Ultra-sharp asymmetric Fano-like resonance spectrum on Si photonic platform

Achieving Fano resonance with an ultra-high slope rate by silicon nitride CROW embedded in a Mach-Zehnder interferometer

Fano resonance with asymmetric line shape is very promising in many applications such as optical switching, sensing, slow light, laser. Fano resonances based on some integrated structures have been demonstrated on the silicon on insulator platform. However, the extinction ratios and slope rates of the most proposed integrated Fano resonances are relatively low, which limits their applications. In this paper, a tunable silicon nitride coupled resonator optical waveguide (CROW) embedded in a Mach-Zehnder interferometer (MZI) is proposed to achieve Fano resonance. Benefiting from fine tuning supported by the low thermo-optic coefficient of the silicon nitride optical waveguide, the optical amplitudes and phases in the two arms of the MZI were accurately adjusted to achieve destructive interference, which gives an ultra-high extinction ratio. Furthermore, high quality factor CROW, supported by the native low loss silicon nitride optical waveguide, greatly shrinks the resonance bandwidth. Combining the above two superiorities, a Fano resonance with a very high extinction ratio of up to 57 dB and slope rate as high as 8.1 × 10⁴ dB/nm was obtained, which is an order of magnitude larger than the reported integrated Fano resonances. We believe that the proposed structure would be a promising candidate for high-performance switching and high-sensitivity sensing.

Absorption enhancement in visible range from Fano resonant silicon nanoparticle arrays embedded in single crystal Mg:Er:LiNbO3synthesized by direct ion implantation

Fano resonant Si nanoparticles (NPs) are synthesized in single-crystal Mg:Er:LiNbO₃using ion implantation and subsequent thermal annealing. The structural and optical properties of the Si NPs embedded in the crystal have been investigated. Spherical particles with radius of about 60 nm are observed by cross-sectional transmission electron microscope, while ion beam analysis are used to characterize the NPs formation process. The absorption of the Mg:Er:LiNbO₃crystals have been enhanced significantly due to the embedded Si NPs, which are induced by the Fano resonance effect in the visible light wavelength band. Periodic structures of spherical Si particles model is proposed and analyzed using the Mie theory to study the optical response features and local fields. As a result, numerical simulations demonstrate that periodicities of the array of Si NPs can yield narrow resonant peaks connected with multiple light scattering by the NPs and displaying a Fano-type resonant profile. The wavelengths of the absorption peak show clear red shift with increasing the radius of NPs and the peak intensity can be enhanced by decreasing the array period. This work opens an avenue to modulate the optical filed by embedding Fano resonant Si NPs for potential application in optical devices.

Integrated photonic devices enabled by silicon traveling wave-like Fabry-Perot resonators

Integrated photonic devices play a key role in modern optical communications, of which optical resonators are important fundamental structures. This work proposes and experimentally demonstrates compact integrated photonic devices based on a traveling wave-like Fabry-Perot (TW-like FP) resonator(s) coupled with waveguides. Add-drop filters based on a single TW-like FP resonator have been realized with a high drop efficiency and the same output direction for the through and drop ports. Particularly, their transmission response can be either symmetric Lorentzian or asymmetric Fano line shape, through adjusting the shift between the two bus waveguides and the waveguide widths. Fano resonance has been demonstrated in a TW-like FP resonator with a very high extinction ratio and large slope rate. The second-order optical filter exhibits low-loss flat-top passbands with small ripples. Owing to the compact size, easy scalability, and large flexibility, TW-like FP cavity-based devices using Fano and Lorentzian resonances will provide new potential applications in integrated photonics.

CORNERSTONE’s Silicon Photonics Rapid Prototyping Platforms: Current Status and Future Outlook

The field of silicon photonics has experienced widespread adoption in the datacoms industry over the past decade, with a plethora of other applications emerging more recently such as light detection and ranging (LIDAR), sensing, quantum photonics, programmable photonics and artificial intelligence. As a result of this, many commercial complementary metal oxide semiconductor (CMOS) foundries have developed open access silicon photonics process lines, enabling the mass production of silicon photonics systems. On the other side of the spectrum, several research labs, typically within universities, have opened up their facilities for small scale prototyping, commonly exploiting e-beam lithography for wafer patterning. Within this ecosystem, there remains a challenge for early stage researchers to progress their novel and innovate designs from the research lab to the commercial foundries because of the lack of compatibility of the processing technologies (e-beam lithography is not an industry tool). The CORNERSTONE rapid-prototyping capability bridges this gap between research and industry by providing a rapid prototyping fabrication line based on deep-UV lithography to enable seamless scaling up of production volumes, whilst also retaining the ability for device level innovation, crucial for researchers, by offering flexibility in its process flows. This review article presents a summary of the current CORNERSTONE capabilities and an outlook for the future.

Independently tunable double Fano resonances based on waveguide-coupled cavities

In this Letter, we first demonstrate periodically and independently tunable double Fano resonances (DFRs) using waveguide-coupled cavities consisting of two silicon microring resonators (MRRs) and a feedback-coupled waveguide. The proposed device is fabricated on the silicon-on-insulator substrate using the standard complementary metal-oxide-semiconductor fabrication process. The DFR can be tuned independently by changing the resonant wavelengths of two MRRs using the thermo-optic effect. The highest extinction ratio of the Fano resonances is measured to be as high as 29.20 dB, which enables this device to be a promising candidate for high-performance multi-wavelength optical switches and high-sensitivity biochemical sensors.