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1. Cryogenic packaging of nanophotonic devices with a low coupling loss < 1 dB

   https://doi.org/10.1063/5.0170324  

   Zeng, Beibei; De-Eknamkul, Chawina; Assumpcao, Daniel; Renaud, Dylan; Wang, Zhuoxian; Riedel, Daniel; Ha, Jeonghoon; Robens, Carsten; Levonian, David; Lukin, Mikhail; et al (October 2023, Applied Physics Letters)

   Robust, low-loss photonic packaging of on-chip nanophotonic circuits is a key enabling technology for the deployment of integrated photonics in a variety of classical and quantum technologies including optical communications and quantum communications, sensing, and transduction. To date, no process has been established that enables permanent, broadband, and cryogenically compatible coupling with sub-dB losses from optical fibers to nanophotonic circuits. Here, we report a technique for reproducibly generating a permanently packaged interface between a tapered optical fiber and nanophotonic devices on diamond with a record-low coupling loss <1 dB per facet at near-infrared wavelengths (∼730 nm) that remains stable from 300 K to 30 mK. We further demonstrate the compatibility of this technique with etched lithium niobate on insulator waveguides. The technique lifts performance limitations imposed by scattering as light transfers between photonic devices and optical fibers, paving the way for scalable integration of photonic technologies at both room and cryogenic temperatures. 

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2. Experimental measurements of AO-Fed photonic lantern coupling efficiencies

   https://doi.org/10.1117/12.2630608  

   Lin, Jonathan; Vievard, Sébastien B.; Jovanovic, Nemanja; Norris, Barnaby R.; Fitzgerald, Michael P.; Betters, Christopher H.; Gatkine, Pradip R.; Guyon, Olivier; Kim, Yoo Jung; Leon-Saval, Sergio G.; et al (August 2022, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation V)

   Geyl, Roland; Navarro, Ramón (Ed.)

   Efficiently coupling light from large telescopes to photonic devices is challenging. However, overcoming this challenge would enable diffraction-limited instruments, which offer significant miniaturization and advantages in thermo-mechanical stability. By coupling photonic lanterns with high performance adaptive optics systems, we recently demonstrated through simulation that high throughput diffraction-limited instruments are possible (Lin et al., Applied Optics, 2021). Here we build on that work and present initial results from validation experiments in the near-infrared to corroborate those simulations in the laboratory. Our experiments are conducted using a 19-port photonic lantern coupled to the state-of-the-art SCExAO instrument at the Subaru Telescope. The SCExAO instrument allows us to vary the alignment and focal ratio of the lantern injection, as well as the Strehl ratio and amount of tip/tilt jitter in the beam. In this work, we present experimental characterizations against the aforementioned parameters, in order to compare with previous simulations and elucidate optimal architectures for lantern-fed spectrographs. 

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3. New Directions for Thermoelectrics: A Roadmap from High‐Throughput Materials Discovery to Advanced Device Manufacturing

   https://doi.org/10.1002/smsc.202300359  

   Song, Kaidong; Tanvir, Ali_Newaz_Mohammad; Bappy, Md_Omarsany; Zhang, Yanliang (April 2024, Small Science)

   Thermoelectric materials, which can convert waste heat into electricity or act as solid‐state Peltier coolers, are emerging as key technologies to address global energy shortages and environmental sustainability. However, discovering materials with high thermoelectric conversion efficiency is a complex and slow process. The emerging field of high‐throughput material discovery demonstrates its potential to accelerate the development of new thermoelectric materials combining high efficiency and low cost. The synergistic integration of high‐throughput material processing and characterization techniques with machine learning algorithms can form an efficient closed‐loop process to generate and analyze broad datasets to discover new thermoelectric materials with unprecedented performances. Meanwhile, the recent development of advanced manufacturing methods provides exciting opportunities to realize scalable, low‐cost, and energy‐efficient fabrication of thermoelectric devices. This review provides an overview of recent advances in discovering thermoelectric materials using high‐throughput methods, including processing, characterization, and screening. Advanced manufacturing methods of thermoelectric devices are also introduced to realize the broad impacts of thermoelectric materials in power generation and solid‐state cooling. In the end, this article also discusses the future research prospects and directions. 

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4. 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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5. Multi-chip heterogeneously integrated array of active three-terminal transistor lasers and passive photonic structures for electronic-photonic integration on silicon

   https://doi.org/10.1117/12.2544009  

   Carlson, John A.; Dallesasse, John M. (February 2020, Proceedings Volume 11285, Silicon Photonics XV)

   Reed, Graham T.; Knights, Andrew P. (Ed.)

   An array of active photonic devices is fabricated in unison after a heterogeneous integration process first metal-eutectically bonds these distinct materials as a distribution onto a silicon host wafer. The patterning out of heterogeneous materials followed by the formation of all photonic devices allows for wide-area fine-alignment without the need for discrete die alignment or placement. The integration process is designed as a CMOS-compatible, scalable method for bringing together distinct III-V epitaxial structures and optical-waveguiding epitaxial structures, demonstrating the capabilities of forming a multi-chip layer of photonic materials. Integrated GaAs-based vertical light-emitting transistors (LET) are designed and fabricated as the active devices whose third electrical terminal provides an electrical interconnect and thermal dissipation path to the silicon host wafer. The performance of these devices as both electrical transistors and spontaneous-emission optical devices is compared to their monolithically-integrated counterparts to investigate improvements in device characteristics when integrated onto silicon. The fabrication methods are modified and optimized for thin-film transferred materials and are then extended to transistor laser (TL) fabrication. Passive waveguiding structures are designed and simulated for coupling light from the active devices, and their fabrication scheme is presented such that it can be similarly performed with transferred materials. Work toward the demonstration of integrated transistor lasers is shown to represent progress toward an electronic-photonic circuit network. The combination of heterogeneous integration with three-terminal photonic structures enables an elegant solution to both packaging and signal interconnect constraints for the implementation of photonic logic in silicon photonics systems. 

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