Effect Of Fabrication Tolerances Research Articles

Comprehensive grating enabled silicon nitride fiber-chip couplers in the SNIR wavelength band.

We present silicon nitride grating enabled fiber-chip coupling in the sub-near-infrared band. We present a comprehensive design and simulation and experimental demonstration of uniform and apodized grating couplers, with and without bottom reflectors. The mode engineering yields a best efficiency of -1.6 dB for apodized grating design, which is further improved to -0.66 dB with a bottom reflector. Experimentally, we demonstrate a coupling efficiency of -2.2 dB for the optimized design. Furthermore, we present a detailed simulation and measurement comparison of various grating parameters and the effect of fabrication tolerances on the grating performance.

Highly Sensitive ELC Resonator Based Differential Sensor

A highly sensitive electric LC resonator-derived differential sensor is proposed in this work, with the major focus on detecting the purity of any reference dielectric material. The proposed sensor is designed with two identical electric-LC (ELC) resonators being loaded on either side of a 50- $\Omega $ microstrip line such that the magnetic wall of the microstrip line is perfectly aligned with that of the resonators. The fabricated unloaded sensor is operating at a resonance frequency of 3.385 GHz, falling between the two ISM bands, exhibiting a peak electric field intensity at the capacitive gap. The working principle of the sensor is analyzed through a lumped element equivalent circuit model. Experimental validation is performed via the fabricated prototype of the developed sensor on Taconic TLY-5 substrate for various standard and unknown dielectric samples. For the accurate testing of various samples using the proposed sensor, an empirical relationship is developed relating the difference in the resonance frequencies of the unloaded and loaded resonators, and the sample thickness. Furthermore, a novel error modeling technique is also incorporated to take into consideration the effect of fabrication tolerance and any possible air gap between the sensor region and the test specimen. The proposed differential sensor possess a substantially higher normalized sensitivity of 4.915% (165 MHz in terms of absolute sensitivity), which is quite useful for applications requiring detection of purity of a product. Its applicability is validated here by detecting the presence of termite infestation in wood sample.

A new improved vertical comb type differential capacitive sensing micro accelerometer using silicon-on-insulator wafer technology

A new and improved approach using vertical combs for the differential capacitive sensing of acceleration using silicon-on-insulator (SOI) wafer technology is presented. The design, which supports a ± 30 g operational range demonstrates the enhanced linear range that is achievable using an SOI approach, which overcomes the limitations of the dissolved wafer process (DWP) technology based on the diffusion layer depth in silicon, used for the fabrication of MEMS accelerometers. Two technological approaches are compared, one having the same thicknesses of fixed and movable interdigitated fingers (DWP) and the other having different thicknesses, using an SOI wafer. A remarkable sensitivity improvement, by a factor of up to two, is achieved for the capacitance change per unit g (deltaC g−1) using the new differential SOI design presented here. The bandwidth of the device is also improved significantly in the SOI design, compared to the DWP design. Furthermore, the effect of temperature (−40 °C to 125 °C) has an almost negligible influence on (deltaC) due to the built-in differential concept of comb-type fingers compared to DWP technology. Cross-axis sensitivity is also very low due to the stable, robust design of the accelerometer offering less stiction sideways and better pull-in stability. Simple analytical relations for dynamically changing overlap capacitance are derived and presented. These analytical results are compared with simulations using Coventorware software and are in agreement to within 1.8% in a linear range of operation up to a tip deflection of 8.5 µm. The effects of fabrication tolerances, including all the process steps, on the sensitivity (deltaC g−1) and bandwidth (BW), are also studied and the results presented. An overall figure of merit (FOM) is included which is better in this study compared to the available literature. Furthermore, only two wafers are needed to fabricate the proposed differential capacitive sensors, compared to conventional push–pull three plate systems using three wafers. A separate deep reactive ion etching (DRIE) step on two different wafers offers better debris removal as compared to the interdigitated fingers cut by a single DRIE step.

Miniaturized Frequency-Selective Surfaces Based on Monolithically Integrated Components

In this article, a novel approach to design low-profile miniaturized frequency-selective surfaces (FSSs) is proposed. The effective miniaturization of the FSS elements, based on square-ring-slot resonators, is accomplished by reactively loading the FSS unit cell with monolithically integrated components. The reactive components, such as capacitors and inductors embedded in the resonant unit cell, are fabricated using a multistep thin-film process based on benzocyclobutene (BCB) resin. The capacitors are built as planar metal-insulator-metal structures using an ultra-thin dielectric layer of BCB, while the multiturn inductors are fabricated as planar spiral structures with two metal layers and BCB as an interlevel dielectric for crossover. The advantages of the proposed approach are the capability to obtain large values of capacitances and inductances within small areas with low parasitics as well as the benefits in cost reduction and easy fabrication by using a planar microfabrication process. A component value variation analysis is performed to study the effect of fabrication tolerances in the reflection and transmission coefficients of the FSS when non-identical small cells are obtained. It has been experimentally validated that a 2.46 mm unit cell resonates at 4.175 GHz with transmission loss of 0.86 dB, achieving a miniaturization level of $\lambda $ /29.

Experimental characterization of directional couplers in InP photonic membranes on silicon (IMOS)

We experimentally study the performance of directional couplers fabricated in indium-phosphide membrane on silicon (IMOS) technology. We both investigate the validity of the coupled mode theory (CMT) applied to directional coupler structures with high index contrast and study the effect of some different topological choices in device fabrication. In particular, besides the conventional curved structures, we consider ultra sharp corner bends that reduce the footprint. The effect of fabrication tolerances on the different guided mode polarizations is also discussed.

Design of compact mode splitters using identical coupled waveguides with slots

In the past, multimode transmission through fibers has not been considered a preferred means of signal propagation due to the intermodal dispersion, which limits the data rate. However, recently, there has been an interest in using different modes as individual channels to increase the overall data rate. However, the challenging task in implementing such a system is that each individual mode has to be excited separately without mixing, and these should remain separated even at the bents and splices, and finally, they need to be collected separately. In this paper, design and optimization of a compact optical mode splitter by introducing a small slot in a silicon nanowire waveguide is demonstrated by employing a full-vectorial finite element method. The authors report here that by creating a slot within a waveguide, the desired coupling length ratio of 1:2 between the fundamental and the second modes can be obtained. The waveguide junctions have also been analyzed by using a rigorous least squares boundary residual method to study power transfer efficiency and effect of fabrication tolerances.

Theoretical investigation of a low-voltage Ge/SiGe multiple quantum wells optical modulator operating at 1310 nm integrated with Si3N4 waveguides

We report on the design and simulation using 3D-FDTD simulation of Si3N4-integrated Ge/SiGe multiple quantum wells (MQWs) optical modulators at the optical wavelength of 1310 nm. The effect of fabrication tolerance and wavelength dependence on the optical coupling performance between the Si3N4 waveguide and the Ge/SiGe MQWs structure as well as the optical modulation performance are reported. The results show that Si3N4-waveguide-integrated Ge/SiGe MQWs optical modulators can attain several key performance requirements in terms of extinction ratio, insertion loss, driving voltage, and fabrication variations with a compact footprint favorable for short-range optical interconnect applications.

ALMA Band 1 Optics (35–50 GHz): Tolerance Analysis, Effect of Cryostat Infrared Filters and Cold Beam Measurements

The Atacama Large Millimeter/Sub-millimeter Array (ALMA) is currently the largest (sub-)mm wave telescope in the world and will be used for astronomical observations in all atmospheric windows from 35 to 950 GHz when completed. The ALMA band 1 (35–50 GHz) receiver will be used for the longest wavelength observations with ALMA. Because of the longer wavelength, the size of optics and waveguide components will be larger than for other ALMA bands. In addition, all components will be placed inside the ALMA cryostat in each antenna, which will impose severe mechanical constraints on the size and position of receiver optics components. Due to these constraints, the designs of the corrugated feed horn and lens optics are highly optimized to comply with the stringent ALMA optical requirements. In this paper, we perform several tolerance analyses to check the impact of fabrication errors in such an optimized design. Secondly, we analyze the effects of operating this optics inside the ALMA cryostat, in particular the effects of having the cryostat IR filters placed next to the band 1 feed horn aperture, with the consequent near-field effects. Finally, we report on beam measurements performed on the first three ALMA band 1 receivers inside test cryostats, which satisfy ALMA specifications. In these measurements, we can clearly observe the effects of fabrication tolerances and IR filter effects on prototype receiver performance.

A 650-GHz Backward Wave Oscillator Based on Axial Loaded Double Defected-Photonic Crystal SWS

Axial loaded Double Defected Photonic Crystal (ADD-PC) with a cylindrical beam channel is introduced as a slow-wave structure (SWS) for backward wave oscillator (BWO) source design. The structural and the geometrical dimensions of the proposed SWS for submillimeter wave regime are realizable using the modern microfabrication processes. Starting from the basic design; the dispersion diagram, the modal phase velocity, and the beam interaction impedance are calculated. The effect of fabrication tolerance on both the operating frequency and the beam interaction impedance is also discussed. Using a custom built numerical electron beam–wave interaction algorithm, the electromagnetic field generation supported by the ADD-PC SWS is analyzed thoroughly. Simulation results indicate that with the proposed BWO, an output power of almost 8 W at 650 GHz with 1.8% conversion efficiency can be achieved.

Effect of fabrication tolerances on the performance of two-dimensional polymer photonic crystal channel drop filters: a theoretical investigation based on the finite element method

Guidelines for the design and fabrication of polymer photonic crystal channel drop filters for coarse wavelength division multiplexing are provided. A Fabry-Perot cavity consisting of a membrane-type slab photonic crystal, where a hole row perpendicular to the propagation direc- tion is removed, is considered. We selected nanoimprinting as the manu- facturing technique. The influence on the cavity performance of several key parameters, i.e., polymer core material, lattice geometry, defect length, and holes' radius, has been investigated in a device compliant with the requirement of the ITU-T G.694.2 standard. A detailed analysis of the fabrication tolerances has been carried out at 1551 nm. The maxi- mum acceptable drift of the geometrical parameters has been accurately evaluated by using the finite element method to prove that the fabrication tolerances do not significantly affect the performance of polymer filters for coarse wavelength division multiplexing, when manufactured by thermal nanoimprinting lithography. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. (DOI:

Millimeter-wave coplanar stripline power dividers

We present the design, fabrication, and measurement of a 2-way modified Wilkinson divider constructed in a coplanar geometry exhibiting ultra wideband isolation, transmission, and port matching in the millimeter-wave frequency range. The proposed divider replaces the lumped resistor in the conventional Wilkinson divider with two quarter-wave length transmission lines, a phase inverter, and two 2Z0 resistors. Except for the three ports that are coplanar waveguides (CPWs), the main body of the divider uses coplanar striplines (CPS). The phase inverter is realized using a simple airbridge-based crossover which is compatible with a modern monolithic microwave integrated circuit process. The divider has a ring-like configuration fabricated on a 620 µm thick semi-insulating GaAs wafer using electron beam lithography (EBL) technology. Three-dimensional (3D) full-wave electromagnetic simulations have been carried out to optimize the design and investigate the possible effect of fabrication tolerance on the performance of the crossover and the divider. Two dividers working at center frequencies of 25 and 80 GHz have been designed, fabricated, and tested. They all show consistent performance in terms of bandwidth, isolation, and port matching. Experimental and simulation results are in excellent agreement.

Enhanced monolithically integrated coherent 120° downconverter with high fabrication yield

Conventional monolithically integrated 90° downconverter suffers from hardware-induced non-linear constellation distortion, which gets worse far away from the central wavelength or when fabrication errors are taken into account. To overcome these problems, a 120° monolithically integrated downconverter with full compensation of hardware non-idealities has been proposed. It is numerically demonstrated that, in a realistic scenario exposed to the combined effects of fabrication tolerances and limited ADC resolution, this approach exhibits a significantly better signal dynamic range and a remarkable improvement of fabrication yield.

Numerical Analysis of Second Harmonic Generation in Soft Glass Equiangular Spiral Photonic Crystal Fibers

In this paper, the accurate and numerically efficient finite element (FE)-based beam propagation method (BPM) has been employed to investigate second harmonic generation (SHG) in highly nonlinear soft glass (SF57) equiangular spiral photonic crystal fibers (ES-PCFs) for the first time. It is shown here that the SHG output power in highly nonlinear SF57 soft glass PCF exploiting the ES design is significantly higher compared with that of silica PCF with hexagonal air-hole arrangements. The effects of fabrication tolerances on the coherence length and the modal properties of ES-PCF are also illustrated. Moreover, phase matching between the fundamental and the second harmonic modes is discussed through the use of the quasi-phase matching technique. Furthermore, the ultralow bending loss in the SF57 ES-PCF design has been successfully analyzed.

Flash program modeling using nonquasi-static and tunneling techniques

We present a detailed and accurate physics based transient simulation for modeling flash memory programming characteristics using nonquasi-static and tunneling equations versus the typical Lucky-Electron Model. The result is a set of simple expressions that were originally developed for a MOSFET and adapted for use in floating gate memory. Of greater importance is the extensive use of physical parameters as opposed to the scale factors and probabilities used in other models. This technique allows floating gate memory designers to determine the nominal programming characteristics of single-level and multi-level memory cells prior to the fabrication process. This technique also allows designers to determine the effects of fabrication tolerances on the performance of the memory cell. The accuracy of this model was validated through comparison with experimental data and simulation results presented in several publications.

Tooth-shaped grating-assisted structure for compact multimode interference coupler

A compact tooth-shaped grating-assisted structure has been proposed for a multimode interference (MMI) coupler and studied theoretically with silica waveguides with silicon oxynitride cores by using a mathematical model based on the sinusoidal mode simple effective index method. The dependence of the access waveguide length and beat length of the grating-assisted MMI (GA-MMI) structure on access waveguide separation (h) is shown. The total length of the GA-MMI coupler is less than that of a grating-assisted two-mode interference (GA-TMI) coupler (h=0) for an access waveguide S bending loss of 0.2 dB. It is also seen that the effect of fabrication tolerance on power imbalance of a GA-MMI coupler is almost close to that of a GA-TMI coupler.

A Double S-Bend Geometry With Lateral Offset for Compact Two Mode Interference Coupler

A double S-bend lateral offset structure has been proposed for the reduction of length and S-bend loss of 2×2 two mode interference (TMI) coupler. The coupling characteristics of the proposed structure are compared with those of conventional TMI structures using a simple mathematical model based on sinusoidal modes. It is seen that the longitudinal beat length for the proposed TMI coupler is reduced by 15% of beat length of a conventional TMI coupler whereas the S-bending loss is reduced by ~ 50% by using lateral offset in the double S-bend structure. The effect of fabrication tolerance on power imbalance for the proposed TMI structure is also compared with other TMI structures. It is seen that the fabrication tolerance for the proposed structure with lateral offset is almost same as that without lateral offset.

A Compact Optical Multiplexer Using Silicon Nano-Waveguides

An ultracompact optical-multiplexer-based two-mode interference (TMI) coupler has been designed for the first time using a mathematical model based on sinusoidal modes and implemented with silicon nano-waveguides. The multiplexing characteristics of the device are verified with the beam propagation method and are also demonstrated experimentally. The coupling length for the TMI coupler for multiplexing of wavelength channels of spacing ~10 nm is five times less than that of a conventional multimode interference (MMI) coupler of width 660 nm. The effect of fabrication tolerance on crosstalk of the TMI coupler is found to be less than that of conventional MMI couplers and of TMI coupler based on tooth-shaped grating structure.

Stress concentration factors at welds in pipelines and tanks subjected to internal pressure and axial force

In this paper, analytical expressions for stress concentration factors in pipes subjected to internal pressure and axial force are derived for a number of design cases based on classical shell theory. The effect of fabrication tolerances in simple butt welds is assessed. Analyses based on classical mechanics are compared with results from axisymmetric finite element analyses for verification of the presented methodology. Stress concentration factors are presented for circumferential butt welds in pipes welded together from pipes with different thicknesses, welds at buckling arrestors, welds at flanged connections in pipelines, and welds at ring stiffeners on the inside and the outside of the pipes. It also includes stress concentration factors at end closures in pipes for gas storage. Larger pipes are fabricated from plates with a longitudinal weld. This fabrication process introduces out-of-roundness in the pipes. The actual out-of-roundness is a function of internal pressure. An analytical expression for the bending stress in the pipe wall due to this out-of-roundness is presented. The derived stress concentration factors can be used together with a hot spot stress S– N curve for calculation of fatigue damage.

A Novel Hybrid Phase-Locked-Loop Frequency Synthesizer Using Single-Electron Devices and CMOS Transistors

This paper proposes a novel phase-locked loop (PLL) frequency synthesizer using single-electron devices (SEDs) and metal-oxide-semiconductor (MOS) field-effect transistors. The PLL frequency synthesizer mainly consists of a single-electron transistor (SET)/MOS hybrid voltage-controlled oscillator circuit, a single-electron (SE) turnstile/MOS hybrid phase-frequency detector (PFD) circuit and a SE turnstile/MOS hybrid frequency divider. The phase-frequency detection and frequency-division functions are realized by manipulating the single electrons. We propose a SPICE model to describe the behavior of the MOSFET-based SE turnstile. The authors simulate the performance of the PLL block circuits and the whole PLL synthesizer. Simulation results indicated that the circuit can well perform the operation of the PLL frequency synthesizer at room temperature. The PLL synthesizer is very compact. The total number of the transistors is less than 50. The power dissipation of the proposed PLL circuit is less than 3 uW. The authors discuss the effect of fabrication tolerance, the effect of background charge and the SE transfer accuracy on the performance of the PLL circuit. A technique to compensate parameter dispersions of SEDs is proposed.

Novel Hybrid Voltage Controlled Ring Oscillators Using Single Electron and MOS Transistors

This paper proposes two kinds of novel hybrid voltage controlled ring oscillators (VCO) using a single electron transistor (SET) and metal-oxide-semiconductor (MOS) transistor. The novel SET/MOS hybrid VCO circuits possess the merits of both the SET circuit and the MOS circuit. The novel VCO circuits have several advantages: wide frequency tuning range, low power dissipation, and large load capability. We use the SPICE compact macro model to describe the SET and simulate the performances of the SET/MOS hybrid VCO circuits by HSPICE simulator. Simulation results demonstrate that the hybrid circuits can operate well as a VCO at room temperature. The oscillation frequency of the VCO circuits could be as high as 1 GHz, with a -71 dBc/Hz phase noise at 1 MHz offset frequency. The power dissipations are lower than 2 uW. We studied the effect of fabrication tolerance, background charge, and operating temperature on the performances of the circuits