E. Krioukov

Sensor based on an integrated optical microcavity

A novel integrated optical sensor based on a cylindrical microcavity (MC) is proposed. A MC sustains so-called whispering-gallery modes (WGMs), in which the energy of the optical field can be efficiently stored. By monitoring the scattering intensity from the MC, one can detect minute changes in the refractive index of the WGM, for instance, as a result of analyte adsorption. Measurement of a change in refractive index of as little as 10(-4) is demonstrated experimentally. The MC-based integrated optical sensor may have a size of approximately 8mum , and it is rugged and inexpensive.

Integrated optical microcavities for enhanced evanescent-wave spectroscopy

The use of integrated optical microcavities (MCs) for enhanced optical spectroscopy and sensing is investigated. The MC sustains high- Q whispering-gallery modes, in which the energy of the optical field can be efficiently stored. The resulting enhanced field can be used to probe fluorescent molecules in the cladding of the MC. Enhanced fluorescence excitation with an integrated optical MC is demonstrated experimentally for what is believed to be the first time. A comparison between a MC and a straight waveguide shows that the MC may give an increase of 40 times in fluorescence excitation. Because of the ultrasmall size of the MC (15 microm in radius), the fluorescence signal may be observed from only 20 molecules in the cladding.

Performance of integrated optical microcavities for refractive index and fluorescence sensing

The performance of a novel sensor based on an integrated optical (IO) disk microcavity (MC) is theoretically studied. The MC is a resonant waveguide structure in which multiple interference of a guided mode occurs. At resonance, the MC is extremely sensitive to refractive index changes and it sustains locally enhanced optical field. Therefore, the MC is naturally suitable as an extremely responsive sensor for measuring minute changes in refractive index and/or fluorescence of an analyte. Combination of multiple interference and extremely small sampling volume (few femtoliters) provides unique sensitivity of the MC device. A factor of 9 increase in fluorescence sensitivity versus waveguide sensor is anticipated. Provided shot-noise limited detection, the refractive index resolution down to 10−9 is feasible with the MC sensor, which exceeds that of the straight waveguide interferometer by the order of magnitude. MC-sensors can be combined into arrays providing high throughput detection of both labeled and non-fluorescent biological species.

Microresonators As Building Blocks For VLSI Photonics

In the last years much effort has been taken to arrive at optical integrated circuits with high complexity and advanced functionality. For this aim high index contrast structures are employed resulting in photonic wires in conventional index guiding waveguides or in photonic bandgap structures. In both cases the number of functional elements within a given chip area can be enhanced by several orders of magnitude: VLSI photonics. In this talk optical microresonators are presented as promising basic building blocks for filtering, amplification, modulation, switching and sensing. Active functions can be obtained by monolithic integration or a hybrid approach using materials with thermo‐, electro‐ and opto‐optic properties and materials with optical gain. Examples are mainly taken from work at MESA+.

Two-photon fluorescence excitation using an integrated optical microcavity: a promising tool for biosensing of natural chromophores

Application of an integrated optics (IO) microcavity (MC) for evanescent excitation of two-photon excited fluorescence (TPF) is demonstrated. The MC provides a high local intensity, which is required for the TPF, because of resonant enhancement of the intracavity power and a strong two-dimensional confinement of the guided mode. Numerical estimations show a large increase, by more than a factor of 10(4) of the TPF intensity at the MC compared to a conventional straight waveguide. This will lead to a significant improvement of the detection limits of UV-absorbing chromophores (down to 10(-8)M) when using the MC as a biosensor. Feasibility of TPF excitation using an IO MC is confirmed experimentally for the first time.

Ultracompact Optical Sensors based on high index-contrast Photonic Structures

There is a strong parallelism between electronic integrated circuits (ICs) and integrated optics. In both cases microand increasingly nano-technology is applied resulting in devices for a broad spectrum of applications: communication, data processing, sensing and others. The most striking difference is the maturity and complexity. Electronic ICs have followed Moores law for about 40 years resulting in the currently more than 100 million transistors in a single chip, whereas in photonic circuitries 10 100 functional elements per chip represent state-of-the-art results. Photonics in this respect is clearly lagging behind and will do so also in hture, as the minimum dimensions of the fimctional elements will be always in the order of the wavelen th of light, i.e. at least some hundreds of nm. But even then, F a density of 10 to lo5 functional elements per optical chip is feasible, so that the tenn Very Large Scale Integrated (VLSI) photonics1 is not an exaggeration. Optical circuits will not simple mimic electronics, but will exploit in a complementary way the unique phenomena offered by light. For example THz bandwidth amplification is straightforward in optical structures with

All-Optical Switching Devices in Integrated Optics Cylindrical Microresonators: An experimental feasibility study

The feasibility of cylindrical microresonators for all-optical switching applications is discussed both theoretically and experimentally. Using experimental results of high finesse cylindrical microresonators we give estimates for the switching powers.

Integrated optical microcavities for spectroscopy

The potential of integrated optical micro cavities (MC) for use in enhanced optical spectroscopy has been studied. The MC devices can sustain high morphological enhancement of optical field due to excitation of high-Q whispering gallery modes. The evanescent near field of the MC can be used to excite spectroscopic signal of molecules pout on top of the MC. Estimation shows that both local excitation field and emitted field can be increased y 2-3 orders of magnitude in the MC on resonance. In total, a gain of 4-8 orders of magnitude in the Raman/fluorescent signal of a molecule near the MC can be expected. In addition, the MC delivers a tunable and measurable enhancement, which is a real benefit in terms of enhanced optical microspectroscopy on-chip. High-Finesse integrated optics cylindrical micro cavities capable of significant field enhancement have been fabricated. Use of various waveguide/MC coupling schemes and design parameters allowed optimization of the devices for the largest intra-cavity power. The result for different micro cavities show prominent enhancement of intra-cavity field correlating with its mode spectrum. The characterization of MC and measurements performed demonstrate feasibility of the MC-based device for optical spectroscopy.