Studies Of Passive Mode-locked Fiber Laser Based On Single-wall Carbon Nanotubes

Passive mode locking laser based on the single wall carbon nanotubes saturableabsorber（SWCNTs-SA）,which is provided with the advantages of simple structure,extremely narrow output pulse, good self-starting property, high beam quality, and soon, has potential application prospect in optical communications, fiber sensing,biological technology, physical technology, micro processing etc. This paper gives thefollowing several aspects of discusses and research based on the nonlinear opticalcharacteristics and application in experiment of passive mode locking fiber laser ofSWCNTs.1. The introduction about the structure and characteristics of Single-walled carbonnanotubes. Describing how the factors of the pipe diameter and concentration ofSWCNTs, as well as function materials impact optical properties of SWCNTs-SAfilm, The film is easy to realize mode locking operation near its linear absorptionpeak; making an introduction about the relationship between the three ordernonlinear optical coefficient and saturable absorption effect of SWCNTs, and thenarrow effect saturable absorber bring to bear light pulse.2. Analysis and simulation of Z-scanning system theory. Presenting Z-scanningtheory model for measuring nonlinear coefficient of optical material, based on thetheory of mathematical analysis and simulation, putting forward to the methods toenhance Z-scanning system measuring accuracy——reducing light beam pulsewidth and waist radius, increasing output energy of the light source, reducing thelinear transmittance of apertures, and selecting rational distance from the lensfocus to the apertures.3. Z-scanning experimental research based on SWCNTs-SA. Preparing uniformitySWCNTs-SA film on glass wafer, and according to the method of improving themeasurement accuracy, building Z-scanning system, fitting the closed and openedholes Z-scanning curve which have be measured, obtaining film three ordernonlinear absorption coefficient and refraction coefficient of homemadeSWCNTs-SA respectively: β=7.8×10^-7cm/W, γ=6.4×10^-11cm²/W, and thethird-order nonlinear susceptibility χ³=2.06×10^-9esu, indicating the homemade SWCNTs-SA film has the very good saturable absorptive effect.4. Mode locking theory and the building and simulation of optical pulse transmissionequation. Having Analysis of the conditions and basic process of the modelocking, building optical pulse transmission equation according to nonlinearschrodinger equation, and simulating the process how the optical pulse in the fiberform mode locking.5. Passive mode locking experiment based on SWCNTs-SA. Coating SWCNTs-SAfilm on fiber end by using optical deposition, when the loss caused by SWCNTsfilm is3.2dB, laser achieve single wavelength mode-locked operation in1562.4nm, whose frequency is8.367MHz; When the loss is7.1dB, the wavelength andfrequency of mode-locked operation is1545.36nm,8.369MHz; When the loss is4.9dB, laser in the mode locking condition, however, the mode-locked centerwavelength can switch one another between1562nm and1546nm by adjustingthe polarization controller, the frequency is8.365MHz, and can observing thephenomenon of unstable harmonic mode-locked in the process of switching.