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Mid-infrared (mid-IR) fiber laser sources at 3.5 μm have wide applications in spectroscopy, environmental monitoring, medicine, and defense countermeasures. In this work, we experimentally investigate a dual-end double wavelength pumped (i.e. both fiber ends pumped by 976 nm and 1973 nm, respectively) Er³⁺: ZBLAN fiber laser at 3.5 μm in detail. In the experiment, we carefully evaluate the lasing characteristics in terms of output power and scalability in contrast to the single-end pumping regime. The dual-end pumped Er³⁺: ZBLAN fiber laser yields a maximum output power of 1.72 W at the launched 1973 nm pump power of 8.39 W limited only by the available output power of the 1973 nm laser pump. The operation wavelength is experimentally found to be in a range from 3440 nm to 3620 nm depending on the pump power level. Lasing characteristics for Er³⁺: ZBLAN fibers with different lengths and doping concentrations and other cavity parameters are also investigated in this pumping regime to optimize the lasing performance.