Ruiqiang Ji

Demonstration of directed XOR/XNOR logic gates using two cascaded microring resonators

We propose and demonstrate a directed optical logic circuit that can perform the XOR and XNOR logic operations consisting of two cascaded microring resonators, i.e., an upper waveguide and an under waveguide. No waveguide crossings exist in the circuit, which is very useful to improve the signal quality and reduce the insertion loss of the device. As proof of principle, XOR and XNOR logic operations with the speed of 10 kb/s are successfully demonstrated. In addition, numerical simulation results indicate that the length difference between the upper waveguide and the under waveguide can change the output spectrum characteristics of the device, which acts like a Mach-Zehnder interferometer (MZI).

Five-port optical router for photonic networks-on-chip

We experimentally demonstrate a spatially non-blocking five-port optical router, which is based on microring resonators tuned through the thermo-optic effect. The characteristics of the microring-resonator-based switching element are investigated to achieve balanced performances in its two output ports. The optical router is fabricated on the SOI platform using standard CMOS processing. The effective footprint of the device is about 440×660 μm2. The microring resonators have 3-dB bandwidths of larger than 0.31 nm (38 GHz), and extinction ratios of better than 21 dB for through ports and 16 dB for drop ports. Finally, 12.5 Gbps high-speed signal transmission experiments verify the routing functionality of the optical router.

Ultra-low-power carrier-depletion Mach-Zehnder silicon optical modulator

We demonstrate a 26 Gbit/s Mach-Zehnder silicon optical modulator. The doping concentration and profile are optimized, and a modulation efficiency with the figure of merit (VπL) of 1.28 V·cm is achieved. We design an 80-nm-wide intrinsic silicon gap between the p-type and n-type doped regions to reduce the capacitance of the diode and prevent the diode from working in a slow diffusion mode. Therefore, the modulator can be driven with a small differential voltage of 0.5 V with no bias. Without the elimination of the dissipated power of the series resistors and the reflected power of the electrical signal, the maximum power consumption is 3.8 mW.

Microring-resonator-based four-port optical router for photonic networks-on-chip

We design and fabricate a four-port optical router, which is composed of eight microring-resonator-based switching elements, four optical waveguides and six waveguide crossings. The extinction ratio is about 13 dB for the through port and larger than 30 dB for the drop port. The crosstalk of the measured optical links is less than -13 dB. The average tuning power consumption is about 10.37 mW and the tuning efficiency is 5.398 mW/nm. The routing functionality and optical signal integrity are verified by transmitting a 12.5 Gb/s PRBS optical signal.

Proof of concept of directed OR/NOR and AND/NAND logic circuit consisting of two parallel microring resonators

We propose and demonstrate a directed OR/NOR and AND/NAND logic circuit consisting of two parallel microring resonators (MRRs). We use two electrical signals representing the two operands of the logical operation to modulate the two MRRs through the thermo-optic effect, respectively. The final operation results are represented by the output optical signals. Both OR/NOR and AND/NAND operations at 10 kbps are demonstrated.

Low-voltage, high-extinction-ratio, Mach-Zehnder silicon optical modulator for CMOS-compatible integration.

We demonstrate a carrier-depletion optical modulator with the driving voltage swing of 2 V and the extinction ratio of 12.79 dB at 12.5 Gbit/s. Even the driving voltage is reduced to 1 V, the the device still has an extinction ratio of 7.67 dB.

Five-Port Optical Router Based on Microring Switches for Photonic Networks-on-Chip

We demonstrate a five-port optical router that is suitable for large-scale photonic networks-on-chip. The optical router is designed to passively route the optical signal travelling in one direction and actively route the optical signal making a turn. In the case that an XY dimension-order routing is used, the passive routing feature guarantees that the maximum power consumption to route the data through the network is a constant that is independent of the network size. The fabricated device has an efficient footprint of ~ 460 × 1000 μm2. The routing functionality of the device is verified by using a 12.5-Gbit/s optical signal. The capability of multiwavlength routing for the optical router is also explored and discussed.

A Universal Method for Constructing N-Port Nonblocking Optical Router for Photonic Networks-On-Chip

We propose a universal method for constructing N-port nonblocking optical routers based on microring resonators. The topologies for five-, six-, seven-, and eight-port nonblocking optical routers are presented. As a case study, we compare the five-port optical router constructed by our method with the previously reported ones. The simulation results show that the mesh photonic network constructed by the proposed five-port optical routers has low insertion loss and high optical signal-to-noise ratio. Moreover, high-radix optical routers can be easily constructed by the proposed method, which can support more complicated and efficient network.

Electro-optic directed logic circuit based on microring resonators for XOR/XNOR operations

We report the implementation of the XOR and XNOR operations using an electro-optic directed logic circuit based on two cascaded silicon microring resonators (MRRs), which are both modulated through the plasma dispersion effect. PIN diodes are embedded around the MRRs to achieve the carrier-injection modulation. The inherent resonance wavelength mismatch between the two nominally identical MRRs caused by fabrication errors is compensated by two local microheaters above each MRR through the thermo-optic effect. Two electrical modulating signals applied to the MRRs represent the two operands of the two operations. Simultaneous bitwise XOR and XNOR operations at 100 Mbit/s are demonstrated.

Electro-Optical Response Analysis of a 40 Gb/s Silicon Mach-Zehnder Optical Modulator

We demonstrate a 40 Gbit/s silicon Mach-Zehnder optical modulator driven by a differential voltage of 0.36 Vpp. The energy efficiency is as low as 32.4 fJ/bit which is near the power efficiency of the ring modulator. We analyze the relationship between the electrical bandwidth and the electro-optical (EO) bandwidth based on the electrical S parameter measurement. Because of the nonlinear response, the electro-optical bandwidths in the small-signal tests are is slightly different when the modulator is biased at different transmission points. But the EO response is much different when the optical phase change is large enough to cover the nonlinear and linear regions at the same time. The nonlinearity can greatly improve the EO response in large-signal test. In our experiment, the rise/fall (20%-80%) time decreases from 13 ps to 10 ps as the driving amplitude increases from 5 V to 6 V under the same reverse bias of 3 V.