When I started out at UC Santa Barbara as a PhD student in 2015, there was no funding until the AIM project proposal got accepted. Without funding no work gets done, so first I am grateful to Prof. Rod Alferness for funding me for the first year and Prof. John Bowers for funding me for the rest of my PhD. To John, thanks for giving me complete freedom at work without which I could not have explored so many different areas in research. I enjoyed our conversation in the monthly meetings with Rod, John and Adel. For the first few months of my PhD I spent a lot of time with Adel doing a literature survey, it was an exciting journey in a new field. To Adel, thanks for filtering out the unsound ideas and helping me frame my thoughts. I enjoyed our white board discussions. To Roger, Clint, Takako and Andy at the Datacom meetings for discussions and helpful feedback. To Tin, for the fun we had at the New York Training conference. To Alex, Warren, Eric and Andy for the excellent office environment. To Alex, for inspiring me to get Scuba certified and also for tips on cooking Thai cuisine. To Aranya, for being my climbing buddy. To Sean, Simran Lawrence, Wilson and many others, for the fun time we had at UCSB badminton intramural. To Chirag, for providing helpful advice when needed. Thanks to Nicolas, Geza, Christos, Sarat, Aditya for helpful discussions. I would also like to thank Minh, Tony, Paolo, Yuan and Alan for their helpful advice. Special Thanks to Songtao for help with high speed measurements. Thanks to my Pappa, Mamma and Sairaj for the support during my PhD and for recharge time in India. Finally I would also thank Jeremiah Hebding, Brett Attaway, and SUNY for their foundry services. v
We present an on-chip wavelength reference with a partial drop ring resonator and germanium photodetector. This approach can be used in ring-resonator-based wavelength-selective switches where absolute wavelength alignment is required. We use the temperature dependence of heater resistance as a temperature sensor. Additionally, we discuss locking speed, statistical variation of heater resistances, and tuning speed of the switches.
Genetically encoded reporters have greatly increased our understanding of biology. While fluorescent reporters have been widely used, photostability and phototoxicity have hindered their use in long‐term experiments. Bioluminescence overcomes some of these challenges but requires the addition of an exogenous luciferin limiting its use. Using a modular approach, Autonomous Molecular BioluminEscent Reporter (AMBER), an indicator of membrane potential is engineered. Unlike other bioluminescent systems, AMBER is a voltage‐gated luciferase coupling the functionalities of the Ciona voltage‐sensing domain (VSD) and bacterial luciferase, luxAB. When co‐expressed with the luciferin‐producing genes, AMBER reversibly switches the bioluminescent intensity as a function of membrane potential. Using biophysical and biochemical methods, it is shown that AMBER switches its enzymatic activity from an OFF to an ON state as a function of the membrane potential. Upon depolarization, AMBER switches from a low to a high enzymatic activity state, showing a several‐fold increase in the bioluminescence output (ΔL/L). AMBER in the pharyngeal muscles and mechanosensory touch neurons of Caenorhabditis elegans is expressed. Using the compressed sensing approach, the electropharingeogram of the C. elegans pharynx is reconstructed, validating the sensor in vivo. Thus, AMBER represents the first fully genetically encoded bioluminescent reporter without requiring exogenous luciferin addition.
1.AbstractGenetically encoded reporters have greatly increased our understanding of biology, especially in neuroscience. While fluorescent reporters have been widely used, photostability and phototoxicity have hindered their use in long-term experiments. Bioluminescence overcomes some of these challenges but requires the addition of an exogenous luciferin limiting its use. Using a modular approach we have engineered Autonomous Molecular BioluminEscent Reporter (AMBER), an indicator of membrane potential. Unlike other luciferase-luciferin bioluminescent systems, AMBER encodes the genes to express both the luciferase and luciferin. AMBER is a voltage-gated luciferase coupling the functionalities of the Ciona voltage-sensing domain (VSD) and bacterial luciferase, luxAB. When AMBER is co-expressed with the luciferin producing genes it reversibly switches the bioluminescent intensity as a function of membrane potential. Using biophysical and biochemical methods we show that AMBER modulates its enzymatic activity as a function of the membrane potential. AMBER shows several-fold increase in the luminescent (ΔL/L) signal upon switching from the off to on state when the cell is depolarized. In vivo expression of AMBER in C. elegans allowed detecting pharyngeal pumping action and mechanosensory neural activity from multiple worms simultaneously. AMBER reports neural activity of multiple animals at the same time and can be used in social behavior assays to elucidate the role of membrane potential underlying behavior.2.Significance StatementThere have been many exciting advances in the development of genetically encoded voltage indicators to monitor intracelluar voltage changes. Most sensors employ fluorescence, which requires external light, potentially causing photobleaching or overheating. Consequently, there has been interest in developing luminescence reporters. However, they require addition of an exogenous substrate to produce light intracellularly. Here, we engineered a genetically encoded bioluminescent voltage indicator, AMBER, which unlike other bioluminescent activity indicators, does not require addition of an exogenous substrate. AMBER allows a large differential signal, a high signal-to-noise ratio, and causes minimal metabolic demand on cells. We used AMBER to record voltage activity in freely-moving C. elegans, demonstrating that AMBER is a important new tool for monitoring neuronal activity during social behavior.
An architecture is presented for realizing 1 Tbps datacenter interconnects using energy efficient silicon photonic ring modulators and QD-MLL. Both these components show excellent agreement with design parameters. High efficiency EO tuners are also reported.
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