1,544 research outputs found
Chromatic dispersion monitoring for high-speed WDM systems using two-photon absorption in a semiconductor microcavity
This paper presents a theoretical and experimental investigation into the use of a two-photon absorption (TPA) photodetector for use in chromatic dispersion (CD) monitoring in high-speed, WDM network. In order to overcome the inefficiency associated with the nonlinear optical-to-electrical TPA process, a microcavity structure is employed. An interesting feature of such a solution is the fact that the microcavity enhances only a narrow wavelength range determined by device design and angle at which the signal enters the device. Thus, a single device can be used to monitor a number of different wavelength channels without the need for additional external filters. When using a nonlinear photodetector, the photocurrent generated for Gaussian pulses is inversely related to the pulsewidth. However, when using a microcavity structure, the cavity bandwidth also needs to be considered, as does the shape of the optical pulses incident on the device. Simulation results are presented for a variety of cavity bandwidths, pulse shapes and durations, and spacing between adjacent wavelength channels. These results are verified experimental using a microcavity with a bandwidth of 260 GHz (2.1 nm) at normal incident angle, with the incident signal comprising of two wavelength channels separated by 1.25 THz (10 nm), each operating at an aggregate data rate of 160 Gb/s. The results demonstrate the applicability of the presented technique to monitor accumulated dispersion fluctuations in a range of 3 ps/nm for 160 Gb/s RZ data channel
MadQCI: a heterogeneous and scalable SDN QKD network deployed in production facilities
Current quantum key distribution (QKD) networks focus almost exclusively on
transporting secret keys with the highest possible rate. Consequently, they are
built as mostly fixed, ad hoc, logically, and physically isolated
infrastructures designed to avoid any penalty to the quantum channel. This
architecture is neither scalable nor cost-effective and future, real-world
deployments will differ considerably. The structure of the MadQCI QKD network
presented here is based on disaggregated components and modern paradigms
especially designed for flexibility, upgradability, and facilitating the
integration of QKD in the security and telecommunications-networks ecosystem.
These underlying ideas have been tested by deploying many QKD systems from
several manufacturers in a real-world, multi-tenant telecommunications network,
installed in production facilities and sharing the infrastructure with
commercial traffic. Different technologies have been used in different links to
address the variety of situations and needs that arise in real networks,
exploring a wide range of possibilities. Finally, a set of realistic use cases
have been implemented to demonstrate the validity and performance of the
network. The testing took place during a period close to three years, where
most of the nodes were continuously active
Dynamical visualization of anisotropic electromagnetic re-emissions from a single metal micro-helix at THz frequencies
微小金属らせんとテラヘルツ光との相互作用を可視化 --次世代超高速移動通信などにおける高性能アンテナへ応用--. 京都大学プレスリリース. 2021-02-09.The capability for actual measurements—not just simulations—of the dynamical behavior of THz electromagnetic waves, including interactions with prevalent 3D objects, has become increasingly important not only for developments of various THz devices, but also for reliable evaluation of electromagnetic compatibility. We have obtained real-time visualizations of the spatial evolution of THz electromagnetic waves interacting with a single metal micro-helix. After the micro-helix is stimulated by a broadband pico-second pulse of THz electromagnetic waves, two types of anisotropic re-emissions can occur following overall inductive current oscillations in the micro-helix. They propagate in orthogonally crossed directions with different THz frequency spectra. This unique radiative feature can be very useful for the development of a smart antenna with broadband multiplexing/demultiplexing ability and directional adaptivity. In this way, we have demonstrated that our advanced measurement techniques can lead to the development of novel functional THz devices
Supersymmetric mode converters
Originally developed in the context of quantum field theory, the concept of
supersymmetry (SUSY) can be used to systematically design a new class of
optical structures. In this work, we demonstrate how key features arising from
optical supersymmetry can be exploited to control the flow of light for mode
division multiplexing applications. Superpartner configurations are
experimentally realized in coupled optical networks, and the corresponding
light dynamics in such systems are directly observed. We show that SUSY can be
judiciously utilized to remove the fundamental mode of a multimode optical
structure, while establishing global phase matching conditions for the
remaining set of modes. Along these lines, supersymmetry may serve as a
promising platform for a new generation of versatile optical components with
novel properties and functionalities.Comment: 14 pages, 4 figure
Automated routing and control of silicon photonic switch fabrics
Automatic reconfiguration and feedback controlled routing is demonstrated in an 8×8 silicon photonic switch fabric based on Mach-Zehnder interferometers. The use of non-invasive Contactless Integrated Photonic Probes (CLIPPs) enables real-time monitoring of the state of each switching element individually. Local monitoring provides direct information on the routing path, allowing an easy sequential tuning and feedback controlled stabilization of the individual switching elements, thus making the switch fabric robust against thermal crosstalk, even in the absence of a cooling system for the silicon chip. Up to 24 CLIPPs are interrogated by a multichannel integrated ASIC wire-bonded to the photonic chip. Optical routing is demonstrated on simultaneous WDM input signals that are labelled directly on-chip by suitable pilot tones without affecting the quality of the signals. Neither preliminary circuit calibration nor lookup tables are required, being the proposed control scheme inherently insensible to channels power fluctuations
Fluorinated and Non-Fluorinated Electro-Optic Copolymers: Determination of the Time and Temperature Stability of the Induced Electro-Optic Coefficient
Organic fluorinated materials demonstrate their excellent electro-optic properties and versatility for technological applications. The partial substitution of hydrogen with fluorine in carbon-halides bounds allows the reduction of absorption losses at the telecommunication wavelengths. In these interesting compounds, the electro-optic coefficient was typically induced by a poling procedure. The magnitude and the time stability of the coefficient is an important issue to be investigated in order to compare copolymer species. Here, a review of different measurement techniques (such as nonlinear ellipsometry, second harmonic generation, temperature scanning and isothermal relaxation) was shown and applied to a variety of fluorinated and non-fluorinated electro-optic compounds
Synchronization of spatiotemporal semiconductor lasers and its application in color image encryption
Optical chaos is a topic of current research characterized by
high-dimensional nonlinearity which is attributed to the delay-induced
dynamics, high bandwidth and easy modular implementation of optical feedback.
In light of these facts, which adds enough confusion and diffusion properties
for secure communications, we explore the synchronization phenomena in
spatiotemporal semiconductor laser systems. The novel system is used in a
two-phase colored image encryption process. The high-dimensional chaotic
attractor generated by the system produces a completely randomized chaotic time
series, which is ideal in the secure encoding of messages. The scheme thus
illustrated is a two-phase encryption method, which provides sufficiently high
confusion and diffusion properties of chaotic cryptosystem employed with unique
data sets of processed chaotic sequences. In this novel method of cryptography,
the chaotic phase masks are represented as images using the chaotic sequences
as the elements of the image. The scheme drastically permutes the positions of
the picture elements. The next additional layer of security further alters the
statistical information of the original image to a great extent along the
three-color planes. The intermediate results during encryption demonstrate the
infeasibility for an unauthorized user to decipher the cipher image. Exhaustive
statistical tests conducted validate that the scheme is robust against noise
and resistant to common attacks due to the double shield of encryption and the
infinite dimensionality of the relevant system of partial differential
equations.Comment: 20 pages, 11 figures; Article in press, Optics Communications (2011
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