The monitoring of certain gases is crucial for obtaining Air quality indicators promoting the environmental monitoring. The detection of greenhouse gases (GHG) is especially on the forefront of heath related issues, also dictated by ambitious climate worldwide accords. Currently used spectroscopic solutions remain coslty and bulky, limiting their widespread adoption. We present a study of a MID-IR spectroscopy system developed on a silicon photonics platform, utilizing a Bragg grating mirror cavity, between an optical Bragg source and grating mirror.
KEYWORDS: Sensors, Manufacturing, Process control, Photodetectors, Composite resins, Machine learning, Composites, Optical sensors, Data modeling, Control systems
This study introduces an innovative approach to enhance the utilization of carbon fiber thermosetting composites in advanced structural engineering by addressing the challenges of high manufacturing costs and limited production rates. We develop, deploy and test an ML pipeline utilizing PIC-based sensors (SOI technology, 220 nm thick, fabricated at IMEC’s MPW). They are based on a Bragg structure, packaged using ball lenses and suitable for operating at 180 degrees Celsius and 5 bar pressure. The focus is on accurately predicting two crucial parameters: Cure time and Temperature Overshoot, vital for determining the process duration and part quality. Using advanced tools and sensors, this study achieves a high prediction accuracy of 98% in millisecond scale while effectively handling the outliers. The ML pipeline allows the real-time process optimization of manufacturing process, minimizing the cost, and providing insights into the quality of the composite part through the in-depth monitoring of the process.
This paper presents a novel design of grating couplers in the SiPh platform, as part of the development of a gas sensing system, that measures specific gas concentration through on-chip absorption based spectroscopy in the mid-infrared. The grating is based on 400 nm SOI rib waveguide platform, targeting gaussian emission profile. We investigate both uniform and non-unifοrm grating designs. We show maximum coupling efficiency optimized by 65% at the center wavelength of 4.3 μm, and broadband response. A tolerance study investigating the Si height and etch depth variations indicate very good tolerance to fabrication imperfections across the investigated spectral range of 4.25-4.35 μm. The proposed methodology can be used to engineer grating coupler emission profiles for other applications and platforms.
We propose a novel design of grating couplers to be used as the building blocks of the optical antennas of Lidar systems, designed in the well-established Si3N4-TriPleX platform, that offers low-loss waveguides and allows the integration of the dispersive grating elements with ultra-low-loss and low-energy photonic beamformer circuits. The grating couplers are based on standard asymmetric double-stripe waveguide geometry and are designed with 100nm spectral range around 1550nm. More specifically, we design non-uniform geometry grating couplers, varying the waveguide width and filling factor, targeting constant effective refractive index across the propagation direction, and thus constant emission angle, while optimizing for a uniform emission profile. The designs allow to achieve low theta angle divergence as well as maximum wavelength steering. The reported design showcases theta angle 3dB divergence of 1o, phi angle 3dB divergence of 20o and wavelength steering of 10 o /100nm. The proposed components show low fabrication complexity and are compatible with standard fabrication processes. A comparison between uniform and non-uniform grating designs is also presented, investigating also their performance in an OPA configuration. The described methodology is based on mode solving simulations (Lumerical FDE) and propagation simulations (Lumerical FDTD), while the OPA profile extraction is performed with Matlab Sensor Array Analyzer Toolbox.
The use of composite materials has seen widespread adoption in modern aerospace industry. This has been facilitated due to their combined favorable mechanical characteristics, namely leveraging their low weight, high stiffness and increased strength. Wide adoption of composites requires an effort to avoid costly and cumbersome autoclave-based manufacturing processes. The up and coming “out-of-autoclave” composite manufacture processes also have to be optimized, to allow for consistent high quality of the parts produced as well as keeping the cost and production speed as low as possible. This optimisation can be achieved offline as well as by trying to have constant monitoring and controlling the resin injection and curing cycles.
Capitalizing on the benefits of Silicon Photonic Integrated Circuits (PICs), namely the fast response, miniature size, ability to operate at high temperatures, immunity to electromagnetic interference (allowing carbon fibers in composites), and their compatibility with CMOS fabrication techniques, a passive PIC based temperature sensor embedded in a composite tool is demonstrated, used to produce RTM-6 composite parts.
The design and development methodology of the PIC based sensor (fabricated in an Multi Project Wafer run of 220 nm Silicon-on-Insulator (SOI) platform and based on periodic Bragg grating elements) as well as the experimental results and comparison with the industry standard thermocouples, during a thermal cycling of the tool are presented. We measured the embedded PIC temperature sensor to have sensitivity of around ~85 pm/°C, while the RTM-6 fabrication cycle requires the tool to operate up to 185°C.
Single photon counting detectors are extremely important in the evolution of quantum technologies. The existing devices for the low-flux measurements are bulky and their implementation cannot be made with small footprints. Integrated photonics aims to allow the miniaturization of these setups. We present simulation results for the design of a single 1x10 multimode interference coupler (MMI) in terms of the power imbalance between the output waveguides, optical losses, and tolerance on the operating wavelength. This component acts as the fundamental building block of a photonic integrated circuit (PIC) in the TriPleX platform, acting as an optical divider that is able to bring down the power to ratio levels of 1:10-5. The central operating wavelength is 850 nm. This PIC is based on five cascaded 1x10 multimode interference couples (MMIs) in a novel function for bringing the power to an exceptionally low, and consistent level with repeatable and reproducible results. The fabricated photonic chips have been characterized in lab settings. The two best-performed PICs have been packaged and incorporated in a laboratory setup with embedded reference standards for optical power measurement in a technique referred to as "self-calibration". They were tested in system settings, where they successfully demonstrated that we have achieved a linear splitting ratio of 1:10-9 by cascading nine splitters.
Fibre thermosetting composites play a major role in the engineering of advanced structures due to their combination of light weight and high strength and stiffness as well as the design flexibility. The high manufacturing cost and the inherently low production rates are the main limiting factors in increasing adoption of composites which can be overcome through the development of manufacturing strategies, materials and methodologies of process optimization and control. An accurate estimation of the stage of cure of thermosetting composites production is critical to deduce the overall process duration and ultimately the manufacturing costs. Challenges arise due to temperature overshoots and lack of direct measurement and control of the cure stage, particularly in thick components where the effects of the exothermic nature of the curing reaction and composite low thermal conductivity are more pronounced. To address these challenges and enabling the real-time process optimization, this study proposes a novel approach based on a machine learning (ML) model using simulation Finite Element Method (FEM) data as well as PIC-based photonic sensors realized on Silicon-on-Insulator (SOI) platform. Two robust Voting regressors, XGBoost and Light Gradient Boosting Machine, are used in the model to accurately (98% accuracy) predict two critical parameters: Cure time and Temperature Overshoot. Using photonic sensors to monitor the process in real time, we present experimental validation of Overshoot on manufacture RTM-6 aerospace composite parts.
Very Large Telescope Interferometers (VLTI) are based on interferometry to combine the light collected by more than one telescopes (such as ESO’s telescopes combining light collected by four 8.2-metre Telescopes), enabling the observation of new phenomena, opening up new research areas. The light beams are brought together using a complex system of free space components based on pairwise combination utilising the ABCD scheme. Currently bulky free space optics, with complex and very voluminous setups (10 beam input results in 180 outputs), are too sensitive to operate in ambient, while require the path difference must be kept in sub-millimetre scale. Photonic Integrated Circuits (PIC) advantages of miniaturization, stability, and precise active phase control, make them good candidates to develop the beam combining circuits. Key elements towards realization of these circuits are power splitters, low-loss crossings and directional couplers, all operating in a wide range of wavelengths (600 nm – 820 nm). However, the splitting ratio of conventional directional couplers is very sensitive to wavelength, which limits the bandwidth and the transmission performance of the devices. In this paper, we present the design methodology on a low-loss, broadband, and large fabrication tolerance, bend directional coupler realised on Silicon Nitride integration platform. FDE simulation tool was employed for waveguide modes and coupled system supermodes calculation, 2D-FDTD for propagation simulations, while the results were verified via 3D-FDTD simulations. The proposed bend directional coupler enhances conventional couplers performance, achieving splitting ratio of +-10% around target splitting value for the whole 220 nm target wavelength range, for a footprint of 100 μm x 20 μm.
With the increased interest in silicon photonics, integration and packaging technologies are essential to transforming photonic integrated circuits (PICs) into functional photonic systems. We describe in detail the process to obtain a fully packaged miniature photonic temperature sensor starting from bare PIC dies having Bragg grating sensors in a silicon waveguide. It is also shown that PICs fabricated via multiproject wafer services can show some variability, e.g., in the effective index, which has significant impact on the device functionality (Bragg wavelength) and optical interface (red-shifted grating coupler spectra at default coupling angles). To obtain a final sensor device that is as small as possible the PIC is interfaced from the back side using a 300 μm ball lens. Furthermore, this ensures that the top surface remains clear of any interfacing fibers. Based on this optical interfacing concept, we developed a solution for integrating a 1 mm × 1 mm sensor PIC with a single-mode fiber and packaging it in a 1.5 mm inner-diameter metal protective tube. The accurate position of the ball lens is ensured using a laser-fabricated fused silica precision holder. It is shown that the additional insertion loss caused by the ball lens interface is very limited. A packaged sensor was achieved by sequentially mounting the holder on a ceramic ferrule and then the PIC on the holder and finally gluing a protective metal tube surrounding the assembly, taking care that the PIC surface is flush with the end face of the tube. We demonstrated this concept by realizing a packaged phase-shifted silicon Bragg grating temperature sensor operating around 1550 nm, which could be read out in reflection using a commercial interrogator. A temperature sensitivity of 73 pm / ° C was found, and we demonstrated sensor functionality up to 180°C.
We demonstrate a sensing platform for composite manufacturing (RTM-6) process based on silicon photonics, being controlled by novel Process Monitoring Optimization Control (PMOC) system. The photonic multi-sensor is based on bragg grating components, allowing measurements of temperature, pressure and refractive index, and is packaged employing a ball lens fiber-to-chip interface. We present results of the packaged temperature photonic sensor regarding bandwidth, linearity and thermo-optic efficiency, being controlled by our PMOC system. We experimentally achieve 0.074 nm/C with R^2 = 0.995 linearity for temperature up to 180°C (RTM-6 compatible) with 1 kHz data acquisition and 0.2°C accuracy.
With the increased interest in silicon photonics, smart integration and packaging technologies are essential to transform photonic integrated circuits (PICs) into functional photonic systems. Especially for sensing, the currently existing standard packaging technologies are too expensive and bulky. We developed a solution for integrating a 1 mm x 1 mm sensor PIC with a single mode fiber and packaging it in a 1.5 mm inner-diameter metal protective tube. The concept relies on interfacing a grating coupler with a fiber from the back side of the PIC employing a 300 μm ball lens mounted in a laser-fabricated fused silica precision holder. It is shown that the additional insertion loss caused by the ball lens interface is very limited. A packaged sensor was achieved by sequentially mounting the holder on a ceramic ferrule, then the PIC on the holder and finally gluing a metal tube surrounding the assembly, taking care that the PIC surface is flush with the end face of the tube. The back side fiber interface ensures that the PIC’s surface remains accessible for sensing, while the tube protects the fiber-to-PIC interface. We demonstrated this concept by realizing a packaged phase shifted silicon Bragg grating temperature sensor operating around 1550 nm, which could be read out in reflection using a commercial interrogator. A temperature sensitivity of 73 pm/°C was found, and we demonstrated sensor functionality up to 180°C.
Composite materials offer significant performance advantages due to their lightweight, high-strength, and high stiffness. This led to their adoption in several industrial sectors with particular emphasis on the aerospace industry which has undergone a transformation towards a composite-dominated new standard. In order to respond to the increased demand, it is mandatory to focus on an efficient and well-controlled curing cycle of the resin, which will lead to a significant reduction of cost and an increase in production speed. We investigate, a photonic solution, able of measure key monitoring values that facilitate optimization of the curing process. Simulation and evaluation results on a bragg grating based photonic integrated sensor, developed in 220 nm Silicon-onInsulator platform, are presented. A multi-sensor deployment is considered, enabling monitoring of the temperature and the refractive index of the resin. Serially coupled bragg grating photonic elements will enable concurrent monitoring of both temperature and refractive index. Several bragg configurations have been investigated and experimentally evaluated, specifically regular and phase-shifted ones. Both TE and TM polarization operation sensors that have been designed and fabricated, will be presented. Their sensitivity on resin temperature and refractive index variation will be discussed, resulting in a comparative study outlining the benefits and disadvantages of each solution. Refractive index sensors are realized by employing post-processing etching techniques on Multi-Project-Wafer run fabricated silicon chips, on top of the periodic bragg grating element. The comparative study takes into consideration TE and TM polarization operation, regular and phase-shifted bragg grating configuration elements, while evaluating their sensitivity in temperature and refractive index variations. Temperatures considered are in the range of 27°C to 200°C, while refractive index values lay between 1.5 and 1.6. A Figure-of-Merit is proposed to facilitate the selection of multi-sensor deployment for specific temperature and refractive index ranges.
Composite materials offer significant performance advantages due to their lightweight, high-strength, and high stiffness. This led to their adoption in several industrial sectors with particular emphasis on the aerospace industry which has undergone a transformation towards a composite-dominated new standard. In order to respond to the increased demand, it is mandatory to focus on an efficient and well-controlled curing cycle of the resin, which will lead to a significant reduction of cost and an increase in production speed. Currently, manufacturers use filling and curing cycles with high safety margins which can be optimized by applying process monitoring techniques, which up to now use thermocouples and dielectric sensors. However, these electric solutions suffer in terms of operating capabilities and the facilitation of integrating them in composite materials (due to their size and electrically conductive aspect when using carbon fibers). We present the design and evaluation of a miniaturized novel photonic integrated sensor, fabricated in 220 nm top SOI platform, capable of measuring key monitoring values that facilitate optimization of the curing process. The operation principle is the spectral shift of a silicon Bragg grating component's resonant wavelength. Bragg grating design and postprocessing of the integrated chip allows for measuring different key values such as temperature, refractive index and pressure all in ~1.5 mm diameter. The fabricated temperature sensors achieve a significant 0.084 nm/°C thermo-optic efficiency with high accuracy (0.5 °C) and repeatability across a very wide dynamic range (temperature 27 to 180 °C).
The ever-increasing demands in traffic fueled by bandwidth hungry applications are pushing data centers to their limits challenging the capacity and scalability of currently established transceiver and switching technologies in data center interconnection (DCI) networks. Coherent optics emerged as a promising solution for inter-DCIs offering unprecedented capacities closer to data centers and relaxing the power budget restrictions of the link. QAMeleon, an EU funded R and D project, is developing a new generation of faster and greener sliceable bandwidth-variable electro-optical transceivers and WSS switches able to handle up to 128 Gbaud optical signals carrying flexible M-QAM constellations and novel modulation techniques. A summary of the progress on the QAMeleon transponder and Reconfigurable Optical Add/Drop Multiplexer (ROADM) concepts is presented in this paper.
The ELI-Beamlines facility, currently under construction in Prague, Czech Republic, will house multiple high power
laser systems with varying pulse energies, pulse durations, and repetition rates. Here we present the status of a high
repetition rate beamline currently under construction with target parameters of 20 fs pulse duration, 100 mJ pulse energy,
and 1 kHz repetition rate. Specifically we present the Yb:YAG thin disk lasers which are intended to pump picosecond
OPCPA, synchronization between pump and signal pulses in the OPCPA, and the first stages of OPCPA.
We report on a temporal jitter-compensated Yb:YAG thin-disc laser as a pump source for the front-end OPCPA of ELIBeamlines high energy and repetition rate system. The main advantage of using picosecond Yb:YAG thin-disc lasers is that relatively high energies in the kHz repetition rate range can be easily accessed. Although in our case the pump laser is optically synchronized to the OPCPA seeding Ti:Sapph laser, the stability of the OPCPA output gets heavily affected by delay jitter due to a large number of roundtrips in the regenerative amplifier cavity and slight ambient temperature drifts. Since interacting pulses are only ~1.5 ps in duration, an additional active stabilization of the pump path length corresponding to sub-100 fs delay precision must be implemented. In our work we demonstrate a novel design of a jitter stabilization system which employs a cross-correlation setup employing parametric amplification in two perpendicularly oriented nonlinear crystals. A small fraction of the OPCPA seed signal is being locked between cross-polarized and delayed replicas of a pump pulse. The feedback signal for the delay compensation is acquired by coupling the polarization-separated parts of the parametrically amplified signal into two channels of a balanced photodetector. The delay stabilization is achieved mainly by adjusting the cavity length of the regenerative amplifier with a piezo-mounted mirror. The proposed setup allows reducing the temporal jitter of Yb:YAG thin-disc regenerative amplifier to tens of fs RMS and maintaining it over extended periods of time.
We present a design of a high average power vacuum compressor unit for 1 kHz repetition rate pump laser operating at 1030 nm. The unit comprises two compressors and two SHG units located in a common vacuum vessel. Both compressors are designed with GDD of -270.5 ps2 for compressing high energy, 1J, 500 ps pulses to 1.5 ps duration with efficiency that exceeds 88.5%. We also considered the feasibility of high efficiency, average power conversion to 515 nm in a range of nonlinear crystals in vacuum. The calculated temperature profiles in large aperture crystals are compared with temperature acceptance bandwidths for the second harmonic generation. It is concluded that in LBO and YCOB crystals the conversion efficiency can exceed 60%, thus allowing generation of 1 kHz train of 1.5 ps pulses at 515 nm with energy exceeding 0.5 J that will be used for pumping the high energy amplifier stages of a femtosecond OPCPA system.
B. Rus, P. Bakule, D. Kramer, G. Korn, J. Green, J. Nóvak, M. Fibrich, F. Batysta, J. Thoma, J. Naylon, T. Mazanec, M. Vítek, R. Barros, E. Koutris, J. Hřebíček, J. Polan, R. Baše, P. Homer, M. Košelja, T. Havlíček, A. Honsa, M. Novák, C. Zervos, P. Korous, M. Laub, J. Houžvička
We present an overview of the projected and/or implemented laser systems for ELI-Beamlines. The ELI-Beamlines
facility will be a high-energy, high repetition-rate laser pillar of the ELI (Extreme Light Infrastructure) project. The
facility will make available high-brightness multi-TW ultrashort laser pulses at kHz repetition rate, PW 10 Hz repetition
rate laser pulses, and kilojoule nanosecond laser pulses that will be used for generation of 10 PW, and potentially higher,
peak power. These systems will allow meeting user requirements for cutting-edge laser resources for programmatic
research in generation and applications of high-intensity X-ray sources, in electron and proton/ion acceleration, and in
dense plasma and high-field frontier physics.
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