Mid-infrared Light Sources Based On Germanium Doped Fiber

The mid-infrared band covers a lot of fundamental absorption peaks of atoms and molecules,and it's also one of the important transmission windows in the air.As a result,there are many applications about mid-infrared optics at many fields such as spectroscopy,medical and military.Mid-infrared light sources based on high nonlinear Germanium doped fibers have good thermal stability,long life time and high anti-electromagnetic interference.In this thesis,we have achieved mid-infrared cascaded Raman output and mid-infrared supercontinuum generation from highly Germanium doped fibers pumped with 2?m pump lasers.The main contains are list as follows.1.A mid-infrared cascaded Raman light source based on Germanium doped fiber was demonstrated.A 98 mol.% Germanium doped fiber was pumped by using a pulsed fiber laser at either 1.950?m or 2.0?m.Cascaded Raman spectra with Stokes lines up to third order at 2.53?m and 2.7?m were achieved,respectively.In the experiment,length of the Germanium doped fiber was optimized.The coupling efficiency of the free space coupling system through which the pump laser was coupled into the Germanium doped fiber,was also optimized by fusion splicing a short single mode fiber to the input end of the Germanium doped fiber and taking multiple discharges.The coupling efficiency is from 50% up to 60%,and the damage threshold of the pump power is from 500 m W up to 1200 m W.The 2.7?m Raman scattering output is the longest wavelength Raman scattering output by using Germanium doped fiber in our knowledge.2.A mid-infrared supercontinuum output based on Germanium doped Fiber is demonstrated.The 98 mol.% Germanium doped fiber is pumped by 2.0?m pulse fiber laser,and broad band supercontinuum of 1.9-2.9?m was achieved.Stimulated Raman scattering,self-phase modulation,cross-phase modulation and four wave mixing etc.lead to the supercontinuum generation.In the progress of the experiment,the length of the Germanium doped fiber is optimized.The coupling efficiency of the free space laser pump coupled into the Germanium doped fiber is also optimized by splicing a very short length(100-200?m)of multi mode fiber with the Ge-doped fiber.The 2.9?m long wavelength limit is the longest so far for Ge-doped fiber pumped by nanosecond fiber laser in our knowledge.