Enhancing the Delay/Advance –Bandwidth Product using degenerate resonances of photonic molecules in a Silicon Photonics Platform

We propose the use of photonic molecules, i.e., coupled silicon ring structures, with triplet resonances for enhancing the delay-bandwidth product for analog modulation. We have designed a photonic molecule, composed of a 20 um radius outer ring resonator with two 5 um radius internally coupled to it. Based on our theoretical model for this device, we find that it is impossible to advance or retard a pulse that is not fully modulated, i. e., with any residual energy within the carrier wavelength. However, for analog full modulation, when the carrier is suppressed, we predict a maximum delay/advance of 500 ps/ 250 ps, respectively, for a bandwidth of 140 GHz, with consequent product delay/advance- bandwidth of 70/35, respectively. This is by far much higher than the published results for integrated photonics where numbers of the order of 18 are demonstrated, although for full band digital modulation. The transmittance experiment for our device showed an asymmetric behavior due to fabrication issues. The experimental results were used to fit our model, and the expected values for the real device were a maximum delay of ~190 ps for one lateral resonance, maximum advance of ~60 ps for the central resonance, and ~25 ps for the other lateral resonance. We performed delay/advance measurements and obtained ~70 ps delay for one resonance and ~30 ps advancement for the other two, qualitatively agreeing with our prediction.