Lateral Misalignment Tolerance Research Articles

A simplified laser-to-chip edge coupling scheme using 3D SU-8 taper

In this work, we design and simulate a three-dimensional (3D) SU-8 tapered edge coupler for effectively guiding light from an edge-emitting semiconductor laser diode directly to a silicon waveguide to realize a hybrid on-chip silicon light source. A series of coupling efficiencies for the commonly used top silicon thicknesses of the silicon-on-insulator wafers from 220 to 3000 nm are obtained, showing that this polymer taper can largely improve the coupling efficiency when the silicon waveguide thickness is moderate, for instance, from 41% (with no taper) to 67% for the 700 nm- thick silicon waveguide under 1 μm gap offset and relax the lateral misalignment tolerance to above one micron by suppressing the butt refractive index contrast and the mode mismatch between the laser diode and the silicon waveguide. Wave transformation inside the tapered coupler and the input silicon waveguide has also been revealed by 3D finite-difference time-domain simulations. This 3D tapered coupler is cost effective and easily fabricated which can have wide practical applications in massive production of various silicon photonic chips based on the present complementary metal-oxide-semiconductor foundry.

A Switched Modular Multi-Coil Array Transmitter Pad With Coil Rectenna Sensors to Improve Lateral Misalignment Tolerance in Wireless Power Charging of Drone Systems

In this article, a Switched Modular Multi-coil Array transmitter pad integrated with coil RecTenna (SMMART) is designed to present an intelligent wireless drone charging system that improves lateral misalignment tolerance. The resultant optimized design constitutes four independent transmitter modules, wherein each includes four spatially distributed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathbf{2\times2}$</tex-math> </inline-formula> array coils. Therefore, the proposed design induces a maximal uniform voltage in the Rx coil region. Moreover, the optimization procedure accounts for the miniaturization of transmitter coil size without compromising the misalignment tolerance by overlapping various transmitter modules. In addition, a novel coil-based detection system for wireless chargeable drone applications is proposed to activate the desired transmitter module based on the position of the receiver coil. The detection system consists of an array of coil rectennas integrated with a switching circuit to reduce the undesired magnetic field, enhancing the link efficiency. The prototype of the charging pad is fabricated using Litz wire, and the S21-based link efficiency is measured using an experimental setup. Besides, the fabricated coil rectenna sensor array system demonstrates a real-application model of the detection system. Hence, the proposed transmitter pad improves lateral misalignment tolerance and is considered a potential wireless drone charging system design.

Relaxed Tolerance Low-Loss Adiabatic Si3N4 to Polymer Waveguide Coupler for Dense Interconnects

Despite significant advances in silicon photonics, optical packaging and interconnection of photonic integrated circuits constitutes a large portion of the associated manufacturing costs. Optical fibers are the dominant approach to optical interconnection. However, techniques that rely on fibers lack scalability, have low efficiency and show poor misalignment tolerance. Proposed alternative solutions using polymer waveguides have shown improved coupling efficiency, misalignment tolerance and scalability. Here we present the design, simulation and the experimental confirmation of an adiabatic silicon nitride taper to polymer waveguide coupler with only 0.52 dB of TE coupling loss at 1550-nm wavelength, excluding material loss. The coupler demonstrates $\pm 4~\mu \text{m}$ of lateral misalignment tolerance with a 1-dB penalty which, to the best of our knowledge, is the highest reported tolerance for silicon nitride to polymer waveguide coupling.

Exciter–Quadrature–Repeater Transmitter for Wireless Electric Vehicle Charging With High Lateral Misalignment Tolerance and Low EMF Emission

In this article, an exciter–quadrature–repeater transmitter pad is proposed in order to achieve high lateral misalignment tolerance and low leakage flux emission in electric vehicle wireless charging applications. In the proposed WPT system, a single half-bridge inverter unit is needed to energize the exciter coil, which is magnetically coupled to two larger quadrature repeater coils. The currents in the two repeater coils naturally adjust based on the lateral misalignment of the receiver pad to reduce the leakage flux density around the charging zone. The system can maintain zero phase shift between excitation voltage and current and achieve constant current charging conditions with fixed compensation capacitors in the ±150-mm lateral misalignment range. In order to verify the attributes of the proposed wireless power transfer (WPT) system, a 3-kW experiment setup with a 200-mm vertical gap was built and compared to a three-coil WPT system, which consists of a small transmitter coil, a single large repeater coil, and a receiver coil. According to the experiment results, even under extreme 150-mm lateral misalignment, the proposed WPT system has 90.7% coil-to-coil transmission efficiency. Furthermore, it achieves a 30% reduction of leakage flux density compared to the three-coil system in the 150-mm lateral misalignment case.

Design of a High Power, LCC-Compensated, Dynamic, Wireless Electric Vehicle Charging System with Improved Misalignment Tolerance

Dynamic wireless power transfer (DWPT) systems are becoming increasingly important for on-the-move electric vehicle (EV) charging solutions, to overcome range anxiety and compensate for the consumed energy while the EV is in motion. In this work, a DWPT EV charging system is proposed to be implemented on a straight road stretch such that it provides the moving EV with energy at a rate of 308 Wh/km. This rate is expected to compensate for the vehicle’s average energy consumption and allow for additional energy storage in the EV battery. The proposed charging system operates at an average power transfer efficiency that is higher than 90% and provides good lateral misalignment tolerance up to ±200 mm. Details of the proposed system’s design are presented in this paper, including EV specifications, inductive link and compensation network design and power electronic circuitry.

Field orientation based three‐coil decoupled wireless transmitter for electric vehicle charging with large lateral receiver misalignment tolerance

A three-coil decoupled transmitter is developed for the inductive power transfer system of electric vehicle charging. The three-coil decoupled transmitter consists of three overlapping rectangular coils with magnetic mutual decoupling and is capable of overcoming large receiver lateral misalignment up to 20 cm. A current optimization method is advanced to derive transmitter coil currents for the multi-phase system that minimizes the coil loss through optimizing the current distribution among transmitter coils. The optimized current distribution reduces the maximum leakage flux by around 40% compared to the best alternative excitation method. The compensation strategy provides unity power factor for high-power transfer phases and allows a single set of compensation capacitors to be used regardless of receiver alignment. The three-coil decoupled transmitter is compatible with a typical three-phase inverter for industrial practical application, which halves the power electronic switches used with previous topologies. The simulation verification is performed at 3.3 kW, achieving 93.76% efficiency at perfect alignment and 92.54% efficiency at 20 cm misalignment. The experimental verification is implemented at 3.3 kW with 200 mm ground clearance, realizing a 92.97% efficiency at perfect alignment and 90.57% efficiency at 20 cm misalignment.

Fabrication-Tolerant and Low-Loss Hybrid Plasmonic Slot Waveguide Mode Converter

Integrated plasmonic structures can concentrate light to deep-subwavelength volumes below the diffraction limit and have been explored in many applications including label-free nanophotonic sensing with single molecule sensitivity, nonlinear conversion, and lasing. However, conversion between the dielectric waveguide mode and the plasmonic mode typically suffers from large mode conversion loss and requires high nanofabrication precision because of the mode mismatch and the precise alignment requirements with the plasmonic slot structure, respectively. Here, we report low-loss conversion between a dielectric waveguide mode and a hybrid plasmonic slot waveguide mode in a structure with a large fabrication tolerance. The measured conversion loss between the dielectric waveguide mode to the hybrid plasmonic slot waveguide mode can be <; 2 dB in the wavelength range of 1.54-1.60 μm under the optimal phase match condition. The loss remains low with a lateral misalignment tolerance of >500 nm. We confirmed enhanced light-matter interaction in the plasmonic slot waveguide region by measuring the enhancement in optical absorption of graphene with and without the plasmonic slot structure. Our results demonstrate a new approach to achieve deep-subwavelength light concentration by using an easy-to-fabricate interface with dielectric waveguides.

Design of Dual Frequency Mixed Coupling Coils of Wireless Power and Data Transfer to Enhance Lateral and Angular Misalignment Tolerance

A dual-resonant mixed coupling structure is proposed to enable lateral and angular misalignment immunity in wireless power and data transfer systems. By considering the duality property of electrical coupling and magnetic coupling, mixed coupling coils make the efficiency of wireless power transfer nearly insensitive to axial and angular misalignment. A complete, sophisticated equivalent circuit is proposed and demonstrates the features of the dual-resonant characteristic and lateral and angular misalignment tolerance. Compared to traditional printed spiral coil systems, the proposed mixed coupling structure reduces decline rate of S21 by 26.4% and 78.1% at 35-mm axial misalignment and 90° angular misalignment at low resonant frequency, respectively. Moreover, at high resonant frequency, S21 only drops 16.5% with 60-mm lateral misalignment and is almost flat for 90° angular misalignment. Last but not least, data communication is also validated by transmitting a 200-kHz frequency shift keying signal, and the probability errors remain at acceptable level when misalignment occurs.

Lateral Misalignment Tolerant Wireless Power Transfer With a Tumbler Mechanism

A transmitting coil with a tumbler structure is presented to improve lateral misalignment tolerance of a wireless power transfer (WPT) system with a planar receiver. The tumbler is made of an acrylic ball and soil. A planar spiral receiving coil wound by Litz wire is centered by Nd–Fe–B magnets. A spherical cap transmitting coil centered also by Nd–Fe–B magnets sticks on the inner surface of the acrylic ball. When lateral misalignment occurs, the transmitting and receiving coils can achieve self-align with the action of magnetic force, and thus the transfer efficiency is improved. A WPT system consisting of two coils with 6 cm outer radii resonated at 107 kHz is studied. A concise theoretical analysis based on circuit model is given first, and then experimental data are reported. The positive correlation between magnetic force and tracking range is given by comparison. Especially, when the transfer distance is 1.5 cm, the WPT system has a 75.5% peak efficiency and a 3.52 W load power at zero lateral misalignment and the tracking range is from 0 to 8.5 cm; In the tracking range the WPT system has a 70.0% average efficiency and the load power maintains over 94.7% of the peak load power. With the increase of transfer distance, the improvements of transfer efficiency and the tracking range both decrease gradually, and the efficiency loss within the tracking range also increases gradually.

Two-photon direct laser writing of beam expansion tapers on single-mode optical fibers

Small misalignments between two standard telecom single-mode fibers in a physical contact connection can lead to large optical losses. It is known that by expanding the mode field diameter of the fiber, the misalignment tolerances can be relaxed. One of the approaches to obtain this beam expansion is to use tapers. We propose an air-clad taper structure to transmit the fundamental mode of a single-mode fiber adiabatically to a 3 times larger mode field area in physical contact expanded beam connectors. This results in a 241.4 μm long linear taper. The taper itself is fabricated on top of a cleaved fiber facet by means of the two-photon polymerization direct laser writing technique. Experimental results for lateral misalignment show excellent agreement with simulated values and give an increase in lateral misalignment tolerance of 1 μm (−1 dB) and 1.8 μm (−3 dB). Total insertion losses down to 0.76 dB are measured, showing the trade-off between achievable insertion loss and misalignment tolerance relaxation. Finally, we show that the use of additive manufacturing techniques in fiber beam expansion applications make it possible to fabricate taper structures with full 3D design freedom and to upscale the process to multi-fiber components.

Analysis of Square and Circular Planar Spiral Coils in Wireless Power Transfer System for Electric Vehicles

Nowadays, wireless power transfer (WPT) has attracted great attention from researchers because it is a safe, convenient, and reliable way to recharge electric vehicles. Square and circular coils are most commonly used in WPT systems. However, there are few analyses of comparing these two geometry windings in detail. In this paper, two analytical models of both square and circular planar spiral coils between two semi-infinite substrates are developed based on Fourier–Bessel transformation and dual Fourier transformation. An analytical calculation of the self- and mutual inductance can be carried out with respect to the main parameters of the WPT systems such as the line spacing, the number of turns of the coils and the properties of the substrate. The analytical models can be used to investigate the different tendencies of self- and mutual inductance of square and circular coils, which is helpful for speeding up the design process. Finally, to compare the lateral misalignment tolerance between square and circular coils, a ${{\text{600}}\,\text{mm}\,\times \,{\text{600}}\,\text{mm}}$ with a nominal 200-mm-gap prototype has been built and tested.

Micro/nanoscale self-aligned optical couplings of the self-organized lightwave network (SOLNET) formed by excitation lights from outside

The self-organized lightwave network (SOLNET) provides “optical solder,” which enables self-aligned optical couplings between misaligned optical devices with different core sizes. We propose a low-cost SOLNET formation method, in which write beams are generated within optical devices by excitation lights from outside. Simulations based on the finite-difference time-domain method reveal that the two-photon processes enhance optical-solder capabilities. In couplings between 600-nm-wide waveguides opposed with 32-μm distance a wide lateral misalignment tolerance of ~2µm to maintain <1dB loss at 650nm in wavelength is obtained. The coupling loss at 1-μm lateral misalignment is 0.4dB. In couplings between 3-μm-wide and 600-nm-wide waveguides, losses at 650nm are 0.1dB for no misalignments and 0.9dB for 1-μm misalignment. These results suggest that SOLNETs provide optical solder with mode size converting functions.

25-Gb/s Operation of a Polymer Optical Waveguide on an Electrical Hybrid LSI Package Substrate With Optical Card Edge Connector

We propose a high-capacity polymer-based optical and electrical LSI package integrated with multimode Si photonic transmitters and receivers. We describe the fabrication and characteristics of the polymer-based hybrid LSI package substrate with a polymer optical waveguide, a mirror, and optical card edge connectors. We fabricated optical mirrors with several angles ranging from 40° to 45° for the Si photonic grating coupler by using a dicing blade at an angle. The dicing mirror changed the emission angle for the grating coupler. We also realized a large lateral misalignment tolerance (±11.5 μm) between the polymer waveguide and MMF for 1 dB of excess loss at 24 channels. We obtained 1-dB coupling loss using an optical card edge connector at 1.3 μm because of the large tolerance. We realized 25-Gb/s error-free transmission per channel at 1.3 μm. We also describe here the error penalty and jitter due to modal noise generated by coupling mismatch.

Low-loss compact multilayer silicon nitride platform for 3D photonic integrated circuits.

We design, fabricate, and demonstrate a silicon nitride (Si(3)N(4)) multilayer platform optimized for low-loss and compact multilayer photonic integrated circuits. The designed platform, with 200 nm thick waveguide core and 700 nm interlayer gap, is compatible for active thermal tuning and applicable to realizing compact photonic devices such as arrayed waveguide gratings (AWGs). We achieve ultra-low loss vertical couplers with 0.01 dB coupling loss, multilayer crossing loss of 0.167 dB at 90° crossing angle, 50 μm bending radius, 100 × 2 μm(2) footprint, lateral misalignment tolerance up to 400 nm, and less than -52 dB interlayer crosstalk at 1550 nm wavelength. Based on the designed platform, we demonstrate a 27 × 32 × 2 multilayer star coupler.

Polymer waveguides self-organized by two-photon photochemistry for self-aligned optical couplings with wide misalignment tolerances

Self-organized optical waveguides formed in a photopolymer using two-photon photochemistry is proposed for self-aligned optical couplings involving nano-scale optical devices with wide tolerances in lateral misalignments. Simulations based on the finite-difference time-domain method revealed that on introducing a 400-nm write beam and a 780-nm write beam into the two-photon photopolymer respectively from two 600-nm-wide waveguides facing each other with 32μm gap a self-aligned coupling waveguide called a two-photon self-organized lightwave network (SOLNET) is formed between the two waveguides. The lateral misalignment tolerance was found to be 3000nm, which is five times larger than the misalignment limit of ~600nm in waveguides formed by conventional one-photon photochemistry. Preliminary experiments demonstrated that the two-photon SOLNETs are formed between multimode optical fibers by introducing a 448-nm write beam and a 780-nm (or 856-nm) write beam from the fibers into a photosensitive organic/inorganic hybrid material, SUNCONNECT®, with doped camphorquinone (or biacetyl).

Source misalignment in multimode polymer tapered waveguides for optical backplanes

Polymer tapered multimode waveguides were modeled using the finite difference wide-angle beam propagation method to investigate whether tapered input waveguide couplers decreasing in width away from the waveguide entrance give improved tolerance to lateral misalign- ments of an optical source compared to straight waveguides and whether there is any effect on angular misalignment tolerance for use in optical backplane interconnections. Input tapered couplers having a larger entrance and tapering down in width do indeed improve the lateral misalignment tolerance compared to straight waveguides but do so at the expense of an increased loss. Tapers have no effect on angular tolerance for strongly driven vertical cavity surface-emitting laser VCSEL sources although they cause a loss of angular tolerance for single-mode fiber sources and VCSELs at low drive currents. © 2007 So-

Low-cost and efficient coupling technique using reflowed sol-gel microlens

In this paper, we present a novel reflow technique for the fabrication of an elliptical microlens array in sol-gel glass. The fabricated refractive microlens array has a very smooth surface, and structural and dimensional conformity with the designed parameters. It is shown that the microlens array can provide high coupling efficiency of a laser diode to a single mode fiber, and relax the lateral and axial misalignment tolerance. The microlens coupling technique has the advantages of low coupling loss, large misalignment tolerances, and small package volume.

Highly efficient coupling semiconductor spot-size converter with an InP/InAlAs multiple-quantum-well core

A highly efficient spot-size converter (SSC) that uses a fiber-coupling tapered semiconductor waveguide is demonstrated. The waveguide core of this device consists of InGaAsP for semiconductor chip coupling and an InP/InAlAs multiple quantum well (MQW) for single-mode fiber (SMF) coupling. The equivalent refractive index of the MQW core is adjusted by controlling the well-to-barrier-layer thickness ratio to expand the chip spot size to that of SMF's. A high coupling efficiency of 1.4 dB can be obtained, and the lateral and axial misalignment tolerances for the SSC are 3 times better than those for conventional semiconductor waveguides. Moreover, this device has high reproducibility because of large fabrication tolerances.

A new confocal combination lens method for a laser-diode module using a single-mode fiber

A new confocal combination lens method is proposed, which can overcome severe misalignment tolerances for an InGaAsP laser diode to single-mode fiber coupling. Lens 2 in the confocal two-lens method is divided into two lenses, that is, lenses 21 and 22. The optimal distance between lenses 1 and 21 is found to be shorter than that for a confocal condition. Lens 22 is attached to the input endface of the single-mode fiber, thus forming a virtual fiber. Using 0.06- and 0.18-pitch GRIN rod lenses as lenses 21 and 22, the lateral and axial misalignment tolerances for the virtual fiber are improved by three and nine times, respectively, in comparison with those for the single-mode fiber. High-coupling efficiency of -3.0 dB of the laser diode to the single-mode fiber can be easily obtained including Fresnel reflections.

Combination lens method for coupling a laser diode to a single-mode fiber

A new combination lens method using a relatively large spherical lens and a virtual fiber is proposed for coupling an InGaAsP laser diode to a single-mode fiber. The virtual fiber is formed by attaching a GRIN rod lens to the input endface of the single-mode fiber. Coupling efficiency of from −3 to −4 dB is easily obtained. Alignment sensitivities of the proposed optical coupling circuit are investigated both theoretically and experimentally. The lateral and axial misalignment tolerances for the virtual fiber are improved three and nine times, respectively, in comparison with those for the single-mode fiber. The measured dependence of the coupling efficiency on the misalignments for the optical components agrees relatively well with the theoretical results through the ray matrix approach.