Quantum technologies hold the promise of revolutionizing computing, communication, and sensing, and integrated photonics stands as a key enabler in this realm. Silicon nitride, with its unique combination of low loss, remarkable non-linear performance, and compatibility with existing semiconductor technologies, has emerged as a promising candidate for the implementation of quantum photonic circuits. Alternately, Lithium-Niobate-OnInsulator (LNOI), a material platform well known for its high electro-optic coefficient, has also turned out to be an attractive choice for quantum integrated circuits with the development of low-loss fabrication processes. Moreover, the integration of on-chip photon sources and superconducting nanowire single-photon detectors (SNSPDs) on these platforms has paved the for scalable quantum circuits minimizing the footprint and eliminating the need for lossy interconnects. However, the integration of these components on a single material platform is often hindered by background photons from the strong classical pump light used for processes such as spontaneous parametric down-conversion (SPDC). Here, we propose silicon-implanted SiN and LNOI waveguides as a novel material platform that acts as a passive filter at visible wavelengths while imparting negligible losses in the telecom band. The implantation process can be selectively patterned with manometer precision enabling enhanced tunability of the process. Furthermore, transmission electron microscopy (TEM) results provide a thorough understanding of the material dynamics at the atomic scale allowing accurate modelling of the mode profiles. This breakthrough advances the scalability of quantum photonic technologies where the source, filters, circuits, and detectors can be integrated on a single platform.
The field of photonic integrated circuits (PIC) has flourished in the past two decades, fueling numerous cutting-edge applications across sensing, networking, data interconnect, and quantum information processing. As a guiding material for PIC, Si
3N
4 has seen extensive use for its ultra-low loss, broad transparency, and diversity in implementation across both thin and thick films. Although the standard, traditional silicon dioxide (SiO
2) on silicon (Si) substrates that underpin the majority of Si
3N
4 photonics face drawbacks in the form of long-wavelength transparency limited by SiO
2, high-stress deposition for anomalous dispersion thick-film Si
3N
4, and leakage loss to the Si layer for low-confinement thin-film Si
3N
4. Featuring increased long-wavelength transparency into the mid-infrared, low-stress deposition of Si
3N
4, and a low index, this work investigates sapphire substrates as alternate hosts for Si
3N
4 photonics with greater spectral coverage and reduced fabrication complexity. This work presents a robust method of fabricating ultra-low loss photonic integrated circuits on a 500-nm-thick Si
3N
4-on-sapphire platform, exhibiting record-low losses below
0.1dB/cm. Implemented using this process are high-Q microrings with intrinsic quality factors in excess of
4.5×106 and coupled-ring photonic molecules to support nonlinear gain. Leveraging the achievable low loss and high-Q, this work further reports the first demonstration of Kerr-comb and soliton generation on the Si
3N
4-on-sapphire platform. These advances in loss, quality factor, and soliton generation on this versatile, broad-transparency platform pave the way for future work in spectroscopy and quantum-enhanced sensing across previously prohibited spectral regions for Si
3N
4 photonics with reduced fabrication complexity.
Silicon photonics based on CMOS technology is a very attractive platform to build compact, low-cost and scalable quantum photonics integrated circuits addressing the requirements of quantum key distribution protocols. We show record low propagation losses below 0.5 dB/cm and below 0.05 dB/cm for silicon and silicon nitride waveguides respectively. We will present our results on integrated components such as hybrid III-V on silicon lasers for weak coherent pulse generation, high-quality microresonators for entangled photon pair generation and we will show our recent developments on high crystalline quality NbN thin films with improved critical temperature for waveguide-integrated superconducting single photon detectors.
Integrated Silicon photonics has played an important role in advancing the applications of quantum information and quantum science. However, due to different material properties, it is challenging to integrate all components with excellent performance based on homogeneous material. Here, by combining high nonlinearity and low losses in a heterogeneous silicon platform, we efficiently generate high-quality photon pairs through spontaneous four-wave mixing in hydrogenated amorphous silicon waveguide and route them off-chip through low loss silicon nitride waveguide. A record high coincidence- to- accidental rate value of 1632.6 (
± 260.4) is achieved in this heterogeneous design with a photon pair generation rate of 1.94 MHz. We also showcase a wide range of multi-channel photon sources with coincidence- to- accidental rate consistently at 200. Lastly, we measure heralded single-photons with a lowest
gH(2)(0) of 0.1085
± 0.0014. Our results demonstrate the heterogeneous silicon platform as an ideal platform for efficient generation of photon pairs and routing them off-chip with low losses. It also paves a way for the future hybrid photonic integrated circuit by collecting distinct features from different materials.
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.
Realizing photonic quantum computing at scale requires integrated circuits that combine ultra-low loss with fast, low-power, low-hysteresis, and low-crosstalk reconfiguration. These requirements are particularly challenging at visible wavelengths, where many quantum resource-state generators, including single-photon sources and quantum memories, naturally operate. Low-confinement silicon nitride waveguides offer the requisite loss performance, but conventional thermo-optic modulators dissipate significant static power, driving thermal crosstalk and precluding cryogenic operation. Visible-wavelength piezo-optomechanical circuits avoid these drawbacks, but existing demonstrations rely either on high-confinement waveguides with propagation losses of 35-100 dB/m, or on low-confinement platforms using foundry-incompatible PZT. Here we combine piezo-optomechanical actuation with a CMOS-foundry-fabricated, low-confinement silicon nitride platform, achieving 2.6 dB/m propagation loss at 780 nm, megahertz-scale modulation bandwidth, a half-wave voltage-length product of 2.8 Vm, and negligible hysteresis. We demonstrate reconfigurable Mach-Zehnder interferometers with 0.63 dB loss per spiral phase shifter, enabling deep, actively reconfigurable visible-wavelength quantum photonic circuits.