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.

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.

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 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 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