Optical Coupling Efficiency Research Articles

Cladded self-written multimode step-index waveguides using a one-polymer approach.

Low-loss optical-coupling structures are highly relevant for applications in fields as diverse as information and communication technologies, integrated circuits, or flexible and highly-functional polymer sensor networks. For this suitable and reliable production methods are crucial. Self-written waveguides are an interesting solution. In this work, we present a simple and efficient one-polymer approach for self-written optical connections between light-guiding structures such as single-mode and multi-mode optical fibers or waveguides that relies on self focusing of the light inside a photopolymerizing mixture. The optical connections are produced in a two-step process by writing into monomer resin using cw laser light in the blue wavelength range and subsequent UV curing. Since only one photopolymerizing resin is required, we reduced the fabrication complexity compared to previous approaches to obtain a waveguide embedded in a rigid cladding material. We discuss the production method, the results obtained as function of relevant process parameters such as writing speed or curing time, and evaluate optical properties and coupling efficiencies.

Efficient optical coupling in AlGaN/GaN quantum well infrared photodetector via quasi-one-dimensional gold grating.

In this letter, a new kind of grating, quasi-one-dimensional gold grating, has been proposed to enhance the optical coupling in AlGaN/GaN quantum well infrared photodetector (QWIP). The electric field distribution, current density and energy flow are analyzed by an algorithm of finite element method (FEM). Significantly enhanced electric field component E(z) perpendicular to multiple quantum wells (MQWs) is explained by introducing the resonant coupling of surface plasmon polariton (SPP) and localized surface plasmon (LSP). The |E(z)|(2) in MQWs reaches 0.85 (V/m(2) when the electric field intensity (|E(0)|(2)) of normal incidence is 1 (V/m(2) at 4.65 μm, showing 2 times and 1.3 times increase compared with that obtained via a one-dimensional gold grating and a two-dimensional gold grating, respectively. The results confirm that the quasi-one-dimensional gold grating provides more plasma excitation source and higher charge density with structure optimization, resulting in a high optical coupling efficiency of 85% in quantum well region.

Vertical waveguide structure optical printed circuit board based on a low-dielectric and transparent PCB materials

This paper suggests an optical printed circuit board (OPCB) having new optical coupling structures, including a laser-drilled and under-filled structure (LD-UFS) and a vertical waveguide structure (VWS). The suggested OPCB has the features of high-speed data transmission as well as highly efficient optical coupling because it was fabricated with low-dielectric and transparent electrical PCB materials through a PCB compatible process. To evaluate and compare the optical and electrical performances of the suggested OPCB with those of other OPCBs, the various types of OPCBs were fabricated and measured. The optical coupling losses of the LD-UFS and the VWS were measured with excellent results of 9.8 and 7.8 dB, respectively, which are lower than that of the basic structure. The electrical 3-dB bandwidth of the OPCB was also evaluated up to more than 40 GHz.

SPAD aptasensor for the detection of circulating protein biomarkers

The need for decentralized clinical tests together with the concept of time and cost saving are pushing the development of portable, miniaturized, compact biosensors with diagnostic and prognostic purpose. Here, we propose an innovative detection system based on a Single Photon Avalanche Diode (SPAD) with high sensitivity and low noise, crucial features for an efficient chemiluminescence biosensor. The SPAD detector, having 60µm diameter, has a Photon Detection Efficiency higher than 55% at 425nm and a Dark Count Rate lower than 100Hz at room temperature. Our design allows a good optical coupling efficiency between sample and detector. A specific biofunctional surface was implemented taking advantage of aptamers, short DNA sequences having high selectivity and affinity toward their targets. We successfully detected physiological levels of Vascular Endothelial Growth Factor (VEGF), a circulating protein biomarker highly correlated with cancer. The SPAD aptasensor showed a Limit of Detection (LoD) in the pM range, stability (up to 42 days) and re-usability (up to seven cycles). This compact biosensor is therefore a promising step toward the actual use of portable microdevices in diagnostics.

Two‐step microfocal lens with enhanced optical coupling efficiency suitable for large‐scale fabrication

A two-step microfocal lens design that can achieve high-efficiency optical coupling is reported. Simulation results show that the lens enhances optical coupling efficiency by over one-third compared with its prototype previously reported. It also slightly reduces the focal spot size. A simple top-down fabrication process flow is discussed, which indicates that the proposed two-step lens can be fabricated at low cost using conventional industrial equipment.

Unlocking the full potential of conducting polymers for high-efficiency organic light-emitting devices.

By carefully tuning the thicknesses of low-optical index PEDOT:PSS and high-index ITO layers in organic light-emitting devices (OLEDs), very high optical coupling efficiencies can be obtained through the generation of appropriate microcavity effects. These experiments result in an external quantum efficiency (EQE) of 33.7% for green phosphorescent OLEDs and even higher EQEs of 54.3% can be obtained by adopting an external out-coupling lens.

Implementation of Chip-Level Optical Interconnect With Laser and Photodetector Using SOI-Based 3-D Guided-Wave Path

A chip-level optical interconnect module combined with a vertical-cavity surface-emitting laser (VCSEL) chip, a photodetector (PD) chip, a driver integrated circuit (IC), and an amplifier IC on a silicon-on-insulator (SOI) substrate with 3-D guided-wave paths is experimentally demonstrated. Such an optical interconnect is developed for the signal connection in multicore processors or memory-to-processor interfaces. The 3-D guided-wave path, consisting of silicon-based 45° microreflectors and trapezoidal waveguides, is used to connect the optical signal between transmitter and receiver. In this paper, the VCSEL and PIN PD chips are flip-chip integrated on a SOI substrate to achieve complete chip-level optical interconnects. Due to the unique 3-D guided-wave path design, a higher laser-to-PD optical coupling efficiency of -2.19 dB and a larger alignment tolerance of ±10μm for the VCSEL/PD assembly are achieved. The measured laser-to-PD optical transmission efficiency can reach -2.19 dB, and the maximum optical power and threshold current of VCSEL is 3.27 mW and 1 mA, respectively. To verify the data transmission, the commercial driver IC and amplifier IC are assembled upon the silicon chip, and the error-free data transmission of 10 Gbps can be achieved when the VCSEL is operated at the driving current of 9 mA.

The design and application of an automatic optical inspection system for the advanced fiber coupler assembly manufacturing process

In this paper an automatic optical inspection system for the advanced fiber coupler assembly manufacturing process is presented. Coupling efficiency variations were compared with axial displacement. The main standard components of light peak fiber couplers were used in the experiment to determine the corresponding offset and position of the optimal optical coupling efficiency in order to achieve a positioning effect. This study used the parameters of lens curvature, focal length and light source for validation using optical design software. An infrared CCD camera was used to extract the coupled light spot images. The curve fitting method and coupling simulation database were used for image processing and to calculate optimal coupling efficiency. Under optimal coupling efficiency, the minimum amount of movement of the translation stages was used to calculate the offset of each axle or the coupling efficiency when tilted. Moreover, a coupling efficiency database was established. The optical axle center offset in the alignment was calculated by comparing the data in the database. Finally, the optical axle center offset or tilt direction was identified through the program to achieve the position of optimal coupling efficiency.

Self‐aligning silicon interposer tiles and silicon bridges for large nanophotonics enabled systems

A two-and-a-half-dimensional (2.5D) platform for enabling silicon nano-photonics and dense electrical interconnections between interposers in a tile-like configuration is presented. Three 20 × 20 mm silicon interposer tiles are assembled directly on an FR4 printed wiring board (PWB), and two 6 × 20 mm silicon bridges are assembled on top of the interposer tiles. Accurate alignment of interposer tiles to bridges, an important metric in enabling highly efficient optical coupling, is provided using positive self-alignment structures (PSASs). It is demonstrated that by using PSAS on two silicon substrates, sub-micron alignment between substrates is possible; in the cascaded configuration involving FR4, <5 μm alignment accuracy is obtained. In addition, electrical interconnection via a bridge using mechanically flexible interconnects (MFIs) is demonstrated, which made non-bonding interconnections from one interposer tile to another via a silicon bridge, allowing silicon bridges as well as the interposer tiles to be replaced. Total silicon interposer area available is 960 mm2.

Design of miniaturized illumination for transvaginal co-registered photoacoustic and ultrasound imaging.

A novel lens-array based illumination design for a compact co-registered photoacoustic/ultrasound transvaginal probe has been demonstrated. The lens array consists of four cylindrical lenses that couple the laser beams into four 1-mm-core multi-mode optical fibers with optical coupling efficiency of ~87%. The feasibility of our lens array was investigated by simulating the lenses and laser beam profiles using Zemax. The laser fluence on the tissue surface was experimentally measured and was below the American National Standards Institute (ANSI) safety limit. Spatial distribution of hemoglobin oxygen saturation (sO2) of a mouse tumor was obtained in vivo using photoacoustic measurements at multiple wavelengths. Furthermore, benign and malignant ovaries were imaged ex vivo and evaluated histologically. The co-registered images clearly showed different patterns of blood vasculature. These results highlight the clinical potential of our system for noninvasive photoacoustic and ultrasound imaging of ovarian tissue and cancer detection and diagnosis.

Wavelength-Selective Optical Filters Based on Metal-Patch Cavities With Slot Waveguide Interfaces

We theoretically propose and investigate the resonant wavelength-selective optical filters based on the subwavelength metallo-dielectric nanopatch cavities and the metal slot waveguides. Using the temporal coupled-mode theory and three-dimensional finite-difference time-domain simulations, we analyze the optical coupling efficiencies and filtering characteristics, which are optimized by adjusting the waveguide-cavity distance to modify the decay rates from the cavity. The proposed optical filters can be extended to multiport channel-dropping filters while maintaining subwavelength-scale dimensions including the coupling regions.

Review of superconducting nanowire single-photon detector system design options and demonstrated performance

We describe a number of methods that have been pursued to develop superconducting nanowire single-photon detectors (SNSPDs) with attractive overall performance, including three systems that operate with >70% system detection efficiency and high maximum counting rates at wavelengths near 1550 nm. The advantages and tradeoffs of various approaches to efficient optical coupling, electrical readout, and SNSPD design are described and contrasted. Optical interfaces to the detectors have been based on fiber coupling, either directly to the detector or through the substrate, using both single-mode and multimode fibers with different approaches to alignment. Recent advances in electrical interfaces have focused on the challenges of scalability and ensuring stable detector operation at high count rates. Prospects for further advances in these and other methods are also described, which may enable larger arrays and higher-performance SNSPD systems in the future. Finally, the use of some of these techniques to develop fully packaged SNSPD systems will be described and the performance available from these recently developed systems will be reviewed.

Design of an Alignment Tolerant Miniature Optical Subassembly Module

A miniature optical subassembly module incorporating a pair of collimating and focusing lenses was proposed and designed to provide affordable alignment tolerance in terms of optical coupling efficiency. The light source was specifically modeled taking advantage of multiple point sources placed on the emitting aperture. This scheme was practically verified to be superior to the conventional scheme involving a single point source by estimating the focal length and spot size of a focused beam. The performance of the proposed source modeling was scrutinized with respect to the number of point sources. The optical coupling of the subassembly to a fiber was investigated theoretically and experimentally in light of the characteristics of the displacement of the focused beam relative to the lateral displacement of the light source. Finally, a tradeoff between the positional 3-dB tolerance of the light source and the maximum available coupling efficiency was established with certitude.

Efficient optical coupling into a single plasmonic nanostructure using a fiber-coupled microspherical cavity

Toward complete coupling between propagating light (PL) and a single localized-surface-plasmon (LSP) nanostructure, we propose a tapered-fiber-coupled microspherical cavity system combining an Au-coated probe tip. This system possesses the unique characteristic of precise adjustability for the fiber-cavity coupling rate and the cavity-plasmon coupling rate, which is indispensable for achieving the critical coupling conditions. We successfully demonstrate the 93% PL coupling into the LSP antenna with an effective area of a 58 nm circle, exceeding the diffraction limit.

In-plane external fiber Fabry–Perot cavity comprising silicon micromachined concave mirror

Light trapping in optical cavities has many applications in optical telecommunications, biomedical optics, atomic studies, and chemical analysis. Efficient optical coupling in these cavities is an important engineering problem that affects greatly the cavity performance. Reported in-plane external fiber Fabry–Perot cavities in the literature are based on flat micromachined mirrors. In this case, the diffraction loss in the cavity is usually overcome by using an expensive-lensed fiber or by inserting a coated lens in the cavity leading to a long cavity with a small free spectral range. In this work, we report a Fabry–Perot cavity formed by a multilayer-coated cleaved-surface single-mode fiber inserted into a groove while facing a three-dimensional concave micromirror; both are fabricated by silicon micromachining. The light is trapped inside the cavity while propagating in-plane of the wafer substrate. Theoretical modeling is carried out, taking into account the effect of asymmetry in the mirror radii of curvature resulting from the micromachining process. A cavity is formed using a concave mirror with 200 and 100 μm in-plane and out-of-plane radii curvature, respectively. The presented cavity has a measured line width of 0.45 nm around 1330 nm showing a quality factor of about 3000, which resembles a one order of magnitude improvement over a flat-mirror cavity.

Highly efficient coupling from an optical fiber to a nanoscale silicon optomechanical cavity

We demonstrate highly efficient coupling of light from an optical fiber to a silicon photonic crystal optomechanical cavity. The fiber-to-cavity coupling utilizes a compact (L ≈ 25 μm) intermediate adiabatic coupler. The optical coupling is lithographically controlled, broadband, relatively insensitive to fiber misalignment and allows for light to be transferred from an optical fiber to, in principle, any photonic chip with refractive index greater than that of the optical fiber. Here we demonstrate single-sided cavity coupling with a total fiber-to-cavity optical power coupling efficiency of 85%.

Single-Step Synthesis of Monolithic Comb-like CdS Nanostructures with Tunable Waveguide Properties

Using a simple in situ seeding chemical vapor deposition (CVD) process, comb-like (branched) monolithic CdS micro/nanostructures were grown. Efficient optical coupling between the backbone and the teeth of the branched architecture is demonstrated by distributing light from an UV-laser-excited spot at one end of the backbone to all branch tips. By varying the deposition conditions, the orientation of the branches with respect to the backbone, their size and density can be tuned as well as the size of the backbone. This in situ seeding CVD method has the potential for a low-cost single-step fabrication of high-quality, micro/nanointegrated photonic devices, with tunable complex waveguiding possibilities.

Low-Cost PCB-Integrated 10-Gb/s Optical Transceiver Built With a Novel Integration Method

A novel integration method for the production of cost-effective optoelectronic printed circuit boards (OE PCBs) is presented. The proposed integration method allows fabrication of OE PCBs with manufacturing processes common to the electronics industry while enabling direct attachment of electronic components onto the board with solder reflow processes as well as board assembly with automated pick-and-place tools. The OE PCB design is based on the use of polymer multimode waveguides, end-fired optical coupling schemes, and simple electro-optic connectors, eliminating the need for additional optical components in the optical layer, such as micro-mirrors and micro-lenses. A proof-of-concept low-cost optical transceiver produced with the proposed integration method is presented. This transceiver is fabricated on a low-cost FR4 substrate, comprises a polymer Y-splitter together with the electronic circuitry of the transmitter and receiver modules and achieves error-free 10-Gb/s bidirectional data transmission. Theoretical studies on the optical coupling efficiencies and alignment tolerances achieved with the employed end-fired coupling schemes are presented while experimental results on the optical transmission characteristics, frequency response, and data transmission performance of the integrated optical links are reported. The demonstrated optoelectronic unit can be used as a front-end optical network unit in short-reach datacommunication links.

Evanescent straight tapered-fiber coupling of ultra-high Q optomechanical micro-resonators in a low-vibration helium-4 exchange-gas cryostat

We developed an apparatus to couple a 50-μm diameter whispering-gallery silica microtoroidal resonator in a helium-4 cryostat using a straight optical tapered-fiber at 1550 nm wavelength. On a top-loading probe specifically adapted for increased mechanical stability, we use a specifically-developed "cryotaper" to optically probe the cavity, allowing thus to record the calibrated mechanical spectrum of the optomechanical system at low temperatures. We then demonstrate excellent thermalization of a 63-MHz mechanical mode of a toroidal resonator down to the cryostat's base temperature of 1.65 K, thereby proving the viability of the cryogenic refrigeration via heat conduction through static low-pressure exchange gas. In the context of optomechanics, we therefore provide a versatile and powerful tool with state-of-the-art performances in optical coupling efficiency, mechanical stability, and cryogenic cooling.

Optical propagation and refraction in silicon complementary metal–oxide–semiconductor structures at 750 nm: toward on-chip optical links and microphotonic systems

This paper analyzes the optical propagation and refraction phenomena in various complementary metal–oxide–semiconductor (CMOS) structures at 750 nm wavelength. Operation at these wavelengths offers the potential realizations of small microphotonic systems and micro-opto-electro-mechanical systems (MOEMS) in CMOS integrated circuitry, since Si-based optical sources, waveguides, and silicon (Si) detectors can all be integrated on a single chip. It could also increase the optical coupling efficiencies to external optical fibers. With the help of Monte Carlo and RSoft BeamPROP simulations, we demonstrate achievements with regard to optimizing vertical emission, focusing, refraction, splitting and wave guiding in 0.35 to 1.2 μm CMOS technology at 750 nm wavelength. The material properties, refractive indices, and thicknesses of various CMOS over-layers were incorporated in the simulations and analyses. The analyses show that both Si nitride and Si oxi-nitride offer good viability for developing such waveguides. Effective single-mode wave-guiding with calculated loss characteristics of 0.65 dB⋅cm −1 , with modal dispersion characteristics of less than 0.2 ps⋅cm −1 and with a bandwidth-length product of higher than 100 GHz-cm seems possible. A first iteration realization of an optical link is demonstrated, utilizing specially designed avalanche-based Si-LEDs and a specially designed first iteration CMOS waveguide. Potential applications of avalanche-based Si LEDs into microphotonic systems and MOEMS are furthermore proposed and highlighted.