Reconversion of higher-order-mode (HOM) output from cladding-pumped hybrid Yb:HOM fiber amplifier.

We demonstrate operation of a cladding-pumped hybrid ytterbium-doped HOM fiber amplifier and reconversion of the HOM output to Gaussian-like beam by using an axicon based reconversion system. The amplifier was constructed by concatenating single-mode and HOM ytterbium-doped double clad fibers, and was excited by a common multimode pump source. A continuous wave (cw) input signal of 97mW was amplified to 100W at the amplifier output, which yielded a gain of more than 30dB.

Accounting for the Occlusion Effect with Insert Earphones.

Background: There are clinical implications associated with knowing when the occlusion effect (OE) must be accounted for during bone conduction (BC) testing because spurious results can occur when errors are made in this regard. The amount of OE produced when insert earphones (IEs) are used varies in the literature; thus, further investigation is warranted.

Purpose: The purpose of this project was to determine the OE during BC threshold measurements under the following occluding conditions used clinically: when using partial insertion (PI) versus full insertion (FI) depth and when occluding one versus both ears.

Self-frequency-shifted solitons in a polarization-maintaining, very-large-mode area, Er-doped fiber amplifier.

We demonstrate soliton self-frequency-shifted, femtosecond-pulse amplification in a newly-developed, polarization-maintaining, Er-doped, very-large-mode-area fiber amplifier. The PM-VLMA Er fiber had a core diameter of 50 μm, an effective area of ~1050 μm, and Er absorption of 50 dB/m. The measured birefringence beat length of the PM-VLMA Er fiber was 14.

High energy, 1572.3 nm pulses for CO LIDAR from a polarization-maintaining, very-large-mode-area, Er-doped fiber amplifier.

We demonstrate the first polarization-maintaining, very-large-mode-area, Er-doped fiber amplifier with ~1100 μm effective area. The amplifier is core pumped by a Raman fiber laser and is used to generate single-frequency, one-microsecond, pulses with pulse energy of 541 μJ, peak power of 700 W, M of 1.1, and polarization extinction > 20 dB.

Axicons for mode conversion in high peak power, higher-order mode, fiber amplifiers.

Higher-order mode fiber amplifiers have demonstrated effective areas as large as 6000 μm2, allowing for high pulse energy and peak power amplification. Long-period gratings are used to convert the fundamental mode to the higher-order mode at the entrance to the amplifier, and reconvert back to the fundamental at the exit, to achieve a diffraction limited beam. However, long period gratings are susceptible to nonlinearity at high peak power.

Polarization maintaining single-mode low-loss hollow-core fibres.

Hollow-core fibre (HCF) is a powerful technology platform offering breakthrough performance improvements in sensing, communications, higher-power pulse delivery and other applications. Free from the usual constraints on what materials can guide light, it promises qualitatively new and ideal operating regimes: precision signals transmitted free of nonlinearities, sensors that guide light directly in the samples they are meant to probe and so on. However, these fibres have not been widely adopted, largely because uncontrolled coupling between transverse and polarization modes overshadows their benefits.

Higher-order mode fiber enables high energy chirped-pulse amplification.

Energy scaling of femtosecond fiber lasers has been constrained by nonlinear impairments and optical fiber damage. Reducing the optical irradiance inside the fiber by increasing mode size lowers these effects. Using an erbium-doped higher-order mode fiber with 6000 µm(2) effective area and output fundamental mode re-conversion, we show a breakthrough in pulse energy from a monolithic fiber chirped pulse amplification system using higher-order mode propagation generating 300 µJ pulses with duration <500 fs (FWHM) and peak power >600 MW at 1.

Scaling the effective area of higher-order-mode erbium-doped fiber amplifiers.

We demonstrate scaling of the effective area of higher-order mode, Er-doped fiber amplifiers. Two Er-doped higher-order mode fibers, one with 3800 μm(2) A(eff) in the LP(0,11) mode, and one with 6000 μm(2) effective area in the LP(0,14) mode, are demonstrated. Output beam profiles show clean higher order modes, and S(2) imaging measurements show low extraneous higher order mode content.

Measuring higher-order modes in a low-loss, hollow-core, photonic-bandgap fiber.

We perform detailed measurements of the higher-order-mode content of a low-loss, hollow-core, photonic-bandgap fiber. Mode content is characterized using Spatially and Spectrally resolved (S2) imaging, revealing a variety of phenomena. Discrete mode scattering to core-guided modes are measured at small relative group-delays.

A higher-order-mode erbium-doped-fiber amplifier.

We demonstrate the first erbium-doped fiber amplifier operating in a single, large-mode area, higher-order mode. A high-power, fundamental-mode, Raman fiber laser operating at 1480 nm was used as a pump source. Using a UV-written, long-period grating, both pump and 1564 nm signal were converted to the LP(0,10) mode, which had an effective area of 2700 microm(2) at 1550 nm.

Diffraction limited amplification of picosecond pulses in 1170 microm2 effective area erbium fiber.

Robust fundamental mode propagation and amplification of picosecond pulses at 1.56 microm wavelength is demonstrated in a core-pumped Er fiber with 1170 microm2 effective area. Record peak power exceeding 120 kW, and 67 nJ pulse energy are achieved before the onset of pulse breakup.