We demonstrate a Silicon-on-Insulator flexible filtering element, relying on two serially coupled micro ring resonators equipped with three thermo-optically tuned Mach-Zehnder interferometers, acting as variable optical couplers. A single electrode configuration is adopted, enabling the low-complexity thermo-optical control of the filtering element for bandwidth and wavelength tuneability. The module's performance has been studied in detail via simulation analysis and the obtained results were verified through experimental evaluation. Wide bandwidth tunability from 9 GHz to 103 GHz is achieved with a power efficiency of 0.284 mW/GHz, while full Free Spectral Range wavelength tuning is achieved with an efficiency of 0.297 mW/GHz. Module's insertion loss lays below 3 dB.

The use of composite materials has seen widespread adoption in modern aerospace industry. This has been facilitated due to their favourable mechanical characteristics, namely, low weight and high stiffness and strength. For broader implementation of those materials though, the out-of-autoclave production processes have to be optimized, to allow for higher reliability of the parts produced as well as cost reduction and improved production speed. This optimization can be achieved by monitoring and controlling resin filling and curing cycles. Photonic Integrated Circuits (PICs), and, in particular, Silicon Photonics, owing to their fast response, small size, ability to operate at higher temperatures, immunity to electromagnetic interference, and compatibility with CMOS fabrication techniques, can offer sensing solutions fulfilling the requirements for composite material production using carbon fibres. In this paper, we demonstrate a passive optical temperature sensor, based on a 220 nm height Silicon-on-Insulator platform, embedded in a composite tool used for producing RTM-6 composite parts of high quality (for use in the aerospace industry). The design methodology of the photonic circuit as well as the experimental results and comparison with the industry standard thermocouples during a thermal cycling of the tool are presented. The optical sensor exhibits high sensitivity (85 pm/°C), high linearity (R² = 0.944), and is compatible with the RTM-6 production process, operating up to 180 °C.

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 present a novel technique for dispersion compensation by exploiting the filtering properties of a fully reconfigurable serially coupled microring resonator (MRR) structure in analog intermediate frequency-over-fiber/mmWave (IFoF/mmWave) fiber/wireless 5G and beyond 5G(B5G)-oriented mobile fronthaul. To this extend, we demonstrate simulation and experimental results on analog photonic processing of 1 Gbaud Quadrature Phase Shift Keying (QPSK) modulated radio signal. By tuning filter's bandwidth in the range of 26 - 69 GHz, and resonance within a resonance free spectral range (FSR) range, dispersion induced power fading mitigation was achieved, for a set of widely adopted intermediate frequencies (IFs) and transmission distances. Analytical calculations carried out in MATLAB environment, highlighting significant improvement of transmission system output power, whereas are verified via transmission system simulations, resulting to error vector magnitude (EVM) improvement up to ~ 30%. Experimental results verified both analytical and transmission simulation results for a series of IFoF downlink transmission system configurations. For widely used wireless transmission configuration at 8.5 GHz IF, by tuning the filter to appropriate bandwidth of 14 GHz and resonance peak properly, successful fiber wireless transmission for over 25 km of fiber was demonstrated, achieving 16.9% EVM for QPSK, below the 3GPP (<17.5%) requirements for 5G NR.

The transition to 6G networks will necessitate advanced infrastructures to handle massive device integration, exponential data growth, and low latency requirements. The proposed 6G architecture will integrate diverse technologies, such as free space optical (FSO) and mmWave, into the existing fiber infrastructure. This work demonstrates a hybrid 6G X-haul solution consisting of 10 km fiber/100 m FSO/5 m mmWave that employs a software-defined network as an interface platform to improve network resilience and flexibility in 6G networks. For this purpose, real-time traffic management and dynamic link switching operate within 600 µs, interacting with the heterogeneous physical layers. This enables the system to adapt to changing conditions and failures, ensuring continuous and uninterrupted connectivity. Experimental results proved that this dynamic software-defined networking-based topology can manage high-capacity data rates of up to 60 Gbps while supporting adaptive modulation schemes below hard decision-forward error correction.

We propose two configurations for the coexistence of sensing and communication signals, exploiting Free Space Optical (FSO) links to transmit commercial 6G traffic and remotely interrogate sensors distributed along distances of 100 m. The sensors are fabricated on a Silicon Photonics (SiPh) platform, to achieve miniaturization and highly compact form of the required features. The first scheme consists of couplers and circulators, while the second utilizes polarization handling elements to multiplex both signals, while a 100-m outdoor Free Space Optical link is utilized for both schemes. The configurations exhibit high stability, with uninterrupted transmission of traffic along the duration of the experiments, while the sensors’ performance is evaluated, with their discrepancies measured below 2%.