A Faraday rotator mirror incorporating a Gaussian bandpass filter was used as the reflected end of an Er-doped superfluorescent fiber source to improve its mean wavelength thermal stability. Several different filters were modeled in this fiber source system, and the optimal central wavelength was chosen to be 1558 nm with the bandwidth of 15 nm. With a Faraday rotator mirror incorporating such a filter in an Er-doped fiber source, the mean wavelength variation was measured to be 8 ppm from 40 C to 60 C. The bandwidth reached 16 nm. The pump power was 70 mW at 974.2 nm and the output power reached 18 mW with 6-m Er-doped fiber.Index Terms-Bandpass filter, superfluorescent fiber source. E RBIUM (Er)-doped superfluorescent fiber sources (SFSs) have been extensively studied in interferometric fiber-optic gyroscopes (IFOGs) [1]- [6]. The gyroscope scale factor depends on the optical mean wavelength of gyro system signals, and the rotation rate can only be measured accurately if this mean wavelength is precisely known. A high-grade IFOG requires that its SFS has a mean wavelength stability in parts per million (ppm) [3], which is primarily affected by the pump power, pump wavelength, the pump state of polarization, the feedback power and the Er-doped fiber (EDF) temperature [2]. The influences of the former four factors can be reduced to ppm level by selecting optimal pump parameters [1], [2], [4], stabilizing pump laser and using high-performance fiber optic components [2], [5]. The main instability source is from the EDF-temperature. It can modify the emission and absorption cross-sections of erbium ions, inducing a drift in the mean wavelength. Values of the thermal coefficient ranging from to ppm C have been reported in different SFS configurations [1], [4], [6]. Even though a temperature controller can be applied on EDF, it is quite power consuming, making the system more complicated, especially when the source works in broad temperature range (over 100 degrees). Different in-line fiber optic filters have also been reported to compensate the mean wavelength drift, such as long period fiber gratings [7], Bragg fiber gratings [8], [9], and photonic bandgap fibers [10]. However, to my knowledge, matched fiber filters are quite hard to be accurately fabricated to compensate a specific fiber source, limiting their practical applications.Fig. 1. DPBS Er-doped superfluorescent fiber source configuration.In this letter, a Faraday rotator mirror (FRM) incorporating a Gaussian bandpass filter was used as the reflected end in a double-pass backward-signal (DPBS) Er-doped SFS. The central wavelength of the bandpass filter was selected to be around 1558 nm corresponding to one emission peak of Er ions. Its bandwidth was set to be 15 nm. The reflected signals were filtered out to force the emission spectrum fixed around the 1558 nm emission peak, stabilizing the mean wavelength variations with temperature. After incorporating such a device into the SFS, the mean wavelength variation can reach less than 8 ppm for the temperature...