Ultrahigh-responsivity waveguide-coupled optical power monitor for Si photonic circuits operating at near-infrared wavelengths.

A phototransistor is a promising candidate as an optical power monitor in Si photonic circuits since the internal gain of photocurrent enables high responsivity. However, state-of-the-art waveguide-coupled phototransistors suffer from a responsivity of lower than 103 A/W, which is insufficient for detecting very low power light. Here, we present a waveguide-coupled phototransistor operating at a 1.3 µm wavelength, which consists of an InGaAs ultrathin channel on a Si waveguide working as a gate electrode to increase the responsivity. The Si waveguide gate underneath the InGaAs ultrathin channel enables the effective control of transistor current without optical absorption by the gate metal. As a result, our phototransistor achieved the highest responsivity of approximately 106 A/W among the waveguide-coupled phototransistors, allowing us to detect light of 621 fW propagating in the Si waveguide. The high responsivity and the reasonable response time of approximately 100 µs make our phototransistor promising as an effective optical power monitor in Si photonic circuits.

Si microring resonator optical switch based on optical phase shifter with ultrathin-InP/Si hybrid metal-oxide-semiconductor capacitor.

We propose a microring resonator (MRR) optical switch based on III-V/Si hybrid metal-oxide-semiconductor (MOS) optical phase shifter with an ultrathin InP membrane. By reducing the thickness of the InP membrane, we can reduce the insertion loss of the phase shifter, resulting in a high-quality-factor (Q-factor) MRR switch. By optimizing the device structure using numerical analysis, we successfully demonstrated a proof-of-concept MRR optical switch. The optical switch exhibits 0.3 pW power consumption for switching, applicable to power-efficient, thermal-crosstalk-free, Si programmable photonic integrated circuits (PICs) based on wavelength division multiplexing (WDM).

Taperless Si hybrid optical phase shifter based on a metal-oxide-semiconductor capacitor using an ultrathin InP membrane.

We propose a III-V/Si hybrid metal-oxide-semiconductor (MOS) optical phase shifter using an ultrathin InP membrane, which allows us to eliminate the III-V taper required for mode conversion between Si and hybrid waveguides. We numerically revealed that thinning a III-V membrane can reduce the insertion loss of the phase shifter while maintaining high modulation efficiency because the optical phase shift is induced by carrier accumulation at the MOS interface. We experimentally demonstrated the proposed optical phase shifter with an ultrathin InP membrane and achieved the modulation efficiency of 0.54 Vcm and the insertion loss of 0.055 dB. Since the taperless structure makes the hybrid integration easier and more flexible, the hybrid MOS optical phase shifter with an ultrathin III-V membrane is promising for large-scale Si programmable photonic integrated circuits.

Spontaneous formation of dye-functionalized gold nanoparticles using reverse micellar systems.

Detailed exploratory and mechanistic investigations on spontaneous formation of dye-functionalized gold nanoparticles (GNPs) using dye-based reverse micellar systems are described in this publication. The accumulated results from spectroscopic and microscopic investigations demonstrated that water molecules confined within nanoscopic enclosure of the self-assembled reverse micelles played critical role in the redox processes of aurate ions to produce GNPs, which are assumed to have approximately constant size distributions. The resulting dye-functionalized GNPs were found to offer their absorption and fluorescence emission tunability by changing the medium polarity as well as to exhibit excellent film-forming properties to give optically homogeneous polystyrene thin films. These key findings in addition to broad applicability of the self-assembling process with a variety of dye analogues have led to a conclusion that the protocol presented here serves as a versatile synthetic method to provide a potential convenience for future development of new organic-inorganic hybrid nanomaterials.