Abstract
We introduce slow-light enhanced subwavelength scale refractive index sensors which consist of a plasmonic metal-dielectric-metal (MDM) waveguide based slow-light system sandwiched between two conventional MDM waveguides. We first consider a MDM waveguide with small width structrue for comparison, and then consider two MDM waveguide based slow light systems: a MDM waveguide side-coupled to arrays of stub resonators system and a MDM waveguide side-coupled to arrays of double-stub resonators system. We find that, as the group velocity decreases, the sensitivity of the effective index of the waveguide mode to variations of the refractive index of the fluid filling the sensors as well as the sensitivities of the reflection and transmission coefficients of the waveguide mode increase. The sensing characteristics of the slow-light waveguide based sensor structures are systematically analyzed. We show that the slow-light enhanced sensors lead to not only 3.9 and 3.5 times enhancements in the refractive index sensitivity, and therefore in the minimum detectable refractive index change, but also to 2 and 3 times reductions in the required sensing length, respectively, compared to a sensor using a MDM waveguide with small width structure.
Highlights
The unique properties of surface plasmons, which are light waves that propagate along metal surfaces, enable a wide range of practical applications, including light guiding and manipulation at the nanoscale [1]
Among different plasmonic waveguiding structures, metal-dielectric-metal (MDM) plasmonic waveguides are of particular interest [9,10,11,12,13,14], because they support modes with deep subwavelength scale over a very wide range of frequencies extending from DC to visible, and are relatively easy to fabricate [15]
We consider a slow-light plasmonic waveguide system consisting of a MDM waveguide side-coupled to arrays of double-stub resonators based on our previous work (Fig. 5(a)) [20], which was implemented experimentally in a recent work
Summary
The unique properties of surface plasmons, which are light waves that propagate along metal surfaces, enable a wide range of practical applications, including light guiding and manipulation at the nanoscale [1]. We investigate RI sensors consisting of a plasmonic slow-light waveguide sandwiched between two conventional MDM waveguides. The two optimized slow-light enhanced subwavelength plasmonic RI sensors result in 3.9 and 3.5 times enhancements in the sensitivity, and in the minimum detectable RI change, and 2 and 3 times reductions in the optimal sensing length, respectively, compared to a sensor using a MDM waveguide with small width system. The two optimized slow-light enhanced sensors have comparable performance in sensitivity, the double-stub resonator system exhibits a small group velocity dispersion over a broader wavelength range and has less power loss, features which are highly desirable for practical sensing applications.
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