Alongkarn Chutinan

Trapping and emission of photons by a single defect in a photonic bandgap structure

By introducing artificial defects and/or light-emitters into photonic bandgap structures, it should be possible to manipulate photons. For example, it has been predicted that strong localization (or trapping) of photons should occur in structures with single defects, and that the propagation of photons should be controllable using arrays of defects. But there has been little experimental progress in this regard, with the exception of a laser based on a single-defect photonic crystal. Here we demonstrate photon trapping by a single defect that has been created artificially inside a two-dimensional photonic bandgap structure. Photons propagating through a linear waveguide are trapped by the defect, which then emits them to free space. We envisage that this phenomenon may be used in ultra-small optical devices whose function is to selectively drop (or add) photons with various energies from (or to) optical communication traffic. More generally, our work should facilitate the development of all-optical circuits incorporating photonic bandgap waveguides and resonators.

Coherent two-dimensional lasing action in surface-emitting laser with triangular-lattice photonic crystal structure

Lasing action of a surface-emitting laser with a two-dimensional photonic crystal structure is investigated. The photonic crystal has a triangular-lattice structure composed of InP and air holes, which is integrated with an InGaAsP/InP multiple-quantum-well active layer by a wafer fusion technique. Uniform two-dimensional lasing oscillation based on the coupling of light propagating in six equivalent Γ−X directions is successfully observed, where the wavelength of the active layer is designed to match the folded (second-order) Γ point of the Γ−X direction. The very narrow divergence angle of far field pattern and/or the lasing spectrum, which is considered to reflect the two-dimensional stop band, also indicate that the lasing oscillation occurs coherently.

Highly confined waveguides and waveguide bends in three-dimensional photonic crystal

We demonstrate a method to create a highly confined waveguide with sharp bend in three-dimensional photonic crystal. By theoretical calculation, we show that a single-mode waveguide can be created in the stacked-bar structure by removing one stripe. Crossing waveguides of the adjacent layers can create the waveguide bend and by this way, the guided modes after and before the bend remain the same so that the transmission through the bend is optimized. These results provide very important guidelines for designing a three-dimensional photonic crystal waveguide.

Wider bandwidth with high transmission through waveguide bends in two-dimensional photonic crystal slabs

We demonstrate the use of a defect to improve the transmission property of waveguide bends in two-dimensional photonic crystal slabs. We show that high reflection in the two-dimensional photonic crystal slab previously reported is due to the fact that the waveguide is multimoded at the bend while it is single moded along the straight waveguide. By making the waveguide single moded at the bend, the transmission property can be significantly improved. An extension of more than twice of high-transmission bandwidth is achieved.

Surface-emitting channel drop filters using single defects in two-dimensional photonic crystal slabs

We report a theoretical analysis of trapping and emission of photons by a single defect in a two-dimensional photonic crystal slab. We show that the tuning of emission wavelength is possible by selecting appropriate geometry of structure while keeping the emission efficiency maximal. The results suggest the possibility of applying it to ultra-small channel add/drop device in wavelength division multiplexed optical communications.

High-efficiency photonic crystal solar cell architecture

Thin silicon solar cells suffer from low light absorption compared to their thick counterparts, especially in the near infra-red regime. In order to obtain high energy conversion efficiency in thin solar cells, an efficient light trapping scheme is required. In this paper, we theoretically demonstrate significant enhancement in efficiency of thin crystalline silicon solar cells by using photonic crystals as the light absorbing layer. In particular, a relative increase of 11.15% and 3.87% in the energy conversion efficiency compared to the optimized conventional design is achieved for 2 microm and 10 microm thicknesses, respectively.

Channel drop filter using a single defect in a 2-D photonic crystal slab waveguide

This paper describes a theoretical and experimental analysis of the channel drop filter using a single defect formed near the two-dimensional (2-D) photonic crystal slab waveguide. First, we calculate the transmission spectrum of a 2-D photonic crystal waveguide and show that high transmittance for a wide wavelength range (/spl sim/60 nm) is obtained in the 1.55-/spl mu/m region. We also show that a defect state having a wavelength within the high transmission wavelength range can be formed in the photonic bandgap by introducing a single defect of appropriate radius. Next, we fabricate several devices and show that the emission wavelength from each defect can be tuned by changing the defect radius. The measured tuning characteristics coincide well with the calculated results. From the near-field pattern of the device, we estimate the emission efficiency of the present device at almost a few tens percent. We clarify the structural condition in order to obtain the maximum output efficiency and show that tuning of emission wavelength while maintaining high output efficiency is possible by selecting appropriate defect radius and position. Based on these results, we propose an ultrasmall channel drop filter for a wavelength-division-multiplex optical communication system.

Semiconductor three-dimensional and two-dimensional photonic crystals and devices

Semiconductor three-dimensional (3-D) and two-dimensional (2-D) photonic crystals and their effects on the control of photons are investigated for possible applications to optical chip and functional devices. First we review our approaches creating full 3-D photonic bandgap crystals at near-infrared wavelengths, and also functional devices based on 2-D photonic crystals where the focus is on surface-emitting-type channel-drop filtering devices utilizing single defects in 2-D photonic crystal slabs. Then, we describe the recent progress on 3- and 2-D crystals. On 3-D crystals, the effect of the introduction of a light emitter into the 3-D photonic crystal is investigated, and the design of a single defect cavity is performed. On the 2-D photonic crystals, the photonic states are investigated from the perspective of their polarization properties.

Development of One Period of a Three-Dimensional Photonic Crystal in the 5–10 µm Wavelength Region by Wafer Fusion and Laser Beam Diffraction Pattern Observation Techniques

One period of a three-dimensional photonic crystal operating in the 5~10-µm-wavelength region is developed, where four layers having a striped pattern are stacked using a wafer fusion and the alignment method based on a laser beam diffraction pattern observation technique. By measuring the transmission spectrum, considerable attenuation (of about 16 dB) is successfully achieved and is in good agreement with the theoretical calculation.

Selectively Transparent and Conducting Photonic Crystals

[*] Prof. N. P. Kherani, Dr. A. Chutinan The Edward S. Rogers Sr. Department of Electrical and Computer Engineering University of Toronto 10 King’s College Road, Room GB254B Toronto, ON M5S 3G4 (Canada) E-mail: kherani@ecf.utoronto.ca Prof. G. A. Ozin, D. P. Puzzo, L. D. Bonifacio Materials Chemistry Research Group, Department of Chemistry University of Toronto 80 St. George Street, Toronto, ON M5S 3H6 (Canada) E-mail: gozin@chem.utoronto.ca P. G. O’Brien Department of Materials Science and Engineering University of Toronto 184 College Street Room 140, Toronto, ON M5S 3E4 (Canada)