ejun Xu

Simulation Demonstration and Experimental Fabrication of a Multiple-Slot Waveguide

A multiple-slot waveguide is presented and demonstrated through theoretical simulation. Taking a double-slot waveguide as an example, the results show a nearly 30% enhancement of optical intensity compared with the traditional single-slot waveguide with the same slot gap width. Therefore, the E-field intensity of the slot can be increased by adding another smaller slot. A double-slot waveguide with oxide and air as low index slot materials is realized experimentally and the formation processes of the slots are analyzed.

An investigation of the mode characteristics of SOI submicron rib waveguides using the film mode matching method

The mode characteristics of SOI (silicon-on-insulator) submicron rib waveguides are very different from those of micrometer-sized ones. Using the full-vector film mode matching method, we propose a simple criterion to determine whether a waveguide mode is guided or not. The single-mode condition for deep-etched waveguides is obtained using this criterion. We also obtain the inherent TM mode leakage and sharp cancelation effects due to TE–TM mode coupling in shallow-etched rib waveguides from numerical simulations, which agree well with the analytical results based on total internal reflection and interference theories.

Fabrication of a Low-Loss SSC Using High-Dose Electron Beam Lithography Exposure With Negative PMMA Resist

A silicon-on-insulator optical fiber-to-waveguide spot-size converter (SSC) using poly-methylmethAcrylate (PMMA) is presented for integrated optical circuits. Unlike the conventional use of PMMA as a positive resist, it has been successfully used as a negative resist with high-dose electron exposure for the fabrication of ultrafine silicon wire waveguides. Additionally, this process is able to reduce the side-wall roughness, and substantially depresses the unwanted propagation loss. Exploiting this technology, the authors demonstrated that the SSC can improve coupling efficiency by as much as over 2.5 dB per coupling facet, compared with that of SSC fabricated with PMMA as a positive resist with the same dimension.

Inductively coupled plasma etching of SOI and its applications in submicron optical waveguide devices

SOI promises a good platform for dense integration of optical devices. However, as dimensions scale down, propagation losses mainly caused by the scattering loss at sidewall had been serious problems. ICP etching of SOI is proved to be an available anisotropic etch technique to make submicron optical waveguide devices. With the help of e-beam lithography, We fabricated Single-mode submicron rib SOI waveguide with propagation loss as low as 1.2 dB/mm. Examples of SOI optical waveguide devices are also presented, such as sharp bends and ring resonators with a quality factor larger than 50,000.

Realization of SOI submicrometer optical waveguide components

Submicrometer channel and rib waveguides based on SOI (Silicon-On-Insulator) have been designed and fabricated with electron-beam lithography and inductively coupled plasma dry etching. Propagation loss of 8.39dB/mm was measured using the cut-back method. Based on these so-called nanowire waveguides, we have also demonstrated some functional components with small dimensions, including sharp 90° bends with radius of a few micrometers, T-branches, directional couplers and multimode interferometer couplers.

High Q microring resonator in silicon-on-insulator rib waveguides

A high quality (Q) factor microring resonator in silicon-on-insulator rib waveguides was fabricated by electron beam lithography, followed by inductively coupled plasma etching. The waveguide dimensions were scaled down to submicron, for a low bending loss and compactness. Experimentally, the resonator has been realized with a quality factor as high as 21,200, as well as a large extinction ratio 12.5dB at telecommunication wavelength near 1550nm. From the measured results, propagation loss in the rib waveguide is determined as low as 6.90dB/cm. This high Q microring resonator is expected to lead to high speed optical modulators and bio-sensing devices.

SOI submicron rib waveguides: Design, fabrication and characterization

We present detailed design, fabrication, and characterization issues of submicron rib waveguides based on silicon-on-insulator. The waveguides fabricated by EBL and ICP processes have propagation loss of 1.8 dB/mm and bend loss of 0.14 dB/90deg for bends with radius of 5 mum.

Design Considerations for a Silicon-based p-i-n Phase Modulator in a Double Ridge Waveguide with Side Isolating Grooves

We present detail design considerations and simulation results of a forward biased carrier injection p-i-n modulator integrated on SOI rib waveguides. To minimize the free carrier absorption loss while keeping the comparatively small lateral dimensions of the modulator as required for high speed operation, we proposed two structural improvements, namely the double ridge (terrace ridge) structure and the isolating grooves at both sides of the double ridge. With improved carrier injection and optical confinement structure, the simulated modulator response time is in sub-ns range and absorption loss is minimized.

SOI based waveguide devices

SOI based waveguide devices are becoming more and more active. The main results of the devices investigated in our team are presented in the paper. Photonic crystal with sharp bends was made and its excess loss is 1.1±0.4dB per mirror. Two kinds of couplers, slot coupler and grating coupler, were successfully fabricated. Coupling loss of the slot coupler is < 3dB between sub-micron optical waveguides and micronscale optical fibers. A coupling efficiency of 40.7% and 3-dB bandwidth of > 40nm of the grating coupler are obtained. Microring and microdisk resonators were simulated and optimized. Their Q factors and extinction ratios are 5.3×104, 14dB, and 2.8×105, 10dB, respectively. SOI PIN diode electro-optical switches with microring, microdisk and MZI were developed. Rise and fall time is 0.37 ns and 2.57 ns, respectively, for a microdisk optical switch.

Mach-Zehnder electro-optic modulator based on silicon nanophotonic waveguide

An electro-optic modulator based on Mach-Zehnder interferometer and embedded PIN diode is demonstrated using silicon nanophotonic waveguide. Measurement results show that the device has high modulation efficiency with a VπL figure of merit of 1.14 V·mm, high modulation depth of 96.27%, and large optical bandwidth from 1500 to 1600 nm. Transmission data rate up to 0.2 Gbps is demonstrated and the rise and fall time are 3.74 ns and 640 ps, respectively.