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.

A novel multiwavelength erbium-doped fiber laser configurationis proposed and demonstrated. The laser can produce simultaneousfour-wavelength lasing oscillations with a minimum wavelength spacing ofonly 0.36 nm in C-band via using two fiber Bragg gratings written in highbirefringence fiber, while ensuring fairly stable room-temperature operation.The laser can also achieve switching modes among four wavelengths bysimple adjustment of two polarization controllers in the cavities. Theconfiguration is based on the polarization hole burning and overlappingcavities principle. The laser has the advantages of simple all-fiberconfiguration, low cost, high stability and operating at room temperature.

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.

A suppressant effect for mode competition of multi-wavelengthlasing oscillations induced by deeply saturated effect in an ordinaryerbium-doped fiber ring laser (EDFRL) was observed and experimentallyinvestigated. Results show that the effect is helpful to obtain stablemulti-wavelength lasing at room temperature in the EDFRL, which offers anew and simple approach to achieve stable multi-wavelength EDF lasing.Stable two-and three-wavelength lasing oscillations were achieved based onthe effect in the ordinary EDFRL for the first time to our best knowledge.The multi-wavelength lasing oscillations were so stable integrated oversmaller than 1ms that the maximum power fluctuation over more than 30minutes of observation was less than 0.1 dB and 0.5 dB for two-wavelengthlasing with a spacing of 1.28 nm and 0.76nm, respectively.

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