Pauline Mechet

Experimental demonstration of reservoir computing on a silicon photonics chip

In todays age, companies employ machine learning to extract information from large quantities of data. One of those techniques, reservoir computing (RC), is a decade old and has achieved state-of-the-art performance for processing sequential data. Dedicated hardware realizations of RC could enable speed gains and power savings. Here we propose the first integrated passive silicon photonics reservoir. We demonstrate experimentally and through simulations that, thanks to the RC paradigm, this generic chip can be used to perform arbitrary Boolean logic operations with memory as well as 5-bit header recognition up to 12.5 Gbit s(-1), without power consumption in the reservoir. It can also perform isolated spoken digit recognition. Our realization exploits optical phase for computing. It is scalable to larger networks and much higher bitrates, up to speeds >100 Gbit s(-1). These results pave the way for the application of integrated photonic RC for a wide range of applications.

Cascadable excitability in microrings

To emulate a spiking neuron, a photonic component needs to be excitable. In this paper, we theoretically simulate and experimentally demonstrate cascadable excitability near a self-pulsation regime in high-Q-factor silicon-on-insulator microrings. For the theoretical study we use Coupled Mode Theory. While neglecting the fast energy and phase dynamics of the cavity light, we can still preserve the most important microring dynamics, by only keeping the temperature difference with the surroundings and the amount of free carriers as dynamical variables of the system. Therefore we can analyse the microring dynamics in a 2D phase portrait. For some wavelengths, when changing the input power, the microring undergoes a subcritical Andronov-Hopf bifurcation at the self-pulsation onset. As a consequence the system shows class II excitability. Experimental single ring excitability and self-pulsation behaviour follows the theoretic predictions. Moreover, simulations and experiments show that this excitation mechanism is cascadable.

Excitability in optically injected microdisk lasers with phase controlled excitatory and inhibitory response

We demonstrate class I excitability in optically injected microdisk lasers, and propose a possible optical spiking neuron design. The neuron has a clear threshold and an integrating behavior, leading to an output rate-input rate dependency that is comparable to the characteristic of sigmoidal artificial neurons. We also show that the optical phase of the input pulses has influence on the neuron response, and can be used to create inhibitory, as well as excitatory perturbations.

Unidirectional III-V microdisk lasers heterogeneously integrated on SOI

We demonstrate unidirectional bistability in microdisk lasers electrically pumped and heterogeneously integrated on SOI. The lasers operate in continuous wave regime at room temperature and are single mode. Integrating a passive distributed Bragg reflector (DBR) on the waveguide to which the microdisk is coupled feeds laser emission back into the laser cavity. This introduces an extra unidirectional gain and results in unidirectional emission of the laser, as demonstrated in simulations as well as in experiment.

A low-power high-speed InP microdisk modulator heterogeneously integrated on a SOI waveguide

We report on the modulation characteristics of indium phosphide (InP) based microdisks heterogeneously integrated on a silicon-on-insulator (SOI) waveguide. We present static extinction ratios and dynamic operation up to 10 Gb/s. Operation with a bit-error rate below 1 × 10(-9) is demonstrated at 2.5, 5.0 and 10.0 Gb/s and the performance is compared with that of a commercial modulator. Power penalties are analyzed with respect to the pattern length. The power consumption is calculated and compared with state-of-the-art integrated modulator concepts. We demonstrate that InP microdisk modulators combine low-power and low-voltage operation with low footprint and high-speed. Moreover, the devices can be fabricated using the same technology as for lasers, detectors and wavelength converters, making them very attractive for co-integration.

Ultracompact Phase Modulator Based on a Cascade of NEMS-Operated Slot Waveguides Fabricated in Silicon-on-Insulator

Phase modulation is one of the key functionalities in an integrated photonics circuit. In the silicon photonics platform, several approaches have been undertaken. The thermooptic effect is slow and relatively power hungry, whereas a carrier-based approach is fast ( >; Gb/s) but lossy and weak. Integration of other (e.g., electrooptic) materials typically struggles with fabrication issues that limit the effect. Here, we present a nanoelectromechanical systems-based approach. By applying a voltage over a freestanding slot waveguide, the slot width will change, resulting in an effective index change and thus a phase change. Using a cascaded structure, the effect can be enlarged without reducing the speed. A phase change of 40° was observed for a voltage of 13 V over a cascade of three 5.8-μm-long freestanding slots. The expected speed is in the MHz range.

Ultrafast and bias-free all-optical wavelength conversion using III-V-on-silicon technology

Using a 7.5 μm diameter disk fabricated with III-V-on-silicon fabrication technology, we demonstrate bias-free all-optical wavelength conversion for non-return-to-zero on-off keyed pseudorandom bit sequence (PRBS) data at the speed of 10 Gbits/s with an extinction ratio of more than 12 dB. The working principle of such a wavelength converter is based on free-carrier-induced refractive index modulation in a pump-probe configuration. We believe it to be the first bias-free on-chip demonstration of all-optical wavelength conversion using PRBS data. All-optical gating measurements in the pump-probe configuration with the same device have revealed that it is possible to achieve wavelength conversion beyond 20 Gbits/s.

Theoretical Analysis of Unidirectional Operation and Reflection Sensitivity of Semiconductor Ring or Disk Lasers

We theoretically and numerically analyze the unidirectional behavior of ring or disk lasers coupled to a bus waveguide with a relatively strong reflector on one side and find analytical expressions for the ratio of the powers in clockwise and counter clockwise modes. At low bias levels, this ratio depends on the coupling coefficients that determine the coupling between clockwise and counterclockwise modes, whereas at high bias levels it also depends strongly on the gain suppression. We also theoretically and numerically investigate the feedback sensitivity of such lasers and come to the conclusion that ring or disk lasers are generally much more sensitive to external reflections than traditional Fabry-Perot, DFB, or DBR lasers. At high bias levels, the feedback sensitivity also depends strongly on the gain suppression, and at high enough power levels, it can be better than that of traditional edge-emitting lasers.

Ultracompact electro-optic phase modulator based on III-V-on-silicon microdisk resonator.

A novel ultracompact electro-optic phase modulator based on a single 9 μm-diameter III-V microdisk resonator heterogeneously integrated on and coupled to a nanophotonic waveguide is presented. Modulation is enabled by effective index modification through carrier injection. Proof-of-concept implementation involving binary phase shift keying modulation format is assembled. A power imbalance of ∼0.6  dB between both symbols and a modulation rate up to 1.8 Gbps are demonstrated without using any special driving technique.

InP Microdisk Lasers Integrated on Si for Optical Interconnects

We review recent theoretical and experimental work on InP membrane microdisk lasers heterogeneously integrated on SOI and coupled to a Si bus waveguide. The lasers can now be fabricated with very high yield, have typical threshold currents of 0.5 mA and output powers of tens of μW, while the total power consumption is restricted to 5 mW. First, we describe various improvements in the fabrication technology and interesting results on the uniformity in device characteristics. In a second part, unidirectional behaviour and reflection sensitivity are briefly discussed. The third part is focused on optical signal regeneration with microdisk lasers. The last part contains a brief summary of optical interconnects based on heterogeneously integrated microdisk lasers and heterogeneously integrated photodetectors.