This thesis work covers both classical and quantum aspects of nonlinear propagation of photons in nanophotonic Silicon waveguides. The work has been carried out within the framework of the project SIQURO, which aims to bring the quantum world into integrated photonics by using the Silicon platform and, therefore, permitting in a natural way the integration of quantum photonics with electronics. The research towards on chip bright quantum sources of photon pairs has been done by investigating Multi Modal Four Wave Mixing in micrometer-size waveguides, thus exploiting the large third order nonlinearity of Silicon. The possibility to induce second order nonlinearities by straining its unit cell has been also analyzed through the study of the electro-optic effect. This has been done with the aim to promote Silicon as a platform for the integration of quantum sources of entangled photons based on Spontaneous Parametric Down Conversion. New quantum interference effects have been reported in a free space unbalanced Mach Zehnder interferometer asymmetrically excited by colour entangled photon pairs. Innovative designs of integrated quantum circuits have been proposed, which extend the capabilities of the quantum circuits demonstrated so far and provide additional functionalities. This work represents a step forward to the realization of self subsistent integrated devices for quantum enhanced measurement, quantum computation and quantum crypthography.
This thesis work covers both classical and quantum aspects of nonlinear propagation of photons in nanophotonic Silicon waveguides. The work has been carried out within the framework of the project SIQURO, which aims to bring the quantum world into integrated photonics by using the Silicon platform and, therefore, permitting in a natural way the integration of quantum photonics with electronics. The research towards on chip bright quantum sources of photon pairs has been done by investigating Multi Modal Four Wave Mixing in micrometer-size waveguides, thus exploiting the large third order nonlinearity of Silicon. The possibility to induce second order nonlinearities by straining its unit cell has been also analyzed through the study of the electro-optic effect. This has been done with the aim to promote Silicon as a platform for the integration of quantum sources of entangled photons based on Spontaneous Parametric Down Conversion. New quantum interference effects have been reported in a free space unbalanced Mach Zehnder interferometer asymmetrically excited by colour entangled photon pairs. Innovative designs of integrated quantum circuits have been proposed, which extend the capabilities of the quantum circuits demonstrated so far and provide additional functionalities. This work represents a step forward to the realization of self subsistent integrated devices for quantum enhanced measurement, quantum computation and quantum crypthography.
The PhD thesis work here presented was carried out within the SiQuro project at the Nanoscience laboratory of the University of Trento. The project started in September 2013 and lasted four years. It was funded by the Provincia Autonoma di Trento (PAT). SiQuro’s goal was to bring the quantum world into integrated photonics by using the silicon platform and, therefore, permitting the integration of quantum photonics with electronics. The vision was to have low cost and mass manufacturable integrated quantum photonic circuits for a variety of different applications in quantum computing and secure communications. It must be said that SiQuro was a challenging and ambitious project, nevertheless important achievements in the quantum photonics arena were reached. My thesis is concentrated on the generation, manipulation and detection of quantum states of light. On one side, this was carried on in strained silicon waveguides, with the final goal to generate MIR entangled photon pairs via SPDC. Alongside, the generation and manipulation of correlated photon pair sources by means of spontaneous FWM in traditional silicon waveguides and microring resonators at telecom wavelength was also investigated. For the detection of MIR photon pairs, a suitable detection unit was developed as well. Moreover, even though the long-term goal of the project was the realization of a silicon quantum photonic circuit, I also implemented free-space quantum optical experiments. For this, I exploited a bulk nonlinear crystal, namely lithium niobate (LiNbO3), which has a well-known sizeable χ(2) nonlinearity.
Silicon-on-insulator (SOI) wafers have been developed for electronic integrated circuits, but are also one of the most promising platforms in photonic integrated circuits due to its low loss, high refractive index, ability to fast phase modulation, and well-developed fabrication technologies. With advantages to handle light with a small volume and high modulation speed, silicon photonics has been intensively investigated as the next generation platform of signal processing, interconnection, and communication devices. Recently, silicon photonics has been attracted great interests in quantum optics communities as optical quantum systems for linear optical quantum computing are achievable using silicon photonic components including beam splitters, phase modulators, and filters and the small footprint of a silicon photonic quantum system has unprecedented performances of high stability and scalability. Here we show our recent results on the fabrication of silicon photonic elements for quantum applications. We fabricated low-loss optical waveguides, efficient fiber-to-waveguide grating couplers, resonator-based optical filters, and tunable beam splitters and tested their performances. A micro-sized heater is attached on a Mach-Zehnder interferometer, showing stable operation as a slow phase modulator. In addition, phase modulators using plasma dispersion effects are under investigation. Finally, the quantum characteristics of photon pairs generated by spontaneous four-wave mixing in silicon waveguides are investigated. These results will be an essential cornerstone for the realization of quantum optical computing and quantum communication devices.
Chip-scale integrated photonic circuits provide an attractive platform for the implementation of many quantum photonic technologies ranging from precise metrology to secure communication and quantum computation. In particular, silicon photonic platforms support micron-scale nonlinear optical sources of non-classical light which can be mass manufactured using the robust fabrication processes pioneered by the CMOS microelectronics industry. Integration of these quantum photonic sources with high-performance classical photonic devices on the same chip is required for truly scalable quantum information technologies. Integrated nonlinear resonators are investigated as sources of quantum mechanically correlated photon pair sources. An all-order dispersion engineering method is presented as a robust design synthesis for micoring sources. In addition, a novel concept of coupled mode dispersion compensation is proposed and demonstrated, providing significantly improved performance characteristics of resonant four-wave mixing sources. Next a photon pair source is demonstrated in a commercial CMOS microelectronics process opening the door to future integration of quantum photonics with electronic logic and control circuits. Classical nonlinear optical measurements of stimulated four-wave mixing are used for the first time to accurately predict the quantum correlations from the same device operating in the photon pair regime. Next the first demonstration of fully on-chip pump rejection is demonstrated with over 95 dB pump extinction improving the figures of merit from previous demonstrations by multiple orders of magnitude, including losses, detected pair rates and size. Finally, proposals for introducing novel degrees of freedom provided by an integrated platform are presented for further improving the performance of both photon pair and classical nonlinear optical sources.
Silicon photonic integrated circuits are a promising platform for realizing large-scale quantum photonic devices. While the linear optical approach has greatly contributed to this field, it is often possible to improve the functionality and scalability by making use of non-linear processes. One interesting process is the interference between two nonlinear optical processes, where the interference occurs by removing the information as to which of two processes have occurred. Recently, we have implemented a non-linear interferometer in the pair-photon generation regime by using spontaneous four-wave mixing in an integrated silicon photonic chip. In this paper, we have improved the performance of our non-linear interference device and evaluated it in detail. This work shows the possibility of integrating and controlling nonlinear-optical interference components for silicon quantum photonics.
Photonic integrated circuits represent a promising platform for applying quantum information science to areas such as quantum computation, quantum communication, and quantum metrology. While the linear optical approach has greatly contributed to this field, it is often possible to improve the functionality and scalability by making use of nonlinear processes. One interesting phenomenon is the interference between two nonlinear optical processes, where the interference occurs by removing the information as to which of two processes have occurred. In this Letter, we demonstrate a nonlinear interferometer in the pair-photon generation regime by using spontaneous four-wave mixing in an integrated silicon photonic chip. We observe a nonlinear interference in the production rate of photon pairs generated from two different four-wave mixing waveguides. We obtain an interference visibility of 96.8%. This work shows the possibility of integrating and controlling nonlinear-optical-interference components for silicon quantum photonics.
Resonant devices are an integral component of the integrated silicon photonics platform, with applications in filters, switches, modulators, delays, sensors etc. High index contrast SOI waveguides can be used to form compact micro-ring resonators with bend radii on the order of micro-meters. This work describes the application of micro-ring resonators in linear and nonlinear silicon photonics. We describe the use of higher-order coupled resonators for use as ultra-high contrast pass-band filters with close to 100 dB extinction. Using the spontaneous four-wave mixing process, a third-order nonlinear Kerr effect, coupled resonator waveguides are shown to be a useful source of heralded single photons, as well as other unique quantum states of light. We also describe four-wave mixing results in silicon micro-resonators, where nonlinear loss effects are mitigated by reverse biased p-i-n diodes, showing potential for high-speed optical signal processing.