Optical Power Loss Research Articles

Ant Colony Optimization-Based Thermal-Aware Adaptive Routing Mechanism for Optical NoCs

Optical networks-on-chip (NoC) based on silicon photonics has been proposed as an emerging on-chip communication infrastructure of chip multiprocessors. However, due to thermal sensitivity of optical devices under on-chip temperature variations, significant thermal-induced optical power loss would offset the benefit of optical NoCs in power efficiency. In this work, we propose a thermal-aware adaptive routing scheme based on ant colony optimization (ACO) to alleviate the thermal issue. The proposed ACO-based routing scheme applies the ACO method to formulate and optimize the routing decisions with the objective of reducing optical power loss under temperature variations. The traditional implementation of the ACO-based routing scheme requires a table in each node to keep and update pheromone, and the table size increases linearly with the number of nodes in the network. To avoid the table overhead, we further propose an approximate ACO-based routing (AACO) scheme based on linear regression. A case study on an <inline-formula> <tex-math notation="LaTeX">$8\times 8$ </tex-math></inline-formula> mesh-based optical NoC under a series of synthetic traffic patterns and real applications shows that the proposed routing schemes are able to select near-optimal paths under varying on-chip temperature variations. We further verify the scalability of the proposed routing schemes in a larger network.

Graphene Based Macrobend Unclad SMF for Monitoring pH Level in Aqueous Environment

Partial unclad fibers with diameters ranging from d=121μm to d=125μm were fabricated using standard telecommunications optical fiber (SMF28) via low cost mechanical swipe-off technique. Graphene oxide (GO) was deposited using drop casting method on the outer side of the partial unclad SMF. IR laser with excitation wavelengths of λ=1310nm and λ=1550nm were launched along the graphene-coated SMF. The sensitivity of graphene based macrobend unclad SMFs were investigated by introducing two different pH of aqueous environment with values of 3.5 (acidic) and 12.5 (alkaline) that acted as sensing media. The optimum power loss was obtained as smallest diameter of partial unclad SMF with d=121μm was appointed. As uncoated SMF was replaced with the GO coated SMF which had been immersed into 3.5pH liquid solution, it was found that the optical power losses were increased about 6.79dBm and 5.15dBm using laser with λ1=1310nm and λ2=1550nm respectively. The uncoated SMFs experienced the increment of power losses about 2.11dBm and 5.15dBm as they were soaked into the solution with pH=12.5 using similar laser of λ1 and λ2. It is noteworthy to highlight the significant of graphene’s employment on macrobend unclad SMF by using λ1=1310nm in which better sensitivity and selectivity represented by maximum changes of power losses were apparently observed for both solutions. The usage of λ=1550nm exhibited poor selectivity where the partial unclad SMF unable to differentiate two contrasting pH solution. In conclusion, graphene based macrobend fiber optic sensor for pH detection was successfully developed by employing partial unclad SMF with cladding diameter of d=121μm and laser wavelength of λ=1310nm due to the enhancement of evanescent field’s strength.

Demonstration of 4 × 100 Gbit/s PAM-4 Transmission Over 40 km in an IM/DD System Based on Narrow Band DMLs

We demonstrate a four-lane wavelength division multiplexing (WDM) intensity modulation and direct detection (IM/DD) system at O-band. The 3-dB bandwidth of directly modulated lasers (DMLs) in this experiment is only 15 GHz. To support 100-Gbit/s/lane PAM-4 transmission in each lane, digital pre-equalization and advanced receiver-side DSPs are adopted to compensate for bandwidth limitation. Moreover, semiconductor optical amplifier (SOA) is utilized at the receiver to compensate for the optical power loss during fiber transmission so that 40-km transmission distance can be achieved. To the best of our knowledge, it is the first time to successfully transmit 400-Gbit/s PAM-4 signals over 40-km SSMF with 15-GHz DMLs.

Hybrid Temperature and Stress Monitoring of Woven Fabric Thermoplastic Composite Using Fiber Bragg Grating Based Sensing Technique.

Process monitoring of woven fabric thermoplastic composite is crucial to enhance the quality of composite products. In this work, a new fiber Bragg grating based technique was proposed to achieve hybrid temperature and stress monitoring according to the changes of wavelength and reflectivity, respectively. The sensor head consisting of a pre-annealed fiber Bragg grating and a steel capillary was properly designed to overcome the challenge of high forming temperatures up to 332 °C, complex woven structure, and high forming pressure of 2 MPa, which hinder the use of the conventional fiber Bragg grating sensor during the forming process. The forming temperature changes of thermoplastic composite in the heating, dwelling, and cooling phases can be precisely measured by the proposed sensor head after using a curve-reconstruction algorithm based on cubic polynomial fitting. The measured difference from the reference thermocouple is 2.92 °C, averaged from three sets of repeated experiments. Meanwhile, the change of the residual stresses of the composite can be illustrated by using the micro-bending-caused optical power loss of the fiber pigtail commencing at the glass-transition temperature in the cooling phase. The decrease of grating reflectivity that was equivalent to the optical loss was discussed by comparing to strain change detected by strain gauges and a calculated theoretical curve. These results are beneficial for developing an advanced in situ monitoring technique and understanding the forming process of the woven fabric thermoplastic composite.

Contention-Aware Routing for Thermal-Reliable Optical Networks-on-Chip

Optical network-on-chip (ONoC) architecture offers ultrahigh bandwidth, low latency, and low power dissipation for new-generation manycore systems. However, the benefits in communication performance and energy efficiency will be diminished by communication contention. The intrinsic thermal susceptibility is another challenge for ONoC designs. Under on-chip temperature variations, core functional devices suffer from significant thermal-induced optical power loss, which seriously threatens ONoCs’ reliability. In this article, we develop novel routing techniques to resolve both issues for ONoCs. By analyzing the thermal effect in ONoCs, we first present a routing criterion at the network level. Combined with device-level thermal tuning, it can implement thermal-reliable ONoCs. Two routing approaches, including a mixed-integer linear programming (MILP) model and a heuristic algorithm (called CAR), are further proposed to minimize communication conflicts based on guaranteed thermal reliability, and meanwhile, maximize the communication energy efficiency in the presence of on-chip thermal variations. By applying the criterion, our approaches achieve excellent performance with largely reduced complexity of design space exploration. The evaluation results based on both synthetic traffic patterns and realistic benchmarks validate the effectiveness of our approaches with an average of 126.95% improvement in communication performance and 16.12% reduction in energy overhead compared to state-of-the-art techniques. CAR only introduces 7.20% performance difference compared to the MILP model and is more scalable to large-size ONoCs.

Residual thickness enhanced core-removed D-shaped single-mode fiber and its application for VOC evaporation monitoring.

A core-removed D-shaped structure with different residual thickness (RT) was manufactured on a single mode silica fiber (SMF) to enhance the sensitivity by using of ultra-precise polishing technology. With six different RTs ranging from ∼55 µm to ∼28 µm, the RT enhancement effect in a D-shaped SMF was researched in detail. The influence of the RT on its transmission spectra was investigated both theoretically and experimentally. Considering a compromise between the multimode interference efficiency and optical power loss, an optimum RT value of 34.09 µm was achieved. The obtained refractive index (RI) sensitivity was 10243 nm/RIU in the RI range of 1.430-1.444, corresponding to a RI resolution of 1.9×10-6 RIU. A high-performance all-fiber sensor was developed to monitor the evaporation process volatile organic compounds (VOCs) based on the RT-enhanced D-shaped SMF. As proof of concept, a 2-hour continuous monitoring was carried to monitor the chloroform and alcohol mixture. As a result, the evaporation of alcohol and chloroform were clearly identified and monitored. The developed RT-enhanced D-shaped fiber sensor provides an alternative way for chemical process monitoring and industrial applications.

An optimized phosphor model coupled with thermal and optical behavior and a thereof ring-shaped phosphor convertor for improving thermal uniformity in laser illuminations

Abstract Due to the high energy density of laser diode (LD), the fluorescent convertor always suffers from serious overheating problems, such as thermal quenching, significant efficiency drop or even material carbonization failure. In this work, we improved the current optical-thermal model by coupling the optical behavior of red (nitride)/yellow (YAG) phosphor and thermal conductivity of different hybrid particles concentrations. According to the theoretical analysis, the thermal sensitive concentration zone was revealed. To avoid the hotspot occurs, a ring-shaped phosphor convertor with two different concentrations was developed. Results showed that the convertor with high-concentration center could reduce the max temperature by 9.4% without obvious optical power loss. Some further research suggestions were also proposed to improve the thermal performances of the laser illumination.

Estimation of power loss spectra in slightly flattened distorted Bragg fiber waveguide

Dispersion characteristic and fiber loss spectra of a Bragg fiber waveguide having slightly flattened distortion are estimated for sensing applications. The characteristic and optical power loss equations of waveguide are obtained by matching the fields at various boundaries under quarter wave stack conditions. It is found that the optimum power loss is inversely proportional to the ninth power of distortion coefficient. The obtained results show that optimum fiber loss decreases with decrease of refractive index of cladding layer 'b' (low refractive index layer) and increase of refractive index of cladding layer 'a' (high refractive index layer). Also, fiber losses are estimated with increase of the high and low refractive index cladding layer losses. This loss spectrum of fiber can be considered as sensing signal. Since obtained fiber losses in distorted Bragg fiber are higher than standard Bragg fiber therefore, the sensitivity of proposed structure is higher than the standard Bragg fiber. Also, the sensitivity increases with the increase of refractive index of core medium. These results would be helpful to design a novel highly sensitive sensor based on hollow core distorted Bragg fiber.

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%.

Design, Fabrication, and Comparison of 3D Multimode Optical Interconnects on Silicon Interposer

While conventional silicon photonic (SiP) waveguides achieve high data rates with low loss, they can only be placed on top of the chip surfaces horizontally. In this article, we present a design approach for multimode chip-to-chip interconnects with similar low-loss and high-bandwidth density properties as SiP waveguides. The state-of-the-art fabrication of optical through silicon via (OTSV) requires conventional back end of line (BEOL) processing with an additional step: metal coating lowers the loss of air-filled TSVs. Alternatively, the TSV is converted into a polymer waveguide by filling of low-loss polymer (Ormocore) to achieve <0.1 dB optical power loss over 380 μm distance. A 3D multimode optical interconnect is measured at 40 Gbit/s with the bit error rate (BER) <10−12 at 1550 nm wavelength. The proposed solution supplies a new path for 3D integration of optical waveguides capable of delivering high-speed data within 3D stacked chips.

Experimentally Derived Feasibility of Optical Camera Communications under Turbulence and Fog Conditions.

Optical camera communications (OCC) research field has grown recently, aided by ubiquitous digital cameras; however, atmospheric conditions can restrict their feasibility in outdoor scenarios. In this work, we studied an experimental OCC system under environmental phenomena emulated in a laboratory chamber. We found that the heat-induced turbulence does not affect our system significantly, while the attenuation caused by fog does decrease the signal quality. For this reason, a novel strategy is proposed, using the camera’s built-in amplifier to overcome the optical power loss and to decrease the quantization noise induced by the analog-digital converter of the camera. The signal quality has been evaluated using the Pearson’s correlation coefficient with respect to a reference template signal, along with the signal-to-noise ratio that has been empirically evaluated. The amplification mechanism introduced allows our system to receive the OCC signal under heavy fog by gradually increasing the camera gain up to 16 dB, for meteorological visibility values down to 10 m, with a correlation coefficient of 0.9 with respect to clear conditions.

Thermal-Aware Design and Simulation Approach for Optical NoCs

For chip multiprocessors, one major challenge is to bridge the increasing speed gap between processor and the global on-chip interconnect delay. By integrating optical interconnects in network-on-chip (NoC) architectures, optical NoCs can overcome the power and bandwidth bottleneck of traditional electrical on-chip networks. However, while considering the thermal sensitivity of silicon photonic devices used in optical NoCs, optical interconnects may not have advantages in power efficiency as compared with their electrical counterparts. To tackle this problem, in this article, we propose a thermal-aware design and simulation approach for optical NoCs. Key techniques include thermal-sensitive optical power loss models from device level to network level, a thermal-aware adaptive routing mechanism, and a thermal-aware simulation platform. The thermal-aware simulation platform enables optical NoC simulation together with on-chip temperature simulation as well as optical thermal effect modeling. With the proposed thermal-aware simulation platform, we conducted a case study of an $8\times 8$ mesh-based optical NoC under a set of synthetic traffic patterns as well as real applications at typical temperature scenarios. By comparing and analyzing different temperature distributions, we can conclude that it can achieves a better optimization effect for the temperature distributions where the hot spots are scattered across the chip.

Means and verification of broadcast technology applied to laser transmission on horizontal link

At present, there has been great progress in the field of the point-to-point laser communication technology, in other words, the traditional laser communication technology has been advanced day by day. Furthermore, in order to search for an effective means of achieving localized laser broadcasting communication within a limited range, an effective method of horizontal link laser broadcasting communication is presented, and the corresponding verifiable broadcast communication system is designed. In addition, the laser broadcasting is systematically studied by one physical model built at the optimal distribution of optical power. First of all, the theoretical model of laser beam expansion and the theoretical model of parallel light curtain are made comparisons and analyzed from the angle of attenuation of optical power, and the optical power loss model of the parallel light curtain is established as a result. Secondly, combined with the theory of optical imaging transformation based on Gaussian beam, the field distribution of far field of parallel light curtain is simulated by one leading optical and illumination design software and the relation between the filed distribution of far field of light curtain and the distance of transmission is revealed. Finally, the superiority and feasibility of the parallel light curtain theory model are verified by field communication experiments in different information channels.

A thermal-sensitive design of a 3D torus-based optical NoC architecture

In order to overcome limitations of traditional electronic interconnects in terms of power efficiency and bandwidth density, optical networks-on-chip (NoC) based on silicon photonics have been proposed as an emerging on-chip communication architecture for chip multiprocessors (CMPs) with large core counts. However, due to thermo-optic effects, wavelength-selective silicon photonic devices such as microresonators suffer from temperature-dependent wavelength shift. In this work, we propose a thermal-sensitive design of a 3D torus-based optical NoC architecture. For the 3D torus-based optical NoC architecture, we propose a hybrid optical-electronic router architecture with a fully-connected 7 × 7 optical switching fabric. Besides, a thermal-sensitive routing algorithm is proposed to optimize the optical power loss in the presence of on-chip temperature variations. Simulation results show that for a set of synthetic traffic patterns, the proposed 3D torus-based optical NoC with the thermal-sensitive routing reduces the average thermal-induced optical power loss by 14.3% and 17% respectively as compared to the matched 3D torus-based optical NoC and the 3D mesh-based optical NoC with the traditional XYZ routing. For a set of real applications, the proposed 3D torus-based optical NoC with the thermal-sensitive routing reduces the worst-case optical power loss by 7.9% and 14.6% respectively as compared to the matched 3D torus-based optical NoC and the 3D mesh-based optical NoC with the traditional XYZ routing.

Prospects for strongly coupled atom-photon quantum nodes

We discuss the trapping of cold atoms within microscopic voids drilled perpendicularly through the axis of an optical waveguide. The dimensions of the voids considered are between 1 and 40 optical wavelengths. By simulating light transmission across the voids, we find that appropriate shaping of the voids can substantially reduce the associated loss of optical power. Our results demonstrate that the formation of an optical cavity around such a void could produce strong coupling between the atoms and the guided light. By bringing multiple atoms into a single void and exploiting collective enhancement, cooperativities ~400 or more should be achievable. The simulations are carried out using a finite difference time domain method. Methods for the production of such a void and the trapping of cold atoms within it are also discussed.

A Geometric Error Modeling Method and Trajectory Optimization Applied in Laser Welding System

In this paper, a geometric error modeling method is carried out on six-axis motion platform (SMP) in laser welding system (LWS), and an optimized algorithm is proposed for the alignment in LWS based on the error model. First, the topological structure of the given SMP is analyzed, and related homogeneous transformation matrices which are used for standing the orientation of SMP are established. By these matrices, the geometric error model is developed mathematically. Then, the error model is used for predicting the alignment deviations. A corresponding series of experiments for calculating the optical power loss in alignment are employed, and the comparison between simulation and experiments results indicate the validation of the error model. Furthermore, an optimized algorithm is applied to search the optimum aligning trajectory. Compared to conventional method, this algorithm has a broader range in searching extreme value, which can reduce the computational volume and improve the efficiency. It is also beneficial for improving the success rate of escaping from the local minimum spot and finding the optimum alignment spot. The error model is helpful to analyze the error propagation process and improve the alignment efficiency in LWS, which can be applied to other similar multi-axis precise system.

Exploitation of wavelength, hardware, and path redundancies in fault-tolerant all-optical DCNs

Abstract Data center performance is affected by three main factors; bandwidth, latency, and reliability of intra-data center interconnection network. Bandwidth and latency are definitely improved by adopting optical technology for intra-data center communication, but fault tolerance of the corresponding optical networks has been raised less. Recently, we introduced two Torus-based, all-optical, and non-blocking networks, i.e. O-TF and O-FTF, addressing reliability of optical networks, and now, in this paper, to address the scalability problem, we propose a novel Optical Clos-based architecture which reduces minimum number of required wavelength channels, as well as, the switch size in each node. Moreover, we examine three different types of redundancies; including (a) wavelength (adopted in O-TF network), (b) hardware (adopted in O-FTF network), and (c) path (adopted Optical Clos)) redundancies, in terms of throughput drop under failures, implementation cost, optical power loss, electrical power, latency, topology, and wiring complexity. In addition to simulating networks utilizing generated traffic based on Microsoft data, realistic traffic has also been considered. Our simulation results confirm that in addition to improving power consumption and latency, O-TF, O-FTF, and O-Clos architectures lead to throughput increment up to 80%, 90%, and 70%, respectively, comparing to WaveCube at the presence of network failure, as result of adopting our proposed fault-tolerant method, named as RAOP.

Speckle-free common-path quantitative phase imaging with high temporal phase stability using a partially spatially coherent multi-spectral light source

Quantitative phase imaging (QPI) has been an important technique for the determination of various biophysical parameters, such as the refractive index and morphology of biological cells and tissues. The technique has been implemented using off-axis and common path digital holographic microscopy (DHM). Off-axis DHM, though being ideal for QPI, offers lower temporal phase stability compared to common path techniques. Common path DHM offers a higher temporal phase stability but, being a coherent imaging technique, suffers from speckle artefacts and spurious interference fringes due to the high coherence of the light source. Both artefacts not only degrade the image quality, but also affect the phase measurement results. In this paper, we report the implementation of common path QPI set-up using a partially spatially coherent multi-spectral light source. The spatial coherence of the red and green color lasers is reduced by using a rotating diffuser. Also, a speckle free QPI was implemented using common path Fresnel biprism interferometer. A Fresnel biprism is used in the self-referencing mode, thus offering the advantage of no optical power loss in addition to high temporal stability and the least speckle artefacts. Furthermore, it is very easy to implement, as the system completely replaces the need for spatial filtering at the source end as well as for the reference beam generation. The experiments have been carried out on industrial and biological samples to prove the effect.

Side polished graded index multimode fiber based refractive index sensor for biology measurement

A side polished graded index multimode fiber based refractive index sensor is proposed for use in biology measurements. The side polished graded index multimode fiber is fabricated using the wheel polishing method; that is, a part of the cladding and core of a graded index multimode fiber are removed to develop a leaking “window” called a side polished region. The optical power loss through this structure is sensitive to the refractive index of the analyte liquid that covers the leaking “window.” A highly linear correlation between the optical power loss and refractive index has been achieved. Additionally, we also investigated the influence of each structure parameter on the sensitivity and linearity. From simulation and experiment results, a fiber core of 50 μm and R of 10 μm are considered as the best choices of fiber structure with a sensitivity is 40.92 dB/RIU in the refractive index range of 1.300–1.450. A bio-culture solution of fetal bovine serum can be easily detected with this structure whose concentration gradient is two percent. It provides a simple and quick method to detect refractive indices in biology measurements from 1.300 to 1.450.

Theoretical Modeling of the Internal Power Flow and Absorption Loss of the Air Mode Based on the Proposed Poynting Vector Analysis in Top-emitting Organic Light-emitting Diodes

We propose the Poynting vector analysis of the air mode in a top-emitting organic light-emitting diode (OLED) by combining the transfer matrix method and dipole source term. The spatial profiles of the time-averaged optical power flow of the air mode are calculated inside and outside the multilayer structure of the OLED with respect to the thickness of the semi-transparent top cathode and capping layer (CPL). We elucidate how the micro-cavity effect controlled by the thickness variation of the semi-transparent top cathode or CPL affects the internal optical power and absorption loss inside the OLED multilayer and the external optical power coupled into the air. When the calculated absorption loss and external power obtained by the proposed Poynting vector and currently-used point dipole models are compared, two calculation results are identical, which demonstrates the validity of the two models.