We successfully fabricated an Nd-doped photonic bandgap (PBG) fiber preform that consists of two different pitch sizes. A 500-mu m thick glass capillary is inserted between the larger-pitched core and the smaller-pitched clad to stabilize the preform structure. The resulting fiber's optical performance was measured and verified. This nested stacking route significantly extends PBG fiber core and clad material choices by decoupling the size constraint between the two.

We successfully fabricated a dispersion-shifted 20-um-core LMA fiber by incorporating four resonant side cores. This fiber was designed to operate at 1640-nm eye-safe wavelength and has been used in a pulsed Raman amplifier to overcome modulational instability. A peak power of 100-kW was obtained from the Raman amplifier.

We successfully fabricated a 40-μm core LMA fiber with distributed <40-nm-passband bandpass filter. The stopband is over 300 nm wide with >30 dB/m average suppression. Output M2 is 1.15 at a coil diameter of 25 cm.

We successfully demonstrate Raman combination of fiber lasers in the 1.55-μm regime at the 100-W average power level. We achieved diffraction-limited 4.5-mJ, 2-ns pulses at 20 kHz PRF.

Building on previous work, we have designed a Nd doped fiber for E-band amplification. Modeling results indicate a fiber design that is applicable to telecom amplifiers.

To analyze recent experiments with a neodymium-doped fiber amplifier operating in the E-band of wavelengths (1350-1450 nm) and embedded in fused silica, we develop a time-dependent model consisting of rate equations for the aggregate ion populations and the radiation intensities along the amplifier axis. Both copropagating and counterpropagating intensities, including amplified spontaneous emission, are incorporated. The wavelength-dependent cross section for excited state absorption is inferred from auxiliary measurements. Steady-state solutions are obtained over a range of seed wavelengths and powers. The resulting gain curves agree with experiment at low to intermediate powers (less than ∼1  mW). With a proposed addition to the system loss, the agreement extends to saturation (∼100  mW).

We have temporally combined 25 equal-amplitude pulses using four cavities, stabilizing cavity round-trip phase by measuring the response to a probe pulse train. Energy enhancement of 18.4 is maintained within 1% RMS.