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.

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.