Emerging applications based on optical beams carrying orbital angular momentum (OAM) will probably require photonic integrated devices and circuits for miniaturization, improved performance, and enhanced functionality. We demonstrate silicon-integrated optical vortex emitters, using angular gratings to extract light confined in whispering gallery modes with high OAM into free-space beams with well-controlled amounts of OAM. The smallest device has a radius of 3.9 micrometers. Experimental characterization confirms the theoretical prediction that the emitted beams carry exactly defined and adjustable OAM. Fabrication of integrated arrays and demonstration of simultaneous emission of multiple identical optical vortices provide the potential for large-scale integration of optical vortex emitters on complementary metal-oxide-semiconductor compatible silicon chips for wide-ranging applications.

We demonstrate efficient generation of correlated photon pairs by spontaneous four wave mixing in a 5 μm radius silicon ring resonator in the telecom band around 1550 nm. By optically pumping our device with a 200 μW continuous wave laser, we obtain a pair generation rate of 0.2 MHz and demonstrate photon time correlations with a coincidence-to-accidental ratio as high as 250. The results are in good agreement with theoretical predictions and show the potential of silicon micro-ring resonators as room temperature sources for integrated quantum optics applications.

Entanglement—one of the most delicate phenomena in nature—is an essential resource for quantum information applications. Scalable photonic quantum devices must generate and control qubit entanglement on-chip, where quantum information is naturally encoded in photon path. Here we report a silicon photonic chip that uses resonant-enhanced photon-pair sources, spectral demultiplexers and reconfigurable optics to generate a path-entangled two-qubit state and analyse its entanglement. We show that ring-resonator-based spontaneous four-wave mixing photon-pair sources can be made highly indistinguishable and that their spectral correlations are small. We use on-chip frequency demultiplexers and reconfigurable optics to perform both quantum state tomography and the strict Bell-CHSH test, both of which confirm a high level of on-chip entanglement. This work demonstrates the integration of high-performance components that will be essential for building quantum devices and systems to harness photonic entanglement on the large scale.

Entanglement is a fundamental resource in quantum information processing. Several studies have explored the integration of sources of entangled states on a silicon chip, but the devices demonstrated so far require millimeter lengths and pump powers of the order of hundreds of milliwatts to produce an appreciable photon flux, hindering their scalability and dense integration. Microring resonators have been shown to be efficient sources of photon pairs, but entangled state emission has never been proven in these devices. Here we report the first demonstration, to the best of our knowledge, of a microring resonator capable of emitting time-energy entangled photons. We use a Franson experiment to show a violation of Bell’s inequality by more than seven standard deviations with an internal pair generation exceeding 10⁷ Hz. The source is integrated on a silicon chip, operates at milliwatt and submilliwatt pump power, emits in the telecom band, and outputs into a photonic waveguide. These are all essential features of an entangled state emitter for a quantum photonic network

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As photonics moves from the single-device level toward large-scale, integrated, and complex systems on a chip, monitoring, control, and stabilization of the components become critical. We need to monitor a circuit non-invasively and apply a simple, fast, and robust feedback control. Here, we show non-invasive monitoring and feedback control of high-quality-factor silicon (Si) photonic resonators assisted by a transparent detector that is directly integrated inside the cavity. Control operations are entirely managed by a CMOS microelectronic circuit that is bridged to the Si photonic chip and hosts many parallel electronic readout channels. Advanced functionalities, such as wavelength tuning, locking, labeling, and swapping, are demonstrated. The non-invasive nature of the transparent monitor and the scalability of the CMOS readout system offer a viable solution for the control of arbitrarily reconfigurable photonic integrated circuits aggregating many components on a single chip.

The ability to rapidly switch between orbital angular momentum modes of light has important implications for future classical and quantum systems. In general, orbital angular momentum beams are generated using free-space bulk optical components where the fastest reconfiguration of such systems is around a millisecond using spatial light modulators. In this work, an extremely compact optical vortex emitter is demonstrated with the ability to actively tune between different orbital angular momentum modes. The emitter is tuned using a single electrically contacted thermo-optical control, maintaining device simplicity and micron scale footprint. On-off keying and orbital angular momentum mode switching are achieved at rates of 10 ms and 20 ms respectively.

Four-wave mixing (FWM) can be either stimulated or occur spontaneously. The first process is intrinsically much stronger and well understood through classical nonlinear optics. The latter, also known as parametric fluorescence, can be explained only in the framework of a quantum theory of light. We experimentally demonstrated that, in a microring resonator, there is a simple relation between the efficiencies of these two processes that is independent of the nonlinearity and ring size. In particular, we have shown the average power generated by parametric fluorescence can be immediately estimated from a classical FWM experiment. These results suggest that classical nonlinear characterization of a photonic integrated structure can provide accurate information on its nonlinear quantum properties.