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1. InP-based polarization rotator-splitter for mid-infrared photonic integration circuits

   https://doi.org/10.1063/1.5055863  

   Chung, Chi-Jui; Midkiff, Jason; Yoo, Kyoung_Min; Rostamian, Ali; Guo, Joel; Chen, Ray_T; Chakravarty, Swapnajit (January 2019, AIP Advances)

   We design and experimentally demonstrate the propagation loss of waveguides and the operation of a single-step etched polarization rotator-splitter (PRS) in low index contrast InGaAs-InP material system at 6.15 μm. Propagation losses 4.19 dB/cm for TM mode and 3.25 dB/cm for TE mode are measured. The designed PRS can achieve near 100% conversion efficiency. This study enables the possibility of monolithic integration of quantum cascade devices with TM-polarized characteristics and TE-guiding two-dimensional slotted photonic crystal waveguide gas sensors for on-chip monolithic absorption spectroscopy. 

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2. Fabrication of Stretchable and Conductive Liquid Metal Microfibers through Coaxial Emulsion Electrospinning

   https://doi.org/10.1002/adem.202402263  

   Liu, Zihan; Ma, Jiexian; Zhang, Pu (February 2025, Advanced Engineering Materials)

   Liquid metal fibers are increasingly used in soft multifunctional materials and soft electronics due to their superb stretchability, high conductivity, and lightweight. This work presents a systematic study of the electrospinning process of liquid metal microfibers. Compared to other methods that usually produce fibers thicker than 100 μm, electrospinning is a facile and low‐cost method of producing liquid metal fibers in the range of 10–100 μm. Specifically, core‐sheath liquid metal microfibers are fabricated with a highly conductive liquid metal core and a super‐stretchable thermoplastic elastomer sheath. This manufacturing process uses a liquid metal emulsion as the core solution, which circumvents manufacturing failures caused by the high surface tension of liquid metals. The influence of key processing parameters such as core flow rate, sheath flow rate, and applied voltage on the fiber diameter and morphology is studied by experiments. The mechanical and electrical properties of the as‐fabricated liquid metal microfibers, mats, and yarns are tested and discussed. 

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3. 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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4. Low-dimensional heat conduction in surface phonon polariton waveguide

   https://doi.org/10.1038/s41467-023-43736-8  

   Pei, Yu; Chen, Li; Jeon, Wonjae; Liu, Zhaowei; Chen, Renkun (December 2023, Nature Communications)

   Abstract Heat conduction in solids is typically governed by the Fourier’s law describing a diffusion process due to the short wavelength and mean free path for phonons and electrons. Surface phonon polaritons couple thermal photons and optical phonons at the surface of polar dielectrics, possessing much longer wavelength and propagation length, representing an excellent candidate to support extraordinary heat transfer. Here, we realize clear observation of thermal conductivity mediated by surface phonon polaritons in SiO₂nanoribbon waveguides of 20-50 nm thick and 1-10 μm wide and also show non-Fourier behavior in over 50-100 μm distance at room and high temperature. This is enabled by rational design of the waveguide to control the mode size of the surface phonon polaritons and its efficient coupling to thermal reservoirs. Our work laid the foundation for manipulating heat conduction beyond the traditional limit via surface phonon polaritons waves in solids. 

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5. Low-Loss D-band SIW Power Divider for Integrated Systems

   Wu, Weifeng; Wang, Xiaopeng; Li, Lei; Hwang, James CM; Fay, Patrick (January 2024, National Radio Science Meeting (NRSM))

   This paper demonstrates a novel approach to the design of D-band power dividers, capitalizing on the benefits of Substrate Integrated Waveguide (SIW) technology in 100-μm thick SiC substrate. By leveraging the unique characteristics of SIW and utilizing silicon carbide as the substrate material, an average insertion loss as low as 0.26 dB, and average return loss of up to 24 dB has been achieved in simulation in D-band. Although D-band dividers employing coplanar waveguides and microstrip lines have been reported, to the best of our acknowledge, this is the first work on D-band SIW power dividers. The SIW technology is compatible with GaN-on-SiC MMIC fabrication process flows, and provides a novel platform for the integration of low-loss millimeter-wave combiners with III-N based electronics. 

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