Generation Of 1.7?m Wide-spectrum Fiber Laser For Optical Coherence Tomography

The third near-infrared window(1600-1870 nm)is between the absorption peaks of water molecules of 1.5 ?m and 1.95 ?m,and includes the light absorption peaks of polymer materials,lipids,cholesterol,collagen,and C-H covalent bonds.The above-mentioned characteristics make fiber lasers working in this window extremely competitive in medical and industrial fields such as biomedical imaging,spectral analysis molecular detection and material processing and attract more and more attention from scientific research institutes.Therefore,in this thesis,researches on a 1.7 ?m wide-spectrum light source and experiment for optical coherence tomography applications are carried out.The specific research contents are as following:1.A mode-locked fiber laser with switchable pulse state in the 1.5 ?m band was studied.The switching between the traditional soliton pulse and the soliton molecular pulse in the1.5?m band was realized,and the switching operation between the two type of pulses is reversible.Among them,the traditional soliton has a pulse width of 822 fs,a 3d B bandwidth of 7.39 nm;adjusting the polarization controller in the cavity can switch the output pulse from the traditional soliton pulse to the soliton molecular pulse.In that case,the pulse width is 493 fs,and the signal-to-noise ratio is 53.86 d B.2.A wide-spectrum light source with working wavelength in the 1.7 ?m band was studied.A fiber amplifier was built to amplify the ultrafast mode-locked laser obtained in the experiment to 89 m W.The single-mode optical fiber,the dispersion-shifted fiber and the highly nonlinear fiber were used as the Raman gain medium successively to realize the generation of wide-spectrum source with the working wavelength in the 1.7 ?m band.In the experiment of pumping dispersion-shifted fiber,a dual-band wide-spectrum light source with peak wavelengths at 1.3 ?m and 1.7 ?m was realized,and the corresponding 3d B spectral widths were 77.8 nm and 174.18 nm.The average power is 13.74 m W.In the experiment of pumping highly nonlinear fiber,a flat supercontinuum with a central wavelength in the 1.7?m band and a 20 d B spectral width of 355.8 nm was realized.After the supercontinuum light source,a fiber Sagnac loop filter was built to achieve modulated multi-wavelength output with a period of 2 nm.3.The application of 1.7 ?m wide-spectrum light source on optical coherence tomography was studied.The experimental application of the 1.7 ?m wide-spectrum light source for optical coherence tomography technology was carried out on optical coherence tomography system with simple structure.The above-mentioned dual-band wide-spectrum light source was applied to the optical coherence tomography system,and the axial resolution of the overall system was measured to be 12.66 ?m.Then the flat supercontinuum light source was applied to the optical coherence tomography system,and after the Sagnac ring was used to filter the supercontinuum,the overall imaging sensitivity was increased by 0.41 d B.The air interlayer between the slides can be clearly seen in the gray-scale image of the slides,and the experiment achieved an imaging depth about 0.1 mm.The above experiment realized the simple application of the 1.7 ?m wide-spectrum light source in the optical coherence tomography system.