Reverse design to achieve an insulated FP cavity over SiC

Recently, the team of Professor Jelena Vu?kovi from Stanford University has realized an optical Fabriparo (FP) cavity that can be used for quantum and nonlinear photonic experiments on insulating silicon carbide based on reverse design, and the generation of second- and third-order nonlinear light in the FP cavity is achieved with the goal of second-order phase matching conditions, so as to extend the stimulated parameter process to the visible spectrum.


The reverse design pattern based on gradient optimization has attracted great attention from researchers, which can achieve operational robustness and compact device size in silicon photovoltaics. To date, there have been many experimental demonstrations of reverse engineering equipment and system applications, such as particle accelerators, optical ranging, and communications. In addition to silicon, reverse engineering is also applied to other materials such as diamond, silicon carbide, lithium niobate, and chalcogenide glass. In order to effectively trigger optical nonlinearities in quantum optics and classical optics, extremely low scattering losses are required. Although low-loss back-engineered reflectors have recently been developed, the highly irregular geometry in the reverse-engineered structure cannot prevent such losses through intrinsic symmetry, so a material with appropriate nonlinearity and easy preparation is required.

Silicon carbide (SiC) has compelling optical properties, including a high refractive index, high second- and third-order nonlinearities, and a wide optically transparent window. All these advantages, combined with proven SiC manufacturing technologies in the electronics industry, make SiC a promising material for the development of next-generation monolithic optoelectronic systems. Although reverse design has been rapidly developed, the application of reverse design to nonlinear photonics has been limited.

Innovative research

Reverse design has revolutionized the field of photonics, enabling the automated development of complex structures and geometries, with unique features unmatched by classic design. However, the application of reverse design in nonlinear photonics has been limited.

Figure 1: Schematic diagram of a reverse-engineered SiC optical cavity (a) device. Light is transmitted through a bus waveguide that is transitively coupled to the waveguide portion of the resonator. (b) Plots of the resonant quality factor vs. the resonant wavelength for 300 μm and 400 μm long devices, with beige areas indicating that the data show robust performance within the standard deviation of the mean. (c) Scatter plots of intrinsic quality factors for different cavity lengths, including the fitted mass factor curves for an FP device with a reflectivity of 99.56%, with (red) and (green) waveguide losses of 3.0 dB/cm. (d) Plot of measurement dispersion versus cavity length. The fitting curve (red), the dispersion relationship is proportional to L−3, and is mainly determined by the dispersion of the reverse-designed reflector. Simulation curve with only waveguide dispersion (blue), proportional to L−2.

In this work, Prof. Jelena Vuckovic’s team realized an optical Fabriparo (FP) cavity that can be used for quantum and nonlinear photonic experiments in an insulated silicon carbide (SiCOI) using a retroengineered reflector using a reverse design technique combined with the good nonlinear optical properties of SiC. The FP cavity is optimized for low scattering loss and manufacturing error robustness at multiple wavelengths, and the FP cavity is constrained for pre-specified dispersion, resulting in a reflector structure with a compact area of 6.75 μm × 1 μm.

Figure 2. Quantum comb below the threshold (a) Diagram of the measurement setup used in the quantum comb generation experiment (EDFA: erbium-doped fiber amplifier, MC: monochromator, DMC: dual monochromator, PD: photodetector, SNSPD: superconducting nanowire single-photon detector) (b) Kerr frequency comb formation below the threshold observed on a single-photon spectrometer (SPOSA). The areas highlighted in beige indicate the frequency of high pump noise. The duration of spectrum acquisition is 20 minutes. (c, d) Cross-correlation measurements were made at pair generation rates of 0.5 MHz (acquisition time 45 minutes) and 0.1 MHz (acquisition time 7.25 hours), respectively, with model numbers μ=±16 and μ=±18, with CAR ratios of 110 and 275, respectively.

The researchers experimentally demonstrated the excellent performance of the inversely engineered optical FP cavity, which achieved spontaneous four-wave mixing, which can generate signal and idle photon pairs, with a CAR index of 275 at a photon generation rate of 0.1 MHz. In addition, the researchers also demonstrated the stimulated parameter oscillation of the C-band and the nonlinear frequency generation at visible wavelengths through third- and second-order nonlinear processes, respectively.

The research team demonstrated the robustness of the device in optimizing the reflectivity band, which can be generated across the entire chip, and the reflectivity is limited by the waveguide loss rather than the retrograde design of the reflector, which provides a reliable path for significant improvements in future devices. At the same time, the experimental results demonstrate the practicability of the inverse design of FP cavities, which is the first experimental demonstration of inverse design in quantum and nonlinear light generation, and is a key supplement to the general capabilities of quantum and nonlinear photonics, especially when combined with highly nonlinear materials such as silicon carbide, highlighting the advantages of inverse design of nonlinear optics.

Figure 3. Diagram of the measuring setup used in the microcomb (a) nonlinear light generation experiment (EDFA: erbium-doped fiber amplifier, PC: polarization controller, OSA: optical spectrum analyzer) was formed in a reverse-engineered silicon carbide resonator. (b) The integral dispersion of the FP device relative to the relative analog-to-digital μ is measured with a central mode of μ=0 (frequency = 194 THz). The dotted line plots the numerical fit of the dispersion with the parameters D1 = 174.8 GHz and D2/2π = 10.1 MHz. (c) OPO telecommunication spectra and SFG visible spectra at different stages of microcomb formation were measured with a threshold power of 400 mW. Inset: Analog outlines of phase-matched telecom and visible modes.

The research results were published in the journal Light: Science & Applications, titled “Inverse-designed silicon carbide quantum and nonlinear photonics”, with Joshua Yang as the first author and Jelena Vu?kovi? as the corresponding author. (Source: LightScienceApplications WeChat public account)

Related Paper Information:‍-023-01253-9

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