Band Gaps In Two-dimensional Photonic Crystals Research Articles

Evolution of the complete photonic bandgap of two-dimensional photonic crystal

In this paper, the complete photonic bandgap (CPBG) of two-dimensional photonic crystals (PCs), which are formed by a square array of solid or hollow dielectric rods connected with dielectric veins, are numerically investigated using the plane wave expansion method. It is clearly demonstrated how the CPBG evolves as the pattern of veins or the type of rods changes. An optimal structure with an ultralarge CPBG is found, whose CPBG reaches Δω=0.22374 (2πc/a), which is larger than those reported in literatures. The proposed structure seems to have promising applications due to its ultralarge CPBG and large fabrication tolerance.

Hollow-core resonator based on out-of-plane two-dimensional photonic band-gap crystal cladding at microwave frequencies

We report on the demonstration of a resonator based on electromagnetic field confinement in a hollow-core by implementing an out-of-plane two-dimensional (2D) photonic band-gap (PBG) crystal cladding. In contrast with in-plane 2D PBG crystal devices, the PBG crystal studied here is perpendicular to the propagation axis. A resonator was constructed with silica rods to prove the concept at frequencies around 30 GHz. We show that the technique has the potential to reach quality factors (Q) of 5×105.

Band gap characteristics of two-dimensional photonic crystals made of a triangular lattice of dielectric rods

Plane wave expansion method is applied to simulate the bandgap of two-dimensional photonic crystals made of a triangular lattice of dielectric rods(circular,hexagon,square cross sections) in air. Moreover, the effect on band gap of a triangular lattice of square dielectric rods in air is discussed as a function of the rotation angle, the refractive index and the filling fraction, respectively. In the low frequency region, the maximum complete photonic band gap appears when the rotation angle equals 17 degrees. the maximum complete photonic band gap can be attained steadily as the refractive index changes continuously. In the high frequency region, the maximum complete photonic band gap appears when the rotation angle equals 30 degrees. The complete photonic band gap is observed when the refractive index is greater than 2.2. The width of complete photonic band gap reaches the maximum when the dielectric refractive index is equal to 2.6.

Nanometer-scale photonic passive and active components for future communications

The advancement of enabling photonic components developed for fiber-optic communication systems began nearly forty years ago while advantages of using light-wave communication in computing systems have been discussed for several decades. Following the history of microelectronics, the size of required photonic components for future communication systems will certainly need to be scaled down dramatically along a route of exploring higher system performance. The concept of photonic bandgap crystals has been around more than two decades. A line-defect within a two-dimensional photonic bandgap crystal provides efficient spatial confinement of light, which is a building block of a variety of routing and processing schemes of light. In contrast, silicon in the form of complementary metal semiconductor oxide (CMOS) platform has been a core in microelectronics. Silicon nanophotonics that allow CMOS platforms to handle light, thus, would offer a wide range of photonic functions that are required for CMOS platforms to further progress. While the photonic bandgap crystal and silicon nanophotonics are still subject to the diffraction limit of light, photonic devices that use surface plasmon polaritons and / or energy transfer mechanisms relying upon optical near-field interactions would pave the road toward ultimate photonic integration beyond the diffraction limit of light.

Variation of group velocity and complete bandgaps in two-dimensional photonic crystals with drilling holes into the dielectric rods

Two-dimensional square lattices of square cross-section dielectric rods in air, designed with an air hole drilled into each square rod, are studied theoretically. By adjusting the shift of the hole position in the square rod in each unit cell, the dielectric distribution of the square rod will be modified. A sizable complete band gap occurs for certain structural parameters and exhibits very flat photonic bands near such gap edge, which resulting in a sharp peak of density of states. In addition, the zero or small group velocities are observed in a broad region of k-space. This structure can be fabricated with materials widely used today and opens a fascinating area for applications in optoelectric devices.

High resolution and aspect ratio two-dimensional photonic band-gap crystal

This paper reports the challenges resolved to realize high aspect ratio pillar-type two-dimensional photonic band-gap crystal (PhC), designed for application at the optical communication wavelengths. Specifically, the issue of a drastically reduced process window of deep UV lithography and deep reactive ion etching, for a super dense array of submicron size pillars with a diameter of 230nm and a spacing of 340nm is treated. A rigorous design of experiments yielded high-resolution PhCs with precise lattice dimensions even near regions of “defect structures” designed for device operations. At the same time, in the etching process, the stringent requirement of an etch angle needed for successful realization of such a super dense array of submicron size PhC lattice was also satisfied to yield sidewalls of high verticality, aspect ratios greater than 50, and scallop-depths of 12nm.

Rapid photon flux switching in two-dimensional photonic crystals

We have investigated the out-of-plane propagation of light in two-dimensional photonic band-gap crystals consisting of long dielectric nanorods. Defects, which sufficiently break the crystal symmetry, can produce photonic states localized at the defect sites. We show that this localization can result in a sharp transition between the state of the out-of-plane light propagation through the entire photonic crystal, and the state in which light propagates only along the defect channels. This switching can be induced by slight changes of the dielectric constant at the defect sites. We propose a practical way of achieving this, and suggest applications.

Experimental observation of superluminal group velocities in bulk two-dimensional photonic bandgap crystals

The authors have experimentally observed superluminal, negative, and infinite group velocities in bulk hexagonal two-dimensional photonic bandgap crystals with bandgaps in the microwave region. The group velocities depend on the polarization of the incident radiation and the air-filling fraction of the crystal.

Strain-tunable photonic band gap crystals

We have designed a two-dimensional strain-tunable photonic band gap crystal by distorting the symmetry of the crystal from a regular hexagonal to a quasihexagonal lattice by means of field driven strain using a piezoelectric material. Calculations predict that the original high symmetry energy bands split up into several strained energy bands depending on the magnitude and direction of the strain. In the proposed structures, we show that 2% (3%) shear strain can be used to tune ∼52% (73%) of the original undistorted absolute band gap of a two-dimensional photonic band gap crystal. These device structures can be used for optical switching and modulation.

Near-infrared microcavities confined by two-dimensional photonic bandgap crystals

Measurements are presented of hexagonal cavities confined by 2D photonic bandgap boundaries etched in an AlGaAs laser-like waveguide heterostructure. The nominal cavity volumes vary between 0.6 and 1.9 /spl mu/m/sup 3/. The photoluminescence of quantum dots embedded in the heterostructure directly probes the cavity horizontal modes and resonances and quality factors of Q/spl sime/1000 are observed.

Photonic band gap guidance in optical fibers

A fundamentally different type of optical waveguide structure is demonstrated, in which light is confined to the vicinity of a low-index region by a two-dimensional photonic band gap crystal. The waveguide consists of an extra air hole in an otherwise regular honeycomb pattern of holes running down the length of a fine silica glass fiber. Optical fibers based on this waveguide mechanism support guided modes with extraordinary properties.