Resonant microcavities coupled to a photonic crystal waveguide for multi-channel biodetection
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1191-OO11-06
Resonant microcavities coupled to a photonic crystal waveguide for multi-channel biodetection Elisa Guillermain and Philippe M. Fauchet Electrical and Computer Engineering Department, University of Rochester, Rochester, NY 14627 USA
ABSTRACT Miniaturized and highly sensitive bio-sensors are attractive in various applications, such as medicine or food safety. Photonic crystal (PhC) microcavities present multiple advantages for rapid and accurate label-free optical detection. But their principle of operation (i.e. observation of a peak in transmission) makes their integration in serial arrays difficult. We present in this paper a multi-channel sensor consisting of several resonant PhC microcavities coupled to the same waveguide. The transmission spectrum shows as many dips as there are cavities, and each of the microcavities can act as an independent sensor. Preliminary results show the fabrication and characterization of a double-channel structure with small defects used as a solvent sensor. INTRODUCTION Many optical sensors rely on the modification of their optical properties when their refractive index changes due to the trapping of the target in the detection area. They allow a label-free detection [1], relying on the red-shift of their optical resonance wavelength. Such bio-detectors include surface plasmon resonance (SPR) [2], Bragg surface wave [3], interferometers [4], waveguides [5], disk resonators [6], photonic crystals (PhC) [7,8,9,10,11,12]. Photonic crystals (PhC), of interest for bio-sensing because of their high sensitivity in a small sensing area (less than 10 µm²), are studied in this paper.
Figure 1. SEM views of (a) a 2D photonic crystal cavity suitable for the sensing of proteins [9]. (b) 1D photonic crystal cavities in a serial configuration allowing multiple detection, proposed by Mandal and Erickson [11].
Fig. 1 shows two types of PhC microcavities for bio-detection applications. The structure showed in Fig. 1(a) is a PhC with a microcavity (smaller hole), whose resonance is in the infrared. At this resonnance wavelength, the electric field of the optical mode is mostly confined in the defect hole, which reduces the detection area to this region. This device has been shown to be suitable for the detection of bovine serum albumin (BSA) attached to a glutaraldehyde functionalization layer. A redshift of 2 nm has been observed after capture of the targeted BSA
molecules forming a layer with an effective thickness of 1.5 nm [9]. Such structures have also been shown to be able to detect bigger particles, for example viruses [10]. Fig. 1(b) shows a SEM top view of a waveguide to which several 1D PhC micro-cavities are coupled [11]. This kind of device is suitable for multi-channel detection (simultaneous multiple detections), allowing for example to target multiple molecules, or to avoid false-positive detection. The input light is globally transmitted through the waveguide, except for the wavelengths corresponding to any of the cavity resonant modes. Because each microcavity is sl
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