Photonic Waveguide Structures Research Articles

Frequency Division Multiple Access with High Performance Based on Several Defect Resonators According to the Fibonacci Sequence in 1D Photonic Star Waveguide Structure

Frequency Division Multiple Access with High Performance Based on Several Defect Resonators According to the Fibonacci Sequence in 1D Photonic Star Waveguide Structure

Dispersion-free characterization of terahertz slab–waveguide modal confinement based on a metal Bragg grating structure

Photonic waveguide structures that use periodic metal grooves and periodically perforated metal slits (PPMSs) can laterally confine Sommerfeld and Zenneck surface waves of metals with the electric field accumulation among metal interspaces in the terahertz (THz) region, instead of the total internal reflection principle of dielectric slab media. For the efficiency enhancements of THz-wave coupling and slab–waveguide confinement, specific integrators with high refractive indices or specified for input angles of transverse magnetic polarized waves, such as prisms, metal blades, and waveguides, are requested to excite spoof surface plasmons in the THz region. However, the integrator-assembled slab–waveguides encounter challenges of THz pulse-wave communication in compact and low-distortion systems. A resonant waveguide grating structure based on PPMSs is experimentally demonstrated to confine THz lateral waves from the plane-wave radiation in free space. The open frame and periodic metal cavities of PPMSs can work as a slab–waveguide to transmit structural confined waveguide modes with forwarding evanescent waves of Fabry–Pérot resonance. For 0.1–1 THz waves, the short wavelengths that are both less than half the metal slit width and 3.75 times the metal thickness can lead to zero dispersion and the highest confinement factor in a slab–waveguide for PPMS-confined THz waves. This behavior is opposite to the high structural dispersion in confined THz waves of surface plasmonic devices.

Three-octave supercontinuum spanning with Z-cut lithium niobate photonic waveguide

We numerically demonstrate three-octave supercontinuum generation using the z-cut lithium niobate waveguide by dispersion engineering. The photonic waveguide structure is designed to exhibit anomalous dispersion when pumped at 1.55 μ m wavelength. By altering the waveguide width, tunable zero-dispersion wave generation has been achieved up to 6 μ m wavelength. Our findings show the broadest supercontinuum spanning in the mid-IR region using a lithium niobate platform, making it a promising candidate for various applications in optical communication, sensing, and imaging.

Iterative eigensolver using fixed-point photonic primitive.

Photonic computing has potential advantages in speed and energy consumption yet is subject to inaccuracy due to the limited equivalent bitwidth of the analog signal. In this Letter, we demonstrate a configurable, fixed-point coherent photonic iterative solver for numerical eigenvalue problems using shifted inverse iteration. The photonic primitive can accommodate arbitrarily sized sparse matrix-vector multiplication and is deployed to solve eigenmodes in a photonic waveguide structure. The photonic iterative eigensolver does not accumulate errors from each iteration, providing a path toward implementing scientific computing applications on photonic primitives.

Waveguide structures and photon splitters fabricated by direct (3 + 1)D laser writing

The problem of high-performance systems for the big data transmission and processing fabrication determines the importance of creating hybrid photonic integrated circuits with complex architecture. We studied of three-dimensional photonic waveguide structures created by direct (3 + 1)D laser writing, with the aim of adding such structures to photonic integrated circuits.

Photonic metamaterial planar optical waveguide structures with all Kerr-type nonlinear guiding films

Photonic metamaterial planar optical waveguide structures with all Kerr-type nonlinear guiding films

Frozen mode in coupled silicon ridge waveguides for optical true time delay applications

We propose a simple photonic waveguide structure that exhibits light propagation modes with vanishing group velocity via mode degeneracy. This enables stationary inflection point dispersion leading to the frozen mode and a true time delay device suitable for ultra-wide-band beamforming for millimeter wave (mmWave) phased arrays. The structure consists of three silicon ridge waveguides in proximity with periodic gaps introduced in the outer waveguides to create a band gap. The structure is complementary metal–oxide–semiconductor compatible with a very small footprint of only about 56 µ m 2 and more resilient to fabrication uncertainties as compared to the previously studied structures. Simulation results show transmission of 70% of the incident wave for the frozen mode at the 1.55 µm (193.6 THz) wavelength through the waveguide. It also enables a delay-bandwidth product of 6.75 along with unprecedented frequency independent bandwidth of about 0.5 THz for RF-mmWave–terahertz beamforming.

Topological effects in integrated photonic waveguide structures [Invited

We review recent advances of topological photonics in coupled waveguide systems. To this end, we discuss the various prevalent platforms, as well as various implementations in one- and two-dimensional systems, including driven, static, nonlinear and quantum systems.

Discrepancies in the free spectral range (FSR) of one-dimensional (1D) photonic crystal/photonic wire coupled-cavities

We present the simulation and experimental demonstration of a coupled-cavity 1D photonic-crystal/photonic-wire (PhC/PhW) structure that produces multiple resonance wavelengths. The combination of several cavities results in the assembly of a spectral response that exhibits multiple resonance wavelengths and potentially leads to the wavelength control required for wavelength division multiplexing (WDM) applications. By using a structure with three distinct in-line cavities, we have obtained three distinct resonance wavelengths—in conformity with the rule that the number of distinct resonance wavelengths is proportional to the number of cavities. The experimental photonic wire waveguide structure had cross-sectional dimensions of 600 nm (width) × 260 nm (height)—with an embedded photonic crystal (PhC) micro-cavity—all based on a silicon-on-insulator (SOI) platform. The embedded PhC structure was tailored to give resonance wavelengths in the C-band and L-band fiber telecommunication range. With the introduction of tapering in the multiple micro-cavity structure, it was possible to obtain three resonance wavelengths that correspond to WDM wavelengths of 1534.87, 1554.63 and 1594.86 nm—whereas, without tapering, the resonance wavelengths were 1645.60, 1670.76 and 1698.68 nm, respectively. We have observed an asymmetric free spectral range (FSR) situation with un-equal resonance wavelength spacing. The taper regions are also responsible for high optical transmission and lower Q-factor values at resonance. Transmission values of 0.17, 0.47 and 0.43 were obtained, together with Q-factor values of 1179.32, 930.05 and 970.35, respectively, without using tapered sections—while transmission values of 0.45, 0.74 and 0.43 were obtained, together with Q-factor values of 1083.24, 850.10 and 885.22, respectively, using tapered sections. (The normalisation values for the experiments were obtained with respect to an unstructured photonic wire). We have demonstrated that the taper structures used must be designed accurately, in order to maximize the transmission values at the desired resonance wavelengths. The demonstration of fabricated device structures that have measured properties that are in close agreement with predictions obtained using finite-difference time-domain (FDTD) computational software is an indication of the precision of the fabrication process. With the introduction of multiple cavities into the structures realised, the number of resonance wavelengths can be tailored for application as WDM components or other wavelength selective filters, such as arrayed-waveguide grating structures (AWGs) and Bragg gratings.

Equal-intensity waves in non-Hermitian media.

A novel type of waves is examined in the context of non-Hermitian photonics. We can identify a class of complex guided structures that support localized paraxial solutions whose intensity distribution is exactly the same as the intensity of a corresponding solution in homogeneous media (free or bulk space). In other words, intensity-wise the two solutions are identical and their phase is different by a factor exp[iθ(x,y)]. The non-Hermitian potential is determined by the phase θ, as well as the amplitude and phase of the bulk space solution that contributes to the imaginary and real part of the potential, respectively. That way we can connect the plane waves and Gaussian beams of free space to constant-intensity waves and what we call the equal-intensity waves (EI waves) in non-Hermitian media. Such a relation allows us to study three different physical problems: Propagating EI waves inside random media, interface lattice solitons, and moving solitons in photonic waveguide structures with free-space characteristics. The relation of EI waves to unidirectional invisibility and Bohmian photonics is also examined.

Highly degenerate photonic waveguide structures for holonomic computation

We investigate an all-out optical setup allowing for generation of non-Abelian geometric phases on its large degenerate eigenspaces. The proposal has the form of an $M$-pod system and can be implemented in terms of integrated photonic waveguide structures. We show that by injecting a larger number of photons into the optical setup, the degeneracy of eigenspaces scales rapidly. After studying the spectral properties of our system for the general case, we show how arbitrary $\mathrm{U}(3)$ transformations can be generated on the dark subspace of an optical tripod filled with two photons. Moreover, a degeneracy in the bright subspaces of the system, absent in any atomic analog, allows for the generation of universal single-qubit manipulations. Finally, we address the complexity issue of holonomic computation. Particularly, we show how two-qubit and three-qubit states can be implemented on a photonic tripod, where a natural multipartite structure is inherited from the spatial mode structure of the waveguides.

Fermionic time-reversal symmetry in a photonic topological insulator.

Much of the recent attention directed towards topological insulators is motivated by their hallmark feature of protected chiral edge states. In electronic (or fermionic) topological insulators, these states originate from time-reversal symmetry and allow carriers with opposite spin-polarization to propagate in opposite directions at the edge of an insulating bulk. By contrast, photonic (or bosonic) systems are generally assumed to be precluded from supporting edge states that are intrinsically protected by time-reversal symmetry. Here, we experimentally demonstrate counter-propagating chiral states at the edge of a time-reversal-symmetric photonic waveguide structure. The pivotal step in our approach is the design of a Floquet driving protocol that incorporates effective fermionic time-reversal symmetry, enabling the realization of the photonic version of an electronic topological insulator. Our findings allow for fermionic properties to be harnessed in bosonic systems, thereby offering alternative opportunities for photonics as well as acoustics, mechanical waves and cold atoms.

Defects modes in one-dimensional photonic filter star waveguide structure

In this work, by the formalism of the interface response theory, we study the existence of defects’ modes in the transmission spectrum of a one-dimensional photonic star waveguide (SWG) structure. The perfect structure presents large forbidden bands (gaps) that come from the periodicity of the system and the resonance states of the grafted lateral branches which play the role of the resonators. The defects modes result from the presence of the defects of the lateral branches level located in two different sites. The behavior of the defects’ modes is analyzed as a function of the defects’ lengths, the number of defectives resonators, the positions of the defects’ and the number of sites. This system can be considered as a selective filter with high performance.

Optimal design strategy for non-Abelian geometric phases using Abelian gauge fields based on quantum metric

Geometric phases, which are ubiquitous in quantum mechanics, are commonly more than only scalar quantities. Indeed, often they are matrix-valued objects that are connected with non-Abelian geometries. Here we show how generalized, non-Abelian geometric phases can be realized using electromagnetic waves travelling through coupled photonic waveguide structures. The waveguides implement an effective Hamiltonian possessing a degenerate dark subspace, in which an adiabatic evolution can occur. The associated quantum metric induces the notion of a geodesic that defines the optimal adiabatic evolution. We exemplify the non-Abelian evolution of an Abelian gauge field by a Wilson loop.

Electrothermal Actuators for SiO₂ Photonic MEMS.

This paper describes the design, fabrication and characterization of electrothermal bimorph actuators consisting of polysilicon on top of thick (>10 ) silicon dioxide beams. This material platform enables the integration of actuators with photonic waveguides, producing mechanically-flexible photonic waveguide structures that are positionable. These structures are explored as part of a novel concept for highly automated, sub-micrometer precision chip-to-chip alignment. In order to prevent residual stress-induced fracturing that is associated with the release of thick oxide structures from a silicon substrate, a special reinforcement method is applied to create suspended silicon dioxide beam structures. The characterization includes measurements of the post-release deformation (i.e., without actuation), as well as the deflection resulting from quasi-static and dynamic actuation. The post-release deformation reveals a curvature, resulting in the free ends of 800 long silicon dioxide beams with 5 -thick polysilicon to be situated approximately 80 above the chip surface. Bimorph actuators that are 800 in length produce an out-of-plane deflection of approximately 11 at 60 dissipated power, corresponding to an estimated 240 actuator temperature. The delivered actuation force of the 800 -long bimorph actuators having 5 -thick polysilicon is calculated to be approximately 750 at 120 .

Continuous Broadband MWP True-Time Delay With PbS-PMMA and PbS-SU8 Waveguides

A new microwave true-time delay (TTD) photonic unit based on the dispersion of PbS colloidal quantum dots (QDs) in a polymethyl methacrylate (PMMA) and the SU8 photoresist is presented. With this aim, the PbS-PMMA and PbS-SU8 nanocomposites are integrated on a silicon platform in the form of the planar and ridge waveguides, respectively. When the PbS QDs on those structures are pumped below their bandgap, a phase shift and a temporal delay in an optically conveyed (at 1550 nm) microwave signal is performed. The results of these devices show potential benefits over current TTD technologies, since the proposed photonic waveguide structures allow real-time adjustment of the temporal delay by tuning the power of the pumping signal, more than 3.5 ps over 25 GHz, and a high level of integration due to the novel proposed photonic waveguide structures and the materials used.

Photonic waveguide structures in photorefractive lithium niobate with pyroelectric mechanism of nonlinear response

Compensation for the nonlinear diffraction of narrow laser beams with wavelengths of 532 and 633nm and the formation of photonic waveguides and waveguide circuits due to the contribution of pyroelectric effect to the nonlinear response of lithium niobate crystal have been experimentally demonstrated. Complete compensation for the linear and nonlinear diffraction broadening of light beams is obtained upon uniform heating of an undoped sample from room temperature to 55◦C.

Special issue of optical and quantum electronics on information photonics

The processing of information using photonics technology is the key tomany emerging applications, for example bioand environmental-sensing, in addition to more conventional uses for data transmission in the rapidly evolving information society. Information photonics thus encompasses the development of new theories, models, devices, systems and applications. This Special Issue presents some recent developments in this exciting field. Its scope includes the design and realization of novel photonic waveguide and signal processing structures, the design, fabrication, and testing of photonic crystals and polarisation maintaining optical fibres, novel photonic configurations incorporating metamaterials, and the use of photonics in bio-sensing and medical diagnostics. The Guest Editors for the Special Issue thank all authors and reviewers for their expert contributions.

The investigation of the photonic waveguide structure made of silicon carbide by means of the method of the singular integral equations

Here we present the analyses of the open (without a metal screen) ridged and photonic waveguide structures by means of the electrodynamical rigorous method of the Singular Integral Equations (SIE). The waveguides are made of a lossy silicon carbide (SiC) material. We have discovered peculiarities of the dispersion characteristics. We have found the numerical solutions to the com- plex wave equations. The dispersion characteristics of both waveguide structures are numerically analyzed and com- pared with each other. It was found that the losses of modes propagating in the waveguide structure with air openings (channels) are smaller than the losses in the waveguide structure without air openings. We came to the conclusion that it is possible to optimize the dispersion characteristics by adding openings of different shapes and sizes into the waveguide structures.

Efficient sensitivity analysis approach based on finite element solutions of photonic structures

We propose, for the first time, an efficient technique for the sensitivity analysis of photonic waveguide structures with arbitrary shapes. Those waveguides are analyzed using the Finite Element Method (FEM). Our technique uses the solution obtained by any FEM solver and without the need of performing any extra FEM simulation, it gives accurate results for the sensitivity of the modal parameters with respect to all the design parameters. This technique is far more efficient than the traditional numerical estimates of the sensitivities.