Abstract
We propose and experimentally demonstrate a modular microring laser (MML) cavity for sensing applications. The proposed MML permits much more design freedom compared with a traditional simple ring cavity by decoupling the performance parameters into several regions in the cavity. Thus, the different biosensor performance parameters can be optimized semi-independently limiting the need for trade-offs on the design of the biosensing device. The first generation MML has been fabricated and tested. A fiber-to-fiber slope efficiency of up to 1.2%, a temperature coefficient of 1.35 GHz/K and a 3σ limit of detection (LOD) of 3.1 × 10-7 RIU without averaging and 6.0 × 10-8 RIU with a 60 s averaging, has been measured for the MML sensor, which is a record-low LOD in on-chip ring cavity optical sensors. Further optimization is possible, capitalizing on the key advantage of the MML concept, namely the potential for designing the laser cavity to achieve the desired optimization goals.
Highlights
Whispering gallery mode (WGM) based optical sensors have been widely studied due to their high sensitivity for the label-free detection of biomarkers [1,2,3,4]
The full-width half maximum (FWHM) of the resonances, their mode splitting and their frequency shift are parameters that can be used to detect nanoparticles or molecules attaching to the surface of the resonator [3,5,6]
A passive cavity resonance shift is typically measured with an optical spectrum analyzer (OSA) or tunable laser, while a lasing cavity resonance can be characterized with a RF spectrum analyzer in a heterodyne detection configuration [8]
Summary
Whispering gallery mode (WGM) based optical sensors have been widely studied due to their high sensitivity for the label-free detection of biomarkers [1,2,3,4]. The frequency shift method can be applied in both passive and active (lasing) cavities. The intrinsic minimal detectable shift, the lower detection limit, is proportional to the resonance linewidth [7], which is much narrower in an active resonator. A passive cavity resonance shift is typically measured with an optical spectrum analyzer (OSA) or tunable laser, while a lasing cavity resonance can be characterized with a RF spectrum analyzer in a heterodyne detection configuration [8]. Since typical RF spectrum analyzers can measure with much smaller frequency step size than OSAs and tunable lasers, a higher resolution in the frequency shift measurement, and a lower measurable limit of detection (LOD) can be achieved
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