High-Resolution Optical Microresonator-Based Sensor Enabled by Microwave Photonic Sidebands Processing

We theoretically and experimentally investigate the high-resolution performance of an optical microresonator-based sensor scheme incorporating microwave photonic sidebands processing. The optical power and phase profiles of the modulation sidebands are equalised to achieve ultrahigh-rejection RF notches with ultranarrow tip width in the electrical spectrum, where environmental changes are detected via the shift in the measurand dependent frequency of the ultradeep RF notch. The proposed structure demonstrates the ability to realise ultrahigh resolution sensing for any optical microresonator response with arbitrary coupling conditions, thus relieving strict fabrication requirements. Furthermore, factors that can disrupt the matching conditions during the dynamic sensing process are also discussed and resolved with the aid of the feedback compensation scheme which increases the resilience of the system against these interferences. As a proof-of-concept, a proposed sensing configuration comprising a dual-drive Mach-Zehnder modulator and a silicon-on-insulator microdisk resonator is demonstrated for temperature sensing. The measured temperature sensitivity is around 8.87 GHz/degrees C and a high rejection ratio of over 60 dB of the RF notch is successfully maintained with an ultranarrow notch tip width that makes up only 0.003% of the whole sensing operation range of 35 GHz. The temperature resolution is significantly improved by about 2500 times compared to the conventional method of direct monitoring of the optical spectrum.