Kengo Miura

Optical Nonreciprocal Devices Based on Magneto-optical Phase Shift in Silicon Photonics

Silicon waveguide optical nonreciprocal devices that use the magneto-optical phase shift are reviewed. The phase shift caused by the first-order magneto-optical effect is effective in realizing optical nonreciprocal devices on semiconductor waveguide platforms. In a silicon-on-insulator waveguide, the low refractive index of the buried oxide layer contributes to the large penetration of the optical field into a magneto-optical material used as an over-cladding layer. This enhances the magneto-optical phase shift and, hence, contributes greatly to reducing the device footprint. A surface-activated direct bonding technique plays a key role in the fabrication of magneto-optical nonreciprocal devices. This technique makes it possible to use a high-quality single-crystalline magneto-optical garnet that exhibits a large first-order magneto-optical effect. An optical isolator based on the magneto-optical phase shift was demonstrated in a silicon waveguide with an optical isolation ratio as high as 30 dB and an insertion loss of 13 dB at a wavelength of λ = 1548 nm. Furthermore, a four-port optical circulator was demonstrated with maximum isolation ratios of 33.5 and 29.1 dB in the cross and bar ports, respectively, at λ = 1543 nm.

Magneto-optical switch with amorphous silicon waveguides on magneto-optical garnet

We fabricated a magneto-optical (MO) switch with a hydrogenated amorphous silicon waveguide on an MO garnet. The switch is composed of a 2 × 2 Mach–Zehnder interferometer (MZI). The switch state is controlled by an MO phase shift through a magnetic field generated by a current flowing in an electrode located on the MZI. The switching operation was successfully demonstrated with an extinction ratio of 11.7 dB at a wavelength of 1550 nm.

Amorphous-Si waveguide on a garnet magneto-optical isolator with a TE mode nonreciprocal phase shift

We fabricated a magneto-optical (MO) isolator with a TE mode nonreciprocal phase shift. The isolator is based on a Mach-Zehnder interferometer composed of 3-dB directional couplers, a reciprocal phase shifter, and a nonreciprocal phase shifter. To realize TE mode operation in the optical isolator, we designed a novel waveguide structure composed of a hydrogenated amorphous silicon waveguide with an asymmetric MO garnet lateral clad on a garnet substrate. The isolator operation is successfully demonstrated in a fabricated device showing the different transmittances between forward and backward directions. The maximum isolation of the fabricated isolator is 17.9 dB at a wavelength of 1561 nm for the TE mode.

Silicon on-chip wavelength-selective switch composed of Mach–Zehnder-interferometer-based switches and microring resonators

We fabricated a wavelength-selective switch composed of microring resonators as wavelength filters and Mach–Zehnder-interferometer-based thermo-optic switches as routing switches. Nonblocking wavelength-selective switching operations for several channels were successfully demonstrated. A wavelength-selective transmittance change of 9.7 dB was obtained at a wavelength channel of 1548 nm, which is one of four wavelength channels in a wavelength range between 1535 and 1570 nm. An electric power of 17.9 mW was applied for switching the thermo-optic switch from a cross state to a bar state. The change in transmittance in other wavelength channels is <1.7 dB.

Mach-Zehnder wavelength selective switch embedded with microring resonators

A wavelength selective switch is proposed for optical wavelength division multiplexing network applications with very short range interconnections. The proposed device uses a Mach–Zehnder interferometer configuration incorporating wavelength selective phase shifters composed of microring resonators between their two arms. Wavelength selectivity is provided by cascaded microring resonators, which are placed in proximity so that the increase in excess loss caused by the difference in resonant wavelengths can be minimized. An on/off switching ratio >20 dB is obtainable when the drop/through transmittance ratio of the cascaded microring resonators is >22 dB and the coupling efficiency deviation from 50% is <1% in the directional couplers constructing the Mach–Zehnder interferometer.

On-chip differential phase monitoring with balanced photodiodes

We present on-chip differential phase shift monitoring between delay lines of a phased array using integrated balanced photodiodes. We compare the results of the differential measurement to a measurement using an external reference Mach-Zender interferometer.

Demonstration of magneto-optical switch with amorphous silicon waveguides on magneto-optic garnet

A magneto-optical (MO) switch with amorphous silicon waveguides on a magneto-optic garnet is fabricated. The device uses the MO phase shift where the magnetic field is applied by the current flow in an electric wiring. The switch exhibited an extinction ratio of 11.7 dB at a wavelength of 1550 nm.