A recent computational result suggests that the diffraction limit can be overcome by all-dielectric metamaterials (S. Jahani et. al., Optica 1, 96 (2014)). This substantially decreases crosstalk between dielectric waveguides paving the way for high density photonic circuits. Here, we experimentally demonstrate, on an standard silicon-on-insulator (SOI) platform, that using a simple metamaterial between two silicon strip waveguides results in about 10-fold increase in coupling length. The proposed structure may lead to significant reduction of size of devices in silicon photonics.
In this letter, we demonstrate the relationship between the incident angles and the polarization states of transmitted beams on the basis of a kind of helical metamaterials. Through finite-difference time-domain simulations, it is found that the polarization states of the transmitted lights can be tuned by changing the incident angles. When the angles vary from 20 ° to -20 ° , the axial ratios of the transmitted lights have significant changes from 1:0.93 to 1:0.59. This phenomenon of the tunable polarization can be explained qualitatively through the analysis of the surface current on the helical wires.
We demonstrate photonic ultra-efficient thermo-optic switches on a 220-nm silicon-on-insulator platform. We used several approaches to increase the tuning efficiency of the switches. We used folded waveguides in a Michelson interferometer configuration to increase the optical interaction length of the light with the heated region, and used a suspended structure to improve thermal isolation. An ultra-low switching power of 50 μW is realized with an extinction ratio of over 26 dB for the transverse electric mode at 1550 nm. The 10%-90% response time of the switch is 1.28 ms, including a 780 μs rise time and a 500 μs fall time. Compared with the best thermo-optic switch in the literature, our device shows approximately an order of magnitude reduction in power consumption.
Fabrication variability significantly impacts the performance of photonic integrated circuits (PICs), which makes it crucial to quantify the impact of fabrication variations before the final fabrication. Such analysis enables circuit and system designers to optimize their designs to be more robust and obtain maximum yield when designing for manufacturing. This work presents a simulation methodology, Reduced Spatial Correlation Matrix-based Monte-Carlo (RSCM-MC), to efficiently study the impact of spatially correlated fabrication variations on the performance of PICs. First, a simple and reliable method to extract physical correlation lengths, variability parameters that define the inverse of the spatial frequencies of width and height variations over a wafer, is presented. Then, the process of generating correlated variations for MC simulations using RSCM-MC methodology is presented. The methodology generates correlated variations by first creating a reduced correlation matrix containing spatial correlations between all the circuit components, and then processing it using Cholesky decomposition to obtain correlated variations for all circuit components. These variations are then used to conduct MC simulations. The accuracy and the computation performance of the proposed methodology are compared with other layout-dependent Monte-Carlo simulation methodologies, such as Virtual wafer-based Monte-Carlo (VW-MC). A Mach-Zehnder lattice filter is used to study the accuracy, and a second-order Mach-Zehnder filter and a 16x16 optical switch matrix system are used to compare the computational performance.
Recent design flows for photonic integrated circuits have been able to take advantage of mature capabilities available in electronic design automation such as schematic driven design and sophisticated circuit verification. Furthermore, new photonic integrated circuit simulators that can interface with electrical circuit simulators have been developed. As a result, photonic design flows are rapidly advancing in maturity. An area that still requires development is the statistical analysis of photonic circuits to be able to predict and improve yield, which is particularly challenging because photonic components tend to be large compared to the wavelength which makes them highly sensitive to phase errors. Furthermore, photonic devices tend to have long range spatial correlations in their parameters that cannot be ignored. In this paper, we present two approaches that enable Monte Carlo analysis of photonic integrated circuits, which include the treatment of spatial correlations, and we show how they can be used to predict the circuit yield. Example circuits include passive filters made from cascaded Mach-Zehnder interferometers and transceivers using active ring modulators.
Silicon photonics has emerged from research labs and is currently being used in a range of commercial products, with significant growth expected over the next few years. Current and future applications include transceivers for datacoms in datacenters and 5G, as well as a variety of sensors from medical diagnostics to LIDAR. Even longer-term applications such as artificial intelligence and quantum information technologies are in development. This growth is supported by a wide range of foundries who offer silicon photonic processes, as well as an ecosystem of design tools. We present an innovative design flow for electronic photonic design automation (EPDA) which fully supports industrial product development. This flow combines the best-in-class tools for schematic capture, co-simulation and implementation, combined with the leading photonic solvers for custom component optimization, parameter extraction and photonic compact model development. We discuss how it combines the maturity of EDA with requirements unique to photonic design.
We demonstrate 3-dB broadband directional couplers that use asymmetric-waveguide-based phase compensation. Average coupling ratios of 46.57% and 48.28% were obtained from 1500 nm to 1600 nm for transverse electric and transverse magnetic modes, respectively.
We present two kinds of broadband and polarization-insensitive metamaterial (MM) absorbers operating in about 0.3–2.5 μm, including a racemic type and a reflected type. Through finite-difference time-domain simulation, we find that both designs are broadband in function and insensitive to polarization. In comparison, we find that the reflected type absorber possesses broader bandwidth (0.36–2.5 μm) and exhibits higher average absorbance (88.9%), while the racemic type is superior in its polarization-insensitivity characteristic. Differing from designs of most planar MM absorbers based on perfect impedance matching, our designs are based on the principle of mutual radiation.
In the last few years, much attention has been paid to the researches of metallic helical metamaterials due to their giant circular dichroism for transmitted lights. However, so far as we know, there is little work concerning the study of their reflection properties, which are also significant questions for the helical metamaterials. In this work, we study the reflection properties of the helical metamaterials by using the Finite-Difference Time-Domain (FDTD) method. The circular dichroism and the reflected polarization states of left-handed single-, double-, triple-, and quadruple-helical structures are investigated, respectively. It's found that both the single- and the double-helical structures perform giant circular dichroism, and their reflected polarization states are related to the handedness of helical structure; while triple- and quadruple-helical structures exhibit no circular dichroism at all, and their reflected polarization states are irrelevant to the handedness of helical structure.
We compare state-of-the-art sub-wavelength grating couplers (SWGCs) based on their coupling efficiencies, 1-dB bandwidths and back reflections. Three types of SWGC, the uniform SWGC, the apodized SWGC, and the broadband SWGC, which use one-dimensional sub-wavelength gratings, are compared for the silicon-on-insulator platform. The SWGCs are designed for the fundamental TE mode, operating at 1550nm.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)
