Study On Mid-IR Supercontinuum Generation From Soft Glass Microstructured Optical Fibers

Recently, with the appearance of the microstructured fiber, the supercontinuum,particularly the middle infrared (mid-IR) supercontinuum for its promising applicationin medicine and security, interests many people. Soft glass microstructured fiber isfictile, high nonlinearity, has a low soften tempreture and has a wide transparentwindow in mid-IR spectrum. It is a kind of perfect material to be used to get mid-IRsupercontinuum. The main research accomplishments are listed below.Firstly, the soft glass microstructured fiber is referred in the paper. Extrusion, themost popular and simple fabricating method, is described in detail. Because thestructure of preform die can be designed flexibly, extrusion is convenient to get fiberswith tailored dispersion profile. Then, the nonlinear shrodingger equation which is thetheory model to describe the propagation of pulse in fiber is formulated in the paper.Secondly, by using the modified nonlinear Schrodinger equation (NLSE) andsplit-step Fourier algorithm, we analyze mechanism of supercontinuum generation, theeffects of wavelength, input pulse duration and the second zero dispersion wavelengthon mid-IR supercontinuum(SC) generation in a microstuctured Chalcogenide As2S3fiber with two zero dispersion wavelength. Through simulation, we discover the selfphase modulation (SPM) is main reason arising new spectrums in the initialpropagation. Raman effects also have some influence on spectrum broadening there.Pulse frequency and duration play important role for the supercomtinuum generation.There are marked differences in the output spectra when we change the frequency andduration of the seed pulse. It is beneficial for mid-IR supercontinuum generation whenthe wavelength of input pulse is close to zero dispersion points. Furthermore, keep thepeak power stable, pulse duration doesn’t effect the output spectrum. However, theshorter input pulse generates flatter supercontinuum.Finally, location of the infrared zero dispersion wavelength has huge influence onthe Mid-IR supercontinuum generation. Because of the raman effects, solitons inabnormal dispersion area between the two zero dispersion wavelength are graduallyclose to the infrared zero dispersion wavelength and amplify the red shifted dispersivewaves. But soliton cannot reach the infrared zero dispersion wavelength because of thespectral recoil from the dispersive waves acts on the soliton to compensate for theRaman frequency shift. That means the second zero dispersion point is related to thesupercontinuum spectral range. So in application, we can design fibers according to the spectrum needed.