Reconfigurable optical logic in silicon platform.

In this paper, we present a novel, scalable, and reconfigurable optical switch that performs multiple computational logic functions simultaneously. The free-carrier depletion effect is used to perform non-volatile switching operations due to its high speed and low power consumption. We adopt the concept of optical memory using a phase-change material to realize the non-volatile reconfigurability without a constant power supply, in addition to providing a large operating bandwidth required for reconfigurability. The proposed reconfigurable optical logic architecture is realized in a compact microdisk resonator configuration, utilizing both the carrier-depletion-based modulation and phase-change optical memory. This is the first time these two modulation schemes are implemented in the same optical microdisk for the purpose of reconfigurable optical logic.

An Integrated Optical Circuit Architecture for Inverse-Designed Silicon Photonic Components.

In this work, we demonstrate a compact toolkit of inverse-designed, topologically optimized silicon photonic devices that are arranged in a "plug-and-play" fashion to realize many different photonic integrated circuits, both passive and active, each with a small footprint. The silicon-on-insulator 1550-nm toolkit contains a 2 × 2 3-dB splitter/combiner, a 2 × 2 waveguide crossover, and a 2 × 2 all-forward add-drop resonator. The resonator can become a 2 × 2 electro-optical crossbar switch by means of the thermo-optical effect, phase-change cladding, or free-carrier injection. For each of the ten circuits demonstrated in this work, the toolkit of photonic devices enables the compact circuit to achieve low insertion loss and low crosstalk. By adopting the sophisticated inverse-design approach, the design structure, shape, and sizing of each individual device can be made more flexible to better suit the architecture of the greater circuit. For a compact architecture, we present a unified, parallel waveguide circuit framework into which the devices are designed to fit seamlessly, thus enabling low-complexity circuit design.

Compact silicon-photonic mode-division (de)multiplexer using waveguide-wrapped microdisk resonators.

We experimentally demonstrate, to the best of our knowledge, the first microdisk-based silicon-photonic mode-division (de)multiplexer circuit, which is compatible with wavelength-division multiplexing for high aggregate bandwidth on-chip optical communications. This circuit uses waveguide-wrapped microdisk resonators, featuring low levels of intermodal crosstalk and insertion loss within an ultracompact footprint. In addition, the proposed device presents an increased free spectral range, allowing for 530 combined data channels. Furthermore, the microdisk structure naturally supports vertically oriented depletion-type pn junctions, which have been shown to reach subfemtojoule-per-bit modulation efficiencies. The high modulation efficiency, compactness, and wide free spectral range of waveguide-wrapped microdisk resonators present the potential for higher bandwidth and lower energy consumption in next-generation data processing and communication applications.

Ultrafast electro-optical disk modulators for logic, communications, optical repeaters, and wavelength converters.

We propose a U-shaped pn junction in a silicon-on-insulator microdisk resonator to effectively double the junction-mode overlap in the state-of-the-art, vertical pn junction microdisk electro-optical (EO) modulators. The U-shaped pn junction promotes the maximum overlap between the junction depletion zone and the whispering gallery optical mode in the microdisk. By fully depleting the p region of the npn-sequenced U-junction, the capacitance is reduced below 3 fF, which significantly improves the speed and power performance. In this work, we implement the high-efficiency, depleted U-junction design to maximize the operating bandwidth of EO modulators, EO logic elements, EO 2 × 2 switches for wavelength-division cross-connects, 2 × 2 reconfigurable optical add-drop multiplexers, optical-to-electrical-to-optical (OEO) repeaters-with-gain, OEO wavelength converters, and 2 × 2 optical-optical logic gates. These devices all operate in the 7.6-to-50 GHz bandwidth range with ultralow energy consumption between 0.4 and 9.8 fJ/bit. By using CMOS-compatible materials and fabrication-feasible design dimensions, our proposed high-performance devices offer a promising potential in next-generation, high-volume electro-optical communications and computing circuits.

Ultracompact CMOS-compatible optical logic using carrier depletion in microdisk resonators.

We present a CMOS-compatible optoelectronic directed logic architecture that achieves high computational throughput (number of operations per second per unit area) by its ultracompact form factor. High speed-to-power performance is also achieved, by the low capacitance and high junction-to-mode overlap of low-radii SOI vertical pn junction microdisk switches. By using wavelength-division multiplexing and two electrical control signals per disk, each switch performs (N)OR, (N)AND, and X(N)OR operations simultaneously. Connecting multiple switches together, we demonstrate higher-order scalability in five fundamental N-bit logic circuits: AND/OR gates, adders, comparators, encoders, and decoders. To the best of our knowledge, these circuits achieve the lowest footprint of silicon-based multigigabit-per-second optical logic devices in literature.