The next-generation chip-on-tip surgical endoscopes require small footprint (1-3 French), hyperspectral imaging capability for multi-biomarker quantification with high frame rate to reduce motion artefacts. These innovations demand high data rate links, which could require twisted-pair cables if transmitted electrically. To eliminate bulky electrical wiring, we propose an all-optical powering and communication chip at the distal end consisting of a monolithically series interconnected Photonic Power Converter and a reflective electroabsorption modulator (REAM) based on a p-i-n diode structure with an embedded multiple quantum well (MQW) absorber. Optical sources for the power generator and reflective modulator are provided remotely over optical fiber, thus removing the need to host power-hungry lasers at the distal tip. To simplify the overall design, the communication scheme takes advantage of the REAM’s dual functionality as a modulator and detector. Here, we have used a commercial REAM designed to operate at 1550nm and a novel Time Division Duplexing (TDD) communication protocol to demonstrate bidirectional transmission at 500 Mb/s over a single-mode fiber on a benchtop in order to examine the feasibility of the scheme. We found that at shorter wavelength near the MQW band-edge, zero-bias operation of the REAM is possible and the required modulation voltage swing is reduced. Operating under zero-bias at 1520nm instead of 1550nm leads to negligible static energy consumption and about 47% reduction in dynamic energy consumption, reaching an 8dB extinction ratio. Additionally, at 1520nm, the photocurrent generation responsivity increases dramatically at zero-bias, allowing the Transimpedance Amplifier (TIA) to be removed from the receiver circuit. This results in reduced footprint and power consumption of the receiver front end circuit.
Photonic chips are becoming increasingly complex, combining even more optical building blocks on the same chip. With this growing complexity we also see an expanding need for, and use of electrical tuning. This imposes opportunities, as photonic circuits can now become reconfigurable at run time, even to the point of creating arbitrary connectivity between functional building blocks, serving as a general-purpose optical processor. But at the same time, large-scale configurability comes with some tremendous challenges in terms of power consumption, electrical and optical packaging, driver electronics and control algorithms. We will discuss our recent progress in these domains in our path to building general-purpose programmable photonic chips. Expanding silicon photonics with high-efficiency electro-optic tuners, high-density packaging solutions, and electronics and software layers to govern the behavior of these photonic circuits that can be used for both photonic and microwave analog signal processing.
KEYWORDS: Waveguides, Microelectromechanical systems, Phase shifts, Liquid crystals, Silicon photonics, Silicon, Photonic integrated circuits, Electrodes, Oxides, Back end of line
The demand for efficient actuators in photonics has peaked with increasing popularity for large-scale general-purpose programmable photonics circuits. We present our work to enhance an established silicon photonics platform with low-power micro-electromechanical (MEMS) and liquid crystal (LC) actuators to enable largescale programmable photonic integrated circuits (PICs).
We give an overview the progress of our work in silicon photonic programmable circuits, covering the technology stack from the photonic chip over the driver electronics, packaging technologies all the way to the software layers. On the photonic side, we show our recent results in large-scale silicon photonic circuits with different tuning technologies, including heaters, MEMS and liquid crystals, and their respective electronic driving schemes. We look into the scaling potential of these different technologies as the number of tunable elements in a circuit increases. Finally, we elaborate on the software routines for routing and filter synthesis to enable the photonic programmer.
KEYWORDS: Short wave infrared radiation, Hypoxia, Fetus, Near infrared spectroscopy, Spectroscopy, Monte Carlo methods, Reflectivity, Sensors, Reflectance spectroscopy, Photon transport, Near infrared
Intra-partum hypoxia is the principal cause of death for every 2 in 10000 infants. Monitoring hypoxia during child-birth will not only prevent infant mortality, but also help prevent cerebral palsy in 10-20% of the surviving babies. Current monitoring techniques either use an indirect biomarker (heart-rate in cardiotocograph) or measure downstream biomarkers intermittently and invasively (fetal blood sampling). For complete fetal wellbeing monitoring, a continuous non-invasive assessment of multiple biomarkers is needed during birth. To address this gap we are developing a noninvasive, continuous sensor based on long wavelength near infrared (LW-NIR) spectroscopic technique for the detection of fetal hypoxia through multiple biomarkers. For specific hypoxia assessment we have identified key optical spectroscopy compatible biomarkers from a list of various biomarkers effected in the physiological processes leading to the development of hypoxia. The key biomarkers identified are – cytochrome-C oxidase, oxygenated and deoxygenated hemoglobin, lactate, pyruvate and pH in the connective tissue in presence of other interferences such as lipids, proteins and other sugars. To translate these biomarkers into a viable diffuse-reflectance probe we assessed the light-tissue interaction in the low-scattering, water-absorption dominated LW-NIR window of 1350-2500 nm using Monte Carlo photon migration model and experimentally verified the penetration depth achievable in fetal tissue phantom to ~0.5 mm, only targeting the capillary bed.
We present our work in the European project MORPHIC to extend an established silicon photonics platform with low-power and non-volatile micro-electromechanical (MEMS) actuators to demonstrate large-scale programmable photonic integrated circuits (PICs).
We present our work to extend silicon photonics with MEMS actuators to enable low-power, large scale programmable photonic circuits. For this, we start from the existing iSiPP50G silicon photonics platform of IMEC, where we add free-standing movable waveguides using a few post-processing steps. This allows us to implement phase shifters and tunable couplers using electrostatically actuated MEMS, while at the same time maintaining all the original functionality of the silicon photonics platform. The MEMS devices are protected using a wafer-level sealing approach and interfaced with custom multi-channel driver and readout electronics.
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