New Designs Unlock Photon Generation in Silicon Carbide and Lithium Niobate

A new method for generating photons via spontaneous parametric down-conversion (SPDC) removes the need for periodic poling, a complex fabrication technique currently limiting the scalability of many photon sources. Tim F. Weiss at Advanced Research Department and colleagues demonstrate a device architecture enabling SPDC across a wide range of frequencies in both 4H Silicon Carbide on-insulator and thin-film Lithium Niobate on-insulator. The design, utilising mode conversion and modal phase-matching, simplifies photon sources and enables compatibility with complementary metal-oxide-semiconductor (CMOS) fabrication, potentially accelerating advancements in quantum photonics and integrated quantum circuits.

High-efficiency photon pair generation via mode conversion in silicon carbide and lithium niobate

Mode conversion efficiencies of 99% and 96% were achieved in 4H Silicon Carbide and Lithium Niobate respectively, exceeding limitations imposed by reliance on periodic poling. This advance is significant because spontaneous parametric down-conversion (SPDC) was previously unattainable in silicon carbide, and the new method eliminates periodic poling, a complex fabrication step that hinders scalability in lithium niobate. The device architecture utilises mode conversion, redirecting light within a waveguide, and subsequent phase-matching to generate photon pairs across a broad range of frequencies.

Designs and calculations for 4H Silicon Carbide on-insulator, where SPDC photon generation was previously unavailable, and thin-film Lithium Niobate on-insulator were successfully demonstrated. This achievement bypasses the need for periodic poling, a manufacturing step traditionally used for these devices in lithium niobate, potentially reducing production costs and increasing scalability. The team employed mode conversion, redirecting light into higher-order TM20 modes before initiating the spontaneous parametric down-conversion (SPDC) process, which splits photons into pairs. Calculations reveal a broad range of viable wavelength combinations for photon pair generation, establishing a platform for SPDC without the fabrication steps and errors associated with periodic poling, and enabling SPDC in materials where it could not previously be realised.

Adiabatic mode conversion for efficient spontaneous parametric down-conversion

Mode conversion is central to this new design, functioning similarly to altering a guitar string’s shape to change its tone, but applied to light waves contained within a waveguide. This technique redirects light from a readily available input mode, a fundamental light wave easily coupled from optical fibres, into a more complex mode required for efficient down-conversion. Carefully engineered waveguide geometry creates a gradual transition, an ‘adiabatic directional coupler’, allowing light to smoothly change its characteristics without significant loss.

This circumvents periodic poling, a traditionally complex process of creating tiny grooves within a material to align light waves for optimal photon pair creation; instead, the design relies on precisely shaping the light itself. A novel design for spontaneous parametric down-conversion (SPDC), a process used to create pairs of light particles called photons, has been developed. This approach avoids periodic poling, a complex fabrication technique needed in conventional photon sources, simplifying production and reducing potential errors. Utilising 4H Silicon Carbide on-insulator and Lithium Niobate on-insulator materials extends SPDC to platforms where it was previously unavailable, while mode conversion, redirecting light within a waveguide, is central to the process, achieving 99% and 96% conversion efficiencies for Silicon Carbide and Lithium Niobate respectively.

Silicon carbide unlocks scalable entangled photon sources without periodic poling

Generating entangled photons is vital for advances in quantum technology, but current methods demand careful material structuring via periodic poling. This process limits both material choice and scalability, and introduces fabrication errors that hinder the creation of reliable photon sources. The authors acknowledge that achieving truly pure photon emission may necessitate additional filtering steps, representing a compromise between the number of photons generated and their quality.

Nevertheless, this new approach represents a major step forward for quantum photonics, even acknowledging that perfect photon purity remains a challenge. Removing the need for periodic poling expands the range of usable materials, notably including silicon carbide where entangled photon generation was previously impossible. This broadened material palette, coupled with compatibility with standard chip manufacturing techniques, promises to lower costs and accelerate the development of scalable quantum devices, a key factor for real-world applications.

A new approach to generating entangled photons without complex material structuring has been demonstrated. This design utilises mode conversion and phase-matching within silicon carbide and lithium niobate, materials previously challenging for this application. The new device architecture establishes a route to generating entangled photons without periodic poling, a complex fabrication process previously essential for many sources. Skillfully altering the characteristics of light within a waveguide via mode conversion, and subsequent phase-matching, enables spontaneous parametric down-conversion (SPDC) in materials like silicon carbide, where it was previously unattainable. This advancement simplifies production and broadens material choices for integrated quantum photonics, potentially accelerating the development of quantum technologies.

The researchers successfully demonstrated a new method for generating entangled photons without relying on periodic poling, a complex fabrication technique. This is significant because it expands the range of materials suitable for creating these photon sources, notably including 4H Silicon Carbide where this was previously impossible. By utilising mode conversion and phase-matching in materials such as lithium niobate, the design simplifies the production of entangled photons and offers compatibility with standard chip manufacturing. The authors suggest further optimisation may be needed to achieve optimal photon purity, balancing the number of photons generated with their quality.