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Damla Ozcelik
12/02/2010
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Overview
 What is Ring Resonator?
 Principles
 Important Parameters
 Fabrication Challenges
 Different Types, Optofluidic RRs (OFRR)
 OFRR Applications
 Sensors
 Particle Transportation
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Whispering Gallery Modes (WGM)
 Wave propagation is confined to the inside of a
cylindrical/spherical surface and guided by it by repeated
reflection
Spheres
Disks
Rings
Domes
John E. Heebner et al., Optical microresonators: theory, fabrication, and
applications (Springer, 2008).
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Disks vs Rings
 Main drawback of
microresonators surface
roughness due to etching
processes low Q factors
 Disks:
 Less scattering loss (1 edge)
 Multi-moded
 Rings:
 More scattering loss (2 edges)
 Single-moded
John E. Heebner et al., Optical microresonators: theory, fabrication, and
applications (Springer, 2008).
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RR Principles
 Wavelength Dependent
 Resonant Frequency

 Intensity Build-Up
 Resonators delay incoming signals via the
temporary storage of optical energy within
the resonator.
 Constructive interference circulating
optical intensity is built up to a higher value
than that initially injected.
 Coherent source
John E. Heebner et al., Optical microresonators: theory, fabrication, and
applications (Springer, 2008).
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Important Parameters
 Quality factor: Sharpness of the resonance. Ratio of the operation
wavelength and the resonant line width. Stored energy divided by the power lost
per optical cycle. (typically: 104 – 109)
 Leff : Effective light-matter interaction length.
 Free Spectral Range (FSR): Distance between resonance peaks.
 Extinction Ratio (ER): The ratio of the intensity on resonance to the
intensity off resonance.
DG Rabus, Integrated Ring Resonators: The Compendium (Springer Series in Optical
Sciences) (Springer Series in Optical Sciences) (Springer, 2007)
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Fabrication Challenges
 The construction of microrings smaller diameter is a challenging effort.
 It requires;
 high index contrast
 anisotropically etched pedestal waveguide designs
 ultrasmooth sidewalls
 The lateral-coupling approach demands strict patterning tolerances typically
requiring e-beam lithography followed by advanced etching techniques.
John E. Heebner et al., Optical microresonators: theory, fabrication, and
applications (Springer, 2008).
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Various Types of RRs
 Race Track
 Multiple RR
 Add-Drop
 All-Pass
DG Rabus, Integrated Ring Resonators: The Compendium (Springer Series in Optical
Sciences) (Springer Series in Optical Sciences) (Springer, 2007)
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All Pass
Add-drop
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Optofluidic RRs (OFRR)
 Bio/Chemical Sensing
 Higher sensitivity
 Planar integration
 Basic Applications:
 Sensors
 Particle Transportation
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OFRR Sensors
 Applications
 medical diagnosis
 environmental monitoring
 food quality control
Ian M. White, Hesam Oveys, and Xudong Fan, “Liquid-core optical ring-resonator
sensors,” Optics Letters 31, no. 9 (May 1, 2006): 1319-1321.
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OFRR Sensors
LCORRs
Analyte binds to
the resonator
surface
Longer
Leff
Δn Change
WGM
Evanescent field
detection
Better
Better
Light-Matter
Interaction
Sensing
Performance
•Small sample volume is needed
Ian M. White, Hesam Oveys, and Xudong Fan, “Liquid-core optical ring-resonator
sensors,” Optics Letters 31, no. 9 (May 1, 2006): 1319-1321.
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Liquid Core OFRR Sensor
 Liquid-core waveguide, MMI
coupler
Microfluidic part
Optical part
(deliver the
sample)
(ring resonator)
Integrated
in
liquid-core
waveguide
 0.11 nl liquid
 Sensitivity: Δλ /Δn =260nm/RIU
Yujian Huang et al., “Integrated silicon optofluidic ring resonator,” Applied
Physics Letters 97, no. 13 (2010): 131110.
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OFRR switch for optical particle transport
 Particles trapped in the evanescent field of
a solid-core waveguide
actively control the
particles’ direction
Change λ
λ On resonance
high optical intensities
gradient force
 Switching fraction: 80%
ParticlesRing
 Particle velocity: 250% in the ring
Allen Yang and David Erickson, “Optofluidic ring resonator switch for optical particle
transport,” Lab Chip 10, no. 6 (2010): 769-774.
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OFRR switch for optical particle transport
 λr=1552.225 nm (on resonance)
 λn= 1553.225 nm (off resonance)
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Thank you
Any Questions?
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