PCRL at SPIE Photonics West 2024 Conference

The Photonics Communications Research Laboratory participated at the SPIE Photonics West Conference 2024 in San Francisco, California, USA, which took place between the 27th of January and the 1st of February.

The members of PCRL showcased groundbreaking research through the presentation of four cutting-edge posters:


  1. Lefteris Gounaridis presented

A novel photonic integrated optical divider based on cascaded multimode interference (MMI) couplers, achieving a splitting ratio of 1:10-9.”


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 1×10 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 1×10 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.

See more: https://spie.org/photonics-west/presentation/A-novel-photonic-integrated-optical-divider-based-on-cascaded-multimode/12889-80


  1. Thenia Prousalidi presented

Integrated broadband bent directional coupler for use in telescope interferometry in the visible (600nm-820nm).


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.

See more: https://spie.org/photonics-west/presentation/Integrated-broadband-bent-directional-coupler-for-use-in-telescope-interferometry/12882-61#_=_


  1. Charalampos Zervos presented

Integrated silicon Bragg grating-based temperature sensor, embedded in composite molds for out-of-autoclave composite parts process monitoring and optimization.


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.

See more: https://spie.org/photonics-west/presentation/Integrated-silicon-Bragg-grating-based-temperature-sensor-embedded-in-composite/12889-69#_=_


  1. Evrydiki Kyriazi presented

Photonic sensor-based machine learning for precise forecasting of cure time and temperature overshoot in resin transfer molding.



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.

See more: https://spie.org/photonics-west/presentation/Photonic-sensor-based-machine-learning-for-precise-forecasting-of-cure/12893-77#_=_