Common digital display systems have evolved into sophisticated optical devices. The rapid market growth in liquid crystal
displays makes the simulation of full systems attractive, promoting virtual prototyping with decreased
development times and improved manufacturability. Realistic simulation using commercial non-sequential ray tracing
tools has been instrumental in this process, but the need to accurately model polarization devices has become critical in
many designs. As display systems seek more efficient use of light and more accurate color representation, the proper
simulation of polarization devices with large acceptance angles is essential. This paper examines non-uniform
polarization effects in the simulation of modern display devices using realistic polarizer and retarder models in the
ASAP® non-sequential ray-tracing environment.
Silicon-on-insulator (SOI) is a widely recognized as a very promising material for high-index integrated photonic chips
because of its compatibility with complementary metal oxide semiconductor (CMOS) technologies. One challenge in
integrating many photonic devices on a single chip is to realize compact waveguide bends and splitters, particularly for
rib waveguide geometries. We report compact SOI rib waveguide 90° bends and splitters with SU8-filled trenches based
on total internal reflection (TIR). We use the two-dimensional finite difference time domain (2D-FDTD) method to
numerically calculate bend and splitter efficiencies. The maximum bend efficiency is 98.0%. The splitter efficiency is
49.0% for transmission and 48.9% for reflection with an 80 nm wide SU8-filled trench. Electron beam lithography
(EBL) is used to accurately position the trench interface relative to the waveguides and to pattern the 80 nm wide trench.
Inductively coupled plasma reactive ion etching (ICP RIE) is used to achieve a vertical sidewall. For fabricated bends
the measured bend loss is 0.32±0.02 dB/bend (93% bend efficiency) for TE polarization at a wavelength of 1.55 microns,
which is the lowest SOI rib waveguide 90° bend loss reported in literature. The initial measured splitter efficiency is
54.6% for transmission and 29.2% for reflection. This can be improved by avoiding defects in fabricated structures.
We discuss the design of a compact ring resonator (RR) and Mach-Zehnder interferometer (MZI) in a low-refractive-index-contrast waveguide material system through the use of air trenches. A narrow air trench at the intersection of one input and two output waveguides can function as a high-efficiency splitter, while wider air trenches operate as waveguide bends. We first discuss the design of individual splitters and bends and then show how they can be used to realize a compact MZI and RR. The RR has a footprint of only 70×100 µm, and its optical efficiency at the drop wavelengths is 86%. The free spectral range and full width at half maximum are 7.2 and 0.5 nm, while the Q factor is >3,000. The MZI occupies only 165×130 µm, and its calculated optical efficiency is 90%.
We propose an integrated waveguide depolarizer for use in interferometric fiber optic gyroscopes (IFOGs) with single-mode fiber coils. The integrated waveguide depolarizer is based on a Mach-Zender interferometer with polarizing beamsplitters. A waveguide polarizing beamsplitter is designed using multiple air trench structures oriented at the Brewster angle. We also analyze the effect of component imperfections on the degree of polarization achievable with an integrated waveguide depolarizer.
High efficiency small-area waveguide bends and splitters for perfluorocyclobutane (PFCB) copolymer materials have been designed with air trench structures (ATSs). An air trench at the intersection of one input and two output waveguides can function as a high efficiency splitter. High efficiency small-area waveguide bends are achieved by placing ATSs at the waveguide bend corners and operate through total internal reflection (TIR). In this paper we discuss bends and splitters that are designed specifically for constructing a ring resonator and a Mach-Zender interferometer. Two dimensional (2-D) finite difference time domain (FDTD) analysis has been used for design. In order to further examine the performance of realistic small-area air trench bend structures, we have also employed three dimensional (3-D) FDTD. From 3-D FDTD simulation results, we find that the 2-D designs are representative of actual devices. By combining small-area air trench bends and splitters, we show how a compact ring resonator can be realized. Simulation results show attractive properties for the proposed ring resonator design. Preliminary ATS etch results of PFCB with CO and O2 shows the possibility of fabricating the proposed devices.
The ability to make small-area bends and splitters in low index contrast waveguide materials is a critical enabler to realize densely integrated planar lightwave circuits (PLCs) in such materials. We discuss two approaches, the first based on photonic crystal (PhC) structures of limited spatial extent and the second on single air trenches. In each case, PhC or air trench regions are used to augment conventional waveguides (CWGs) to permit drastic reductions in overall device size while preserving the traditional advantages of CWGs such as straightforward design for single mode operation, low propagation loss, low fiber coupling loss, low dispersion, and mature microfabrication processes. We show how these approaches can be used to realize example devices having a very small footprint, including Mach-Zender interferometers and ring resonators.
We previously proposed the hybrid integration of photonic crystals (PhCs) and conventional index-guided waveguides (CWGs) as a potentially attractive method of realizing compact waveguide elements for large-scale planar lightwave circuits (PLCs). We now examine 90-deg bends and beamsplitters in PhC/CWG structures in which the waveguide core has a high refractive index (3.25) and yet a low refractive index contrast (1.54%) with the clad material. A PhC structure composed of a triangular or square array of air holes is placed at the intersection of input and output waveguides to obtain high efficiency 90-deg bends. We find that diffraction from the boundary of the PhC region with CWG limits the optical efficiency of the bend. To overcome this we use a rigorous design tool based on a microgenetic algorithm (µGA) and a finite difference time domain (FDTD) method to optimize the boundary layer to suppress the unwanted diffraction. We find that this approach yields improvements in the bend efficiency at a wavelength of 1.55 µm from 56.2 to 92.5% (for a triangular PhC structure, TE polarization) and from 72.0 to 97.4% (square PhC structure, TM polarization).
Hybrid photonic crystal (PhC) and conventional waveguide (CWG) structures have been proposed to achieve ultracompact waveguide bends and splitters with very high efficiency (>99.0%). Such elements are enablers to realize large scale planar lightwave circuits (PLCs) with low index contrast waveguide materials such as silica and polymers. In this paper, we first discuss high efficiency 90 degree bends and splitters and then show how these can be used to create compact ring resonators. These in turn can be used as building blocks for add/drop filters, band pass filters, wavelength division multi-/demultiplexers, and all optical switches.
We have proposed the hybrid integration of photonic crystals (PhCs) and conventional index-guided waveguides (CWGs) as a potentially attractive method of realizing compact waveguide elements for large-scale planar lightwave circuits (PLCs). In this paper we briefly review the properties of PhC/CWG 90° bends in low index, low index contrast waveguides and then extend them to waveguides with high index and low index contrast. We find that diffraction from the boundary of the PhC region limits the optical efficiency of the bend. To overcome this we use a rigorous design tool based on a micro-genetic algorithm (microGA) and a finite difference time domain (FDTD) method to optimize the boundary layer to suppress the unwanted diffraction. We find that this approach yields an improvement in the bend efficiency for light at 1.55 micron from 80% to 95%.
We discuss the use of multiple layer air trench and silicon strip structures to realize high efficiency 90° bends for low index contrast waveguides. We use a micro-genetic algorithm (mGA) coupled with a 2-D finite difference time domain method to perform rigorous electromagnetic optimization of multi-layer structures for single mode waveguides. We find that a 3-layer air trench structure can be designed for a 90° waveguide bend that exhibits 97.2% efficiency for TM polarized light at a wavelength of 1.55 μm. We are also able to design five- and six-layer silicon strip bends that have high efficiency for both TE and TM polarizations. For example, simulation results for a six-layer design show 95.2% and 97.2% for TE and TM polarizations, respectively. Moreover, the bend efficiency for each polarization state is greater than 90% over a broad wavelength range (1.5 μm to 1.7 μm).