Quantum Dot Nucleation in Glass Microsphere Resonators Anu Tewary (student) and Mark Brongersma (PI)

Stanford University, DMR0444257

• A thin layer of Si-rich oxinitride (SRON) film was deposited on the sphere by collaborators at Kaist, S. Korea (Prof. Shin’s group)

Exploiting Si Nanoparticle Precipitation in glass microspheres

• Such a glass sphere acts as tiny optical cavities in which light can be stored and manipulated

• We fiber-coupled the coated SiO2 microsphere resonators.

• We demonstrated an ultra-low power-length product (5.1x10-10 Wm) all-optical, switch using the coated spheres (Publication 2)

• We used furnace and CO2 laser anneals to nucleate and grow Si nanoparticles in the SRON films (publication 1).

75 µm

• A 150 m diameter glass sphere was made by heating the tip of a SiO2 glass fiber with a CO2 laser.

200 nm

SRON

SiO2 Sphere

• The optical fiber couples light from a pump and signal laser into the microsphere. The pump light gets absorbed by the Si nanoparticles, causing an index shift that switches the signal.

(1) A. Tewary et. al, Appl. Phys. Lett. 88, 093114 (2006). & (2) A. Tewary et. al, Accepted for publ. JSTQE (2006)

Quantum Dot Nucleation in Glass Microsphere Resonators Anu Tewary (student) and Mark Brongersma (PI)

Stanford University, DMR0444257

• All-optical fiber switches are important devices that have been researched for many years mainly because of the critical need for low-loss, low-power, fiber-interfaced, optically addressable switching devices in optical communication and fiber sensor systems. We report a novel low-energy, all-optical fiber switch that consists of a silica microsphere resonator coated with a silica layer containing silicon nanocrystals. A signal at 1450 nm and a pump at 488 nm are coupled into the microsphere through a tapered fiber. When a pump pulse is launched into the sphere, it is absorbed by the nanocrystal layer, causing the sphere to heat up and change its refractive index. The index change can be exploited to switch the signal by shifting the microsphere resonance. A resonance wavelength shift of 5 pm, sufficient to fully switch the signal, was observed with a pump pulse energy of only 85 nJ. The product of the switching peak power (3.4 µW) and the device’s characteristic dimension (a diameter of 150 µm) is 5.1×10-10 Wm, one of the lowest values reported for an all-optical switch.

An impression of our research and outreach

Quantum Dot Nucleation in Glass Microsphere Resonators Anu Tewary (student) and Mark Brongersma (PI)

Stanford University, DMR0444257

• Our group hosted a summer student from Turkey (Umut Eser) and taught him how to synthesize and optically characterize light emitting Si nanostructures.

• Brongersma has been involved with outreach to high school student groups

• Two female PhD students are funded under this NSF grant

• The project is interdisciplinary and builds on materials and optical sciences

• We started a new collaboration with a group at KAIST in South Korea and had students from their University over to perform measurements in our laboratory.

• The results from this research have been incorporated in Brongersma’s course on nanophotonics and a tutorial taught to people in industry and VCs.