A system is disclosed which suppresses relative intensity noise in a fiber optic gyroscope. A high-speed intensity modulator is placed in the gyroscope light path between the fiber light source and a tap coupler which provides a sample of the modulated signal for use in a feedback loop. A photodetector receives the sampled signal and provides current-to-voltage conversion of the signal. A high-bandwidth voltage amplifier then adjusts the gain and phase of the converted signal and drives the intensity modulator in such a manner as to stabilize the control loop and provide suppression of relative intensity noise. The present system modulates the intensity of the light at a frequency which is sufficiently high to allow suppression of high frequency components of the relative intensity noise.
A method for determination of/compensation for the bias/random walk errors induced by the light source in fiber-optic Sagnac interferometers employing a modulation method for stochastically independent shifting of the operating point to the points of highest sensitivity. A reference beam is output from the light beam emitted from the light source of the interferometer and passed to the fiber coil to produce a proportional reference intensity signal. Such signal is demodulated with the demodulation pattern of the rotation rate control loop to demodulate the rotation rate intensity signal (proportional to rotation rate). The demodulated reference intensity signal measures the bias/random walk errors to be determined. Demodulation of the reference intensity signal is simultaneous with that of the rotation rate intensity signal so that components of the reference and rotation rate intensity signals (each resulting from light components simultaneously emitted from the light source) are identically demodulated.
An arrangement for reducing the effects of pump signal relative intensity noise (RIN) in a Raman fiber amplifier. A portion of the output from a pump laser source is applied as an input to a compensating, lower power laser module, where fluctuations in the output power of the pump laser are used to control the bias current applied as an input to the compensating laser such that as the pump power increases, the bias current (and lower power laser output) decreases; conversely, as the pump power decreases, the bias current applied as an input to the compensating laser will be increased. The result is a relatively flat gain as seen by the information signal, thus minimizing the transfer of relative intensity noise from the pump to the signal.
A system and method is provided which suppresses relative intensity noise in a fiber optic gyroscope by taking advantage of the frequency response of erbium fiber. In operation, the gain provided by the erbium fiber is added to the gain of the other components in the feedback loop to provide for stable loop performance up to about 250 kHz. The frequency response of the erbium fiber of about 3 kHz also provides a 6 db per octave roll-off, which, when used in a negative feedback control loop for controlling the current flowing to the gyroscope light source, allows for a relative intensity noise control loop with a bandwidth much greater than 3 kHz; this may be used in high performance gyroscope applications.
