THERMAL EFFECTS IN DOPED FIBERS

A theoretical analysis of the pump-induced temperature change and asso ciated thermal phase shift occurring in a pumped doped fiber is presen ted. Although the primary de,ices targeted are all-optical switches ba sed on doped fibers, where such effects can be detrimental, this analy sis is also applicable to lasers, amplifiers, and other doped fiber de vices. The effects of a single pump pulse, multiple pulses and continu ous wave (CW) pumping are investigated, both in the dynamic and steady -state regimes. Simple expressions are derived for the thermal relaxat ion time constant of a fiber, and for its steady-state temperature ris e and thermal phase shift under CW pumping. This study predicts that i n all-optical fiber switches utilizing a reasonably good dopant the th ermal effect due to a single short pulse is negligible in all interfer ometers, while the steady-state effect can be sizable in a standard fi ber Mach-Zehnder but is negligible in a twin-core fiber, a two-mode fi ber, and a specially designed Mach-Zehnder interferometer.