Pump-probe measurement of metastable state lifetime reduced by cooperative upconversion in a high-concentration erbium-doped fiber.

We report measurements of the metastable state lifetime in a high-concentration erbium-doped fiber. We use a single-wavelength pump-probe technique that allows us to measure the average lifetime over the entire fiber length. A reduction in the lifetime of approximately 20% caused by a cooperative upconversion effect is clearly observed when the input power is increased up to 10 mW.

Recovery of population inversion in an erbium-doped fiber amplifier observed by temporally resolving amplified spontaneous emissions.

We report on the recovery of population inversion in a CW-pumped erbium-doped fiber amplifier. Spontaneous emissions after the input of signal pulses were temporally resolved. The recovery time for population inversion was estimated to be a few hundred microseconds.

Effective permittivities with exact second-order accuracy at inclined dielectric interface for the two-dimensional finite-difference time-domain method.

Accuracy degradation at a dielectric interface in simulations using the finite-difference time-domain method can be prevented by assigning suitable effective permittivities at the nodes in the vicinity of the interface. The effective permittivities with exact second-order accuracy at the interface inclined to the Yee-lattice axis are analytically derived for what we believe to be the first time. We discuss two interfaces with different inclined angles between their normal and the Yee-lattice axis in the case of two-dimensional TE polarization.

Accurate modeling of dielectric interfaces by the effective permittivities for the fourth-order symplectic finite-difference time-domain method.

The fourth-order finite-difference time-domain (FDTD) method using a symplectic integrator propagator can calculate the propagation of the electromagnetic waves with very low dispersion error in the region of a constant or smoothly varying index profile. An additional technique is required for the problem with the discontinuous dielectric interfaces. We derived the third-order effective permittivities at dielectric interfaces for the fourth-order FDTD method in the case of 2D TE polarization.

Analysis and demonstration of single-passband response and tuning characteristics in a chirped ladder interferometric filter for a widely tunable laser diode.

We have designed and demonstrated a chirped ladder-type tunable filter and discussed its potential application for a tunable diode laser. A ladder interferometric filter normally has a periodic passband, which makes it impossible to stabilize laser oscillation frequency. To overcome this drawback, we have designed, fabricated, and characterized a novel chirped tunable ladder filter.