Experimental demonstration of a 4,294,967,296-QAM-based Y-00 quantum stream cipher template carrying 160-Gb/s 16-QAM signals.

We demonstrate a 4,294,967,296-quadrature amplitude modulation (QAM) based Y-00 quantum stream cipher system carrying a 160-Gb/s 16-QAM signal transmitted over 320-km SSMF. The ultra-dense QAM cipher template is realized by an integrated two-segment silicon photonics I/Q modulator.

Broadly and finely tunable hybrid silicon laser with nanosecond-scale switching speed.

We demonstrate a hybrid silicon tunable laser with wide tunability and rapid switching speed for applications in sensing and optical networks. By implementing an optimized carrier injection phase shifter design, the filters of the silicon laser cavity may be efficiently controlled, enabling both fine and broad wavelength tuning across a 56 nm range, in addition to a rapid 10 ns switching time. The laser emits up to 10 dBm output power, and the linewidth is near 200 kHz. The fast wavelength switching demonstrated here may be employed in data center and access networks, while the potential for rapid wavelength sweeping is attractive for optical sensing and imaging applications.

Self-biasing of carrier depletion based silicon microring modulators.

We report on the self-biasing effect of carrier depletion based silicon microring modulators (MRM) by demonstrating that a silicon MRM can generate open eye diagrams for non-return-to-zero (NRZ) on-off keying (OOK) modulation without an external reverse bias supplied to it. Two modulator configurations are investigated namely single-ended drive in a ground-signal-ground and differential drive in a ground-signal-signal-ground pad configurations. The single-ended modulator is designed with an on photonic integrated circuit (PIC) 50 Ω termination. Open eye diagrams are obtained at 25 Gbit/s and 36 Gbit/s NRZ OOK modulations. We carry-out thorough experimental characterization of the self-biasing of single-ended MRM under various operating conditions of input optical power, carrier wavelength, ring quality factor and extinction ratio as well as modulation speeds, driving voltage swing and pattern length. We demonstrate that the self-biasing is robust and works well in almost all tested conditions. The differential drive MRM is designed with a high impedance without an on-PIC 50 Ω termination. Open eye diagrams are obtained at 30 Gbit/s and 60 Gbit/s NRZ OOK modulations for modulating voltage swing of ∼2.5 Vpp. As demonstrated, the self-biasing works well in both single-ended and differential drive configurations as well as for on-PIC 50 Ω terminated and non-terminated MRMs. The electrical passive parts are all co-designed and fabricated on the same silicon chip as the PIC. The reported self-biasing eliminates the need of having bipolar DC biases supplied to the anode and cathode of the differential drive modulator and allows for simpler driver / modulator interfaces without inductive bias tees.

Inter-polarization mixers for coherent detection of optical signals.

Electro-magnetic (EM) mixers are fundamental building blocks in communication systems. They are used in frequency/wavelength filters, interferometric modulators, amplitude-phase receivers, to name a few. Traditional EM mixers have two or more input ports and work only for co-polarized signal and local-oscillator (LO) incident on its inputs. Here we report on novel designs, in silicon, of inter-polarization EM mixers operating at 1550 nm wavelength. The 180-degree optical mixer comprising a single input port is demonstrated to coherently mix orthogonally polarized signal and LO. Using the proposed 180-degree mixer, we report on a novel design for a 90-degree optical mixer on silicon with small footprint, broadband response, low loss and good fabrication tolerance. It exploits birefringence of a waveguide to achieve broadband and fabrication-tolerant 90° phase difference between the signal/LO relative phase in the in-phase and quadrature components. A monolithic silicon photonics coherent receiver is demonstrated using the reported 90-degree mixer, and its operation at 22 Gbaud and 44 Gbaud is shown. These mixers pave the way for novel coherent receiver architectures in long-haul, metro, passive optical networks and data-center interconnect applications.

Simultaneous four-channel thermal adaptation of polarization insensitive silicon photonics WDM receiver.

We propose a novel approach to demonstrate simultaneous multi-wavelength locking during temperature changes in a silicon photonic polarization insensitive microring-based wavelength division multiplexing (WDM) receiver. The DC component of a single monitoring photodetector at the through port of the microring filter array is exploited as a feedback signal with no additional power consumption. This feedback signal is used in control circuitry to properly tune the microring filters using ohmic heating, thus creating a feedback loop for thermal adaptation. We describe the necessary information, specifically each microring filter's room temperature resonant wavelength and tunability, which can be used to calibrate and achieve proper wavelength configurability and locking. In addition, we describe a simple control algorithm based on an adaptive gradient method often used in machine learning, allowing the receiver to endlessly demultiplex at different temperatures. We successfully achieve thermal adaptation over a temperature range >37°C and demultiplex a 4 × 25 Gb/s on-off-keying signal of 150 GHz channel spacing, all while the polarization is scrambling.

Simultaneous wavelength locking of microring modulator array with a single monitoring signal.

A microring modulator array coupled to a common bus waveguide can be used to construct low power, compact and flexible wavelength-division-multiplexing (WDM) transmitters. However, due to extremely small working bandwidths of the rings, it is challenging to find the right resonant wavelength setting and locking the resonance to an external laser. In the paper, we propose a novel technique enabling simultaneous wavelength locking of a microring modulator array with a single monitor, together with automatically optimizing the wavelength setting. We experimentally demonstrate locking three rings over a temperature range >40 °C at 3x20 Gb/s on-off-keying (OOK) modulation and ~3x75 Gb/s discrete multi-tone (DMT) modulation.

Photonic-to-plasmonic mode converter.

A novel photonic-to-plasmonic mode converter for efficiently converting a silicon strip waveguide mode to a gap surface plasmon polariton (SPP) of a metallic slot structure is proposed. A conversion efficiency of more than 85% is found for metallic slots with a slot size of 30-50 nm. Calculations show that high conversion efficiencies can be achieved for various cladding materials with refractive indices of 1.44, 1.6, and 1.7. The optical 1 dB bandwidth of the converter is around 200 nm. The proposed mode converter shows a good tolerance with respect to fabrication errors, and it requires a simple fabrication procedure only.