Photonic crystal tapers for ultracompact mode conversion.
ABSTRACT We have studied the coupling of a classic ridge waveguide with a two-dimensional photonic crystal (PC) waveguide, using finite-difference time-domain calculations. The ridge waveguide exhibits only a weak refractive-index confinement of light, as it is commonly used in buried-heterostructure or ridge-waveguide lasers. The light is coupled to a PC waveguide that consists of one missing row along the ?K direction in a triangular lattice of air cylinders in AlGaAs. We compare various designs for PC tapers with that of a classic taper and for butt coupling. The calculation yields high coupling efficiency that exceeds 80% for a 2.5-microm-long PC taper. In addition, the dependence of the efficiency on the PC air-fill factor and on alignment tolerances is analyzed.
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ABSTRACT: We design an extremely compact photonic crystal waveguide spatial mode converter which converts the fundamental even mode to the higher order odd mode with nearly 100% efficiency. We adapt a previously developed design and optimization process that allows these types of devices to be designed in a matter of minutes. We also present an extremely compact optical diode device and clarify its general properties and its relation to spatial mode converters. Finally, we connect the results here to a general theory on the complexity of optical designs.Optics Express 12/2012; 20(27):28388-97. · 3.55 Impact Factor
Article: Nanophotonic computational design.[Show abstract] [Hide abstract]
ABSTRACT: In contrast to designing nanophotonic devices by tuning a handful of device parameters, we have developed a computational method which utilizes the full parameter space to design linear nanophotonic devices. We show that our method may indeed be capable of designing any linear nanophotonic device by demonstrating designed structures which are fully three-dimensional and multi-modal, exhibit novel functionality, have very compact footprints, exhibit high efficiency, and are manufacturable. In addition, we also demonstrate the ability to produce structures which are strongly robust to wavelength and temperature shift, as well as fabrication error. Critically, we show that our method does not require the user to be a nanophotonic expert or to perform any manual tuning. Instead, we are able to design devices solely based on the user's desired performance specification for the device.Optics Express 06/2013; 21(11):13351-67. · 3.55 Impact Factor
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ABSTRACT: The mode-order conversion characteristics of a heterostructure formed by regular photonic crystals (PCs) with high symmetry and PCs with low symmetry are analyzed numerically. The working principle of the proposed mode-order converter is based on the phase retardation of the incident beam while propagating through the PC heterostructure. This type of phase delay arises from the effective refractive index difference between the symmetrical PC and the asymmetric PC, called a modified annular PC (MAPC), at the specified frequency regimes a/λ=0.281–0.34. Further optimizations that are carried out improve the mode-order conversion bandwidth, reaching up to 24%. By means of such a novel-type configuration, a propagating fundamental mode can be transformed into higher-order modes at the output with adequate transmission efficiency.Journal of the Optical Society of America B 11/2013; 30(11):3086-. · 2.21 Impact Factor