Study the role of non-linear resonant cavities in photonic crystal-based decoder switches

In this paper, we are going to design and propose a novel structure for all optical decoder. The proposed structure is composed of optical power splitters and a four-port optical switch. The four-port optical switch simply is a non-linear optical demulitiplexer. For achieving non-linear behaviour for the demultiplexer, we will employ defect rods made of doped glass which has high Kerr coefficient. The final structure has three input ports and four output ports. Port E acts as enable port, which will be used activating or deactivating the total structure. A and B are the control ports, by which one can control when the structure is active, which port of the structure to be active. The optical intensity of the input ports required appropriate operation of the structure is about 20 W/μm². The maximum switching frequency of the proposed structure is 2 GHz. Reduced input optical intensity is the main characteristics of the present work. Numerical methods such as plane wave expansion and finite difference time domain were used for performing the required calculations.     

Efficient multiresolution time-domain analysis of arbitrarily shaped photonic devices

A multiresolution time-domain (MRTD) technique is proposed and applied to the analysis of arbitrarily shaped photonic devices. The suggested method implements the multiresolution analysis in the context of method-of-moments for the solution of Maxwell?s equations. To improve the capabilities of the proposed method, the uniaxial perfectly matched layers absorber for the MRTD is rigorously incorporated and better performance is reported over the conventional finite-difference time-domain. Various numerical examples demonstrate the stability and numerical precision of the suggested MRTD method for both linear and nonlinear applications. Moreover, the application of the suggested MRTD scheme for the design of a photonic crystal-based optical wavelength filter and for the analysis of a frequency converter is presented.     

Design of photonic crystal-based all-optical AND gate using T-shaped waveguide

Abstract

We present a new configuration of all-optical AND gate based on two-dimensional photonic crystal composed of Si rods in air. Two AND gate structures with and without probe input are proposed. The proposed structures are designed with T-shaped waveguide without using nonlinear materials and optical amplifiers. The performance of the proposed AND gate structures is analyzed and simulated by plane-wave expansion and finite difference time domain methods. The AND gate without probe input needs only one T-shaped waveguide, whereas the AND gate with probe input needs two T-shaped waveguides. The former AND gate offers a bit rate of 6.26 Tbps with a contrast ratio of 5.74 dB, whereas the latter AND gate offers a bit rate of 3.58 Tbps whose contrast ratio is 9.66 dB. It can be expected that these small size T-shaped structures are suitable for large-scale integration and can potentially be used in on-chip photonic integrated circuits.     

Nonlinear analysis of a photonic crystal laser

An approximate nonlinear analysis of light generation in two-dimensional square- and triangular-lattice photonic crystal lasers including gain saturation effects is presented for the TE modes. This model extends earlier studies which took into account only TM modes. Our approach is based on coupled mode theory. With the help of an energy theorem and a threshold field approximation an approximate formula relating the small signal gain required to obtain a given output power to the structure parameters has been obtained. It has been used to calculate laser characteristics revealing an optimum coupling strength for which laser structure achieves maximum power efficiency.     

Accurate sensitivity analysis of photonic devices exploiting the finite-difference time-domain cavity adjoint variable method

For what is believed to be the first time, the central adjoint variable method (CAVM) is applied to the sensitivity analysis of photonic devices using the finite-difference time-domain (FDTD) technique. The FDTD-CAVM technique obtains accurate sensitivities of any desired response with respect to the different design parameters. Our technique requires only one extra FDTD simulation to extract the sensitivities with respect to all the design parameters regardless of their number. Cost-free sensitivities of the power reflectivity are also derived without any additional simulation. The results show a very good agreement between the CAVM sensitivities and those obtained using the expensive central finite difference approximation.     

Application of time-domain finite-volume method to some radiation problems in two and three dimensions

Maxwell's curl equations in the time domain are cast into a conservation form and discretized using a finite-volume procedure. The Lax-Wendroff explicit scheme is then used to solve the discretized Maxwell's equations, resulting in second-order accuracy with respect to both time and space. This time-domain scheme does not require an interlaced mesh for electric and magnetic fields. Radiation pattern and input impedance of some typical parallel-plate waveguides and mutual coupling for arrays of parallel-plate waveguides are computed and, whenever possible, compared with closed form exact or approximate solutions. Radiation patterns for a two-dimensional horn and a rectangular waveguide are presented.<>     

Free-space excitation of resonant cavities formed from cloaking metamaterial

We propose a new class of resonant electromagnetic structures, and study their response to free-space illumination. The structures consist of partial cylindrical shells that have the cloaking material properties proposed by Pendry et al. [Science 2006, 312, 1780]. These metamaterial shells have apertures that allow the propagation of incident irradiation into an interior resonant cavity. We use full wave time-harmonic analysis to study the field distribution inside the cavity, and show that an analogue of Whispering Gallery Modes (WGMs) can be efficiently excited via free-space illumination.     

Optical modulator based on coupled photonic crystal cavities

Abstract

We propose and numerically investigate an optical signal modulator based on two-photonic crystal nanobeam cavities coupled through a waveguide. The suggested modulator shifts the resonant frequency over a scalable range. We design a compact optical modulator based on photonic crystal nanobeams cavities that exhibits high stability to manufacturing. Photonic crystal waveguide tuning in the low-intensity region of the resonant mode is demonstrated. The advantages of the suggested approach over the single-resonator optical modulator approaches include the possibilities to shift the modulator frequency over a scalable range that depends on switching energy level and to effectively electrically tune the device in the low-intensity region of the resonant mode.     

Bottom-up photonic crystal cavities formed by patterned III-V nanopillars

We report on the formation and optical properties of bottom-up photonic crystal (PC) cavities formed by III-V nanopillars (NPs) via catalyst-free selective-area metal-organic chemical vapor deposition on masked GaAs substrates. This method of NP synthesis allows for precise lithographic control of NP position and diameter enabling simultaneous formation of both the photonic band gap (PBG) region and active gain region. The PBG and cavity resonance are determined by independently tuning the NP radius r, pitch a, and height h in the respective masked areas. Near-infrared emission at 970 nm is achieved from axial GaAs/InGaAs heterostructures with in situ passivation by laterally grown InGaP shells. To achieve out-of-plane optical confinement, the PC cavities are embedded in polydimethylsiloxane (PDMS) and removed from the growth substrate. Spatially and spectrally resolved 77 K photoluminescence demonstrates a strong influence of the PBG resonance on device emission. Resonant peaks are observed in the emission spectra of PC cavities embedded in PDMS.     

Nonlinear resonant characteristics of shallow fluid layers

Results are presented from an experimental investigation of the motion of a shallow layer of water in a square tank that was oscillated horizontally with small amplitude at frequencies close to the natural frequency of the layer. The aim was to assess the validity of certain theoretical predictions relating to nonlinear resonance in shallow layers based on asymptotic analysis. These concern the hysteretic nature of the resonance profile and the existence of non-trivial oscillatory components associated with shock-like discontinuities in the derived solution for the free surface configuration. The experimental results support the theoretical predictions and show a coincidence in parameter space between the regions of hysteresis and oscillatory transition.     

Modulation of coupling in a photonic switch by resonant interference

A novel photonic switch structure is described in which the coupling of light between two fiber waveguides is controlled by the resonant interference of a third waveguide. The switching action is controlled by a small variation of the index of refraction of the control waveguide by the application of either photo-optical (Kerr) techniques or electro-optical (Pockels) techniques. The control waveguide can be either a fiber waveguide or a slab waveguide. The equations for the waveguide coupling were obtained by analytical approximations from coupled-mode theory. A beam-propagation simulation was also used. The results of the two models were compared. Multiple resonant interferences were observed in the case of a slab waveguide.     

Polarization response of two-dimensional metallic photonic crystals studied by terahertz time-domain spectroscopy

The polarization characteristics of a terahertz (THz) wave transmitted through two-dimensional (2-D) metallic photonic crystals (MPCs) are investigated. The 2-D MPCs studied in this paper are metal slabs perforated periodically with circular holes. We measured the polarization characteristics of the THz wave using a THz time-domain spectroscopic system with wire grid polarizers in the time and frequency domains. The linearly polarized incident THz wave changes its polarization direction and becomes elliptic after it transmits through the sample. This phenomenon is highly sensitive to the incident angle. It is shown that the frequency range at which the polarization rotation occurs is related to the lattice constant of a photonic crystal, indicating the importance of photonic band modes of the 2-D MPC in the mechanism of the phenomenon.     

Nonlinear resonant response of imperfect extensible Timoshenko microbeams

This paper investigates the nonlinear size-dependent dynamics of an imperfect Timoshenko microbeam, taking into account extensibility. Based on the modified couple stress theory, the nonlinear equations of motion for the longitudinal, transverse, and rotational motions are derived via Hamilton’s energy method. A high-dimensional finite degree-of-freedom system of ordinary differential equations is obtained by the application of the Galerkin scheme. This set of equations is solved through use of the pseudo-arclength continuation method. A stability analysis is conducted via use of the Floquet theory. The resonant motion characteristics of the microbeam are examined by plotting the frequency-response and force-response curves. The effect of system parameters on the resonant response of the system is highlighted.     

Experimental demonstration of photonic bandgaps in azopolymer resonant waveguide grating systems

Photonic bandgaps are demonstrated in one-dimensional corrugated waveguides in the infrared range. A coupling grating is superimposed with single and double Bragg gratings on an azopolymer film by a simple optical process, which allows easy control of the grating spacing. Light is coupled to the TE(0) resonant mode, and gaps in the dispersion curve are introduced by careful selection of the gratings. The analysis is carried out by measuring the transmission through the waveguide as a function of the wavelength and angle of incidence of a probe beam. This results in a direct measurement of the dispersion curves, which are in excellent agreement with theory.     

Ordered systems of site-controlled pyramidal quantum dots incorporated in photonic crystal cavities

The coupling of a prescribed number of site-controlled pyramidal quantum dots (QDs) with photonic crystal (PhC) cavities was studied by polarization and power-dependent photoluminescence measurements. The energy of the cavity mode could be readily tuned, making use of the high spectral uniformity of the QDs and designing PhC cavities with different hole radii. Efficient coupling of the PhC cavity modes both to the ground state and to the excited state transitions of the QDs was observed, whereas no evidence for far off-resonant coupling was found.     

Nonlinear optical responses in two-dimensional photonic crystals

A two-dimensional (2D) highly nonlinear lithium niobate (LN) photonic crystal (PhC) waveguide is fabricated with the aim of studying its nonlinear optical properties. We show a large enhancement of the second-harmonic generation (SHG) in the 2D LN PhCs, originating from resonance between the external pump laser field and a photonic band mode. The SHG enhancement results agree well with the experimental photonic band structure obtained by an angle-dependent optical reflectivity and the theoretical band structure generated by three-dimensional finite-difference time-domain calculations. These results open new possibilities for the use of 2D LN PhC waveguide in integrated nonlinear optical applications.     

Scattering matrix approach to the resonant states and Q values of microdisk lasing cavities

We develop a scattering matrix approach for the numerical calculation of resonant states and Q values of a nonideal optical disk cavity with an arbitrary shape and with an arbitrary varying refraction index. The developed method is applied to study the effect of surface roughness and inhomogeneity of the refraction index on Q values of microdisk cavities for lasing applications. We demonstrate that even small surface roughness (deltar < or approximately equal to lambda/50) can lead to a drastic degradation of high-Q cavity modes by many orders of magnitude. The results of the numerical simulation are analyzed and explained in terms of wave reflection at a curved dielectric interface, combined with an examination of Poincaré surfaces of section and of Husimi distributions.     

A time-domain analysis of a multiplex-bus system

The author presents a technique, using time-domain analysis, to determine the performance of a multiplex-bus system when the bus is shared by a number of identical devices. An algorithm is also developed to implement the technique into a software package. The author has verified the correctness of his time-domain analysis using frequency-domain analysis. His technique is simple and easy to implement compared to the conventional frequency-domain technique