Description: Description:        Vahala Research Group

 

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High Sensitivity Nanoparticle Detection with Microtoroids
We demonstrate a highly sensitive nanoparticle and virus detection method by using a thermal-stabilized reference interferometer in conjunction with an ultrahigh-Q microcavity. Sensitivity is sufficient to resolve shifts caused by binding of individual nanobeads in solution down to a record radius of 12.5 nm, a size approaching that of single protein molecules. A histogram of wavelength shift versus nanoparticle radius shows that particle size can be inferred from shift maxima. Additionally, the signal-to-noise ratio for detection of Influenza A virus is enhanced to 38:1 from the previously reported 3:1. The method does not use feedback stabilization of the probe laser. It is also observed that the conjunction of particle-induced backscatter and optical-path-induced shifts can be used to enhance detection signal-to-noise.

As reported by: Tao Lu, et al in PNAS

Also see: Tao Lu et al, Patent pending (US20100085573)

 

Description: Description: CQED intro

 

 

Strong Coupling on a Microelectronic Chip
Working with Prof. Jeff Kimble and coworkers in the Caltech Physics department, we have recently achieved strong coupling between individual caesium atoms and the whispering galley mode of the toroidal microresonator. The coherent coupling rate for interactions near the surface of the resonator is determined from observations of transit events for single atoms falling through the resonatorís evanescent field. This work opens the way for investigations of optical processes with single atoms and photons, such as implementation of quantum networks, scalable quantum logic with photons, and quantum information processing on atom chips.

As reported by Aoki, T et al in Nature

 

Description: Description: 3rd harmonic intro
Visible Emission by 3rd Harmonic Generation
Nonlinear harmonic generation is widely used to extend the emission wavelength of laser sources. These devices typically require high peak powers to generate sufficient nonlinear optical response. We have demonstrated continuous-wave, visible emission from a silica microresonator on a silicon chip by third-harmonic generation. Emission is observed with pump powers <300 microWatts. Emission across the visible spectrum is shown using infrared, pump waves in the telecom band. In addition to providing low-pump-power, continuous-wave operation, this result opens a new application of silicon microphotonic devices by linking the mature telecom sources into the visible and UV bands.

Reported by Carmon, T. and Vahala, K. in Nat. Phys

 

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Free Ultra-high Q Microtoroids
The special fabrication process of the silica microtoroids limits the range of possible integration choices for these resonators. So those photonic devices that rely on coupling of these resonators to an integrated waveguide or their mutual coupling cannot be realized. We describe techniques that may enable fabrication of a new class of photonic devices based on free UH-Q microresonators.  Preliminary results show that by employing simple techniques we can detach the microtoroid from the silicon pillar without any damage to the microtoroid structure and maintain their quality factor above 10 million.
As reported by: Hossein-Zadeh, M. and Vahala, K. in Optics Express
 
 
 

 

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Ultra-High Q Microtoroid Resonator
The circulation of light within dielectric volumes enables storage of optical power near specific resonant frequencies and is important in a wide range of fields including cavity quantum electrodynamics, photonics, biosensing and nonlinear optics. Here we demonstrate a process for producing silica toroidal microresonators-on-a-chip with Q factors in excess of 100 million using a combination of lithography, dry etching and a selective reflow process. Such a high Q value was previously attainable only by droplets or microspheres and represents an improvement of nearly four orders of magnitude over previous chip-based resonators.
As reported by Armani, D et al in Nature
 

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Optomechanical GHz Oscillator and Spectroscopy
Just like the spectral signature of materials originates from molecular vibrations, photonic devices have many spectral lines originating from their different mechanical modes. Our group has excited these modes using the radiation pressure produced by light circulating within the device (1, 2, 3) which oscillate regeneratively at controllable mechanical eigen-frequencies up to microwave rates. There is no feedback or externally-applied modulation in the experiment and the optical input is continuous. Microwave-rate oscillations build-up from an inherent parametric process. This is therefore both a spectroscopic technique and a micro-mechanical device.  
As reported by Carmon, T. and Vahala, K. in PRL
 

Description: Description: oscillator-intro02

 
Radiation-pressure-driven micromechanical oscillator
As Q factor is increased in microresonators, there will be a natural tendency for these devices to experience a radiation pressure induced instability. This instability is manifested as a regenerative oscillation (at radio frequencies) of the mechanical modes of the microcavity. Embodied within this chip-based device, this mechanism can benefit both research into macroscale quantum mechanical phenomena and improve the understanding of the mechanism within the context of LIGO. It also suggests that new technologies are possible which will leverage the phenomenon within photonics.
As reported by: Rokhsari, H. et al in Optics Express
also Kippenberg, T. et al in Physical Review Letters
Carmon, T. et al in Physical Review Letters

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Description: Description: toroid_intro03

 
Phonon Laser Action in a Tunable Two-Level System
The phonon analog of an optical laser has long been a subject of interest. We demonstrate a compound microcavity system, coupled to a radio-frequency mechanical mode, that operates in close analogy to a two-level laser system. An inversion produces gain, causing phonon laser action above a pump power threshold of around 7  μW. The device features a continuously tunable gain spectrum to selectively amplify mechanical modes from radio frequency to microwave rates. Viewed as a Brillouin process, the system accesses a regime in which the phonon plays what has traditionally been the role of the Stokes wave. For this reason, it should also be possible to controllably switch between phonon and photon laser regimes. Cooling of the mechanical mode is also possible.
As reported by Grudinin et al in PRL
Also see a Viewpoint by J. Khurgin
Nature News: 'Sasers' set to stun
 
 

Description: Description: Nanocrystal_Intro

Planar Nanocrystal Quantum Dot Lasers
In collaboration with Prof. Harry Atwater, Prof. Axel Scherer, and co-workers, chemically synthesized nanocrystal, CdSe/ZnS core/shell, quantum dots are coated on the surface of an ultrahigh-Q toroidal microcavity and lasing is observed at room and liquid nitrogen temperatures by pulsed excitation of the quantum dots, either through tapered fiber or free space. Minimum thresholds were achieved when the quantum dot surface coverage was optimized and tapered optical fibers were used to efficiently deliver the pump pulses to the active gain region of the toroidal microcavity. The minumum threshold energy achieved was 9.9 fJ.
As reported by: Min, B. et al in APL
 
 
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Putting Lightís Light Touch to Work
A.Cho. Science V.328, p. 812
 

 
 updated August 10, 2011
 

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