Steady-state Field Distribution Research Articles

Photonic crystal terahertz wave logic AND-XOR gate

Terahertz wave logic gates are one of the key devices required in terahertz wave communication systems and signal processing systems. In this paper, we design a logic gate to realize the function of AND gate and XOR gate. The logic AND-XOR gate is based on two large photonic crystal ring resonators, one small ring resonator and photonic crystal branch waveguides. The structure is analyzed and simulated by treating the plane wave expansion and finite difference time domain methods. The steady-state field distributions and output power characteristics of the gate are analyzed. The simulation results show that the designed device with the feasibility can be used in terahertz wave integrated digital circuit.

Compact TE/TM polarization splitters for 1.31 and 1.55 μm wavelengths in LiNbO3 photonic wires

Ultra-compact TE/TM polarization splitters in LiNbO3 photonic wires with same bending waveguide in input and output transition regions at 1.31μm and 1.55μm wavelengths have been proposed, respectively. Their operating principles are based on the directional coupling mode. Their optimization designs are achieved by using commercial software COMSOL Multiphysics. Calculated steady-state field distributions indicate that guided lightwaves in both quasi-TM and quasi-TE polarizations can be spatially separated from different output waveguides ports. The transmittances of quasi-TE and quasi-TM polarization at 1.31μm wavelength are 90% and 88.5%, respectively. And that at 1.55μm are 88.6% and 84.7%, respectively. The total lengths of the devices for 1.31μm and 1.55 wavelengths are 47μm and 36.52μm, respectively. Moreover, the coupling length dependences of the transmittances, the optical transmission bandwidths, and fabrication sensitivities are evaluated, respectively. The simple and compact polarization splitters are expected to be applied to highly dense LN photonic integrated circuits.

Optical switch based on the liquid–crystal-modulated self-collimating photonic crystals

In this paper, a compact optical switch for self-collimated light beams in a liquid–crystal-modulated photonic crystal is proposed. The designed optical switch is working at 1550 nm. The equi-frequency contours and band diagram of the structure are calculated by using plane wave expansion method. The transmission spectra for different liquid crystal rotation angle are computed with finite-difference time-domain method. Meanwhile, the steady-state field distributions of the light propagation in the structure are presented. The designed optical switch may find important applications in the photonic integrated circuits.

Novel All Optic Logic Gates using 2D Photonic Crystal Structure

A novel scheme for implementation of all-optical logic gate based on 2D photonic crystal structure has been proposed. The design and simulation of novel all-optical logic gates based on two dimensional photonic crystals are reported in this paper. The proposed PCS is comprised of two-dimensional lattice of air holes in a square Silicon substrate having refractive index of 3.15. The operational wavelength of the input ports is 1.55 μm. Since the structure is a simple geometric in its dimension with clear operating principle, it is potentially applicable for photonic integrated circuits. The logic operations are realized by a control signal and the input signal (s) applied across two adjacent faces, while the output is obtained along one of the remaining face. No control signal is used for AND Gate, However to realize OR, NOT and NOR Gates a control signal is applied at the third face. With same structure one can realize all optic logic gates. The steady state field distributions at different input sates are obtained by FDTD simulation. The results indicate the potential candidature of the photonic crystal for optical digital integrated circuits.

TE/TM polarization splitters in LiNbO3 photonic wires

Ultra-compact TE/TM polarization splitters in LiNbO3 photonic wires with two parallel LN optical waveguide at 1.31μm wavelength have been presented. The operating principle of the polarization splitter is based on the directional coupling mode and easy to design by using commercial software Optiwave FDTD. Calculated steady-state field distributions indicate that guided lightwaves in both TM and TE polarizations can be spatially separated from different output waveguides ports. The transmittances of TE and TM in the proposed polarization splitter at 1.31μm wavelength are 98.3% and 96.2%, respectively. The bandwidth of TE mode with transmittances more than 93% is greater than 40nm. And that of TM with transmittances more than 90% is greater than 60nm. The coupling length and total length of the device are 39μm and 37μm, respectively. In addition, the dependences of the transmittance on coupling length for TE/TM polarization in the proposed structure are demonstrated, respectively. The simple and compact wavelength splitter is expected to be applied to highly dense LN photonic integrated circuits.

Ultracompact wavelength splitters in LiNbO3 photonic wires

Ultracompact wavelength splitters in LiNbO 3 photonic wires with three different structures for 1.31 and 1.55 μm wavelengths with transverse magnetic (TM) polarization have been presented. The devices are based on the operating principle of a directional coupler in two parallel dielectric waveguides and can be designed by using the finite element method. Calculated steady-state field distributions indicate that 1.31 and 1.55 μm wavelengths are spatially separated. In a particular structure, the transmittances at 1.31 and 1.55 μm wavelength are 99.4% and 95%, respectively. The total lengths of the three different structures are 39.8, 40, and 42.6 μm, respectively. Moreover, the coupling length dependences of the transmissions, the optical transmission bandwidths, and fabrication sensitivities are evaluated, respectively.

Optomechanical Self-Channeling of Light in a Suspended Planar Dual-Nanoweb Waveguide

It is shown that optomechanical forces can cause nonlinear self-channeling of light in a planar dual-slab waveguide. A system of two parallel silica nanowebs, spaced ~100 nm and supported inside a fiber capillary, is studied theoretically and an iterative scheme developed to analyze its nonlinear optomechanical properties. Steady-state field distributions and mechanical deformation profiles are obtained, demonstrating that self-channeling is possible in realistic structures at launched powers as low as a few mW. The differential optical nonlinearity of the self-channeled mode can be as much as 10×10(6) times higher than the corresponding electronic Kerr nonlinearity. It is also intrinsically broadband, does not utilize resonant effects, can be viewed as a consequence of the extreme nonlocality of the mechanical response, and in fact is a notable example of a so-called accessible soliton.

Laser nanotrapping and manipulation of nanoscale objects using subwavelength apertured plasmonic media

We study the net radiation force on dielectric nanowires above a planar plasmonic medium consisting of a nanostructured gold film on a glass substrate. The film has a subwavelength aperture and the medium is illuminated by a continuous plane wave. We compute the steady-state field distribution by using two-dimensional finite element analysis, and we evaluate the force on the nanowires above the aperture by using the Maxwell stress tensor. We show that the vertical position of a nanowire can be controlled by either tuning the wavelength of the laser source or tapering the aperture. We experimentally check the conclusions of the theory by realizing laser nanotrapping of dielectric beads near the surface of nanostructured metal. Our results demonstrate the potential of using nanostructured plasmonic media for the controlled optical manipulation of nanowires and nanoparticles, including their application as “plasmonic sieve” for separation based on size and/or refractive index.

Modeling of steady-state field distributions in blocked impurity band detectors

Steady-state electric field and carrier distributions are calculated for blocked impurity band (BIB) detectors in the absence of external illumination. The results illustrate the role of space charge in the blocking layer. Calculations are presented for Ge:Ga, though the input is easily modified for other materials. The numerical model allows for observation of the effect of spatial doping variations and interface gradients. The BIB field distribution is highly dependent on the purity and compensation in the blocking layer, as well as interface sharpness. In some cases, space charge effects can cause a collapse of the field at the blocker/absorber interface or the contact and resultant low field regions in the blocking layer.

Steady-state conduction in high density polyethylene with field-dependent mobility

A theory of steady-state conduction of injected space-charge-limited carriers (SCLCs) into high density polyethylene (HDPE) is presented. Injected carriers are deeply trapped at crystalline-amorphous boundaries before the steady state is reached. At elevated temperatures, they are thermally excited to the conduction band in the crystalline regions, and then hop with field-dependent mobility through defect states of the amorphous regions. A hopping site separation of 2.2 nm, corresponding to 9.4×1019/cm3, yields good agreement with experimental current-field characteristics for fields up to 0.5 MV/cm, in the temperature range 61–85.5 °C. The final current I versus field F and temperature T equation shows that the activation energy of the detrapping and transport processes are additive on a semilog plot of I/T vs 1/T. The total activation energy is 1.15 eV at 0.2 MV/cm, in agreement with others. The steady-state field distributions in the sample are calculated, and are independent of temperature in the above temperature and field ranges. The conditions under which our theory reduces to that of simple SCLC, field-independent mobility theory, and differences in conduction between linear low density polyethylene and HDPE are discussed.

Transient Analysis of Microstrip Gap in Three-Dimensional Space (Short Paper)

In this paper, we deal with the microstrip gap that should be analyzed in three-dimensional space. The time variations of the electric field at each surface of the stripline having a finite metallization thickness are analyzed. Our method of analysis is based on both an equivalent circuit of Maxwell's equations and Bergeron's method. The former has advantages in the vector analysis by using all electromagnetic components. The latter has advantages in the time-domain analysis of the field. Therefore, our method can analyze field variations in three-dimensional space and time. We present the time variation of the instantaneous electric-field distributions below the strip, at the side of the strip, and at the gap end surface. These results show how the steady-state field distribution grows in the gap.

Coupling of power from a circular confocal laser with an output aperture

An iteration technique is used for a theoretical study of the field distributions and diffraction losses at the reflectors of an asymmetric confocal cylindrical resonator having an output hole in one mirror for the low-loss TEM <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">00</inf> and TEM <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</inf> modes with Fresnel numbers of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N = 0.8</tex> and 1.2. A digital computer is used to numerically iterate an initially launched uniform distribution as it reflects back and forth between the mirrors until a steady-state field distribution occurs. The edge and coupling hole diffraction losses and the power coupled from an output hole in one mirror are also computed. The presence of the coupling hole produces a perturbation of the field distribution with distortion of the field increasing for increasing Fresnel number and for low-order modes. The relationship between hole radius and power output is presented. An optimum-size coupling hole may be selected from this data, which will yield maximum power output in the mode of operation desired. It has been found that, with the use of a coupling hole, mode selection of the lowest order TEM <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">00</inf> mode is possible for resonators having large Fresnel numbers ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N &gt; 1.0</tex> ).

Imposition of sinusoidal flux by feedback for analogue and digital computation of the field distribution in a.c.-magnetised ferromagnetic laminas

The paper gives a method of imposing a sinusoidal flux when computing the electromagnetic Maxwellian field distribution in a lamina which is considered to be plane, and infinite in two directions. The static hysteresis loop has been modelled by a polygonal line. The method has been developed on an analogue computer, and then adapted for digital computation. This avoids the need for iterative computing, and maintains the stability and the convergence achieved with the analogue computation; it also avoids difficulties common to analogue function generators. Both analogue and digital computers need, at the most, one quarter of a period to start computing the steady-state field distribution, and the complete solution is obtained in a single computer run, extended to three quarters of a period only. Agreement between the computed and the measured magnetisation current is poor; it is thought that the main divergence results from the disagreement between the assumed and the actual behaviour of the material. Recognisable, but relatively insignificant, errors result from modelling the hysteresis loop by a polygonal line, and from limitation of the number of steps into which the width of the lamina has been divided.

Resonant Modes in a Maser Interferometer

A theoretical investigation has been undertaken to study diffraction of electromagnetic waves in Fabry-Perot interferometers when they are used as resonators in optical masers. An electronic digital computer was programmed to compute the electromagnetic field across the mirrors of the interferometer where an initially launched wave is reflected back and forth between the mirrors. It was found that after many reflections a state is reached in which the relative field distribution does not vary from transit to transit and the amplitude of the field decays at an exponential rate. This steady-state field distribution is regarded as a normal mode of the interferometer. Many such normal modes are possible depending upon the initial wave distribution. The lowest-order mode, which has the lowest diffraction loss, has a high intensity at the middle of the mirror and rather low intensities at the edges. Therefore, the diffraction loss is much lower than would be predicted for a uniform plane wave. Curves for field distribution and diffraction loss are given for different mirror geometries and different modes. Since each mode has a characteristic loss and phase shift per transit, a uniform plane wave which can be resolved into many modes cannot, properly speaking, be resonated in an interferometer. In the usual optical interferometers, the resolution is too poor to resolve the individual mode resonances and the uniform plane wave distribution may be maintained approximately. However, in an oscillating maser, the lowest-order mode should dominate if the mirror spacing is correct for resonance. A confocal spherical system has also been investigated and the losses are shown to be orders of magnitude less than for plane mirrors.