Slow light enhanced sensitivity of resonance modes in photonic crystal biosensors

Abstract

We demonstrate experimentally that in photonic crystal sensors with a side-coupled cavity-waveguide configuration, group velocity of the propagating mode in the coupled waveguide at the frequency of the resonant mode plays an important role in enhancing the sensitivity. In linear L13 photonic crystal microcavities, with nearly same resonance mode quality factors ∼7000 in silicon-on-insulator devices, sensitivity increased from 57 nm/RIU to 66 nm/RIU as group index in the coupled waveguide increased from 10.2 to 13.2. Engineering for highest sensitivity in such planar integrated sensors, thus, requires careful slow light design for optimized sensor sensitivity.

Analysis of ultra-high sensitivity configuration in chip-integrated photonic crystal microcavity bio-sensors

“…The high Q enhances the interaction time between the optical mode and the analyte while the larger mode volume results in larger fill fraction, both factors resulting in higher sensitivity We demonstrated experimentally in our side-coupled two-dimensional (2D) PC cavity-waveguide architecture that the magnitude of the slow-down factor in the coupling waveguide contributes to enhanced light-matter interaction. 11 Over successive generations, we demonstrated experimentally 50 fM (3.35 pg/ml) sensitivity to the detection of the specific binding of avidin to biotin 12 with a L55 type PC microcavity (55 missing holes).…”

“…[10][11][12] Fig. 4 plots dk versus concentration for 4 different PC microcavities, L13, L21, L55, and L13 with defect hole.…”

“…Later, designs increased the analyte overlap with cavity modes, also referred as fill fraction, for enhanced sensitivity. 9 Recently, we showed that an increased cavity length results in an increase in the quality factor (Q-factor) of the resonance mode [10][11][12] that allows smaller changes in concentration to be distinguished. The high Q enhances the interaction time between the optical mode and the analyte while the larger mode volume results in larger fill fraction, both factors resulting in higher sensitivity We demonstrated experimentally in our side-coupled two-dimensional (2D) PC cavity-waveguide architecture that the magnitude of the slow-down factor in the coupling waveguide contributes to enhanced light-matter interaction.…”

“…The resonance mode closest to the PCW transmission band edge is considered. [10][11][12] We consider defect holes >90 nm diameter for better fabrication tolerance and yield in high volume manufacturing. We refer to such low-index defects as defect holes, rather than nanoholes elsewhere.…”

“…Typically, in silicon 2D PCs, light is coupled from a PC waveguide (PCW) into an adjacent PC microcavity. [9][10][11][12] An isolated PC microcavity is considered for simulations in order to eliminate the effect of coupling between the PC microcavity and the PCW in cavity-waveguide coupled sensors. [10][11][12] Simulations considered water (refractive index RI ¼ 1.33) as the ambient medium and a silicon effective index (n eff ) ¼ 2.9 for operation at 1550 nm.…”