Breaking the trade-off between sensitivity and Q-factor for high-Q slot mode photonic crystal nanobeam cavity biosensors with optomechanical feedback

Here, a method to eliminate the trade-off between quality factor (Q-factor) and sensitivity of a one dimensional slot mode photonic crystal nanobeam cavity biosensor is presented. Applied method utilizes an optomechanical feedback mechanism in order to generate transverse gradient optical forces inside the cavity. A pump mode is utilized in order to generate the optical force, triggered by intrusion of analyte into the background medium. The amount of generated force is controlled via an interference mechanism at the output realized by the feedback loop. By utilizing created optical force, slot width of the nanobeam cavity is dynamically tuned and the quality factor degradation due to the decrease in the refractive index contrast of the cavity is compensated by enhancing the field confinement inside the cavity. With the contribution of the slot width tuning to the resonant wavelength shift, sensitivity of the biosensor is increased without any degradation of the Q-factor. Numerical analyses regarding the cavity design and the elimination of trade-off are provided. Obtained results show that the both performance can be increased at the same time.