Automatic Correction Assisted Microwave Photonic Sensor System for Resolution Enhancement in Humidity Measurement

In the paper, we propose the automatic correction assisted microwave photonic sensor system in humidity measurement with greatly enhanced resolution throughout the measurement range. The humidity sensing probe is based on the microresonator coated with hydrophilic material. By realizing the automatic correction on the modulation sidebands being filtered by the microresonator, the impact of the optical resonance line-shape variation caused by the refractive index change of the hydrophilic cladding in response to the humidity change on creating the perfect cancellation of RF beating currents is well mitigated. The resulting RF transmission notch which synchronously shifts with the optical resonance is thus maintained with ultra-high rejection and ultra-narrow tip width, greatly enhancing the resolution performance. The proposed system was experimentally demonstrated using the humidity sensor probe made from the microdisk resonator coated with PMMA, the refractive index of which will increase or decrease correspondingly with the rise or drop of the environmental humidity at room temperature. The measured RF notch tip widths are kept 19800-fold narrower than the optical notch of the microresonator and only occupy 0.015
⁰
/
₀₀
of the total RF scanning range. Thus, a high humidity resolution of 0.0015 %RH can be achieved in the whole humidity measurement range.