Ring Resonators & Optofluidic Applications Damla Ozcelik 12/02/2010

Overview What is Ring Resonator? OFRR Applications Principles Important Parameters Fabrication Challenges Different Types, Optofluidic RRs (OFRR) OFRR Applications Sensors Particle Transportation

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).  

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).  

RR Principles Wavelength Dependent Intensity Build-Up 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).  

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)

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).  

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)

All Pass Add-drop

Optofluidic RRs (OFRR) Bio/Chemical Sensing Higher sensitivity Planar integration Basic Applications: Sensors Particle Transportation

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.  

OFRR Sensors LCORRs Small sample volume is needed Longer Leff Better Analyte binds to the resonator surface Δn Change WGM Evanescent field detection Longer Leff 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.  

Integrated in liquid-core waveguide Liquid Core OFRR Sensor Liquid-core waveguide, MMI coupler 0.11 nl liquid Sensitivity: Δλ /Δn =260nm/RIU Integrated in liquid-core waveguide Optical part (ring resonator) Microfluidic part (deliver the sample) Yujian Huang et al., “Integrated silicon optofluidic ring resonator,” Applied Physics Letters 97, no. 13 (2010): 131110.  

OFRR switch for optical particle transport Particles trapped in the evanescent field of a solid-core waveguide Switching fraction: 80% Particle velocity: 250% in the ring Change λ actively control the particles’ direction λ On resonance high optical intensities gradient force ParticlesRing Allen Yang and David Erickson, “Optofluidic ring resonator switch for optical particle transport,” Lab Chip 10, no. 6 (2010): 769-774.  

OFRR switch for optical particle transport λr=1552.225 nm (on resonance) λn= 1553.225 nm (off resonance)

Thank you Any Questions?