PIC-Based Continuous Frequency Tuning of the Optoelectronic Oscillator

The paper explores optoelectronic oscillator (OEO) output frequency control by adjusting the integrated optical time delay line in the OEO feedback loop. The developed mathematical model demonstrates the continuous nature of output OEO frequency tuning for the continuous phase incursion change in the OEO feedback loop. We created a photonic integrated circuit (PIC) numerical model for verification in the Ansys Lumerical Software. The PIC is designed for the generic silicon-on-insulator platform. We applied an unbalanced Mach-Zehnder interferometer with tunable couplers as an integrated optical time delay line. Numerical simulations showed that the applied time delay line provides an output OEO frequency change range of 360 MHz within a voltage range from -3.2 to 0.5 V. In this case, the time delay tuning step is 6 ps/V, and the corresponding output frequency step is 30 MHz/ps. For the precision digital-to-analog converter (DAC), an output OEO frequency tuning step is 7.2 kHz for the minimum DAC voltage step 40 µV.