We present a novel design for a Sagnac loop filter (SLF) whose periodic output spectrum can be fully controlled by cascading a small-birefringence loop (SBL) with a high-birefringence loop (HBL). We develop a detailed theoretical analysis, using the Jones vector method, to calculate the transfer function of the tunable SLF. It has been quantitatively shown that both the transmission coefficient and the phase of the SLF can be controlled by adjusting the orientation angle of the birefringent axes of the SBL in the plane of polarization. The theory has been confirmed by experimental results where a stress-induced SBL was mechanically rotated to tune both the wavelength and the power of a periodic output spectrum. Such a tunable SLF is used in the design of a multiwavelength erbium-doped fiber laser in the C band.
© 2008 Optical Society of America
Fiber Optics and Optical Communications
Original Manuscript: May 13, 2008
Revised Manuscript: July 17, 2008
Manuscript Accepted: September 2, 2008
Published: October 1, 2008
Mohammad Aleem Mirza and George Stewart, "Theory and design of a simple tunable Sagnac loop filter for multiwavelength fiber lasers," Appl. Opt. 47, 5242-5252 (2008)