Abstract
We report a theoretical and experimental study of coupling between a whispering-gallery-mode (WGM) microdisk resonator and a fiber taper which exchange energies at two distinct regions. We observe an oscillatory behavior in the coupling strength as a function of the distance between the two coupling regions when a fiber taper is moved laterally above the resonator at fixed vertical distance. This oscillation is clearly seen in the linewidth of the resonance as well as in the on-resonance transmission. A theoretical model considering for two-point coupling successfully explains the experimental observations as being a result of the interference between the light fields coupled into and out of the resonator at two distinct regions and the light transmitted through the waveguide. Critical coupling in two-region coupling is a collective result of the coupling at two different coupling regions, and does not require critical coupling at both or at any one of the two coupling regions. This relaxes the conditions for achieving critical coupling in waveguide-resonator systems. The discovery of this previously unnoticed oscillatory behavior in two-region coupling between a WGM resonator and a waveguide will benefit both fundamental studies and practical applications based on WGM resonators.
Highlights
A resonator coupled to a waveguide constitutes a very simple yet powerful platform to carry out fundamental research on optomechanics[1,2,3] and quantum information science[4] and practical applications ranging from low-threshold lasing[5] to high-performance sensing[6,7,8,9,10]
The scanning electron microscope (SEM) image depicting the side view of the edge of the microdisk WGM resonator is shown in Fig. 2a, which clearly shows the shape of the inverted-wedge resonator providing the structure parameters used in the numerical simulation
Benefiting from this unique structure, we have demonstrated oscillatory coupling as well as critical coupling achieved with the coupling coefficient of κi at a value that is just sufficient for the resonator to operate in the under-coupling regime for one-point coupling scheme (|κ| < 1 − e−2απr ) as shown in Fig. 3c and d
Summary
A resonator coupled to a waveguide constitutes a very simple yet powerful platform to carry out fundamental research on optomechanics[1,2,3] and quantum information science[4] and practical applications ranging from low-threshold lasing[5] to high-performance sensing[6,7,8,9,10]. Ghulinyan et al.[21] showed that the dynamics of the RWC process differs significantly from the conventional picture when the waveguide is moved vertically with respect to the resonator with the lateral distance kept constant. The vertical oscillatory RWC effect was interpreted via the coupling mode theory by considering the RWC as the coupling between two parallel waveguides
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
