Time-division multiplexing of pump wavelengths to achieve ultrabroadband, flat, backward-pumped Raman gain

We describe a simple scheme, which we call the Raman smart pump, to allow for the achievement of flat gain over broad bands with backward-pumped Raman amplification. The proposed method, based on time-division multiplexing, also removes all interaction among the various pump wavelengths and allows for dynamic gain control through simple electronic means.     

Dependence of Gordon-Haus timing jitter on the ratio of the forward and backward pump powers

The Gordon-Haus timing jitter of optical pulses in dispersion-managed communication systems with distributed amplification is studied. The jitter penalty for equal forward and backward pump powers and a pump spacing of 100 km is almost 9 dB lower than the jitter penalty for lumped amplification and an amplifier spacing of 100 km.     

Dynamics of Si-H vibrations in an amorphous environment

We present results of the first vibrational photon-echo, transient-grating, and temperature dependent transient-bleaching experiments on a-Si:H. Using these techniques, and the infrared light of a free electron laser, the vibrational population decay and phase relaxation of the Si-H stretching mode were investigated. Careful analysis of the data indicates that the vibrational energy relaxes directly into Si-H bending modes and Si phonons, with a distribution of rates determined by the amorphous host. Conversely, the pure dephasing appears to be single exponential, and can be modeled by dephasing via two-phonon interactions.     

Optical properties of the In(1) center in KCl

We report both experimental and theoretical studies of the optical properties in KCl of a defect-associated In center whose sole previously identified optical transition was a strong absorption band peaking at 610 nm. With the aid of an optical tagging technique, we have been able to identify with that center two new but much weaker absorption bands peaking at 860 and 960 nm, respectively. We show that the energy splittings, relative strengths, and less perfectly, the polarizations of those three transitions make fit to the In⁰(1) center model, i.e., the model, initially developed for the Tl⁰(1) center, of a neutral atom perturbed by the field of an adjacent anion vacancy. However, in contrast to the Tl⁰(1) center, the In⁰(1) center lacks a significant emission, excluding its use as a laser gain medium.     

Enhanced range for OTDR-like dispersion map measurements

We report on enhancement of the range, reliability, and accuracy of optical-time-domain-reflection- (OTDR-) like measurement of an optical fiber's dispersion map, D(z), through the combined use of Raman gain, an appropriate seed at the four-wave mixing frequency, and a greatly improved algorithm for reduction of the data. In particular, in measurements made from only one end of the fiber, we have demonstrated a range of 75 km in dispersion-shifted fiber and of 22.5 km in high-loss dispersion-compensating fiber.     

Collision-induced time shift of a dispersion-managed soliton and its minimization in wavelength-division-multiplexed transmission

The formula for the time shift of a dispersion-managed soliton that results from its collision with other solitons in different channels consists of two terms, one related to the frequency shift during collision, and the other related to the residual frequency shift after collision. It is found that an optimal relative delay exists between pulses in adjacent channels after each dispersion-managed span that balances the contributions from the two terms and minimizes the overall time shift, leading to a substantial improvement in transmission performance.     

Guiding filters for massive wavelength division multiplexing in soliton transmission

In soliton transmission, third-order dispersion of the transmission fibers tends to cause unacceptable variation in the filter strength parameter eta over the wide wavelength bands required for massive wavelength division multiplexing. We show how to vary the mirror reflectivities of etalon filters with wavelength, such that eta , in soliton units, nevertheless remains at the optimal value across the entire transmission band, and we show how to achieve the required R(lambda) accurately and reproducibly by making the etalons from gratings written in fiber.