Jake Bromage

Raman amplification for fiber communications systems

Raman amplification has enabled dramatic increases in the reach and capacity of lightwave systems. This tutorial explains why, focusing on amplifier design options, sources of noise in Raman amplifiers, and novel pumping schemes.

Design of bidirectionally pumped fiber amplifiers generating double Rayleigh backscattering

Optimum pumping schemes for bidirectionally pumped distributed fiber amplifiers are evaluated that simultaneously minimize the beat noise between signal and amplified spontaneous emission, as well as between signal and double Rayleigh backscattering. A way of adding a constraint on signal power to describe operation in a strong Kerr fiber nonlinearity regime is included. We show that one can find an optimum Raman net gain, as well as a percentage of forward to total Raman pumping maximizing the signal-to-noise ratio at the end of a transmission line using bidirectionally Raman-pumped transmission fibers.

Real-time SPIDER: ultrashort pulse characterization at 20 Hz

We present an implementation of spectral phase interferometry for direct electric-field reconstruction (SPIDER) which characterizes ultrashort optical pulses in the spectral or temporal domain at a rate of 20 Hz. This apparatus was used in real-time as a diagnostic tool to optimize our 1 kHz regeneratively amplified laser system for the shortest duration pulses.

S-band erbium-doped fiber amplifiers for WDM transmission between 1488 and 1508 nm

We evaluated S-band Er:Al/Ge/SiO/sub 2/ fiber amplifiers with a /spl sim/1525-nm fundamental-mode cutoff to suppress C-band ASE. In all-EDFA transmission tests, they produced no penalties aside from expected OSNR impairment, demonstrating suitability of S-band EDFAs for WDM transmission.

OMEGA EP high-energy petawatt laser: progress and prospects

OMEGA EP (extended performance) is a petawatt-class addition to the existing 30-kJ, 60-beam OMEGA Laser Facility at the University of Rochester. It will enable high-energy picosecond backlighting of high-energy-density experiments and inertial confinement fusion implosions, the investigation of advanced-ignition experiments such as fast ignition, and the exploration of high-energy-density phenomena. The OMEGA EP short-pulse beams have the flexibility to be directed to either the existing OMEGA target chamber, or the new, auxiliary OMEGA EP target chamber for independent experiments. This paper will detail progress made towards activation, which is on schedule for completion in April 2008.

High-dynamic-range single-shot cross-correlator based on an optical pulse replicator

The operation of a single-shot cross-correlator based on a pulse replicator is described. The correlator uses a discrete sequence of sampling pulses that are nonlinearly mixed with the pulse under test. The combination of a high reflector and partial reflector replicates an optical pulse by multiple internal reflections and generates a sequence of spatially displaced and temporally delayed sampling pulses. This principle is used in a cross-correlator characterizing optical pulses at 1053 nm. A dynamic range higher than 60 dB is obtained over a temporal range larger than 200 ps.

Dual-order Raman pump

This letter presents the design of a dual-order Raman fiber laser to be used as a pump for distributed Raman amplification. In particular, noise figure, gain ripple, and tunability are measured and analyzed in comparison to first-order Raman amplification. The tradeoff between noise figure improvement and increased nonlinear penalty is also discussed.

Highly sensitive, single-shot characterization for pulse widths from 0.4 to 85 ps using electro-optic shearing interferometry

Single-shot characterization using electro-optic shearing interferometry (EOSI) is shown for pulse widths ranging from their transform limit (0.4 ps) to 200x their limit (85 ps). In EOSI, the spectral phase is reconstructed by interfering two spectrally sheared replicas of the pulse under test, where the shear is produced by applying linear temporal-phase modulation. We present a new reconstruction algorithm for accurately characterizing chirped pulses, even if the pulse extends beyond the linear region of the phase modulation. Furthermore, since EOSI does not rely on nonlinear optical processes, it requires only 1 nJ pulse energies for all pulse widths, corresponding to a single-shot sensitivity 1000x higher than previously demonstrated.

Analysis and suppression of parasitic processes in noncollinear optical parametric amplifiers

The influence of parasitic processes on the performance of ultra-broadband noncollinear optical parametric amplifiers (NOPAs) is investigated for walk-off and non-walk-off compensating configurations. Experimental results with a white-light-seeded NOPA agree well with numerical simulations. The same model shows that 10% of the output energy of an amplified signal can be transferred into a parasitic second harmonic of the signal. These findings are supported by quantitative measurements on a few-cycle NOPA, where a few percent of the signal energy is converted to its second harmonic in the walk-off compensating case. This effect is reduced by an order of magnitude in the non-walk-off compensating configuration. A detailed study of the phase-matching conditions of the most common nonlinear crystals provides guidelines for designing NOPA systems.

Amplified spontaneous emission in pulse-pumped Raman amplifiers

We discuss amplified spontaneous emission (ASE) generated in Raman amplifiers that are counter-pumped with trains of pulses. Our experimental and theoretical results show that if the peak power of the pump pulses is too high, the ASE output from the amplifier can be significantly higher than that from a continuous-wave pumped amplifier providing the same gain. This effect places a lower limit on the duty cycle of pump pulses one can use for a given level of Raman gain. Furthermore, we report an additional ASE enhancement if there is insufficient walkoff between the pump pulses and copropagating ASE to average the effects of higher frequency pump intensity noise. As a result, less pump intensity noise can be tolerated when pulse-pumping a fiber having a zero-dispersion wavelength located midway between the pump and signal wavelengths.