Symmetrical Optical Waveguide Research Articles

Optofluidic passive parity-time-symmetric systems.

This research introduces a novel methodology of harnessing liquids to facilitate the realization of parity-time (PT)-symmetric optical waveguides on highly integrated microscale platforms. Additionally, we propose a realistic and detailed fabrication process flow, demonstrating the practical feasibility of fabricating our optofluidic system, thereby bridging the gap between theoretical design and actual implementation. Extensive research has been conducted over the past two decades on PT-symmetric systems across various fields, given their potential to foster a new generation of compact, power-efficient sensors and signal processors with enhanced performance. Passive PT-symmetry in optics can be achieved by evanescently coupling two optical waveguides and incorporating an optically lossy material into one of the waveguides. The essential coupling distance between two optical waveguides in air is usually less than 500 nm for near-infrared wavelengths and under 100 nm for ultraviolet wavelengths. This necessitates the construction of the coupling region via expensive and time-consuming electron beam lithography, posing a significant manufacturing challenge for the mass production of PT-symmetric optical systems. We propose a solution to this fabrication challenge by introducing liquids capable of dynamic flow between optical waveguides. This technique allows the attainment of evanescent wave coupling with coupling gap dimensions compatible with standard photolithography processes. Consequently, this paves the way for the cost-effective, rapid and large-scale production of PT-symmetric optofluidic systems, applicable across a wide range of fields.

Singular optical propagation properties of two types of one-dimensional anti- PT -symmetric periodic ring optical waveguide networks

Two types of one-dimensional (1D) anti- PT -symmetric periodic ring optical waveguide networks, consisting of gain and loss materials, are constructed. The singular optical propagation properties of these networks are investigated. The results show that the system composed of gain materials exhibits characteristics of ultra-strong transmission and bidirectional reflection. Conversely, the system composed of loss materials demonstrates equal transmittance and reflectance at some frequencies. In both the systems, a new type of total reflection phenomenon is observed. When the imaginary part of the refractive indices of waveguide segments is smaller than 10−5, the system shows bidirectional transparency with the transmittance tending to be 1 and reflectivity to be smaller than 10−8 at some bands. When the refractive indices of the waveguide segments are real, the system will be bidirectional transparent at the full band. These findings may deepen the understanding of anti- PT -symmetric optical systems and optical waveguide networks, and possess potential applications in efficient optical energy storage, ultra-sensitive optical filters, ultra-sensitive all-optical switches, integrated optical chips, stealth physics, and so on.

Ultimate efficiency of the quasi-perfect CPA laser constructed of a one-dimensional finite periodic parity-time-symmetric optical waveguide network

In this paper, the ultimate efficiency of the coherent perfect absorber and laser (CPA laser) generated by a one-dimensional (1D) two-connect two-material finite periodic parity-time (PT) symmetric optical waveguide network is studied. It is found that producing a perfect CPA laser four conditions need to be satisfied, but unfortunately they cannot be filled simultaneously, and consequently, a perfect CPA laser is impossible to be achieved. Nevertheless, for a optical waveguide network with given material and unit cell structure, the quasi-perfect CPA laser that generates ultimate efficiency can be designed by means of high-order infinitesimal constraint conditions. The maximal transmissivity and minimal overall output coefficient produced by our designed quasi-perfect CPA laser reach 3.81×1015 and 1.19×10−14, respectively, which are, respectively, 9 orders of magnitude larger and 7 orders of magnitude smaller than the corresponding best reported results. It may possess potential applications in integrated optics, high power lasers, optical signal pulse recovery, highly sensitive optical coherent filters and linear optical switches, etc.

Frozen mode regime in an optical waveguide with a distributed Bragg reflector

We introduce a glide symmetric optical waveguide exhibiting a stationary inflection point (SIP) in the Bloch wavenumber dispersion relation. An SIP is a third-order exceptional point of degeneracy (EPD) where three Bloch eigenmodes coalesce to form a so-called frozen mode with vanishing group velocity and diverging amplitude. We show that the incorporation of chirped distributed Bragg reflectors and distributed coupling between waveguides in the periodic structure facilitates the SIP formation and greatly enhances the characteristics of the frozen mode regime. We confirm the existence of an SIP in two ways: by observing the flatness of the dispersion diagram and also by using a coalescence parameter describing the separation of the three eigenvectors collapsing on each other. We find that, in the absence of losses, both the quality factor and the group delay at the SIP grow with the cubic power of the cavity length. The frozen mode regime can be very attractive for light amplification and lasing in optical delay lines, sensors, and modulators.

Simulation of switchers for CNOT-gates based on optical waveguide interaction with coupled mode theory

The paper is devoted to simulation of interactions in the system of two symmetrical slab optical waveguides, that guide exactly two guided modes with the aim to use the directional coupler as a switcher for CNOT gate in the waveguide model of quantum-like computations. The coupling mode theory is used to solve the system of Maxwell equations. The asymptotic analysis is applied to simplify the system of differential equations, so an approximate analytic solution can be found. The solution obtained is used for the quick directional coupler parameters adjusting algorithm, so the power exchange in the system occurs as that of correctly working CNOT-gate switcher. Moreover, the finite difference method is used to solve the stricter system of equations, that additionally takes into account the process of power exchange between different order guided modes, so the computational error of the device can be estimated. It was obtained, that the possible size of the device may not exceed 1 mm in the largest dimension, while the computational error does not exceed 3%.

Tunable thermal diffusion and heat accumulation in transparent materials based on varying the scanning speed of a femtosecond laser

Based on heat accumulation effects, symmetric optical waveguides in glass can be obtained via femtosecond laser irradiation. Such modification inside glass is interesting in terms of developing integrated mini-optical devices with 3-D structures and micro channels for biosensors. This work experimentally investigated the formation of micro-channels inside porous glass irradiated with an 800 nm, 100 fs, and 250 kHz femtosecond laser with scanning speeds ranging from 250 μm/s to 1000 μm/s at a fixed power of 300 mW. Strong heat accumulation effects were thus observed at laser scanning at 250μm/s, which offered significant variations in structure morphology.

Extraordinary characteristics of one-dimensional PT-symmetric ring optical waveguide networks with near-isometric and isometric arms

We construct one-dimensional -symmetric ring optical waveguide networks with near-isometric and isometric arms and investigate their extraordinary optical properties. It is found that the features for the former and the latter are quite different, although extraordinary ultrastrong transmission and reflection exist in both of them. When the former changes to be the latter, the extraordinary optical properties will all change remarkably, and the fitting formulae are obtained. The bidirectional invisibility only exists in the former and the principle is analyzed. This work may be helpful for designing ultra-narrow optical filters, ultra-sensitive optical switches, and resonant component for high-monochromatic lasing.

Extraordinary transmission and reflection in -symmetric two-segment-connected triangular optical waveguide networks with perfect and broken integer waveguide length ratios**Project supported by the National Natural Science Foundation of China (Grant Nos. 11674107, 61475049, 11775083, 61875057, 61774062, and 61771205) and Special Funds for the Cultivation of Guangdong College Students’ Scientific and Techonlogical Innovation, China (Grant No. pdjhb0139).

By adjusting the waveguide length ratio, we study the extraordinary characteristics of electromagnetic waves propagating in one-dimensional (1D) parity-time-symmetric (-symmetric) two-segment-connected triangular optical waveguide networks with perfect and broken integer waveguide length ratios respectively. It is found that the number and the corresponding frequencies of the extremum spontaneous -symmetric breaking points are dependent on the waveguide length ratio. Near the extremum breaking points, ultrastrong extraordinary transmissions are created and the maximal can arrive at, respectively, and in both kinds of networks. However, bidirectional invisibility can only be produced by the networks with broken integer waveguide length ratio, whose mechanism is explained in detail from the perspective of photonic band structure. The findings of this work can be useful optical characteristic control in the fabrication of -symmetric optical waveguide networks, which possesses great potential in designing optical amplifiers, optical energy saver devices, and special optical filters.

Light Stops at Exceptional Points.

Almost twenty years ago, light was slowed down to less than 10^{-7} of its vacuum speed in a cloud of ultracold atoms of sodium. Upon a sudden turn-off of the coupling laser, a slow light pulse can be imprinted on cold atoms such that it can be read out and converted into a photon again. In this process, the light is stopped by absorbing it and storing its shape within the atomic ensemble. Alternatively, the light can be stopped at the band edge in photonic-crystal waveguides, where the group speed vanishes. Here, we extend the phenomenon of stopped light to the new field of parity-time (PT) symmetric systems. We show that zero group speed in PT symmetric optical waveguides can be achieved if the system is prepared at an exceptional point, where two optical modes coalesce. This effect can be tuned for optical pulses in a wide range of frequencies and bandwidths, as we demonstrate in a system of coupled waveguides with gain and loss.

Phase transition in multimode nonlinear parity-time-symmetric waveguide couplers.

Parity-time-symmetric (-symmetric) optical waveguide couplers offer new possibilities for fast, ultracompact, configurable, all-optical signal processing. Here, we study nonlinear properties of finite-size multimode -symmetric couplers and predict the nonlinear oscillatory dynamics that can be controlled by three parameters: input light intensity, gain and loss amplitude, and input beam profile. Moreover, we show that this dynamics is driven by a transition triggered by nonlinearity in these structures, and we demonstrate that with the increase of the number of dimers in the system, the transition threshold decreases and converges to the value corresponding to an infinite array. Finally, we present a variety of periodic intensity patterns that can be formed in these couplers depending on the initial excitation.

Flexible photonic components in glass substrates.

This paper demonstrates the fabrication and measurements of flexible photonic lightwave circuits in glass substrates. Using temporally and spatially shaped ultrafast laser pulses, highly symmetrical and low-loss optical waveguides were written in flexible glass substrates with thicknesses ranging from 25 µm to 100 µm. The waveguide propagation loss, measured by optical frequency domain reflectometry, was 0.11 dB/cm at 1550 nm telecommunication wavelength. The bend loss of the waveguide is negligible at a radius of curvature of 1.5 cm or greater. Additionally, the waveguides are thermally stable up to 400°C. This paper presents alternatives to fabricating flexible photonics in traditionally used polymeric materials.

Nonlinear parity-time symmetric closed-form optical quadrimer waveguides: attractor perspective

We report a study on a closed-form nonlinear parity-time symmetric optical quadrimer waveguides system with a specific coupling scheme. The system yields power saturation behavior in the modes, which may be attributed to the inherent attractor in the system. A detailed analysis has been provided to confirm the attractor aspect of the system. This work also addresses a crucial issue regarding choice of initial conditions while carrying out numerical simulation for such systems.

Study on Trace Sample of Chronic Skin Ulcer with a Symmetrical Optical Waveguide-Based Surface Plasmon Resonance Biosensor

A prototype of symmetrical optical waveguide (SOW)-based surface plasmon resonance (SPR) sensing system is developed. Based on a polydopamine and matrix metalloproteinase-9 (MMP-9) antibody sensing protocol, trace samples of secretions from the chronic skin ulcer are detected with the SPR sensing system, and the detection results are compared with conventional enzyme-linked immunosorbent assay (ELISA) results, showing the clinical utility of the SPR detector. Considering the capability of trace sample and high-throughput detections, the SOW-based SPR sensing system has great potential in other clinical applications.

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 surface 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 humor of Diabetes and Cataract patient whose blood glucose level is normal are analyzed and the results demonstrated that this sensor shows great potential in monitoring the blood sugar and can be adapted in the field of biological monitoring in the future.

Parity–time-symmetric closed form optical quadrimer waveguides

A closed form parity–time symmetric quadrimer optical waveguide structure, reminiscent of the four-state quantum system found in quantum optics, was studied. The beam dynamics of the structure were studied numerically. The effect of inclusion of nonlinearity and dispersion was also briefly investigated and is discussed.

Spin-orbit and tensor interactions of light in inhomogeneous isotropic media

Propagation of polarized vortex light beams in a rotationally symmetric graded-index optical waveguide is investigated by solving analytically the three-component field Maxwell's equations. An operator approach to calculate the average values describing the propagating beams is developed. Polarization-dependent transmission associated with spin-orbit interaction for left- and right-handed circularly polarized Gauss-Laguerre light beams is shown.

A symmetrical optical waveguide based surface plasmon resonance biosensing system

In this work, we propose a MgF2/Au/MgF2/Analyte based, angle-interrogation surface plasmon resonance sensor. This symmetrical structure results in higher surface electric field strengths, and longer surface propagation lengths and depths. A refractive index resolution of 8.1×10−8RIU in fluid protocol and 3.5×10−7RIU in atmosphere protocol is acquired by a simple SPR imaging system. In order to demonstrate the biomedical applications of this system, we detect Escherichia coli with different concentrations using dopamine film on the sensor surface to immobilize antibodies. A detection limit of 103cfu/mL of E. coli bacteria is acquired from this system.

Nonlinear Schrödinger equation for a -symmetric delta-function double well

The time-independent nonlinear Schrödinger equation is solved for two attractive delta-function-shaped potential wells where an imaginary loss term is added in one well, and a gain term of the same size but with opposite sign in the other. We show that for vanishing nonlinearity the model captures all the features known from studies of parity–time-(-) symmetric optical waveguides, e.g., the coalescence of modes at an exceptional point at a critical value of the loss/gain parameter, and the breaking of symmetry beyond. With the nonlinearity present, the equation is a model for a Bose–Einstein condensate with loss and gain in a double-well potential. We find that the nonlinear Hamiltonian picks as stationary eigenstates exactly such solutions which render the nonlinear Hamiltonian itself symmetric, but observe coalescence and bifurcation scenarios different from those known from linear -symmetric Hamiltonians.This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘Quantum physics with non-Hermitian operators’.

A Temperature Sensor Based on a Symmetrical Metal-Cladding Optical Waveguide

A compact temperature sensor based on a symmetrical metal-cladding optical waveguide using free-space coupling is proposed and demonstrated theoretically and experimentally. The symmetrical Au-cladding optical waveguide is based on a thin LiNbO3 slab sandwiched between two metal films, which serve as the coupling layer and reflecting panel, respectively. The sensitivity of this sensor of 9.08 × 10−2 deg/°C, 6.6 × 10−2 deg/°C and 4.8 × 10−2 deg/°C corresponding to 3238-order, 3237-order and 3236-order modes, respectively, are obtained. Higher resolution is predicted with a larger linear expansion coefficient material and a higher resolution θ/2θ goniometer.

Investigation of Properties of Symmetrical Al-Cladding Optical Waveguides Modulated by the Voltage

The symmetrical Al-cladding optical waveguide is fabricated. The waveguide consists of LiNbO3 slab used as guiding wave layer. LiNbO3 slab is sandwiched between two aluminum films which are served as the coupling layer and reflecting panel respectively. The interesting properties of the waveguide modulated by the voltage have been investigated from theories and experiment by using free-space coupling method. The experimental results also show that the ultrahigh-order is very sensitive to the electric voltage applied on the two aluminum films. The interesting properties of the waveguide and the low price of fabrication may provide opportunities for new application of various optical devices.