Vertical Coupler Research Articles

An Efficient Full-Wave Electromagnetic Analysis for Capacitive Body-Coupled Communication

Measured propagation loss for capacitive body-coupled communication (BCC) channel (1 MHz to 60 MHz) is limitedly available in the literature for distances longer than 50 cm. This is either because of experimental complexity to isolate the earth-ground or design complexity in realizing a reliable communication link to assess the performance limitations of capacitive BCC channel. Therefore, an alternate efficient full-wave electromagnetic (EM) simulation approach is presented to realistically analyze capacitive BCC, that is, the interaction of capacitive coupler, the human body, and the environment all together. The presented simulation approach is first evaluated for numerical/human body variation uncertainties and then validated with measurement results from literature, followed by the analysis of capacitive BCC channel for twenty different scenarios. The simulation results show that the vertical coupler configuration is less susceptible to physiological variations of underlying tissues compared to the horizontal coupler configuration. The propagation loss is less for arm positions when they are not touching the torso region irrespective of the communication distance. The propagation loss has also been explained for complex scenarios formed by the ground-plane and the material structures (metals or dielectrics) with the human body. The estimated propagation loss has been used to investigate the link-budget requirement for designing capacitive BCC system in CMOS sub-micron technologies.

High efficiency germanium-assisted grating coupler.

We propose a fiber to submicron silicon waveguide vertical coupler utilizing germanium-on-silicon gratings. The germanium is epitaxially grown on silicon in the same step for building photodetectors. Coupling efficiency based on FDTD simulation is 76% at 1.55 µm and the optical 1dB bandwidth is 40 nm.

Design of an ultra-short coupler in an asymmetric twin-waveguide structure using transformation optics.

An integrated vertical coupler that transfers light from the lower passive waveguide to the upper active waveguide in an asymmetric twin-waveguide integration structure (in InGaAsP/InP material system) is designed using transformation optics (TO). The length of the coupler is as short as 3μm, which is two orders of magnitude shorter than that of traditional tapered couplers. According to three-dimensional full-wave simulations, the designed optimized coupler has a high coupling efficiency of 94.9%, and a low reflection at the wavelength of 1.55μm. Subsequently, quasi-conformal mapping is employed to reduce the material complexity and to make it possible to realize the coupler by purely using an isotropic dielectric material. Applying TO to integrated photonic devices may motivate new applications, and improve integration density on the InP platform.

Low-Cost Interfacing of Fibers to Nanophotonic Waveguides: Design for Fabrication and Assembly Tolerances

The high cost and low scalability of interfacing standard optical fibers to nanophotonic waveguides hinder the deployment of silicon photonics. We propose a mechanically compliant low-cost interface with integrated polymer waveguides. Our concept promises better mechanical reliability than a direct fiber-to-chip coupling and a dramatically larger bandwidth than diffractive couplers. Our computations show a 0.1-dB penalty over a 200-nm bandwidth, whereas typical two-polarization vertical couplers show a ~1-dB penalty over a 30-nm bandwidth. In this paper, we present a comprehensive analysis of the design space using optimization routines to achieve a fabrication- and assembly-tolerant design. We demonstrate the concept feasibility through extensive tolerance analysis with parameter control assumptions derived from low-cost manufacturing.

One order enhancement of detectivity in quaternary capped InAs/GaAs quantum dot infrared photodetectors due to vertical coupling of quantum dot layers

The spectral and electrical properties of vertically coupled quaternary (InAlGaAs) capped InAs/GaAs quantum dot infrared photodetector with different capping thicknesses are investigated, and compared with a conventional quaternary capped uncoupled detector. Electronic coupling between quantum dot layers leads to a reduction in the ground state energy level and hence greater electronic confinement, which reduces the dark current and enhances the detectivity. These expectations are confirmed by our experimental results. Most significantly one order enhancement in peak detectivity (from 1.1×109cmHz1/2/W to 2.48×1010cmHz1/2/W) is observed for optimized coupled quantum dot infrared photodetector compared to uncoupled device. The optimal interlayer barrier thickness which gives maximum detectivity is explained in terms of the interplay between electronic coupling and strain buildup in the heterostructure.

Vertical Directional Couplers With Ultra-Short Coupling Length Based on Hybrid Plasmonic Waveguides

We propose and analyze a series of vertical directional couplers based on SOI-compatible hybrid plasmonic waveguides. We investigate two configurations: metal-insulator-metal (MIM) and insulator-metal-insulator (IMI). Both slab and three-dimensional analyses show that MIM directional couplers have better coupling performance such as sub-micron coupling length and lower loss. To ensure the normalized power loss lower than 5%, the coupling length can be chosen as short as 0.492 μm (about one third of the wavelength 1.55 μm). The coupler size can be traded for even lower power loss. In one example, a less-compact design yields 3% power loss, while maintains sub-micron coupling length. We further verified our design with beam propagation analysis. The analysis independently verifies the compact MIM design does show guided mode coupling length along vertical direction can be as short as 0.492 μm.

A Three-Dimensional Silicon Nitride Polarizing Beam Splitter

A 3-D polarizing beam splitter based on a silicon nitride (Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ) vertical directional coupler is experimentally demonstrated. A new planarization technique by incorporating conventional chemical-mechanical lapping with a dry-etching process is developed, in order to obtain a flat film surface for the second Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> core deposition after the first-layer waveguide is formed. Both the Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> layer thicknesses are 200 nm. As there is a material refractive index mismatch between the vertically separated waveguides, the polarization splitter can be realized with a bottom waveguide width of 1.55 μm and a top core width of 1.35 μm. The transverse electric (TE) polarized light can be transmitted completely to the cross-layer output-port, whereas the transverse magnetic (TM) polarized wave outputs mostly from the port at the input layer. A high-extinction ratio and a wide operation bandwidth can be achieved. An extinction ratio of 26 dB for the cross-layer output-port at 1550-nm wavelength and that of 16 dB for the input-layer output-port are obtained. There is an excess coupling loss of for the TE light, but a 1-dB loss for the TM wave.

A 0.15-mm-Thick Noncontact Connector for MIPI Using a Vertical Directional Coupler

A noncontact and housing-less thin–thick connecting method was developed for mobile industry processor interface (MIPI) applications. This paper describes the world's first 0.15-mm-thick connector using a vertical directional coupler (VDC) which enables simultaneous two-link communication with one coupler without fatal performance degradation. We have analyzed the conditions for isolating two links in a coupler, and the design method is discussed. A fully balanced pulse transmitter implemented in 90-nm CMOS technology significantly suppressed electromagnetic interference (EMI), which agrees well with MIPI requirements. An experimental liquid crystal display interface system reached a maximum data rate of 2.3 Gb/s/link at a bit error rate of less than <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$10^{-12}$</tex> </formula> and a power consumption of 1.47 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$~$</tex></formula> pJ/b. The timing margin of single link was 320 ps ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$=$</tex></formula> 64% U.I.) and of two links was 305 ps ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$=$</tex> </formula> 61% U.I.) at 2.0 Gb/s.

Realizing vertical light coupling and splitting in nano-plasmonic multilevel circuits

We present a novel technique for vertical coupling of light guided by nanoscale plasmonic slot waveguides (PSWs). A triangularly-shaped plasmonic slot waveguide rotator is exploited to attain such coupling with a good efficiency over a wide bandwidth. Using this approach, light propagating in a horizontal direction is efficiently coupled to propagate in the vertical direction and vice versa. We also propose a power divider configuration to evenly split a vertically coupled light wave to two horizontal channels. A detailed parametric study of the triangular rotator is demonstrated with multiple configurations analyzed. This structure is suitable for efficient coupling in multilevel nano circuit environment.

Novel Miniaturized Dual-Band Bandpass Filter with High Suppression Using Low-Temperature Co-Fired Ceramic Technology

A novel low-temperature co-fired ceramic dual-band bandpass filter with a compact size and high selectivity is reported using vertically coupled lines and semi-lumped resonators. Due to the source–load coupling and the characteristics of the resonators, five transmission zeros are introduced to improve the selectivity of the filter. A dual-band filter located at 2.45 and 5.2 GHz has been designed and fabricated in a low-temperature co-fired ceramic substrate to verify the proposed design concept. With the assistance of the vertical coupling structure and low-temperature co-fired ceramic technology, the filter occupies an area of 7.3 × 6.2 mm2.

Transmission-Efficient Structures of Bent and Crossing Silicon Slot Waveguides

We present transmission-efficient bent and crossing silicon slot waveguides for compact silicon slot waveguide-based circuits. To begin with, using the 3-D vector finite-element method, we investigate the transmission characteristics of a bent silicon slot waveguide with an asymmetric slot that is connected to straight waveguides. Numerical results show that the transmission efficiency can be improved by optimizing a taper structure that is introduced between the bend of an asymmetric slot waveguide and its straight input/output waveguides. Next, we investigate the transmission characteristics of a 3-D crossing silicon slot waveguide that has a vertical coupler. Numerical results show that our crossing structure can achieve a high transmission efficiency compared with conventional structures.

Highly-efficient fully resonant vertical couplers for InP active-passive monolithic integration using vertically phase matched waveguides

A new active-passive monolithic integration approach for photonic components based on vertical evanescent coupling is presented. Two vertically stacked waveguides are used in order to provide full resonant power transfer between them and avoiding the need of tapered structures. Light confinement in each waveguide is achieved combining strong lateral asymmetric structures and bent waveguides, both defined during lithography. Low propagation losses for the active waveguide and coupling efficiencies to the passive section as high as 97% have been obtained.

Integrated refractive index sensor based on hybrid coupler with short range surface plasmon polariton and dielectric waveguide

In this paper, an integrated sensor based on the vertical hybrid coupler composed of a short range surface plasmon polariton (SRSPP) waveguide and a SiNx dielectric waveguide has been studied theoretically and experimentally in detail by varying the structure parameters and the thickness of detection layer. It is demonstrated that the output power of the sensor changes significantly with the refractive index of the detection layer and the resolution is estimated to be as high as 7.3×10−6 refractive index units. The sensing range can be adjusted coarsely and delicately by varying the thickness of SRSPP waveguide and the width of the SiNx waveguide, respectively. Owing to the highly bounded mode field of SRSPP, the sensor is also applied to detect a 5nm-thick variation of detection layer with thickness detection sensitivity as high as 0.67dB/nm. Further, the sensor is used to detect the bisphenol A.

Ion beam irradiation induced fabrication of vertical coupling waveguides

Vertically coupled waveguides have been fabricated on a silicon-on-insulator platform using a combination of reactive ion etching to pattern the device layer and high-energy proton beam irradiation followed by electrochemical etching to pattern the substrate. Infra-red light can be coupled from the lower rib waveguide within the substrate into the upper waveguide within the device layer. By varying the proton energy along the lower waveguide, we have fabricated a tapered profile which is thin at the coupling region for higher efficiency and thicker towards the outer ends for easier coupling of light. A typical coupling efficiency of 26% has been achieved.

High-efficiency optical coupling to planar photodiode using metal reflector loaded waveguide grating coupler

For the realization of optoelectronic integrated circuits, it is required to incident light perpendicularly to a planar Si photodiode. We propose a high-efficient vertical optical coupler using an amorphous Si optical waveguide grating coupler with top reflector, which is transparent at 850 nm wavelength range. The optical waveguide (width of 300 nm $$\times $$ height of 100 nm) coupler is analyzed by using finite element method. The coupling efficiency of 80 % is calculated at the grating period of 380 nm, the duty ratio of 0.75 and the depth of 35–65 nm with top metal reflector.

Vertical Noise Coupling From On-Chip Switching-Mode Power Supply in a Mixed-Signal Stacked 3-D-IC

In this paper, we propose a fast and accurate model of the vertical noise coupling from an on-chip switching-mode power supply (SMPS) to a low noise amplifier (LNA) in a stacked 3-D-IC. To achieve both speed and accuracy, the model is based on the analytic formulas of static R, L, and C parasitic extraction, and includes consideration of the phase difference in the on-chip inductors using a new iterative calculation method. The proposed model and the prediction of vertically coupled noise at the LNA output using the model are experimentally validated on a fabricated stacked 3-D-IC consisting of an onchip SMPS and LNA. Good agreement with the measurements is confirmed in both the frequency domain and the time domain. The enhancements of the proposed model, including the broad model bandwidth (<; 4 GHz) as good as 3-D EM solver and 99% reduction of the simulation elapsed time (2 s) from 3-D EM solver, are confirmed. This paper also analyzes: 1) the impact of vertical noise coupling on the RF signal gain performance of the LNA and 2) the impact of variation in the stacking configuration, location, and thickness of the stacked LNA on the vertical noise coupling using the proposed model. Based on the results of our analysis, this paper proposes and verifies an effective method to reduce the vertical noise coupling using the proposed model.

Low-cost board-to-board optical interconnects using molded polymer waveguide with 45 degree mirrors and inkjet-printed micro-lenses as proximity vertical coupler

We demonstrate intra- and inter-board level optical interconnects using polymer waveguides and waveguide couplers consisting of both 45 degree total internal reflection (TIR) mirrors and inkjet-printed micro-lenses. Surface normal couplers consisting of 50 µm × 50 µm waveguides with embedded 45 degree mirrors are fabricated using a nickel mold imprint. Micro-lenses, 70 µm in diameter, are inkjet-printed on top of the mirrors. We characterize the optical transmission between waveguides located on different boards in terms of insertion loss, mirror coupling loss, and free space propagation loss as a function of interconnection distance in free space. Each mirror contributes 1.88 dB loss to the system, corresponding to 65% efficiency. The printed micro-lenses improve the transmission by 2-4 dB (per coupler). Data transmission at 10 Gbps reveals that inter-board interconnects has a bit error rate (BER) of 1.1 × 10(-10) and 6.2 × 10(-13) without and with the micro-lenses, respectively.

Rigorous supermode solutions in a strong absorption slab waveguide and application to design of a waveguide photodetector

A rigorous supermode solution method in a strong absorption slab multilayer waveguide is performed. The method is directed toward finding solutions for a sophisticated complex determinant in a complex plane. The rigorous results are applied to design a waveguide photodetector that has a configuration of a vertical directional coupler. Absorption lengths of the supermodes and coupling length of the coupler are calculated based on an effective index approach by using the rigorous results of the strong absorption slab multilayer waveguide to optimize the directional coupling waveguide photodetector.

Development of a vertical optical coupler using a slanted etching of InP/InGaAsP waveguide

We demonstrate a simple and efficient optical coupler for vertical coupling between optical fibers and InP-based waveguides using a slant-etched mirror. The angle of the etched mirror can be controlled by using an aluminum jig with a beveled surface inserted under the substrate during RIE (reactive ion etching) of InP/InGaAsP. The off-chip coupler is fabricated simultaneously with a high-mesa waveguide with only one etching process. Coupling loss of 7.3dB between the tapered single-mode fibers is obtained within the wavelength of 1530-1570nm.

Numerical analysis of the coupling mechanism in long-range plasmonic couplers at 155 μm

We study the coupling mechanism between a high refractive index contrast waveguide and a plasmonic thin-film waveguide in the IR range. We also propose a novel design of a vertical coupler based on loading the plasmonic waveguide with a high refractive index contrast medium on each side. We achieve a coupling efficiency and an insertion loss of about 95% and 0.2dB, respectively, with a coupling length of only 2.85μm at the working wavelength of 1.55μm.