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1. Compact atto-joule-per-bit bus-coupled photonic crystal nanobeam switches

   https://doi.org/10.1117/12.2649250  

   Shen, Jianhao; Donnelly, Daniel; Chakravarty, Swapnajit (March 2023, Proceedings of SPIE)

   García-Blanco, Sonia M.; Cheben, Pavel (Ed.)

   The benefits of photonics over electronics in the application of optical transceivers and both classical and quantum computing have been demonstrated over the past decades, especially in the ability to achieve high bandwidth, high interconnectivity, and low latency. Due to the high maturity of silicon photonics foundries, research on photonics devices such as silicon micro ring resonators (MRRs), Mach-Zehnder modulators (MZM), and photonic crystal (PC) resonators has attracted plenty of attention. Among these photonic devices, silicon MRRs using carrier depletion effects in p-n junctions represent optical switches manufacturable in the most compact magnitude at high volume with demonstrated switching energies ~5.2fJ/bit. In matrix multiplication demonstrated with integrated photonics, one approach is to couple one bus straight waveguide to several MRRs with different resonant wavelengths to transport signals in different channels, corresponding to a matrix row or column. However, such architectures are potentially limited to ~30 MRRs in series, by the limited free-spectral range (FSR) of an individual MRR. We show that PC switches with sub-micron optical mode confinements can have a FSR >300nm, which can potentially enable energy efficient computing with larger matrices of ~200 resonators by multiplexing. In this paper, we present designs for an oxide-clad bus-coupled PC switch with 1dB insertion loss, 5dB extinction, and ~260aJ/bit switching energy by careful control of the cavity geometry as well as p-n junction doping. We also demonstrate that air-clad bus-coupled PC switches can operate with 1dB insertion loss, 3dB extinction, and ~80aJ/bit switching energy. 

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2. Photon pair generation using a silicon photonic hybrid laser

   https://doi.org/10.1063/1.5040118  

   Wang, Xiaoxi; Ma, Chaoxuan; Kumar, Ranjeet; Doussiere, Pierre; Jones, Richard; Rong, Haisheng; Mookherjea, Shayan (August 2018, APL Photonics)

   We report photon pairs and heralded single photons generated at 1310 nm wavelengths using silicon photonics technology, demonstrating that comparable performance could be achieved when a silicon microring resonator was pumped either by a desktop laser instrument or by an electrically injected, room-temperature hybrid silicon laser. Measurements showed that 130 kilo-coincidence-counts per second pair rates could be generated, with coincidences-to-accidentals ratio approximately 100 at about 0.34 mW optical pump power and anti-bunching upon heralding with second-order intensity correlation g(2)(0) = 0.06 at about 0.9 mW optical pump power. These results suggest that hybrid silicon lasers, which are ultra-compact and wafer-scale manufacturable, could be used in place of packaged, stand-alone lasers for generating photon pairs at data communication wavelengths and enable large-scale, cost-effective manufacturing of integrated sources for quantum communications and computing. 

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3. Integrating planar photonics for multi-beam generation and atomic clock packaging on chip

   https://doi.org/10.1038/s41377-023-01081-x  

   Ropp, Chad; Zhu, Wenqi; Yulaev, Alexander; Westly, Daron; Simelgor, Gregory; Rakholia, Akash; Lunden, William; Sheredy, Dan; Boyd, Martin M.; Papp, Scott; et al (December 2023, Light: Science & Applications)

   Abstract The commercialization of atomic technologies requires replacing laboratory-scale laser setups with compact and manufacturable optical platforms. Complex arrangements of free-space beams can be generated on chip through a combination of integrated photonics and metasurface optics. In this work, we combine these two technologies using flip-chip bonding and demonstrate an integrated optical architecture for realizing a compact strontium atomic clock. Our planar design includes twelve beams in two co-aligned magneto-optical traps. These beams are directed above the chip to intersect at a central location with diameters as large as 1 cm. Our design also includes two co-propagating beams at lattice and clock wavelengths. These beams emit collinearly and vertically to probe the center of the magneto-optical trap, where they will have diameters of ≈100 µm. With these devices we demonstrate that our integrated photonic platform is scalable to an arbitrary number of beams, each with different wavelengths, geometries, and polarizations. 

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4. 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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5. Sub-volt high-speed silicon MOSCAP microring modulator driven by high-mobility conductive oxide

   https://doi.org/10.1038/s41467-024-45130-4  

   Hsu, Wei-Che; Nujhat, Nabila; Kupp, Benjamin; Conley, Jr, John_F; Rong, Haisheng; Kumar, Ranjeet; Wang, Alan_X (January 2024, Nature Communications)

   Abstract Silicon microring modulator plays a critical role in energy-efficient optical interconnect and optical computing owing to its ultra-compact footprint and capability for on-chip wavelength-division multiplexing. However, existing silicon microring modulators usually require more than 2 V of driving voltage (V_pp), which is limited by both material properties and device structures. Here, we present a metal-oxide-semiconductor capacitor microring modulator through heterogeneous integration between silicon photonics and titanium-doped indium oxide, which is a high-mobility transparent conductive oxide (TCO) with a strong plasma dispersion effect. The device is co-fabricated by Intel’s photonics fab and our in-house TCO patterning processes, which exhibits a high modulation efficiency of 117 pm/V and consequently can be driven by a very low V_ppof 0.8 V. At a 11 GHz modulation bandwidth where the modulator is limited by the RC bandwidth, we obtained 25 Gb/s clear eye diagrams with energy efficiency of 53 fJ/bit. 

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