Microresonator

Proceedings Microresonators as Building Blocks for VLSI Photonics... 

Figure 2. Microresonator with two adjacent waveguides serving as in- and output port (a) top view (b) schematic spectral response to a constant input intensity (FSR free spectral range).

Figure 3. Cross section of the two basic geometries for microresonators with port waveguides (a) vertical arrangement (h) lateral arrangement (the dashed region indicates the analyte layer). The structure in this case is fabricated in silicon-based technology, with the index of refraction of Si02 and Si3N4 1.45 and 2.0 respectively.

Figure 4. The drop power of a microresonator as a function of phase shift for different values of roundtrip losses a, c.q finesse F.

The microresonator therefore can also be used as a sensitive absorption sensor. In both set-ups as refractive or absorption sensor, the ultimate sensitivity is determined by the slope of the resonance peak, which is related to the resonator losses. 

In the foregoing the description of microresonators was limited to the index guiding type. Resonators with the same functionality can be implemented in PBG structures5. In these cases, with the high index contrast used, the cavity volume is even more reduced resulting in FSRs of 10 - 100 nm. 

Figure 5. Cross section (a) and top view (b) of an integrated optical microresonator sensor with radius R = 15 tun.

Figure 7. Light scattering of a microresonator with a water cladding (a) spectra obtained as response to a tunable laser with clearly visible high finesse resonances (b) CCD camera images of the microresonator obtained off-resonance, (c) idem on-resonance.

Figure 8. Optical spectroscopy of a indocyanine green dye solution (10 5 M in water) (a) fluorescence spectrum obtained by excitation around 780 nm (b) excitation spectrum obtained on top of a microresonator the rectangle in the inset shows the area from which the fluorescence signal is collected.

The complexity increases even more if one starts incorporating multisensor functions, Figure 13. Even if for improved performance the filter elements would consist of cascaded microresonators selecting 8 wavelengths, the complete multi-sensor with 96 microresonators could still fit on a few mm2. In this way an optical nose or optical tongue with only a modest power supply and without optical peripheral equipment would become feasible. 

Figure 12. Schematic lay-out of compact optical sensor chip without need of external optical apparatus with identical microresonators as sensors LED broad band source, for example Light Emitting Diode, MR-F microresonator used as optical filter, MR-S microresonator used as optical sensor, PD Photo Diode.

Klunder D.J.W., Photon Physics in Integrated Optics Microresonators, Ph.D. thesis, University of Twente, 135 p (2002). 

Surface Acoustic Wave and Microresonance-Based Sensors... 

Microresonator Sensors Made in Polymers with Functional Chromophore Dopants... 

The sensors are intended to be built with microresonators of high extinction for a large dynamic range in such case the normalized optical power at the output of the fiber can be express as19... 

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