Yun, S.H., Richardson, D.J., Culverhouse, D.O. and Kim, B.Y.
Wavelength-swept fiber laser with frequency shifted feedback and resonantly swept intra-cavity acousto-optic tunable filter
IEEE Journal of Selected Topics in Quantum Electronics, 3, (4), . (doi:10.1109/2944.649546).
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This paper concerns a Wavelength-Swept Fiber Laser (WSFL) incorporating frequency shifted feedback and an intra-cavity passband filter, in which the wavelength of the modeless output is linearly, continuously and repeatedly tuned (in time) over a given range by modulation of the filter peak wavelength and filter strength. We show both numerically and experimentally that amplifier noise plays a key role in determining the operating modes of frequency-shifted fiber laser systems and that a noisy amplifier can be used to suppress the natural tendency of such lasers to pulse allowing for continuous wave, modeless operation. Furthermore, we show that significant narrowing of a WSFL instantaneous swept linewidth can be obtained if the filter peak transmission wavelength is resonantly swept so as to follow the wavelength shift per pass due to the acousto-optic frequency shift. Using these ideas we go on to demonstrate and characterize a high power, diode-driven, Er3+/Yb3+ WSFL incorporating a bulk-optic Acousto-Optic Tunable Filter (AOTF). Linewidths 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 generation of user definable average spectral output by synchronous modulation of the filter strength and multi-wavelength pulsed output at higher sweep rates. Excellent agreement between the experimental results and those of the numerical modelling is obtained. Our simulations show that reduced linewidth (<0.02 nm) and improved scan linearity should be readily achievable with realistic system improvements. We believe such sources to be of considerable physical and practical interest with applications ranging from sensor array monitoring, device characterization through to low coherence measurement technology.
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