Properties Of Two-dimensional Photonic Crystals Research Articles

High Optical Reflection in Two-dimensional ZnO-Si Photonic Crystals Induced by Coupled Optical Micro-cavities

Photonic crystals can exhibit relevant optical properties when transmitting or reflecting a light beam. In particular in a two-dimensional photonic crystal the reflective properties can be of interest and consequently optimized for different technological applications such as tunable laser cavities, photovoltaic solar systems, and selective high reflection mirrors among many others. Taking this motivation into account, a study of the reflective optical properties of two-dimensional photonic crystals built on a hybrid substrate of ZnO:Si has been developed. The aim of the present research is to demonstrate the feasibility to control the optical reflectance spectra of a two-dimensional photonic crystal by the inclusion of an array of optical micro-cavities in a regular photonic structure. Moreover, in this research an explanation of the origin of the high optical reflectance predicted by numerical calculations and confirmed by experimental measurements in a photonic crystal that contains an array of micro-optical cavities is also given. The results of numerical calculations of the optical properties of one of the photonic crystals studied determined that the origin of the increase in its optical reflectance is the light emission from the silicon present in the ZnO-Si substrate where the photonic structure was built. Strong resonant modes of the optical electric field stablished mainly in silicon present in two types of resonant cavities recognized in the photonic crystal favor the stimulated emission of light that gives rise to the high optical reflectivity.

Enhancement of the Luminescence Signal from Self-Assembled Ge(Si) Nanoislands due to Interaction with the Modes of Two-Dimensional Photonic Crystals

The results of studies of the luminescence properties of two-dimensional photonic crystals formed on the basis of silicon structures with self-assembled Ge(Si) nanoislands are reported. The possibilities of substantially enhancing the luminescence response of the active medium (Ge(Si) nanoislands) in the wavelength range 1.2–1.6 μm are shown for such structures. The specific features of the luminescence response of a photonic crystal in the vicinity of the Γ point of its Brillouin zone are studied. It is shown that, along with the broadband response characteristic of the radiative modes of photonic crystals, high-Q resonances, for which the Q factor exceeds 103, can also be observed in such structures. The last-mentioned resonances are observed in a certain range of lattice parameters of photonic crystals.

Zero Refractive Index Properties of Two-Dimensional Photonic Crystals with Dirac Cones**Supported by the National Natural Science Foundation of China under Grant Nos 11504336 and 61805214, and the Fundamental Research Funds for the Central Universities under Grant No 265201430.

The zero refractive index properties of two-dimensional photonic crystals (PCs) are studied theoretically. Three necessary conditions for PCs to mimic the zero index materials (ZIMs) are obtained. In addition, through a comparative study of the properties for two representative PC structures with different types of Dirac cones, we find that the PC with a Dirac-like cone which meets the three necessary conditions does not behave as a ZIM in some cases. Further analysis shows that its non-zero index properties originate from the flat dispersion band. These findings clarify the fundamental physical issue of which type of Dirac cone PC can mimic a real ZIM.

Tuning full photonic band gap with plasma frequency in two-dimensional photonic crystals composed of anisotropic dielectric rods in plasma background

In this study, we analyze full photonic band gap formation and properties of two-dimensional photonic crystals with square lattice, composed of anisotropic tellurium rods with different geometric shapes in a plasma background. Using the finite-difference time-domain method, we discuss the tunability of the full photonic band gap width as a function of the plasma frequency for different values of tellurium rod’s parameters. The calculated results show that our proposed structures represent full photonic band gaps with considerable width, which are dependent on plasma frequency.

Calculation of reflectivity spectra for semi-infinite two-dimensional photonic crystals

This work involves the development of a finite-element method model to examine the optical properties of two-dimensional photonic crystals (PCs). The model is capable of studying the effect of a finite number of periods in a PC structure. The new design minimizes computational resources by modeling a PC with one infinite dimension with periodic boundary conditions while modeling the second with finite dimensions. This allows for calculation of transmission and reflection spectra across the PC structure. A finite difference frequency domain (FDFD) model has been created for calculation of the photonic band structure. This is compared with the reflection spectra obtained through the reflection model and is found to closely match. The reflection model capabilities are demonstrated by calculating the reflection spectrum for various parameters: period length, number of periods, incident light polarization, and material properties. Effects of varying these parameters are demonstrated. For example, the reflectivity of a GaAs/Air PC was found to reach greater than 95% when the PC has 10 periods; it exceeds 99% with 13 periods and reaches 99.9% at 15 periods.

Change in magnetic properties of two-dimensional magnetic photonic crystals using a light stimulus

The study of magnetooptical properties of the two-dimensional photonic crystals based on the doped silicon plates covered by a cobalt layer, which is several nanometers in thickness and lies on a chrome layer several tens of nanometers thick, shows quasi-periodic changes in the magnetic properties of the system when interacting with electromagnetic radiation. Oscillations on angular dependences of the equatorial magnetooptical Kerr effect are related to the fulfillment of resonance conditions when the standing electromagnetic wave, which contributes to the spin rotation in the system and thereby to the change of its magnetic properties, is formed in the magnetic plate.

Band gap properties of two-dimensional photonic crystals with rhombic lattice

A new structure of two-dimensional photonic crystals (PCs) with rhombic lattice is proposed in this paper. It provides more flexibility in the design of photonic crystal devices and makes the designer be able to choose a more suitable lattice angle to satisfy different demands. The first Brillouin zone (1st BZ) of this structure is discussed and the general wave vectors are derived. The plane wave expansion (PWE) method is used to analyze the band gap properties. The impact of different lattice angels on the band gaps is analyzed, and the band gap map is also given.

Resonance properties of two-dimensional photonic crystals

The resonance properties of two-dimensional photonic crystals, which are manifested by the localization of radiation inside these objects at frequencies corresponding to their bandgap boundaries, have been theoretically studied. This effect is compared to resonances in photonic crystals with violated internal structure, which are related to the generation of defect modes.

Absolute band gap engineering of anisotropic square and triangular photonic crystals

We analyze the band gap properties of two-dimensional photonic crystals created by square and triangular lattices of rods, considering that the rods are formed of a dielectric core surrounded by an interfacial layer of anisotropic tellurium. Using the plane wave analysis, we study the modification of the band gap spectrum when the rods are infiltrated with different dielectric core and discuss the optimization strategies leading to the maximum value of the absolute band gap.

Properties of two-dimensional photonic crystals with octagonal quasicrystalline unit cells

The bandstructures of two-dimensional photonic crystals with octagonal quasicrystalline unit cells have been calculated. The existence of photonic band-gaps in such structures is demonstrated, and results showing the variation of the spectral position and width of the photonic band-gaps with the size of the unit cell and filling fraction within the unit cell are presented.

Band-gap properties of two-dimensional low-index photonic crystals

We study the band-gap properties of two-dimensional photonic crystals created by a lattice of rods or holes conformed in a symmetric or asymmetric triangular structure. Using numerical plane-wave method, we calculate a minimum value of the refractive-index contrast for opening both partial and full two-dimensional spectral gaps for both TM- and TE-polarized waves. We also analyze the effect of ellipticity of rods and holes and their orientation on the threshold value and the relative size of the band gaps.

Second-harmonic superprism effect in photonic crystals

By exploitation of the nonlinear optical properties of two-dimensional photonic crystals, a second-harmonic superprism effect is demonstrated. The anisotropy of the dispersion curves allows control of the propagation direction of the second-harmonic field. Smooth variations of the fundamental wavelength or the angle of incidence produce a drastic angular shift of the second-harmonic emission.

Fabrication and optical properties of two-dimensional photonic crystals of CdSe pillars

The combination of electron beam lithography and electrochemical deposition has been employed to fabricate well-controlled submicrometer-scale CdSe pillars. The formation of the wurtzite crystal structure of CdSe pillars has been confirmed by x-ray diffraction and Raman spectra. Quite interestingly, we found that the intensity of micro-photoluminescence can be greatly enhanced at the specially designed two-dimensional photonic crystals (PCs) based on Maxwell’s equations. This peculiar phenomenon can be explained quite well in terms of the effects of PCs. PCs can provide a photonic bandgap for the emission in the lateral dimensions so that the emission of CdSe pillars cannot propagate in the lateral plane and can only propagate upward with respect to PCs. Besides, PCs can also provide a pathway for the phase match between guided modes and radiation modes to avoid total internal reflection. Thus, the detected PL intensity normal to the lateral plane can be greatly enhanced.

Birefringence in porous anodic aluminum oxide

Birefringence properties of a disordered two-dimensional photonic crystal are demonstrated experimentally for the first time. It is proposed to use porous anodic aluminum oxide, which has anisotropy on the scale of the wavelength of light, as a new birefringent material in the optical range. An original method for studying the birefringence properties of two-dimensional photonic crystals based on the use of monochromatic light is described.

Optical Characteristics of Two-Dimensional Photonic Crystals in Anodic Aluminum Oxide Films

The optical properties of two-dimensional photonic crystals (PhCs) in anodic aluminum oxide (AAO) films obtained using a simple and low-cost pre-patterning procedure are described. The prepatterning of the initial Al film surface was carried out by imprinting with an optical diffraction grating; the anodization of the prepatterned sample led to the formation of a good quality, large-area PhC with a triangular lattice of air holes (lattice period a=0.48 µm, hole radius r=0.2 µm) in an AAO film. The optical transmission spectra of the sample were measured at visible wavelengths in the range of 0.4–1.0 µm for various incidence angles and linear polarizations of the probing light. The detailed analysis of the transmission data indicates a photonic band gap in the 0.9–1.0 µm wavelength range for light waves linearly polarized in the direction perpendicular to the axes of PhC pores.

Diffraction properties of two-dimensional photonic crystals

We show that the envelope of the diffraction efficiency of a two-dimensional photonic crystal can exhibit spectral regions of very small diffraction efficiency (<5×10−3), while in other regions, the diffraction efficiency is near unity. The experimental results on higher bands of hexagonal, silicon-based photonic crystals agree well with corresponding numerical calculations and highlight the prominent role of the surface termination, an aspect which cannot be described by the photonic band structure alone. We speculate about possible applications of such additional spectral filters in Raman and photoluminescence spectroscopy.

Properties of two-dimensional photonic crystals in elastomers

Properties of two-dimensional photonic crystals in elastomers

Transmission spectroscopy of photonic crystals in a silicon-on-insulator waveguide structure

Optical properties of two-dimensional photonic crystals (PCs) integrated in a silicon-on-insulator stripe waveguide are reported. Transmission measurements are done on a wide wavelength range (1.1–1.7 μm) by coupling a white-light source in the cleaved edge of the sample and collecting light at the other cleaved side of the waveguide. PC mirrors and one-dimensional (1D) Fabry–Pérot cavities formed between two PC reflectors have been fabricated and characterized. The photonic band gap of the mirror is observed in the Γ–M direction for the transverse electric like guided modes. For the waveguide with the 1D Fabry–Pérot cavity, resonant modes appear within the gap. It is found that the experimental spectra are in very good agreement with both the theoretical photonic band structure and the theoretical transmission calculated by finite difference time domain.

Optical and confinement properties of two-dimensional photonic crystals

We describe experiments on a quasi-two dimensional (2-D) optical system consisting of a triangular array of air cylinders etched through a laser-like Ga(Al)As waveguiding heterostructure. Such a configuration is shown to yield results very well approximated by the infinite 2-D photonic crystal (PC). We first present a set of measurements of the optical properties (transmission, reflection, and diffraction) of slabs of these photonic crystals, including the case of in-plane Fabry-Perot cavities formed between two such crystals. The measurement method makes use of the guided photoluminescence of embedded quantum wells or InAs quantum dots to generate an internal probe beam. Out-of-plant, scattering losses are evaluated by various means. In a second part, in-plane micrometer-sized photonic boxes bounded by circular trenches or by two-dimensional photonic crystal are probed by exciting spontaneous emission inside them. The high quality factors observed in such photon boxes demonstrate the excellent photon confinement attainable in these systems and allow to access the detail of the modal structure. Last, some perspectives for applications are offered.

Use of guided spontaneous emission of a semiconductor to probe the optical properties of two-dimensional photonic crystals

We describe an experimental setup, which allows assessing the optical properties of two-dimensional photonic crystals combined with a waveguide geometry, and etched into a light-emitting (GaAs/InGaAs) semiconductor. By means of a guiding layer, the spontaneous emission of the material is used as a built-in source to probe the properties of the etched microstructure, conveniently compared to the usual measurement schemes. We show polarized transmission and coefficients largely depending on the photonic crystal orientation.