Waveguide-type optical passive ring resonator gyro using phase modulation spectroscopy technique

Abstract

Abstract. We report the first demonstration of silica waveguide optical passive ring resonator gyro ͑OPRG͒ based on the phase modulation spectroscopy technique. The ring resonator is composed of a 6-cm-long silica waveguide. Observed from the resonance curve, the free spectral range ͑FSR͒ of the resonator, the full width at half maximum ͑FWHM͒ of the resonance curve, the finesse ͑F͒ of the resonator, and the resonance depth are 3.4 GHz, 62 MHz, 54.8, and 70%, respectively. The detection sensitivity of this OPRG will be 7.3ϫ 10 −5 rad/ s. In the experiments, there is an acoustic-optical modulator ͑AOM͒ in each light loop. We lock the lasing frequency at the resonance frequency of the silica waveguide ring resonator for counterclockwise ͑CCW͒ lightwave; the frequency difference between the driving frequencies of the two AOMs is equivalent to the Sagnac frequency difference caused by gyro rotation. Thus, the gyro output is observed. A small, robust, tactical-grade performance gyro is vital for the successful implementation of the smart weapons and surveillance apparatus. A waveguide-type optical passive ring resonator gyro ͑OPRG͒ is a promising candidate. 1,2The OPRG is a frequency-sensitive device. The gyro rotation is determined by the resonance frequency difference in the clockwise ͑CW͒ and counterclockwise ͑CCW͒ lightwaves due to the Sagnac effect.1 Light circulating many turns in the ring resonator can build up the Sagnac effect. Thus, a short-length sensing loop is required. In this letter, the phase modulation ͑PM͒ spectroscopy technique is chosen to detect the gyro signal using LiNbO 3 phase modulators.3 In the PM spectroscopy technique, the modulating signal and feedback signal do not interact, moreover the LiNbO 3 phase modulators are easy to be integrated with other optical devices. They will make the OPRG compact. Figure 1 shows a schematic diagram of the experimental setup of the OPRG system. The resonator is composed of a 6-cm-long silica waveguide ring and a directional coupler ͑C4͒. The wavelength of the laser is 1550 nm and the diameter of the resonator is 1.9 cm, so the scale-factor of the OPRG is 1 0.84ϫ 10 4 Hz/ rad s −1 .The silica planar lightwave circuit ͑PLC͒ is the key rotating sensing element in the OPRG. It consists of two input/output directional couplers ͑C2 and C3͒ and one resonator coupler ͑C4͒. The coupling ratio of couplers C2 and C3 is designed as 50%. The coupling ratio of coupler C4 is optimized by the total loss in the ring resonator, including propagation loss of silica waveguide ring, excess loss due to the curvature, and excess loss through coupler C4. Considering the temporal coherence of the laser, the resonance curve of a ring resonator is given by 4,5where is the resonance depth; ␦ is the phase shift around one trip of the ring;1/2 ͓exp͑−⌬f͔͒; ␣ R is the total propagation loss in the ring; k C and ␣ C are the coupling ratio and coupling loss of resonator coupler C4, respectively; ⌬f is the spectral linewidth of the laser; and is the optical transmission time in the ring a...

Direct-Coupled Large-Diameter Silica on Silicon Waveguide Ring Resonator Used in Microoptic Gyro

“…It is mainly because the CW and CCW lightpath always have less difference under the test. For the demodulation curve, some papers Zhang et al 2007;Ma et al 2006) take the linear approximation near the resonance. But the linear range was not pointed out.…”

Transfer function of optical waveguide ring resonator in frequency domain for micro-optic gyro

“…This is figure 1 In order to derive the expression for the power transmission of such a resonator, assume that the couplers are lossless and have a frequency independent field coupling coefficient k. When the optical wave at port 4 has circulated one turn in the ring waveguide at steady-state resonance. The electric field amplitude at port 2 can be written as 2 4…”

“…Resonant micro-optic gyro (R-MOG), which has excellent advantages such as high reliability, wide dynamic range, small size, and low cost, is one of the most promising candidates for the next generation inertial rotation sensors [1][2][3] . Angular velocity can be obtained in R-MOG by sensing the resonant frequency difference between the counterpropagating light beams transmitting in the waveguide ring resonator.…”

Study of photonic resonant angular velocity sensors as alternative gyro technology

“…Resonance frequencies of these modes are split by rotation and, according to the Sagnac effect, the difference between them (Δf) is proportional to the cavity angular rate Ω. The measurement of this difference, allowing the angular velocity estimation, is carried out by the closed-loop readout optoelectronic system which is based on the phase modulation spectroscopy [20] and includes the two photodiodes, the optoelectronic (OE) processing unit, whose key element are the modulators and the frequency shifters, and the electronic unit providing the sensor output and the two feedback electric signals controlling the OE processing unit.…”