The reflection and transmission characteristics of a high-birefringence fiber loop mirror (HiBi-FLM),which is composed of a standard fiber coupler and one-section or multisection high-birefringence fibers(HBFs), are analyzed and discussed in detail. Theoretical reflectivity and transmissivity expressions forHiBi-FLMs with one-, two-, and three-section HBFs were obtained. The procedure for calculating reflectivityand transmissivity for HiBi-FLMs with n-section HBFs is given. Experimental results have verifiedthe theoretical model. The basic characteristics of the one-section HiBi-FLM when strain and hightemperature are applied to HBFs were analyzed and investigated theoretically and experimentally. Theexperimental results are in good agreement with the theoretical analysis. Furthermore, a strain–temperature sensor that makes use of those characteristics, which is new for applications of HiBi-FLMs,has been proposed and demonstrated.

We propose and demonstrate an ultrasensitive photonic crystal fiber refractive index sensor by introducing theavoided-crossing effect in a bent-controlled fluid-filled photonic-bandgap fiber (FF-PBGF). By controlling the bendradius of the FF-PBGF, resonant couplings between the fundamental core mode and the cladding modes are realizedand transmission notches are observed in the transmission band of the FF-PBGF. By changing the refractive index ortemperature of the bent FF-PBGF, a sensitivity of 32,400 nm per refractive index unit (or 13:1 nm=℃) is achieved,which is the highest for a fiber device to date, to our best knowledge.

The temperature tuning properties of a liquid crystal (LC) photonic bandgap fiber's bandgap transmissionwas investigated in this study. Because of the special temperature responses of the LC's indices andits phase transition property, the bandgap transmission was found to have different temperature responsesat different temperature ranges below the LC's clearing point temperature. At temperatureslower or higher than the LC's clearing point, the bandgap transmissions are quite different, which permitsswitching with an extinction ratio as large as 45 dB. At temperatures around the LC's clearing point,the bandgap transmission was depressed.

High order resonances between fundamental core mode andcladding LP01 supermodes are demonstrated in long period fiber gratings(LPFGs) inscribed in all-solid photonic bandgap fibers for the first time toour knowledge. The resonance wavelengths of the LPFGs calculated byway of photonic bandgap theory agree with the experimental results. Thetemperature responses of these resonance peaks have been theoretically andexperimentally investigated. In addition, the mechanism of LPFG formationhas been researched deeply through coupled-mode theory (CMT) and thecutback experiments.

A suppressant effect for mode competition of multi-wavelengthlasing oscillations induced by deeply saturated effect in an ordinaryerbium-doped fiber ring laser (EDFRL) was observed and experimentallyinvestigated. Results show that the effect is helpful to obtain stablemulti-wavelength lasing at room temperature in the EDFRL, which offers anew and simple approach to achieve stable multi-wavelength EDF lasing.Stable two-and three-wavelength lasing oscillations were achieved based onthe effect in the ordinary EDFRL for the first time to our best knowledge.The multi-wavelength lasing oscillations were so stable integrated oversmaller than 1ms that the maximum power fluctuation over more than 30minutes of observation was less than 0.1 dB and 0.5 dB for two-wavelengthlasing with a spacing of 1.28 nm and 0.76nm, respectively.