Output Waveguide Research Articles

Temperature Dynamics in Rat Brains Exposed to Near-Field Waveguide Outputs at 2.8 GHz.

Biological effects in the microwave band of the radiofrequency (RF) spectrum are thermally mediated. For acute high-power microwave exposures, these effects will depend on transient time-temperature histories within the tissue. In this article, we summarize the transient temperature response of rats exposed to RF energy emanating from an open-ended rectangular waveguide. These exposures produced specific absorption rates of approximately 36 and 203 W/kg in the whole body and brain, respectively. We then use the experimentally measured thermal data to infer the baseline perfusion rate in the brain and modify a custom thermal modeling tool based upon these findings. Finally, we compare multi-physics simulations of rat brain temperature against empirical measurements in both live and euthanized subjects and find close agreement between model and experimentation. This research revealed that baseline brain perfusion rates in rat subjects could be larger than previously assumed in the RF thermal modeling literature, and plays a significant role in the transient thermal response to high-power microwave exposures. © 2021 Bioelectromagnetics Society.

Compact low-loss low-crosstalk echelle grating demultiplexer on silicon-on-insulator for CWDM

This letter reports on the design of an ultra-compact echelle grating (EG) demultiplexer in O-band for Coarse wavelength division multiplexing (CWDM) systems based on silicon-on-insulator (SOI) and proposes an optimization idea. The correlation between optical performance and design parameters of EG device is analyzed based on the theory of Finite-difference time-domain (FDTD), providing a more accurate optimization reference. Further optimization is achieved by secondary adjustment of the blaze angle of grating facets and the position of output waveguides according to the simulated field distribution. The device has four channels with channel spacing of 20 nm and a small footprint of only 140×100 µm2. The simulated insertion loss for all channels is lower than 2 dB with insertion loss uniformity of below 1dB, and the crosstalk is better than 40 dB.

Nonreciprocal photonic composited Su–Schrieffer–Heeger chain

We explore nonreciprocity based on the topological zero modes of a finite asymmetric composited Su–Schrieffer–Heeger (SSH) chain composed of spinning ring cavities theoretically. Here, the first cavity on the short side is designed as a rotating cavity, whose frequency is related to the transmission direction of the light due to the Fizeau light-dragging effect. There are two topological edge modes (TEMs) and one topological interface mode in the middle of the bandgap for the composited SSH chain. The structural asymmetry reduces the transmittance of the system significantly due to symmetry breaking of the field distribution induced for the three modes. However, a small amount of frequency shift of the rotating cavity by Fizeau drag can greatly increase the transmittance by compensating the asymmetry of the structure for one TEM. Therefore, by introducing the input and output waveguides to couple the two outermost ring cavities, we construct an efficient nonreciprocal chain (the maximum isolation ratio can exceed 50 dB) with significant characteristics of monochromaticity and robustness in a narrow frequency range. Moreover, we prove that choosing appropriate system parameters can reduce the requirements of frequency shift. Our work combines nonreciprocity and one-dimensional topological structure organically and provides a scheme to achieve long-range nonreciprocity with topological protection, which is a crucial element in the classical and quantum technologies of computing and information.

Refractive Index Sensor for Detection of N2, He and CO2 Gases based on Square Resonance Nanocavity in 2D Photonic Crystal

In this work, the design and simulation of high-sensitivity gas optical sensor (GOS), based on photonic crystals with refractive index different of linear materials is presented. The lattice index is cubic and the dielectric rods are made of silicon and are designed in a square shape. In the proposed optical sensor, three resonance nanocavities are used, the central nanocavity is made of silicon with a refractive index of nSi = 2.6, and the sub-nanocavities located in the path of the input waveguide and the output waveguide This optical sensor is able to detection of N2, He and CO2 gases from the air. Numerical simulation results are obtained using two-dimensional FDTD method. The use of three resonance nanocavities and the distances between the dielectric rods increased the sensitivity and quality factor of the structure. The proposed optical sensor has a sensitivity of S = 400 nm/RIU and a quality factor of Q.f = 1080.615, and the power transmission is about TE = 100%. The figure of merit is equal to FOM = 258.333 ± 8.333 RIU-1. It is designed to integrate the structure with small dimensions as much as possible. The overall dimensions of the structure are 72.6 µm2, which can be easily used in optically integrated circuits

Compact full‐color laser beam scanning image projector based on a waveguide‐type RGB combiner

AbstractA packaged red‐green‐blue (RGB) laser module based on a waveguide‐type combiner is demonstrated. The module has characteristic features such as (a) a compact size and lightweight, (b) almost perfectly aligned RGB laser beams owing to a single waveguide output, and (c) a configuration with only a few mechanical elements. The typical package size is 10 × 5 × 5 mm for an outside focusing lens type and 11 × 4.8 × 3 mm for an inside focusing lens type. Light intensity monitors and a temperature monitor are also equipped for the inside focusing lens type.Furthermore, a compact RGB laser beam scanning module is demonstrated. Clear full‐color high‐definition video images are obtained. Thus, these modules based on waveguide‐type combiners can provide compact imaging projectors with clear images. Compact Lidar scanners and laser sources for various sensors are also candidate applications.

Design and two-photon direct laser writing of low-loss waveguides, tapers and S-bends

Despite the rapid developments in the field of two-photon polymerization-based direct laser writing, limited attention has been paid to the efficient design of optical waveguide-based building blocks. To fill that gap, we have numerically investigated air-clad waveguides, tapers, and S-bends, with the aim to minimize insertion losses, whilst reducing the device sizes. We have first demonstrated waveguides with square and circular cross-sections that are mode-matched with single-mode optical fibers featuring insertion losses below −0.6 dB and −1.5 dB around 1550 nm for lengths of respectively 0.2 mm and 1 mm. We have also identified parabolic tapers that allow for adiabatic transition between a wide range of input and output waveguide sizes. These shapes allow, for example, tapering down from 15 µm to 2 µm diameter waveguides over a length as short as 43.2 µm. We have fabricated a series of such components and confirmed their nearly lossless performance with insertion loss measurements. Finally, we have designed and optimized S-bends with Bezier curve shapes. As a proof-of-principle demonstration, we have fabricated a 160 µm long S-bend that offsets the waveguide axis by 50 µm. The insertion loss of the resulting 400 µm long component, which also included two parabolic tapers, was less than −1.7 dB. Apart from providing design rules and ready-to-use recipes for fabricating low-loss 3D-printed waveguide-based building blocks, we project that our work will spark the development of a series of efficient photonic devices that rely on these components and that can be exploited in diverse application fields.

Quasi-linear response of an integrated optical waveguide sensor by a double output readout method

This paper reports quasi-linear response of the signal with cantilever deflection for an integrated optical waveguide biosensor by a double output readout method. The readout method uses a double output waveguide structure to divide the received light into two power signals, further for achieving the differential signal as the operating signal. With this method, the operation signal has a good monotonicity with cantilever deflection in range of ± 0.4 µm.

Characterization Techniques of Millimeter-Wave Orthomode Transducers (OMTs)

We report on advanced techniques for the accurate characterization of millimeter-wave Orthomode Transducers (OMTs) enabling the derivation of the fundamental parameters of such devices, i.e., the insertion loss, the return loss, the cross-polarization, and the isolation. These techniques include standard frequency-domain and time-domain VNA (Vector Network Analyzer) measurement methods, which can be applied to remove the effects of the waveguide transitions necessary to access the OMT ports and excite the desired modes. After reviewing the definition of the OMT parameters, we discuss the test equipment, the VNA calibration procedures as well as the VNA time-domain time-gating method for application in OMT characterization. We present simplified equations that relate the calibrated VNA measured quantities with the OMT S-parameters, illustrate various characterization methods, and examine various OMT experimental test setups. The advantages and disadvantages of each of the OMT characterization procedures are presented and compared among them. We provide a list of waveguide components required in the OMT test setups (adapters, loads, quarter-wave and longer waveguide sections, feed-horn, etc.), discuss the error terms introduced by such components and examine their impact on the measured values. Furthermore, we identify strategies to mitigate or remove the effects of the measured errors, to derive the desired OMT parameters. Different OMT configurations, with a distinct orientation of the waveguide input and outputs, are discussed. Although the presented techniques refer to the characterization of a specific configuration of a W-band OMT, the described methods can be applied to other OMT configurations and frequency ranges (from microwave to THz frequencies), therefore having a general validity.

Highly-efficient waveguide-type red–green–blue laser beam combiners for compact projection-type displays

A waveguide-type RGB laser beam combiner was fabricated and its optical properties were measured and analyzed through comparison with a simulation. The combiner has three different waveguides for RGB light inputs, three directional couplers, and a single output waveguide. The fabricated combiner shows an excellent multiplexing efficiency of as high as 96.4%. The size of the multiplexing region of the fabricated combiner is as small as 2.3 mm. Furthermore, by optimizing the combiner structure, it was found that the multiplexing efficiency hardly depends on the gap width of the directional coupler in the combiner. The polarization dependence of the multiplexing efficiency was also measured. The difference in multiplexing efficiency between the TE and TM modes is within 4% when using the optimized combiner structure, demonstrating the small polarization dependence of the multiplexing efficiency. Thus, the fabricated combiner exhibit’s high performance, as well as excellent fabrication reproducibility, leading to the realization of compact laser scanning image projectors.

Efficient tunable plasmonic mode converters infiltrated with nematic liquid crystal layers

This paper presents two efficient tunable plasmonic mode converters in the infrared regime. The proposed configurations consist of silver layer with etched rectangular holes as metal insulator metal waveguides with central cavities. The holes are infiltrated by nematic liquid crystal (NLC) material to increase the transmission through the suggested designs. Additionally, the NLC is used to have tunable operation where the modes at the output port can be controlled. The simulations are carried out using full vectorial finite element method. The first design has a single output port which converts the TM mode into the TEM mode with high transmission conversion efficiency of 70%. Further, the second structure allows the generation of the two plasmonic modes simultaneously in two output waveguides. During the biased state, the s- mode transmission conversion efficiency reaches 50% while the transmission of a- mode at the unbiased state is equal to 49%. It is expected that the proposed tunable mode converters will play an important role in the development of the plasmonic-photonic circuits.

Design, simulation and characterization of integrated photonic spectrographs for astronomy: generation-I AWG devices based on canonical layouts.

We present an experimental study on our first generation of custom-developed arrayed waveguide gratings (AWG) on a silica platform for spectroscopic applications in near-infrared astronomy. We provide a comprehensive description of the design, numerical simulation and characterization of several AWG devices aimed at spectral resolving powers of 15,000-60,000 in the astronomical H-band. We evaluate the spectral characteristics of the fabricated devices in terms of insertion loss and estimated spectral resolving power and compare the results with numerical simulations. We estimate resolving powers of up to 18,900 from the output channel 3-dB transmission bandwidth. Based on the first characterization results, we select two candidate AWGs for further processing by removal of the output waveguide array and polishing the output facet to optical quality with the goal of integration as the primary diffractive element in a cross-dispersed spectrograph. We further study the imaging properties of the processed AWGs with regards to spectral resolution in direct imaging mode, geometry-related defocus aberration, and polarization sensitivity of the spectral image. We identify phase error control, birefringence control, and aberration suppression as the three key areas of future research and development in the field of high-resolution AWG-based spectroscopy in astronomy.

Enhancing the impedance matched bandwidth of bottle microresonator signal processing devices.

Light pulses entering an elongated bottle microresonator (BMR) from a transversely oriented input-output waveguide (microfiber) slowly propagate along the BMR length and bounce between turning points at its constricting edges. To avoid insertion losses and processing errors, a pulse should completely transfer from the waveguide into the BMR and, after being processed, completely return back into the waveguide. For this purpose, the waveguide and BMR should be impedance matched along the pulse bandwidth. Here we show how to enhance the impedance matched bandwidth by optimization of the BMR effective radius variation in a small vicinity of the input-output waveguide.

Design and modeling of a photonic integrated device for optical vortex generation in a silicon waveguide

We propose and numerically verify a design of the photonic integrated circuit for in-plane generation of a 1st azimuthal order vortex mode in dielectric rectangular waveguides. Radiation is introduced into the proposed structure in a standard way through two grating couplers. Applying a mode coupling and specific phase shift, a field with the required amplitude-phase distribution is formed directly in the output waveguide. The geometric dimensions of the device are simulated and optimized to fit the technological parameters of the silicon-on-insulator platform.

Magnetically controlled three-channel phononic switch

This study includes the design procedure of a novel three-channel switch based on solid–solid phononic crystals. This elastic switch is externally controlled by the magnetic field. Proposed 1 × 3 switch is designed using Young’s modulus variations (ΔE effect) of magnetostrictive materials due to change in the magnetic field intensity. The change in the elastic constant shifts the defect mode frequency position. A fundamental phenomenon in this switch is the major frequency shift, which is equal to 100 kHz for Terfenol-D Young’s modulus reduction of 18%. It should be noted that this frequency shift occurs in presented phononic structure with a lattice constant equals to 500 μm. The major frequency shift is due to Terfenol-D high sensitivity to the magnetic field and using the hollow cylinders in output waveguides of structure. The elastic switch simulation is accomplished by finite element method. The crosstalk worst case in the proposed switch is −17 dB, which shows the device suitable performance.

Optical switch with ultra high extinction ratio using electrically controlled metal diffusion.

An optical switch with ultra high extinction ratio is proposed. Optical switching is realized using the resistive switching effect through the lateral coupling between the input nanophotonic waveguide and output waveguide at a wavelength of 1550 nm. The coupled waveguide system is engineered to increase the number of mode beats in a unit length of the device. An increase in the number of mode beats and controlled diffusion of metal ions through a thin dielectric layer with an applied electric field is responsible for a high optical extinction ratio of 27 dB for a 20 µm long device. Compared to electrical control by plasma dispersion in silicon, the resistive switching effect enables a reduction in the coupling length and an increase in the waveguide absorption, leading to an almost 100 times higher extinction ratio. The proposed compact on-chip silicon-based nanophotonic resistive device is a potential candidate for a large-scale integrated photonic circuit for applications in optical switching, modulation, memory, and computation.

Design Plasmonic Optical 4 × 2 Encoder Based on 2D Photonic Crystal Ring Resonator

Digital encoders are one of the key devices required in optical communication and digital signal processing systems. In this paper, a new photonic crystal structure is used to design all-optical 4 × 2 encoder constructed from GaAs rods with square lattice in the pentane background based on plasmonic effect. Gold rods have also been used at the interface of dielectric rods and lines defect, which create plasmonic properties into the photonic crystal structure. The designed optical device is composed of four input waveguides and two output waveguides with two ring resonators at the resonant wavelength of 1.14 μm with TM polarization. The presented encoder platform has the small size of 19 μm × 33 μm that makes it to integration into compact all-optical processing systems. The encoder operation is simulated and analyzed with numerical finite-difference time-domain (FDTD) method and plane wave expansion (PWE) method. In the proposed structure, we have shown that by selecting the appropriate radius size for the resonant cavities, the desirable wavelength can be obtained. The maximum values of transmission efficiency for the first and second outputs are 82% and 96%, respectively. Resonant cavities are also located in the crystal lattice in such a way that by activating third input, 50% and 48% of the input signal will be obtained in each output ports indicating (1,1) logic state. So the new plasmonic photonic crystal encoder could be future applicable in the field of optical computing.

A novel metamaterial gain-waveguide nanolaser

Researchers in silicon photonics have been searching for suitable and efficient light-emitting sources that are compatible with silicon-on-insulator technology. In this work, a novel continuous-wave silicon compatible metamaterial nanolaser was designed and numerically demonstrated. This novel nanolaser was constructed around a new metamaterial traveling-wave gain-waveguide, which was placed in line with silicon-on-insulator input and output waveguides, and lases at 1550 nm (i.e., in the telecom range) when pumped at 800 nm. The metamaterial waveguide consists of periodic and alternating nanoscale gain stripes (InGaAsP) and air gaps. It supports fundamental single-mode propagation for both pump and laser signals. It can efficiently couple light into the input and output silicon waveguides. The laser gives simultaneous forward and backward outputs. Besides, the metamaterial allows for efficient pump-power absorption and laser emission, which results in an almost ideal internal quantum efficiency (≅99.1%), low lasing threshold (≅200 µW), very good lasing slope efficiency (≅43.5%), and narrow laser linewidth (≅0.88 nm).

Design optimization of silicon-based 1.55 μm InAs/InGaAs quantum dot square microcavity lasers with output waveguides

We optimize the structure of a silicon-based InAs/InGaAs quantum dot square microcavity laser with an output waveguide structure. By designing a new laser structure, the emission wavelength is extended to 1550 nm. We investigate the structure parameters that affect the quality factor and optical mode of the square microcavity, including the side length of the microcavity, the width of the output waveguide, the cladding layer thickness and the etching depth. By connecting the output waveguide at the edge-midpoint of the square microcavity, both the unidirectional emission and mode selectivity can be obtained, which avoids mode competition. The 1550 nm wavelength single-mode laser is beneficial and has reat significance for the development of silicon-based optoelectronic integration.

30‐3: Student Paper: Polarization State Exploration and Management in Waveguide Display with Polarization Volume Gratings

In this work, we focus on the polarization state input, propagation and output of waveguide display device using polarization volume holographic gratings (PVH) as couplers. First, a detailed study of the transmissive PVH (T‐PVH) is presented in terms of diffraction efficiency, polarization selectivity and polarization output, which is expected to be used as the waveguide input/output couplers. The configuration here called “Slanted T‐PVH” has the advantageous property of maintaining orthogonal circular output polarization states. Then, the polarization state management of light propagating in waveguide is considered. The issue that the polarization state of the light can change as it propagates in the waveguide due to total internal reflection (TIR) is made clear, that has a negative effect on the waveguide PVH input/output couplers efficiency, image uniformity, and the polarization multiplexing capability. Finally, it is shown that applying compensators to correct the polarization state change can solve the polarization state change in a waveguide.

Investigation and suppression of asymmetric modes competition in Cerenkov device by conductivity anisotropic material loading

Efficient and stable operation of Cerenkov devices relies on effective mode control, which means efficient generation of the operation mode and effective suppression of the competition modes. This paper explores the feasibility of suppressing asymmetric modes by loading a conductivity anisotropic material in Cerenkov devices. We theoretically study the dispersion characteristics of a slow-wave structure (SWS) loaded with a conductivity anisotropic material. The theoretical analyses indicate that asymmetric modes such as the HE11 mode have a low net temporal growth rate in a SWS coaxially loaded with the anisotropic material, of which the azimuthal conductivity is in the transition region from good to poor conductor. Accordingly, an anisotropic material with suitable azimuthal conductivity effectively suppresses asymmetric mode competition while maintaining the original characteristics of the symmetric TM modes. Furthermore, we numerically investigate the effectiveness of asymmetric mode suppression by anisotropic material loading using a 3D particle-in-cell CHIPIC code. A coaxially loaded conductivity anisotropic material effectively suppresses the asymmetric HE11 mode in a Ku-band Cerenkov device, and a pure quasi-TEM mode is obtained in the output waveguide. The output power of the generator is 2.9 GW, and the efficiency is 44%. This study provides a feasible method to eliminate asymmetric modes in Cerenkov devices, which may lead to a wide range of applications.