Optronics Technologies (Greece)

In this paper, we present the development of a miniaturized Laser Doppler Vibrometer (LDV) system, based on the 3D hybrid integration of the Si3N4 platform of LioniX (TriPleX) and the polymer platform of FhG-HHI (PolyBoard). The photonic integrated circuit (PIC) supports all the functionalities of an LDV system including the splitting of the input light to the measurement and the reference beam, the introduction of an optical frequency shift up to 100 kHz, polarization handling and detection of the reflected measurement beam, using a heterodyne detection technique. The optical frequency shift is accommodated in the TriPleX section of the PIC based on a simple serrodyne scheme, where a phase modulator is driven with a sawtooth signal with the desired frequency. The modulation of the optical field is based on the stress-optic effect utilizing thin-films of PZT deposited on top of the waveguide structures of the TriPleX platform, capable of supporting modulation frequencies up to several MHz. The PolyBoard part enables polarization handling and heterodyne detection of the reflected beam using micro-optic elements on chip, including a polarization beam splitter (PBS), a half wave plate (HWP), and a pair of balanced detectors with four photodiodes that are flip chip bonded on the top. The TriPleX and the PolyBoard platform were brought together based on the 3D hybrid integration, using mode size converters and vertical directional couplers with coupling losses lower than 15 dB. On-chip beating, using the integrated photodiodes is experimentally demonstrated.

We propose a novel concept for the implementation of 2-dimensional (2D) optical phased arrays (OPAs) with end-fire waveguides as antenna elements (AEs), and we present its theoretical model and experimental proof. The concept is based on the use of 3-dimensional (3D) photonic integrated circuits (PICs) with multiple waveguiding layers on the PolyBoard platform. In their simplest form, the 3D PICs comprise AEs at different layers, vertical and lateral couplers for the distribution of light among the AEs, and phase shifters for the execution of the 2D beam scanning process. Using the field equivalence principle, we model the radiated field from the single-mode waveguide of the platform at 1550 nm, and we find that the expected beam width is 12.7°. We also investigate the perturbation that is induced into propagating fields inside parallel waveguides in proximity, and we conclude that waveguide spacings down to 6 µm can be safely used for development of uniform OPAs in the PolyBoard platform. For OPAs with 6 µm pitch and 4 AEs, we find that the maximum steering angle is 14.0° and the expected angular clearance, wherein the main radiation lobe is higher than any grating lobe by at least 3, 6 and 10 dB is 10.8°, 7.6° and 2.8°, respectively. Based on our simulations, we design and fabricate single- and 2-layer PICs with 1 × 4 and 2 × 4 OPAs. The lateral pitch of the OPAs ranges from 10 down to 6 µm, while the vertical pitch is 7.2 µm. We experimentally characterize these OPAs and validate the potential of the 2-layer PICs for 2D beam scanning on the azimuthal and elevation plane. The beam profiles and the main scanning parameters such as the maximum steering angle and the relative intensity between the main and the grating lobes are found in excellent agreement with our simulations.

Within the European project HAMLET, we develop a large scale photonic integrated circuit as a flexible interface between the optical front-haul part and the wireless access part at the remote antenna units (RAU) of future 5G networks. The circuit will be based on the hybrid integration of a polymer platform (PolyBoard) with a low-loss silicon-nitride platform (TriPleX), and will accommodate a number of processing functionalities in the digital and analog domains including optical beamforming. The analog optical link on-chip will be based on the use of graphene-based electro-absorption modulators in the polymer part of the circuit and will be able to transfer through the optical beamforming network radio signals at 28 GHz with 1 Gbaud symbol rate and modulation format up to 64-QAM. In this paper, we present early experimental results with bulk components that emulate the operation and evaluate the expected performance of our optical system on-chip.

New technologies for ultradense WDM-PON (udWDM-PON), enabled by coherent techniques and low-cost devices, are developed for an efficient utilization of the optical spectrum, revealing that the “Wavelength-to-the-User” concept can be feasible. In this paper, an udWDM-PON with only 6.25-GHz channel spacing is implemented with conventional DFB lasers, for a splitter-based PON infrastructure with 256 ONUs. The results of the analysis of udWDM access network architecture with respect to their associated complexity, cost, and migration scenarios, exhibit the potential for higher aggregate throughput, higher split ratios, and node consolidation, when compared to competing technologies.

The traffic carried by core optical networks grows at a steady but remarkable pace of 30-40% year-over-year. Optical transmissions and networking advancements continue to satisfy the traffic requirements by delivering the content over the network infrastructure in a cost and energy efficient manner. Such core optical networks serve the information traffic demands in a dynamic way, in response to requirements for shifting of traffics demands, both temporally (day/night) and spatially (business district/residential). However as we are approaching fundamental spectral efficiency limits of singlemode fibers, the scientific community is pursuing recently the development of an innovative, all-optical network architecture introducing the spatial degree of freedom when designing/operating future transport networks. Spacedivision- multiplexing through the use of bundled single mode fibers, and/or multi-core fibers and/or few-mode fibers can offer up to 100-fold capacity increase in future optical networks. The EU INSPACE project is working on the development of a complete spatial-spectral flexible optical networking solution, offering the network ultra-high capacity, flexibility and energy efficiency required to meet the challenges of delivering exponentially growing traffic demands in the internet over the next twenty years. In this paper we will present the motivation and main research activities of the INSPACE consortium towards the realization of the overall project solution.