E-band Nd amplifier based on wavelength selection in an all-solid micro-structured fiber.

A Nd fiber amplifier with gain from 1376 nm to 1466 nm is demonstrated. This is enabled by a wavelength selective waveguide that suppresses amplified spontaneous emission between 850 nm and 1150 nm. It is shown that while excited state absorption (ESA) precludes net gain below 1375 nm with the exception of a small band from 1333 nm to 1350 nm, ESA diminishes steadily beyond 1375 nm allowing for the construction of an efficient fiber amplifier with a gain peak at 1400 nm and the potential for gain from 1375 nm to 1500 nm.

1.2W laser amplification at 1427nm on the F to I spectral line in an Nd doped fused silica optical fiber.

A 9.3dB improvement in optical gain and a 100x improvement in total optical power over prior published experimental results from the F to I transition in an Nd doped fused silica optical fiber is demonstrated. This is enabled via an optical fiber waveguide design that creates high spectral attenuation in the 1050-1120nm-wavelength range, a continuous spectral filter for the primary F to I optical transition.

Scalable waveguide design for three-level operation in Neodymium doped fiber laser.

We have constructed a double clad neodymium doped fiber laser operating on the three-level F→I transition. The laser has produced 11.5 W at 925 nm with 55% slope efficiency when pumped at 808 nm, comparable to the best previous results for a double-clad fiber configuration on this transition.

Patterned flattened modes.

We show that field-flattened strands may be added to and arbitrarily positioned within a field-flattened shell to create patterned, flattened modes. Patterning does not alter the effective index or flatness of the flattened mode but does alter the characteristics of other modes; we show that it can improve a flattened mode's bend performance significantly. Patterning provides a new and potentially valuable waveguide design tool that may lead to higher-power transport and laser fibers.

Widely tunable 11 GHz femtosecond fiber laser based on a nonmode-locked source.

An 11 GHz fiber laser built on a modulated cw platform is described and characterized. This compact, vibration-insensitive, fiber-based system can be operated at wavelengths compatible with high-energy fiber technology, is driven by an RF signal directly, and is tunable over a wide range of drive frequencies. The demonstration system when operated at 1040 nm is capable of 50 ns bursts of 575 micropulses produced at a macropulse rate of 83 kHz where the macropulse and micropulse energies are 1.

Field-flattened, ring-like propagation modes.

We present a method for designing optical fibers that support field-flattened, ring-like higher order modes, and show that the effective and group indices of its modes can be tuned by adjusting the widths of the guide's field-flattened layers or the average index of certain groups of layers. The approach provides a path to fibers that have simultaneously large mode areas and large separations between the propagation constants of their modes.

First selective mode excitation and amplification in a ribbon core optical fiber.

We propose and demonstrate amplification of a single high-order mode in an optical fiber having an elongated, ribbon-like core having an effective mode area of area of 600 µm(2) and an aspect ratio of 13:1. When operated as an amplifier, the double-clad, ytterbium doped, photonic crystal fiber produced 50% slope efficiency and a seed-limited power of 10.5 W, corresponding to a gain of 24 dB.

Mode conversion in rectangular-core optical fibers.

Mode conversion from the fundamental to a higher-order mode in a rectangular-core optical fiber is accomplished by applying pressure with the edge of a flat plate. Modal analysis of the near and far field images of the fiber's transmitted beam determines the purity of the converted mode. Mode conversion reaching 75% of the targeted higher-order mode is achieved using this technique.

High brightness, quantum-defect-limited conversion efficiency in cladding-pumped Raman fiber amplifiers and oscillators.

We present a detailed theoretical investigation of cladding-pumped Raman fiber amplification in an unexplored parameter space of high conversion efficiency (> 60%) and high brightness enhancement (> 1000). Fibers with large clad-to-core diameter ratios can provide a promising means for Raman-based brightness enhancement of diode pump sources. Unfortunately, the diameter ratio cannot be extended indefinitely since the intensity generated in the core can greatly exceed that in the cladding long before the pump is fully depleted.

Brightness enhancement in a high-peak-power cladding-pumped Raman fiber amplifier.

We demonstrate a cladding-pumped Raman fiber amplifier (CPRFA) whose brightness-enhancement factor depends on the cladding-to-core diameter ratio. The pump and the signal are coupled independently into different input arms of a pump-signal combiner, and the output is spliced to the Raman amplifier fiber. The CPRFA generates 20 microJ, 7 ns pulses at 1100 nm at a 2.

High-gain photonic crystal fiber regenerative amplifier.

We have demonstrated a photonic crystal fiber-based regenerative amplifier at 1.078 microm. The input signal pulse energy is 20 pJ in a 12 ns pulse at a 3 kHz repetition rate.

Analysis of the scalability of diffraction-limited fiber lasers and amplifiers to high average power.

We analyze the scalability of diffraction-limited fiber lasers considering thermal, non-linear, damage and pump coupling limits as well as fiber mode field diameter (MFD) restrictions. We derive new general relationships based upon practical considerations. Our analysis shows that if the fiber's MFD could be increased arbitrarily, 36 kW of power could be obtained with diffraction-limited quality from a fiber laser or amplifier.