Near Infrared-Controlled Whispering Gallery Mode Resonator Sensor

In this letter, a near infrared (NIR) controlled whispering gallery mode resonator sensor is presented. The resonator incorporates a high-resistivity silicon (HRS) disk, which is placed in the proximity of a microstrip line. The strength of the coupling in the resonator is controlled through illumination of the HRS disk by the NIR radiation. By tuning the amount of this illumination, and without making any change in the physical structure of the resonator, it is shown that the resonator can be easily adjusted to operate in its most sensitive way: critical coupling condition. Under this condition, the transparency level of the sample-under-test to the NIR radiation strongly affects the level of coupling from the microstrip line to the resonator, and as a consequence, the sensing mechanism is realized. For verification of the proposed sensing technique, experiments over salty liquid and aqueous glucose solution are carried out. The sensor operates at a frequency of 29.08 GHz and shows high sensitivity of 0.76-1.62 dB/(mg/ml).