Rapid developments in computer science have led to the increasing demand for efficient computing systems. Linear photonic systems rose as a favorable candidate for workload-demanding architectures, due to their small footprint and low energy consumption. Mach Zehnder Interferometers (MZI) serve as the foundational building block for several photonic circuits, and have been widely used as modulators, switches and variable power splitters. However, combining MZIs for realizing multiport splitters remains a challenge, since the exponential increase in the number of devices and the consequential increase in losses is limiting the performance of the MZI based multiport device. To overcome such limitations, incorporating alternative and low loss integration platforms combined with a generalized design of the MZI could allow the realization of a robust variable power splitter. In this work, we present for the first time a 4×4 Generalized Mach Zehnder Interferometer (GMZI) incorporated on a Si3N4 photonic integration platform and we experimentally demonstrate its operation as a variable power splitter. We developed an analytical model to describe the operation of the 4×4 GMZI, allowing us to evaluate the impact of several parameters to the overall performance of the device and investigate the device’s tolerance to fabrication imperfections and design alternations. Its experimental evaluation as a variable power splitter reveals a controlled imbalance that ranges up to 10 dB in multiple output ports of the device, validating the theoretically derived principles of operation.
Recent societal demands in climate awareness call for rapid launch of space optical spectrographs, such as to be capable of putting state-of-the-art technology in short timeframe into orbit. As a consequence, it is of paramount importance to compress instruments’ construction schedules down to the ultimately necessary need. Because calibration and characterization (C&C) partially takes place after full instrument assembly, it is de facto on the time-plan critical path, bearing antagonist requirements: measurement accuracy shall be guaranteed without jeopardizing the instrument delivery date. To solve this problem, Airbus has explored multiple paths in order to propose an instrument's "Design for Calibration": the method consists in integrating C&C at the very beginning of the instrument development in order to respond efficiently to the identified needs. First, all planned tests are exhaustively simulated and analyzed with tools validated before measurements, ensuring full control of the overall C&C throughout the entire lifecycle of the project. Next, Airbus strongly enforces its strategy of measuring relevant parameters as soon as they are accessible, hence providing early characterization out of the critical path. Then, the remaining parameters have been thoroughly analyzed to provide a lean optical ground support equipment (OGSE) architecture capable of responding to current challenges. Moreover, it enables full automation, enforcing its time-efficiency by minimizing overheads. Although rapidity is ensured, measurement accuracies are simultaneously kept compliant. Finally, this work presents also disruptive photonics hardware investigated by Airbus to provide calibration for relaxing design: optically filtered supercontinua and optical microcombs.
Integrated tunable lasers based on the co-integration of InP-based SOAs with low-loss Si3N4 dielectric waveguides have emerged as promising solutions in applications where the control of light phase is fundamental. Μicrowave photonics, coherent communications and LIDARs are only some of the applications where sub-KHz linewidths have already been achieved. Nevertheless, the majority of these demonstrations are based on Si3N4 platforms featuring thicknesses lower than 300nm and providing modes with effective indices below 1.6 imposing a major restriction on the achievable FSR values and devices’ footprint. In this work, we present the design of Vernier ring-inspired reflectors based on an 800nm- thick Si3N4 platform providing a TE fundamental mode with an effective index close to 1.71 for a width of 800nm, a group index close to 2.08 at λ=1550nm wavelength, and propagation losses as low as 0.2dB/cm. The proposed thick- Si3N4 designs are based on a simple dual ring Vernier configuration achieving an experimental FSR near 38nm and a 15dB side-mode suppression. These results are in close agreement with the ones obtained theoretically through a detailed Transfer Matrix Formulation verifying the accuracy of the presented semi-analytical model. This simulation model is then employed for the prediction of the performance of more advanced structures such as triple cascaded and high-order Vernier Ring designs, towards extending the achievable FSR and SMSR metrics.
In this work, we present the design process and experimental evaluation of a 1×2 asymmetric power splitters based on the self-imaging principle that is applied on an ultra-low-loss 800nm thick Si3N4 platform. The asymmetry in the multimode interference region is induced by removing a rectangular piece from the edge of the coupler, prompting a disruption at the interference pattern and adjusting accordingly the splitting power ratio. The design of the MMIs operating in the 1500- 1600nm wavelength region was realized through 3D-FDTD calculation method and the experimental results agree with theory providing an error of 5% in splitting ratio and less than -0.6dB insertion losses.
The integration of optical sources in Si photonic transceivers has relied so far on externally coupled III-V laser dies within the assembly. These hybrid approaches are however complex and expensive, as there are additional cost-increasing factors coming from the redundant testing of the pre- and post-coupled laser photonic chips. Further optimization of Photonic Integrated Circuits (PICs) cost and performance can be obtained only with radical technology advancements, such as the “holy grail” of Silicon Photonics; the monolithic integration of III-V sources on Si substrates. MOICANA project funded by EU Horizon 2020 framework targets to develop the technological background for the epitaxy of InP Quantum Dots directly on Si by Selective Area Growth with the best-in-class, in terms of losses and temperature sensitivity, in a CMOS fab, i.e. the SiN waveguide technology. In addition, MOICANA will develop the necessary interface for the seamless light transition between the III-V active and the SiN passive part of the circuitry featuring advanced multiplexing functionality and a combination of efficient and broadband fiber coupling. Through this unique platform, MOICANA aims to demonstrate low cost, inherent cooler-less and energy efficient transmitters, attributes stemming directly from the low loss SiN waveguide technology and the QD nature of the laser’s active region. MOICANA is targeting to exploit the advantages of the monolithic integrated PICs for the demonstration of large volume single-channel and WDM transmitter modules for data center interconnects, 5G mobile fronthaul and coherent communication applications.
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