Waveguide In Terms Research Articles

Van der Waals Materials for Overcoming Fundamental Limitations in Photonic Integrated Circuitry.

With the advance of on-chip nanophotonics, there is a high demand for high-refractive-index and low-loss materials. Currently, this technology is dominated by silicon, but van der Waals (vdW) materials with a high refractive index can offer a very advanced alternative. Still, up to now, it was not clear if the optical anisotropy perpendicular to the layers might be a hindering factor for the development of vdW nanophotonics. Here, we studied WS2-based waveguides in terms of their optical properties and, particularly, in terms of possible crosstalk distance. Surprisingly, we discovered that the low refractive index in the direction perpendicular to the atomic layers improves the characteristics of such devices, mainly due to expanding the range of parameters at which single-mode propagation can be achieved. Thus, using anisotropic materials offers new opportunities and novel control knobs when designing nanophotonic devices.

Machine Learning Non-Reciprocity of a Linear Waveguide With a Local Nonlinear, Asymmetric Gate: Case of Strong Coupling

Abstract We study nonreciprocity in a passive linear waveguide augmented with a local asymmetric, dissipative, and strongly nonlinear gate. Strong coupling between the constituent oscillators of the waveguide is assumed, resulting in broadband capacity for wave transmission. The local nonlinearity and asymmetry at the gate can yield strong global nonreciprocal acoustics, in the sense of drastically different acoustical responses depending on which side of the waveguide a harmonic excitation is applied. Two types of highly nonreciprocal responses are observed: (i) Monochromatic responses without frequency distortion compared to the applied harmonic excitation, and (ii) strongly modulated responses (SMRs) with strong frequency distortion. The complexification averaging (CX-A) method is applied to analytically predict the monochromatic solutions of this strongly nonlinear problem, and a stability analysis is performed to study the governing bifurcations. In addition, we build a machine learning framework where neural net (NN) simulators are trained to predict the performance measures of the gated waveguide in terms of certain transmissibility and nonreciprocity measures. The NN drastically reduces the required simulation time, enabling the determination of parameter ranges for desired performance in a high-dimensional parameter space. In the predicted desirable parameter space for nonreciprocity, the maximum transmissibility reaches 40%, and the transmitted energy varies by up to three orders of magnitude depending on the direction of wave transmission. The machine learning tools along with the analytical methods of this work can inform predictive designs of practical nonreciprocal waveguides and acoustic metamaterials that incorporate local nonlinear gates.

Recent Progress in Short and Mid-Infrared Single-Photon Generation: A Review

The generation of single photons in the mid-infrared spectral region is attracting the interest of scientific and technological research, motivated by the potential improvements that many important and emerging applications, such as quantum sensing, metrology and communication, could benefit from. This review reports the progress in short and mid-infrared single photon generation, focusing on probabilistic sources based on the two non-linear processes of spontaneous parametric downconversion (SPDC) and four wave mixing (FWM). On one hand, numerical simulations of mid-infrared SPDC are described as a powerful tool to assist and guide the experimental realization, along with the implementation and engineering of novel non-linear materials. On the other hand, the advantages offered by FWM in silicon waveguides in terms of integration, miniaturization and manufacturability are presented, providing an optimal technology for integrated quantum applications.

Dispersion properties of a slab waveguide with a graded-index core layer and a nonlinear cladding using the WKB approximation method

Graded-index waveguides deserve investigation because they are more practical than those of step-index profiles. In this communication, a three-layer slab waveguide in which the core film has an exponentially graded refractive index is assumed. In this case, the film and substrate layers merge smoothly to form one layer of refractive index n ( x ) which is equal to n f at the cladding–film boundary and n s deep in the substrate layer. The cladding layer is made of a Kerr-type nonlinear material. An exact solution to such a waveguide structure is not possible. Approximation techniques are usually used in these cases. We employ the WKB approximation method to find an approximate dispersion relation of the proposed waveguide in terms of the asymmetry parameters a , b , and V . The universal dispersion curves are studied in detail. A number of interesting features are observed, such as the lack of a cutoff thickness related to the symmetric waveguide structure of a = 0 . The b -values are all less than one, which corresponds to guided modes.

Py-fmas: A python package for ultrashort optical pulse propagation in terms of forward models for the analytic signal

We present a flexible, open-source Python package for the accurate simulation of the z-propagation dynamics of ultrashort optical pulses in nonlinear waveguides, especially valid for few-cycle pulses and their interaction. The simulation approach is based on unidirectional propagation equations for the analytic signal. The provided software allows to account for dispersion, attenuation, four-wave mixing processes including, e.g., third-harmonic generation, and features various models for the Raman response. The propagation equations are solved on a periodic temporal domain. For z-propagation, a selection of pseudospectral methods is available. Propagation scenarios for a custom propagation constant and initial field pulses can either be specified in terms of a HDF5 based input file format or by direct implementation using a python script. We demonstrate the functionality for a test-case for which an exact solution is available, by reproducing exemplary results documented in the scientific literature, and a complex propagation scenario involving multiple pulses. Program summaryProgram Title: py-fmasCPC Library link to program files:https://doi.org/10.17632/7s2cv9kjfs.1Developer's repository link:https://github.com/omelchert/py-fmasCode Ocean capsule:https://codeocean.com/capsule/8221780Licensing provisions: MITProgramming language: Python3Supplementary material: Reference manual, extended user guide, and usage examples are hosted on gitHub pages under https://omelchert.github.io/py-fmas.Nature of problem: Solves for the z-propagation dynamics of spectrally broad ultrashort optical pulses in single mode nonlinear waveguides in terms of propagation models for the analytic signal of the optical field [1–3]. The implemented models include, e.g., third-harmonic generation and the Raman effect.Solution method: The initial real-valued optical field is defined on a periodic one-dimensional temporal grid and converted to the complex-valued analytic signal. z-stepping is performed via spectral methods. The software implements a selection of algorithms with fixed or adaptive stepsize, commonly used in nonlinear optics for solving nonlinear Schrödinger type equations.Additional comments including restrictions and unusual features: The range of applicability of the provided software is equivalent to that of the forward Maxwell equation [4]. For reasonably chosen initial conditions, it can be used beyond the unidirectional approximation as a bidirectional model for a complex field, allowing to describe forward and backward waves coupled through nonlinear interactions [1]. The software implements various models for the Raman response and allows to calculate spectrograms, detailing the time-frequency composition of the analytic signal. Additionally, a convenience class for analyzing propagation constants is provided.

A Novel Mode-Matching Formulation of Multifurcated Waveguide Junctions

In this paper, we present a mode-matching-based formulation for the electromagnetic analysis of multifurcated waveguide problems, that is, the junction of a number of input waveguides with an output region of larger cross-section area. A generalized scattering matrix (GSM) representation is obtained for relating the forward and backward modal field amplitudes in each of the waveguides in terms of coupling integrals representing the conservation of the reaction of the electromagnetic fields. Numerical results for several multifurcated coaxial waveguide devices are provided to validate the formulation. Comparisons against the finite-element method demonstrate that the present approach can accurately model multifurcated waveguide problems. The method introduced here provides useful matrix formulas that allow us to model multi-port waveguide devices by reusing well-known coupling integrals of two-port problems.

Fano Resonance Ion Sensor Enabled by 2D Plasmonic Sub-Nanopores-Material

Silicon photonics has shown great potential in integrated biochemical sensing. However, it is challenging to detect ions selectively, which is crucial in several biochemical application. In this paper, we propose and demonstrate a newly designed ion sensor by combining two-dimensional (2D) plasmonic and sub-nanoporous K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> MoO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> with a silicon waveguide. A T-shaped waveguide coupled with a microring resonator (MRR) generates Fano resonance at all resonance modes. Sharp Fano-like spectra were optimized by numerically simulating the structure of the waveguide in terms of the coupling coefficients, phase factor, and MRR power loss. In our design, a Fano resonance wavelength shift is caused by a refractive index change based on the interaction between 2D near-infrared plasmonic K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> MoO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> . Moreover, the alteration in plasmonic absorption leads to a variation in transmission power. This dual-sensing output method is unique compared with existing methods that utilize optical ion sensors. Our results demonstrate that the micro-scale silicon waveguide combined with a 2D plasmonic material exhibits excellent potential as a chemical sensor.

Thermo Optical Phase Shifter With Low Thermal Crosstalk for SOI Strip Waveguide

The trade-offs of using thermo-optical phase shifter in different standard CMOS silicon-on-insulator (SOI) structures (strip and rib waveguides) are studied. Twelve different thermo-optic phase shifters, considering metal and highly doped silicon (both n- and p-type), are studied using numerical simulations and measurements. The performance of heater type, size, and distance to the strip waveguide in terms of energy efficiency, crosstalk, and response time is investigated. The required power to reach π phase shift is measured and compared with the numerical simulation. The time response and the corresponding figure of merit of the interferometer affected by each heater is analyzed and the design strategies for optimizing the designs are discussed. A new compact design for the phase shifter is suggested with low thermal crosstalk (ΔT < 0.1 °C at a distance of 10 μm) and low electrical power consumption (Pπ = 13.2 mW).

Long-range directional transport of valley information from transition metal dichalcogenides via a dielectric waveguide.

Understanding the chiral light-matter interaction offers a new way to control the direction of light. Here, we present an unprecedently long-range transport of valley information of a 2D-layered semiconductor via the directional emission through a dielectric waveguide. In the evanescent near field region of the dielectric waveguide, robust and homogeneous transverse optical spin exists regardless of the size of the waveguide. The handedness of transverse optical spin, determined by the direction of guided light mode, leads to the chiral coupling of light with valley-polarized excitons. Experimentally, we demonstrated ultra-low propagation loss which enabled a 16 µm long propagation of directional emission from valley-polarized excitons through a ZnO waveguide. The estimated directionality of exciton emission from a valley was about 0.7. We confirmed that a dielectric waveguide leads to a better performance than does a plasmonic waveguide in terms of both the directional selectivity of guided emission and the efficiency of optical power reaching the ends of the waveguide when a propagation length is greater than ∼10 µm. The proposed dielectric waveguide system represents an essential platform for efficient spin/valley-photon interfaces.

Low-loss low thermo-optic coefficient Ta2O5 on crystal quartz planar optical waveguides

Optical resonator-based frequency stabilization plays a critical role in ultra-low linewidth laser emission and precision sensing, atom clocks, and quantum applications. However, there has been limited success in translating traditional bench-top stabilization cavities to compact on-chip integrated waveguide structures that are compatible with photonic integration. The challenge lies in realizing waveguides that not only deliver low optical loss but also exhibit a low thermo-optic coefficient and frequency noise stability. Given the problematic sources of frequency noise within dielectrics, such as thermorefractive noise, resonators with small thermo-optic response are desirable for on-chip reference cavities. We report the first demonstration of a Ta2O5 (tantala) waveguide core fabricated on a crystal quartz substrate lower cladding with TEOS-PECVD SiO2 upper cladding. This waveguide offers significant advantages over other waveguides in terms of its low thermo-optic coefficient and reduced thermorefractive-related frequency noise. We describe the waveguide structure and key design parameters as well as fabrication considerations for processing tantala on quartz waveguides. We report a waveguide thermo-optic coefficient of −1.14 × 10−6 RIU/K, a value that is over 6 times smaller in magnitude than that of SiO2-substrate tantala waveguides, with a propagation loss of 1.19 dB/cm at 1550 nm and &amp;lt;1.33 dB/cm across the 1525 nm–1610 nm wavelength range. Within a 1.6 mm radius ring resonator, we demonstrate a 2.54 × 105 intrinsic Q factor. With the potential for very low loss and the ability to control the thermal response, this waveguide platform takes a key step toward creating thermally stable integrated resonators for on-chip laser frequency stabilization and other applications.

Investigations on europium aluminum incorporated polymer composite optical waveguide amplifier

The gain performance of 50-iun core diameter graded-index (GI) multimode europium aluminum benzyl methacrylate (Eu-Al/BzMA) waveguide was investigated by numerically solving rate and propagation equations using MATLAB. At a fixed waveguide length of 10 cm and gain medium concentration of 13 wt.%, optical gain was found to be dependent on pump power and input signal power. This paper utilized a 532 nm wavelength pump with power varied from 100 mW to 500 mW, together with low (-30 dBm) and high (0 dBm) input signal powers, within the amplification range of 580 to 640 nm wavelength. With the highest pumping power of 500 mW and the lowest input signal power of -30 dBm, a 29-dB optical gain with wavelength of 617 nm was observed from forward pumping amplification. For comparison, an identical waveguide in terms of properties was fabricated through an innovative fabrication method for polymer waveguide—the Mosquito method. The fabricated waveguide was then experimentally tested for -30 dBm input signal power with 200 mW pump power in the attempt to realize future real-world applications of short reach networks such as in Local Area Network (LAN) and in-vehicle optical interconnects.

Defected waveguide structure designs and characteristics

AbstractThis article presented defected waveguide structure (DWS) designs and characteristics with microstrip‐fed circular monopole antenna for ultrawideband applications. Typically, waveguide is often designed and employed as antenna and filter application in its rigid dimension. The reconfigurable design toward the waveguide in terms of structural alteration with DWS was found less concerned among researchers although defected ground structure and defected microstrip structure have been applied widely. The motivation of this article was to propose the different DWS designs and characteristics in terms of the S‐parameters result. DWS in basic square geometry with different configurations of straight lines were introduced and compared with FR4 substrate waveguide. Simulated S‐parameters results were modeled in terms of equivalent circuit and measured for validation. For practical measurement, waveguide ports at both open‐ended surface of waveguide were replaced by the monopole antenna. For the modeled S‐parameters results, the square DWS design and square DWS with horizontal straight lines showed quite similar characteristics with higher S11 and lower S21 above frequency 9 GHz. Whereas square DWS with vertical straight lines and square DWS with both horizontal vertical straight lines showed higher S11 and lower S21 below frequency 3.5 GHz. Square DWS with vertical straight lines achieved the lowest S21 around −70 dB below 3.5 GHz and lower S21 around −50 dB at frequency 10.3 GHz. Thus, DWS is proposed for the future smart antenna technology as it can be further modified to meet the different requirements without changing the antenna configuration.

Ultra-deep sub-wavelength mode confinement in nano-scale graphene resonator-coupled waveguides.

Graphene is capable of supporting very slow waves due to sustaining surface plasmon polaritons (SPPs) at THz frequencies, whereas the metal counterpart can support such modes only at optical frequencies. In this paper, a graphene-based resonator-coupled waveguide supporting transverse-magnetic-polarized SPP modes is rigorously studied, which is capable of providing ultra-deep sub-wavelength mode confinement at the working frequency of 40THz. First, graphene is described both electronically and electromagnetically, as in these regards, graphene's quantum capacitance plays an important role, which is calculated via its DC characteristic. Since we aim to excite extremely slow waves in graphene waveguides, namely, SPP modes, it is necessary to contemplate a non-local conductivity model to characterize graphene. Furthermore, SPP modes create strong fields at the vicinity of a graphene strip in addition to high mode confinement, accentuating the importance of including nonlinear phenomena in characterizing the wave vector of SPP (WVP) modes. Furthermore, the WVP associated with a graphene waveguide is perturbed when placing another waveguide next to it. In this work, these phenomena are explored in detail to design a graphene-based resonator-coupled waveguide, which is superior to a single graphene-based waveguide in terms of confining propagating waves. Here, a comprehensive methodology is established for assessing miniaturized graphene devices, in which nonlinear, coupling, and spatial dispersion phenomena significantly affect their characteristics.

Hybrid Plasmonic–Photonic–Organic Modulators With Low Insertion Loss and High Modulation Depth

In this article, a novel hybrid plasmonic–photonic–organic electro-optical modulator based on Pockels effect is designed and numerically investigated by employing finite difference time domain and finite element methods at a wavelength of $\lambda \,= \,{\text{1.55}}\,\mu {\text{m}}$ . The presented modulator exhibits unique features such as the half-wave voltage–length product of 0.08 V⋅mm being in the range of modern plasmonic modulators. However, the design presented in this article represents a very low insertion loss of less than 2 dB in the wavelength range of 1.45–1.65 μ m. Moreover, the modulator has an energy consumption of approximately 25 fJ/Bit, modulation depth of approximately 35% and 80% at applied voltages of 5 and 10 V, and electro-optical bandwidth of more than 70 GHz. As the key component of the modulator, a novel hybrid plasmonic slot waveguide is introduced, which combines tight light confinement of plasmonic waveguides with the low loss feature of photonic waveguides. In particular, the presented waveguide enables tight light confinement and guiding in slots as narrow as 40 nm with remarkably low loss of less than 0.2 dB/ μ m, which makes them attractive for other applications in addition to the designed modulator. In this paper, the presented waveguides are thoroughly investigated and compared with plasmonic slot waveguides in terms of loss and modal characteristics.

Studies on different geophysical and extra-terrestrial events within the Earth-ionosphere cavity in terms of ULF/ELF/VLF radio waves

The space between the two spherical conducting shells, Earth surface and the lower boundary of the ionosphere, behaves as a spherical cavity in which some electromagnetic signals can propagate a long distance and is called Earth-ionosphere waveguide. Through this waveguide ultra low frequency (ULF), extremely low frequency (ELF) and very low frequency (VLF) signals can propagate efficiently with low attenuation. Resonances which occur for ELF waves due to round-the-world propagation interfering with $2n \pi $ phase difference are called Schumann resonances. Lightnings are the main sources of energy continuously producing these electromagnetic radiations from the troposphere. Some fixed frequency signals are also transmitted through the waveguide from different stations for navigation purposes. The intensity and phase of these signals at a particular position depend on the waveguide characteristics which are highly influenced by different natural events. Thus the signatures of different geophysical and extra-terrestrial events may be investigated by studying these signals through proper monitoring of the time series data using suitable techniques. In this article, we provide a review on ULF, ELF and VLF signals within the waveguide in terms of different geophysical and extra-terrestrial events like lightning, earthquakes, Leonid meteor shower, solar flares, solar eclipse, geomagnetic storms, and TLEs etc.

PROPAGATION AND CHARACTERIZATION OF NOVEL GRADED AND LINEARLY CHIRPED TYPE'S OF REFRACTIVE INDEX PROFILE SYMMETRIC PLANAR SLAB WAVEGUIDE BY NUMERICAL MEANS

We characterize the alpha power and chirped types of refractive index profile planar slab waveguide in terms of TE/TM mode study, waveguide dispersion study, mode profile properties, power confinement factor and universal b-V graph. Our own developed finite element method has been efficiently applied to analyze the symmetric planar slab waveguide having a complicated refractive index profile. There is a requirement for a high accuracy of numerical technique to analyze the arbitrary refractive index waveguide, as at some frequency the TE and TM modes are smeared on each other, and it is difficult to distinguish them while analyzing. This paper successfully demonstrates the different TE/TM modes supported by the waveguide with respect to alpha-power and linearly chirped types of refractive index profile. The main contribution of our work is to identify the TE/TM mode numerically for a complex refractive index planar slab waveguide and to characterize them in terms of their performance parameters. Then we apply the mode propagation concept to estimate the propagation phenomena in alpha-power and chirped types of refractive index profile waveguide. All the results presented in this paper are simulated in MATLAB only. Our study reveals that waveguide dispersion and number of allowed guided modes are small while for the case of triangular index profile followed by chirped profile and maximum for step index profile case. Hence triangular and chirped types of refractive index profile waveguide seem to be more efficient for long haul optical communication systems.

Transmission properties in waveguides: an optical streamline analysis

We present a novel approach to study transmission through waveguides in terms of optical streamlines. This theoretical framework combines the computational performance of beam propagation methods with the possibility to monitor the passage of light through the guiding medium by means of these sampler paths. In this way, not only can the optical flow along the waveguide be followed in detail, but also a fair estimate of the transmitted light (intensity) can be accounted for by counting streamline arrivals with starting points statistically distributed according to the input pulse. Furthermore, this approach allows elucidation of the mechanism leading to energy losses, namely, a vortical dynamics, which can be advantageously exploited in optimal waveguide design.

Comparative study of asymmetric versus symmetric planar slab dielectric optical waveguides

In this paper we have studied the asymmetric versus symmetric planar waveguide in terms of their usefulness in optical fiber communication systems. We have explored the thin waveguide versus thick waveguide first. Later on usefulness of asymmetric versus symmetric waveguide is carried out to target for WDM optical network application. All kinds of optical network components are fabricated on Si substrate with the point of view of their application. Here asymmetric planar structure may be more useful compared to symmetric waveguide in terms of their non-uniform power confinement properties. However, the symmetric waveguide structure may be more useful for their high power confinement properties. It is well known that the thin symmetric waveguide supports at least one mode. However the thick waveguide may support many even as well as odd modes. We study the power confinement properties for symmetric as well as asymmetric waveguide structure. We conclude that higher order modes show the nonlinear power variations. Mode field profile for various cases is discussed as well. Comparative study between asymmetric versus symmetric waveguide has a lot of significance in optical network area. It has been shown through analysis that in asymmetric waveguide, the power flows more through film region in the case of fundamental mode. Power confinement properties for asymmetric waveguide versus symmetric waveguide have been studied.

Fabrication of a cyclic olefin copolymer planar waveguide embedded in a multi-channel poly(methyl methacrylate) fluidic chip for evanescence excitation.

The fabrication and characterization of a novel cyclic olefin copolymer (COC) waveguide embedded in a poly(methyl methacrylate), PMMA, fluidic chip configured in a multi-channel format with an integrated monolithic prism for evanescent fluorescence excitation are reported. The fabrication approach allowed the embedded waveguide to be situated orthogonal to a series of fluidic channels within the PMMA wafer to sample fluorescent solutions in these channels using the evanescence properties of the waveguide. Construction of the device was achieved using several fabrication techniques including high precision micromilling, hot embossing and stenciling of a polymer melt to form the waveguide and coupling prism. A waveguide channel was fabricated in the fluidic chip's cover plate, also made from PMMA, and was loaded with a COC solution using a pre-cast poly(dimethylsiloxane), PDMS, stencil containing a prism-shaped recess. The PMMA substrate contained multiple channels (100 microm wide x 30 microm deep with a pitch of 100 microm) that were situated orthogonal to the waveguide to allow penetration of the evanescent field into the sampling solution. The optical properties of the waveguide in terms of its transmission properties and penetration depth of the evanescent field in the adjacent solution were evaluated. Finally, the device was used for laser-induced fluorescence evanescent excitation of a dye solution hydrodynamically flowing through multiple microfluidic channels in the chip and processed using a microscope equipped with a charge-coupled device (CCD) for parallel readout. The device and optical system were able to image 11 channels simultaneously with a limit-of-detection of 7.1 x 10(-20) mol at a signal-to-noise ratio of 2. The waveguide was simple to manufacture and could be scaled to illuminate much higher channel numbers making it appropriate for high-throughput measurements using evanescent excitation.

Damage-Free Design of a Megasonic Waveguide for Single-Wafer Processing

Megasonic cleaning process as a wet cleaning process is routinely used in the semiconductor industry for the removal of contaminant particles from wafer surfaces. The wafer surfaces can be cleaned effectively by choosing the proper chemicals, acoustic pressure, and the frequency of acoustic field. In the present study, we propose the design improvement of a megasonic waveguide to minimize wafer damage from the bubble cavitation. The conventional direct-type waveguide is compared with the newly designed and developed indirect-type waveguide in terms of its performance in minimizing the damage of wafers having 70 nm poly-Si patterns.