Bozena Jaskorzynska

Design of a channel drop filter in a two-dimensional triangular photonic crystal

A design of a channel drop filter in a two-dimensional photonic crystal with a triangular lattice of air holes is presented. The requirement of the accidental degeneracy of the frequency is achieved by tuning the radii of the air holes in the cavity system. In contrast to the other designs proposed, the present one does not involve either inclusion of additional materials or an extra small feature size.

Models and measurements for the transmission of submicron-width waveguide bends defined in two-dimensional photonic crystals

Reference LOEQ-CONF-2001-012View record in Web of Science Record created on 2007-08-31, modified on 2017-05-12

Numerical study on combined stimulated Raman scattering and self-phase modulation in optical fibers influenced by walk-off between pump and Stokes pulses

We numerically examine the dynamics of stimulated Raman scattering combined with self-phase modulation for intense 100-psec-long input pulses in a dispersive single-mode optical fiber. Linear dispersion is treated in a first-order approximation by introducing group-velocity mismatch between pump and Stokes pulses. It is shown how this mismatch combined with pump depletion leads to asymmetric distortions of both pulse shapes and frequency chirps. The resulting delay of the Stokes peak is found to reach higher values for lower input pump powers. For sufficiently long fibers the emerging pump pulse has a one-peak structure, in contrast to the two-peak structure in the dispersionless case. The existence of an optimum fiber length to obtain the shortest Stokes pulse for a given input pulse is shown.

Photonic crystal optical filter based on contra-directional waveguide coupling

Wavelength-selective operation of an optical filter (add/drop) based on a contra-directional photonic crystal waveguide coupler is demonstrated. The waveguides are defined as line defects in a two-dimensional triangular photonic crystal fabricated in an InP/GaInAsP heterostructure. The device is characterized using the end-fire method for the drop functionality. The experimental data are in good agreement with the theoretical results predicted by finite-difference time-domain simulations.

Frequency chirp and spectra due to self-phase modulation and stimulated Raman scattering influenced by pulse walk-off in optical fibers

A numerical study is presented on the frequency chirp and spectra of light pulses affected by both self-phase modulation and stimulated Raman scattering in optical fibers. The asymmetric distortion of pump and Stokes spectra is attributed to walk-off between the pulses and found to be in good agreement with recent experimental results. The stationary-phase method is employed to explain the relation between the structure of the spectra and the form of the pulse chirp. An analytic expression describing the chirp of a depletable pump and of the first Stokes pulse is given for negligible walk-off. The dominant influence of self-phase modulation over the cross phase modulation on the buildup of the chirp in the case of large walk-off and severe pump depletion is shown.

Low-loss InP-based photonic-crystal waveguides etched with Ar/Cl2 chemically assisted ion beam etching

We demonstrate low-loss photonic-crystal (PC) waveguides realized in InP by Ar/Cl2 based chemically assisted ion beam etching. The waveguides are obtained as line defects in a triangular lattice of holes etched through a three-layer InP/GaInAsP/InP heterostructure. By optimizing the etching parameters so that the physical and the chemical components are balanced we succeed in obtaining holes deeper than 2 μm even for a hole diameter as small as 220 nm. The quality of the PCs etched by two different process conditions is compared by using the shape and the position of one of the mode gaps as an assessment tool. The measured transmissions spectra indicate that the PC waveguides etched with an optimized process exhibit losses smaller than 1 dB/100 μm. This is to date the lowest loss value reported for PC waveguides in semiconductor heterostructures at optical communication wavelengths.

Wave propagation through a photonic crystal in a negative phase refractive-index region

The wave propagation through a photonic crystal with a triangular lattice of air holes realized in the InP-InGaAsP heterostructure are studied theoretically for the transverse magnetic modes. The photonic crystal possesses a negative refractive index, and the self-focus of the beam is successfully observed. The weak side beams are observed due to high-order Bloch waves in the photonic crystal. The coupling efficiency for the outgoing waves to a waveguide is also studied.

Modeling and optimization of low-repetition-rate high-energy pulse amplification in cw-pumped erbium-doped fiber amplifiers

We numerically study amplification of low-repetition-rate high-energy pulses in a cw-pumped erbium-doped fiber amplifier. Maximizing the pulse-energy gain by optimization of the dopant and modal field radii resulted in improvements of as much as 7.3 dB with a 60-mW pump compared with a fiber with small radii suitable for amplification of cw signals. Output pulse energies of 0.15 mJ are possible at the same pump power. The improvements stem from a suppression of the losses from amplified spontaneous emission when the radii are made large.

Observation of strongly nonquadratic homogeneous upconversion in Er/sup 3+/-doped silica fibers and reevaluation of the degree of clustering

From careful studies of the 1530-nm fluorescence decay, we obtain the rate of energy transfer upconversion as a function of the inverted population for a series of nine highly Er-doped silica fibers (with concentrations from 0.3 to 8.6/spl middot/10/sup 25/ Er/sup 3+/-ions per m/sup 3/). The results demonstrate that the slow component (microsecond to millisecond scale) of the upconversion, usually referred to as the homogeneous upconversion, is clearly nonquadratic in its dependence on the inverted population, contrary to previous assumptions in the literature. In a second part, we present a new detailed model for energy transfer upconversion, permitting-to our knowledge for the first time-calculation of the rate of migration accelerated upconversion for any given spatial distribution of Er/sup 3+/-ions. We demonstrate that the results from the decay measurements may be explained with this model. Next, we review the results from a CW green fluorescence detection experiment for the determination of the degree of clustering, which was previously performed on five of the nine fibers. We find accordance between these results and our model, with parameters consistent with those needed to fit the results of the decay experiment, and we arrive at a new conclusion about the nature of clustering.

Suppression of the Raman self-frequency shift by cross-phase modulation

The Raman self-frequency shift of ultrashort pulses in dispersive optical fibers can be suppressed by cross-phase modulation from a copropagating pump pulse. In both analytical and numerical analyses, we show that the interaction of group-velocity dispersion, cross-phase modulation, and intrapulse stimulated Raman scattering results in a periodic rather than a progressive self-frequency shift.