Waveguide Material Research Articles

Spatiotemporal imaging of nonlinear optics in van der Waals waveguides.

Van der Waals (vdW) semiconductors have emerged as promising platforms for efficient nonlinear optical conversion, including harmonic and entangled photon generation. Although major efforts are devoted to integrating vdW materials in nanoscale waveguides for miniaturization, the realization of efficient, phase-matched conversion in these platforms remains challenging. Here, to address this challenge, we report a far-field ultrafast imaging method to track the propagation of both fundamental and harmonic waves within vdW waveguides with femtosecond and sub-50 nanometre spatiotemporal precision. We focus on light propagation in slab waveguides of rhombohedral-stacked MoS2, a vdW semiconductor with large nonlinear susceptibility. Our method allows systematic optimization of nonlinear conversion by determining the phase-matching angles, mode profiles and losses in waveguides without prior knowledge of material optical constants. Using this approach, we show that both multimode and single-mode rhombohedral-stacked MoS2 waveguides support birefringent phase matching, demonstrating the material's potential for efficient on-chip nonlinear optics.

A Review on Multi-Geometrical Antenna Reflector

Parabolic antennas are among the most important devices for long-distance communications because of their significant advantages in terms of directivity, gain, and power handling capabilities. Hat feeds are frequently used as feeders for parabolic antennas because they exhibit low levels of cross-polarisation, low sidelobes, and low reflection coefficients. However, hat feeds possess a limited impedance bandwidth (IBW) range of just 30% and are not suitable for use in wideband applications. More work is being done with the objective of increasing the hat feed’s bandwidth capacity. The fundamental structure of a hat feed comprises a hat sub-reflector, circular waveguide, and dielectric material to provide structural support. The hat feeder had a bandwidth capacity of 10% at first. Later, the Chinese hat feed was introduced and used, resulting in a notable enhancement of the bandwidth, with an increase of 18%. The hat feed's geometric structure is redesigned with the help of a generic algorithm optimisation to further enhance the bandwidth, resulting in a 33% improvement.

Synthesis and optical properties of fluorinated polyurethaneimide electro-optic waveguide polymer

Fluorinated polyurethaneimide (PUI) electro-optic waveguide polymer with polyurethane and polyimide chain segment structures was synthesized by stepwise polymerization using the synthesized amino ester oligomer pu and imide oligomer pi as monomers. Since the main chain structure of the synthesized PUI had the functionality of both polyurethane and polyimide chain segment structures, it combines the excellent thermal and film-forming properties of polyurethanes and polyimides, as well as lower optical transmission loss in the near-infrared wavelength band. The glass transition temperature (Tg) of PUI was 182 °C, and the 5% heat loss decomposition temperature was 325 °C. The PUI had good optical properties with an optical propagation loss of 1.10 dB/cm and an electro-optic (EO) coefficient (γ33) of 86 pm/V at a wavelength of 1550 nm. A Mach-Zehnder interferometric polymer waveguide EO modulator had been designed and fabricated by using the PUI as a waveguide electro-optic core layer. The prepared polymer waveguide EO modulator showed a good electro-optic modulation response at a wavelength of 1550 nm under an applied 1 kHz sinusoidal modulation signal. The results showed that the synthesized PUI met the performance requirements for the preparation of polymer optical waveguide devices and was a polymer electro-optic waveguide material with good overall performance.

Quantized Dirac cones generated by one-dimensional multi-connected optical waveguide networks

This paper introduces one-dimensional (1D) limited periodic multi-connected vacuum optical waveguide networks (LPMVOWN), a fascinating class of photonic bandgap structures designed to produce Dirac cones. Unlike previously explored materials such as graphene, metamaterials, photonic crystals, and phononic crystals, optical waveguide networks produce a sequence of Dirac cones while also exhibiting quantum properties in the angular frequencies corresponding to these cone points. We used the topological translational periodicity inherent in optical waveguide networks to establish analytical relationships governing the angular frequency, slope, and number of Dirac cones generated by the system. These relationships are used to elucidate how parameters like the waveguide length ratio of the units, the number of waveguide connections, and the waveguide material influence these properties. This analysis improves our understanding of linear, degenerate, and concatenated energy band structures, as well as their potential applications. Furthermore, it offers valuable insights for enhancing the control of electromagnetic wave propagation and provides experimentalists with greater convenience and flexibility in their research endeavours.

A magnetically switchable demultiplexer via Terfenol-D in phononic crystal

This study introduces a novel approach for developing a controllable demultiplexer by applying a magnetic field to Terfenol-D cylinders within a solid–solid phononic crystal structure. Dynamic controllable demultiplexers are essential devices in acoustic and optical communication networks, yet adjustable elastic demultiplexers are notably lacking in current sound systems and acoustic communication technologies. The proposed phononic crystal-based demultiplexer features a square lattice (12 × 19) composed of tungsten cylinders embedded in a poly methyl methacrylate (PMMA) substrate. The switchable design consists of two identical, symmetrical parts separated by an input waveguide. In addition, each unit includes an output channel, a common input channel, and a square ring resonator, with the output channel side-coupled to the input bus waveguide. Moreover, Terfenol-D, a magnetostrictive material, is utilized in the hollow cylinders of the output channels. Switchability of the elastic demultiplexer outputs is achieved by dynamically altering the Young’s modulus of the Terfenol-D cylinders through the application of a magnetic field. This magnetic influence modifies the Young’s modulus of the Terfenol-D material in the output waveguides, enabling controllability. By varying the magnetic field applied to the demultiplexer, we find two distinct values of Young’s modulus within the structure. These two values facilitate the high transmission of two desirable peaks with narrow bandwidth through the output channels, allowing for switchable functionality based on the magnetic field’s position. The proposed demultiplexer demonstrates an average crosstalk value of −25.34 dB, indicating strong performance, along with a high average quality factor (Q) of 1773.5 and low average insertion losses of 0.85 dB in the MHz frequency range. The solid–solid elastic controllable demultiplexer is simulated using the finite element method, showcasing its potential for practical applications.

Multimode interference coupler based on general interference for integrated optical and quantum optic devices: a review

Integrated optics play important role in the development for optical network devices, optical processing, instrumentation and quantum information device. Here, multimode interference (MMI) coupler is one of basic component preferred for these integrated optic devices in which MMI coupler based on general interference (GIMMI) has been focused for large scale integrated optic devices because of compact size in comparison to MMI coupler based restricted interference (RIMMI). In this paper, we have reviewed different GIMMI structures reported previously. Different waveguide materials are mentioned and compared for fabrication of GIMMI device. The coupling behaviors and modal analysis of GIMMI couplers and their different tapered structures are estimated by using simple model based on sinusoidal modes showing reduced coupling lengths in down tapered structures in comparison to other structures. The excess loss, polarization dependence loss and crosstalk versus fabrication tolerances are obtained to compare their performances revealing almost same losses and fabrication tolerance. The paper reports the use of the GIMMI coupler in wavelength multiplexing, power splitting, switching, optical processing. Finally, Quantum optic application of GIMMI coupler is shown indicating high quantum fidelity of 50:50 coupling ratio.

Dynamic Dipole Moment of Luminescent Liquid Crystals Enabled Highly Efficient Active Waveguide Materials Design and Synthesis

AbstractOrganic optical waveguide materials have attracted considerable attention for their promising applications in photonic and optoelectronic devices. However, for most materials, excellent light‐loss properties at high temperature cannot be obtained due to many factors. Consequently, realizing efficient optical waveguide materials that perform well at elevated temperatures remains a significant challenge. In this study, relying on the luminescent properties and self‐assembly properties of luminescent liquid crystals (LLCs), successfully fabricated materials are present for highly efficient active optical waveguides. A systematically synthesized set of LLCs with different structures is named according to the substituent type and the position of the cyano group, namely α‐DECN, α‐DEEOCN, β‐DECN, and β‐DEEOCN. Notably, α‐DECN and β‐DECN reveal hexagonal columnar phase, while α‐DEEOCN and β‐DEEOCN exhibit smectic phase. Optical waveguide experiments have revealed that the obtained LLCs showed highly efficient optical waveguide behavior, where the lowest light loss reached 0.15 dB mm−1 at room temperature. Remarkably, these LLCs show even lower light loss at high temperatures, with the light loss reaching 0.11 dB mm−1 as the lowest point. Further experimental results indicate that this phenomenon is attributed to the change in the dipole moment of these molecules. This research forms a significant groundwork for advanced exploration in optical waveguide material.

Fabrication of high power 1.5 µm wavelength InGaAsP/InP BH lasers having dilute waveguide structure

1.5 µm wavelength high power buried heterojunction (BH) semiconductor lasers having dilute waveguide structure have been fabricated. The optical field is dragged down toward the n side of the device by the dilute waveguide layer, lowering the optical confinement factor of the p doped material and active material, which helps to enlarge the laser output light power. Compared with thick InGaAsP cladding layer, the dilute waveguide material is easy to be grown and has higher thermal conductivity. The slope efficiency of the obtained dilute waveguide BH lasers is notably higher than that of the BH lasers having no dilute waveguide. Our studies show that the dilute waveguide structure is promising for the fabrication of high power BH lasers.

Refractive index tuning and birefringence effect in crosslinked siloxane-acrylate copolymers for optical waveguide applications

Tunability of refractive index of polymeric waveguide material could be made by controlling free volume as well as polarizability of constituent materials. Two acrylate-co-polysiloxane series of different crosslinking network were synthesised by utilizing different crosslinker and monomer feeding ratio. Using Claussius-Mossotti/Lorentz-Lorentz (CM/LL) model, fractional free volumes were calculated showing a decrease in the experimental (nexp) compared to theoretical (ni) refractive indices. Curing agent with asymmetrical configuration induce a crosslink network of higher birefringence. They were respectively fabricated into multimode channel waveguide whose core-clad refractive index differences (Δn) show values in the range 0.0049–0.0408.

Flexible organic crystal with dual mechanical bending capabilities and optical waveguiding directionality

The study of organic luminescent crystal material has become a hot topic in the field of flexible optoelectronics. In this context, we report a crystal of 2,5-dihydro-3,6-bis (pentanamine) dimethyl terephthalate, which exhibits the unique property of self-doping, coupled with dual mechanical bending capabilities. Notably, the crystal exhibits optical waveguide properties, which highlights its potential application in flexible optoelectronics. In this work, through a simple "self-doping” process and controlled morphology, we obtained the synthesis of high-quality bulk organic crystals of varied sizes that not only bend elastically but also bend plastically as the molecular layer undergoes slippage. Subsequent, analysis of the crystal structure was conducted to investigate the reason for its dual mechanical bending capabilities. Our findings suggested that the optical waveguide is not only available in linear shape, elastic bending shape, and plastic bending shape, but also in large-size flake crystals. More importantly, the propagation of light in this crystal is directional owing to the anisotropy of the crystals. It is also proven that organic crystals have the potential to be applied in advanced optoelectronic devices, offering the possibility of their application as directional waveguide materials.

Fabrication and Characterization of PDMS Waveguides for Flexible Optrodes.

With the growth of optogenetic research, the demand for optical probes tailored to specific applications is ever rising. Specifically, for applications like the coiled cochlea of the inner ear, where planar, stiff, and nonconformable probes can hardly be used, transitioning from commonly used stiff glass fibers to flexible probes is required, especially for long-term use. Following this demand, polydimethylsiloxane (PDMS) with its lower Young's modulus compared to glass fibers can serve as material of choice. Hence, the long-term usability of PDMS as a waveguide material with respect to variations in transmission and refractive index over time is investigated. Different manufacturing methods for PDMS-based flexible waveguides are established and compared with the aim to minimize optical losses and thus maximize optical output power. Finally, the waveguides with lowest optical losses (-4.8dB cm-1 ± 1.3dB cm-1 at 472nm) are successfully inserted into the optogenetically modified cochlea of a Mongolian gerbil (Meriones unguiculatus), where optical stimuli delivered by the waveguides evoked robust neuronal responses in the auditory pathway.

Characterisation of optical waveguides for photonic integrated circuits

Fast signal processing at the speed of light is the main advantage of photonic integrated circuits. Therefore, these circuits have good prospects for the implementation of mathematical calculations, including matrix to vector multiplication. The purpose of the research was to create and investigate a technique for automatic measurement of brightness distribution along optical waveguides of analogue photonic integrated circuits. Empirical methods (observation, measurement, comparison, experiment) and a complex method (analysis and synthesis) have been used during the research. The proposed technique uses a digital camera that captures images of optical waveguide illuminated by light emitting diodes and image processing software to calculate brightness distribution. This technique determines the best approximation of this distribution, calculates parameters of brightness non-uniformity and losses of optical radiation. Measurements of a set of optical waveguides help to identify the best candidates for photonic integrated circuits. It has been found that optical waveguides with grinded surfaces acting as diffusive scattering have good combination of smooth brightness distribution and small losses of optical radiation. Due to multiple diffuse reflection and scattering within waveguide material, these waveguides are promising candidates for analogue photonic integrated circuits. All other waveguides with non-processed surface, with grooves or grinded with a large grain have sufficient losses of optical radiation. These losses are usually caused by the exit of optical radiation from waveguide surface. The obtained results are necessary for accurate design of circuits that takes into account scattering and losses in optical waveguides. The proposed technique can be applied in automatic technological process of manufacturing a fast and economical photonic matrix to vector multiplication, which does not require expensive electron-beam, optical or laser lithographic equipment

Power-efficient programmable integrated multiport photonic interferometer in CMOS-compatible silicon nitride

Silicon nitride (SiN x ) is an appealing waveguide material choice for large-scale, high-performance photonic integrated circuits (PICs) due to its low optical loss. However, SiN x PICs require high electric power to realize optical reconfiguration via the weak thermo-optic effect, which limits their scalability in terms of device density and chip power dissipation. We report a 6-mode programmable interferometer PIC operating at the wavelength of 1550 nm on a CMOS-compatible low-temperature inductance coupled plasma chemical vapor deposition (ICP-CVD) silicon nitride platform. By employing suspended thermo-optic phase shifters, the PIC achieves 2× improvement in compactness and 10× enhancement in power efficiency compared to conventional devices. Reconfigurable 6-dimensional linear transformations are demonstrated including cyclic transformations and arbitrary unitary matrices. This work demonstrates the feasibility of fabricating power-efficient large-scale reconfigurable PICs on the low-temperature ICP-CVD silicon nitride platform.

Synthesis and characterization of fluorinated polyurethaneimide electro-optic waveguide material with novel structure

Abstract Structurally novel fluorinated polyurethaneimide (PUI) electro-optic polymer based on chromophore molecule b, diisocyanate MDI and anhydride BPAFDA was synthesized by stepwise polymerization of oligomer PUI with fluorinated aromatic diamines BATB and BATPP. Electro-optic (EO) PUI chain structure had the structure of polyimide and polyurethane chain segments, integrating the advantages of polyimide and polyurethane. The PUI possessed good film-forming property, a high glass transition temperature (T g = 193 °C) and good thermal stability (5 % weight loss temperature T d up to 320 °C). Y-Structured inverted ridge polymer optical waveguides were designed and fabricated using the PUI as the waveguide core material. The PUI had good optical performance with an EO coefficient (γ33) of 79 pm/V and 1.1 dB/cm optical propagation loss at a wavelength of 1550 nm. The results showed that the synthesized PUI met the performance requirements for the preparation of polymer optical waveguide devices and was suitable as a polymer electro-optic waveguide material.

Silicon nitride thin-films deposited by radiofrequency reactive sputtering: Refractive index optimization with substrate cooling in a nitrogen-rich atmosphere

Silicon nitride (SiN) is widely used as a core material in optical waveguides due to its optical properties. The deposition of SiN thin-films by radiofrequency (RF) reactive sputtering is commonly used in low-temperature processes, where the thin-films optical properties can be optimized by controlling the deposition parameters (sputtering power, gases ratio, etc.). This work presents the deposition of several SiN thin-films by RF reactive sputtering with different sputtering powers (ranging from 180 W to 300 W), with a nitrogen-argon ratio of 16:4, and performing substrate cooling in a nitrogen-rich atmosphere immediately after deposition, consisting in keeping the substrate under 16 sccm of nitrogen until it reaches 25 °C. The refractive indices of the SiN thin-films were assessed through ellipsometry, obtaining a maximum refractive index of 1.906 at 400 nm. SiN thin-films were also analyzed by energy-dispersive spectroscopy (EDS) and atomic force microscopy (AFM).

An experimental investigation and multiphysics simulation of thermoelectric temperature controller for AWG chips

The refractive index of silicon-based waveguide materials is highly sensitive to temperature and stress, and the effective refractive index of the waveguide varies with temperature changes. Thus, it is critical to reduce the temperature dependence of Arrayed Waveguide Grating (AWG) devices and to precisely control the center wavelength of AWGs. In this study, the thermoelectric cooler (TEC) was designed and fabricated to control the temperature of the thermal AWG chip, which did not require any material replacement or reprocessing of the AWG chip. Different magnitudes and polarities of voltage are applied to the TEC to regulate its operational state (heating or cooling). A multiphysics simulation model of a thermal AWG device is established and validated through transient and steady-state experiments. This study investigated the influence of different conditions (input voltage, environmental temperature) on the temperature and maximum stress of the AWG chip. A conformal TEC was designed and its performance was compared with that of the square TEC. The energy consumption of the conformal TEC was also tested and analyzed. The results show that in a 25 °C ambient environment, the TEC can control the temperature of the AWG chip in the range of 1.5–78.3 °C, significantly expanding the current operational temperature range of 65.0–85.0 °C when using Positive Temperature Coefficient (PTC) heaters. Under the same conditions, when using the conformal TEC as the temperature control device, the temperature gradient on the AWG chip is reduced by 1.37 °C during cooling and 2.80 °C during heating. The maximum stress value in the core layer is always lower, with a maximum reduction of 3.61 MPa. TEC can set the ideal operating temperature of the AWG chip according to the actual operating environment of the product, which reduces the energy consumption of TEC. A comparison is made between the average power consumption of the conformal TEC and the PTC heater under two operating conditions: a 25 °C constant-temperature environment and a natural environment. The average power consumption can be reduced by up to 97.87 % and 93.02 %, respectively. This study holds significant guidance for solving the temperature dependence problem of AWG devices and the application of thermoelectric coolers in the field of optical communication.

Laser Glass deposition of single-mode glass fibers for the fabrication of chip-scale photonic circuits

The use of glass, particularly fused silica (FS), instead of polymers or semiconductors as optical waveguide material is advantageous due to broadband transmission, reduced propagation losses, and enhanced thermal and mechanical stability. In this contribution, laser glass deposition for the chip-scale fabrication of FS-based optical waveguides is investigated. We use a CO2 laser with emission at a wavelength of 10.6 µm to weld conventional single-mode glass fibers onto a FS substrate, with the aim of maintaining the waveguide properties of the fibers. Synchronized translational and rotational axis movements allow for positioning of the waveguides in arbitrary geometries. Furthermore, a CO2 laser-based cleaving method is introduced, which facilitates on-chip creation of waveguide end facets for optical coupling. An analysis of the cleave geometry in dependence on process parameters as well as optical coupling losses are presented. Coupling losses of 0.88 dB for a laser-cleave and propagation losses of 0.56 dB/cm for a 10 cm on-chip welded fiber were achieved. The results pave the way for on-chip integration of fiber-based systems like lasers, sensing devices or optical communication networks.

Constructing highly efficient and ultra-stable (against Temperature, Humidity and Sunlight) luminescent solar concentrators by using dendritic CsPbBr3@SiO2 particles

Conventional perovskite quantum dots (PQDs) suffer long-term stability, further limiting practical application of luminescent solar concentrators (LSCs). In this work, novel dendritic CsPbBr3@SiO2 particles with bright solid-state green light emission and 46 % of photoluminescence quantum yield (PLQY) have first been synthesized via one-step solid-phase calcination method. The dendritic CsPbBr3@SiO2 particles have then been used as fluorescent material for construction of LSCs along with using organosilicon polymers with better compatibility as waveguide materials. Single-layer thin film LSCs and overall curing LSCs are easily prepared by the casting and curing method, exhibiting high external optical efficiency (ηopt) of 7.88 % and 10.92 %, respectively. The maximum internal quantum efficiency (ηint) of thin film LSCs and overall curing LSCs reach 45.09 % and 44.07 %, respectively, while their maximum external quantum efficiency (ηext) of 29.42 % and 34.07 % are obtained, respectively. Importantly, both types of LSCs show excellent stability, maintaining above 92 % of the initial ηopt under high-relative-humidity (RH = 90 %), high-temperature (60 °C) and sunlight exposure conditions for two weeks or room temperature environment for twenty weeks. Moreover, both types of LSCs at optimal conditions have good transparency (>40 % over 515 nm of light wavelength). Otherwise, both types of LSCs have higher ηopt than that of the previous related work.

Process optimization of infrared chalcogenide glass based on the scattering detection

Chalcogenide glasses with less optical losses are highly demanded as optical materials for micro lense, waveguide and fiber devices. However, it is still challengeable to reduce the optical losses in infrared chalcogenide glasses with opaque visible light. Herein, an improved 3D distribution of scattering sources is established in this study to test and compare the concentration and distribution of defects in As38S62, Ge28Sb12Se60 and As40Se60 chalcogenide glasses. Furthermore, by comparing the scattering images of serial As40Se60 glass prepared under various melting, quenching and annealing temperatures, the preparation process was optimized to reduce its scattering loss. In addition, this study introduced a scheme that could be widely applied to optimize processing of other infrared glasses and devices glass to reduce their scattering losses.

Design and optical waveguide behavior of full-color emitting materials with adjustable band gap

Optical waveguide materials that span the entire visible spectrum is paramount for the efficacious operation of photon transmission devices in many contexts. Notably intriguing is the use of manipulating the band gap to finely modulate chromatic diversity within the luminous material. In this context, we synthesized three distinct organic small molecules, employing carbazole's inherent proclivity as the electron donor, while engaging thiophene, pyrimidine, and fluorenone as adept electron acceptor moieties. Evidently, our investigation unveiled a remarkable metamorphosis in the emitted fluorescence, wherein the chromatic spectrum transitions from blue to green, and subsequently to orange, as the electron acceptor group's capacity for electron absorption diminishes. Interestingly, the three materials manifest an inherent propensity for facile preparation into one-dimensional nanostructures, characterized by smooth surfaces, concurrently exhibiting commendable performance as optical waveguides. Our findings deepen a comprehensive understanding of the design of materials with the full visible spectrum, which might lead to innovations in the design of photonic integrated structures.