Beam Propagation Method Analysis Research Articles

Passive parity-time-symmetry-breaking transitions without exceptional points in dissipative photonic systems [Invited

Over the past decade, parity-time ($\mathcal{PT}$)-symmetric Hamiltonians have been experimentally realized in classical, optical settings with balanced gain and loss, or in quantum systems with localized loss. In both realizations, the $\mathcal{PT}$-symmetry breaking transition occurs at the exceptional point of the non-Hermitian Hamiltonian, where its eigenvalues and the corresponding eigenvectors both coincide. Here, we show that in lossy systems, the $\mathcal{PT}$ transition is a phenomenon that broadly occurs without an attendant exceptional point, and is driven by the potential asymmetry between the neutral and the lossy regions. With experimentally realizable quantum models in mind, we investigate dimer and trimer waveguide configurations with one lossy waveguide. We validate the tight-binding model results by using the beam propagation method analysis. Our results pave a robust way toward studying the interplay between passive $\mathcal{PT}$ transitions and quantum effects in dissipative photonic configurations.

Design considerations for quasi-phase-matching in doubly resonant lithium niobate hexagonal micro-resonators

Fabrication capabilities of high optical quality hexagonal superstructures by chemical etching of inverted ferroelectric domains in lithium niobate platform suggests a route for efficient implementation of compact hexagonal microcavities. Such nonlinear optical hexagonal micro-resonators are proposed as a platform for second harmonic generation (SHG) by the combined mechanisms of total internal reflection (TIR) and quasi-phase-matching (QPM). The proposed scheme for SHG via TIR-QPM in a hexagonal microcavity can improve the efficiency and also the compactness of SHG devices compared to traditional linear-type based devices. A simple theoretical model based on six-bounce trajectory and phase matching conditions was capable for obtaining the optimal cavity size. Furthermore numerical simulation results based on finite difference time domain beam propagation method analysis confirmed the solutions obtained by demonstrating resonant operation of the microcavity for the second harmonic wave produced by TIR-QPM. Design aspects, optimization issues and characteristics of the proposed nonlinear device are presented.

Beam propagation method for analysis of Er-doped integrated optics devices

A method of calculating the gain and the output signal based on the beam propagation method and rate equations is presented. It employs the complex atomic susceptibility in the paraxial wave equation to calculate light propagation in integrated optics devices. As an example, an erbium-doped waveguide planar splitter is analyzed.

Finite-difference time-domain beam propagation method for analysis of three-dimensional optical waveguides

A three-dimensional time-domain beam propagation method has been developed using an alternating-direction implicit method that can be solved by the standard Thomas algorithm. The presented method achieves second-order accuracy not only in space but also in time and has the advantage of allowing a larger time step than that in the conventional finite-difference time-domain method. The effectiveness of the present method is demonstrated through the analysis of pulse propagation in an optical fibre with a facet.

Laser-to-fiber optical coupling scheme with a long working distance by use of thermally overexpanded fiber

A laser-diode-optical-fiber coupling scheme that uses aspherically ended thermally overexpanded fiber is proposed. The scheme is verified by both an analytical formalism and a wide-angle beam-propagation method analysis in cylindrical coordinates.

Monolithic integration of spot-size converters with 1.3-μm lasers and 1.55-μm polarization insensitive semiconductor optical amplifiers

To reduce packaging costs, it is necessary to use passive alignment between the laser diodes and optical fiber. Such an alignment requires low-coupling loss and large positional alignment tolerances. This is achievable with integrated spot-size converters, which permit to match the near field of a laser to that of a flat-end single-mode fiber (SMF). In this paper, we first review briefly the different technological approaches to realize spot-size converters. Then, we focus on the double-core structure developed both for 1.3-/spl mu/m Fabry-Perot lasers and 1.55-/spl mu/m semiconductor optical amplifiers (SOAs). The spot-size expansion is simulated using a two-dimensional (2-D) beam propagation method analysis. Short spot-size converters (100 /spl mu/m) integrated with 1.3-/spl mu/m lasers and 1.55-/spl mu/m SOAs exhibit beam divergences as low as 12/spl deg//spl times/12/spl deg/ and 12/spl deg//spl times/15/spl deg/, respectively. The performances of devices with integrated spot-size converters are reported and discussed. A 2-in wafer process is used thanks to the versatility of the double-core structure and its compatibility with buried ridge stripe technology.

Improved bidirectional beam propagation method for analysis of reflection on nonparallel interfaces

An improved bidirectional beam propagation method (IBBPM) is proposed, to allow the analysis of optical wave reflection and transmission in waveguiding structures with multiple nonparallel interfaces.

Iterative finite difference beam propagation method analysis of nonlinear optical waveguide excitation problem

AbstractThe beam propagation method (BPM), used widely for analyzing optical waveguides and optical circuits, is also being applied to devices that include nonlinear materials. However, in the analysis of nonlinear optical devices using the conventional BPM, in many cases it is assumed that the field intensity distribution does not change within the step length in propagation direction. Therefore, for accurate calculation, the step size in the propagation direction must be extremely small, which results in long calculation times.Therefore, this paper proposes and formulates a numerical method where the solution is forced to converge by the iterative calculation of a difference equation over each propagation step of the Crank‐Nicolson BPM method. Using this method, first, we analyzed the case where the fundamental TE mode propagates in the dielectric slab waveguide that has a Kerr‐like nonlinear cladding. By calculating the emission angle of the optical beam into the cladding, the present method is compared with the conventional method. After it is demonstrated that this present method is effective, the dependency of the optical beam emission angle for the incident power is shown. Furthermore, the effect of the beamwidth on the excitation is analyzed in the case where a nonlinear stationary wave is excited by a Gaussian beam and the interesting results are proved.

Beam propagation method analysis of transverse-electric waves propagating in a nonlinear tapered planar waveguide

The propagation of TE-polarized guided waves in a nonlinear tapered waveguide is studied. The incident fields are chosen from the stable branches of the nonlinear dispersion curve in its uniform section. The propagations of the field in both directions are calculated by the beam-propagation method. Wave propagation in the tapered waveguide is discussed in terms of the nonlinear dispersion curves of the waveguide. Depending on the intensity, the field can radiate as a spatial soliton or it can have an abrupt transition between the guided mode and the surface polariton. The wave propagation of an incident field that is composed of a dominant TE0 wave and a small TE1 wave is investigated. Finally, using a property of this wave propagation, we present a new device for continuous signal routing.

Beam propagation method analysis of optical waveguide lenses

Focusing characteristics of optical waveguide lenses are analyzed by the beam propagation method (BPM) instead of the ray tracing method. By use of the BPM, we can observe field distributions of a converging or diverging light beam after it passes through a waveguide lens. Variations of the spot width and magnitude of diffraction can immediately be evaluated with this calculation. The BPM calculations are used for a mode-index, Luneburg, and geodesic lenses. For the application of the method to the geodesic lens, the surface deformation is converted into an equivalent index.

Beam-propagation method analysis of a nonlinear directional coupler

The beam-propagation method is employed to analyze nonlinear directional-coupler operation for various combinations nonlinear materials and initially mismatched guides. A mixed focusing-defocusing configuration is found optimal results.

A beam propagation method analysis of active and passive waveguide crossings

A beam propagation method is employed to analyze the characteristics of crossed optical waveguides and related switches, based on such crossed waveguides. The complex coupling properties of passive crossings are highlighted and general design guidelines for passive devices as well as for switches are given.