Imperfections of a phase modulator driven below the proper modulation frequency of a fiber gyroscope
can cause offset of the output signal, limiting long term stability. Bias drift induced by non-linear effects
in the phase modulator was studied and altenative ways of stabilizing a short loop length gyro were
implemented. Long term drift figures below 0.2°/h rms were achieved in a highly birefringent fiber gyro
with a 160 m-long sensing spool.