Photonic Integrated Circuit

Integration of Optical Isolator with Laser Diode
Integrated Isolator
Generalized Treatment of Coupled Waveguide

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.



Published Papers

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.

Published Papers

Generalized Treatment of Coupled Waveguide

Tapered coupled waveguides in which waveguide structure varies along light propagation direction have the advantages of insensitivity to fabrication errors and wavelength-flattened characteristics. The purpose of this research is to fully exploit the design of the tapered coupler. The coupling characteristics are discussed in a generalized model based on the waveguide normalization.

Published Papers