General coupled-mode analysis of a geometrically symmetric waveguide array with nonuniform gain and loss

The exceptional point(EP)is one of the typical properties of parity–time-symmetric systems,arising from modes coupling with identical resonant frequencies or propagation constants in optics.Here we show that in addition to two different modes coupling,a nonuniform distribution of gain and loss leads to an offset from the original propagation constants,including both real and imaginary parts,resulting in the absence of EP.These behaviors are examined by the general coupled-mode theory from the first principle of the Maxwell equations,which yields results that are more accurate than those from the classical coupled-mode theory.Numerical verification via the finite element method is provided.In the end,we present an approach to achieve lossless propagation in a geometrically symmetric waveguide array.

A saccharides sensor developed by symmetrical optical waveguide-based surface plasmon resonance

We proposed a new saccharides sensor developed by symmetrical optical waveguide(SOW)-based surface plasmon resonance(SPR).This unique MgF_(2)/Au/MgF_(2)/Analyte film structure results in longer suface plasmon wave(SPW)propagation lengths and depths,leading to an increment of resolution.In this paper,we managed to decorate the dielectric interface(MgF_(2) layer)by depositing a thin polydopamine film as surface adherent that provides a platform for secondary reactions with the probe molecule.3-Aminophenylboronic acid(3-PBA)is chosen to be the saccharides sense probe molecule in the present work.The aqueous huumnor of Diabetes and Cataract patient whose blood glucose level is normal are analyzed and the results dermonstrated that this sensor shows great potential in monitoring the blood siugar and can be adapted in the field of biological monitoring in the future.

Investigation of the limit of lateral beam shifts on a symmetrical metal-cladding waveguide

This paper reports that Goos-Hǎnchen （GH） shifts occurring on a symmetrical metal-cladding waveguide are experimentally identified. It was found that there exists a critical thickness of the upper metal layer, hcr, above which negative shift is observed and, reversely, positive shift occurs. Both positive and negative GH shifts near the critical thickness do not vary dramatically and can achieve a maximum on the submillimeter scale, which is different from simulated results using the stationary-phase method. It also shows that this critical thickness, hcr, can be obtained at the position for zero reflectivity by setting the intrinsic damping to be the same as the radiative damping. The GH effects observed near the critical thickness are produced by extreme distortion of the reflected beam profiles, which limits the amplitude of the GH shift and, further, the sensitivity of the GH optical sensor based on the symmetrical metal-cladding waveguide.

All-optical modulator based on a ferrofluid core metal cladding waveguide chip

We propose a novel optical intensity modulator based on the combination of a symmetrical metal cladding optical waveguide （SMCW） and ferrofluid, where the ferrofluid is sealed in the waveguide to act as a guiding layer. The light matter interaction in the ferrofluid film leads to the formation of a regular nanoparticle pattern, which changes the phase match condition of the ultrahigh order modes in return. When two lasers are incident on the same spot of the waveguide chip, experiments illustrate all-optical modulation of one laser beam by adjusting the intensity of the other laser. A possible theoretical explanation may be due to the optical trapping and Soret effect since the phenomenon is considerable only when the control laser is effectively coupled into the waveguide.

Engineering optical gradient force from coupled surface plasmon polariton modes in nanoscale plasmonic waveguides

We explore the dispersion properties and optical gradient forces from mutual coupling of surface plasmon polariton（SPP） modes at two interfaces of nanoscale plasmonic waveguides with hyperbolic metamaterial cladding.With Maxwell＇s equations and Maxwell stress tensor,we calculate and compare the dispersion relation and optical gradient force for symmetric and antisymmetric SPP modes in two kinds of nanoscale plasmonic waveguides.The numerical results show that the optical gradient force between two coupled hyperbolic metamaterial waveguides can be engineered flexibly by adjusting the waveguide structure parameters.Importantly,an alternative way to boost the optical gradient force is provided through engineering the hyperbolic metamaterial cladding of suitable orientation.These special optical properties will open the door for potential optomechanical applications,such as optical tweezers and actuators.

Polymer-coated symmetrical metal-cladding waveguide for chemical vapor detection with high sensitivity

An optical platform for sensitive detection of chemical vapor based on a polymer-coated symmetrical metal-cladding waveguide is proposed.The diffusion of chemical vapor usually leads to a combinational effect in the polymer layer,i.e.,swelling and refractive index change.Owing to the high sensitivity of ultrahigh-order modes,the vapor-induced effect will give rise to a dramatic variation of the reflected light intensity.For proof-of-concept,a good linearity and a low detection limit of toluene and benzene are experimentally demonstrated with an amorphous Teflon AF polymer layer.

Proposal of an InP-based few-mode transmitter based on multimode interference couplers for wavelength division multiplexing and mode division multiplexing applications

An In P-based monolithically integrated few-mode transmitter aiming at the combination of wavelength division multiplexing（WDM） and mode division multiplexing（MDM） technologies is proposed. The core elements of the proposed transmitter are mode converters and a wavelength-mode division multiplexer that are all based on multimode interference（MMI） couplers. Simulations show that the wavelength-mode division multiplexer has a large fabrication tolerance of 30 and 0.5 μm for the length and the width of the device, respectively.A low loss below 0.26 dB for the passive parts of the transmitter is obtained in the whole C-band wavelength range.