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We numerically investigate the design of a wavelength de-multiplexer based on a tapered photonic crystal waveguide. The tapered waveguide is generated by reducing the width of the channel which, in turn, provides a gradual change in the effective index for the guided modes. Depending on the wavelength, the grading effect enables the propagating beam to be trapped at different spatial positions along the waveguide. Furthermore, alternation on the tapering angle, i.e. changing the slope of the tapered waveguide, will result in a spatial shifting of the trapping locations. Thus, the structure can be adjusted to pick up the frequencies of interest at the chosen positions. Numerical results show that, by placing vertical line defects as drop channels at specific locations, different wavelengths can be properly guided along the drop channels that are transverse to the main waveguide., ERICSON, ADVA OPT NETWORKING, SILICON LABS, BHE, MobiTel, ROHDE ; SCHWARZ, ICREAICREA Funding Source: Custom

Optical Parity-Time (PT-) symmetric systems support unusual properties. When the symmetric coupling between internal modes is broken the system becomes strongly unidirectional resulting in novel effects such as asymmetric reflections, invisibility or asymmetric mode coupling. Here, we propose a new class of nanophotonic PT-axisymmetric systems which lead to an extreme field enhancement and high localization at the P-symmetry center when the coupling of inward propagating waves is favored due to the asymmetric radial coupling. We expect the effect to have direct applications such as rendering broad aperture lasers into bright and narrow output beam sources., IEEE Photon Soc, ICREAICREA Funding Source: Custom

We propose a new approach of optical field management based on a local Hilbert transform, where the nonHermitian potentials generating arbitrary vector fields of directionality, (p) over right arrow((r) over right arrow), with desired shapes and topologies are designed. We derive a local Hilbert transform to build systematically such potentials, by modifying background potentials (being either regular or random, extended or localized). In particular, we explore particular directionality fields, for instance in the form of a focus to create sinks for probe fields, to generate vortices in the probe fields, and others. Physically, the proposed directionality fields provide a flexible new mechanism for dynamically shaping and precise control over probe fields leading to novel effects in wave dynamics., IEEE Photon Soc, IEEE, Univ Politehnica Bucharest, APEX Technologies, Photonics, OptoSigma, neaspec, Schaefer, Inst Lacznosci Panstwowy Inst Badawczy, NATO SPS Research grant [SPS 985048]; Spanish Ministerio de Ciencia e InnovacionInstituto de Salud Carlos IIISpanish Government; European Union FEDEREuropean Commission [FIS2015-65998-C2-1-P]; AMRDEC [W911NF-16-2-0069], We acknowledge financial support from NATO SPS Research grant (SPS 985048), from Spanish Ministerio de Ciencia e Innovacion, and European Union FEDER through project FIS2015-65998-C2-1-P, and from AMRDEC via project W911NF-16-2-0069.

Since the advent of transformation optics a decade ago [1], the ability to achieve optical cloaking has become a matter of practical realization. However, so far extreme material requirements and large device areas have significantly posed an obstacle to realize compact cloaking schemes that are fully functional. Here, by taking a different approach and by following our recently developed general theorem to control the scattering behaviour of an arbitrary object on a specific demand [2], we show that nearly perfect bidirectional optical cloaking effect can be generated for any type of object with a given shape and size. Contrary to previous approaches, we reveal that such a method is always able to produce local refractive indices larger than one and that neither gain nor lossy materials are required. Furthermore, by means of numerical calculations, we demonstrate a highly tunable broad operational bandwidth of 550 nm (covering 650-1200 nm interval) and an angular aperture of 36 degrees for both directions and polarizations. With these unprecedented features, we expect that the present work will hold a great potential to enable a new class of optical cloaking structures that will find applications particularly in communication systems, defence industry and in other related fields., Authors acknowledge financial support of NATO SPS research grant No: 985048. H.K. also acknowledges partial support of the Turkish Academy of Science., IEEE, IEEE Photon Soc, FYLA, OptoSigma, LIGHT TEC, Ajuntament Girona, AE Tech, NATO SPSNATO (North Atlantic Treaty Organisation) [985048]; Turkish Academy of ScienceTurkish Academy of Sciences

[No abstract available], European Phys Soc, Quantum Elect ; Opt Div, IEEE Photon Soc, Opt Soc, World Photon Congress, EPS Young Minds

Optical Parity-Time (PT-) symmetric systems support unusual properties. When the symmetric coupling between internal modes is broken the system becomes strongly unidirectional resulting in novel effects such as asymmetric reflections, invisibility or asymmetric mode coupling. Here, we propose a new class of nanophotonic PT-axisymmetric systems which lead to an extreme field enhancement and high localization at the P-symmetry center when the coupling of inward propagating waves is favored due to the asymmetric radial coupling. We expect the effect to have direct applications such as rendering broad aperture lasers into bright and narrow output beam sources., IEEE Photon Soc, ICREAICREA Funding Source: Custom

We numerically investigate the design of a wavelength de-multiplexer based on a tapered photonic crystal waveguide. The tapered waveguide is generated by reducing the width of the channel which, in turn, provides a gradual change in the effective index for the guided modes. Depending on the wavelength, the grading effect enables the propagating beam to be trapped at different spatial positions along the waveguide. Furthermore, alternation on the tapering angle, i.e. changing the slope of the tapered waveguide, will result in a spatial shifting of the trapping locations. Thus, the structure can be adjusted to pick up the frequencies of interest at the chosen positions. Numerical results show that, by placing vertical line defects as drop channels at specific locations, different wavelengths can be properly guided along the drop channels that are transverse to the main waveguide., ERICSON, ADVA OPT NETWORKING, SILICON LABS, BHE, MobiTel, ROHDE ; SCHWARZ, ICREAICREA Funding Source: Custom

We propose a new approach of optical field management based on a local Hilbert transform, where the nonHermitian potentials generating arbitrary vector fields of directionality, (p) over right arrow((r) over right arrow), with desired shapes and topologies are designed. We derive a local Hilbert transform to build systematically such potentials, by modifying background potentials (being either regular or random, extended or localized). In particular, we explore particular directionality fields, for instance in the form of a focus to create sinks for probe fields, to generate vortices in the probe fields, and others. Physically, the proposed directionality fields provide a flexible new mechanism for dynamically shaping and precise control over probe fields leading to novel effects in wave dynamics., IEEE Photon Soc, IEEE, Univ Politehnica Bucharest, APEX Technologies, Photonics, OptoSigma, neaspec, Schaefer, Inst Lacznosci Panstwowy Inst Badawczy, NATO SPS Research grant [SPS 985048]; Spanish Ministerio de Ciencia e InnovacionInstituto de Salud Carlos IIISpanish Government; European Union FEDEREuropean Commission [FIS2015-65998-C2-1-P]; AMRDEC [W911NF-16-2-0069], We acknowledge financial support from NATO SPS Research grant (SPS 985048), from Spanish Ministerio de Ciencia e Innovacion, and European Union FEDER through project FIS2015-65998-C2-1-P, and from AMRDEC via project W911NF-16-2-0069.

[No abstract available], European Phys Soc, Quantum Elect ; Opt Div, IEEE Photon Soc, Opt Soc, World Photon Congress, EPS Young Minds

With the development of various recent tools to control electromagnetic wave propagation, such as transformation optics, the long-sought dream of rendering objects invisible has become a matter of practical implementation. However, the required index profile derived with such techniques leads to material properties that are not readily available in nature and, hence, various experimental simplifications and performance scarifications are inevitable. Therefore, it has been a widespread belief that perfect cloaking cannot be achieved with conventional materials. Here, we follow a different direction and provide a unique method based on scattering cancellation rather than conventional coordinate transformations, and show that perfect invisibility can be indeed achieved for any specified angular range and operational bandwidth by employing merely all-dielectric materials. The presented method is based on our recently proposed generalized Hilbert-like transform [1] that is able to eliminate the undesired scattered waves for any type of object, regardless of its shape/size, by directly tailoring the object's scattering potential. In this direction, we show that the impinging wave on an object can be perfectly restored owing to the effective cancellation of the scattered waves emanating from the object and the surrounding index profile. We demonstrate this effect by experimental analyses conducted at the gigahertz regime. The proposed method represents an important step towards the ultimate goal of cloaking arbitrarily large objects at various wavelength regimes and may have profound implications especially in non-invasive near-field probing applications, where conventional transformation optics based cloaks fail to provide the interaction of the wave with the object.

With the development of various recent tools to control electromagnetic wave propagation, such as transformation optics, the long-sought dream of rendering objects invisible has become a matter of practical implementation. However, the required index profile derived with such techniques leads to material properties that are not readily available in nature and, hence, various experimental simplifications and performance scarifications are inevitable. Therefore, it has been a widespread belief that perfect cloaking cannot be achieved with conventional materials. Here, we follow a different direction and provide a unique method based on scattering cancellation rather than conventional coordinate transformations, and show that perfect invisibility can be indeed achieved for any specified angular range and operational bandwidth by employing merely all-dielectric materials. The presented method is based on our recently proposed generalized Hilbert-like transform [1] that is able to eliminate the undesired scattered waves for any type of object, regardless of its shape/size, by directly tailoring the object's scattering potential. In this direction, we show that the impinging wave on an object can be perfectly restored owing to the effective cancellation of the scattered waves emanating from the object and the surrounding index profile. We demonstrate this effect by experimental analyses conducted at the gigahertz regime. The proposed method represents an important step towards the ultimate goal of cloaking arbitrarily large objects at various wavelength regimes and may have profound implications especially in non-invasive near-field probing applications, where conventional transformation optics based cloaks fail to provide the interaction of the wave with the object.

A general procedure to design objects that are intrinsically invisible (without the necessity of an external cloak) has not been demonstrated so far. Here we propose a flexible method to design such self-cloaked objects by uncoupling the scattered waves from the incident radiation via judiciously manipulating the scattering potential of the object. We show that such a procedure is able to yield optical invisibility for any arbitrarily shaped object within any specified frequency bandwidth by simply employing isotropic nonmagnetic dielectric materials, without the usage of loss or gain material. The validity of the design principle has been verified by direct experimental observations of the spatial electric field profiles and scattering patterns at the microwave regime. Our self-cloaking strategy may have profound implications especially in noninvasive probing, cloaked sensor applications, and scattering-free non-Hermitian optics based systems. © 2018 American Chemical Society., NATO SPS Research Grant [985048 ]; Spanish Ministerio de Ciencia e Innovacion; European Union FEDER Project [FIS2015-65998-C2-1-P]; Turkish Academy of Science

We propose an approach based on a local Hilbert transform to design non-Hermitian potentials generating arbitrary vector fields of directionality, p→(r→), with desired shapes and topologies. We derive a local Hilbert transform to systematically build such potentials by modifying background potentials (being either regular or random, extended or localized). We explore particular directionality fields, for instance in the form of a focus to create sinks for probe fields (which could help to increase absorption at the sink), or to generate vortices in the probe fields. Physically, the proposed directionality fields provide a flexible mechanism for dynamical shaping and precise control over probe fields leading to novel effects in wave dynamics.

We propose a new type of add-drop microring resonator made of gain and loss materials. Microring resonators are compact, narrow band, and optical channel dropping filters. In such linear systems, light transmission to side-coupled signal waveguides is always symmetric. However, we prove that properly arranging a gain and loss modulation in the microring resonator provides a new functionality: asymmetric transmission; so that different resonant modes can be promoted depending on the input channel. This can be achieved when the resonator holds parity-time (PT-) symmetry, with periodic gain-loss and index modulations. PT-symmetry in optics generally requires that the index and gain-loss modulations are dephased by a quarter of the wavenumber of the modulation. Besides, we show that a simple half-gain half-loss microring also produces analogous results to a periodic PT-symmetric system. The results are numerically proved and also accounted by a simple analytical model. The effect of using complex modulated resonators with smaller periodicities is also analyzed., The work of M. Botey, R. Herrero, and K. Staliunas was supported by the Spanish Ministerio de Educacion y Ciencia under Project FIS2011-29734-C02-01. The work of H. Kurt was supported in part by the Turkish Academy of Sciences.

We propose a new approach of optical field management based on a local Hilbert transform, where the non-Hermitian potentials generating arbitrary vector fields of directionality, p?(r?), with desired shapes and topologies are designed. We derive a local Hilbert transform to build systematically such potentials, by modifying background potentials (being either regular or random, extended or localized). In particular, we explore particular directionality fields, for instance in the form of a focus to create sinks for probe fields, to generate vortices in the probe fields, and others. Physically, the proposed directionality fields provide a flexible new mechanism for dynamically shaping and precise control over probe fields leading to novel effects in wave dynamics. © 2019 SPIE., AMRDEC [W911NF-16-2-0069]

We propose a feasible invisibility approach to suppress the scattering of waves from or to given directions and for particular frequencies, i.e., invisibility on demand. We derive a generalized Hilbert transform for a specific invisibility arrangement relating the two quadratures of the complex permittivity of an object. The scheme allows either designing objects to be invisible, or alternatively modifying the complex susceptibility of a given object to render invisibility. The theoretical proposal is further confirmed by finite-difference time-domain numerical calculations. Moreover, following an iterative chain of generalized Hilbert transforms, we propose the invisibility on demand with additional constraints, i.e., restricting the required modification of the complex refractive index within practical limits by avoiding gain areas. The proposed concept not only opens a venue of real or complex valued index landscapes, but also bridges the gap between Hermitian and non-Hermitian optical systems by unifying these systems under one single generalized design theory., Ministerio de Ciencia e Innovación[FIS2015-65998-C2-1-P] ; Türkiye Bilimler Akademisi[985048]

We propose and experimentally demonstrate a demultiplexer with point-defect resonators and a reflection feedback mechanism in a photonic crystal waveguide (PCW). A tapered PCW has been chosen as the necessary reflector, which enhances the drop efficiency. Due to the variation of the single-mode waveguide width of the tapered PCW, spatial alteration of the effective refractive index can be achieved. This phenomenon is used to reflect back the forward propagating wave which is then coupled again to the drop channels via the resonators. High transmission efficiency to the dropout channels is numerically predicted by calculations, either in two- and three-dimensional models, and analytically described by a coupled-mode theory. Moreover, an experimental realization in the microwave regime provides confirmation that the targeted wavelengths can be properly transmitted at the drop channels with low crosstalk and relatively high efficiencies. (C) 2015 Optical Society of America