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1. Inverse-designed, normal incidence polarizing and polarization demultiplexing grating couplers for multi-core fiber

   Michael J. Probst, Alec M. (October 2022, IEEE International Photonics Conference)

   We experimentally demonstrate normal-incidence grating couplers designed using topology optimization to couple into multi-core fiber. The insertion loss of the polarizing and polarization demultiplexing gratings was –5.5 dB and –7.7 dB, which is within 0.8 dB of the performance obtained using a fiber array. 

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2. Fiber array to chip attach using laser fusion splicing for low loss

   https://doi.org/10.1364/OE.492752  

   Nauriyal, Juniyali; Song, Meiting; Zhang, Yi; Granados-Baez, Marissa; Cardenas, Jaime (June 2023, Optics Express)

   With the ever-increasing need for higher data rates, datacom and telecom industries are now migrating to silicon photonics to achieve higher data rates with reduced manufacturing costs. However, the optical packaging of integrated photonic devices with multiple I/O ports remains a slow and expensive process. We introduce an optical packaging technique to attach fiber arrays to a photonic chip in a single shot using CO₂laser fusion splicing. We show a minimum coupling loss of 1.1 dB, 1.5 dB, and 1.4 dB per-facet for 2, 4, and 8-fiber arrays (respectively) fused to the oxide mode converters using a single shot from the CO₂laser. 

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3. Low-loss fiber-to-chip interface for lithium niobate photonic integrated circuits

   Lingyan He, Mian Zhang (January 2019, Optics letters)

   Integrated lithium niobate (LN) photonic circuits have recently emerged as a promising candidate for advanced photonic functions such as high-speed modulation, nonlinear frequency conversion, and frequency comb generation. For practical applications, optical interfaces that feature low fiber-to-chip coupling losses are essential. So far, the fiber-to-chip loss (commonly >10  dB/facet) has dominated the total insertion losses of typical LN photonic integrated circuits, where on-chip losses can be as low as 0.03–0.1 dB/cm. Here we experimentally demonstrate a low-loss mode size converter for coupling between a standard lensed fiber and sub-micrometer LN rib waveguides. The coupler consists of two inverse tapers that convert the small optical mode of a rib waveguide into a symmetrically guided mode of a LN nanowire, featuring a larger mode area matched to that of a tapered optical fiber. The measured fiber-to-chip coupling loss is lower than 1.7 dB/facet with high fabrication tolerance and repeatability. Our results open the door for practical integrated LN photonic circuits efficiently interfaced with optical fibers. 

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4. Low-loss fiber-to-chip interface for lithium niobate photonic integrated circuits

   https://doi.org/10.1364/OL.44.002314  

   He, Lingyan; Zhang, Mian; Shams-Ansari, Amirhassan; Zhu, Rongrong; Wang, Cheng; Marko, Lončar (April 2019, Optics Letters)

   Integrated lithium niobate (LN) photonic circuits have recently emerged as a promising candidate for advanced photonic functions such as high-speed modulation, nonlinear frequency conversion, and frequency comb generation. For practical applications, optical interfaces that feature low fiber-to-chip coupling losses are essential. So far, the fiber-to-chip loss (commonly $>10\mathrm{dB}/\text{facet}$) has dominated the total insertion losses of typical LN photonic integrated circuits, where on-chip losses can be as low as 0.03–0.1 dB/cm. Here we experimentally demonstrate a low-loss mode size converter for coupling between a standard lensed fiber and sub-micrometer LN rib waveguides. The coupler consists of two inverse tapers that convert the small optical mode of a rib waveguide into a symmetrically guided mode of a LN nanowire, featuring a larger mode area matched to that of a tapered optical fiber. The measured fiber-to-chip coupling loss is lower than 1.7 dB/facet with high fabrication tolerance and repeatability. Our results open the door for practical integrated LN photonic circuits efficiently interfaced with optical fibers. 

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5. Machine Learning Based Prediction of Erbium-Doped Fiber WDM Line Amplifier Gain Spectra

   Zhu, Shengxiang; Gutterman, Crag L.; Mo, Weiyang; Li, Yao; Zussman, Gil; Kilper, Daniel C. (January 2018, 2018 European Conference on Optical Communication)

   Machine learning based modelling of Erbium-Doped Fiber Amplifiers (EDFA) is used to determine wavelength dependent gain for use in optical transmission systems, and achieves root mean square error (RMSE) of 0.08, 0.18, and 0.27 dB under input ranges of +/- 3, 6, 9 dB. 

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