Enabling Single-Mode (SM) operation in Large-Mode-Area (LMA) fiber amplifiers and lasers is critical, since a SM
output ensures high beam quality and excellent pointing stability. In this paper, we demonstrate and test a new design
approach for achieving ultra-low NA SM rod fibers by using a spatially Distributed Mode Filter (DMF). This approach
achieves SM performance in a short and straight rod fiber and allows preform tolerances to be compensated during draw.
A low-NA SM rod fiber amplifier having a mode field diameter of ~60μm at 1064nm and a pump absorption of 27dB/m
at 976nm is demonstrated.
We demonstrate electrical tunability of a fiber laser using a liquid crystal photonic bandgap fiber. Tuning of the laser is
achieved by combining the wavelength filtering effect of a liquid crystal photonic bandgap fiber device with an
ytterbium-doped photonic crystal fiber. We fabricate an all-spliced laser cavity based on a liquid crystal photonic
bandgap fiber mounted on a silicon assembly, a pump/signal combiner with single-mode signal feed-through and an
ytterbium-doped photonic crystal fiber. The laser cavity produces a single-mode output and is tuned in the range 1040-
1065 nm by applying an electric field to the silicon assembly.
Liquid crystal photonic bandgap fibers represent a promising platform for the design of all-in-fiber optical devices,
which show a high degree of tunability and exhibit novel optical properties for the manipulation of guided light. In this
review paper we present tunable fiber devices for spectral filtering, such as Gaussian filters and notch filters, and devices
for polarization control and analysis, such as birefringence control devices and switchable and rotatable polarizers.