Katsumi Nakatsuhara

Wavelength Tunable Operation in Si Waveguide Grating That Has a Ferroelectric Liquid Crystal Cladding

We obtained the wavelength selective operation in a grating Si rib waveguide that has an ferroelectric liquid crystal (FLC) cladding. The FLC cladding gives a phase shift change for the traveling lightwave in the waveguide in accordance with the polarity of the applied voltage. We propose the wavelength selective filter using this operation and demonstrate the selective switching and the tunable operation of our fabricated device. We also report its time response and dependence on the applied voltage and propose a new operating method to achieve a continuous phase change by using the FLC layer that has binary characteristics.

Latching operation in a tunable wavelength filter using Si sampled grating waveguide with ferroelectric liquid crystal cladding

A tunable wavelength filter fabricated with a latching function is proposed. The proposed tunable wavelength filter consists of a silicon sampled grating waveguide and ferro-electric liquid crystal (FLC) cladding. The sampled grating waveguide in a silicon-on-insulator (SOI) wafer achieved narrower stop bands than that with the conventional uniform grating structure. Enhanced wavelength shift was also obtained due to the increased effect in FLC by using a thinner silicon core. Bistable switching operation with the fabricated device, which was latching without state-sustaining power, was successfully demonstrated. Its switching and latching characteristics are also reported.

Tunable Optical Filter With Cascaded Waveguide Fabry–Pérot Resonators Featuring Liquid Crystal Cladding

We developed and fabricated a tunable optical filter using Si-waveguide multiple-cavity Fabry-Pérot resonators with ferro-electric liquid crystal cladding. The proposed filter can be monolithically integrated with other Si photonics devices because no cleaved facets are required. Also, the bistable characteristic of ferro-electric liquid crystal cladding means the power consumption is low. We tested wavelength operation in the fabricated device and determined that it was able to obtain a phase shift of 0.38 π. It also had improved resonant wavelength characteristics.

Demonstration of switching operation in a symmetric Mach-Zehnder interferometer switch using Si waveguide with a ferro-electric liquid crystal cladding

We proposed and fabricated a novel optical switching device using a Si-waveguide symmetric Mach-Zehnder interferometer having a ferro-electric liquid crystal cladding. We demonstrated the wavelength switching operation with the experimental device fabricated at 1550 nm wavelength.

Si-Waveguide with Ferro-Electric Liquid Crystal Cladding for Use in Optical Switching Devices

We studied a silicon (Si) waveguide using ferro-electric liquid crystal (FLC) cladding for various applications in optical networks. The FLCs in the cladding layer change their effective refractive index corresponding to the applied voltage polarity, and give a phase shift to the traveling lightwave in the waveguides. The phase change coefficients of three-layer slab waveguides with FLC/Si/SiO 2 structure were calculated. We observed an amplitude change in the output light of an experimental modulator consisting of a Mach-Zehnder interferometer with FLC-cladding Si-rib waveguides on a silicon-on-insulator wafer, and evaluated the phase shift at a wavelength of 1550 nm. We propose optical switching devices using Si-rib waveguide Mach-Zehnder interferometers having FLC cladding. Switching of experimental devices operating at 1550 nm wavelength was demonstrated.

A wavelength switching operation of a Si-waveguide asymmetric Mach-Zehnder interferometer having a ferro-electric liquid crystal cladding

We proposed and fabricated a novel optical switching device using a Si-waveguide asymmetric Mach-Zehnder interferometer with a ferro-electric liquid crystal cladding. We demonstrated the wavelength switching operation with the experimental device fabricated at 1550 nm wavelength.

Switching Operation in Tunable Add-Drop Multiplexer With Si-Grating Waveguides Featuring Ferroelectric Liquid Crystal Cladding

We propose a tunable add-drop multiplexer in a silicon waveguide Mach-Zehnder interferometer that has a sampled grating structure and ferroelectric liquid crystal (FLC) cladding, which we fabricated. The effective coupling coefficient that was decreased by the sample grating structure led to a narrow stop bandwidth in the grating waveguide. The FLC material caused a change in the Bragg conditions for lightwave propagation in the waveguide according to the direction of the electric field applied to FLC. The switching operation of the fabricated device, which separated the input and reflected signals without a circulator, was successfully demonstrated. The time response, dependence on voltage, and memory operation of the fabricated device based on FLC characteristics are also reported.

Tunable wavelength selective operation in grating silicon waveguide having ferroelectric liquid crystal cladding

We proposed and fabricated a wavelength selective switch with grating Si-waveguide having ferroelectric liquid crystal cladding. We demonstrated the tunable wavelength selective operation and obtained about 20dB of extinction ratio at 1530.5nm-wavelength.

Optical routing switches incorporating ferroelectric liquid crystals for use in photonic networks (Invited Paper)

Optical switching allows us to make the photonic network flexible and expandable. We have been studying two types of optical switches incorporating ferro-electric liquid crystals (FLCs). One type of them is a polarization-controlled free-space optical switch whose operation principle is based on the polarization switching by FLC cells. It has a novel integrated structure consisted with FLC polarization control devices (FLC-PCDs), thin-film beam-splitters and mirrors. The FLC-PCD with a metal mirror electrode is the key element in this switch. The design theory for the FLC-PCD to achieve an accurate 90-degree polarization switching for the oblique incident light has been developed and verified by experiments. 2x2 and 4x4 optical switches were fabricated for optical communication wavelengths of 1300 and 1550nm and their feasibility was demonstrated. The other switch type is a waveguide switch composed of an optical waveguide having FLC claddings. The FLCs in the cladding layer change their effective refractive index corresponding to the applied voltage polarity, providing the phase shift of the travelling lightwave in the waveguide. The operation principle of the switch has been confirmed by an experimental Si waveguide Mach-Zehnder interferometer (MZI) having FLC claddings.

Bragg reflector waveguide array with ferroelectric liquid crystal cladding for optical tunable wavelength filters

A tunable wavelength filter array is proposed, which consists of a 1 ? 6 multimode interferometer silicon waveguide splitter and Bragg reflector waveguides with ferroelectric liquid crystal (FLC) cladding. The transmission characteristics of the proposed device were reported, which were theoretically and experimentally obtained. Different operating wavelengths were obtained by using different waveguide widths with the same grating period. The stop bandwidth we obtained with a sampled grating was narrower than that in conventional uniform grating structures. Bistable tuning operation with a 0.8 nm shift in wavelength characteristics, which had six different Bragg wavelengths, was demonstrated. The distribution of the optical axis in the FLC cladding layer was also measured using a system for birefringence measurements.