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1. Efficient on-chip green light generation via frequency upconversion in SiN–transfer-printed LN hybrid waveguides

   https://doi.org/10.1364/OL.560034  

   Sumon, Md_Saiful_Islam; Vorobev, Artem_S; Ghosh, Samir; Atar, Fatih_Bilge; Maraviglia, Nicola; Nikor, Sk_Shafaat_Saud; Devarapu, Ganga_Chinna_Rao; Maddi, Chiranjeevi; Faruque, Imad_I; Dwivedi, Sarvagya; et al (May 2025, Optics Letters)

   We demonstrate efficient on-chip green light generation via frequency upconversion in silicon nitride–thin-film lithium niobate (SiN-TFLN) hybrid waveguides, obtained by transfer printing LN coupons on selected areas of photonic integrated circuits (PICs). By utilizing modal phase matching (MPM), our devices achieve a high normalized conversion efficiency of 42.5% W⁻¹cm⁻²in a single-pass, 2.4-mm-long waveguide configuration. The SiN–LN transition in the waveguide inherently facilitates mode conversion, transforming a higher-order second-harmonic mode into a fundamental TE mode, ensuring coherent, narrow-linewidth, green light emission. Our waveguide platform gives rise to a wavelength shift of ∼1 nm for every 10 nm of waveguide width variation and temperature-induced wavelength tuning of ∼0.02 nm/°C. 

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2. Broadband Low‐Loss Unidirectional Reflection On‐Chip with Asymmetric Dielectric Metasurface

   https://doi.org/10.1002/lpor.202500216  

   Jeong, Heijun; Hayran, Zeki; Liu, Yuan; Xiao, Yahui; Lee, Hwaseob; Wang, Zi; Klamkin, Jonathan; Monticone, Francesco; Gu, Tingyi (June 2025, Laser & Photonics Reviews)

   Abstract Metasurface has emerged as a powerful platform for controlling light at subwavelength thickness, enabling new functionalities for imaging, polarization manipulation, and angular momentum conversion within a flat surface. An integrated asymmetric metasurface simultaneously achieving broadband, low loss forward power transmission, and significant back reflection suppression in multi‐mode waveguides is explored. The tapering along the direction of light propagation leads to low loss and space‐efficient mode conversion. Enhanced by a double‐flipped structure, a thin (2.5 µm) metasurface can simultaneously achieve high conversion efficiency (>80%), and back‐reflection efficiency of 90% over a 200 nm wavelength range. Such single‐side reflectors can be one of the enabling components for gain‐integrated adaptive optics on a chip. 

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3. A multi-layer platform for low-loss nonlinear silicon photonics

   https://doi.org/10.1063/1.5115234  

   MacFarlane, Neil; Kossey, Michael_R; Stroud, Jasper_R; Foster, Mark_A; Foster, Amy_C (November 2019, APL Photonics)

   We demonstrate four-wave mixing (FWM) interactions in a-Si:H waveguides in a multilayer integrated silicon photonic chip. The a-Si:H waveguides are accessed through interlayer couplers from waveguides composed of SiNx. The interlayer couplers achieve a coupling of 0.51 dB loss per transition at the target wavelength of 1550 nm. We observe greater idler power extraction and conversion efficiency from the FWM interaction in the interlayer-coupled multilayer waveguides than in single-material waveguides. 

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4. Mode-evolution-based ultra-broadband polarization beam splitter using adiabatically tapered extreme skin-depth waveguide

   https://doi.org/10.1364/OL.434110  

   Mia, Md_Borhan; Ahmed, Syed_Z; Jaidye, Nafiz; Ahmed, Ishtiaque; Kim, Sangsik (September 2021, Optics Letters)

   We present an ultra-broadband silicon photonic polarization beam splitter (PBS) using adiabatically tapered extreme skin-depth (eskid) waveguides. Highly anisotropic metamaterial claddings of the eskid waveguides suppress the crosstalk of transverse-electric (TE) mode, while the large birefringence of the eskid waveguide efficiently cross-couples the transverse-magnetic (TM) mode. Two eskid waveguides are adiabatically tapered to smoothly translate TM mode to the coupled port via mode evolution while keeping the TE mode in the through port. The tapered cross-section of the eskid PBS was designed numerically, achieving a large bandwidth at 1400–1650 nm with extinction ratios $><\#comment/>20\mathrm{d}\mathrm{B}$. We experimentally demonstrated the tapered-eskid PBS and confirmed its broad bandwidth at 1490–1640 nm, limited by laser bandwidth. With its mode evolution, the tapered-eskid PBS is tolerant to fabrication imperfections and should be crucial for controlling polarizations in photonic circuits. 

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5. Widely tunable single-mode interband cascade lasers based on V-coupled cavities and dependence on design parameters

   https://doi.org/10.1116/6.0003376  

   Wang, Zhanyi; Gong, Jingli; He, Jian-Jun; Li, Lu; Yang, Rui Q; Gupta, James A (March 2024, Journal of Vacuum Science & Technology B)

   We report an investigation of V-coupled cavity interband cascade (IC) lasers (ICLs) emitting in the 3-μm wavelength range, employing various waveguide structures and coupler sizes. Type-II ICL devices with double-ridge waveguides exhibited wide tuning ranges exceeding 153 nm. Type-I ICL devices with deep-etched waveguides achieved single-mode emission with wavelength tunable over 100 nm at relatively high temperatures up to 250 K. All devices exhibited a side-mode suppression ratio higher than 30 dB. By comparing the performance of all devices with different sizes and configurations, a good tolerance against the structural parameter variations of the V-coupled cavity laser (VCCL) design is demonstrated, validating the advantages of the VCCL to achieve single-mode emission with wide tunability. 

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