Silica and silica-doped high quality factor (Q) optical resonators have demonstrated ultra-low threshold lasers based on numerous mechanisms (eg rare earth dopants, Raman). To date, the key focus has been on maintaining a high Q, as that determines the lasing threshold and linewidth. However, equally important criteria are lasing efficiency and wavelength. These parameters are governed by the material, not the cavity Q. Therefore, to fully address this challenge, it is necessary to develop new materials. We have synthesized a suite of silica and polymeric materials with nanoparticle and rare-earth dopants to enable the development of microcavity lasers with emission from the near-IR to the UV. Additionally, the efficiencies and thresholds of many of these devices surpass the previous work. Specifically, the silica sol-gel lasers are co- and tri-doped with metal nanoparticles (eg Ti, Al) and rare-earth materials (eg Yb, Nb, Tm) and are fabricated using conventional micro/nanofabrication methods. The intercalation of the metal in the silica matrix reduces the clustering of the rare-earth ions and reduces the phonon energy of the glass, improving efficiency and overall device performance. Additionally, the silica Raman gain coefficient is enhanced due to the inclusion of the metal nanoparticles, which results in a lower threshold and a higher efficiency silica Raman laser. Finally, we have synthesized several polymer films doped with metal (eg Au, Ag) nanoparticles and deposited them on the surface of our microcavity devices. By pumping on the plasmonic resonant wavelength of the particle, we are able to achieve plasmonic-enhanced upconversion lasing.
While there are several methods for creating a blue microlaser, most have very high lasing thresholds and are not
integrated on a silicon substrate. The present work demonstrates a blue laser based on the upconversion of thulium in a
doped silica sol-gel microtoroid resonant cavity integrated on a silicon wafer. The thulium is pumped at 1060nm, and
emission occurs near 780nm and 450nm. The high intensity of the circulating optical field in the microcavity increases
the photon interaction pathlength and interaction time with the thulium atoms, enabling sub-mW thresholds at both blue
and near-IR lasing emissions.
Optical cavities have successfully demonstrated the ability to detect a wide range of analytes with exquisite sensitivity. However, optimizing other parameters of the system, such as collection efficiency and specificity, have remained elusive. This presentation will discuss some of the recent work in this area, including 3D COMSOL Multiphysics models including mass transfer and binding kinetics of different cavity geometries and covalent attachment methods for a wide range of biological and synthetic moieties. A few representative experimental demonstrations will also be presented.
While many new label-free optical sensing techniques are focusing on increasing the sensitivity or decreasing the limit
of detection, the balance between sensitivity, specificity and collection efficiency are critical, particularly for detection in
complex media. For example, although high Q optical resonant cavities are inherently sensitive, the collection efficiency
of these devices is quite poor, particularly when compared to sensors with larger active sensing areas. By optimizing all
three parameters, even further advancements in sensing technologies are possible.
Historically, integrated photonic devices have been fabricated from inorganic material systems, such as silicon, silicon nitride, silica and gallium arsenide. As a result of their inherently low material loss and compatibility with nanofabrication tools, high performance waveguides and resonant cavities have been demonstrated. However, to achieve many of the desired performance metrics, it is necessary to implement active stabilization systems. For example, as a result of the thermo-optic effect, the resonant wavelength of a microcavity will change with temperature, resulting in an unpredictable resonant wavelength without temperature stabilization. Therefore, new materials and material systems are desired. One approach is to combine the inorganic materials conventionally used in telecommunications with organic polymeric materials. These hybrid systems offer the ability to tune the optical and mechanical properties of the inorganic materials, achieving athermal or temperature-independent performance. Additionally, given the wide range of polymeric material available, new material systems with previously unrealized behavior are possible; for example, materials which mechanically respond to UV, humidity and specific chemicals. Using silica toroidal whispering gallery mode resonant cavities as the device platform, a series of hybrid organic/inorganic resonators were fabricated. Several different types of organic layers were studied, varying both the specific polymeric material and the deposition method. For example, polyisobutylene was coated on the devices using either a spin-coating method or a surface initiated cationic polymerization process. With the wide range of possible organic materials, many different devices have been fabricated, including athermal devices, humidity and bio/chemical sensors, and microlasers.
Cavity ring down measurement approach is a promising technique for biosensing as it is insensitive to intensity
uctuations of a laser source. This technique in conjunction with ultra high Q microcavities have a great
potential for ultra sensitive biosensing. Until now, most work on microcavity biosensors has been based on
measurement of the resonant frequency shift induced by binding event on surface of the microcavity. Such
measurements suer from the noise due to intensity
uctuations of the laser source. However, the binding event
will also introduce shift in quality factor of the microcavity, which can be tracked by using cavity ring down
spectroscopy. In this work, we report on experimental demonstration of application of ring down measurement
approach to microcavities for biosensing by tracking disassociation phase of a biotin-streptavidin reaction. These
measurements were performed by using a bioconjugated ultra high Q microtoroidal cavity immersed in a liquid
microacquarium. We found that disassociation curves agree with previously reported results on the protein
Developing on-chip, dynamically reconfigurable visible lasers that can be integrated with additional optical and
electronic components will enable adaptive optical components. In the present work, we demonstrate a reconfigurable
quantum dot laser based on an integrated silica ultra high-Q microcavity. By attaching the quantum dot using a
reversible, non-destructive bioconjugation process, the ability to remove and replace it with an alternative quantum dot
without damaging the underlying microcavity device has been demonstrated. As a result of the absorption/emission
characteristics of quantum dots, the same laser source can be used to excite quantum dots with distinct emission