Dimensional Photonic Crystal Slab Research Articles

Realization of pressure sensor based on a GaAs-based two dimensional photonic crystal slab on SiO2 substrate

Realization of pressure sensor based on a GaAs-based two dimensional photonic crystal slab on SiO2 substrate

Two-dimensional photonic crystal slabs as a tunable polarization mode converter

Two dimensional photonic crystal slabs with elliptical holes exposed to the normal incident laser light are proposed and designed as a tunable broadband polarization rotator. The photonic crystal electric field mode due to the eccentricity and orientation of the holes will provide a mean to exchange power between two orthogonal polarization states. Around guided resonance wavelengths of photonic crystals with 45° oriented elliptical holes, 20% polarization mode conversion is achieved. By tuning of the difference of the two radii of the elliptical holes we are able to span a bandwidth of 130nm and 70nm around wavelengths of 1445nm and 1650nm. The unique properties of these devices such as ease of engineering and simplified light coupling scheme will make them a promising polarization mode converter in high speed polarization-multiplexed optical transmission systems.

Multichannel W3 Y-branch filter in a two dimensional triangular-lattice photonic crystal slab

We demonstrate the design, fabrication and characterization of a highly efficient multichannel W3 Y-branch filter in a two dimensional triangular-lattice photonic crystal slab. The coupling properties between high-order waveguide modes and fundamental resonant modes are investigated. By finely adjusting the size of resonant cavities, four higher-order mode channels with different output wavelengths are experimentally realized, which is in agreement with the theoretical simulations. The results show that this kind of filter may be useful in optical integrated circuits with high coupling and transmission efficiency.

Design of an air-slot mode-gap nanocavity in a two dimensional photonic crystal slab

We present a novel and simple design of an air-slot mode-gap photonic crystal (PC) nanocavity by introducing a linear air slot to the center of a line-defect waveguide in a two dimensional triangular-lattice silicon PC slab. A high quality factor (Q factor) of 8.42×105 and an ultrasmall mode volume of 0.998 cubic wavelength are achieved in an optimized air-slot nanocavity which is a suitable choice for the strong matter-field interaction in free space. The high Q cavities with ultrasmall mode volume are important for applications such as quantum computation and nonlinear optics.

Analysis of light scattering off photonic crystal slabs in terms of Feshbach resonances

Techniques to deal with Feshbach resonances are applied to describe resonant light scattering off one dimensional photonic crystal slabs. Accurate expressions for scattering amplitudes, free of any fitting parameter, are obtained for isolated as well as overlapping resonances. They relate the resonance properties to the properties of the optical structure and of the incident light. For the most common case of a piecewise constant dielectric function, the calculations can be carried out essentially analytically. After establishing the accuracy of this approach we demonstrate its potential in the analysis of the reflection coefficients for the diverse shapes of overlapping, interacting resonances.

Configuration analysis of sensing element for photonic crystal based NEMS cantilever using dual nano-ring resonator

Photonic crystal (PhC) based channel drop filters including two hexagonal rings in a two dimensional (2-D) photonic crystal silicon slab of hexagonal lattice are integrated on microcantilevers for nanoelectromechanical systems (NEMS) sensor applications. The proposed two hexagonal rings are named as dual nano-ring (DNR) resonator. The sensing characteristics of dual nano-ring (DNR) resonator at various positions adjacent to the junction of the microcantilever and the substrate are investigated. The derived quality factors is over 3000, and the minimum detectable force can be as small as 7.58 nN. Moreover, the continuous wave field distribution modeling is deployed to explain the origins of resonant mechanisms occurred in deformed DNR resonator under various applied forces.

All optical switch based on Fano resonance in metal nanocomposite photonic crystals

We investigate the potential of plasmonic resonance in metal nanocomposite materials for the design of photonic crystal all optical switches by numerical methods. We study the absorption effect of the plasmonic resonance on the Fano resonances of one dimensional photonic crystal slabs covered by a metal nanocomposite layer. It is shown that the absorption reduces the contrast of the Fano resonances. However, for adequate metal nanoparticle concentrations it is possible to achieve both sufficiently sharp Fano resonance and strong Kerr nonlinearity, which provides a suitable condition for the design of high contrast and low threshold switches.

Electro-optical modulator in a polymerinfiltrated silicon slotted photonic crystal waveguide heterostructure resonator

We present a novel concept of a compact, ultra fast electro-optic modulator, based on photonic crystal resonator structures that can be realized in two dimensional photonic crystal slabs of silicon as core material employing a nonlinear optical polymer as infiltration and cladding material. The novel concept is to combine a photonic crystal heterostructure cavity with a slotted defect waveguide. The photonic crystal lattice can be used as a distributed electrode for the application of a modulation signal. An electrical contact is hence provided while the optical wave is kept isolated from the lossy metal electrodes. Thereby, well known disadvantages of segmented electrode designs such as excessive scattering are avoided. The optical field enhancement in the slotted region increases the nonlinear interaction with an external electric field resulting in an envisaged switching voltage of approximately 1 V at modulation speeds up to 100 GHz.

Optimized focusing properties of photonic crystal slabs

We propose an optimization procedure for focusing operation in finite two dimensional photonic crystal slabs. The device consists of a triangular lattice air holes etched in a semiconductor matrix at a nanometer scale to operate at 1.55 μm. To reach simultaneously an effective refractive index equal to −1 along with a very high transmission coefficient whatever optical wave incidence, the parameters as the lattice period and/or filling factor are precisely adjusted depending on the slab thickness. The method relies on Fabry–Perot resonances engineering in the air/crystal/air cavity constituting the lens.

Towards observation of sub-diffractive pulse propagation in photonic crystals

It is shown that sub-diffractive (self-collimating) propagation of ultrashort pulses of narrow light beams is possible in two dimensional planar photonic crystal slabs (in particular made with air holes in Si3N4 slab) where the sub-diffractive propagation of monochromatic beam of visible light has been demonstrated previously both theoretically and numerically. We found that the sub-diffractive propagations of the pulses of duration of more than 40fs are indistinguishable from that of monochromatic beams. However, for the pulses with duration less than 40fs their propagation peculiarities associated with asymmetric spatiotemporal misshaping, spatial and temporal broadening come into play. The effects are pronounced for the pulses of duration less than 20fs. The phenomena are shown for both TM and TE polarized light by means of numerical integration of 2D Maxwell’s equations with finite-difference time-domain technique.

Nonlinear equation method for band structure calculations of photonic crystal slabs

In this letter a nonlinear equation method based on effective-medium approximation is presented to calculate the band structure of photonic crystal slabs. At a definite wave vector, the normalized frequency is inversely proportional to the effective refractive index of the photonic crystals. Effective-medium approximation is used to calculate the effective refractive indices of the two dimensional photonic crystals and photonic crystal slab. The corresponding relation between the band structure of the photonic crystal slab and that of two dimensional photonic crystals is given by a nonlinear equation. Through the nonlinear equation, the three dimensional photonic crystal slabs problems are simplified as two dimensional simulations. The results by this method agree very well with those of three dimensional finite-difference time-domain method and the calculation is much faster.

Diverse imaging of photonic crystal by the effects of channeling and partial band gap

Diverse imaging of point source by a two-dimensional photonic crystal slab with square lattice is studied by the finite-difference time-domain method. Given proper frequencies, there seems to be some special directions like channels guiding the light propagation inside the photonic crystal, along which some images will be created. It is suggest that except negative refraction there should be other mechanisms making point image by two dimensional photonic crystal slab.

High resolution three-port filter in two dimensional photonic crystal slabs

An in-plane, three-port filter consisting of input/output waveguides and two point-defect cavities in a 2D PC slab is designed and fabricated, where a new feedback method is introduced, and its transmission properties are measured. The measured minimum output wavelength spacing between two channels is 1.5 nm, which is realized by slightly adjusting the size of the resonant cavities. The measured resonant wavelengths of two cavities agree well with the calculated ones and the quality factors of the cavities are almost the same. It is believed that this kind of filter may be useful in optical integrated circuits with high density.

Mode mixing in asymmetric double-trench photonic crystal waveguides

We investigate, both experimentally and theoretically, the waveguiding properties of a double-trench waveguide in which a conventional single-mode strip waveguide is embedded in a two-dimensional photonic crystal (PhC) slab formed in silicon-on-insulator wafers. We demonstrate that the bandwidth for relatively low-loss (50 dB/cm) waveguiding is significantly expanded to 250 nm, covering almost all the photonic bandgap owing to nearly linear dispersion of the TE-like waveguiding mode. The flat transmission spectrum, however, is interrupted by numerous narrow stop bands. We found that these stop bands can be attributed to anticrossing between TE-like (positive parity) and TM-like (negative parity) modes. This effect is a direct result of the strong asymmetry of the waveguides that have an upper cladding of air and lower cladding of oxide.

Momentum space design of high-Q photonic crystal optical cavities

The design of high quality factor (Q) optical cavities in two dimensional photonic crystal (PC) slab waveguides based upon a momentum space picture is presented. The results of a symmetry analysis of defect modes in hexagonal and square host photonic lattices are used to determine cavity geometries that produce modes which by their very symmetry reduce the vertical radiation loss from the PC slab. Further improvements in the Q are achieved through tailoring of the defect geometry in Fourier space to limit coupling between the dominant momentum components of a given defect mode and those momentum components which are either not reflected by the PC mirror or which lie within the radiation cone of the cladding surrounding the PC slab. Numerical investigations using the finite-difference time-domain (FDTD) method predict that radiation losses can be significantly suppressed through these methods, culminating with a graded square lattice design whose total Q approaches 10;5 with a mode volume of approximately 0.25 cubic half-wavelengths in vacuum.

Channel-Add Operation of a Device Using Defects in a Two-Dimensional Photonic Crystal Slab

AbstractA channel add-filtering function of a device based on defects in a two dimensional photonic crystal slab is investigated in addition to a channel drop-filtering function reported previously. It is considered that photons irradiated to a point defect from free space are trapped by the point defect, are transferred to a line defect waveguide nearby, and are emitted from the waveguide edge. It is shown that the spectrum of the add-filtering function is almost same as that of the drop-filtering function, which demonstrates that photons can be not only dropped-from but also added-to a line-defect waveguide through the resonant trapping by point defects.