Kato Group

Nanoscale Quantum Photonics Laboratory, RIKEN

Research:Optical coupling of individual carbon nanotube emitters to silicon microdisk resonators

Microdisk resonators are dielectric disks with diameters of a few microns, and they work as an optical microcavity. They support whispering gallery modes in which optical waves are guided along the circumference of the disk by continuous internal reflection. Since they are traveling wave resonators, they can be coupled to waveguides with high efficiency, making them a preferred choice for use in silicon photonics.

Here, in an effort to integrate carbon nanotube emitters into silicon photonic circuits, we demonstrate a device consisting of an individual nanotube and a silicon microdisk resonator that is compatible with integration into silicon photonics. The emission from nanotubes is coupled to the resonator, while the emission is controlled by utilizing the interaction of the evanescent fields of the cavity modes to the nanotubes.

device structure
Device structure

Microdisk resonators are fabricated from silicon-on-insulator (SOI) substrates which consist of a thin silicon and silicon dioxide layers stacked on top of a thick silicon layer. Stamdard semiconductor fabrication techniques are used to form a disk structure out of the top silicon layer, and the oxide layer becomes the supporting posts for the disks.

SEM of a microdisk
Scanning electron micrograph of a microdisk
PLE of a microdisk
Photoluminescence excitation spectroscopy of a microdisk

Catalyst is placed around the microdisk resonator to suspend the nanotubes onto the microdisks by chemical vapor deposition, and Photoluminescence measurements are performed on these devices. As shown in the figure, we observe a sharp peak on top of nanotube spectrum, demonstrating enhancement of photoluminescence. Furthermore, imaging measurements show that nanotube emission circulates within the disk.

PL of a nanotube on a microdisk
Photoluminescence spectrum of a carbon nantube suspended onto a microdisk resonator
PL image of a sample
Photoluminescence image of a microdisk

To learn more about this work, please refer to Optical control of individual carbon nanotube light emitters by spectral double resonance in silicon microdisk resonators S. Imamura, R. Watahiki, R. Miura, T. Shimada, Y. K. Kato Appl. Phys. Lett. 102, 161102 (2013). Link to publisher pdf