ABSTRACT
We report the numerical and experimental study of probe pulse deformation in a forward-pumped distributed Raman amplifier on a 40-km standard single mode fiber. Distributed Raman amplification can improve the range of OTDR-based sensing systems, but it could result in pulse deformation. A smaller Raman gain coefficient can be used to mitigate pulse deformation. The sensing performance can still be maintained by compensating for the decrease in the Raman gain coefficient by increasing the pump power. The tunability of the Raman gain coefficient and pump power levels are predicted while keeping the probe power below the modulation instability limit.
ABSTRACT
Higher-order mode converters that work over a broad wavelength range are needed for various applications. A new, to the best of our knowledge, simple and cost-effective LP02 mode converter is fabricated by tapering a bundle of single-mode fibers. The device excites the LP02 mode in a four-mode step index fiber with a mode purity higher than 10 dB. The polarization-dependent cross talk of the device is measured using the S2 technique. The LP02 mode selectivity of the device is measured over the entire C and L bands by selectively launching different modes into the device using a spatial light modulator.
ABSTRACT
We have fabricated an air-cladded mode-group selective photonic lantern, which can (de)multiplex the first two mode groups of a standard two-mode step-index fiber. Instead of relying on a low-index capillary tube, our simple solution uses air to form the surrounding "cladding" and thereby enable guiding at the end of the taper. Characterization of a 25-mm long lantern taper results in multiplexing crosstalk values between -20 dB and -12 dB for both modal inputs. The de-multiplexing values were around -12 dB for the fundamental mode, and slightly higher for the first higher-order (LP11) mode. Microscopic imaging of a taper cross section having a width of 30 µm reveals the presence of an uncollapsed airhole in the structure between the three fibers. The impact of such an airhole is numerically investigated using an eigenmode expansion method based on a full-vectorial mode solver, and is found to play an important role in assuring a more adiabatic mode conversion through the taper.
