257 research outputs found
Exceptional Points in a Non-Hermitian Topological Pump
We investigate the effects of non-Hermiticity on topological pumping, and
uncover a connection between a topological edge invariant based on topological
pumping and the winding numbers of exceptional points. In Hermitian lattices,
it is known that the topologically nontrivial regime of the topological pump
only arises in the infinite-system limit. In finite non-Hermitian lattices,
however, topologically nontrivial behavior can also appear. We show that this
can be understood in terms of the effects of encircling a pair of exceptional
points during a pumping cycle. This phenomenon is observed experimentally, in a
non-Hermitian microwave network containing variable gain amplifiers.Comment: 7 pages, 7 figures. The first author did the experiment, and the
second author did the theoretical stud
Computing matrix inversion with optical networks
With this paper we bring about a discussion on the computing potential of
complex optical networks and provide experimental demonstration that an optical
fiber network can be used as an analog processor to calculate matrix inversion.
A 3x3 matrix is inverted as a proof-of-concept demonstration using a fiber
network containing three nodes and operating at telecomm wavelength. For an NxN
matrix, the overall solving time (including setting time of the matrix elements
and calculation time of inversion) scales as O(N^2), whereas matrix inversion
by most advanced computer algorithms requires ~O(N^2.37) computational time.
For well-conditioned matrices, the error of the inversion performed optically
is found to be less than 3%, limited by the accuracy of measurement equipment.Comment: 5 page
Pixelated-core Large Pitch Optical Fibre Design
AbstractThis paper is reporting design and simulation of a pixelated-core large pitch optical fibre. With this new design, existence of higher order modes, mode instability at high power levels, mode shrinking and gain reduction upon bending has been solved and the bending loss is negligible in the frequently used bending radius of 3cm to 5cm. Even down to 3mm bending radius, magnitude of bending loss can also be suppressed by three orders
Measurement of a topological edge invariant in a microwave network
We report on the measurement of topological invariants in an electromagnetic
topological insulator analog formed by a microwave network, consisting of the
winding numbers of scattering matrix eigenvalues. The experiment can be
regarded as a variant of a topological pump, with non-zero winding implying the
existence of topological edge states. In microwave networks, unlike most other
systems exhibiting topological insulator physics, the winding can be directly
observed. The effects of loss on the experimental results, and on the
topological edge states, is discussed.Comment: 10 pages, 10 figure
Photonic Crystal Fiber–Based Interferometric Sensors
Photonic crystal fibers (PCFs), also known as microstructured optical fibers, are a highlighted invention of optical fiber technology which have unveiled a new domain of manipulating light in engineered fiber waveguides with unparalleled flexibility and controllability. Since the report of the first fabricated PCF in 1996, research in PCFs has resulted in numerous explorations, development and commercialization of PCF-based technologies and applications. PCFs contain axially aligned air channels which provide a large degree of freedom in design to achieve a variety of peculiar properties; numerous PCF-based sensors have been proposed, developed and demonstrated for a broad range of sensing applications. In this chapter, we will review the field of research on design, development and experimental achievement of PCF-based interferometric sensors for physical and biomedical sensing applications
Optical Fibre Long-Period Grating Sensors Operating at and around the Phase Matching Turning Point
Optical fibres have been exploited as sensors for many years and they provide a versatile platform with a small form factor. Long-period gratings (LPGs) operating at and around the phase matching turning point (PMTP) possess some of the highest sensitivities to external perturbations in the family of LPG-based sensor devices. This type of optical fibre grating has been demonstrated as a sensor for use in a wide range of applications. In this review chapter, an overview of PMTP LPGs is presented and the key developments, findings and applications are highlighted. The fabrication considerations and sensor limitations are also discussed
Controllable group delay in a θ-shaped microfiber resonator with coupled-resonator-induced transparency
The control of Light velocity is theoretically and experimentally demonstrated in a θ-shaped microfiber resonator with coupled-resonator-induced transparency. By adjusting the structure parameters, group delays from -60ps to 200ps are achieved in the all-fiber resonator
Pump RIN-induced impairments in unrepeatered transmission systems using distributed Raman amplifier
High spectral efficiency modulation format based unrepeatered transmission systems using distributed Raman amplifier (DRA) have attracted much attention recently. To enhance the reach and optimize system performance, careful design of DRA is required based on the analysis of various types of impairments and their balance. In this paper, we study various pump RIN induced distortions on high spectral efficiency modulation formats. The vector theory of both 1st and higher-order stimulated Raman scattering (SRS) effect using Jones-matrix formalism is presented. The pump RIN will induce three types of distortion on high spectral efficiency signals: intensity noise stemming from SRS, phase noise stemming from cross phase modulation (XPM), and polarization crosstalk stemming from cross polarization modulation (XPolM). An analytical model for the statistical property of relative phase noise (RPN) in higher order DRA without dealing with complex vector theory is derived. The impact of pump RIN induced impairments are analyzed in polarization-multiplexed (PM)-QPSK and PM-16QAM-based unrepeatered systems simulations using 1st, 2nd and 3rd-order forward pumped Raman amplifier. It is shown that at realistic RIN levels, negligible impairments will be induced to PM-QPSK signals in 1st and 2nd order DRA, while non-negligible impairments will occur in 3rd order case. PM-16QAM signals suffer more penalties compared to PM-QPSK with the same on-off gain where both 2nd and 3rd order DRA will cause non-negligible performance degradations. We also investigate the performance of digital signal processing (DSP) algorithms to mitigate such impairments
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