Mitigating probe pulse deformation in Raman amplification in OTDR fiber sensing systems.

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.

Broadband air-clad LP02 mode converter using a tapered mode transition.

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.

Break up of the azimuthal symmetry of higher order fiber modes.

We investigate Bessel-like modes guided in a double cladding fiber where the outer cladding is an aircladding. For very high order LP(0X) -modes, the azimuthal symmetry is broken and the mode is no longer linearly polarized. This is observed experimentally and confirmed numerically. The effect is investigated numerically using a full vectorial modesolver and is observed to be dependent on the fiber design. The effect on the diffraction free propagation distance of the modes is investigated using a fast Fourier transform propagation routine and compared to the properties of an ideal circularly symmetric mode. The free space properties of modes suffering from break up of azimuthal symmetry are also investigated experimentally by measuring the free space propagation of a LP(016)-mode excited in the double cladding fiber.

Dynamic characterization and amplification of sub-picosecond pulses in fiber optical parametric chirped pulse amplifiers.

We show a first-time demonstration of amplification of 400 fs pulses in a fiber optical parametric amplifier. The 400 fs signal is stretched in time, amplified by 26 dB and compressed back to 500 fs. A significant broadening of the pulses is experimentally shown due to dispersion and limited gain bandwidth both in saturated and unsaturated gain regimes.