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Parametric sources in quantum optics usually require some form of spectro-temporal control for conditional generation of high-purity single-photon states, but their properties have not yet been optimized using integrated microchips. Using external short-pulse lasers and separate devices for pump preparation and for photon generation, as is traditional, incurs many impediments such as reduced performance, increased loss, high cost, and limited scalability. To overcome these limitations, here we demonstrate a circuit including high-bandwidth, high-extinction ratio electro-optic modulators for pump-pulse preparation fully integrated with high-quality factor (Q) microresonators for efficient parametric nonlinearity, together with seamlessly interconnecting waveguides. The microchip uses different optical materials on a common platform and a multi-layer integrated photonic architecture. Using this, we control the joint spectrum of room-temperature biphoton generation for the first time on a single integrated microchip, and demonstrate that the theoretical purity bound can be achieved.

Integrated photonics at near-IR (NIR) wavelengths currently lacks high bandwidth and low-voltage modulators, which add electro-optic functionality to passive circuits. Here, integrated hybrid thin-film lithium niobate (TFLN) electro-optic Mach–Zehnder modulators (MZM) are shown, using TFLN bonded to planarized silicon nitride waveguides. The design does not require TFLN etching or patterning. The push–pull MZM achieves a half-wave voltage length product (V_πL) of 0.8 V.cm at 784 nm. MZM devices with 0.4 cm and 0.8 cm modulation length show a broadband electro-optic response with a 3 dB bandwidth beyond 100 GHz, with the latter showing a record bandwidth to half-wave voltage ratio of 100 GHz/V and a high extinction ratio exceeding 30 dB. Such fully integrated high-performance NIR electro-optic devices may benefit data communications, analog signal processing, test and measurement instrumentation, quantum information processing and other applications.

Strategies for improved fabrication of integrated thin-film lithium niobate electro-optic (EO) Mach–Zehnder modulators (MZMs) are reported using scalable processes and designs. The MZM devices utilize direct bonding of unetched and unpatterned thin-film lithium niobate to patterned and planarized silicon photonic microchips. The latter contains silicon nitride waveguide structures of various widths that are used to form hybrid modes that are suitable for high-bandwidth low-voltage EO modulators based on Pockels effect. We report that the incorporation of appropriately designed outgassing channels and certain modifications to key processing steps helped achieve a greater than 99% reduction in void density during bonding. Void reduction is critically important for these traveling-wave hybrid MZM devices in which the optical mode is controllably distributed between multiple thin layers and propagates over millimeter-scale lengths.