Comparing different nonlinearities in readout systems for optical neuromorphic computing networks

Nonlinear activation is a crucial building block of most machine-learning systems. However, unlike in the digital electrical domain, applying a saturating nonlinear function in a neural network in the analog optical domain is not as easy, especially in integrated systems. In this paper, we first investigate in detail the photodetector nonlinearity in two main readout schemes: electrical readout and optical readout. On a 3-bit-delayed XOR task, we show that optical readout trained with backpropagation gives the best performance. Furthermore, we propose an additional saturating nonlinearity coming from a deliberately non-ideal voltage amplifier after the detector. Compared to an all-optical nonlinearity, these two kinds of nonlinearities are extremely easy to obtain at no additional cost, since photodiodes and voltage amplifiers are present in any system. Moreover, not having to design ideal linear amplifiers could relax their design requirements. We show through simulation that for long-distance nonlinear fiber distortion compensation, using only the photodiode nonlinearity in an optical readout delivers BER improvements over three orders of magnitude. Combined with the amplifier saturation nonlinearity, we obtain another three orders of magnitude improvement of the BER.

Wideband MOEMS for the Calibration of Optical Readout Systems

The paper proposes a technology based on UV-LIGA process for microoptoelectromechanical systems (MOEMS) manufacturing. We used the original combination of materials and technological steps, in which any of the materials does not enter chemical reactions with each other, while all of them are weakly sensitive to the effects of oxygen plasma. This made it suitable for long-term etching in the oxygen plasma at low discharge power with the complete preservation of the original geometry, including small parts. The micromembranes were formed by thermal evaporation of Al. This simplified the technique compared to the classic UV-LIGA and guaranteed high quality and uniformity of the resulting structure. To demonstrate the complete process, a test MOEMS with electrostatic control was manufactured. On one chip, a set of micromembranes was created with different stiffness from 10 nm/V to 100 nm/V and various working ranges from 100 to 300 nm. All membranes have a flat frequency response without resonant peaks in the frequency range 0–200 kHz. The proposed technology potentially enables the manufacture of wide low-height membranes of complex geometry to create microoptic fiber sensors.

Precision Magnetometers for Aerospace Applications: A Review

Aerospace technologies are crucial for modern civilization; space-based infrastructure underpins weather forecasting, communications, terrestrial navigation and logistics, planetary observations, solar monitoring, and other indispensable capabilities. Extraplanetary exploration—including orbital surveys and (more recently) roving, flying, or submersible unmanned vehicles—is also a key scientific and technological frontier, believed by many to be paramount to the long-term survival and prosperity of humanity. All of these aerospace applications require reliable control of the craft and the ability to record high-precision measurements of physical quantities. Magnetometers deliver on both of these aspects and have been vital to the success of numerous missions. In this review paper, we provide an introduction to the relevant instruments and their applications. We consider past and present magnetometers, their proven aerospace applications, and emerging uses. We then look to the future, reviewing recent progress in magnetometer technology. We particularly focus on magnetometers that use optical readout, including atomic magnetometers, magnetometers based on quantum defects in diamond, and optomechanical magnetometers. These optical magnetometers offer a combination of field sensitivity, size, weight, and power consumption that allows them to reach performance regimes that are inaccessible with existing techniques. This promises to enable new applications in areas ranging from unmanned vehicles to navigation and exploration.

Current Review of Optical Neural Interfaces for Clinical Applications

Neural interfaces, which enable the recording and stimulation of living neurons, have emerged as valuable tools in understanding the brain in health and disease, as well as serving as neural prostheses. While neural interfaces are typically based on electrical transduction, alternative energy modalities have been explored to create safe and effective approaches. Among these approaches, optical methods of linking neurons to the outside world have gained attention because light offers high spatial selectivity and decreased invasiveness. Here, we review the current state-of-art of optical neural interfaces and their clinical applications. Optical neural interfaces can be categorized into optical control and optical readout, each of which can be divided into intrinsic and extrinsic approaches. We discuss the advantages and disadvantages of each of these methods and offer a comparison of relative performance. Future directions, including their clinical opportunities, are discussed with regard to the optical properties of biological tissue.

Characterization with X-rays of a Large-Area GEMPix Detector with Optical Readout for QA in Hadron Therapy

Quality Assurance (QA) in hadron therapy is crucial to ensure safe and accurate dose delivery to patients. This can be achieved with fast, reliable and high-resolution detectors. In this paper, we present a novel solution that combines a triple Gas Electron Multiplier (GEM) and a highly pixelated readout based on a matrix of organic photodiodes fabricated on top of an oxide-based thin-film transistor backplane. The first LaGEMPix prototype with an active area of 60 × 80 mm2 was developed and characterized using low energy X-rays. The detector comprises a drift gap of 3.5 mm, a triple-GEM stack for electron amplification, and a readout featuring 480 × 640 pixels at a 126 µm pitch. Here, we describe the measurements and results in terms of spatial resolution for various experimental configurations. A comparison with GAFCHROMIC® films and the GEMPix detector used in the charge readout mode was performed to better understand the contribution to the spatial resolution from both the electron diffusion and the isotropic emission of photons. The measurements were compared to Monte Carlo simulations, using the FLUKA code. The simulation predictions are in good agreement with the GEMPix results. Future plans with respect to applications in hadron therapy are discussed.

Directional Dark Matter Searches with CYGNO

The CYGNO project aims at developing a high resolution Time Projection Chamber with optical readout for directional dark matter searches and solar neutrino spectroscopy. Peculiar CYGNO’s features are the 3D tracking capability provided by the combination of photomultipliers and scientific CMOS camera signals, combined with a helium-fluorine-based gas mixture at atmospheric pressure amplified by gas electron multipliers structures. In this paper, the performances achieved with CYGNO prototypes and the prospects for the upcoming underground installation at Laboratori Nazionali del Gran Sasso of a 50-L detector in fall 2021 will be discussed, together with the plans for a 1-m3 experiment. The synergy with the ERC consolidator, grant project INITIUM, aimed at realising negative ion drift operation within the CYGNO 3D optical approach, will be further illustrated.

Commissioning of a High Pressure Time Projection Chamber with Optical Readout

The measurements of proton–nucleus scattering and high resolution neutrino–nucleus interaction imaging are key in reducing neutrino oscillation systematic uncertainties in future experiments. A High Pressure Time Projection Chamber (HPTPC) prototype has been constructed and operated at the Royal Holloway University of London and CERN as a first step in the development of a HPTPC that is capable of performing these measurements as part of a future long-baseline neutrino oscillation experiment, such as the Deep Underground Neutrino Experiment. In this paper, we describe the design and operation of the prototype HPTPC with an argon based gas mixture. We report on the successful hybrid charge and optical readout using four CCD cameras of signals from 241Am sources.