Electronics and Optoelectronics Based on Tellurium.

As a true 1D system, group-VIA tellurium (Te) is composed of van der Waals bonded molecular chains within a triangular crystal lattice. This unique crystal structure endows Te with many intriguing properties, including electronic, optoelectronic, thermoelectric, piezoelectric, chirality, and topological properties. In addition, the bandgap of Te exhibits thickness dependence, ranging from 0.

2D Reconfigurable Memory Device Enabled by Defect Engineering for Multifunctional Neuromorphic Computing.

In this era of artificial intelligence and Internet of Things, emerging new computing paradigms such as in-sensor and in-memory computing call for both structurally simple and multifunctional memory devices. Although emerging two-dimensional (2D) memory devices provide promising solutions, the most reported devices either suffer from single functionalities or structural complexity. Here, this work reports a reconfigurable memory device (RMD) based on MoS/CuInPS heterostructure, which integrates the defect engineering-enabled interlayer defects and the ferroelectric polarization in CuInPS, to realize a simplified structure device for all-in-one sensing, memory and computing.

Precursor-Confined Chemical Vapor Deposition of 2D Single-Crystalline SeTe Nanosheets for p-Type Transistors and Inverters.

Two-dimensional (2D) tellurium (Te) is emerging as a promising p-type candidate for constructing complementary metal-oxide-semiconductor (CMOS) architectures. However, its small bandgap leads to a high leakage current and a low on/off current ratio. Although alloying Te with selenium (Se) can tune its bandgap, thermally evaporated SeTe thin films often suffer from grain boundaries and high-density defects.

Uncovering the Role of Crystal Phase in Determining Nonvolatile Flash Memory Device Performance Fabricated from MoTe-Based 2D van der Waals Heterostructures.

Although the crystal phase of two-dimensional (2D) transition metal dichalcogenides (TMDs) has been proven to play an essential role in fabricating high-performance electronic devices in the past decade, its effect on the performance of 2D material-based flash memory devices still remains unclear. Here, we report the exploration of the effect of MoTe in different phases as the charge-trapping layer on the performance of 2D van der Waals (vdW) heterostructure-based flash memory devices, where a metallic 1T'-MoTe or semiconducting 2H-MoTe nanoflake is used as the floating gate. By conducting comprehensive measurements on the two kinds of vdW heterostructure-based devices, the memory device based on MoS/h-BN/1T'-MoTe presents much better performance, including a larger memory window, faster switching speed (100 ns), and higher extinction ratio (10), than that of the device based on the MoS/h-BN/2H-MoTe heterostructure.

Cost-effective fiber-to-lithium niobate chip coupling using a double-side irradiation self-written waveguide.

In recent years, integrated lithium niobate (LN) chips have been widely used for developing a variety of photonic devices, such as high-speed electro-optical (EO) modulators and frequency comb generators. A major challenge for their practical applications is the high coupling loss between micrometer-scale LN waveguides and optical fibers. Lensed fibers and special taper structures are commonly used to tackle the coupling issue.

Quantitative study in coupling loss reduction under a large mode-field mismatch using a self-written waveguide.

The coupling loss between optical devices is a critical factor affecting the performance of optical interconnect. This paper quantitatively studies the effectiveness of using a dye-doped-epoxy-based self-written waveguide (SWW) to reduce the coupling loss in optical interconnect caused by large mode-field mismatch and lateral offset. We formed SWW between single-mode fiber (SMF) with different mode-field diameters (MFD) and a 5 × 2 µm rectangular channel waveguide-under-test (WUT).

High-sensitivity magnetic sensor based on the evanescent scattering by a magnetorheological film.

We present a simple concept to implement a magnetic sensor that uses evanescent scattering by a suspended magnetorheological (MR) film above a planar waveguide. The soft MR film embedded with ferromagnetic particles is to induce scattering on the evanescent field of a planar waveguide at a proximity distance. This distance can be controlled precisely by a magnetic field.

Scalable selective high order mode pass filter architecture with asymmetric directional couplers.

We propose a novel design architecture to realize scalable selective mode filter based on the asymmetric directional coupler structure. In this structure, any arbitrary high-order mode can pass, whereas other unwanted modes are blocked. Furthermore, multiple optical modes can be blocked by only adjusting the structural parameters.

Investigation of evanescent scattering for low-distortion submicron vibration sensing using ferromagnetic cantilevers.

In this study, we investigate the dynamic performance of a previously reported evanescent-scattering platform for submicron vibration sensing with low distortions. The platform consists of self-assembled ferromagnetic cantilevers located above a liquid-cladded optical waveguide. Theoretical analyses show enhancement of sensitivity and dynamic sensing range by reducing the waveguide core-cladding index difference.

Precise control of evanescent scattering by self-assembled ferromagnetic particles for optical sensing with tunable sensitivity.

We propose an optical sensing platform that uses evanescent scattering through precise manipulation of self-assembled ferromagnetic particle columns. The movement of the column tips can be controlled dynamically down to a submicron range by an external actuation, namely, a magnetic field, for interacting with evanescent wave propagation along an optical waveguide that causes a change in its output intensity for optical sensing. To demonstrate the idea, an AC current sensor with only a 5 mm interaction length is proposed and realized.

Broadband high-order mode pass filter based on mode conversion.

We report a unique concept to implement a high-order mode pass filter using mode converters. Our proposed design method implements a high-order mode pass filter of any order, uses different mode converters available, and applies to a variety of planar lightwave circuit material platforms. We fabricate a broadband fundamental mode filter device using a Mach-Zehnder interferometer and Y-junctions to demonstrate our idea.

Efficient design of polarization insensitive polymer optical waveguide devices considering stress-induced effects.

We present an approach for the efficient design of polarization insensitive polymeric optical waveguide devices considering stress-induced effects. In this approach, the stresses induced in the waveguide during the fabrication process are estimated first using a more realistic model in the finite element analysis. Then we determine the perturbations in the material refractive indices caused by the stress-optic effect.

Reconfigurable two-mode mux/demux device.

A reconfigurable two-mode mux/demux device in planar waveguide was proposed. The simulated mux/demux extinction ratio was ≥ 35 dB with ≤ 0.4 dB excess loss.

High extinction ratio and low transmission loss thin-film terahertz polarizer with a tunable bilayer metal wire-grid structure.

A thin-film terahertz polarizer is proposed and realized via a tunable bilayer metal wire-grid structure to achieve high extinction ratios and good transmission. The polarizer is fabricated on top of a thin silica layer by standard micro-fabrication techniques to eliminate the multireflection effects. The tunable alignment of the bilayer aluminum-wire grid structure enables tailoring of the extinction ratio and transmission characteristics.

Two-mode mode multiplexer/demultiplexer in polymer planar waveguide.

We proposed a two-mode multiplexer/demultiplexer (mux/demux) device using an unbalanced Mach-Zehnder interferometer with Y junctions. The proposed device had simulated extinction ratio greater than 30 dB for both mux and demux operations with an excess loss of 0.17 dB.

Experimental study on the performance of a variable optical attenuator using polymer dispersed liquid crystal.

We applied polymer dispersed liquid crystal (PDLC) as the cladding material in a polymer-based variable optical attenuator. Three polymer inverted channel waveguides were fabricated, two with PDLC upper cladding (aligned PDLC and nonaligned PDLC) and one with aligned liquid crystal upper cladding. Upon operation, the waveguides with aligned upper claddings show relatively lower threshold and cutoff voltages compared to those with nonaligned PDLC cladding.

Apodization of terahertz Bragg gratings in subwavelength polymer fiber.

We report on an apodization scheme for terahertz fiber Bragg gratings. The grating consists of only 90 ablated notches on two opposite sides of a subwavelength polymer fiber. The grating strength can be effectively tuned by controlling the longitudinal shift between the two-sided notches, and apodization can be achieved by applying an envelope profile.

Terahertz filter with tailored passband using multiple phase shifted fiber Bragg gratings.

Transmission filters for the terahertz domain having a shaped bandpass have been modeled and demonstrated. The filter designs were based on the desired filter type and bandwidth, and implemented by cascading quarter wave phase shifted fiber Bragg gratings written in Topas polymer subwavelength fiber. As an example, a 5-pole Chebyshev filter with <3 GHz bandwidth was designed and fabricated.

Study of optical anisotropies in benzocyclobutene thin films for the efficient design of optical waveguide devices.

We study the in-plane/out-of-plane anisotropies in refractive indices (n) and in thermo-optic coefficients (dn/dT) of benzocyclobutene (BCB) thin film on a substrate. Both nonoxidized and oxidized films are investigated. Aside from the stress-induced effects, oxidation has significant influence on the refractive index anisotropy.

Low-loss ultracompact optical power splitter using a multistep structure.

We propose a low-loss ultracompact optical power splitter for broadband passive optical network applications. The design is based on a multistep structure involving a two-material (core/cladding) system. The performance of the proposed device was evaluated through the three-dimensional finite-difference beam propagation method.

Simultaneous measurement of thermo-optic and stress-optic coefficients of polymer thin films using prism coupler technique.

We present a simple method for simultaneous measurement of thermo-optic and stress-optic coefficients of polymer thin films by measuring the film refractive indices as a function of temperature (dn/dT). Usually, such dn/dT value is considered as the thermo-optic coefficient. However, in the thin film systems, the measured dn/dT values result from both the thermo-optic and stress-optic effects.

Three-dimensional broadband polymer optical waveguide switch matrix.

A 1 x 4 3D broadband polymer optical waveguide switch matrix is demonstrated. The fabricated device, which contains four vertically coupled thermo-optic switches, has a compact construction (only 9 mm in length) and a power consumption of 45 mW. Compared with the corresponding planar ones, this 3D switch matrix has two distinct features.