Research

Photonic integrated circuits

Integration of optical isolator with laser diode

Integration of optical isolator with laser diode

We developed a technology to integrate an optical isolator and a laser diode by wafer direct bonding of magneto-optical crystal with III-V compound semiconductor.

Wafer direct bonding

The direct bonding technique provides the wafer bonding without adhesive. The direct bonding of magnetooptic garnets to III-V compound semiconductors is invesitgated in this research group. It has been demonstrated that (LuNdBi)3(FeAl)5O12 wafers on which optical waveguides are fabricated are bonded onto InP substrates and GaInAsP layer MOCVD-grown on the InP substrate.

Optical isolator integrated with laser diode

An optical isolator protects optical active devices, such as a laser diode and an optical amplifier from unwanted reflected light. This is essential to stabilize the operation of active devices. The novel optical isolator composed of semiconductor waveguide, which is integrable with LD, is investigated. The isolator employs nonreciprocal phase shift in an in-plane magnetized magnetooptic crystal. The magnetooptic crystal like an iron garnet is directly bonded with III-V semiconductor guiding layer by using wafer direct bonding. The features of the device are single polarization operation and easy control of magnetization.

The above figure illustrates the operation of the isolator employing nonreciprocal phase shift. Lightwave launched out from the laser diode passes to the right output port as indicated in red color.
The lightwave reflected back from the external circuit propagates as indicated in blue color, which is not injected into the laser diode.

High-functioning switching devices

Wavelength-selective switch for on-chip WDM networks

Optical fiber communication is capable of long distance transmission with high capacity using wavelength division multiplexing (WDM) technology. Recently, it is required even in short-distance communiations such as rak-to-rack and board-to-board links. Wavelength-slective switches (WSSs) are typically based on free-space optics employing switching elements such as MEMS and liquid crystal on silicon (LCOS). We have proposed a novel WSS structure based on silicon photonic platform.

Low-power-consumption magneto-optic switch with self-holding operation

We have proposed a novel self-holding optical switch which holds its switching state without any power supply and consumes power only when the state is changed. This feature is useful for optical cross-connect sysytems or reconfigurable photonic integrated circuits. Magneto-optical (MO) effect in the MO garnet induces phase shift in the interferometer arms. The magnetization of MO garnet is fixed by magnetic field from magnetic-recording medium. Control signals of pulsed current flips the magnetization of the magnetic-recording medium and then changes the optical switching state.

Waveguide magneto-optical memory

Photonic computing device for AI photonic accelerator

Convolutional neural network with non-volatile optical gate

Visible-light devices with optical waveguides

Planar beam scanner with magneto-optical effect