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.

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 stable room-temperature multi-wavelength Brillouin–Raman fiber laser with a ring cavity configurationwas proposed and experimentally investigated. An obvious suppressant effect for unstable modehopping of multi-wavelength lasing oscillations induced by deeply saturated effect was observed inthe ring cavity configuration. Stable room-temperature multi-wavelength lasing oscillations with morethan 30 lasing lines and wavelength spacing of 0.076nm were obtained with only 250mW Raman pumppower and a section of high nonlinear fiber with a length of 1.5km. The lasing output is so stable that themaximum power fluctuations for the foremost three Stokes lines over more than 20 min of observationwere less than 0.30 dB. The lasing stability of the laser was also compared with a linear cavity configurationwith the same gain components and pump conditions. While using the linear laser cavity configuration,obvious mode hopping was observed. The minimum value of the maximum power fluctuationsat all lasing lines over more than 10min of observation was more than 0.90 dB.

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.