Bending Losses In Waveguides Research Articles

Finite-Difference Mode Solver for Curved Waveguides With Angled and Curved Dielectric Interfaces

A finite-difference scheme for accurately analyzing step-index dielectric waveguides with angled and curved dielectric interfaces has been proposed by Chiang Here, this formulation is generalized to take into account a possible curvature of the entire waveguide along the propagation direction, and it is shown how Perfectly Matched Layers can be incorporated in order to accurately compute the bending or curvature loss of dielectric waveguides with step-index profiles of arbitrary shape. Furthermore, the formulation of the interface equations that relate the fields and their derivatives on both sides of a dielectric interface has been simplified, so that their implementation no longer requires any further explicit conversions between coordinate systems.

Bending loss of terahertz pipe waveguides

We present an experimental study on the bending loss of terahertz (THz) pipe waveguide. Bending loss of pipe waveguides is investigated for various frequencies, polarizations, core diameters, cladding thicknesses, and cladding materials. Our results indicate that the pipe waveguides with lower guiding loss suffer lower bending loss due to stronger mode confinement. The unexpected low bending loss in the investigated simple leaky waveguide structure promises variety of flexible applications.

Using quasi-guided modes for modeling the transfer behavior of bent dielectric slab waveguides

Abstract. The connection of two straight dielectric multimode slab waveguides by a circular bent waveguide is analyzed by means of quasi-guided modes. These modes correspond to the well known leaky modes, but own real eigenvalues, thus the mathematical description is simpler. Furthermore they are derived as approximate solutions of the exact theory. This work will first give a brief introduction to the basic theory, followed by a discussion of the properties of quasi-guided modes. After a validation by comparison with a numerical simulation using the Finite Integration Technique, results for the bending loss of multimode waveguides are presented.

Bending and coupling losses in terahertz wire waveguides

We present an experimental study of several common perturbations of wire waveguides for terahertz pulses. Sommerfeld waves retain significant signal strength and bandwidth even with large gaps in the wire, exhibiting more efficient recoupling at higher frequencies. We also describe a detailed study of bending losses. For a given turn angle, we observe an optimum radius of curvature that minimizes the overall propagation loss. These results emphasize the impact of the distortion of the spatial mode on the radiative bend loss.

Study on the characteristics of erbium-doped waveguide ring laser

A theoretical model of the erbium-doped waveguide ring laser is established according to the theory of erbium-doped waveguide amplifier and the transmission matrix of waveguide directional coupler. The influence of bend radius, coupling coefficient and doped erbium ion concentration on the characteristics of waveguide ring laser is investigated. It is shown that due to the co-action of waveguide bend loss and other relevant loss there is an optimal bend radius which can provide simultaneously low threshold pumping power and high laser light output power. As one part of the resonator’s loss, the laser light coupling coefficient of directional coupler has an impact on the laser property. The analysis indicates that the laser achieves the high output power when the coupling coefficient is about 0.2. The threshold pumping power is the minimum when the doped erbium ion concentration is 0.85×1026 m−3. Increasing the concentration of doped erbium ions will enhance the output power of laser light as long as the concentration doesn’t introduce remarkable up-conversion effect. The results give a good theoretical basis for the design and fabrication of erbium-doped waveguide ring laser devices.

Fabrication and Evaluation of Nano-Scale Optical Circuits Using Sol-Gel Materials With Photo-Induced Refractive Index Variation Characteristics

Nano-scale optical circuits with core thickness of ~ 230 nm and core width of ~ 1 mum were fabricated and evaluated, using the photo-induced refractive index variation sol-gel materials, whose refractive index gradually increases by UV light exposure and baking. Propagation loss of linear waveguides was 1.86 dB/cm for TE mode and 1.89 dB/cm for TM mode at 633 nm in wavelength, indicating that there were small polarization dependences of ~ 0.03 dB/cm. Spot sizes of guided beams along core width direction and along core thickness direction were, respectively, 0.6 and 0.3 mu m for both TE mode and TM mode. Bending loss of S-bending waveguides was reduced from 0.44 to 0.24 dB for TE mode with increasing the bending curvature radius from 5 to 60 mu m. Although the bending loss for TM mode was slightly higher than that for TE mode, the difference was less than 10%. Branching loss of Y-branching waveguides was reduced from 1.33 to 0.08 dB for TE mode, and from 1.34 to 0.12 dB for TM mode with decreasing the branching angle from 80deg to 20deg. From these results, it is concluded that the photo-induced refractive index variation sol-gel materials can realize miniaturized optical circuits with sizes of several tens of microns and guided beam confinement within a cross section area less than 1.0 mum2 with small polarization dependences, indicating potential applications to intra-chip optical interconnects.

Finite element analysis and experimental verification of SOI waveguide bending loss

AbstractBending and transition losses in silicon‐on‐insulator rib waveguides were calculated using finite‐element analysis of equivalent straight waveguides with perfectly matched boundary layers. Experimental loss measurements of silicon‐on‐insulator waveguides with various bend radii reveal that this technique accurately predicts loss and minimum bend radius for efficient design. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 699–702, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24135

Intrinsic integrated optical temperature sensor based on waveguide bend loss

Curvature of a multimode integrated optical waveguide reduces the numerical aperture and induces radiation losses. In this paper, we study this phenomenon and we present a geometrical approach to calculate the local numerical aperture and the intensity attenuation. We exploit the bending effect on the local numerical aperture to make a new intrinsic temperature sensor. The simulation results are validated for the silica/silicone integrated optical case. The principal performances of the silica/silicone temperature sensor are the extended temperatures range (−50 to 200 °C) with an excellent linearity response (1%) between 20 and 200 °C.

Microring-Resonator Cross-Connect Filters in Silicon Nitride: Rib Waveguide Dimensions Dependence

We report a systematic study of monolithic microring-resonator cross-connect filters with various waveguide widths and heights in silicon-nitride-on-silica substrates. Our experiments reveal that for particular deeply etched rib heights and slab heights, the microring-resonance Q factors rise nearly linearly as a function of the submicrometer waveguide width, while the extinction ratios generally drop nonlinearly. From the measurements, we are able to extract the microring loss and the waveguide-microring coupling coefficient at various waveguide widths and heights by using a Fabry-Perot-like model. The trends of the extracted microring loss and coupling coefficient are in qualitative agreement with the trends of the numerically simulated curved rib waveguide bend loss and straight rib waveguide evanescent field amplitude at the coupling distance

Design optimization of polymer electrooptic modulators

A versatile and numerically efficient finite-element method-based approach has been developed and used to solve the associated quasi-static Laplace equation for electrodes, the full-vectorial wave equation for optical waveguides, and the evolutionary beam-propagation method for bend designs, to characterize the Mach-Zehnder-based polymer modulators incorporating ridge-type waveguide structures. The effects of the rib height and the waveguide width on a single-mode operation, the symmetry of the beam profile, the insertion loss, and the bending loss of the polymer rib waveguides are presented. Further, the effect of the rib height, the waveguide width, and the electrode width on the key modulator parameters, such as V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pi</sub> L, N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> , and Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> are presented, and as a consequence, an optimized design is reported.

Experimental evaluation of curved polymer waveguides with air trenches and offsets

Excess waveguide bend loss can be minimized through the use of offsets and air trenches. Offsets, used for reducing the junction loss between straight and curved waveguides, and air trenches, which prevent bend radiation loss, were simulated by a three-dimensional, semivectorial beam propagation method. Low loss polymer waveguide bend structures, employing both offsets and trenches, were fabricated. A reduction of the 180° bend insertion loss from 17.7to3.0dB with a bending radius (BR) of 1.5mm is experimentally confirmed at λ=1.55μm. BR ranging from 5to0.5mm are evaluated with decent match when compared with simulation results. The polarization dependent loss is BR dependent with a maximum value of 0.4dB when the BR is reduced to 0.5mm. The experimental results confirm that the joint use of air trenches and junction offsets is effective in reducing the bend radii of low index contrast polymer waveguides in planar lightwave circuits.

Design of integrated wavelength monitor based on a Y-branch with an S-bend waveguide

Departing from conventional concerns about lowering waveguide bend loss, wavelength dependence of a bending waveguide is investigated and utilized in wavelength measurement. With a beam propagation method, a Y-branch device with an S-bend waveguide is optimally designed as an integrated ratiometric wavelength monitor, which can be employed in wavelength measurement for optical communications and fiber Bragg grating or Fabry-Perot filter based optical sensing.

Full-vectorial finite element method in a cylindrical coordinate system for loss analysis of photonic wire bends

This paper presents a new full-vectorial finite-element method in a local cylindrical coordinate system, to effectively analyze bending losses in photonic wires. The discretization is performed in the cross section of a three-dimensional curved waveguide, using hybrid edge/nodal elements. The solution region is truncated by anisotropic, perfectly matched layers in the cylindrical coordinate system, to deal properly with leaky modes of the waveguide. This approach is used to evaluate bending losses in silicon wire waveguides. The numerical results of the present approach are compared with results calculated with an equivalent straight waveguide approach and with reported experimental data. These comparisons together demonstrate the validity of the present approach based on the cylindrical coordinate system and also clarifies the limited validity of the equivalent straight waveguide approximation.

Mode conversion losses in silicon-on-insulator photonic wire based racetrack resonators

Two complimentary types of SOI photonic wire based devices, the add/drop (A/D) filter using a racetrack resonator and the Mach-Zehnder interferometer with one arm consisting of an identical resonator in all-pass filter (APF) configuration, were fabricated and characterized in order to extract the optical properties of the resonators and predict the performance of the optical delay lines based on such resonators. We found that instead of well-known waveguide bending and propagation losses, mode conversion loss in the coupling region of such resonators dominates when the air gap between the racetrack resonator and access waveguide is smaller than 120nm. We also show that this additional loss significantly degrades the performance of the optical delay line containing cascaded resonators in APF configuration.

Propagation Losses in Curved Integrated Optical Waveguides Based on Oxidized Porous Silicon

The propagation losses are evaluated for the first time in curved integrated (buried) optical waveguides (WGs) based on oxidized porous silicon. In the visible red range, the losses decrease from 20 to 5 dB per 90° bending (for about 0.4 dB/cm loss in the straight WG) when the WG curvature radius increases from 125 to 2500 μm. The main component of the total bending losses in WGs is related to the coupling loss on the passage from straight to curved WG parts. Additional losses are introduced by the regions of incompletely oxidized porous silicon on the walls of curved WGs.

Bend loss attenuator by carrier injection in InGaAsP∕InP

A compact InGaAsP/InP waveguide bend loss attenuator with electrically modulated bend loss is demonstrated. The carrier injection device exhibits better than 15 dB modulation and &lt;20 ns response time. The bend loss attenuator requires less than half the current of a comparable straight waveguide attenuator to achieve 3 dB attenuation.

The impact of CMP and underlying back-end topographical features on losses in deposited dielectric waveguides

The bending losses in rectangular dielectric waveguides deposited on a chemical mechanical polished (CMP) surface above the metal interconnect/interlayer dielectric stack of a processed Si wafer are modeled and estimated. CMP efficiently removes local topography and microroughness, but leaves long-range surface profile undulations due to variations in the metal pattern density. These surface undulations are then transferred to the waveguides deposited on this surface. A beam propagation method (BPM) waveguide simulation program and an equation for bending loss developed by Marcuse have been used to examine the bending losses seen by waveguides deposited on such a surface. In order to simplify the simulation of the bending losses of the waveguides, the undulations are modeled as a series of arcs, which is shown to be a good approximation. It was determined that under typical conditions, the bending losses may be ignored as they are less than 0.1 dB/cm, which is below the range of typical propagation losses for a straight guide.

Experimental study of bent multimode optical waveguides

Bend losses of bent multimode waveguides have been experimentally studied. The results experimentally verify a simple analytical expression based on ray optics that can be used to determine bend losses in bent multimode waveguides. We have also shown that bend-induced losses in such multimode optical waveguides are wavelength independent.

Performance analysis of three dimensional high index contrast dielectric waveguides

This paper presents the implementation of a parallelized Finite- Difference Time-Domain method, based on the Message Passing Interface (i.e. MPI), which is used to study the modal properties of three-dimensional (3D) dielectric waveguide structures. To this end, we also use the leastsquare method to obtain the wave vector, beta, along the axis of propagation. Lastly, bending losses in arbitrary-angle waveguides are also discussed.

Losses in single-mode silicon-on-insulator strip waveguides and bends

We report the fabrication and accurate measurement of propagation and bending losses in single-mode silicon waveguides with submicron dimensions fabricated on silicon-on-insulator wafers. Owing to the small sidewall surface roughness achieved by processing on a standard 200mm CMOS fabrication line, minimal propagation losses of 3.6+/-0.1dB/cm for the TE polarization were measured at the telecommunications wavelength of 1.5microm. Losses per 90 masculine bend are measured to be 0.086+/-0.005dB for a bending radius of 1microm and as low as 0.013+/-0.005dB for a bend radius of 2microm. These record low numbers can be used as a benchmark for further development of silicon microphotonic components and circuits.