Silicon Photonics Enable Next-Generation Quantum Devices

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Researchers at the National Institute of Standards and Technology (NIST) have greatly improved the efficiency and power output of a series of chip-scale devices that generate laser light at different colors while using the same input laser source. The researchers developed on-chip microresonators with optical parametric oscillators that support the operation of a range of distinct quantum technologies, such as miniature optical atomic clocks and quantum computers. These technologies will require simultaneous access to multiple, widely varying laser colors within a small region of space.

Further, because the researchers’ methodology could be applied to existing silicon photonics platforms with heterogeneously integrated pump lasers, the development could enable flexible, coherent light generation across a broad range of wavelengths and with high output power and efficiency.

The researchers began by studying nonlinear optical devices, including those made of silicon nitride, in which the color of the laser light entering a device can differ from the color that exits it. They experimented with converting incoming light into two different frequencies and demonstrated that the conversion process can occur within a silicon nitride microresonator. As the light traveled thousands of times around the ring-shaped microresonator, it grew strong enough to be converted into the two different frequencies. The two colors were then coupled into a waveguide that transported the light to where it was needed.

The dimensions of the microresonator and the color of the input laser light determine which colors are generated. The researchers fabricated several different microresonators, each with slightly different dimensions, to provide access to a range of output colors on a single chip, all from the same input laser.

Although this was an important first step, the process was found to be highly inefficient, converting less than 0.1% of the input laser light into one of the two output colors. Most of this inefficiency could be traced back to poor coupling between the microresonator ring and the waveguide.
Four nanophotonic resonators, each slightly different in geometry, generate different colors of visible light from the same near-infrared pump laser. Courtesy of NIST.
Four nanophotonic resonators, each slightly different in geometry, generate different colors of visible light from the same near-infrared pump laser. Courtesy of NIST.
The researchers redesigned the straight waveguide to be U-shaped and to wrap around a portion of the ring. They designed broadband pulley-waveguide couplers using coupled-mode simulations. The pulley waveguides for broadband, near-critical coupling exploited the connection between the waveguide-resonator coupling rate and conversion efficiency. This modification made it possible for the team to convert about 15% of the incoming light to the desired output colors — more than 150× the amount that was converted in the previous experiments.

In addition, the converted light now demonstrated more than 1 mW of power over a range of wavelengths, from the visible to the near-infrared. The researchers estimated on-chip output powers for the signal and idler waves to be between 1 and 5 mW. This is enough power to generate quantum states of light, such as single-photon states, from single atoms or atom-like systems such as quantum dots. These milliwatt power levels can also provide sufficient power for laser stabilization.

Increasing the coupling between the ring and the waveguide and suppressing effects that could interfere with the color conversion further improved the power output and efficiency of the technique. These enhancements further increased the output laser power to as high as 20 mW and allowed as much as 29% of the incident laser light to be converted to the desired output colors. The researchers achieved high performance by suppressing competitive processes and by strongly overcoupling the output light.

By developing the methodology on a platform compatible with silicon photonics, the researchers have made it suitable for wide-scale deployment outside of laboratory settings.

The research was published in APL Photonics ( and Nature Communications (

Published: April 2023
integrated photonics
Integrated photonics is a field of study and technology that involves the integration of optical components, such as lasers, modulators, detectors, and waveguides, on a single chip or substrate. The goal of integrated photonics is to miniaturize and consolidate optical elements in a manner similar to the integration of electronic components on a microchip in traditional integrated circuits. Key aspects of integrated photonics include: Miniaturization: Integrated photonics aims to...
integrated optics
A thin-film device containing miniature optical components connected via optical waveguides on a transparent dielectric substrate, whose lenses, detectors, filters, couplers and so forth perform operations analogous to those of integrated electronic circuits for switching, communications and logic.
The term quantum refers to the fundamental unit or discrete amount of a physical quantity involved in interactions at the atomic and subatomic scales. It originates from quantum theory, a branch of physics that emerged in the early 20th century to explain phenomena observed on very small scales, where classical physics fails to provide accurate explanations. In the context of quantum theory, several key concepts are associated with the term quantum: Quantum mechanics: This is the branch of...
Nanophotonics is a branch of science and technology that explores the behavior of light on the nanometer scale, typically at dimensions smaller than the wavelength of light. It involves the study and manipulation of light using nanoscale structures and materials, often at dimensions comparable to or smaller than the wavelength of the light being manipulated. Aspects and applications of nanophotonics include: Nanoscale optical components: Nanophotonics involves the design and fabrication of...
Research & TechnologyeducationNISTLasersintegrated photonicsintegrated opticsOpticscomponentsmicroresonatormicroresonatorsKerr resonatorssilicon photonicsquantumquantum deviceslight-matter couplingnanophotonicsAmericasTechnology News

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