Ring resonators

Other frequently used resonators are dielectric cavities and loop-gap resonators (also called split-ring resonators) [12]. A dielectric cavity contains a diamagnetic material that serves as a dielectric to raise the effective filling factor by concentratmg the B field over the volume of the sample. Hollow cylinders machmed from Ilised quartz or sapphire that host the sample along the cylindrical axis are conunonly used. 

Fig. 2.1 Basic microring resonator structures and their output characteristics, (a) One ring resona tor and one bus waveguide and (b) the corresponding resonance spectrum at the through port, (c) One ring resonator and two bus waveguides and (d) the corresponding resonance spectrum at the through port and drop port. Reprinted from Ref. 15 with permission. 2008 Institute of Electrical and Electronics Engineers...

For a microring resonator with a waveguide width of 5 pm and coupling gap of 200 nm, a resonance extinction ratio of 12 dB for TE polarization and 9 dB for TM polarization has been achieved, as shown in Fig. 2.10. The ring resonator had a race track shape with circular sections of 500 pm radius and straight coupling section of 100 pm in length. The width of the two exposed strips is about 50 pm. 

Rapid Chemical Vapor Detection Using Optofluidic Ring Resonators... 

So far, there are four basic ring resonator configurations that can potentially be used as a vapor sensor, the first three of which are shown in Fig. 6.1. They include... 

Fig. 6.1 Various configurations of ring resonator vapor sensors...

Fig. 6.3 Four layer model for the OFRR vapor sensor. OD ring resonator outer diameter / polymer thickness d ring resonator wall thickness , n2, n2, and are the refractive indices for the medium inside (air), polymer, silica ring resonator, and medium outside (air), respectively...

For the OFRR-based vapor sensor, the ring resonator wall thickness has a significant impact on the sensor performance. Since the polymer layer is treated as the extension of the ring resonator, the relative thickness between the wall and the polymer determines the radial intensity distribution of the WGMs. As a result,... 

Fig. 6.6 (a) k2 as a function of polymer thickness for the first three WGMs. Dashed line indicates the k2 position for the first order ring resonator wall mode in the absence of the polymer layer. The simulation parameters are the same as in Fig. 6.4, except that the polymer RI, n2, is 1.7. (b) The WGM radial distribution of the second order mode for various polymer thicknesses indicated by the arrows in (a). Vertical lines indicate the boundaries of the ring resonator wall and the polymer layer. Reprinted from Ref. 29 with permission. 2008 Optical Society of America... 

Ksendzov, A. Homer, M. L. Manfreda, A. M., Integrated optics ring resonator chemical sensor with polymer transduction layer, Electron. Lett. 2004,40, 63 65... 

Sun, Y. Shopova, S. I. Frye Mason, G. Fan, X., Rapid chemical vapor sensing using optofluidic ring resonators, Opt. Lett. 2008, 33, 788 790... 

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