Fig. 1. Measurement system for backscattering of ring laser resonator^[10]

Fig. 2. (a) Measurement system for backscattering characteristics of resonator fiber optic gyro; (b) Measuring result of backscattering characteristics of resonator fiber optic gyro^[12] (AOM: Acoustic optical modulator)

Fig. 3. (a) Measurement system for backscattering of ring resonator in silica planar lightwave circuit; (b) Measurement result of backscattering of ring resonator in silica planar lightwave circuit^[14]

Fig. 4. Fiber ring interferometer^[18]

Fig. 5. (a) Backscattering in IFOG; (b) Phase error due to backscattering in IFOG^[20]

Fig. 6. Optical structure of IFOG^[23]

Fig. 7. Structure of asymmetric phase modulator^[24]

Fig. 8. (a) Measurement system of photonic crystal fiber; (b) Measurement result of hollow-core photonic crystal fiber; (c) Measurement result of polarization-maintaining photonic crystal fiber^[26] (OTDR: Optical time domain reflectometry, PMF：Polarization maintaining fiber, PM-PCF: Polarization maintaining photonic crystal fiber, HC-PCF: Hollow core photonic crystal fiber)

Fig. 9. Optical path structure of RFOG^[29]

Fig. 10. (a) Two main types of backscattering noise in RFOG; (b) Separation of intensity resonant peaks of backscattering beam in RFOG when rotate^[31]

Fig. 11. Optical path structure of RFOG to eliminate backscattering noise^[31] (PM: Phase modulator, AOM: Acoustic optical modulator, PSD: Phase sensitive demodulator, PZT: Piezoelectric transducer)

Fig. 12. Optical path structure of RFOG using phase-locked lasers^[44] (OPLL: Optical phase lock-loop, PM: Phase modulator, IM: Intensity modulator)

Fig. 13. Optical path structure of RFOG using coherent detection^[48] (C: Coupler, PM: Phase modulator, AOM: Acoustic optical modulator, TA: Tunable attenuator, BPF: Bandpass filter, LPF: Low-pass filter)

Fig. 14. (a) Optical path structure of RFOG using broadband source; (b) Measurement result of RFOG using broadband source^[49] (MIOC: Multifunction integrated-optics chip)

Fig. 15. Optical path structure of BFOG^[51]

Fig. 16. (a) Optical path structure of BFOG to remove lock-in phenomena by frequency biasing; (b) Signal beat frequency in BFOG without frequency biasing; (c) Signal beat frequency in BFOG with frequency biasing^[53] (P: Pump light, B: Stimulated Brillouin scattering)

Fig. 17. Optical path structure of BFOG to remove lock-in phenomena by push-pull phase modulation^[54] (C: Coupler, PM: Phase modulator, PC: Polarization controller)

Fig. 18. (a) Optical path structure of waveguide resonant gyro based on single sine phase modulation^[14]; (b) Optical structure of waveguide resonant gyro based on double sine phase modulation^[61] (C: Coupler, PM: Phase modulator, LIA: Lock-in amplifier, PI: Proportional integrator, LDC: Laser diode controller, FBC: Feedback circuit)

Fig. 19. Suppression of backscattering noise in microsphere resonator by Faraday rotators^[66]

Fig. 20. (a) Optical path structure of Brillouin laser gyro based on SiO₂ micro ring resonator; (b) First generation of micro-resonator Brillouin gyro by Vahala research group^[67]; (c) Second generation of micro-resonator Brillouin gyro by Vahala research group^[70]