Fiber optic gyroscope architectures that incorporate both a WDM-based wavelength control and a wavelength reference based on a narrowband fiber Bragg grating, with the latter component providing significant improvement in the stability of the wavelength reference by calibrating out wavelength errors associated with a WDM-based wavelength control scheme. The top extent has a small torus and a large torus. Alternatively, manual valves are provided to be manually opened by an operator to open a fuel gas supply passage to supply the fuel gas such that residue is purged by the fuel gas through the discharge passage, thereby enabling fuel supply and purge of residue at starting of power generation, without using an external power source.