Electro-optical Logic 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.

Multiplexer as a universal computing element for electro-optic logic systems

It is shown that any combinational function can be implemented by a multiplexer of appropriate width. Since these logic elements can also perform sequential operations, entire digital systems can be implemented with multiplexers. Such systems are of particular relevance to optical implementations as multiplexers using liquid crystal electro-optic elements can be realised. The large number of pixels available on a single display leads to the concept of significant optical systems implemented using two-dimensional arrays of uncommitted multiplexers. Since the multiplexer width is critical in determining the system efficiency, the implementation of commonly occurring logic functions is presented to determine the optimum width.

Electro-optical logic operations with two-electrode distributed feedback injection lasers

A complete set of and, or, nand, nor, and invert logic gates is demonstrated using a distributed feedback (DFB) injection laser with two-electrode current control. The logic operation is based on the high-speed two-wavelength switching using the two-mode degeneracy property of DFB lasers that we have demonstrated recently. A 400-ps switching time, limited by the speed of the electrical signal, was observed. The device is compatible with future photonic integrated circuit and wide-band optical fiber transmission technologies.