1-D Photonic Wire Microcavities for Refractive Index Sensing

The ability to detect small refractive index changes in analytes is of uttermost importance for biological and healthcare application. These changes of index can be directly correlated to the presence of small amounts of different chemicals of interest. 1-D photonic wire microcavities, (nanobeams -free standing photonic wires)  are a configuration of interest for sensors due to their appealing properties. We present a simple optical technique of detection based on nanobeams that gives good sensitivity for various chemicals. The sensitivity, S = λ/n where λ is relative resonance wavelengths and n is relative refractive index, has greater value than 200 nm/RIU. We believe that such devices open the route for small footprint cheap biological sensor.

This research project addresses an emerging demand for low-cost, room-temperature, compact and flexible optical sources in the near- and mid-infrared part of the spectrum due particularly to an increasing need for sensing applications, e.g. environmental, clinical analysis, life sciences, food monitoring, pharmaceutical, security and forensics. 


Transmission spectrum of the nanobeam cavities with Q ~ 20 000 (red circled). The inset (a) shows resonance wavelength peaks shift from 1290 nm to 1294 nm when the bulk refractive index changes from 1.333 to 1.350. The inset (b) shows linear relationship between relative shifts and different refractive indexes. Simulations of the  sensitivity  are ~ 200 nm/RIU.  



  • P Velha, E Picard, T Charvolin, E Hadji, J C Rodier, P Lalanne, D Peyrade, “Ultra-High Q/V Fabry-Perot microcavity on SOI substrate”, Optics express; 15(24):16090-6, December 2007. http://dx.doi.org/10.1364/OE.15.016090
  • A.R.Md Zain, Marco Gnan, Harold M. H. Chong, Marc Sorel and Richard M. De La Rue, “Tapered Photonic Crystal Micro-cavities Embedded in Photonic Wire Waveguides with Large Resonance Quality-Factor and HighTransmission’, IEEE Photonic Technology Letts, 20 (1), page 6 – 8,
    1st of January 2008. http:// eprints.gla.ac.uk/5931/1/5931.pdf
  • href="http://eprints.gla.ac.uk/view/author/3919.html">A.R.Md Zain, N.P.Johnson, M.Sorel and R.M.De La Rue,” Ultra high Quality
    Factor One Dimensional Photonic Crystal/Photonic Wire Micro-cavities in
    Silicon-on-Insulator (SOI)”, Optics Express, 16 (16), August 2008.  http://dx.doi.org/10.1364/OE.16.012084
  • 'Design and Fabrication of High Quality-Factor 1-D Photonic Crystal/Photonic
    Wire Extended Microcavities', Ahmad Rifqi Md Zain, Nigel P. Johnson, Marc Sorel
    and Richard M. De La Rue,  IEEE Photonics Technology Letters, 22(9), pp. 610 -
    612, 1st May (2010).  http://eprints.gla.ac.uk/34807/