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.

We demonstrate an electrically tunable Sagnac filter based on a photonic bandgap fiber that is realized by infusing liquid crystal into a solid-core air-hole photonic crystal fiber. The filter enables an electrical tuning with a range of about 26nm for one single interference minimum in the transmission bandgap from 1330 to 1650nm wavelength. The tuning efficiency is averaged to 0.53nm/V. © 2008 Optical Society of America

A dual-core photonic bandgap fiber (PBGF) is demonstrated byinfusing a high-index liquid into a dual-core air-silica photonic crystal fiber(PCF). Extremal couplings have been experimentally observed. Thetemperature tunable characteristics of the dual-core PBGF's bandgapguiding and dual-core coupling are experimentally and numericallyinvestigated. When we rise temperature, the dual-core PBGFs’ bandgapshave been changed: compression of bandwidth, blue-shift and depression ofthe guiding band. Especially, the dual-core coupling is temperature tunablebecause of the tunability of the infusion liquid’s index. We find that the riseof temperature increases the coupling length which results in the blue-shiftof the resonant peak wavelengths with a speed of 1.9nm/℃, for a 20mmdual-core PBGF.

A gain and gain-flatness improved L-band dual-pass Raman fiber amplifier (RFA) utilizing a photoniccrystal fiber (PCF) as gain medium is demonstrated. By introducing complementary gain spectra of typicalforward and backward pumping single-pass RFA using the same PCF, we finally achieve average net gainlevel of 22.5 dB with a ±0.8 dB flattening gain in 20-nm bandwidth from 1595 nm to 1615 nm, which israre in RFAs with only one single pump and no flattening filter. Compared with the single-pass pump configurations,gain level, flatness and bandwidth are greatly improved by using the dual-pass amplificationconfiguration. The limitation of this configuration caused by multi-path interference (MPI) noise andstimulated Brillouin scattering (SBS) is also discussed.

A stable and narrow wavelength spacing multiwavelength erbium-doped fiber laser is proposed and demonstrated. The laser can producesimultaneous dual-and triple-wavelength lasing oscillations with a narrow wavelength spacing of less than 0.1nm via using a singlefiber Bragg gratings written in polarization-maintaining (PM) fiber. By adjusting polarization controller, the wavelength spacing of dualwavelengthlasing oscillations can be tuned to as small as 0.032nm. The maximum amplitude variation for every lasing wavelength is lessthan 0.5 dB. The room-temperature operation principle is based on the polarization hole burning and deeply saturated effect in an ordinaryerbium-doped fiber ring laser (EDFRL). The laser has the advantages of simple all-fiber configuration, low cost, high stability andoperating at room temperature

A novel approach to simultaneous force and temperature measurement is proposed and demonstrated inthis paper. The sensing element is based on a single long-period grating (LPG) formed by irradiating thejoint of a microstructured optical fiber (MOF) and standard single mode fiber (SMF) with CO2 laserpulses. The grating exhibits two groups of attenuation bands with distinctly different responses to temperatureand force: the resonant notches in the MOF involving couplings between fundamental mode andcore LP11 modes are almost temperature insensitive but highly sensitive to force, while resonant notchesin the SMF coming out of couplings between fundamental mode and cladding modes show high sensitivityto temperature but marginal sensitivity to force. Based on the LPG, a simple and efficient dualparametersensor simultaneously measuring temperature and force with a sensitivity of ∼0:086nm=℃and∼−2:18nm=N, respectively, is achieved. Furthermore, we propose a simple sensing configuration forsimultaneous strain and temperature measurement.