backreflection noise is constructed, and the frequency spectra of the photodetector outputs before and after adopting HPMT are analyzed. Theoretical analysis shows that the backreflection noise spectra will split from each other as a result of the hybrid phase modulation. In association with the pectinate-filter characteristics of digital correlation detection, the backreflection noise can be suppressed. Finally, the RIOG experimental setup is established and compared with opposite-slope triangle phase-modulation technology. HPMT has the advantage of suppressing backreflection noise, with the RIOG bias stability greatly improved from 2.34 to 0.22 deg/s (10 s integration time).