Hidetaka Nishi

Integrated photonic devices based on silicon photonic wire waveguide platform

Silicon photonic wire waveguides, featuring very strong optical confinement and compatibility with silicon electronics, provide a compact photonic platform on which passive, dynamic, and active photonic devices can be integrated. We have already developed a low-loss waveguide platform and integrated various photonic devices. For passive devices, we have developed polarization-independent wavelength filters using a monolithically integrated polarization diversity circuit, in which waveguide-based polarization manipulation devices are implemented. The polarization-dependent loss of a ring resonator wavelength filter with polarization diversity is less than 1 dB. For dynamic devices, we have developed compact carrier-injection-type variable optical attenuators (VOAs). The length of the device is less than one millimeter, and the response time is nanosecond order. The device has already been made polarization independent. We have recently monolithically integrated these fast VOAs with low-dark-current germanium photodiodes and achieved synchronized operation of these devices. For nonlinear devices, a free-carrier extraction structure using a PIN junction implemented in the waveguide can increase the efficiency of nonlinear functions. For example, in a wavelength conversion based on the Four-wave-mixing effect, the conversion efficiency can be increased by 6 dB.

40-km SSMF Transmission of 56/64-Gb/s PAM-4 Signals Using 1.3-μm Directly Modulated Laser and PIN Photodiode

For low-cost reach extension of 400G Ethernet, >50-Gb/s PAM-4 at 1.3-μm over 40-km is demonstrated without optical amplification, enabled by a high-speed and high launch power directly modulated laser, PIN-photodiode, and low-complexity equalization.

Polarization diversity circuit based on a double-core structure consisting of silicon photonic wire and silicon-oxinitride waveguide

We devised a silicon photonic circuit with polarization diversity. The circuit consists of polarization splitters and rotators. The splitter is based on simple 10-micrometer-long directional couplers. The polarization extinction ratio is 23 dB and excess loss is less than 0.5 dB. The rotator consists of a silicon waveguide embedded in an off-axis siliconoxynitride waveguide. A 35-micrometer-long rotator gives a rotation angle of more than 72 degrees and excess loss of about 1 dB. Both devices can be made by using planar fabrication technology and do not require a complex structure such as three-dimensional forming. Using these devices, we developed a polarization diversity circuit for a ringresonator wavelength filter. The polarization dependent loss of the filter with polarization diversity is about 1 dB. A 10- Gbps data transmission with scrambled polarization is demonstrated.