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Research On Supercontinuum Spectrum Generation In Optical Fibers

Posted on:2008-06-09Degree:DoctorType:Dissertation
Country:ChinaCandidate:G XiaFull Text:PDF
GTID:1118360272466970Subject:Physical Electronics
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Recently, due to the extensive applications in the high-speed optical communication systems (DWDM and OTDM), the coherent SC laser source has drawn intensive attentions. This source can be obtained by the SC generation in certain optical fibers effectively based on the effect of high-order soliton compression (SEC), adiabatic soliton compression (ASC) and self-phase modulation (SPM) of seed pulses in the fibers. In this dissertation, we focus on the mechanism and characteristics of the SC generation by these three methods, and several theoretical and experimental studies have been carried out as follows:(1) The SC spectrum generation based on SEC is investigated. The determinant effect of dispersion slope of the fibers on the wide and flat SC spectra generated has been analyzed in details. The negative effect of high-order nonlinearities and its corresponding suppression have also been discussed.(2) The SC spectrum generation based on ASC is investigated. With and without high-order nonlinearities, the effect of the particular dispersion profile of dispersion- decreasing fiber (DDF) on the final compression factor has been studied based on the analysis of the basic pulse compression principles.(3) The theory of SC generation in a normal dispersion-flattened fiber (NDFF) is further modified. We find that wave breaking does occur during the seed pulse evolution in NDFF, which takes place at the propagating distance point Lw b ? 1.06 LD LNL and can be confirmed by the pulse chirp evolution. This point is also the critical point of spectral broadening nonlinear effect, before which the nonlinear effect is SPM and after which are SPM and FWM. The pulse spectral broadening in the initial stages is dominated by the SPM. Thereafter, SPM is impaired while FWM enhanced, and the spectrum will further broaden remarkably, the bounding threshold of which is Lm ax2 ? 5.6 LD LNL. The characteristic of SC noise manifests the dynamic responses of typical SC spectral structures to the seed pulse amplitude noise that are close related to the evolution. The propagation distance of the best noise performance of SC spectrum consists in the region where the dominant role is exchanged between the two nonlinerities.(4) We probe into the SC generation in a highly nonlinear fiber (HNLF) with large normal dispersion of 40GHz pulse trains. We find that it is inefficient to generate SC spectrum just by increasing the fiber length or the amplifier output power. To enhance the SC generation in the fiber, it is availed to implement the new scheme that applies the chirp-pulse compensation technique: The widest SC spectrum can be obtained in the improved new scheme that utilizes a two-stage all-fiber pulse compressor remarkably, but also with the largest ripples. The reason is that the quality of the compressed pulse entering the last section HNLF is negatively affected greatly by the fiber 3rd dispersion of SMF and HNLF. In this scheme, we experimentally obtained broadband 40GHz coherent source with 23.3nm (10dB bandwidth) in the C-band finally.
Keywords/Search Tags:Supercontinuum (SC), Pulse compression, Self-phase modulation, Chirp compensation, Normal dispersion-flattened fiber (NDFF), Highly nonlinear fiber (HNLF)
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