Cascaded Microring Resonator Research Articles

Silicon Photonics Research in Hong Kong: Microresonator Devices and Optical Nonlinearities

In this review paper we showcase recent activities on silicon photonics science and technology research in Hong Kong regarding two important topical areas-microresonator devices and optical nonlinearities. Our work on silicon microresonator filters, switches and modulators have shown promise for the nascent development of on-chip optoelectronic signal processing systems, while our studies on optical nonlinearities have contributed to basic understanding of silicon-based optically-pumped light sources and helium-implanted detectors. Here, we review our various passive and electro-optic active microresonator devices including (i) cascaded microring resonator cross-connect filters, (ii) NRZ-to-PRZ data format converters using a microring resonator notch filter, (iii) GHz-speed carrier-injection-based microring resonator modulators and 0.5-GHz-speed carrier-injection-based microdisk resonator modulators, and (iv) electrically reconfigurable microring resonator add-drop filters and electro-optic logic switches using interferometric resonance control. On the nonlinear waveguide front, we review the main nonlinear optical effects in silicon, and show that even at fairly modest average powers two-photon absorption and the accompanied free-carrier linear absorption could lead to optical limiting and a dramatic reduction in the effective lengths of nonlinear devices.

Microresonator-enhanced Raman amplification

We study Raman amplification in cascaded microring resonator structures and the scaling of conversion efficiency with respect to parameters such as bandwidth, free spectral range, and number of resonators. We also compare the efficiency of cascaded resonator structures to that of standard waveguides of equivalent group delay, where improvement of more than 1 order of magnitude is obtained in a more compact structure. In these studies, we use linear and nonlinear parameters relevant to silica and silicon integrated optics and include effects due to the two-photon absorption and the generation of free carriers.

Nonlinear phase shift of cascaded microring resonators

We study cascaded microring resonator (CMRR) configurations as general nonlinear phase-shifting elements that exhibit enhanced nonlinear sensitivity and flattened transmission characteristics. We show that even when the material itself has large two-photon absorption, CMRR devices with five rings facilitate a factor-of-10 enhancement of the optical nonlinearity when compared with a channel waveguide having the same group delay. In addition, high throughput in intensity can be maintained up to a 3π phase shift.