Showing papers by "Lawrence Shah published in 2017"

Robust multimaterial chalcogenide fibers produced by a hybrid fiber-fabrication process

Abstract: Double-crucible cane fabrication of highly purified chalcogenide-glass was combined with multimaterial thermal fiber drawing to produce robust low-loss 0.2 NA chalcogenide fibers. Optical transmission losses were shown to be less than 1.1 dB/m at wavelengths of 1.5, 2.0 and 4.6 μm. Fiber transmission > 97% at the 1.5 μm design wavelength was demonstrated using single-layer anti-reflection coatings that were durable under temperature, humidity and abrasion tests. Tensile-strength tests proved that the mechanical strength of the fiber was improved by a factor of 1000 compared to a jacket-free chalcogenide fiber. Multiwatt power transmission in single mode fiber was demonstrated.

SBS Threshold Dependence on Pulse Duration in a 2053 nm Single-Mode Fiber Amplifier

Abstract: Stimulated Brillouin scattering (SBS) is the first nonlinear effect that limits power scaling of narrow linewidth fiber lasers. Nonlinearities typically have a reduced impact when operating at longer wavelengths. However, the SBS gain is considered wavelength independent. To investigate this further, a pulsed 2053 nm source with MHz-linewidth is amplified to >100 W peak powers in single-mode, thulium-doped fiber. The SBS thresholds were measured while varying the pulse duration. Analyzing the SBS threshold measurements suggests that the peak Brillouin gain coefficient is ∼12.2 pm/W with a spontaneous Brillouin bandwidth of ∼17.5 MHz in the passive single-mode fiber at 2053 nm. While the peak Brillouin gain coefficient is comparable to those reported at shorter wavelengths, the spontaneous Brillouin bandwidth is significantly narrower. This indicates that long wavelength sources can inhibit the onset of SBS more readily than short wavelength sources.

High Power 2053 nm Transmission through Single-mode Chalcogenide Fiber

Abstract: An in-house drawn chalcogenide fiber sustained 12.2 MW/cm2 CW irradiation on the facet without damage, limited by available laser power. After depositing single-layer, anti-reflection coatings on the fiber facets, 90.6% transmission was achieved with 10.2 W output.

Nonlinear processes associated with the amplification of MHz-linewidth laser pulses in single-mode Tm:fiber

Abstract: This work studies the accumulated nonlinearities when amplifying a narrow linewidth 2053 nm seed in a single mode Tm:fiber amplifier. A 30 ns). The pulses are subsequently amplified and the repetition rate is further reduced using a second acousto-optic modulator. It is well known that spectral degradation occurs in such fibers for peak powers over 100's of watts due to self-phase modulation, four-wave mixing, and stimulated Raman scattering. In addition to enabling a thorough test bed to study such spectral broadening, this system will also enable the investigation of stimulated Brillouin scattering thresholds in the same system. This detailed study of the nonlinearities encountered in 2 μm fiber amplifiers is important in a range of applications from telecommunications to the amplification of ultrashort laser pulses.