Semiconductor Rib Waveguides Research Articles

Study of H-field using higher-order compact (HOC) finite difference method (FDM) in semiconductor rib waveguide structure

Following the recent success with polarized E-field solutions, an efficient and highly accurate semi-vectorial H-field mode solver is proposed for various rib waveguides based on higher (fourth)-order compact FDM in combination with a conjugate gradient (CG) type of iteration. Here, optical waveguide modeling is designed by incorporating the modal index and modal birefringence concept into the refractive index profiles (RIPs) of two specific semiconductor (GaAs/GaAlAs and GeSi) rib waveguide structures for simulating the performances of various photonic integated circuits and corresponding field profiles of guided modes are shown through the surface and contour plots. It is to be confirmed that the used algorithm takes full account of vertical and horizontal discontinuities of RIPs in cell interfaces within the specific waveguide structure where the numerical results ensure its behavior for stability and convergence with less computational time. For Hx and Hy modes, computed modal index and normalised index values are found to be in perfect agreement with other published results. Most importantly, the variations of these indices with waveguide structure parameters help to identify their optimized values which play very decisive role so far as their fabrications are concerned. Also study of confinement factor computation and modal birefringence provides some important additional deep understanding with which the optimized index values clearly verify the material dependence for effective wave propagation.

Study of optical modal index for semi conductor rib wave guides using higher order compact finite difference method

In this paper, a higher order compact finite difference method in combination with conjugate gradient iteration scheme has been used for optical modal index study of four different semi conductor rib wave guide structures in GaAs/GaAlAs and GeSi material systems. Obtained results for modal indices and normalized indices are used to optimize the structure parameters of the wave guides under consideration and confirm the degree of guidance for propagating waves through various structures in line with the results as obtained by other researchers. Confinement factors for different structures are calculated in support of the data to verify the acceptability of our method.

Optical confinement study of different semi conductor rib waveguides using higher order compact finite difference method

Semi conductor optical wave guides with well defined refractive index profile and geometric shapes which help to understand the propagation properties are widely used in the field of integrated optics. Accordingly rib waveguides are considered, as this structure allows the greatest versatility in device design in which the basic concept employed is its compositional changes in the vertical direction where the three regions of the rib structure are divided into zones with specific refractive indices. As for these types of structures no precise analytic solution is obtained, different numerical techniques have been implemented for their study in terms of their modal analysis. So an accurate higher order compact (HOC) finite difference method (FDM) in combination with conjugate gradient method (CGM) is used here for the investigation of refractive index profile of GaAs and GeSi rib waveguide structure to show their effect on transmission properties of the guided wave using Helmholtz wave equation. The difference in surface and contour plots of the polarized E-field solution clearly shows the material dependence of transmitted waves. We have also studied the variation of optical confinement factor with a number of parameters to understand the propagation properties appropriately as per the requirement of various guided wave optoelectronic devices.

Higher order compact (HOC) finite difference method (FDM) to study optical confinement through semiconductor rib wave guides

Higher order compact (HOC) finite difference method (FDM) to study optical confinement through semiconductor rib wave guides

Polarization conversion at the discontinuities in semiconductor opto-electronic systems

The origin of unexpected polarization conversion at the junctions between two semiconductor rib waveguides is demonstrated by using full-vectorial numerical approaches.

Efficient analysis of integrated optical circuits by the spectral index method

AbstractThe ability to optimise the performance of today's opto‐electronic circuits over a range of operational parameters and fabrication tolerances is foremost in the designer's mind. The ability to investigate the effects of tolerancing and integration upon device performance over a range of wavelengths is highly desirable for their successful exploitation. The spectral index (SI) method is a well‐established method traditionally used for the analysis of the modal properties of semiconductor rib waveguides. In this paper the efficiency and accuracy of the SI method is exploited for the first time in a scattering‐matrix approach to the analysis of complex integrated optical circuits. The SI approach yields highly accurate results with minimal computational effort. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 68–73, 2003

The single-mode condition for semiconductor rib waveguides with large cross section

A comparison of the single-mode condition for semiconductor rib waveguides with large cross section obtained by the effective index method and the corrected formula proposed by Soref et al. [see IEEE Journal of Quantum Electronics, vol. 27, p. 1971, 1991] with experimental data is carried out. It is found that the effective index method is in a better agreement with Rickman's experimental data than the modified version. Moreover a stronger condition is proposed for single-mode design purposes.

Intersecting rib waveguide structures with reduced crosstalk

A numerical study of the throughput and crosstalk in intersecting semiconductor rib waveguides was carried out using the beam propagation method. The fraction of the optical power that couples out of one input waveguide and into the crossed waveguide falls to below 3% for crossing angles greater than 4°. Two simple modifications to the waveguide shape at the X-crossing region were found to reduce the crosstalk for crossing angles between 4° and 10° such that the crosstalk to throughput ratio may be reduced by up to a factor of 100 while the throughput is reduced by, at most, a few percent. In device structures that combine X-crossings with curved waveguide sections our results permit greater design flexibility and improved overall loss and crosstalk performance.

Reduced coupling loss using a tapered-rib adiabatic-following fiber coupler

We present the design and experimental demonstration of a tapered-rib adiabatic-following fiber coupler (TRAFFIC). This device is an adaptation of a Shani-Henry mode converter fabricated in (Al)GaAs and designed to increase the coupling efficiency of conventional optical fibers to tightly-confined semiconductor rib waveguide devices. This approach offers the potential of significantly reducing fiber butt coupling losses from the typical values of 7 to 10 dB to values of <1 dB. This long-standing packaging problem is one of the major impediments to the widespread acceptance of semiconductor-based optoelectronics. Moreover, the design can be implemented with minimal increase in fabrication complexity since it uses only a straightforward modification to epitaxial growth, and one additional lithography and etching step.

Crosstalk reduction in intersecting rib waveguides

A numerical study of the throughput and crosstalk in intersecting semiconductor rib waveguides was carried out using the beam propagation method. The fraction of the optical power that couples out of one input waveguide and into the crossed waveguide falls to below two percent for crossing angles greater than four degrees. A simple modification to the waveguide shape at the X-crossing region was found to reduce the crosstalk for crossing angles between four and ten degrees. The crosstalk to throughput ratio is reduced by up to a factor of nine while the throughput is reduced by, at most, a few percent. In device structures that combine X-crossings with curved waveguide sections this permits greater design flexibility and improved overall loss and crosstalk performance.

Molecular Dynamics Approach to the Mode Analysis of Optical Waveguides

A novel numerical method, based on a molecular dynamics algorithm for coupled harmonic oscillators, is applied to the mode analysis of arbitrary-shaped optical waveguides. We describe in detail the relationships between the vibrational equation of motion for lattice dynamics and the discretized form of the wave equation for light. This mapping is useful for the analysis of the characteristics of optical waveguides. The efficiency of the method is demonstrated by application of the method to the mode analysis of a semiconductor rib-waveguide.

The Spectral Index Method for Semiconductor Rib and Ridge Waveguides

The Spectral Index Method for Semiconductor Rib and Ridge Waveguides

New technique for finite difference analysis of optical waveguide problems

AbstractThe method of effective penetration depth is used to produce a novel scalar or polarized finite difference approach for the solution of optical rib waveguide field problems. The new method is quicker than previous finite difference approaches and requires less computer memory. Propagation constant values are presented for a range of semiconductor rib waveguides and are found to be indistinguishable from benchmark results produced using earlier methods of analysis. A simple polarization correction formula recently derived is confirmed by utilizing the good accuracy of these results. This enables discussion of the relationship between quasi‐TE, quasi‐TM and scalar modes, and a further substantial reduction of the cpu time.

Single-mode optically activated phase modulator on GaAs/GaAlAs compound semiconductor rib waveguides

We report on an optically activated phase modulator (OAM) and modulator array on GaAs-GaAlAs compound semiconductor rib waveguides. A rib waveguide device with an optical activation window of 5 μm in diameter was fabricated. Optical activation was produced by using a HeNe 632.8 nm wavelength as the free-carrier generator and a 1.3 μm laser as the signal carrier. A 33% modulation depth was observed and 10−2 index modulation was experimentally confirmed on an OAM working in the phase modulation regime. OAMs working in both phase- and cutoff-modulation regimes were further determined by considering the variation of the waveguide confinement factor. An 8.2 dB modulation depth was observed on an OAM working at the cutoff regime. Furthermore, the activation source for the free-carrier generation is in the mW power region, which significantly reduces the size and cost of all optical switching devices.

Micro-optical circuit design using AUTOCAD and finite element analysis

A semiconductor rib waveguide was designed using AUTOCAD for layout and the finite difference beam propagation method to calculate field distribution. The near-field method accomplished by an IR image processing system was used to investigate the field distribution in the 1.3-μm region.

Highly accurate vector correction for optical waveguide propagation constants

A vector correction is derived to the propagation constants obtained from a polarised analysis of graded-index optical waveguides. This general formula is reduced to a form suitable for use with semiconductor rib and strip-loaded waveguides. Corrected propagation constants calculated for a range of semiconductor rib waveguide structures coincide with available results from a full vector approach. Moreover, the vector correction term is always small, underpinning the accuracy of this simple and fast polarised approach for the first time.

Analysis of multilayer semiconductor rib waveguides with high refractive index substrates

The waveguiding properties of semiconductor rib waveguides with high refractive index substates are studied using the spectral index method. The propagation constants of leaky modes in such two-dimensional structures are calculated for the first time. The method is applied to the design of high wall GaAs/AlGaAs rib waveguides. Results indicate that the number of low-loss modes can be controlled by careful positioning of the substrate relative to the guiding region.

A comparison of Lanczos electric field propagation methods

The authors analyze the losses of a strongly guiding semiconductor rib waveguide Y-junction with the aid of various propagation algorithms based on Lanczos reduction. Although for the example Lanczos procedures adequately describe electric field propagation in the Fresnel approximation, the Helmholtz implementation converges unacceptably slowly. They therefore propose a finite-difference wide-angle approach which employs a power-series expansion of the forward propagation operator. The computational efficiency of the method is comparable to that of the Fresnel formalism with little or no reduction in accuracy from the Helmholtz technique.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Polarisation correction applied to scalar analysis of semiconductor rib waveguides

A simple formula is derived which is applied as a quasi-TE- or quasi-TM-mode corrector to the propagation constant values obtained from a scalar treatment of semiconductor rib waveguides. The resulting polarised propagation constants agree favourably with well established benchmark values for both types of mode. The present approach offers advantages in the speed and simplicity of solution.

Rigorous effective index method for semiconductor rib waveguides

A saddle point variational principle, for estimating the propagation constant of an optical rib waveguide mode from a discontinuous trial function, is generalised to provide a theoretical underpinning for the familiar effective index method. It is shown that better accuracy can be achieved in a rigorous manner, while maintaining much of the simplicity that makes the original effective index approach so attractive.