A FREQUENCY DOWNCONVERSION SCHEME FOR SENSING SYSTEMS BASED ON AN INTEGRATED OPTOELECTRONIC OSCILLATOR

Nowadays, optical sensors and their interrogation systems attract high attention from different research groups around the world. At the same time, a frequency interrogation method has already demonstrated its advantages in various applications. However, such method implementations based on an optoelectronic oscillator scheme needs simple and cost-effective frequency measurement methods. In this article we demonstrate an optoelectronic oscillator-based sensing scheme with a frequency downconversion scheme. As the optical sensor we utilized a phase-shifted waveguide Bragg grating for the liquid refractive index measurement. This grating is the notch filter in the optoelectronic oscillator feedback loop. The influence of external factors (in this case liquid refractive index change) leads to the grating resonant peak shift, which results in the optoelectronic oscillator output frequency shift. In turn, the frequency downconversion scheme reduces the output optoelectronic oscillator frequency value that allows to reduce sensing system’s complexity as well as the cost. For the optoelectronic oscillato numerical simulation, we used Ansys Lumerical software. In the simulation we change liquid refractive index from 1.39 to 1.391. In this case the optoelectronic oscillator output frequency changes in range from 3,01 to 12,89 GHz. The sensor interrogation frequency is 12,5 MHz. Also, we considered the frequency downconversion scheme implementation possibilities with commercially available devices. In conclusion it was found out, that our sensing system can be applied for the analysis of various liquids, including the detection and assessment of pathologies in blood and other biological fluids.