Biomedical Engineering Reference
In-Depth Information
6134
6132
6130
6128
6126
6124
6122
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6114
0
50
100
150
pixels
Fig. 6.8.
Line-cut from a processed image taken by the SRIB setup. Etch marks
at three different heights are seen: 4, 12, and 16 nm. The thickness of the oxide was
∼
6,130 nm, initially.
Although the present data show that the system can image 250 spots with
subnanometer sensitivity, balancing the laser intensity fluctuations and using
a better imaging system is expected to improve sensitivity to 0.1 nm with
more than 10,000 spots.
6.3 Optical Sensing of Biomolecules Using Microring
Resonators
6.3.1 Basics on Microring Resonators
Integrated devices featuring resonant microcavities with high quality factors
(Q) such as toroids, disks, rings, and spheres have been used as add-drop
filters, optical switches, and in laser applications [29-33]. These devices have
recently become popular for research in biochemical sensing [34-38] as the
demand for highly sensitive and compact devices to detect biomolecules in-
creased. Light is confined within the microring cavities by total internal re-
flections resulting in high Q resonant modes. When the refractive index of the
cladding or the outside medium changes (e.g., due to binding of molecules), a
new guiding condition is obtained for the mode, causing a shift in the resonant
wavelength.
