For input coupling from single-mode optical fibers to photoreceivers made with silicon photonics integrated circuits (Si-PICs), we constructed a polarization-insensitive optical surface coupler with ...a vertically curved silicon waveguide. The polarization insensitivity was attained by the equalization of the radiative transmission losses of TE and TM polarizations in the vertically curved waveguide (VCW) structure while keeping the straight structure of the spot-size converter (SSC) connected above the curved structure. Numerical simulations revealed that the radius of curvature of <inline-formula> <tex-math notation="LaTeX">6~\mu \text{m} </tex-math></inline-formula> or larger nearly enabled the equalization, and thus we developed a bending technology using ion implantation to realize simultaneously a VCW radius of curvature of <inline-formula> <tex-math notation="LaTeX">6~\mu \text{m} </tex-math></inline-formula> and a straight SSC of length <inline-formula> <tex-math notation="LaTeX">7~\mu \text{m} </tex-math></inline-formula> by varying the implantation angles. The bent silicon core was subsequently coated with SiO 2 by plasma-enhanced chemical vapor deposition to function as a collimation lens. The coupling properties of the fabricated coupler and the single-mode fiber with a mode-field diameter of <inline-formula> <tex-math notation="LaTeX">5~\mu \text{m} </tex-math></inline-formula> exhibited a polarization dependence loss of less than 0.25 dB, a 1-dB bandwidth of 180 nm, and coupling losses of about 1.6 dB at 1550 nm wavelength. A sharp inversely tapered Si waveguide that affects these characteristics significantly can be formed by applying ArF-immersion lithography on the 45-nm-node and hence fabrication is compatible with mass production processes.
A chip-surface optical coupler based on a vertically curved Si waveguide was demonstrated for coupling with high-numerical-aperture single-mode optical fibers with a mode-field diameter of 5 µm. This ...device features a dome-like SiO2 coupler cap, which acts as collimation lens. We succeeded in fabricating this structure using an isotropic SiO2 deposition technique employing plasma-enhanced chemical vapor deposition and obtained a light output that approximates that of a 5-µm-waist Gaussian beam. The fabricated coupler showed a coupling loss of less than 4.2 dB and a 0.5-dB-loss bandwidth above 150 nm for TE-polarized light.
We investigated the switching dynamics of optical modulators consisting of a Si waveguide with a VO
cladding layer by utilizing the photothermal effect, which induces a metal-insulator transition in ...VO
. The devices exhibited stable optical switching with a high extinction ratio exceeding 16 dB. The switching time of the insulator-to-metal transition (heating process) ranged from tens of nanoseconds to microseconds depending on the incident light power, and that of the metal-to-insulator transition (cooling process) was several microseconds regardless of the incident light power. The heat transfer in the devices was numerically simulated to reproduce the switching characteristics and revealed that the temperature change in the first few micrometers of the VO
/Si waveguide governed the switching time. The thermal structural design of the device is thus of key importance to improve the switching speed of the device.
The high-performance silicon optical coupler is one of the significant functional devices, which will be required to enable mass commercialization of silicon photonic integrated circuits (Si-PICs). ...In this work, we investigated the bending shapes for each device length and have successfully fabricated a very low-loss and broadband 5-μm-beam-spot surface optical coupler based on a lensed-top vertically curved silicon waveguide by adjusting the dose conditions used in the ion implantation process. The fabricated device showed a coupling loss of 2.4 dB, which included a waveguide loss of approximately 0.5 dB and a 0.5-dB-loss bandwidth of more than 220 nm for the transverse electric polarization in the 1.55-μm wavelength band. This coupling device will greatly contribute to the progress in the development of Si-PICs using the coarse wavelength division multiplexing technique.
Many kinds of attractive new applications, such as image sensors, stationary X-ray sources, and the column-less SEM, are investigated as post field emission displays that use a gated nano electron ...source. The fabrication of the gated nano electron source is overviewed from the conventional method to the latest one, especially in regarding to the gate formation process. Multi-stacked gate electrode formation using an etch-back method was developed recently, which is a very attractive method for generating a focused electron beam. The traditional Spindt-type emitter fabrication method is also being improved to the one that is easier and applicable to large area substrates. Using a double-layered photoresist as a lift-off layer and using HiPIMS sputtering instead of an e-beam evaporator was proposed. Thin film-type FEA fabrication is also improved to make vertically standing thin film by ion irradiation, which is applicable for making an emitter array on a large sized substrate.
This study is focused on energy harvesting. The goal was to develop a new energy-harvesting system using a pressure regulator and establish an efficient energy flow model within it. The harvested ...electrical energy can be used as a power source for devices around the regulator, such as primary battery-powered gas meters, thereby enabling battery-free operation. Here, we focus on pressure regulators for LP and city gases, which are used by a vast number of consumers. We systematically modeled complicated energy-conversion processes using the transfer matrix method to maximize the recovered electrical energy. Under normal gas usage conditions, the gas flow is low, and the harvested energy is limited. However, it surpasses the energy supplied by the primary batteries. The results obtained under the actual operational conditions were compared with those calculated using a theoretical model. Within the system, a DC motor and an AC motor were used as generators, and the results were compared. When a DC motor was used as the generator under 0.05 MPa, 0.8 L/m, and maximum power-harvesting load conditions, the harvested power was 0.237 W, which is sufficient to drive the meters. Additionally, the error between the experimental and theoretical results ranged from 2.6% to 4.6%. When an AC motor was used as a generator, the harvested energy was 0.015 W and the error was -14.7%. Utilizing this theoretical model allows for the calculation of the optimal conditions for energy harvesting from various pressure regulators, thereby offering design guidelines for energy-harvesting systems.
To obtain high device fabrication uniformity and reproducibility for vertically curved silicon waveguide optical coupler, we developed the high accuracy ion implantation bending (IIB) method by ...incorporating a tungsten mask that can partially shield the ion implantation. The developed IIB method improved the positional accuracy of the origin of vertically curved Si wire bending from a wet etching-level of 1 m order to a dry etching-level of several 100 nm order, and we obtained a fabrication accuracy of about less than 0.4 m of the tip position of the Si-wire vertically curved structures.
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