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1. Octave-spanning microcomb generation in 4H-silicon-carbide-on-insulator photonics platform

   https://doi.org/10.1364/PRJ.449267  

   Cai, Lutong ; Li, Jingwei ; Wang, Ruixuan ; Li, Qing ( March 2022 , Photonics Research)

   Silicon carbide has recently emerged as a promising photonics material due to its unique properties, including possessing strong second- and third-order nonlinear coefficients and hosting various color centers that can be utilized for a wealth of quantum applications. Here, we report the design and demonstration of octave-spanning microcombs in a 4H-silicon-carbide-on-insulator platform for the first time, to our knowledge. Such broadband operation is enabled by optimized nanofabrication achieving$>1$million intrinsic quality factors in a 36-μm-radius microring resonator, and careful dispersion engineering by investigating the dispersion properties of different mode families. For example, for the fundamental transverse-electric mode whose dispersion can be tailored by simply varying the microring waveguide width, we realized a microcomb spectrum covering the wavelength range from 1100 nm to 2400 nm with an on-chip power near 120 mW. While the observed comb state is verified to be chaotic and not soliton, attaining such a large bandwidth is a crucial step towards realizing$f-2f$self-referencing. In addition, we also observed a coherent soliton-crystal state for the fundamental transverse-magnetic mode, which exhibits stronger dispersion than the fundamental transverse-electric mode and hence a narrower bandwidth.

    

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2. Progress in neuromorphic photonics

   https://doi.org/10.1515/nanoph-2016-0139  

   Ferreira de Lima, Thomas ; Shastri, Bhavin J. ; Tait, Alexander N. ; Nahmias, Mitchell A. ; Prucnal, Paul R. ( January 2017 , Nanophotonics)

   Abstract As society’s appetite for information continues to grow, so does our need to process this information with increasing speed and versatility. Many believe that the one-size-fits-all solution of digital electronics is becoming a limiting factor in certain areas such as data links, cognitive radio, and ultrafast control. Analog photonic devices have found relatively simple signal processing niches where electronics can no longer provide sufficient speed and reconfigurability. Recently, the landscape for commercially manufacturable photonic chips has been changing rapidly and now promises to achieve economies of scale previously enjoyed solely by microelectronics. By bridging the mathematical prowess of artificial neural networks to the underlying physics of optoelectronic devices, neuromorphic photonics could breach new domains of information processing demanding significant complexity, low cost, and unmatched speed. In this article, we review the progress in neuromorphic photonics, focusing on photonic integrated devices. The challenges and design rules for optoelectronic instantiation of artificial neurons are presented. The proposed photonic architecture revolves around the processing network node composed of two parts: a nonlinear element and a network interface. We then survey excitable lasers in the recent literature as candidates for the nonlinear node and microring-resonator weight banks as the network interface. Finally, we compare metrics between neuromorphic electronics and neuromorphic photonics and discuss potential applications. 

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3. Broadband blind source separation by integrated photonics

   https://doi.org/10.1109/IPC48725.2021.9593033  

   Zhang, Weipeng ; Huang, Chaoran ; Shastri, Bhavin J. ; Prucnal, Paul ( October 2021 , IEEE Photonics Conference (IPC))

   Blind source separation (BSS) becomes popularly useful with the need for increased bandwidth utilization. However, the traditional radio-frequency (RF) electronics hardly offer the BSS the demanded frequency agility because of the inherent bandwidth limitation. The emerging integrated photonics, fortunately, can be an efficacious alternative. Here, we demonstrate a photonic BSS approach based on the microring (MRR) weightbank that achieves blind source separation of up to 13.8 GHz bandwidth. In addition, by implementing an improved MRR control method with an accuracy of up to 8.5 bits, the reduced errors give confidence in solving BSS problems with a large ill-condition number. 

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4. Characteristics of 1D ordered arrays of optical centers in solid-state photonics

   https://doi.org/10.1088/2515-7647/acccc3  

   Kling, Trevor ; Hosseini, Mahdi ( April 2023 , Journal of Physics: Photonics)

   Collective interaction of emitter arrays has lately attracted significant attention due to its role in controlling directionality of radiation, spontaneous emission and coherence. We focus on light interactions with engineered arrays of solid-state emitters in photonic resonators. We theoretically study light interaction with an array of emitters or optical centers embedded inside a microring resonator and discuss its application in the context of solid-state photonic systems. We discuss how such arrays can be experimentally realized and how the inhomogeneous broadening of mesoscopic atomic arrays can be leveraged to study broadband collective excitations in the array.

    

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5. Non‐Volatile Reconfigurable Integrated Photonics Enabled by Broadband Low‐Loss Phase Change Material

   https://doi.org/10.1002/adom.202002049  

   Fang, Zhuoran ; Zheng, Jiajiu ; Saxena, Abhi ; Whitehead, James ; Chen, Yueyang ; Majumdar, Arka ( March 2021 , Advanced Optical Materials)

   Phase change materials (PCMs) have long been used as a storage medium in rewritable compact disk and later in random access memory. In recent years, integration of PCMs with nanophotonic structures has introduced a new paradigm for non‐volatile reconfigurable optics. However, the high loss of the archetypal PCM Ge₂Sb₂Te₅in both visible and telecommunication wavelengths has fundamentally limited its applications. Sb₂S₃has recently emerged as a wide‐bandgap PCM with transparency windows ranging from 610 nm to near‐IR. In this paper, the strong optical phase modulation and low optical loss of Sb₂S₃are experimentally demonstrated for the first time in integrated photonic platforms at both 750 and 1550 nm. As opposed to silicon, the thermo‐optic coefficient of Sb₂S₃is shown to be negative, making the Sb₂S₃–Si hybrid platform less sensitive to thermal fluctuation. Finally, a Sb₂S₃integrated non‐volatile microring switch is demonstrated which can be tuned electrically between a high and low transmission state with a contrast over 30 dB. This work experimentally verifies prominent phase modification and low loss of Sb₂S₃in wavelength ranges relevant for both solid‐state quantum emitter and telecommunication, enabling potential applications such as optical field programmable gate array, post‐fabrication trimming, and large‐scale integrated quantum photonic network.

    

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