Theoretical modeling of high-power thulium-sensitized holmium fluorozirconate glass (Tm:Ho:ZBLAN) fiber lasers operating on the 2 micrometer transition in holmium is presented. High output power in single-mode is achieved by pumping the inner cladding of double clad fiber with single-mode core with high-power multimode cw diode lasers. The higher output powers possible with the double-cladded fiber laser (or DCFL) over the core- pumped fiber laser means that these particular lasers are suited to a number of medical applications which require output of high power and low divergence. In a preliminary step to optimize these devices, a computer model has been developed to analyze the performance of the device when the length of the fiber configuration and doping are varied. It is shown that the form of the coupling coefficient which relates the transfer of power from nonabsorbing modes to absorbing modes which propagate within the inner cladding and core of the fiber is paramount to the operation of the DCFL.