Horizontal Waveguide Research Articles

Analysis of BCB and SU 8 photonic waveguide in MZI architecture for point-of-care devices

The proposed refractive index-based biosensor made of cost-effective polymer material in Mach-Zehnder configuration with novel horizontal slot waveguide structure offers high sensitivity. Due to the recent demand for low-cost point-of-care biosensor, silicon wafer-based polymer material has the potential for developing new hybrid waveguides for sensors. Hence we designed BenzoCycloButene (BCB), SU8 material as the core, and polymethyl methacrylate (PMMA) clad on a silicon wafer. The novelty of proposed BCB and SU8 horizontal slot waveguide structure of 2.5 μ m wide and 1.8μ m thick with a slot height of 400 ​nm, which handles the analyte effectively without any external sample holder. In Mach-Zehnder Interferometer architecture, reference arm 1 ​cm and sensing arm at a length of 1.1 ​cm with analyte refractive index of cancer cell (RI ​= ​1.401) and Influenza A type virus (RI ​= ​1.48) are used. Effective mode index of BCB core and SU8 are investigated through Finite-difference time domain (FDTD) analysis, and sensitivity results are calculated. Detection of disease are plotted in the transmission spectrum with reference to normal human serum (RI ​= ​1.35). This horizontal slot waveguide of BCB core achieves a sensitivity of 19280 nm/RIU and SU8 horizontal slot core waveguide provides a sensitivity of 16500 nm/RIU, which is higher in this polymer based refractive index biosensing.

Efficient mode (de)multiplexer with two cascaded horizontal polymer waveguide directional couplers.

In this paper, we present an efficient polymer two-mode (de)multiplexer with two cascaded horizontal waveguide asymmetric directional couplers (ADCs). Through extensive simulations, the optimized waveguide core dimensions were determined, and the distance L from the starting position of the first ADC to the cascaded position was 35300 µm. With the cascaded ADCs, the E21x mode of the wider waveguide was coupled into the E11x mode of the narrower waveguide with a coupling ratio of 96.73% at 1550 nm when the separation between the waveguide cores was 5 µm. The coupling ratio and extinction ratio of the fabricated (de)multiplexer reached a maximum of 96.12% and 14.21 dB at 1540 nm, respectively. The coupling ratios were greater than 90% in the wavelength range 1533-1565 nm with a minimum insertion loss of 9.75 dB. The influence of different cascaded positions on the mode coupling ratio, mainly caused by the large phase difference between the modes owing to the slowly varying envelope approximation, is analyzed theoretically and verified experimentally. The proposed cascaded two-mode (de)multiplexer can reduce the preparation process requirements and increase the channel capacity of optical communication systems.

Design of a low power silicon-plasmonic hybrid electro-optic modulator relied on ITO

In this paper, a low power silicon-plasmonic hybrid electro-optic modulator relied on Indium Tin Oxide (ITO) has been proposed and designed. The proposed modulator is based on a three-coupled waveguide; two silicon waveguides and one hybrid plasmonic waveguide. A hybrid plasmonic horizontal waveguide with two ITO layers separates two silicon waveguides. Balancing between extinction ratio (ER) and insertion loss (IL) requires a trade-off when designing an optical modulator. The structure is proposed as a modulator that alleviates this trade-off. The structure has two ITO layers with an epsilon near zero (ENZ) effect for increasing light-matter interaction, maximizing optical mode's attenuating and disrupting the optical coupling. In the designed structure, amplitude modulation with high ER and, at the same time, low IL are obtained. The designed device is broadband with low power consumption. The ER, IL, and power consumption values were 16.05 dB, 0.3 dB, and 16.2 fJ. The finite-difference time-domain (FDTD) method is used to investigate the properties of the proposed modulator.

Plasmonic Tamm states in periodic stubbed MIM waveguides: analytical and numerical study

We investigate both analytically and numerically the existence of localized surface modes, the so-called plasmonic Tamm states (PTSs), in a new and versatile platform based on a periodic array of metal-insulator-metal (MIM) stubs grafted along a MIM waveguide. By considering a semi-infinite structure in which we modify the length of the segment at the surface, we show the existence of surface states inside the bandgaps of the periodic structure and investigate the dependence of the localized modes as a function of the geometrical parameters and the boundary conditions applied at the surface. Three types of surface boundary conditions are considered, namely, two limiting cases of zero surface impedance (or perfect electric conductor), infinite surface impedance (or perfect magnetic conductor), and a third case where the structure is in contact with a real metal. In the latter case, we show that the existence of the interface state can be demonstrated based on topological arguments using the Zak phase. We also demonstrate that if a finite size comb-crystal is vertically grafted along a horizontal waveguide, the PTSs can be detected from the dips in the amplitudes of transmission and reflection coefficients as well as from the peaks in their delay times and the local density of states (LDOS). Our theoretical study is first performed analytically with the help of a Green’s function method, which allows the calculation of the dispersion relations of the bulk and surface modes and the LDOS, as well as the transmission and reflection coefficients of the plasmonic comb-like structure. Then, these results are confirmed by a numerical simulation utilizing a 2D finite element method. Besides providing a deep physical analysis of the PTSs, our work demonstrates the capability of the analytical method as a predictive approach in more complex structures. The proposed designs in this paper can be useful to realize highly sensitive plasmonic nanosensors.

Compact and efficient three-mode (de)multiplexer based on horizontal polymer waveguide couplers.

A compact and efficient polymer three-mode (de)multiplexer with two cascaded waveguide directional couplers fabricated on the same substrate along the horizontal direction is proposed. Three waveguides formed two couplers, where two narrower waveguides were placed on either side of the central waveguide. By optimizing the core height and width, the two couplers can ensure that the E11x mode of the two narrower waveguides are highly coupled into the E21x and E31x modes of the central waveguide at a wavelength of 1310 nm. The structural size of the fabricated three-mode (de)multiplexer using ultraviolet (UV) lithography technology is in agreement with the designed value. The fabricated device, which is 35 mm long, exhibits coupling ratios of 98.07% and 95.43% for the two couplers, respectively. The insertion losses of the three waveguides are 5.23 dB, 8.58 dB, and 14.39 dB, respectively. The device can achieve the multiplexing of three modes in two dimensions, which can increase the channel capacity of optical communication.

Study and Simulation of a Sensor Based on 2D Photonic Crystals for the Detection of Aromatic Compounds: C6H5I, C6H5F and C6H5Cl

A new study was presented on a new sensor based on two-dimensional photonic crystals (Phc's) to detect the following three organic materials: iodobenzene (C6H5I), fluorobenzene (C6H5F), chlorobenzene (C6H5Cl). These materials have dielectric constants (εr) equal to 2.623; 2.140; 2.318, respectively. The proposed sensor is a structure made of silicon rods submerged in air plus a ring resonator. The ring resonator is stuck between two horizontal waveguides. At the end of the ends of the structure there are four ports where port 1 and 2 belong to the top guide and port (3) and (4) the bottom one. In order to analyze the behavior of the sensor, a plane wave expansion approach (PWE) and the finite element method (FEM) are applied. Thanks to the MATLAB and COMSOL simulation software, we were able to obtain the following numerical results: the norm of the electric field, the total energy density and this last magnitude according to the refractive indices of the different organic materials used. We could observe variations in energy density for each material. So, this change is due to their refractive index which varies from one material to another. In this study, we have fixed the other parameters like the constant of the lattice "a" and the radius "r" and we are interested in the dielectric constants (εr) or more precisely the refractive index (n), the latter proves that it is one of the important parameters for detection.

Fano Resonance Using Surface Plasmon Polaritons in a Nano-disk Resonator Coupled to Perpendicular Waveguides for Amplitude Modulation Applications

In this paper, an all-optical plasmonic modulator is proposed. The structure consists of an InGaAsP nano-disk resonator, surrounded by a Si ring-shaped resonator which is located inside a circular cavity, and two perpendicular metal–insulator-metal plasmonic waveguides. The structure also contains a graded stub filter to separate the control signal from the data signal at the output port. The horizontal and vertical waveguides are used for data and control signals, respectively. Using two separate waveguides for data and control signals causes a suitable isolation between two such signals. The finite-difference time-domain (FDTD) method is used for numerical investigation of the proposed structure, and we use a very detailed Drude-Lorentz model for modeling Ag. To provide more insight, the time-domain behavior of the designed amplitude modulator is also investigated. It is worth mentioning that the Kerr effect is used to modulate the data signal. The most remarkable advantages of the proposed structure are high extinction ratio, isolated data and control ports, low pump intensity, tunable data wavelength, small footprint, and simple structure. Based on the mentioned properties, this modulator has the potential to be used in complex integrated optical circuits.

Demonstration of a Polymer-Based Single Step Waveguide by 3D Printing Digital Light Processing Technology for Isopropanol Alcohol-Concentration Sensor

A polymer based horizontal single step waveguide for the sensing of alcohol is developed and analyzed. The waveguide is fabricated by 3-dimensional (3D) printing digital light processing (DLP) technology using monocure 3D rapid ultraviolet (UV) clear resin with a refractive index of n = 1.50. The fabricated waveguide is a one-piece tower shaped ridge structure. It is designed to achieve the maximum light confinement at the core by reducing the effective refractive index around the cladding region. With the surface roughness generated from the 3D printing DLP technology, various waveguides with different gap sizes are printed. Comparison is done for the different gap waveguides to achieve the minimum feature gap size utilizing the light re-coupling principle and polymer swelling effect. This effect occurs due to the polymer-alcohol interaction that results in the diffusion of alcohol molecules inside the core of the waveguide, thus changing the waveguide from the leaky type (without alcohol) to the guided type (with alcohol). Using this principle, the analysis of alcohol concentration performing as a larger increase in the transmitted light intensity can be measured. In this work, the sensitivity of the system is also compared and analyzed for different waveguide gap sizes with different concentrations of isopropanol alcohol (IPA). A waveguide gap size of 300 µm gives the highest increase in the transmitted optical power of 65% when tested with 10 µL (500 ppm) concentration of IPA. Compared with all other gaps, it also displays faster response time (t = 5 seconds) for the optical power to change right after depositing IPA in the chamber. The measured limit of detection (LOD) achieved for 300 µm is 0.366 µL. In addition, the fabricated waveguide gap of 300 µm successfully demonstrates the sensing limit of IPA concentration below 400 ppm which is considered as an exposure limit by “National Institute for Occupational Safety and Health”. All the mechanical mount and the alignments are done by 3D printing fused deposition method (FDM).

Plasmonic all-optical metal–insulator–metal switches based on silver nano-rods, comprehensive theoretical analysis and design guidelines

In this paper, all-optical plasmonic switches are proposed and analyzed. These structures consist of a rectangular resonator filled with a Kerr-type material (AuSiO2) which is coupled to isolated metal–insulator–metal plasmonic waveguides. The resonators contain periodic arrays of nano-rods with rectangular and triangular patterns. The horizontal and vertical waveguides are used for data and control signals, respectively. Using two separate paths for the data and control signals results in suitable isolation between the signals. The finite difference time domain (FDTD) method is used for numerical investigation of the designed structures. To provide more insight, the FDTD results of the building blocks of the switches are compared with transmission line method results. The most important benefits of the proposed topologies are requiring lower pump intensities, needing smaller footprints and having isolated data and control ports. The proposed switch needs a pump intensity equal to 193.2 mW/μm2 and requires a 0.593 μm2 footprint area. A 11.3 dB contrast ratio exists between the On and Off states of the switch. Based on the mentioned advantages, these switches have the potential to be used in complex integrated optical circuits.

Enhancing CO2 photo-biochemical conversion in a newly-designed attached photobioreactor characterized by stacked horizontal planar waveguide modules

Aiming at alleviating the adverse effects on attached microalgae biofilm growth caused by heterogeneous spatial light distributions within the attached cultivation photobioreactors (PBRs), an innovative PBR integrated with stacked horizontal planar waveguide modules (SHPW-PBR) was proposed in this work. Different from the conventional PBR, the emergent light from the external LED light bars were guided and evenly redistributed within the SHPW-PBR by the planar waveguides and hence provided light energy for microalgae cells photoautotrophic growth. In comparison with the control PBR, the average light intensity illuminating the attached Chlorella vulgaris biofilm in the SHPW-PBR was elevated by 204.11% and contributed to a 145.20% improvement on areal C. vulgaris biofilm production. Thereafter, responses of attached C. vulgaris biofilm growth in the SHPW-PBR to various light intensities were evaluated and the maximum areal C. vulgaris biofilm density reached 90.43 g m−2 under the light intensity of 136 μmol m−2 s−1 after 9 days cultivation. Furthermore, the SHPW-PBR can be easily scaled-up by increasing the quantity of the stacked planar waveguide modules and thus shows great potential in biofilm-based biomass production.

Efficient adjustable light couplers of integrated III-V nanowire emitters on silicon waveguides based on ring resonators.

The development of integrated vertical III-V nanowire (NW) stimulated emitters in silicon photonics while achieving an efficient light coupling through vertical III-V NW lasers into horizontal optical silicon waveguides is demanding. This is mainly due to the directionality and contradiction of the simultaneously satisfied low threshold stimulated emission conditions of the vertical NWs and efficient light coupling from the NW emitters into the horizontal silicon waveguide. However, we propose a new, to the best of our knowledge, design by taking advantage of resonating features of ring structures and theoretically demonstrate that an interfacial ring resonator between GaAs NW emitters and the silicon waveguide achieves a coupling efficiency up to about 70% at a given wavelength. We also show that the interfacial resonator enables us to adjust the coupling efficiency from about 10% to over 70%. The adjustable coupling efficiency might also be a solution to compromise between the low threshold stimulated emission of NWs and efficient light coupling for realizing efficient silicon couplers based on integrated III-V NW lasers in silicon photonics. Besides the simple fabrication process compared to counterparts, we believe that the novel structure is promising for future optical on-chip data communication in silicon photonics, and the results are expandable to varying wavelengths and materials.

Realization of a plasmonic optical switch using improved nano-disk resonators with Kerr-type nonlinearity: A theoretical and numerical study on challenges and solutions

In this paper, a novel all-optical plasmonic switch is presented. For the proposed structure, a nano-disk resonator coupled to parenthesis-shaped adjunctions and perpendicular metal–insulator–metal waveguides are used. The insulator which is used here, is an optically nonlinear Kerr-type material (InGaAsP). The data and control pulses are injected to the horizontal and vertical waveguides, respectively. Allocating two separate waveguides for the data and control signals prevents these signals from interfering with each other. One of the main benefits of the proposed switch is that a single wavelength can be used for the data and control signals. It prevents the amplitude modulation of the output signal and eliminates the need for harmonic suppression filters. The finite difference time domain (FDTD) method is used for numerical investigation of the switch. Based on the numerical simulations, the switch can operate for control pulses as narrow as 3 ps at 1028 nm. In addition to FDTD, analytical formulas have also been presented to model the switch, which are in excellent agreement with FDTD results. To provide a better perspective, besides the conventional frequency domain analysis, the time domain simulations are also presented. The main advantages of the proposed topology are: the ability to use an identical wavelength for data and control pulses (which originates from the novel resonator shape), having separate and isolated input and output data and control ports, requiring a small footprint area of 1.37μm2, the simplicity of fabrication due to its simple and symmetric structure and finally the robustness of the design, where other nonlinear materials with higher Kerr indices can also be easily used to redesign the switch.

Compact and low-power all-optical surface plasmon switches with isolated pump and data waveguides and a rectangular cavity containing nano-silver strips

Abstract In this paper, a plasmonic all-optical switch based on a novel topology is presented. The structure is composed of a rectangular cavity coupled with two cross waveguides. Several silver strips with a tapered pattern are inserted in the rectangular cavity to create a sharp edge in the transmission spectrum of the data signal. The cavity and waveguides are filled with a non-linear insulator with high Kerr-type nonlinearity. The vertical and horizontal waveguides are used for passing the data and pump signals, respectively. When in addition to the data signal, the pump signal is also applied, the refractive index of the Kerr material changes, which triggers the switching mechanism. Allocating two different paths for the data and pump signals results in a desirable isolation between these signals. The proposed switch is numerically simulated using finite difference time domain (FDTD) method. In order to verify the FDTD simulation results, the basic switch structure is also analyzed using the transmission line method. Compact size (considering two different input ports), low pumping intensity, simplicity, symmetrical structure, suitable isolation and high contrast ratios are the marked characteristics of the proposed all-optical switch. As a result, such a structure has the potential to be used in complex integrated optical circuits.

Diode optical amplifier with phase control of the output wave for high-power laser systems with coherent beam combining

A three-section optical diode amplifier is simulated, whose sections have different amplitude-phase coupling coefficients R (linewidth enhancement factors). We show that it is possible to change the output wave phase for a constant output power due to only a difference in the value of this coefficient. In a single-mode amplifier, the first section has a horizontal waveguide formed by the gain (gainguided), and the other two sections are formed by change of the refractive index (index-guided). The values of the current in the first two sections are found, at which the phase changes by more than 2π at a constant output power of 2W. Such amplifiers can be integrated into single-crystal bars, which makes them adaptive for use in kilowatt laser systems with a coherent combining of beams.

Femtosecond Laser Writing of Optical Waveguides by Self-Induced Multiple Refocusing in LiTaO3 Crystal

We report on a one-step fabrication method of horizontal dual-line waveguides supporting TE guidance in LiTaO3 crystal utilizing multiple refocusing mechanisms of the femtosecond laser. Through the nonlinear process, multiple foci can be formed spontaneously with the interval of a few micrometers along the laser propagation direction. The number and the separation of focal spots, even the entire length of laser-induced tracks, could be modulated by varying the laser parameters. Taking advantage of this spontaneous phenomenon, we further implemented the multi-scan technique to write two parallel damage lines along transverse direction, realizing stress-induced waveguides by horizontal light confinement. Moreover, using this method, one-step two-channel guidance could also be demonstrated by adjusting the pulse energy. The fabrication details and waveguiding performances were studied by both experimental and computational methods. This paper opens the alternative way to construct complex integrated platforms in LiTaO3 crystal by using femtosecond laser writing.

Design of a uniform-illumination two-dimensional waveguide head-up display with thin plate compensator.

Nonuniform illumination is one of the factors in degrading image performance of geometrical waveguide-based head-up display. The two-dimensional (2-D) waveguide expanding the exit pupil along two orthogonal directions makes illumination uniformization more intractable. To solve this problem, the reasons for nonuniform illumination in 2-D geometrical waveguide were probed and a novel waveguide structure incorporating illumination compensator was proposed. A bilayer illumination compensator was first presented to change the period of rays propagating in waveguide to improve the inter-pupil illumination uniformity and inter-field illumination uniformity. Then optimized coating design for different partially reflective mirrors in horizontal waveguide and the vertical one allowed further improvement of these two kinds of illumination uniformity, raising both up to 70%. A matched catadioptric projection optics using freeform surface was designed and integrated with the resultant 2-D geometrical waveguide, achieving a head-up display with an eye relief of 400 mm, an eyebox of 80 mm × 80 mm and a field of 24° × 15°. A prototype of the proposed 2-D geometrical waveguide display was developed and demonstrated.

On-Line Monitoring of Pipe Wall Thinning by a High Temperature Ultrasonic Waveguide System at the Flow Accelerated Corrosion Proof Facility.

Pipe wall thinning and leakage due to flow accelerated corrosion (FAC) are important safety concerns for nuclear power plants. A shear horizontal ultrasonic pitch/catch technique was developed for the accurate monitoring of the pipe wall-thickness. A solid couplant should be used to ensure high quality ultrasonic signals for a long operation time at an elevated temperature. We developed a high temperature ultrasonic thickness monitoring method using a pair of shear horizontal transducers and waveguide strips. A computer program for on-line monitoring of the pipe thickness at high temperature was also developed. Both a conventional buffer rod pulse-echo type and a developed shear horizontal ultrasonic waveguide type for a high temperature thickness monitoring system were successfully installed to test a section of the FAC proof test facility. The overall measurement error was estimated as ±15 μm during a cycle ranging from room temperature to 150 °C. The developed waveguide system was stable for about 3300 h and sensitive to changes in the internal flow velocity. This system can be used for high temperature thickness monitoring in all industries as well as nuclear power plants.

Study of microwave heating of reference liquids in a coaxial waveguide reactor using the experimental, semi-analytical and numerical means

In this work, a new application of coaxial waveguides for microwave heating of individual liquid substances and reaction mixtures is considered. The studied reactor is a small hollow coaxial waveguide in which liquids (methanol or ethanol) are exposed to microwaves generated by a miniature semiconductor source of 2.45-GHz frequency. The temperature of a liquid in the coaxial chamber is measured using an IR temperature sensor, thermocouple and optic fiber probes through non-radiating (in microwave range) openings in the thick copper reactor's wall, with the satisfactory accord between their readings at the medium-level power (10 W). The dynamics of microwave heating is studied using the semi-analytical and numerical simulations, which prove to be in good agreement with the experimental data. Two semi-analytical models of microwave heating in the coaxial waveguide as particular cases of the general electromagnetic-thermal problem are developed. One of them is the lumped system model in which uniformity of the temperature field is assumed. It gives good agreement with the measurements and is physically justified at late heating times. Another one is a simplified non-uniform heating model which is based on consideration of a convective turbulent boundary layer in a short horizontal coaxial waveguide. This model furnishes a quantitative explanation of the measured temperature difference at opposite ends of this waveguide over the entire heating period. The results of this study are interesting for development of miniature reactors for on-demand chemistry and pharmacy.

Silicon slot fin waveguide on bonded double-SOI for a low-power accumulation modulator fabricated by an anisotropic wet etching technique.

We propose a new low VπL, fully-crystalline, accumulation modulator design based on a thin horizontal gate oxide slot fin waveguide, on bonded double Silicon-on-Insulator (SOI). A combination of anisotropic wet etching and the mirrored crystal alignment of the top and bottom SOI layers allows us for the first time to selectively pattern the bottom layer from above. Simulations presented herein show a VπL = 0.17Vcm. Fin-waveguides and passive Mach-Zehnder Interferometer (MZI) devices with fin-waveguide phase shifters have been fabricated, with the fin-waveguides having a transmission loss of 5.8dB/mm and a 13.5nm thick internal gate oxide slot.

A U-shape shear horizontal waveguide sensor for on-line monitoring of liquid viscosity

The shear horizontal (SH) wave in plate waveguides is of great advantage in fluid viscosity measurement as it only has in-plane displacements and causes a pure shear leakage in fluids, while the current excitation of non-dispersive SH waves in the strip with a finite width is very limited. In this work, we proposed a new pitch-catch scheme to excite and receive a relatively pure quasi-SH0 wave in the U-shape strip waveguide. Based on the attenuation measurement on the quasi-SH0 wave immersed in a viscous fluid, the viscosity of the fluid can be quantitatively monitored. Firstly, the wave field of the excited quasi-SH0 was analyzed by using finite element simulations and the results demonstrate the effectiveness of the excitation method we proposed. Then, the U-shape waveguide sensor for viscosity measurement was presented, and a series of experiments were conducted on different concentrations of glycerol-water solutions with different viscosity (1cP-1600cP) under a wide temperature range (20℃–80℃). By calibrating the measured attenuation curves, the viscosity can be derived and the measurement uncertainty is less than 6% referring to a standard rotational viscometer. The proposed shear horizontal waveguide sensor is mechanically robust and quite suitable for online monitoring of fluid viscosity in industrial applications.