Characterization Of Waveguides Research Articles

Waveguide Characteristics Near the Second Bragg Condition

We show that in an optical waveguide with no material losses at wavelengths near the second-order Bragg condition, there exists two pairs of modes. One pair has identical propagation constants but have different attenuation coefficients, while a second pair with identical propagation constants (different from the first pair) and have different attenuation coefficients. The four attenuation coefficients may have either a positive value, representing power leaking out of a waveguide mode or a negative value, representing power from an external source leaking into a mode. Moreover, a mode with a positive (negative) attenuation before the second Bragg condition, has a negative (positive) attenuation after the second Bragg condition. Radiation near the second-order Bragg condition of a periodic waveguide typically occurs at an angle perpendicular or nearly perpendicular to the propagation direction of the waveguide because the scattering centers have a period equal to or close to the period of the longitudinal propagation constant of the mode. In this paper, stable numerical solutions for the modes of periodic dielectric structures are developed using Floquet-Bloch theory. One primary focus in this paper illustrates a unique method of analyzing such modes using eigenvectors forming a Hilbert space, allowing for expansion of arbitrary vectors and their derivatives used for calculations such as that involving group velocities. The dimension of the vector space is determined by the number of space harmonics used in the solution of the Floquet-Bloch equations. The accuracy of the numerical solutions is affected by the number of space harmonics; as that number is increased, the number of waveguide partitions must be increased to maintain a given accuracy.

Fano Resonance and Sensing Characteristics of MIM Waveguide with H-Type Cavity

Fano Resonance and Sensing Characteristics of MIM Waveguide with H-Type Cavity

Fabrication of Polymer Optical Waveguides by Digital Ultraviolet Lithography

We present the design, fabrication and characterization of polymer optical waveguides using a digital ultraviolet (UV) lithography. Grayscale optical exposure with a nonlinear compensation in quadratic form is applied to minimize the stitching loss of the transition zone between two adjacent subpatterns. Proximity effects in lithography process are compensated based on an exposure dose-map that is calculated under the approximation of scattered light pixel with a Gaussian distribution. The bending loss and propagation loss of the fabricated polymer waveguides are experimentally characterized to be around 0.1 dB/90°-bend and 0.238 dB/mm, respectively. Moreover, 1 × 2 multimode-interference power splitter, 1 × 2 Y-branch power splitter and microring resonator are demonstrated to show the feasibility of the lithography technology on rapid fabrication of waveguides. Such a UV lithography technology flexibly manipulates huge-number light pixels for all-digital grayscale and dynamic optical exposure and thus can enable the fabrication of novel optical waveguide-based devices and sensors, such as 2.5D waveguides for multimode crossing and polymer waveguide devices for biosensing.

Fabrication and characterization of ridge waveguide in MgF2 crystal at mid-infrared 4 μm wavelength (invited)

Fabrication and characterization of ridge waveguide in MgF2 crystal at mid-infrared 4 μm wavelength (invited)

High Dynamic Range Microwave Displacement and Rotation Sensors Based on the Phase of Transmission in Groove Gap Waveguide Technology

This research is focused on the design and realization of displacement sensors in gap waveguide technology. It is shown that with a small but fundamental change in the structure of a conventional gap waveguide, a linear displacement can be sensed. To this end, a unique feature of gap waveguides, i.e. the fact that no electrical connection between the top and bottom parts of the gap waveguide is required, is used. It is further shown that the concept can be also used for the development of rotation sensors. To validate the proposed concept linear and angular displacement sensors are designed and simulated. A prototype of the proposed linear displacement sensor is fabricated for demonstration. Agreement between the computed and measured results validates the concept.

Fivefold Helically Corrugated Waveguide for High-Power W-Band Gyro-Devices and Pulse Compression

The design, simulation, manufacture, and measurement of a W-band fivefold (5F) helically corrugated waveguide (HCW) is reported. The 5F HCW is based on the coupling of the traveling TE₃₁ and near cutoff TE₂₁ modes to create an operating eigenwave. The fabricated test structure has circular waveguide ports and features elliptical polarizer sections and broadband TE₁₁ to TE₃₁ mode converters on either side of the 5F HCW. The optimized mode converter design, based on a fourfold (4F) HCW, has a predicted power conversion efficiency greater than 90% from 89 to 102.5 GHz, and 96% peak efficiency at 94 GHz. The optimization of the 5F HCW geometry produced an eigenwave suitable for gyro-devices, but the optimization could equally well have been directed to applications such as pulse compression and microwave undulators. Analysis of simulated electric field profiles showed that the propagating power in the 5F HCW was increased by a factor of 6 over that in the 3F HCW at equivalent peak electric field strength. This is due to the larger diameter of the waveguide. Test structures were manufactured through a combination of precision machining of a sacrificial mandrel, copper growth by electroforming followed by removal of the aluminum mandrel by chemically etching. Measurements of the 5F HCW structure's dispersion showed excellent agreement with the prediction over the design range of 90-98 GHz.

On-chip stimulated Brillouin scattering in As[formula omitted]S[formula omitted] waveguides with soft claddings of Benzocyclobutene

On-chip stimulated Brillouin scattering (SBS) can be implemented with arsenic trisulfide (As2S3) waveguides and benefits various applications of microwave photonic, signal processing and sensing. While stiff top-claddings of silica on the waveguides can help to enhance the opto-acoustic interaction in SBS, the soft cladding can facilitate the realization of narrow linewidth Brillouin lasers. Herein, we systematically study the on-chip SBS characteristics of the ridge As2S3 waveguides with soft claddings of Benzocyclobutene (BCB). Specifically, an optical propagation loss lower than 0.2 dB/cm and a Brillouin gain coefficient of approximately 300 m−1 W−1 at the Brillouin frequency of 7.70 GHz have been demonstrated. In particular, the linewidth of the Brillouin gain spectrum is broadened to be about 60 MHz. The influence of waveguide width on the SBS properties is systematically studied and the mostly-concerned linewidth broadening effect with respect to different waveguide dimensions has been found to be negligible. As an application of the fabricated BCB-cladded As2S3 waveguide, we have demonstrated the microwave bandpass filter with a suppression ratio of up to 23 dB. The As2S3 waveguides with BCB claddings may provide an effective and economic platform for on-chip SBS applications, such as integrated notch filter, Brillouin amplifiers, Brillouin lasers.

Performance analysis of alcohols sensing with optical sensor procedure using circular photonic crystal fiber (C-PCF) in the terahertz regime

In this study, a TOPAS-based optical sensor for detecting alcohols in drinks and liquids, made of circular air holes (CAH) in the cladding and a hexahedron core is suggested here. In addition, COMSOL Multiphysics program for development and analysis of the sensing qualities of a PCF-based sensor using finite element technical as a solution. In the THz frequency band, the described C-PCF structure has an exceptionally high relative sensitivity of 86.60%, 88.70%, and 84.71%, and low confinement losses (CLs) are 5.75 × 10−08, 6.11 × 10−08 dB/m and 5.70 × 10−08 dB/m for three alcohols such as Ethanol (n = 1.354), Butanol (n = 1.399), and Propanol (n = 1.387), respectively at monitoring region of 1 THz. Alcohol is widely used in both the food and beverage sectors and chemical operations. The detection methods of alcohol thus must be accurate, accurate, and reliable. This content modeling and analysis in the terahertz frequency range is a novel TOPAS-based photonic crystal fiber (C-PCF). Moreover, the total power fraction and effective area are also determined in the terahertz frequency range. Due to its excellent waveguiding characteristics, this suggested sensor has the potential to be employed in alcohols detection as well as polarization preserving terahertz wave applications.

Self-supported light induced polymer waveguide for thin optical fiber interconnection

Self-written polymer waveguides were integrated by single photon photopolymerization between two single mode fibers with a diameter of 80 µm. The fiber size and photopolymerizable liquid sample allowed bridge length only up to 200 µm long. The optical transmission characteristics of polymer waveguides were investigated in the spectral range of (350 to 1750 nm). The polymer channels showed an average insertion loss value of about 3.5 dB, with bright optical modes on the surface of polymer bridges, making these polymeric photonic structures useful in sensing applications.

Terahertz analysis of a highly sensitive MIM-SRR-TiO2 nanostructure for bio-sensor applications with the FDTD method

This work analyzes the transmission line characteristics of a plasmonic metal-insulator-metal (MIM) waveguide and a square ring resonator (SRR) for dual band applications. The MIM-SRR-based bio-sensor using 3-Aminopropyl triethoxy silane (APTES) and titanium dioxide ( T i O 2 ) as a precursor material are proposed and investigated in this paper. The MIM waveguide characteristics such as propagation length and effective refractive index have been obtained using the finite differential time domain (FDTD) solver of CST studio suite. The MIM-based SRR band-pass filter was designed and analyzed at 1300 nm (230.6 THz) and 1600 nm (187.37 THz) wavelengths. In this work, the bio-compatibility material T i O 2 is used as an agent of bio-molecules detection, and APTES is used as a linker between silicon dioxide and T i O 2 . The proposed MIM-SRR- T i O 2 -based bio-sensor is operated at 1320 nm (227.115 THz) and 1630 nm (183.922 THz). The proposed MIM-SRR-APTES- T i O 2 bio-sensor is operating at dual pass bands of 1415 nm (211.867 THz) and 1762 nm (170.143 THz). The proposed MIM-SRR-APTES- T i O 2 has a Q -factor of 22.353 and 20.655 and a sensitivity of 571.02 and 877.86 nm/RIU at 1415 and 1762 nm, respectively. APTES and T i O 2 are responsible for detecting cervical cancer, which is generally observed in woman. The scalability and multiplexing capability of semiconductor-based technology, silicon photonic ring resonators, are promising analytical tools for detecting various sensing applications. The overall size of the proposed bio-sensor is 1200 n m × 300 n m × 60 n m .

Self-calibration technique for characterization of integrated THz waveguides

Emerging high-frequency accelerator technology in the terahertz regime is promising for the development of compact high-brightness accelerators and high resolution-power beam diagnostics. One resounding challenge when scaling to higher frequencies and to smaller structures is the proportional scaling of tolerances which can hinder the overall performance of the structure. Consequently, characterizing these structures is essential for nominal operation. Here, we present a novel and simple self-calibration technique to characterize the dispersion relation of integrated hollow THz-waveguides. The developed model is verified in simulation by extracting dispersion characteristics of a standard waveguide a priori known by theory. The extracted phase velocity does not deviate from the true value by more than $ 9 \times 10^{-5} ~\%$. In experiments the method demonstrates its ability to measure dispersion characteristics of non-standard waveguides embedded with their couplers with an accuracy below $ \approx 0.5~\% $ and precision of $ \approx 0.05~\% $. Equipped with dielectric lining the metallic waveguides act as slow wave structures, and the dispersion curves are compared without and with dielectric. A phase synchronous mode, suitable for transverse deflection, is found at $ 275~\text{GHz} $.

Nonlinear loss characterization of continuous wave guiding in silicon wire waveguides

Accurate propagation loss characterization of silicon waveguides is increasingly demanded for silicon-photonics-(Si-Ph) applications with high-power continuous-wave-(CW) light sources. We report on nonlinear loss parameters of silicon wire waveguides for 1.31 μm wavelength CW light extracted from transmission data measured for different lengths and polarizations. Such parameters were, so far, unavailable, although they are required for accurately modeling Si-Ph optical circuits. More-than-ten-times enhancement of two-photon absorption from prior results for short pulse light was observed at power densities ranging up to 4.7 × 1011 W m−2 while free carrier absorption was suppressed. We estimate the nonlinear loss of the waveguides using the parameter values obtained.

Microscopic imaging along tapered optical fibers by right-angle Rayleigh light scattering in linear and nonlinear regime.

The evolution of the light intensity along an optical waveguide is evaluated by analysing far-field right-angle Rayleigh light scattering. The method is based on point by point spectral mapping distributed along the optical waveguide with a micrometric spatial resolution given by a confocal microscope, a high spectral resolution given by a spectrometer, and a high signal-to-noise ratio given by a highly cooled detector. This non-destructive and non-invasive experimental method allows the observation of the general Rayleigh scattering profile of the optical waveguide in a nominal operation, i.e., whatever the power or the wavelength of the light source, and can be applied to micrometer-scale waveguides of several centimeters in length, for which the longitudinal characterization is challenging. Applied to a tapered optical fiber, called nanofiber, with submicrometer final diameter and several centimeters long, the method has proved its capacity to collect different optical characteristics such as optical losses, mode beatings, transition from core-cladding to cladding-air guidance for different modes, localization of punctual defects, leaking of high order modes no longer guided by the fiber. Furthermore, the experimental results are successfully compared to measurements provided by the state-of-the-art Optical Backscatter Reflectometer system, and to numerical simulations. Moreover, coupled to the spectral resolution of the spectrometer, the method have allowed the distributed measurements of the Raman cascading process along the nanofiber, for the first time to our knowledge. The experimental technique developed in this work is complementary to other characterization methods generally focused on the optical parameters of the waveguide input or output. This technique can also be extended to others waveguides whatever its geometry which represents a strong interest for deepen optical characterization of photonics waveguides, or for other optical regimes characterized by spectral evolution of the field propagating along the waveguide.

Polarization characteristics of shallow-etched SOI ridge waveguide with non-rectangular cross section

Polarization characteristics of shallow-etched SOI ridge waveguide with non-rectangular cross section

Single‐Crystal Organic Heterostructure for Single‐Mode Unidirectional Whispering‐Gallery‐Mode Laser

AbstractOrganic single crystals have attracted great attention for solid‐state lasers owing to their smooth morphologies with inherent optical microcavity, ordered molecular packing mode with minimized defects density, and high photoluminescence quantum efficiency. However, the organic single‐crystal lasers, including whispering‐gallery‐mode (WGM) lasers with nondirectional emission and Fabry–Perot (F–P) lasers with inherent high‐lasing threshold, cannot achieve state‐of‐the‐art performance. Herein, the hierarchical self‐assembly of organic single‐crystal heterostructures made from cube‐shaped microdisks with optical gain and microwires with optical waveguide characteristics is demonstrated, which realize the unidirectional WGM laser action with a low‐lasing threshold of ≈600 nJ cm−2. The lattice mismatch rate principle contributes to the growth of these single‐crystal organic heterostructures. More significantly, the waveguide‐coupled WGM microcavity with a coupling coefficient of 28.8% proves that the unidirectional outcoupling of the single‐crystal WGM lasers from the single‐crystal wire waveguides is achieved. The results will pave an alternative avenue for high‐performance organic single‐crystal lasers.

Low loss hybrid plasmon polariton Mach-Zehnder modulators

We propose a hybrid plasmon polariton (HPP) Mach-Zehnder modulator (MZM) structure that combines the tight optical confinement of plasmonic waveguides and narrow slot waveguides with the low loss feature of photonic waveguides. Compared with conventional surface plasmon polariton (SPP) modulators, the HPP modulator exhibits lower propagation loss and better overall performance. Simulations based on the finite difference time-domain (FDTD) and finite element method (FEM) predict a half-wave voltage-length product of 0.078 V·mm for the HPP modulator. Meanwhile, the propagation loss is only 0.2 dB/μm, which is less than half of that for an SPP modulator. The modulation bandwidth of a 10-μm-long HHP modulator exceeds 650 GHz, while the total insertion loss of the device is estimated to be lower than 4 dB.

EXCITATION OF MAGNETOPLASMA OSCILLATIONS IN SEMICONDUCTOR STRUCTURES BY FLUXES OF CHARGED PARTICLES

The subject of the papers is the processes of analysis and physical model of excitation (amplification) of magnetoplasma oscillations (helicons) by fluxes of charged particles (electrons) in the presence of a constant magnetic field. This model is based on the Cherenkov mechanism for converting kinetic energy of particles into the energy of natural electromagnetic oscillations of solid-state (semiconductor) structures under resonance conditions when the particle velocities coincide with phase velocities of oscillations. The aim here is to justify the formulation of theoretical studies basing on the proposed physical model of generation (amplification) of electromagnetic oscillations (emergence of oscillation instabilities, i.e., exponential growth of their amplitude). We define parameters intervals for the external magnetic field, particle fluxes and types of semiconductor structures which this physical model is applied to. We perform theoretical study of the influence charged particle fluxes have on waveguide characteristics of semiconductor structures. The study justifies the possibility of generation and amplification of magnetoplasma oscillations in the submillimeter range. Our objectives are theoretical studies of the interaction of moving charges with electromagnetic oscillations of a semiconductor structure under conditions of Cherenkov radiation. The methods used are the method of successive approximations for solving the dispersion equations for a system of charged particle flux - semiconductor structure within the framework of hydrodynamic approach. The following results are obtained: Theoretical studies of the functioning of semiconductor components of electrical radio equipment in the presence of charged particle fluxes have been carried out. It is shown that the effect of the particle flux is characterized by the emergence of oscillation instabilities in the semiconductor structure. We have determined one of the mechanisms for the excitation of magnetoplasma oscillations based on the interaction of moving charges with the intrinsic fields of the structures that constitute a semiconductor unit. Such equipment failures occur under conditions of Cherenkov radiation. We have shown that this interaction leads to appearance of a mode of oscillation generation. The results of a comparative analysis of the data obtained in this work make it possible to use the proposed physical model to determine the criteria for the occurrence and development of instabilities of magnetoplasma oscillations. Conclusions. The results obtained in this work can be used in the development of active microwave range devices (amplifiers, generators and transducers of electromagnetic oscillations of the millimeter and submillimeter bands). The comparative analysis of quantitative estimates of the growth rates of oscillation instabilities, depending on the spatial configuration of the acting field (when induced current is parallel to the structure boundary), carried out in this work, provides a solution to the problem of optimizing the operating characteristics of active microwave devices.

Elastic Organic Crystals Based on Barbituric Derivative: Multi-faceted Bending and Flexible Optical Waveguide.

Elastic organic single crystals with light-emitting and multi-faceted bending properties are extremely rare. They have potential application in optical materials and have attracted the extensive attention of researchers. In this paper, we reported a structurally simple barbituric derivative DBDT, which was easily crystallized and gained long needle-like crystals (centimeter-scale) in DCM/CH3 OH (v/v=2/8). Upon applying or removing the mechanical force, both the (100) and (040) faces of the needle-like crystal showed reversible bending behaviour, showing the nature of multi-faceted bending. The average hardness (H) and elastic modulus (E) were 0.28±0.01 GPa and 4.56±0.03 GPa for the (040) plane, respectively. Through the analysis of the single crystal data, it could be seen that the van der waals (C-H⋅⋅⋅π and C-H⋅⋅⋅C), H-bond (C-H⋅⋅⋅O) and π⋅⋅⋅π interactions between molecules were responsible for the generation of the crystal elasticity. Interestingly, elastic crystals exhibited optical waveguide characteristics in straight or bent state. The optical loss coefficients measured at 627 nm were 0.7 dBmm-1 (straight state) and 0.9 dBmm-1 (bent state), while the optical loss coefficient (α) were 1.5 dBmm-1 (straight state) and 1.8 dBmm-1 (bent state) at 567 nm. Notably, the elastic organic molecular crystal based on barbituric derivative could be used as the candidate for flexible optical devices.

Study of Forward and Backward Modes in Double-Sided Dielectric-Filled Corrugated Waveguides.

This work studies the propagation characteristics of a rectangular waveguide with aligned/misaligned double-sided dielectric-filled metallic corrugations. Two modes are found to propagate in the proposed double-sided configuration below the hollow-waveguide cutoff frequency: a quasi-resonant mode and a backward mode. This is in contrast to the single-sided configuration, which only allows for backward propagation. Moreover, the double-sided configuration can be of interest for waveguide miniaturization on account of the broader band of its backward mode. The width of the stopband between the quasi-resonant and backward modes can be controlled by the misalignment of the top and bottom corrugations, being null for the glide-symmetric case. The previous study is complemented with numerical results showing the impact of the height of the corrugations, as well as the filling dielectric permittivity, on the bandwidth and location of the appearing negative-effective-permeability band. The multi-modal transmission-matrix method has also been employed to estimate the rejection level and material losses in the structure and to determine which port modes are associated with the quasi-resonant and backward modes. Finally, it is shown that glide symmetry can advantageously be used to reduce the dispersion and broadens the operating band of the modes.

Footprint Analysis of CMOS Compatible Silicon-on-Insulator Based Photonic Waveguides

Aim: Establish the efficient footprint size, i.e., the total substrate width of photonic waveguides (Ridge, Rib, and Slot) under the fundamental mode propagation constraints. Objective: By varying the total substrate width for all photonic waveguides (Ridge, Rib, and Slot) with respect to four major waveguide parameters, namely effective refractive index, propagation loss, propagation length, and confinement percentage, the converged values of these waveguide parameters have to be obtained. Methods and Materials: The Finite Element Method (FEM) based simulations, using the COMSOL Multiphysics, have been used to study the modal characteristics of photonic waveguides to achieve their efficient footprint size. Results: The total substrate widths have been obtained for all four parameters and considering the impact of all these waveguide parameters simultaneously, the efficient total substrate width has been recognized as 2500 nm, 4000 nm, and 3000 nm, respectively, for Ridge, Rib, and Slot waveguides. Conclusion: The efficient waveguide footprints, i.e., the total substrate widths for the three photonic waveguides, namely Ridge, Rib and Slot waveguides have been established.