Kuniaki Kakihara

Nonreciprocal microresonators for the miniaturization of optical waveguide isolators.

By introducing nonreciprocal phase shifts into microresonators, we propose new designs for the miniaturization of optical waveguide isolators and circulators. We present detailed design procedures, and numerically demonstrate the operation of these magneto-optical devices. The device sizes can be reduced down to several tens of micrometers. The nonreciprocal function of these devices is due to nonreciprocal resonance shifts. Next, the operation bandwidth can be expanded by increasing the number of resonators (the filter order). This is demonstrated by comparing the characteristics of a single-resonator structure with those of a three-resonator structure. This paper furthermore presents the nonreciprocal characteristics of three-dimensional resonators with finite heights, leading to a guideline for the design of nonreciprocal optical circuits. This involves a demonstration of how the resonators with selected parameters are practical for miniaturized nonreciprocal circuits.

Full-vectorial finite element method in a cylindrical coordinate system for loss analysis of photonic wire bends

This paper presents a new full-vectorial finite-element method in a local cylindrical coordinate system, to effectively analyze bending losses in photonic wires. The discretization is performed in the cross section of a three-dimensional curved waveguide, using hybrid edge/nodal elements. The solution region is truncated by anisotropic, perfectly matched layers in the cylindrical coordinate system, to deal properly with leaky modes of the waveguide. This approach is used to evaluate bending losses in silicon wire waveguides. The numerical results of the present approach are compared with results calculated with an equivalent straight waveguide approach and with reported experimental data. These comparisons together demonstrate the validity of the present approach based on the cylindrical coordinate system and also clarifies the limited validity of the equivalent straight waveguide approximation.

Genetic-Algorithm Assisted Design of C-Band CROW-Miniaturized PCW Interleaver

We investigate the design of a miniaturized C-band photonic-crystal waveguide (PCW) interleaver, employing coupled-resonator optical waveguide (CROW) ring resonators. An optimization approach based on a genetic algorithm (GA) has been applied to the filter components, such as tapers and directional couplers, leading to low reflection and high phase linearity. To evaluate the interleaver transmittivity function, an S-matrix approach is worked out, based on the optimized building blocks. A sensitivity analysis is performed to evaluate the effect of parameter tolerances.

Reversed dispersion slope photonic bandgap fibers for broadband dispersion control in femtosecond fiber lasers

Higher-order-mode solid and hollow core photonic bandgap fibers exhibiting reversed or zero dispersion slope over tens or hundreds of nanometer bandwidths within the bandgap are presented. This attractive feature makes them well suited for broadband dispersion control in femtosecond pulse fiber lasers, amplifiers and optical parametric oscillators. The canonical form of the dispersion profile in photonic bandgap fibers is modified by a partial reflector layer/interface placed around the core forming a 2D cylindrical Gires-Tournois type interferometer. This small perturbation in the index profile induces a frequency dependent electric field distribution of the preferred propagating higher-order-mode resulting in a zero or reversed dispersion slope.

Generalized Simple Theory for Estimating Lateral Leakage Loss Behavior in Silicon-on-Insulator Ridge Waveguides

In this paper, we numerically investigate the lateral leakage loss behavior for TM-like modes in silicon-on-insulator ridge wave guides. If the waveguide width is set to satisfy a certain condition, the leakage loss of the TM-like mode leads to be a minimum. When utilizing TM-like modes in the ridge wave guides, it is the main drawback that the tolerance for the variations in the waveguide width and operation wavelength is too small. In this paper, we propose a novel ridge waveguide structure, where a dimple is introduced at the ridge region. It is shown from the finite-element analysis that the ridge waveguide with a dimple is both low loss and fabrication tolerant.

Nonlinearity enhancement and dispersion management in bismuth microstructured fibers with a filled slot defect

We investigate nonlinearity enhancement and dispersion management in microstructured fibers with a slotted-defect infiltrated with highly-nonlinear liquid. Using slot-defected-core bismuth microstructured fibers, gamma as high as 11,000 W-1km-1 and dispersion-flattened characteristics at telecom-band is possible.

Design of Ultra-Small Polarization Splitter Based on Silicon Wire Waveguides

We propose a novel design of ultra-small polarization splitter based on silicon wire waveguides. Numerical simulations show that a 12-μm-long polarization splitter with the extinction ratio better than -20 dB in entire C-band is achievable.

Hollow-core photonic bandgap fibers with broadband negative dispersion slope

Hollow-core photonic bandgap fibers exhibiting negative dispersion slope over a wide wavelength range around one micron for the fundamental air-core mode are presented by the introduction of partial reflector layer around the core.

Impact of structural deformations on polarization conversion in high index contrast waveguides

The objective of this paper is the detailed study of polarization conversion in deformed high index contrast (HIC) waveguides. The type of deformation considered here is the slanted sidewalls of buried channel waveguides. Polarization conversion of HIC waveguides are investigated for possible core refractive indices ranging from 2 (SiN(x)) to 3.5 (Si), by using numerical schemes based on the finite-element and beam propagation methods. The numerical results show that polarization conversion can be greatly magnified in HIC channel waveguides. For example, in Si-wire waveguides, complete polarization conversions can occur within just tens of micrometers.

Design of Ultra-Small Polarization Splitter Based on a Resonant Coupling between Silicon Wire and Slot Waveguides

We propose an ultra-small polarization splitter based on a resonant tunneling phenomenon. Numerical simulations show that a 16-?m-long polarization splitter with extinction ratio better than -20 dB on the entire C-band is achievable.