G. R. Williams

Continuous-wave ultraviolet laser action in strongly scattering Nd-doped alumina

We report electrically pumped, cw laser action near 405 nm from Nd(3+) -doped delta -alumina nanopowders. To our knowledge, this is the first report of stimulated emission from the high-lying F(2) -excited states, achieved through feedback from strong elastic scattering of light over transport path lengths shorter than half a wavelength.

Soliton logic gate using low-birefringence fiber in a nonlinear loop mirror

We demonstrate, using numerical simulations, a new all-optical logic gate that combines the mechanisms of soliton dragging and nonlinear-optical loop mirrors (NOLM’s). The design uses specially wrapped low-birefringence polarization-maintaining fiber, which we recently demonstrated in the NOLM configuration. Combining the soliton dragging and NOLM effects increases the timing window of the gate, and using the low-birefringence fiber minimizes the number of cross splices required. For example, we show that by using only one cross splice we can achieve a switching energy of 5.3 pJ and a total timing window of 3.3 pulse widths. We also present a set of design rules for our low-birefringence NOLM.

Experimental cascaded operation of low-birefringence nonlinear-optical loop mirrors

We experimentally demonstrate the operation of a low-birefringence (low-bi) nonlinear-optical loop mirror (NOLM) that has the advantages of low switching energy, tolerance to timing jitter, and cascadability. Because cascading two all-optical logic gates is an important step toward high-speed optical signal processing and header processing in time-division-multiplexed networks, we also demonstrate the cascaded operation of two low-bi NOLMs. Using a passively mode-locked fiber laser that produces 450-fs pulses at a wavelength of 1.55 microm, we achieve a 10.7:1 switching contrast ratio and a 2.7-pulse-widths-wide timing window after the cascaded gates. The results agree well with theoretical predictions and confirm the advantages of the long interaction length associated with orthogonally polarized pulses in low-bi (Deltan ~ 3.0 x 10(-6)) polarization-maintaining fiber.

Experimental demonstration of a low-latency fiber soliton logic gate

We experimentally demonstrate switching in a 50 m-long soliton logic gate with a switching energy of 40 pJ using 490 fs pulses at 1.553 /spl mu/m from an erbium-doped fiber laser. A full characterization of this gate shows a peak contrast ratio of 4.2:1, a timing window of 1.1 pulse width and cascadable operation. To our knowledge, the gate length of 50 m is at least six times shorter than other designs with comparable switching energies. The low-latency of this gate is possible due to a low-birefringent polarization-maintaining fiber that possesses a high polarization extinction ratio of up to 20 dB with a low birefringence of 2.6/spl times/10/sup -6/. The low birefringence leads to a longer walk-off length between two orthogonally polarized pulses, where the walk-off length for 490 fs pulses is 56 m. We also study this gate numerically and find good agreement between the simulations and experiments.