Fig. 1. Structural diagram of optical fiber coupler. (a) 2×2 coupler; (b) 3×3 coupler

Fig. 2. Principle diagram of coupling phase shift detection of single-mode optical fiber coupler based on hybrid Sagnac interferometer

Fig. 3. Theoretical output spectra of hybrid Sagnac interferometer with 2×2 coupler

Fig. 4. Output spectra when detecting coupling phase shift of 2×2 single-mode coupler

Fig. 5. Device for coupling phase shift detection of 3×3 single-mode optical fiber coupler

Fig. 6. Output spectra when detecting coupling phase shift of 3×3 single-mode coupler

Fig. 7. Test results of temperature sensitive characteristics of coupling phase shift of 2×2 coupler