Input Waveguide Research Articles

Input coupling enhancement through antenna incorporation in thin Au-mica trench waveguides

The ability of both bowtie and semicircle antennas to enhance waveguide input coupling efficiency in thin trench waveguides was studied for broadband applications. The waveguide outputs of trench waveguides with and without antennas were measured using a tunable laser with wavelengths ranging from 570 nm to 960 nm under both parallel and perpendicular polarization conditions. The results indicated that the waveguides with antennas performed better than the trench waveguide alone for parallel polarization conditions with maximum enhancements of 51 and 32 from the simulations, and 14.4 and 5.2 experimentally for the bowtie and semicircle, respectively. Conversely, there was no significant enhancement for the perpendicular polarization. This was attributed to the excitation of either the gap mode or the surface plasmon mode, depending on polarization.

Integrated Plasmonic Infrared Photodetector Based on Colloidal HgTe Quantum Dots

AbstractThis paper presents a 2300 nm wavelength photodetector which comprises a spin‐deposited colloidal HgTe quantum dot (QD) film on a metal‐insulator‐metal (MIM) plasmonic waveguide. This photodetector is an integrated device based on the complementary metal‐oxide‐semiconductor compatible silicon‐on‐insulator platform. The device employs input and output silicon waveguide grating couplers, and HgTe QDs are used as the infrared photosensing material. Infrared light is coupled to the strongly confined MIM waveguide mode, which shrinks the device footprint and improves the light detection efficiency simultaneously. A room temperature responsivity of 23 mA W−1 and a noise‐equivalent power of 8.7 × 10−11 W Hz−1/2 at 2300 nm wavelength are achieved by the photodetector at 2.14 W mm−2 (measured at the input to the plasmonic waveguide) with a device footprint of 15 µm × 0.35 µm. The light intensity–dependent photocurrent, the current noise spectral density, and the 3 dB operation bandwidth are all characterized. The charge transfer properties of the organic HgTe QD films are further analyzed based on field effect transistor measurements.

Compact general interference hybrid-plasmonic multimode interferometers used for optical hybrid.

We propose three general interference multimode interferometers (MMIs) based on hybrid plasmonic waveguides (HPWs). Among them, the general 2×2 and 4×4 MMIs are designed for a 90° optical hybrid, while the 3×3 MMI is for a 120° optical hybrid. First, by considering the mode interference characteristics inside the multimode HPWs, a compromise between the number of guided modes and the device length is obtained at a determined height of the SiO2 interlayer of the HPW. Also, by analyzing the characteristics of multimode propagation in the HPW-MMI, it is found that the optimal positions of self-images would shift from their theoretical ones. In addition, tapered HPW sections are implemented to improve the coupling efficiencies for lights coupled into/out of the multimode section. Therefore, by optimizing the width and length of the multimode section, and especially the position of the input and output single-mode waveguides, the appropriate structure parameters of three HPW-MMIs are obtained, where the footprints of the 2×2, 3×3, and 4×4 HPW-MMIs are only 1.96×5.4 μm2, 2.18×12.0 μm2, and 2.52×11.5 μm2, respectively. The simulation results show that, at the wavelength of 1550nm, the 2×2 HPW-MMI exhibits a transmission of 75.6%, a maximum transmissions imbalance of 0.55dB, and a phase error of 3.68°; the 3×3 HPW-MMI exhibits a transmission of 69.2%, a maximum transmissions imbalance of 0.43dB, and a phase error of 4.66°; and the 4×4 HPW-MMI exhibits a transmission of 68.5%, a maximum transmissions imbalance of 0.91dB, and a phase error of 4.81°. All these performances meet the standard industry requirements.

Translational MEMS Platform for Planar Optical Switching Fabrics.

While 3-D microelectromechanical systems (MEMS) allow switching between a large number of ports in optical telecommunication networks, the development of such systems often suffers from design, fabrication and packaging constraints due to the complex structures, the wafer bonding processes involved, and the tight alignment tolerances between different components. In this work, we present a 2-D translational MEMS platform capable of highly efficient planar optical switching through integration with silicon nitride (SiN) based optical waveguides. The discrete lateral displacement provided by simple parallel plate actuators on opposite sides of the central platform enables switching between different input and output waveguides. The proposed structure can displace the central platform by 3.37 µm in two directions at an actuation voltage of 65 V. Additionally, the parallel plate actuator designed for closing completely the 4.26 µm air gap between the fixed and moving waveguides operates at just 50 V. Eigenmode expansion analysis shows over 99% butt-coupling efficiency the between the SiN waveguides when the gap is closed. Also, 2.5 finite-difference time-domain analysis demonstrates zero cross talk between two parallel SiN waveguides across the length of the platform for a 3.5 µm separation between adjacent waveguides enabling multiple waveguide configuration onto the platform. Different MEMS designs were simulated using static structural analysis in ANSYS. These designs were fabricated with a custom process by AEPONYX Inc. (Montreal, QC, Canada) and through the PiezoMUMPs process of MEMSCAP (Durham, NC, USA).

Nanoscale plasmonic detector of wave intensity difference and uni-directional waveguide

In this paper, a new nanoscale plasmonic differential detector of wave intensities is proposed. This structure can be useful for calibration applications and for finding out if a wave intensity is high enough to pass a threshold level or not. Next, a nanoscale plasmonic uni-directional waveguide is presented. The distinction of this waveguide with similar cases is that the one-way wave-guiding is provided by adding a properly located controlling source, without employing any non-reciprocal material. This feature can be used in many applications that only uni-directional wave propagation is desirable. Both structures have been designed in metal–insulator–metal structure including cavity resonators. The operations are based on the coupling of the wave from input waveguides to the cavity resonators and decoupling to output waveguides in the cavity resonance wavelengths. The simulation results of performance of the structures, as elements applicable to photonic integrated circuits, have been obtained using the numerical method of the finite difference time domain.

Design of a low-crosstalk half-wavelength pitch nano-structured silicon waveguide array

An ultra-compact half-wavelength pitch silicon waveguide array with very low crosstalk is proposed and analyzed in this work. We first show the design of a pair of low-crosstalk silicon waveguides with only half-wavelength spacing, where the placement of two thin silicon strips asymmetrically in between the waveguides is key to having very low crosstalk. We next extend this nano-structured two-waveguide design to form a low-crosstalk half-wavelength pitch silicon waveguide array. Coupled-mode theory shows that, for an array length of 1mm, the insertion loss of the input waveguide is as low as -0.13 dB for the TE-like mode at 1550nm, and the crosstalk in all other waveguides remains below about -18 dB. This half-wavelength pitch waveguide array also exhibits a favorable fabrication error tolerance when taking into account the waveguide width variations in practice. It offers a promising platform for realization of integrated optical phased arrays for solid-state lidars with a large field of view.

Input and Output Couplers for an Oversized Coaxial Relativistic Klystron Amplifier atKa-Band

We propose a novel system of input and output couplers, excited in azimuthal symmetric and stable mode of operation, for an oversized coaxial relativistic klystron amplifier (OCRKA) at Ka -band. A mode converter is introduced in the output coaxial waveguide to provide a tunnel for the input waveguide and fix the inner and outer conductors of the OCRKA. After characterizing the proposed input and output couplers, the high-frequency structure of the OCRKA is designed and then optimized by Computer Simulation Technology. The simulated frequency and loaded quality factor of the input, output, and idler cavities are validated against measurement. Also, the beam–wave interaction of the OCRKA using the proposed input and output couplers is simulated by particle-in-cell software, the average saturated output power of 880 MW of the OCRKA at Ka -band, with 29.3% electronic efficiency and 58-dB saturated gain are obtained. Moreover, no pulse shortening of the output power waveform is observed during the simulation time of 100 ns, which indicates that the proposed input and output couplers can suppress the higher order mode self-oscillation in the Ka -band OCRKA studied here.

Ultra‐fast and compact all‐optical half adder using 2D photonic crystals

Using a two-dimensional photonic crystal lattice, a compact and simple structure has been introduced in the present study to construct an all-optical half adder. The designed structure operates under the interference effect. The phase difference has been created in different states by putting the point defects and the difference in the length of the input waveguides. To do analyses, the finite-difference time-domain method and the plane wave expansion have been used. The advantages of this design include the small dimensions, high possibility of construction, compatibility with the silicon-based technology, and equality of the output power in the logic states 0 and 1. The contrast ratio calculated for the port Sum and the port Carry has been equal to 9.3 and 8.22 dB. The response time has been equal to 0.22 ps, generating the data transfer rate of 4.55 Tbps.

HWCVD a-Si:H interlayer slope waveguide coupler for multilayer silicon photonics platform.

We present interlayer slope waveguides, designed to guide light from one level to another in a multi-layer silicon photonics platform. The waveguide is fabricated from hydrogenated amorphous silicon (a-Si:H) film, deposited using hot-wire chemical vapor deposition (HWCVD) at a temperature of 230°C. The interlayer slope waveguide is comprises of a lower level input waveguide and an upper level output waveguide, connected by a waveguide on a slope, with vertical separation to isolate other crossing waveguides. Measured loss of 0.17 dB/slope was obtained for waveguide dimensions of 600 nm waveguide width (w) and 400 nm core thickness (h) at a wavelength of 1550 nm and for transverse electric (TE) mode polarization.

A 135-190 GHz Broadband Self-Biased Frequency Doubler using Four-Anode Schottky Diodes.

This paper describes the design and demonstration of a 135–190 GHz self-biased broadband frequency doubler based on planar Schottky diodes. Unlike traditional bias schemes, the diodes are biased in resistive mode by a self-bias resistor; thus, no additional bias voltage is needed for the doubler. The Schottky diodes in this verification are micron-scaled devices with an anode area of 6.6 μm2 and an epitaxial layer thickness of 0.26 μm. For accurate design of the doubler, the 3D-EM model of the Schottky diode is built up to extract the parasitic parameters induced by the diode package when frequency rises up to the terahertz band. In order to implement broadband working, input waveguide steps, output suspended microstrip steps, and output probe with bias filter are all used as matching elements for impedance matching. Measured results show that the doubler exhibits a 3 dB bandwidth of 34% from 135 GHz to 190 GHz, with a conversion efficiency of above 4% when supplied with 100 mW of input power. A 17.8 mW peak output power with a 10.2% efficiency was measured at 166 GHz when the input power was 174 mW. The measured results agree well with the simulated results, which indicates that the self-bias scheme for Schottky diode-based frequency multipliers is feasible and effective.

An Integrated Few-Mode Power Splitter Based on Multimode Interference

A 1 × 2 integrated four-mode power splitter based on multimode interference is proposed and experimentally demonstrated for the first time. A three-dimensional simulation is used to optimize the core/cladding refractive index difference and the input waveguide position for the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">00</sub> , TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> , TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> , and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> input waveguide modes. Minimum insertion loss (IL) and mode-dependent loss (MDL) of 0.1 and 0.2 dB are predicted, respectively. IL and MDL less than 1 dB can be maintained over a bandwidth of approximately 50 and 25 nm, respectively. The device was fabricated on SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and experimentally characterized. The variation of the power splitting ratio for each mode is less than 0.4 dB over the full C-band, and the excess losses of the splitter for all four modes exceed the IL of a straight waveguide by less than 1.85 dB.

Mid-infrared GaAs/AlGaAs micro-ring resonators characterized via thermal tuning.

Micro-ring resonators with a decoupling waveguide have been manufactured from GaAs/Al0.2Ga0.8As, accommodating mid-infrared wavelengths, and were characterized via thermal tuning. A Q-factor of 1900, a thermal full width at half maximum of 8 °C, and a thermal free spectral range of 18 °C have been achieved. The low Q-factor indicates comparatively high coupling efficiency from the input waveguide into the decoupling waveguide. The micro-ring resonators shown herein are suitable structures for advanced mid-infrared chem/bio sensing strategies via resonant-cavity enhancement. In addition, they offer high spectral resolution for evanescent field sensing strategies via effective wavelength de-multiplexing waveguide structures.

Reconfigurable Mode (De) Multiplexer via 3-D Triple-Waveguide Directional Coupler With Optical Phase Change Material

A three-dimensional reconfigurable mode (de) multiplexer (3DRM-(De)MUX) is proposed based on a triple-waveguide directional coupler with optical phase change material, which consists of an input waveguide on the upper layer, a bus waveguide on the lower layer, and an intermediate waveguide on the upper layer with a Ge2Sb2Se4Te1 (GSST) cap layer. The self-holding “ off ” and “ on ” states of the proposed 3DRM-(De)MUX can be switched by triggering the amorphous and crystalline states of GSST, respectively. The proposed 3DRM-(De)MUX is optimized by using the full-vectorial finite element method and 3-D full-vectorial finite difference time domain method. The simulated results show that the proposed 3DRM-(De)MUX for switching between the quasi-TE0 and quasi-TE1 modes is with a compact coupling length of only 12.0 μm, a broad bandwidth of 100 nm, the mode extinction ratios of 18.25 dB and 14.0 dB, and the insertion losses (ILs) of –0.38 and –1.14 dB for the “ off ” and “ on ” states, respectively. A more compact 3DRM-(De)MUX can also be achieved for the quasi-TM1 mode with the coupling length of 8.28 μm, IL of –0.12 dB (–1.98 dB), and mode crosstalk of –16.37 dB (–13.23 dB) for the “ off ” (“ on ”) state, respectively. The proposed 3DRM-(De)MUX can be applied in 3-D on-chip mode division multiplexing networks for flexible mode routing and switching.

Ka-satellite Communication: A Filter with High Restraint in Band-stop

Based on theoretical calculation and CST simulation, a Ka band-pass filter with high restraint in Band-stop is designed for the purpose of satellite communication. Resonators are formed by introducing appropriate capacitive posts at suitable intervals along the waveguide. High restraint in band-stop can be realized by moving the first post and last post into the input and output coupling waveguide, which can reach the requirements of satellite communication.

Integrated 25 GHz and 50 GHz spectral line width dense wavelength division demultiplexer on single photonic crystal chip

We propose a new integrated demultiplexer model using the two-dimensional photonic crystal (2D PC) through the hexagonal resonant cavity (HRC) for the International Telecommunication Union (ITU) standard. The integrated model of demultiplexer for both 25 GHz and 50 GHz has been designed for the first time. The demultiplexer consists of bus input waveguide, drop waveguide, Hexagonal Resonant Cavity (HRC), 6 Air Hole Filter (6-AHF), 7 Air Hole Filter (7-AHF). The 7-AHF is used to filter 25GHz wavelength, and the 6-AHF filter is used to filter 50 GHz wavelength. The Q-factor on the designed demultiplexer is flexible based on the idea of increasing the number of air holes between drop waveguide and resonant cavity. The demultiplexer is designed to drop maximum 8 resonant wavelengths. One side of demultiplexer is able to drop 50 GHz ITU standard wavelengths, which are of 1556.3 nm, 1556.7 nm, 1557.1 nm and 1557.5 nm, and further the other facet is able to drop 25 GHz wavelengths, which are of 1551.4 nm, 1551.6 nm, 1551.8 nm, and 1552.0 nm. The proposed demultiplexer may be carried out within the integrated dual system. This system is able to lessen the architecture cost and the size is miniaturized substantially.

Photonic crystal waveband de-multiplexers

Abstract In this paper, we theoretically present a silicon photonic-crystal waveguide for waveband de-multiplexing. The waveguide is composed of three different microcavities, and three output ends. The three different microcavity waveguide branches allow the respective resonant wavelength channels go from the waveguide input end to the respective output end. The air hole and microcavity sizes are properly designed so that the microcavity waveguide can realize the respective transmission spectrum. With air-holes square array structure, the presented waveguide can apply to an optical window covering λ = 1.2–1.8 µm. The analytical techniques and numerical results indicate that the peak transmission at the three optical windows could reach 86.6%, 63.5% and 97.7%. This waveguide could provide a potential use as a building block of integrated photonic circuits.

A Low-Loss Crossing of Silicon Waveguides for Optical Switches on CMOS Platform

A novel waveguide crossing with low crosstalk and crossing loss was proposed and prototyped on the Si platform. The design consists a pair of tapered Si waveguides instead of a single waveguide at the crossing point, producing a mismatch of the mode fields between the input waveguide and crossing waveguide. The tapered Si waveguides with SiN x outer cores demonstrate extremely low-loss waveguide crossing. An optical switch is prototyped by the crossing with a ring resonator, demonstrating a low-crossing loss and crosstalk, a high extinction ratio, and yet a small footprint.

Electro-optic deflection in a lithium niobate quasi-single mode waveguide with microstructured electrodes.

We propose an electro-optic mode deflection device based on an annealed proton exchange (APE) waveguide in lithium niobate, associated with isosceles-triangle-shaped array electrodes and a horn-shaped input waveguide. The input waveguide is tapered down to ensure that the output of the device has a good beam quality, i.e., a quasi-single mode in this case. This new device allows beam deflection at a relative low voltage and large deflection angle. At an APE-waveguide width of 80 μm, mode deflections of 0.265 and 0.240 μm/V are obtained for 1064 and 980 nm, respectively. This beam deflection device can be applied in high-speed optical switch, and beam smoothing of a high-power laser, etc.

All-optical logic gates based on metallic waveguide arrays

Abstract All-optical logic gates based on metallic waveguide arrays (MWGAs) are proposed. The supermodes of surface plasmon polaritons (SPPs) are excited selectively by different input fields. According to the field distribution of different input fields, the appropriate position of output port is chosen for different logic functions, which the lengths of waveguides are different for different gates: L1 = 0.68 μm is for OR gate and NOT gate; L2 = 0.38 μm is for AND gate; L3 = 0.32 μm is for XOR gate. OR gate and NOT gate can be realized in the same MWGA by choosing different input waveguides. The intensity contrast ratios between the output logic “1” and “0” are 9.3–13.98 dB. The logic gates based on MWGAs can provide a new method for logic functions in photonic integrated circuits.

Athermal echelle grating filter in silicon-on-insulator using a temperature-synchronized input.

Athermal design of integrated photonic devices can reduce the need for active temperature stabilization and consequently the energy required to operate photonic integrated circuits. For silicon photonic filters such as AWGs which employ wire or ridge waveguides, temperature insensitivity can be achieved using cladding materials with negative thermo-optic coefficients. On the other hand, in echelle grating filters the inteference takes place in the slab free-propagation region, and therefore the modal overlap with the cladding is small, rendering this method ineffective. In this work we present an approach to design an athermal echelle grating filter exploiting a temperature-synchronized Mach-Zehnder interferometer as input. This reduces the spectral shift over a temperature range of 20 K to less than ±45 pm compared to the 1.6 nm shift for the same echelle grating with a conventional waveguide input. Furthermore, the proposed design relies exclusively on a standard fabrication process for silicon-on-insulator photonic devices and exhibits a good tolerance to fabrication uncertainties.