Emmanuel Anemogiannis

Multilayer waveguides: efficient numerical analysis of general structures

An efficient numerical method for accurately determining the real and/or complex propagation constants of guided modes and leaky waves in general multilayer waveguides is presented. The method is applicable to any lossless and/or lossy (dielectric, semiconductor, metallic) waveguide structure. The method is based on the argument principle theorem and is capable of extracting all of the zeros of any analytic function in the complex plane. It is applied to solving the multilayer waveguide dispersion equation derived from the well known thin-film transfer matrix theory. Excellent agreement is found with seven previously published results and with results from two limiting cases where the propagating constants can be obtained analytically. >

Transmission characteristics of long-period fiber gratings having arbitrary azimuthal/radial refractive index variations

A numerical method is presented for determining the transmittance of long-period (LP) fiber-gratings having arbitrary azimuthal/radial refractive index variations. The method uses coupled-mode theory and includes both the sine and cosine character of the LP modes. The model treats interactions between the fundamental LP/sub 01/ mode and high-azimuthal-order cladding modes. The method utilizes the transfer matrix method to model cylindrical layers both in the core and the cladding regions.

Bound and quasibound state calculations for biased/unbiased semiconductor quantum heterostructures

A complex transcendental equation valid for a wide range of electron energies for semiconductor quantum heterostructures under unbiased or biased conditions is derived. Its complex roots have as real parts the structure eigenenergy levels, and their imaginary parts are directly related to the lifetime of the corresponding eigenenergies. A numerical method is presented that is capable of extracting all these complex eigenenergies. The method is based on the argument principle theorem from complex number theory. Therefore, all the energy levels and lifetimes of bound and quasibound states can be determined. Energy levels and lifetimes can also be calculated in the presence of scattering events when these are modeled with an energy broadening imaginary potential. Extensive comparisons between this numerical method and other currently used techniques are included, proving the generality and the accuracy of this new method. >

Efficient solution of eigenvalue equations of optical waveguiding structures

A general numerical method is presented that is capable of extracting all the zeros of a complex equation. This method allows accurate determination of the complex propagation constants of general multilayer optical and microwave planar waveguides, the computation of energy states and their lifetimes of semiconductor heterostructures, and the roots of complex transcendental equations from other scientific disciplines. The method differs from previous approaches in that the time-consuming differentiation of the complex function is not required. Furthermore, the present method is not affected by the presence of complex poles and so can be used for the solution of meromorphic transcendental equations. In practice, the method is found to be much faster than other rigorous approaches. >

Quasi-bound states determination using a perturbed wavenumbers method in a large quantum box

A perturbed wavenumbers method (PWM) is presented that is capable of determining the quasi-bound-state eigenenergies and their lifetimes for quantum heterostructures having arbitrary potential profiles. The numerical method presented solves the single-band effective-mass Schrodinger equation without using complex energies. It is applicable to quantum structures that are symmetric, asymmetric, unbiased, or biased. For multiple quantum heterostructures, extensive comparisons of this numerical method with other currently used techniques are included. In addition, a modified density of states formulation is presented and applied to these example cases.

Tuning, attenuating, and switching by controlled flexure of long-period fiber gratings

Azimuthal variations in the refractive index that are inherent in CO(2) -laser-induced long-period fiber gratings (LPFGs) coupled to small controlled flexure of the LPFG produce a wide variety of transmission characteristics as a function of LPFG curvature. The particularly useful cases of (1) wavelength tuning at a constant attenuation and (2) variable attenuation (switching) at a constant wavelength are demonstrated by flexing of LPFGs that have been appropriately axially rotationally oriented relative to the plane of curvature.

Optimization of multilayer integrated optics waveguides

A numerical method is described that provides the means for optimizing any objective function representing a general multilayer integrated optics waveguide. In this way, the physical parameters of the multilayer structure can be set so that the performance of the device is optimized. The method uses any standard numerical minimization algorithm in conjunction with the argument principle method. The method has been successfully applied for the optimization of a multilayer immunosensor and a TE-mode polarizer. The advantages of the method are its generality, its efficiency, its accuracy, and its applicability to a wide range of planar integrated optics devices. >

Quasibound state determination of arbitrary-geometry quantum heterostructures

The operation and performance of semiconductor electronic and optoelectronic quantum-heterostructures devices are critically dependent on the quasibound states of these structures. In this paper a unified set of four numerical methods is presented that are capable of determining the quasibound-state eigen-energies and their lifetimes in quantum heterostructures having arbitrary potential profiles. The methods are applicable to symmetric, asymmetric, unbiased or biased devices. All the numerical approaches solve the single-band effective-mass Schrodinger equation. The numerical methods are shown to be both numerically efficient and accurate.

Integrated optical architectures for tapped delay lines

An integrated optics (IO) device that is an implementation of an IO tapped delay line is discussed. It is capable of performing discrete convolution of an optical pulse sequence with a preset digital function. Several architectures for the device are presented. A systematic realization of the preset function samples that permits efficient utilization of all the input light power and maximization of the output signal-to-noise ratio (SNR) for the device is discussed. A detailed analysis of what determines the number of preset samples that can be realized and how to realize them on a LiNbO/sub 3/ crystal is given. Two digital filter design examples are presented, and the quantization error effects on their performance are examined. The same architectures are shown to implement digital-to-analog (D/A) conversion and systolic multiplication of a Toeplitz matrix with a vector having the form of optical pulses. >

Nanostructure optical emitters based on quasibound electron energy levels

Abstract Given two energy states (levels) in a quantum well formed by two potential barriers of finite thickness, elementary quantum mechanics tells us that the lower energy state is more tightly bound than the upper state. This produces a longer spatial confinement lifetime in the lower state than in the upper state. This ratio of lifetimes is opposite to that needed for laser action between these states. Furthermore, the lifetime of the lower energy state must be significantly shorter than the electron scattering time for the upper state. These facts have blocked the development of lasers based on these transitions. However, in this paper we report experimental and analytical results on a versatile type of semiconductor heterostructure that overcomes these difficulties. Unlike previous devices, this structure relies on an optical transition between two states which are both above-barrier quasibound states in the ‘classical’ continuum. The oscillator strength is large and the operation of the device clearly demonstrates coherent electron wave behavior. Such structures could represent the basis for a new room-temperature infrared semiconductor laser.