Multi-wavelength selective crossbar switch.

Here we demonstrate an 8x4 multi-wavelength selective ring resonator based crossbar switch matrix implemented in a 220-nm silicon photonics foundry for interconnecting electronic packet switches in scalable data centers. This switch design can dynamically assign up to two wavelength channels for any port-port connection, providing almost full connectivity with significant reduction in latency, cost and complexity. The switch unit cell insertion loss was measured at 0.8 dB, with an out-of-band rejection of 32 dB at 400 GHz channel separation. All the ring resonator heaters were thermally tuned, with heaters controlled by a custom 64-channel DAC driver. Detailed measurements on the whole switch showed standard deviation of 2 dB in losses across different paths, standard deviation of 0.33 nm in resonant wavelength and standard deviation of 0.01 nm/mW in ring heater tuning efficiency. Data transmission experiments at 40 Gbps showed negligible penalty due to crosstalk paths through the switch.

On-chip wavelength locking for photonic switches.

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.

An Autonomous Molecular Bioluminescent Reporter (AMBER) for Voltage Imaging in Freely Moving Animals.

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.