John V. Hryniewicz

Very high-order microring resonator filters for WDM applications

High-order microring resonators having from 1 to 11 coupled cavities are demonstrated. These filters exhibit low loss, flat tops, and out-of-band rejection ratios that can exceed 80 dB. They achieve performance that is suitable for commercial applications.

Optical sensing of biomolecules using microring resonators

A biosensor application of vertically coupled glass microring resonators with Q/spl sim/12 000 is introduced. Using balanced photodetection, very high signal to noise ratios, and thus high sensitivity to refractive index changes (limit of detection of 1.8/spl times/10/sup -5/ refractive index units), are achieved. Ellipsometry and X-ray photoelectron spectroscopy results indicate successful modification of biosensor surfaces. Experimental data obtained separately for a bulk change of refractive index of the medium and for avidin-biotin binding on the ring surface are reported. Excellent repeatability and close-to-complete surface regeneration after binding are experimentally demonstrated.

Propagation loss in single-mode GaAs-AlGaAs microring resonators: measurement and model

We report propagation loss measurements in single-mode GaAs-AlGaAs racetrack microresonators with bending radii from 2.7 /spl mu/m to 9.7 /spl mu/m. The experimental data were found to be in good agreement with a physical-loss model which accounts for the bending loss, the scattering loss due to surface roughness on the waveguide sidewalls, and the transition loss at the straight-to-bend waveguide junctions. The model also enables us to identify the dominant loss mechanisms in semiconductor microcavities. We found that for racetracks with large bending radii (greater than 4 /spl mu/m, in our case) the loss due to surface-roughness scattering in the curved waveguides dominates, whereas for small-radius rings, the modal mismatch at the straight-to-bend waveguide junctions causes the biggest loss. This result suggests that circular-shaped rings are preferable in the realization of ultrasmall low-loss microcavities. We also show that the round-trip propagation loss in small-radius racetrack microresonators can be minimized by introducing a lateral offset at the straight-to-bend waveguide junctions.

Vertically coupled microring resonators using polymer wafer bonding

A new technique is presented to make vertically coupled semiconductor microring resonators that eases the fabrication process with devices more robust to ring-to-waveguide misalignments. Single-mode microring optical channel dropping filters are demonstrated for the first time in this configuration with Qs greater than 3000 and an on-resonance channel extinction greater than 12 dB. A 1/spl times/4 multiplexer/demultiplexer crossbar array with second-order microrings was also made and exhibited channel-to-channel crosstalk lower than 10 dB.

Broadband optical absorbance spectroscopy using a whispering gallery mode microsphere resonator

We demonstrate the ability to excite and monitor many whispering gallery modes (WGMs) of a microsphere resonator simultaneously in order to make broadband optical absorbance measurements. The 340 microm diameter microsphere is placed in a microfluidic channel. A hemispherical prism is used for coupling the WGMs into and out of the microsphere. The flat surface of the prism seals the microfluidic channel. The slight nonsphericity in the microsphere results in coupling to precessed modes whose emission is spatially separated from the reflected excitation light. The evanescent fields of the light trapped in WGMs interact with the surrounding environment. The change in transmission observed in the precessed modes is used to determine the absorbance of the surrounding environment. In contrast to our broadband optical absorbance measurements, previous WGM sensors have used only a single narrow mode to measure properties such as refractive index. With the microfluidic cell, we have measured the absorbance of solutions of dyes (lissamine green B, sunset yellow, orange G, and methylene blue), aromatic molecules (benzylamine and benzoic acid), and biological molecules (tryptophan, phenylalanine, tyrosine, and o-phospho-L-tyrosine) at visible and ultraviolet wavelengths. The microsphere surface was reacted with organosilane molecules to attach octadecyl groups, amino groups, and fluorogroups to the surface. Both electrostatic and hydrophobic interactions were observed between the analytes and the microsphere surface, as indicated by changes in the measured effective pathlength with different organosilanes. For a given analyte and coated microsphere, the pathlength measurement was repeatable within a few percent. Methylene blue dye had a very strong interaction with the surface and pathlengths of several centimeters were measured. Choosing an appropriate surface coating to interact with a specific analyte should result in the highest sensitivity detection.

Tunable bandwidth microring resonator filters

Tunable bandwidth, tunable line-shape filters are realized by incorporating Mach-Zehnder interferometers as directional coupler elements within higher order microring resonators. A flat-top bandwidth tuning range of 2.7 GHz to 21 GHz is demonstrated.

Etch‐mask of pyrolytic‐photoresist thin‐film for self‐aligned fabrication of smooth and deep faceted three‐dimensional microstructures

Etch‐mask thin‐film material that is particulate‐free and topographically smooth has been created from a standard photoresist spun onto standard semiconductor substrates such as gallium arsenide, indium phosphide, and silicon, and then pyrolyzed by exposing to a temperature of 300 °C in air atmosphere for 1 min on a standard laboratory hot‐plate. The resulting pyrolytic‐photoresist thin‐film is chemically inert to many standard organic solvents including the solvent of photoresist itself and to many inorganic reagents used in semiconductor processing. Therefore the pyrolytic‐photoresist can be patterned by sulfur hexafluoride reactive ion etching via a standard photoresist mask. Upon stripping the standard photoresist in a mixture of 1:1/acetone:developer agitated ultrasonically, the remaining patterned pyrolytic‐photoresist performs as an excellent etch‐mask in chemically assisted ion beam etching and reactive ion etching systems. Thus it can be a key material in the multilayer masking technique used to ...

Microring resonators: the promise of a powerful biochemical sensor platform

Microring resonators constitute ideal microspots where the target reaction are spatially confined and exhibit high signal density. These devices have very high quality factors, Q up to 10/sup 8/ which translates to enhanced sensitivity and signal-to-noise ratio. The combination of high Q and small geometry leads to significant power buildup within the microcavity and can allow the accurate detection of very few molecular events on the ring surface. We have designed and fabricated devices with different geometries and optimized operational wavelength ranges. In addition to high volume microfabrication, Hydex/sup /spl trade// allots us to functionalize the ring using established immobilization protocols for antibodies, nucleic acids, receptors and artificial sensing layers. Preliminary testing used the well documented and versatile biotin-avidin complex to immobilize an antibody biofilm. With Hydex/sup /spl trade// we can design highly-sensitive, readily portable label-free and reagent-free assays.

Experimental Observations of Optical Bistability in Semiconductor Microring Resonators

We present measurements of optical bistability in GaAs/AlGaAs optical microring resonators at 1.55µm wavelength.

Wavelength selective mirror using notched microring resonators

We have demonstrated a very compact GaAs/AlGaAs wavelength-selective mirror notched microring resonators. This device has applications in second-order filtering, wavelength rejection filters and laser linewidth reduction.