All-optical RZ-OOK to NRZ-OOK format conversion based on two-ring resonators

• Two-ring resonators-based RZ-OOK to NRZ-OOK format converter is proposed.
• #1 ring resonator should work at the critical coupling condition.
• #2 ring resonator’s loss should be made as low as possible.
• RZ-OOK signals with variable duty-cycles (33%, 50%, 67%) can be converted.
• By reducing resonators’ radii, the converter is compatible with higher bitrates.

Based on spectral shaping principle, we propose a novel all-optical return-to-zero (RZ) to non-return-to-zero (NRZ) on–off-keying (OOK) format converter based on two-ring resonators. Influences of the coupling coefficients and loss on the spectral responses of two-ring resonators are investigated detailedly. Results demonstrated that good conversion performance can be achieved by suppressing the sideband spikes and narrowing the spectral outline of injected RZ-OOK signal. In addition, our two-ring resonators can convert RZ-OOK signals with variable duty-cycles (33%, 50%, 67%) to NRZ-OOK format with larger eye-opening extinction ratio, which makes it much feasible for interfacing different parts of future optical networks.