K. Toyama

Optical Kerr-effect in fiber-optic Brillouin ring laser gyroscopes

The optical Kerr effect in a reciprocal fiber-optic Brillouin ring laser gyroscope is investigated. It is found that the Kerr effect, as the major error source of the rotation rate measurement in this gyroscope, causes a bias of beat frequency with nonlinear dependence on rotation rate. A differential Stokes power of 1 mW inside the ring resonator is measured to produce a beat frequency bias of 69 Hz, which agrees well with the theoretical expectation.<<ETX>>

Lock-in reduction technique for fiber-optic ring laser gyros.

We have demonstrated a Brillouin fiber-optic gyro that utilizes push-pull phase modulation in the ring cavity to suppress frequency locking. This in-line modulation allows an all-fiber system with optical reciprocity. A tenfold reduction of the width of the lock-in range is observed experimentally.

Temperature effects in a Brillouin fiber ring laser.

Temperature effects in a Brillouin fiber ring laser have been investigated. The results show that temperature plays a major role in many different laser characteristics such as lasing frequency, mode hopping, spontaneous pulsing, and frequency mode pulling. Thermal coefficients for the Brillouin frequency shift and for the frequency difference between the pump wave and the first-Stokes wave were measured and are consistent with theoretical predictions based on published basic material parameters. Experimental observation and measurement of the temperature dependence of the spontaneous pulsing threshold show that temperature is a key parameter that may be important in uncovering the physical mechanism underlying spontaneous pulsing.

Digital integrating fiber-optic gyroscope with electronic phase tracking

A novel demodulation scheme for interferometers with optical phase modulation is described. The optical phase shift is measured by mixing a train of square digital pulses with a photodetector current and adjusting the pulse spacing by using an electronic closed loop. The optical phase shift is tracked with deviation less than 0.007 rad, which can be easily corrected by using a look-up table. An experimental optically open-loop fiber-optic gyroscope that uses this demodulation shows a linear scale factor in good agreement with theory.

Synthetic heterodyne detection in a fiber-optic ring-laser gyro

A synthetic heterodyne detection scheme for ring-laser gyros to sense both rotation rate and direction is presented. This scheme is compatible with the sinusoidal push-pull phase-modulation technique for suppressing frequency locking. The good experimental results achieved in a fiber-optic Brillouin ring-laser gyro show the potential of this detection scheme in applications.

Frequency stability of a Brillouin fiber ring laser

The oscillation frequency in a Brillouin Fiber Ring Laser (BFRL) is determined mainly by the axial mode of the cold resonator located under the Brillouin gain curve that experiences the highest gain. This oscillation frequency is therefore temperature dependent since both the Free Spectral Range (FSR) and the gain curve center depend on the temperature.