Average Optical Loss Research Articles

A 3nm-thick, quasi-single crystalline Cu layer with ultralow optoelectrical losses and exceptional durability

An ultrathin, highly crystalline, two-dimensional Cu layer is necessary for simultaneously achieving ultralow electrical and optical losses in transparent electrodes. However, perfect Cu wetting on heterogeneous oxide substrates has not yet been achieved. Herein, we report the Ge-mediated fabrication of an ultrathin, highly crystalline, complexly continuous Cu layer. The unique surfactant-like segregation of atomic Ge towards the outermost boundaries of the Cu geometries remarkably enhanced Cu wetting on the ZnO substrate. Numerical simulation indicated that the enhanced wetting can be attributed to the simultaneous decreases in the thermodynamic cohesive and formation energies at the surface and interface of the Cu nanostructures owing to Ge segregation. This enabled the fabrication of an ultrathin (∼3 nm), highly crystalline, two-dimensional Cu layer in a ZnO/Cu/ZnO configuration, which exhibited a record-low average optical loss at a near-bulk resistivity (8 × 10−8 Ω m) comparable to those of conventional Ag electrodes; it also showed exceptional durability in water, ozone, and high-temperature (up to 400 °C) environments. These unique features would ensure the development of highly reliable optoelectrical devices employing Cu superstructure-based transparent electrodes as inexpensive alternatives to Ag-based transparent electrodes.

Experimental analysis of the optical loss of a dusty Fresnel lens with a novel solar flux test system

The effect of dust deposition on a point-focus Fresnel lens is experimentally analyzed using a novel outdoor solar flux test system. The solar flux maps of the concentration region of the Fresnel lens are obtained. A detailed mathematical heat transfer model of the thermocouple is developed to calculate the solar flux density at a given spot temperature. The solar flux intensity and shape, spot temperature, dust deposition density, and imaging distance are analyzed. The flux spot exhibits an ellipsoidal Gaussian distribution. As the dust density increases from 0 g/m2 to 5 g/m2, the peak flux exhibits a decrease of 57.4%, and the spot temperature decreases from 307 °C to 98.1 °C. An average optical loss of 16.69% is obtained for each 1 g/m2 increase in the dust density. Error sources and estimates of the system are analyzed. The experimental measurements are in good agreement with the theoretical values. The deviation is within 8.33%, and the maximum deviation is 18.39 kW/m2.

Inter-layer light transition in hybrid III-V/Si waveguides integrated by µ-transfer printing.

We demonstrate low-loss and broadband light transition from III-V functional layers to a Si platform via two-stage adiabatic-crossing coupler waveguides. A 900-µm-long and 2.7-µm-thick III-V film waveguide consisting of a GaInAsP core and InP cladding layers is transferred onto an air-cladding Si photonic chip by the µ-transfer printing (µ-TP) method. An average optical coupling loss per joint of 1.26 dB is obtained in C + L telecommunication bands (1530-1635 nm). The correlation between alignment offset and measured optical coupling loss is discussed with the frequency distribution of µ-TP samples. We also performed a photoluminescence measurement to investigate the material properties in the GaInAsP layer to see if they are distorted by the strong bending stress produced during the pick-up and print steps of the µ-TP process. The peak intensity reduction of 80-90% and a wavelength shift of 0-5 nm (blue shift) were observed after the process. The series of fundamental studies presented here, which combine multiple analyses, contribute to improving our understanding of III-V/Si photonic integration by µ-TP.

Toward a High-Performance and Low-Loss Clos–Benes-Based Optical Network-on-Chip Architecture

As chip multiprocessors (CMPs) keep growing in capability, on-chip communication efficiency is crucial to the overall performance. However, on-chip networks based on electronic switches suffer from excessive power consumption and limited performance. In order to take advantages of optical interconnect, we propose an optimized design toward a high-performance and low-loss Clos–Benes-based hierarchical optical network-on-chip (NoC) for large-scale CMPs. We propose several key techniques, including a loss-aware adaptive (LAA) routing for intraswitch Benes network, a priority-based round-Robin virtual output queue selection and a $Q$ -learning-based heuristic routing for interswitch Clos network, and a local transfer link (LTL) technique to improve the traffic locality. A case study on a 256-core CMP under uniform traffic shows that the network throughput is increased by 346.7%, 61%, and 12.9%, respectively, than the mesh, fattree, and the traditional generic Clos–Benes optical NoC. On average of a set of real applications, the application end-to-end delay is reduced by 47.6%, 28.2%, and 19.4%, respectively, than the mesh, fattree, and the traditional generic Clos–Benes network. Meanwhile, the average optical power loss is decreased by 11.8% and 49.9%, respectively, as compared to the mesh and fattree. As compared to a baseline Clos–Benes network, the use of LAA routing together with the LTL could reduce the average optical power loss by 28.4%.

Highly transparent and conductive oxide-metal-oxide electrodes optimized at the percolation thickness of AgOx for transparent silicon thin-film solar cells

Highly transparent and conductive oxide-metal-oxide (OMO) electrodes comprising aluminum-doped zinc-oxide (AZO) and ultrathin Ag or oxygen (O2)-doped Ag (AgOx) metal layers were fabricated for use in thin-film silicon solar cells. The surface morphologies of the metal layers and the transparencies and conductivities of OMO electrodes were investigated near the percolation thickness values of the metal layers. The percolation metal thickness, which means the metal layer is morphologically continuous, could be used to optimize the transparent OMO electrode. Additionally, thin Ag-based OMO (AgOx OMO) with superior performance could be fabricated by adding O2. The optimized AgOx OMO electrodes yielded the highest average transmittance (Tavg) of 93.5% and the lowest average optical loss (OLavg) of 1.01% within 500–800 nm at the percolation thickness of ~6 nm, thus, maintaining low conductivity. These outcomes were superior to the responses of the percolated Ag OMO (Tavg = 87.2%; OLavg = 1.01%). Using the OMO structure at the rear electrode, transparent hydrogenated amorphous silicon thin-film solar was fabricated for building integrated photovoltaic windows. The best figure-of-merit (FOM; equal to the product of Tavg and efficiency η) values of the OMO-based transparent solar cells could be obtained for percolated OMO structures. The cells using AgOx OMO (AgOx cells) performed better than the Ag cells; the best FOMs of AgOx and Ag cells were 140.8 (Tavg = 27.8%; η = 5.51%) and 104.6% (Tavg = 18.9%; η = 5.54%), respectively. These results could contribute to the development of high-performance transparent solar cells or optoelectronic devices.

Air-clad suspended nanocrystalline diamond ridge waveguides.

A hybrid group IV ridge waveguide platform is demonstrated, with potential application across the optical spectrum from ultraviolet to the far infrared wavelengths. The waveguides are fabricated by partial etching of sub-micron ridges in a nanocrystalline diamond thin film grown on top of a silicon wafer. To create vertical confinement, the diamond film is locally undercut by exposing the chip to an isotropic fluorine plasma etch via etch holes surrounding the waveguides, resulting in a mechanically stable suspended air-clad waveguide platform. Optical characterization of the waveguides at 1550 nm yields an average optical loss of 4.67 ± 0.47 dB/mm. Further improvement to the fabrication process is expected to significantly reduce this waveguide loss.

Optical Switches Based on Silicon Photonics for ROADM Application

We demonstrate compact and low-loss 8 × 8 silicon photonic switch modules, which are applicable to transponder aggregators (TPAs) in colorless, directionless, and contentionless reconfigurable optical add-drop multiplexers. Newly designed silicon optical switch chips incorporating spot size converters with polarization insensitive and wavelength insensitive properties over C/L bands are packaged. The developed module shows about 6-dB average excess optical loss, including optical coupling loss, on all 64 optical paths with low-polarization-dependent loss and low crosstalk. Using these compact optical switch modules, we construct a TPA prototype featuring over 100-port optical switch subsystem densely mounted on one board and confirm its feasibility.

Direct tracking error characterization on a single-axis solar tracker

The solar trackers are devices used to orientate solar concentrating systems in order to increase the focusing of the solar radiation on a receiver. A solar concentrator with a medium or high concentration ratio needs to be orientated correctly by an accurate solar tracking mechanism to avoid losing the sunrays out from the receiver. Hence, to obtain an appropriate operation, it is important to know the accuracy of a solar tracker in regard to the required precision of the concentrator in order to maximize the collector optical efficiency. A procedure for the characterization of the accuracy of a solar tracker is presented for a single-axis solar tracker. More precisely, this study focuses on the estimation of the positioning angle error of a parabolic trough collector using a direct procedure. A testing procedure, adapted from the International standard IEC 62817 for photovoltaic trackers, was defined. The results show that the angular tracking error was within ±0.4° for this tracker. The optical losses due to the tracking were calculated using the longitudinal incidence angle modifier obtained by ray-tracing simulation. The acceptance angles for various transversal angles were analyzed, and the average optical loss, due to the tracking, was 0.317% during the whole testing campaign. The procedure presented in this work showed that the tracker precision was adequate for the requirements of the analyzed optical system.

Optical Losses through Gaps of CPCs with One-Sided Flat Absorber

In this work, the angular dependence of optical losses through gaps, constructed by truncating reflectors near the absorbers, of CPCs with one-sided flat absorber was presented, and the annul radiation loss through gaps of east-west aligned CPCs is theoretically investigated. Results show that the optical losses are mainly resulted from direct radiation loss through gaps due to direct irradiation on gaps, and the loss of radiation that arrive on gaps from reflectors after multiple reflections is considerable small and can be neglected in solar calculations especially for truncated CPCs. Results also show that the annual direct radiation loss is dependent on geometric parameters of CPCs but seems independent on solar resource in sites where CPCs are used, and the annual radiation loss of full CPCs oriented in east-west direction with the tilt-angle of aperture being yearly fixed is almost identical to average optical loss of the CPC over its acceptance angle.

Optical losses due to tracking error estimation for a low concentrating solar collector

The determination of the accuracy of a solar tracker used in domestic hot water solar collectors is not yet standardized. However, while using optical concentration devices, it is important to use a solar tracker with adequate precision with regard to the specific optical concentration factor. Otherwise, the concentrator would sustain high optical losses due to the inadequate focusing of the solar radiation onto its receiver, despite having a good quality.This study is focused on the estimation of long-term optical losses due to the tracking error of a low-temperature collector using low-concentration optics. For this purpose, a testing procedure for the incidence angle modifier on the tracking plane is proposed to determinate the acceptance angle of its concentrator even with different longitudinal incidence angles along the focal line plane. Then, the impact of maximum tracking error angle upon the optical efficiency has been determined. Finally, the calculation of the long-term optical error due to the tracking errors, using the design angular tracking error declared by the manufacturer, is carried out.The maximum tracking error calculated for this collector imply an optical loss of about 8.5%, which is high, but the average long-term optical loss calculated for one year was about 1%, which is reasonable for such collectors used for domestic hot water.

Industry Compatible Embossing Process for the Fabrication of Waveguide-Embedded Optical Printed Circuit Boards

We demonstrate a cost-effective embossing process for the fabrication of waveguide-embedded optical printed circuit boards (OPCBs). The process involves the application of a polydimethylsiloxane mold for the production of polymer waveguides on a copper-clad FR4 substrate followed by the conventional lamination process. The embossing process is carefully tailored for the commercial polymer materials that are developed specifically to withstand the high temperature and high pressure environment during lamination. With this process, we are able to produce high-quality waveguide-embedded OPCBs with good repeatability. Our typical OPCB samples, each of which consists of 12 130-mm long fully embedded channel waveguides with a core size of approximately 50 × 50 μm and a pitch of 250 μm, show an average optical loss in the range 0.16-0.22 dB/cm at the wavelength 850 nm. The OPCBs survive the reflow process at 245 °C with a small change in the optical loss. The embossing process can be readily integrated with the existing PCB manufacturing process and thus offers a practical solution to mass production of OPCBs.

Optical-electrical printed wiring board for high-speed computing applications

Optical-electrical printed wiring boards were fabricated featuring mechanical transfer (MT)-compatible interconnections for out-of-plane optical signal routing with an average optical link loss of 10.7 dB. Commercially available components were integrated into an optical layer for out-of-plane optical routing, including light turning devices that feature spherical micro lens arrays, a total internal reflection mirror, and alignment slots compatible with standard MT connectors. The feasibility of the optical-electrical printed wiring board is discussed in detail to demonstrate its compatibility with common printed circuit board manufacturing processes. The optical-electrical printed wiring board prototypes survived thermal cycling (−40°C to 85°C) and humidity exposure (95% humidity) showing an overall degradation of 18 dB ) occurred after environmental aging life testing at 110°C for 216 h.

Refractive Index Dispersion and Optical Dielectric Properties of Poly(N-Carbazole)/Poly(vinylpyrrolidone) Blends

Different compositions of blended poly (N-carbazole) (PVK) with polyvinylpyrrolidone (PVP) were prepared. The optical properties such as infinite frequency refractive index (n∞), average oscillator wavelength (λ0), oscillator strength (So), dispersion energy (Ed), oscillator energy (Eo) and optical dielectric loss have been calculated. The refractive index of polymer blending systems significantly changes with the volume composition of PVP and shows a normal dispersion behavior. Mean while, the values of n∞, Ed and Eo increase with the increase of PVP composition. Both of the real and imaginary part of the dielectric constant decrease as the wavelength increase. Thus, it reveals that the polymer composition has influenced the optical properties of the polymer blending system.

Fully Flexible Optoelectronic Foil

In this paper, we present a process to embed commercially available optical material layers into a flexible foil. Patterning of the embedded layers results in highly transparent low-loss flexible waveguides. Bending of the foil down to a bending radius of 5 mm causes no additional optical propagation losses. Vertical cavity surface emitting laser's and photodiodes are thinned down to 20 m and are embedded inside the cladding layer of the waveguides. They are optically coupled with the use of embedded micromirror plugs. The result is a thin foil of 150 m thickness with embedded active optical low-loss links. The presented links show an average total optical loss of 6.4 dB and a clear open-eye diagram at 1.2 Gb/s. The foil characteristics do not change after humidity and temperature cycling.

A reconfigurable thin-film filter-based 2 x 2 add-drop fiber-optic switch structure

A reconfigurable 2 /spl times/ 2 add-drop fiber-optic switch structure is proposed by incorporating the independent mechanical control and alignment of an off-the-shelf thin-film filter with a reflective optical element. Cascading several 2 /spl times/ 2 add-drop switches gives a low-cost polarization-independent wavelength routing system with the limitation in optical loss that can be compensated by using optical amplifiers. The experimental result indicates a measured average optical loss of <1.30 dB at the center wavelength. In addition, the measured optical coherent crosstalk values at the center wavelength are -15 and -22 dB when the thin-film filter and the mirror are in the optical path, respectively. A very low polarization-dependent loss of <0.07 dB is also investigated.

FLC SLM을 이용한 편광의존형 2×2 광스위치

We demonstrated a polarization dependent type 2<TEX>$\times$</TEX>2 optical switch, using a binary reflection type SLM. Reflection type FLC was used as a half wave retardation plate. Two inputs were controlled by each SLM for the desired output direction. In conclusion, in the "1" state the average optical loss was 6.6 ㏈, and in the "0" state the average optical loss was 14.6 ㏈, and measured the switching speed as 75 <TEX>$mutextrm{s}$</TEX>. By using this method, a polarization dependent type 2<TEX>$\times$</TEX>2 optical switch can be demonstrated and the possibility of a 4-port WDM optical switch also verified.

Single-crystal Y2O3-ZrO2 rectangular waveguides for ultrahigh-temperature sensing applications.

High-quality Y2O3-ZrO2 single-crystal rectangular waveguides have been developed for ultrahigh-temperature sensing applications. Five waveguides, 0.55-1.12 mm wide and 52-65 mm long, were fabricated from a bulky cubic 21.2-mol. % Y2O3 stabilized ZrO2 single crystal that had been precisely cut and finely polished. At 900-nm wavelength, the average optical loss of these waveguides is approximately 0.016 dB/cm, which is much lower than that of Y2O3-ZrO2 single-crystal optical fibers grown by the laser-heated pedestal growth method. The tested waveguides survived a temperature higher than 2,300 degrees C, and their mechanical strength and chemical resistance were also acceptable. Experimental results show that these waveguides are promising for ultrahigh-temperature sensing applications.

Liquid crystal-based self-aligning &lt;inline-formula&gt;&lt;math display="inline" overflow="scroll"&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/math&gt;&lt;/inline-formula&gt; wavelength routing module

A novel retroreflective polarization insensitive 2x2 fiber optic switch (FOS) using programmable quarter waveplates (QWPs) is introduced. Key features include low polarization sensitivity and a selfaligning module via a compact retroreflective structure. A proof of concept 2 x 2 FOS using ferroelectric liquid crystal (FLC)-based programmable QWPs is demonstrated, providing a response speed of 394 ?s and a low 10.14-mW total electrical power consumption for the worst case. Multiwavelength switch operation in the 1550-nm wavelength region indicates an average optical loss of 6.02 dB with a ±0.18-dB loss fluctuation, and an optical coherent crosstalk of -21.6 dB with a ±0.84 dB variation over a 60-nm bandwidth. The temperature dependence of our switch is investigated over a 17°C range, indicating an average 5.80-dB optical loss with a ±0.13-dB fluctuation, and an average optical coherent crosstalk of -20.5 dB with a fluctuation of ±0.42 dB. An average polarization dependent loss of 0.4 dB is also measured. A time-multiplexed FLC device addressing technique is introduced for FOS to achieve long duration operation.

A new optical fiber multiplexer for distortion-free light transfer in multichannel fiber optic sensor systems

The present paper describes the development of a concept for the construction and design of optical signal multiplexing devices for highly efficient and distortion-free switching and transfer of light in fiber optic sensor systems. On the basis of the developed concept, an optical fiber multiplexer (OF multiplexer) for a measuring system with fiber optically guided sensors was constructed, manufactured and characterized. A mathematical model for the OF multiplexer light transfer function was calculated and an automatic adjustment developed. The average optical loss including connectors is around 1.5 dB and the maximum transmitted power is about 1 kW by use of 1000 μm fibers within a wavelength range of 250–900 nm.

Small-tilt micromirror-device-based multiwavelength three-dimensional 2×2 fiber optic switch structures

Small-tilt micromirror-based 232 fiber optic switch array structures are proposed using fixed mirrors and fiber interconnections. A multiwavelength 232 fiber optic switch based on this small-tilt micromir- ror is experimentally demonstrated. The key innovation in this architec- ture is the use of a specially located fixed mirror to form a symmetric 2 32 retroreflective switching structure. These 2 32 fiber optic switch struc- tures can also provide a fault-tolerant design using a macropixel ap- proach. A two-dimensional digital micromirror device (2D-DMD) from Texas Instruments (TI) designed to operate in the visible band is used to represent the small-tilt micromirrors in our experimental demonstration. Multiwavelength switch operation is characterized by changing the oper- ating wavelength of the tunable laser. The measured average optical coherent crosstalk is 222 dB with 60.9 dB fluctuation over 40 nm, lim- ited by the on-off ratio of the 2D-DMD. The measured average optical loss is 14.8 dB at a 1.55-mm operating wavelength, limited by the visible wavelength design TI 2D-DMD, three-port optical circulators, fiber adapt- ers, and free-space-to-fiber coupling efficiency. © 2000 Society of Photo- Optical Instrumentation Engineers. (S0091-3286(00)02002-X)