High-speed Optical Processing Research Articles

Design and analysis of a photonic crystal-based all-optical 3-input OR gate for high-speed optical processing

Design and analysis of a photonic crystal-based all-optical 3-input OR gate for high-speed optical processing

Fiber Bragg grating-electromagnetically induced transparent fast optical switch

Here, an all-optical switch is modeled in the form of fiber Bragg grating (FBG) based on electromagnetically induced transparency (EIT) phenomena dealing with a three-level EIT silicon (Si) nanocrystalline medium. The EIT consists of two fields, namely a strong control and weak probe fields that interact with the medium. Fast-optical switching of the probe is achieved by applying a pulsed control field, which relies on both steady-state and transient density matrices. The effects of four significant parameters of interest, i.e., Rabi frequency of the control field, EIT nanocrystal density, FBG length, and spontaneous decay rate, have been extensively investigated to optimize the probe transmission. Subsequently, the time-dependent density matrix is solved to obtain the response time of the FBG-EIT switch. Eventually, FBG is modeled such that low index layers contain EIT material and the high index layers do not. The FBG-EIT switch satisfies the criteria of maximum transmission and minimum rise time to give out the optimal operational condition. Despite the optical switching is in OFF mode at Ωc=0 THz demonstrating a high FBG reflectance, the reflectance suddenly vanishes at a certain Ω c s to satisfy the equivalence of low and high refractive indices (switching ON). Therefore, a fast-optical switch is envisaged operating as large as 100 GHz in theory. The future applications of the FBG- EIT include the fast Q-switching of fiber lasers, ultra-fast modulation, optical quantum communication, and high speed optical processing and computation.

Enhanced performance configuration for fast-switching deformed helix ferroelectric liquid crystal continuous tunable Lyot filter.

In this paper, we present a novel design configuration of double DHFLC wave plate continuous tunable Lyot filter, which exhibits a rapid response time of 185 μs, while the high-contrast ratio between the passband and stop band is maintained throughout a wide tunable range. A DHFLC tunable filter with a high-contrast ratio is attractive for realizing high-speed optical processing devices, such as multispectral and hyperspectral imaging systems, real-time remote sensing, field sequential color display, and wavelength demultiplexing in the metro network. In this work, an experimental prototype for a single-stage DHFLC Lyot filter of this design has been fabricated using photoalignment technology. We have demonstrated that the filter has a continuous tunable range of 30 nm for a blue wavelength, 45 nm for a green wavelength, and more than 50 nm for a red wavelength when the applied voltage gradually increases from 0 to 8 V. Within this tunable range, the contrast ratio of the proposed double wave plate configuration is maintained above 20 with small deviation in the transmittance level. Simulation and experimental results showed the proposed double DHFLC wave plate configuration enhances the contrast ratio of the tunable filter and, thus, increases the tunable range of the filter when compared with the Lyot filter using a single DHFLC wave plate. Moreover, we have proposed a polarization insensitive configuration for which the efficiency of the existing prototype can theoretically be doubled by the use of polarization beam splitters.

A special issue on High-Speed Optical Transmission and Processing

The rapid growth in network capacity and traffic rates raises the significance of high-speed optical transmission and processing. Recent progress in optical communication systems in relation to multiplexing technologies in different degrees of freedom, advanced multi-level modulation formats, coherent detection and digital signal processing has facilitated dramatic increases in transmission capacity. To be compatible with high-speed optical transmission, highspeed optical processing has gained increased interest to enable fast data manipulation in the optical domain and avoid cumbersome optical-electrical-optical conversions at network nodes. Recent progress in nonlinear-optical devices has led to enhanced efficiency, flexibility and functionality of ultrafast nonlinear-optical signal processing. It is expected that these advances in high-speed optical transmission and processing will pave the way to achieve superior performance of high-speed optical networks. It is our intention to bring the research community’s attention to these hot topics in optical communication systems and networks. In this “Special Issue on High-Speed Optical Transmission and Processing”, 8 review articles and 2 research articles focusing on relevant subjects by internationally active groups in the field are specially presented. In the review articles, Dr. Xiang Zhou at AT&T Labs—Research in USA reviewed the recent progress in transmission of 400 Gb/s wavelength-division multiplexing (WDM) channels for optical networks with standard 50 GHz grid. The enabling modulation, coding, line system technologies, and the existing challenges were discussed. Dr. Zhengxuan Li at Shanghai Jiao Tong University talked about the key technologies and system proposals of time and wavelength-division multiplexing passive optical networks (TWDM-PON). Dr. Thomas G. Brown at University of Rochester in USA presented light field manipulation in the spatial degree of freedom, showing fascinating effects in focusing, propagation, illumination, and imaging. Dr. Chaotan Sima at University of Southampton in UK summarized progress and recent developments of photonic Hilbert transforms. Dr. Claudio Porzi at the TeCIP Institute of Scuola Superiore Sant’Anna di Pisa in Italy reviewed on the use of semiconductor optical amplifier-Mach-Zehnder interferometer (SOA-MZI) for photonic add/drop and switching operations. Dr. Li Huo at Tsinghua University reported recent works in 100 Gb/s signal regeneration and processing. Dr. Wei Jin at the Hong Kong Polytechnic University discussed different types of air-silica photonic crystal fibers (PCFs) and their wide applications. Dr. Sigang Yang showed recent development of fiber optical parametric oscillators (FOPO) based on highly nonlinear dispersion-shifted fiber. In the research articles, Dr. Xia Guo at Beijing University of Technology targeted scalable light-emitting diodes (LEDs) and vertical-cavity surface-emitting lasers (VCSELs) with tunnel-regenerated multi-active-region (TRMAR) structure. Dr. Muhammad Idrees Afridi at Beijing University of Posts and Telecommunications analyzed the impact of Rayleigh backscattering on single/dual feeder fiber wavelength-division multiplexing passive optical network (WDMPON) architectures. Overall, articles in this special issue cover the recent achievements of high-speed optical transmission and processing, particularly the latest emerging technologies and wide applications. We hope the readers will find them interesting and inspiring.

Recognition of Wavelength-Multiplexed Hierarchical Label with Acoustooptic Waveguide Circuit

High-speed optical processing for packet routing can overcome the bottleneck in large-capacity photonic networks. We have studied collinear acoustooptic (AO) switches and applications to optical label recognition. Since the parallel combination of collinear AO switches can handle wavelength-division-multiplexed (WDM) optical pulses, the recognition of optical labels encoded in spectral and time domains can be realized. In this report, we discuss the recognition of layer-structure labels for hierarchical routing control. By employing WDM time-series labels including identifying bits, labels corresponding to each layer can be recognized. The recognition characteristics are confirmed by computer simulation.

All-optical high-speed signal processing with silicon–organic hybrid slot waveguides

Integrated optical circuits based on silicon-on-insulator technology are likely to become the mainstay of the photonics industry. Over recent years an impressive range of silicon-on-insulator devices has been realized, including waveguides1,2, filters3,4 and photonic-crystal devices5. However, silicon-based all-optical switching is still challenging owing to the slow dynamics of two-photon generated free carriers. Here we show that silicon–organic hybrid integration overcomes such intrinsic limitations by combining the best of two worlds, using mature CMOS processing to fabricate the waveguide, and molecular beam deposition to cover it with organic molecules that efficiently mediate all-optical interaction without introducing significant absorption. We fabricate a 4-mm-long silicon–organic hybrid waveguide with a record nonlinearity coefficient of γ ≈ 1 × 105 W−1 km−1 and perform all-optical demultiplexing of 170.8 Gb s−1 to 42.7 Gb s−1. This is—to the best of our knowledge—the fastest silicon photonic optical signal processing demonstrated. A silicon–organic hybrid slot waveguide with a strong optical nonlinearity is demonstrated to perform ultrafast all-optical demultiplexing of high-bit-rate data streams. The approach could form the basis of compact high-speed optical processing units for future communication networks.

Recognition of Wavelength-multiplexed Labels with Acoustooptic Waveguide Circuit for Hierarchical Photonic Routing

High-speed optical processing for packet routing can overcome bottleneck in large- capacity photonic networks. We have studied on collinear acousto-optic (AO) switches and applications to optical label recognition. Since parallel combination of collinear AO switches can handle wavelength-division-multiplexed (WDM) optical pulses, recognition for optical labels encoded in spectral and time domains can be realized. In this report, we discuss recognition of layer-structure labels for hierarchical routing control. By employing WDM time-series labels in- cluding identifying bits, the labels corresponding to each layer can be recognized. The recognition characteristics are conflrmed by computer simulation.

Geospatial Remote Sensing Using Advanced Sensor Systems

ABSTRACTRecently, various nanoscale materials, devices, and systems with remarkable properties have been developed, with numerous unique applications in chem.-bio sensors, nanophotonics, and nanobiotechnology. This presentation covers satellite and aerial remote sensing science and methodologies employing nanotechnology based advanced sensor systems to improve performance, resolutions, and security. Increased demand on monitoring, surveillance due to global war on terrorism, weather prediction, and environmental pollution detection and monitoring have necessitated geospatial sensing with high accuracy, speed, and authenticity. Plasmonic interactions on the nanoscale and nanophotonics have produced new phenomena and technologies surpassing the realms of possibilities with conventional photonics and electronics. These new technologies could include high spatial resolution near-field imaging, high efficiency information processing and transferring, high capacity optical data storage, flexible- and high contrast displays, and precise detection, control and manipulation of nanoscale devices and integrated systems. Elements utilizing refractive or diffractive surfaces have found applications in novel sub-wavelength nanostructures satellites. The nanophotonics structures coupled with lightweight structures and advanced nanotechnology based sensors have resulted in launching of nano-satellites by several countries. The use of nanophotonics in space through the combination of micro, nano, integrated and fibre-optic technologies is to reduce susceptibility of the system to EMI, reduction in the weight of the signal cables (< 1/20 of electrical), higher information transmission capacity (GHz), reduced weight and volume, opto-isolation of critical spacecraft subsystems, high speed optical processing of RF and microwave signals, low propagation loss, and enhanced security encryption capabilities. Carbon Nanotubes (CNTs) based field emission electron gun (FEG) employ low voltage for emission and are actively researched as cold cathode microwave generation devices. CNTs based composites provide light-weight and compact platform with mechanical and thermal robustness. Such satellite system can be placed in low Earth orbit (LEO) to medium Earth orbit (MEO) as multi-sensor satellite imagers with panchromatic, multi-spectral, area and hyper spectral sensors on a single focal plane array (FPA), to achieve medium to high resolution (2.5m to 15m) spatial sampling, wide swaths (up to 45km) and noise equivalent reflectance (NER) values of less than 0.5%. An evaluation of security risks, vulnerability, and strategies is presented for communications technologies used in gathering, processing, storing, and disseminating global environmental micro and nano sensors and satellite data.

Toward Applications of Slow Light Technology

Scientists working for the Defense Advanced Research Projects Agency (DARPA) are making progress toward the development of robust, integrated devices that can slow, store and process light pulses. Their research will have a far-reaching impact on high-speed optical processing, telecommunications networks and quantum information science.

A fast low-power optical memory based on coupled micro-ring lasers

The increasing speed of fibre-optic-based telecommunications has focused attention on high-speed optical processing of digital information. Complex optical processing requires a high-density, high-speed, low-power optical memory that can be integrated with planar semiconductor technology for buffering of decisions and telecommunication data. Recently, ring lasers with extremely small size and low operating power have been made, and we demonstrate here a memory element constructed by interconnecting these microscopic lasers. Our device occupies an area of 18 x 40 microm2 on an InP/InGaAsP photonic integrated circuit, and switches within 20 ps with 5.5 fJ optical switching energy. Simulations show that the element has the potential for much smaller dimensions and switching times. Large numbers of such memory elements can be densely integrated and interconnected on a photonic integrated circuit: fast digital optical information processing systems employing large-scale integration should now be viable.

Semiconductor optical amplifier-based all-optical gates for high-speed optical processing

Semiconductor optical amplifiers are useful building blocks for all-optical gates as wavelength converters and OTDM demultiplexers. The paper reviews the progress from simple gates using cross-gain modulation and four-wave mixing to the integrated interferometric gates using cross-phase modulation. These gates are very efficient for high-speed signal processing and open up interesting new areas, such as all-optical regeneration and high-speed all-optical logic functions.