Long period fiber gratings are fabricated in the cladding rods ofall-solid photonic bandgap fibers (PBGFs) by point-by-point side UVillumination. Resonant couplings from fundamental mode to guided andradiative supermodes (rod modes), and bandgap-like modes are identified.We obtained a detailed insight over the modal and dispersive properties ofthe PBGF through a series of theoretical and experimental investigations onthe spectral characteristics and the responses to temperature and high-indexliquid of the LPGs.

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.

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.

We have proposed directional couplers operated by resonantcoupling in all-solid photonic bandgap fibers structure which consist of acladding with an array of high-index rods in silica background, two coresformed by omitting two rods, and some defect rods introduced by reducingthe diameter of the high-index rods between the cores. The resonant effectinduced by the avoided crossing between core-guided supermodes anddefect-guided modes significant decreases the coupling length. Thedirectional couplers proposed in this paper are almost polarizationindependent and have potential application in realizing integrating all-fibercommunication devices