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1. Ultra-high extinction-ratio silicon photonic polarization beam splitter with anisotropic metamaterials

   https://doi.org/10.1364/IPRSN.2021.ITh2B.4  

   Ahmed, Syed Z.; Ahmed, Ishtiaque; Mia, Borhan; Jaidye, Nafiz; Kim, Sangsik (January 2021, Optica Publishing Group)

   We present an ultra-high extinction-ratio silicon photonic polarization beam splitter with anisotropic metamaterial claddings. Exceptional coupling with anisotropic metamaterial achieved 58- 60 dB (46-48 dB) extinction-ratios for TE (TM) mode and the large birefringence resulted in a short coupling length (14.5 µm). 

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2. Efficient Conversion to Very High Order Modes in Silicon Waveguides

   https://doi.org/doi.org/10.1364/CLEO_SI.2019.SM3J.6  

   Dave, Utsav D; Lipson, Michal (May 2019, Conference on Lasers and Electrooptics)

   We demonstrate robust mode conversion up to the 12th higher order mode in silicon waveguides by using an optimized adiabatic directional coupler and using subwavelength waveguides. The conversion efficiency is better than -1.5 dB over a 75 nm bandwidth and tolerating ±30 nm fabrication variations. 

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3. III/V silicon hybrid laser based on a resonant Bragg structure

   https://doi.org/10.1364/AO.390522  

   Davis, Jordan_A; Kim, Myun_Sik; El_Amili, Abdelkrim; Trotter, Douglas_C; Starbuck, Andrew_L; Dallo, Christina; Pomerene, Andrew_T; DeRose, Christopher_T; Lentine, Anthony_L; Fainman, Yeshaiahu (May 2020, Applied Optics)

   We demonstrate a laser tunable in intensity with gigahertz tuning speed based on a III/V reflective semiconductor optical amplifier (RSOA) coupled to a silicon photonic chip. The silicon chip contains a Bragg-based Fabry–Perot resonator to form a passive bandpass filter within its stopband to enable single-mode operation of the laser. We observe a side mode suppression ratio of 43 dB, linewidth of 790 kHz, and an optical output power of 1.65 mW around 1530 nm. We also investigate using a micro-ball lens as an alternative coupling method between the RSOA and the silicon chip. 

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4. Highly efficient fiber to Si waveguide free-form coupler for foundry-scale silicon photonics

   https://doi.org/10.1364/PRJ.514999  

   Ranno, Luigi; Sia, Jia Xu Brian; Popescu, Cosmin; Weninger, Drew; Serna, Samuel; Yu, Shaoliang; Kimerling, Lionel C.; Agarwal, Anuradha; Gu, Tian; Hu, Juejun (May 2024, Photonics Research)

   As silicon photonics transitions from research to commercial deployment, packaging solutions that efficiently couple light into highly compact and functional sub-micrometer silicon waveguides are imperative but remain challenging. The 220 nm silicon-on-insulator (SOI) platform, poised to enable large-scale integration, is the most widely adopted by foundries, resulting in established fabrication processes and extensive photonic component libraries. The development of a highly efficient, scalable, and broadband coupling scheme for this platform is therefore of paramount importance. Leveraging two-photon polymerization (TPP) and a deterministic free-form micro-optics design methodology based on the Fermat’s principle, this work demonstrates an ultra-efficient and broadband 3-D coupler interface between standard SMF-28 single-mode fibers and silicon waveguides on the 220 nm SOI platform. The coupler achieves a low coupling loss of 0.8 dB for the fundamental TE mode, along with 1 dB bandwidth exceeding 180 nm. The broadband operation enables diverse bandwidth-driven applications ranging from communications to spectroscopy. Furthermore, the 3-D free-form coupler also enables large tolerance to fiber misalignments and manufacturing variability, thereby relaxing packaging requirements toward cost reduction capitalizing on standard electronic packaging process flows. 

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5. Thermo-optic properties of silicon-rich silicon nitride for on-chip applications

   https://doi.org/10.1364/OE.396969  

   Nejadriahi, Hani; Friedman, Alex; Sharma, Rajat; Pappert, Steve; Fainman, Yeshaiahu; Yu, Paul (August 2020, Optics Express)

   We demonstrate the thermo-optic properties of silicon-rich silicon nitride (SRN) films deposited using plasma-enhanced chemical vapor deposition (PECVD). Shifts in the spectral response of Mach-Zehnder interferometers (MZIs) as a function of temperature were used to characterize the thermo-optic coefficients of silicon nitride films with varying silicon contents. A clear relation is demonstrated between the silicon content and the exhibited thermo-optic coefficient in silicon nitride films, with the highest achievable coefficient being as high as (1.65±0.08) ×10⁻⁴K^-1. Furthermore, we realize an SRN multi-mode interferometer (MMI) based thermo-optic switch with over 20 dB extinction ratio and total power consumption for two-port switching of 50 mW. 

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