OPTICALFIBERS USINGCR:FORSTERIWLASER

Atpresent time therevis agrowing demand forhigh precision metrology intheoptical domain for: commnnications, navigation, fundmental physics etc. A recent breaktrough in themethods ofprecision measurements became possible duetothedevelopment ofhighly stable femtosecond lasers andintroduction ofspecial optical fibers (photonic crystal fibers, tapered fibers) forgeneration ofbroad spectnrm. Mostofthis workhastaken advantage ofthe, highly-developed Ti:Sapphire laser with thespectrum broadened from400to1200nm.The development offemtosecond lasers operating atlonger wavelengths isbeneficial tocover a highly employed spectral range of1- 2 micron. Cr:Forsterite laser canbeasuitable candidate. This laser emits atawavelength of1.2-1.3pnandits spectrum canbebroadened inahighly nonlinear fiber. Thecavity ofaCr:F laser hadaZ-shaped configuration. Thegain crystal was17mm long. Apair ofSF6prisms wasused tocontrol dispersion inthecavity. TheCr:F crystal was mounted inabrass holder whose temperature wasmaintained at100 Candwaspumped bya commercial 10W 1.06gmYb-fiber laser. Stable, self-sustained generation ofultrafast optical pulses hasbeenobtained with pulses asshort as40'fs. Thecorresponding spectrum was centered on1260nmandhadabandwidth of40nmatFWHM.Thepuls'e repetition rate was 100MHzandtheaverage output power wasupto500mW at5.5W oftheabsorbed pump power. Theapproach toproduce fibers with varying along length chromatic dispersion hasbeen developed. Thismethod perfo'rms aprecise control ofthefiber corediameter during the drawing. Thistechnology became possible owing todigital signal processing usedforthe control ofthedrawing process. Atpresent fibers withvarious dispersion functions canbe produced. Dispersion variations from15to-Sps/nm/km insingle-mode regime at1550nm wavelength arepossible, keeping theoptical loss atthesame level asforconventional fibers. Thetechnology allows fibers with anecessary length dependence ofthediameter tobe fabricated. During thedrawing process information about thecurrent diarneter isprocessed by acomputer andcompared withtheprearranged value. A control signal produced bythe computer ispassed tothedrawing unit. Soft- andhardwares havebeendeveloped toobtain single-mode fibers with chromatic dispersion varying along length, thefiber length being in