V. A. Tolmachev

Electrotunable in-plane one-dimensional photonic structure based on silicon and liquid crystal

The model of the electro-optical effect, due to the reorientation of liquid crystal molecules from a pseudoisotropic to a homeotropic state, in a composite photonic structure with a liquid crystal filler, is elaborated. A composite (110) grooved silicon photonic structure for the middle infrared range was designed and fabricated on a silicon-on-insulator platform. Polarized reflection spectra, demonstrating the electro-optical effect, have been obtained by means of Fourier transform infrared microscopy. The relative shift of the band edge at half intensity in the region of 10μm was found experimentally to be 1.6% compared to 2.2% as predicted by theory.

Method of construction of composite one-dimensional photonic crystal with extended photonic band gaps

A method of photonic band gap extension using mixing of periodic structures with two or more consecutively placed photonic crystals with different lattice constants is proposed. For the design of the structures with maximal photonic band gap extension the gap map imposition method is utilised. Optimal structures have been established and the gap map of photonic band gaps has been calculated at normal incidence of light for both small and large optical contrast and at oblique incidence of light for small optical contrast.

Silicon photonic crystal filter with ultrawide passband characteristics

We report on what is believed to be the first example of an ultrawide, bandpass filter, based on a high-contrast multicomponent one-dimensional Si photonic crystal (PC). The effect of the disappearance of a limited number of flat stopbands and their replacement with extended passbands is demonstrated over a wide IR range. The passbands obtained exhibit a high transmission of 92% to 96% and a substantial bandwidth of 1800 nm, which is spectrally flat within the passband. The multicomponent PC model suggested can be applied to the design of any micro- or nanostructured semiconductor or dielectric material for application across a wide spectral range.

One-dimensional photonic crystal obtained by vertical anisotropic etching of silicon

The potentialities of vertical anisotropic etching of (110) silicon for the fabrication of one-dimensional photonic crystal with a high refractive index contrast have been studied. It is shown that advances toward the near-IR spectral range are limited by the mechanical strength of thin silicon walls. The device structures obtained consist of 50 trenches, 114 µm deep, with 1.8-µm-thick Si walls (structure period 8 µm). Their reflectance spectra in the wavelength range 2.5–16.5 µm show good agreement with calculation results, although the main photonic band gap at λ≈28±10 µm remained outside the spectral region of measurements.

Design of one-dimensional composite photonic crystals with an extended photonic band gap

A technique for photonic band gap (PBG) extension based on mixing photonic crystals with different lattice constants or filling factors is suggested. For the design of photonic crystals with maximal PBG extension the gap map imposition method is utilized. Gap maps for composite photonic crystals based on Si-air structures are calculated and used to predict optimal structures for fabrication.

Fabrication Technology of Heterojunctions in the Lattice of a 2D Photonic Crystal Based on Macroporous Silicon

Design and fabrication technology of a microcavity structure based on a double heterojunction in macroporous silicon is suggested. The fabrication process of a strip of a 2D photonic crystal constituted by a finite number of lattice periods and the technique for defect formation by local opening of macropores on the substrate side, followed by filling of these macropores with a nematic liquid crystal, are considered.

Numerical methods for calculation of optical properties of layered structures

Three methods, namely 2×2 and 4×4 transfer matrix methods as well as scattering matrix method, for simulation of the transmission and reflection spectra of the layered structures are described in this paper. The advantages of each of these methods for simulation of the optical spectra of one-dimensional photonic crystals are analyzed. The modified 2×2 transfer matrix method is suggested for calculation of the reflection and transmission coefficients of the layered structures in situation when the incident light beam has a cone-like shape.

Optical Contrast Tuning in Three-Component One-Dimensional Photonic Crystals

In this study, three-component 1-D photonic crystal (PC) structures were investigated by modeling them as two-component PCs with an additional regular layer. The gap map (GM) approach and the transfer matrix method (TMM) were used in order to mathematically describe these structures. The introduction of a third component to a 1-D PC allows manipulation of the optical contrast to a high degree of precision by varying the thickness and refractive index of the additional layer. The introduction of a third component to the 1-D PC partially reduces the area of the photonic stopbands (SBs) on the GM, leaving the rest of SB area unchanged from that in the GM for the original, two-component, PC. Using this approach to decrease optical contrast in PCs, omnidirectional bands (ODBs) can be obtained in high-contrast periodic structures constructed from, for example, an array of silicon and air. Several mathematical models of three-component 1-D PCs are discussed, some of which may have practical applications.

Polarized infrared and Raman spectroscopy studies of the liquid crystal E7 alignment in composites based on grooved silicon

Alignment of liquid-crystal filler molecules and the electro-optical effect in composite photonic crystals based on grooved silicon are studied. It is found that the nematic liquid crystal molecules that fill the grooves are predominantly aligned in a planar configuration with respect to the silicon walls. The liquid crystal molecules are realigned homeotropically with respect to the groove walls under the influence of an electric field. The effect detected can be used to adjust the photonic band gap of a one-dimensional photonic crystal.

Design of one-dimensional photonic crystals using combination of band diagram and photonic gap map approaches

The design of one-dimensional photonic crystals and the analysis of their optical properties have been performed using band diagram and forbidden gap map methods. It has been shown that the latter method is more useful for practical applications since (i) it can be applied for any number of periods and (ii) it is more suitable for the selection of a filling fraction in a wide range of values using a single graphical presentation. Three different types of photonic crystals with small, medium, and high optical contrast were modeled using both methods. The features of the omnidirectional band gap formation for photonic crystals with small optical contrast and low number of periods have been explained. The formation of a one-dimensional photonic structure with limited number of periods and omnidirectional band gap close to that for an infinite periodic structure has been discussed.