Unravelling the mysteries of the complex neural network dynamics of the brain is of utmost importance to science as it might lead to a deeper understanding of perception, cognition and consciousness. Numerous techniques are being used for brain imaging including intracellular electrophysiology, calcium imaging and microelectrode arrays imaging. However, all these technologies are facing severe limitations in the spatio-temporal resolutions and are thus unable to resolve fast real-time single neuron activity over a larger area of the brain. I will discuss our recent efforts in developing a new technique for neuroscience that offer wide-field brain imaging with unprecedented spatio-temporal resolution. It is based on magnetic field sensing of the neuron activity using magneto-optically sensitive Nitrogen-Vacancy color centers in a diamond crystal combined with light microscopy.
Space division multiplexing (SDM) is currently widely investigated in order to provide enhanced capacity thanks to the utilization of space as a new degree of multiplexing freedom in both optical fiber communication and on-chip interconnects. Basic components allowing the processing of spatial modes are critical for SDM applications. Here we present such building blocks implemented on the silicon-on-insulator (SOI) platform. These include fabrication tolerant wideband (de)multiplexers, ultra-compact mode converters and (de)multiplexers designed by topology optimization, and mode filters using one-dimensional (1D) photonic crystal silicon waveguides. We furthermore use the fabricated devices to demonstrate on-chip point-to-point mode division multiplexing transmission, and all-optical signal processing by mode-selective wavelength conversion. Finally, we report an efficient silicon photonic integrated circuit mode (de)multiplexer for few-mode fibers (FMFs).
We have designed and for the first time experimentally verified a topology optimized mode (de)multiplexer, which
demultiplexes the fundamental and the first order mode of a double mode photonic wire to two separate single mode
waveguides (and multiplexes vice versa). The device has a footprint of ~4.4 μm x ~2.8 μm and was fabricated for
different design resolutions and design threshold values to verify the robustness of the structure to fabrication tolerances.
The multiplexing functionality was confirmed by recording mode profiles using an infrared camera and vertical grating
couplers. All structures were experimentally found to maintain functionality throughout a 100 nm wavelength range
limited by available laser sources and insertion losses were generally lower than 1.3 dB. The cross talk was around -12
dB and the extinction ratio was measured to be better than 8 dB.
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