2D Silicon Photonic Crystals Research Articles

Targeted Positioning of Quantum Dots Inside 3D Silicon Photonic Crystals Revealed by Synchrotron X-ray Fluorescence Tomography.

It is a major outstanding goal in nanotechnology to precisely position functional nanoparticles, such as quantum dots, inside a three-dimensional (3D) nanostructure in order to realize innovative functions. Once the 3D positioning is performed, the challenge arises how to nondestructively verify where the nanoparticles reside in the 3D nanostructure. Here, we study 3D photonic band gap crystals made of Si that are infiltrated with PbS nanocrystal quantum dots. The nanocrystals are covalently bonded to polymer brush layers that are grafted to the Si–air interfaces inside the 3D nanostructure using surface-initiated atom transfer radical polymerization (SI-ATRP). The functionalized 3D nanostructures are probed by synchrotron X-ray fluorescence (SXRF) tomography that is performed at 17 keV photon energy to obtain large penetration depths and efficient excitation of the elements of interest. Spatial projection maps were obtained followed by tomographic reconstruction to obtain the 3D atom density distribution with 50 nm voxel size for all chemical elements probed: Cl, Cr, Cu, Ga, Br, and Pb. The quantum dots are found to be positioned inside the 3D nanostructure, and their positions correlate with the positions of elements characteristic of the polymer brush layer and the ATRP initiator. We conclude that X-ray fluorescence tomography is very well suited to nondestructively characterize 3D nanomaterials with photonic and other functionalities.

Frequency modulated hybrid photonic crystal laser by thermal tuning.

We demonstrate frequency modulation (FM) in an external cavity (EC) III-V/silicon laser, comprising a reflective semiconductor optical amplifier (RSOA) and a silicon nitride (SiN) waveguide vertically coupled to a 2D silicon photonic crystal (PhC) cavity. The PhC cavity acts as a tunable narrowband reflector giving wavelength selectivity. The FM was achieved by thermo-optical modulation of the reflector via a p-n junction. Single-mode operation was ensured by the short cavity length, overlapping only one longitudinal laser mode with the reflector. We investigate the effect of reflector modulation theoretically and experimentally and predict a substantial tracking of the resonator by the laser frequency with very small intensity modulation (IM).

High resolution wide range pressure sensor using hexagonal ring and micromachined cantilever tips on 2D silicon photonic crystal

Abstract Design of a pressure sensor workable from megapascal (MPa) to gigapascal (GPa) pressure range is proposed on a two dimensional triangular/hexagonal lattice silicon (Si) photonic crystal (PhC) arrangement. In order to ensure high resolution sensing over this wide pressure range, a hexagonal shaped ring of hexagonal unit cells and two micromachined silicon cantilever tips are considered on the photonic crystal arrangement. The concept of using micromachined cantilever tip in a PhC arrangement for optical sensing of pressure is novel. Moreover, use of hexagonal ring with hexagonal unit cells make the structure more sensitivity than other types of ring arrangement. It is shown that the two silicon cantilever tips can be used to detect applied pressure from 1 MPa to 10 MPa with resolution of 1 MPa and 10 MPa to 100 MPa with a resolution of 10 MPa, respectively. Detection of applied pressure from 20 MPa to 10 GPa with the resolution of 20 MPa can be done using the hexagonal ring of hexagonal unit cells. The entire design is done using the MPB (MIT Photonic Bands) and MEEP (MIT Electromagnetic Equation Propagation) simulators freely available from MIT, USA.

Fabrication of 3D Photonic Crystals toward Arbitrary Manipulation of Photons in Three Dimensions

The creation of large-area, unintentional-defect-free three-dimensional (3D) photonic crystals in the optical regime is a key challenge toward the realization of the arbitrary 3D manipulation of photons. In this article, we discuss an advanced fabrication method of 3D silicon photonic crystals based on the highly accurate alignment and wafer bonding of silicon-on-insulator (SOI) wafers. We introduce an advanced alignment system, in which the alignment process is automated by image recognition and feed-back control of stages, and show that it achieves an alignment accuracy better than ~50 nm. The bonding of SOI wafers is also investigated to obtain 3D crystals composed of highly pure crystalline silicon. We show the fabrication results of large-area 3D photonic crystals based on such considerations and demonstrate the successful introduction of artificial defects as functional components, such as coupled waveguide pairs or waveguides/nanocavities. We expect that these will be pioneering results toward the arbitrary 3D control of photons using 3D photonic crystals.

Silicon and porous silicon mid-infrared photonic crystals

A 3D silicon micromachining method based on proton beam writing combined with electrochemical anodization of p-type silicon enables fabrication of mid-infrared photonic crystals made of silicon and porous silicon. Here, example structures of silicon 1D and 2D photonic crystals are demonstrated. Progress and problems of fabricating 3D photonic crystals made of silicon are discussed. The strategy of fabricating photonic crystals purely made of porous silicon, and the characterization method of all these mid-infrared structures, are discussed. Due to the flexibility of this fabrication method, photonic devices and integrated photonic circuits may be built on a single chip, for which two 2D silicon photonic crystals with one on top of the other are demonstrated.

Analysis of tunable bandgaps in liquid crystal-infiltrated 2D silicon photonic crystals

We present a theoretical study on two-dimensional photonic crystals composed of silicon and the E7 liquid crystal. We analyze how the optical axis orientation of the liquid crystal influences the photonic bands and bandgaps, for the case when the Maxwell equations can be decoupled into the TE and TM modes. We consider two different structures, a triangular lattice of E7 liquid crystal cylinders in a silicon background and a triangular lattice of silicon cylinders in an E7 liquid crystal background. The effect of the liquid crystal anisotropy on the geometry of the irreducible Brillouin zone allows us to propose a simplified way to calculate the photonic bandgaps. Results show that the bandgap width and center frequency have a 60° periodicity for both structures. Using the plane-wave expansion method, we determined the maximum bandgap and the optimal radius of the cylinders for each structure. Finally, for the second structure, we propose an optical switch with a 50% duty cycle. These structures can be applied to design tunable photonic devices.

Thermal emission properties of 2D and 3D silicon photonic crystals

We present measurements of the thermal emission properties of 2D and 3D silicon photonic crystals with and without substrate heated resistively as well as passively with an aluminium hotplate. The out-of-plane and in-plane emission properties were recorded and compared to numerical simulation. It turned out that for the in-plane 2D photonic crystal and out-of-plane 3D photonic crystal emission a photonic stop gap effect is visible. For the out-of-plane 2D photonic crystal emission, no photonic bandgap effect is observable but instead strong silicon oxide emission from native oxide inside the pores of silicon are observable. A model for the modified thermal emission is presented.

Photonic Crystals: Shaping the Flow of Thermal Radiation

AbstractIn this paper we explore theory, design, and fabrication of photonic crystal (PhC) based selective thermal emitters. In particular, we focus on tailoring spectral and spatial properties by means of resonant enhancement in PhC's. Firstly, we explore narrow-band resonant thermal emission in photonic crystals exhibiting strong spectral and directional selectivity. We demonstrate two interesting designs based on resonant Q-matching: a vertical cavity enhanced resonant thermal emitter and 2D silicon PhC slab Fano-resonance based thermal emitter. Secondly, we examine the design of 2D tungsten PhC as a broad-band selective emitter. Indeed, based on the resonant cavity coupled resonant modes we demonstrate a highly selective, highly-spectrally efficient thermal emitter. We show that an emitter with a photonic cut-off anywhere from 1.8 μm to 2.5 μm can be designed.

All-optical switching in 2D silicon photonic crystals with low loss waveguides and optical cavities

A study of the optical transmission of low-loss W1.5 photonic crystal waveguides built on silicon membranes and operating at telecom wavelengths is presented. The feasibility of performing all-optical switching is demonstrated for W1.5 waveguides coupled with L3 cavities, systems amenable for incorporation in on-chip devices. Switching of waveguide transmission is achieved by means of optical excitation of free carriers using a 2.5 ns pump laser. Experimental results are reproduced by finite-difference time-domain simulations which model the response of the finite system and band structure calculations describing the infinite, ideal one.

Linear and non‐linear optical experiments based on macroporous silicon photonic crystals

AbstractMacroporous silicon is a model system for 2D silicon photonic crystals. In this review, we describe our recent theoretical and experimental advances in the macroporous silicon technology as well as in novel near‐field optical experiments concerning modified light emission from photonic crystal cavities and waveguides. We also review our recent work on tuning silicon photonic crystals by free‐carriers or non‐linear effects and compare the two tuning mechanisms. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Optical characterisation of 2D macroporous silicon photonic crystals with bandgaps around 3.5 and 1.3 μm

Transmission measurements were performed on thin 2D silicon photonic crystals (PCs) with 1–4 crystal rows in order to investigate the effect of a finite structure and to obtain an estimate of the crystal thickness necessary to minimize crosstalk between adjacent waveguides. For wavelengths deep within the H-bandgap a strong exponential decay revealing an attenuation constant of 10 dB per crystal row was measured. For opto-electronic applications, the lattice constant of macroporous Si was successfully downscaled from a pitch of 1.5 to 0.5 μm. Reflection measurements performed at these structures show good agreement with corresponding bandstructure calculations exhibiting a complete bandgap around λ=1.3μm.