Study On Optical Pulse Compression Via Stimulated Brillouin Scattering And Supercontinuum Generation In Optical Fibers

Since the end of the20th century, the research in the field of nonlinear fiberoptics has been rapidly developed with the appearance of the rare earth doped fiberlaser and fiber amplifier. On one hand, nonlinear effects in optical fibers havenegative impacts on the performance of optical signal in the optical communicationsystem, such as pulse broadening, signal distortion, inter channel crosstalk and so on.On the other hand, nonlinear effects have important applications in the field ofall-optical information processing and broadband optical source, such as all-opticalwavelength converter, optical switch, optical buffer, and multichannel WDM source.Therefore, we should suppress these negative impacts on the communication systemas much as possible. And meanwhile, by using these nonlinear effects in optical fiberswe can develop new types of optical communication devices, which will play animportant role in scientific research and practical applications.At present, the further increasing of information capacity is limited by the speedof electronic devices in communication systems. The key solution of this problem isto develop new types of all-optical devices to replace the electronic devices. In theconstruction of future ultrahigh speed optical network, optical switch and router aremain constituent parts. The key element of optical router is optical buffer. Therefore,to develop novel all-optical delay lines or buffers is one of the frontiers in photonicsresearch.Recently, the researchers have proposed several methods to realize all-opticalbuffers. Among them all-optical time delay based on stimulated Brillouin scattering inoptical fibers is one of the most promising candidates. However, the time delay isalways accompanied a pulse broadening by using this method. In telecommunication,this pulse broadening will increase the bit rate error and have negative impacts on theperformances of signal. Concern with this problem, we proposed a new method torealize tunable pulse compression via doublet Brillouin gain lines in optical fibers. In this work, we obtained the evolutions of output pulses by numerically solving thenonlinear Schrodinger equations and the coupled pulse-propagation equations ofBrillouin double gain lines in optical fibers. When varied the frequency separationbetween two gain lines, we achieved a tunable pulse compression of output pulses.The compression ratio varied from1.63to0.29, that is to say the pulse width ofoutput pulse could be compressed to0.29times of its initial. However, with thedecrease of the compression ratio, the distortion of the trailing edge of the outputpulse increased. To optimize the pulse distortion effect, we discussed in details theimpact factor of the frequency separation, pump power, and pulse shapes of inputpulse on pulse distortion. We have considered that all-optical pulse compression basedon Brillouin double gain lines can find enormous applications in the final section ofthe cascaded Brillouin delay lines in optical communication systems.Another work is the experimental study of supercontinuum generation based onthe tellurate microstructure fiber. We designed and fabricated the passivelymode-locked femtosecond fiber laser and tellurate microstructure fiber. Thefemtosecond fiber laser is obtained by a ring cavity fiber laser mode locking using asaturable absorber incorporating carbon nanotubes. The wavelength of output pulse is1560nm, the pulse width (full width at half maximum FWHM) is440fs, and therepetition rate is50MHz. After amplifying by two erbium-doped fiber amplifiers(EDFA), which pumped by a laser diode at980nm and a Raman fiber laser at1480nm, the average power of femtosecond pulse is up to246mW. Then the effect ofsupercontinuum generation from1300nm up to2100nm was observed when theamplified femtosecond pulse was coupled into a tellurate microstructure fiber. Thissupercontinuum source can act as multichannel communication source in thewavelength division multiplex (WDM) system. Furthermore, it can also find potentialapplications in the fields of infrared optics sense, electro-optical warfare, and so on.