WAVELENGTH-SWEPT FIBER LASER WITH FREQUENCY SHIFTED FEEDBACK AND RESONANTLY SWEPT INTRACAVITY ACOUSTOOPTIC TUNABLE FILTER

This paper concerns a wavelength-swept fiber laser (WSFL) incorporatin g frequency shifted feedback and an intracavity passband filter, in wh ich the wavelength of the modeless output is linearly, continuously an d repeatedly tuned (in time) over a given range by modulation of the f ilter peak wavelength and filter strength, We show both numerically an d experimentally that amplifier noise plays a key role in determining the operation of frequency-shifted fiber laser systems and that a ''no isy'' amplifier can be used to suppress the natural tendency of such l asers to pulse, allowing for continuous wave, modeless operation, Furt hermore, we show that significant narrowing of a WSFL instantaneous sw ept linewidth can be obtained if the filter peak transmission waveleng th is resonantly swept so as to follow the wavelength shift per pass d ue to the acoustooptic frequency shift, Using these ideas we go on to demonstrate and characterize a high-power diode-driven Er3+/Yb3+ WSFL incorporating a bulk-optic acoustooptic tunable filter (AOTF), Linewid ths as narrow as 9 GHz, sweep ranges up to 38 nm and output powers as high as 100 mW are obtained, Furthermore, we demonstrate the generatio n of user definable average spectral output by synchronous modulation of the filter strength and multiwavelength pulsed output at higher swe ep rates, Excellent agreement between the experimental results and tho se of the numerical modeling is obtained, Our simulations show that re duced linewidth (<0.02 nm) and improved scan linearity should be readi ly achievable with realistic system improvements, We believe such sour ces to be of considerable physical and practical interest, with applic ations ranging from sensor array monitoring and device characterizatio n through to low-coherence interferometry.