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.

A simple technique for achieving wavelength tunable andamplitude-equilibrium dual-wavelength fiber laser source based on adual-pass Raman/Brillouin amplification configuration is proposed andexperimentally investigated. A stable room-temperature dual-wavelengthlasing oscillations with average channel power of more than 1 mW andsignal-to-noise ratio of more than 30 dB were obtained with only 250 mWRaman pump power. The dual-wavelength lasing oscillations withwavelength spacing of 0.076nm were so stable that the maximum powerfluctuations and wavelength shifts over more than 10 minutes of observationwere less than 0.5 dB and 0.002nm, respectively. The dual-wavelengthlasing output can also be tuned in a range of -35nm from 1545.090nm to 1580.078nm with an amplitude-equilibrium of less than a peak powerdifference of 0.25 dB at the two wavelengths.

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.