Honeycomb Photonic Crystal Waveguides in a Suspended Silicon Slab (original) (raw)
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Photonic Crystal Materials and Devices X, 2012
Sub-micron waveguides and cavities have been shown to produce the confinement of elastic and optical waves in the same devices in order to benefit from their interaction. It has been shown that square and honeycomb lattices are the most suitable to produce simultaneous photonic and phononic band gaps on suspended silicon slabs. The introduction of line defects on such "phoxonic" (or optomechanical) crystals should lead to an enhanced interaction between confined light and sound. In this work we report on the experimental measurements of light guiding through waveguides created in these kinds of two-dimensional photonic crystal membranes. The dimensions of the fabricated structures are chosen to provide a "phoxonic" bandgap with a photonic gap around 1550 nm. For both kinds of lattice, we observe a hightransmission band when introducing a linear defect, although it is observed for TM polarization in the honeycomb lattice and for TE in the square. Using the plane-wave expansion and the finite element methods we demonstrate that the guided modes are below the light line and, therefore, without additional losses beside fabrication imperfections. Our results lead us to conclude that waveguides implemented in honeycomb and square lattice "phoxonic" crystals are a very suitable platform to observe an enhanced interaction between propagating photons and phonons.
Design and fabrication of silicon photonic crystal optical waveguides
Journal of Lightwave Technology, 2000
We have designed and fabricated waveguides that incorporate two-dimensional (2-D) photonic crystal geometry for lateral confinement of light, and total internal reflection for vertical confinement. Both square and triangular photonic crystal lattices were analyzed. A three-dimensional (3-D) finite-difference timedomain (FDTD) analysis was used to find design parameters of the photonic crystal and to calculate dispersion relations for the guided modes in the waveguide structure. We have developed a new fabrication technique to define these waveguides into silicon-on-insulator material. The waveguides are suspended in air in order to improve confinement in the vertical direction and symmetry properties of the structure. High-resolution fabrication allowed us to include different types of bends and optical cavities within the waveguides. Index Terms-Finite-difference time-domain (FDTD) methods, nanooptics, optical device fabrication, photonic bandgap (PBG) materials, photonic crystals (PCS), photonic crystal waveguides.
Design and Optimization of a 1.55 µm Waveguide Based on Silicon Planar Photonic Crystals
American Journal of Applied Sciences, 2010
Background: Silicon based Planar Photonic Crystals (PPC) are used for the design of a 1.55 µm waveguide. Line defects are then formed in the PPC structures, by removing rows of holes, to obtain a Planar Photonic Crystal Waveguide (PPCW). Objective: First, we varied the thickness of the Silicon slab and the pore radius in order to obtain optimum design parameters leading to a large and complete bandgap. Next, we present a study of the guided modes in the PPCW for different widths of the waveguide by removing 1, 2 and 3 rows (W1, W2 and W3) of holes from the crystal. Methodology: Band structure calculations were performed using a block-iterative frequency-domain code to find the design parameters of both triangular and square photonic crystal slab lattices of air holes. The frequency domain method for Maxwell's equations in a plane-wave basis was used to calculate the dispersion relations for the guided modes for several widths of the waveguides. Results: The structure with the larger width has a much more complicated dispersion diagram. The most important difference between the three structures (W1, W2 and W3) is that in the case of the wider waveguide, several modes exist at all bandgap frequencies. Conclusion: The structures with a single line defect (W1), there are no leaky modes in the frequency range in which modes become guided. This result indicates that this structure is most preferable.
Silicon-based two-dimensional photonic crystal waveguides
Photonics and Nanostructures-fundamentals and Applications, 2003
A review of the properties of silicon-based two-dimensional (2D) photonic crystals is given, essentially infinite 2D photonic crystals made from macroporous silicon and photonic crystal slabs based on silicon-on-insulator basis. We discuss the bulk photonic crystal properties with particular attention to the light cone and its impact on the band structure. The application for wave guiding is discussed for both material systems, and compared to classical waveguides based on index-guiding. Losses of resonant waveguide modes above the light line are discussed in detail.
Silicon-based photonic crystal slabs: two concepts
IEEE Journal of Quantum Electronics, 2002
We compare theoretically two different concepts of vertical light confinement in two-dimensional (2-D) silicon photonic crystals. Light guidance obtained by variation of the refractive index in an SiO 2 /Si/SiO 2 sandwich structure leads to a complete bandgap for all directions and polarizations with a gap-midgap ratio of about 8.5% and a bandgap for even modes only of about 27%. The complete bandgap is 50% smaller than for 2-D photonic crystals due to the lower confinement of light in the high-index material silicon and polarization mixing. Light guidance obtained by a vertical variation of the porosity, i.e., pore radius, leads under optimum conditions to a bandgap for even modes only, with a gap-midgap ratio of about 10%. The feasibility of such a structure is shown for macroporous silicon where the pore diameter can be varied with depth. In both cases, the optimum slab thickness can be approximated by classical waveguide optics, reducing the parameter space for optimization.
High Quality-Factor 1-D-Suspended Photonic Crystal/Photonic Wire Silicon Waveguide Micro-Cavities
IEEE Photonics Technology Letters, 2009
We have successfully fabricated and characterized suspended one-dimensional (1-D) photonic crystal/photonic wire (PhC/PhW) waveguide micro-cavities based on silicon-on-insulator (SOI). Our experiments have shown an enhancement of the resonance -factor from 18 700 to approximately 24 000, with normalized optical transmission of 70%, after removing the silica cladding underneath the silicon waveguide. We have also demonstrated that, for this condition, the resonance peak wavelength can be controlled by varying the length of the micro-cavity. These results were obtained by removing the silica cladding below the silicon waveguide to produce a "hanging" wire waveguide. The three-dimensional (3-D) finite-difference time domain (FDTD) simulation approach used shows good agreement with measured results.
Band structure of honeycomb photonic crystal slabs
Journal of Applied Physics, 2006
Two-dimensional (2D) honeycomb photonic crystals with cylinders and connecting walls have the potential to have a large full band gap. In experiments, 2D photonic crystals do not have an infinite height, and therefore, we investigate the effects of the thickness of the walls, the height of the slabs and the type of the substrates on the photonic bands and gap maps of 2D honeycomb photonic crystal slabs. The band structures are calculated by the plane wave expansion method and the supercell approach. We find that the slab thickness is a key parameter affecting the band gap size while on the other hand the wall thickness hardly affact the gap size. For symmetric photonic crystal slabs with lower dielectric claddings, the height of the slabs needs to be sufficiently large to maintain a band gap. For asymmetric claddings, the projected band diagrams are similar to that of symmetric slabs as long as the dielectric constants of the claddings do not differ greatly.
3D integration of photonic crystal devices: vertical coupling with a silicon waveguide
Optics Express, 2010
Two integrated devices based on the vertical coupling between a photonic crystal microcavity and a silicon (Si) ridge waveguide are presented in this paper. When the resonator is coupled to a single waveguide, light can be spectrally extracted from the waveguide to free space through the far field emission of the resonator. When the resonator is vertically coupled to two waveguides, a vertical add-drop filter can be realized. The dropping efficiency of these devices relies on a careful design of the resonator. In this paper, we use a Fabry-Perot (FP) microcavity composed of two photonic crystal (PhC) slab mirrors. Thanks to the unique dispersion properties of slow Bloch modes (SBM) at the flat extreme of the dispersion curve, it is possible to design a FP cavity exhibiting two quasidegenerate modes. This specific configuration allows for a coupling efficiency that can theoretically achieve 100%. Using 3D FDTD calculations, we discuss the design of such devices and show that high dropping efficiency can be achieved between the Si waveguides and the PhC microcavity.
Design of waveguides in silicon phoxonic crystal slabs
2010
We consider the problem of designing waveguides in nanostructures presenting simultaneously a phononic and a photonic band gap. We specifically opt for designs in perforated silicon membranes that can be conveniently obtained using silicon-on-insulator technology. Geometrical parameters for simultaneous photonic and phononic band gaps are first chosen, based on the finite element analysis of a perfect phoxonic crystal of circular holes. A plain core waveguide is then defined, and simultaneous slow light and elastic guided modes are identified. Joint confinement of light and elastic waves with group velocities reduced by a factor of approximately 30 is predicted.
Design and optimization of 2D photonic crystal waveguides based on silicon
The existence and properties of photonic band gaps was investigated for a square lattice of dielectric cylinders in air. Band structure calculations were performed using the transfer matrix method as function of the dielectric constant of the cylinders and the cylinder radius-to-pitch ratio r/a. It was found that band gaps exist only for transverse magnetic polarization for a dielectric contrast larger then 3.8 (index contrast >1.95). The optimum r/a ratio is 0.25 for the smallest index contrast. For silicon cylinders (n = 3.45) the widest gap is observed for r/a = 0.18. Band structure calculations as function of r/a show that up to four gaps open for the silicon structure. The effective index was obtained from the band structure calculations and compared with Maxwell–Garnett effective medium theory. Using the band structure calculations we obtained design parameters for silicon based photonic crystal waveguides. The possibility and limitations of amorphous silicon,silicon germanium and silicon-on-insulator structures to achieve index guiding in the third dimension is discussed.