Jianfeng Ding

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.

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.

XOR and XNOR operations at 12.5 Gb/s using cascaded carrier-depletion microring resonators

We report the implementation of the XOR and XNOR logical operations using an electro-optic circuit, which is fabricated by CMOS-compatible process in the silicon-on-insulator (SOI) platform. The circuit consists of two cascaded add-drop microring resonators (MRRs), which are modulated through electric-field-induced carrier depletion in reverse biased pn junctions embedded in the ring waveguides. The resonance wavelength mismatch between the two nominally identical MRRs caused by fabrication errors is compensated by thermal tuning. Simultaneous bitwise XOR and XNOR operations of the two electrical modulating signals at the speed of 12.5 Gb/s are demonstrated. And 20 Gb/s XOR operation at one output port of the circuit is achieved. We explain the phenomena that one half of the resonance regions of the device are much more sensitive to the round-trip phase shift in the ring waveguides than the other half resonance regions. Characteristic graphs with logarithmic phase coordinate are proposed to analyze the sensitivity of the demonstrated circuit, as well as several typical integrated optical structures. It is found that our circuit with arbitrary chosen parameters has similar sensitivity to MRRs under the critical coupling.

High-Speed Silicon Mach–Zehnder Optical Modulator With Large Optical Bandwidth

We report a carrier-depletion silicon Mach-Zehnder optical modulator with large optical bandwidth by adopting two symmetric arms. The fiber-to-fiber loss of the device is about 7.2-8 dB in the wavelength range from 1525 to 1565 nm. We have used the truncation method to accurately measure the loss of the optical splitter and combiner, and the on-chip loss is about 3.8 dB. The dynamic extinction ratios at the speed of 40 Gb/s are 4.9-6.4 dB in the wavelength range from 1529 to 1565 nm. By analyzing the dependence of the optical bandwidth on the optical path difference between the two arms, we find that there is an unexpected optical path difference of around 3.3 μm between the two arms, which is considered to originate from the nonuniform morphologies of the waveguide and the nonuniform doping profiles along the two arms and is responsible for the slight wavelength dependence of the static and dynamic response of the silicon Mach-Zehnder optical modulator.

Demonstration of a directed optical decoder using two cascaded microring resonators

We propose and demonstrate a directed optical decoder that can perform the decoding function from a two-bit electrical signal to a four-bit optical signal based on two cascaded microring resonators. We use two electrical signals regarded as a two-bit electrical signal to modulate the two microring resonators through the thermo-optic effect and four optical signals regarded as a four-bit optical signal appear at the output ports, respectively. The device operating at 10 kbps is demonstrated.