InP DFB lasers are flip-chip bonded to 300mm Si photonic wafers using a pick-and-place tool with an advanced vision system, realizing high-precision and high-throughput passive assembly. By careful co-design of the InP-Si Photonics electrical, optical and mechanical interface, as well as dedicated alignment fiducials, sub-300nm post-bonding alignment precision is realized in a 25s cycle time. Optical coupling losses of -1.5±-0.5dB are achieved at 1550nm wavelength after epoxy underfill, with up to 40 mW of optical power coupled to the SiN waveguides on the Si photonics wafer. The bonding interface adds less than 10% to the series resistance of the laser diodes and post-bonding thermal resistance is measured to be 76K/W (or 27K.mm/W), mostly dominated by heat spreading resistance in the InP lasers as suggested by in-depth thermal modeling. Although the assembled lasers suffer from significant, unintentional optical backreflection from the fiber grating couplers used for optical characterization, laser linewidths well below 1MHz have been measured under specific drive conditions, as supported by a detailed laser noise analysis. Finally, we demonstrate the ability of bonded laser assemblies to pass early reliability tests.

Ring modulators for silicon photonic (SiPho) optical transceivers are extremely thermally sensitive and require thermal tuning for stable operation. This tuning is achieved with integrated heaters and in this work two aspects of the heaters are investigated: firstly, how to thermally model the heater-waveguide system in a SiPho ring modulator. Secondly, how to improve the energy efficiency by adapting the design in order to minimize the thermal tuning power consumed by the heater. Silicon substrate undercut (UCUT) is done in order to achieve out-of-plane thermal isolation and prevent heat flow directly into the Si substrate below the device. Introducing the UCUT increases the heater efficiency ($\eta _{h}$) with a factor X3.08. It is shown that the influence of the UCUT cross section on the heater efficiency can be neglected, only the total area and metals significantly influence the thermal behaviour. Comparison between electro-thermal and pure thermal simulation shows very similar behaviour. Finally, the UCUT causes an increase in thermal time constant with factor X3.68.

Thermal modelling of photonic integrated circuits (PICs) is required for circuit design and for the development of thermal control algorithms. In this work, we present a methodology for obtaining a compact dynamic thermal RC-model of a PIC. PICs are sensitive to thermal coupling, and in this paper it is shown that traditional resistive coupling does not suffice and a new coupling method is derived. The case study to which the new methodology is applied, is a dense wavelength division multiplexing ring filter with 8 channels. With the obtained RC-model, computational time is reduced from 5.5 hours for finite element simulation to <1 second for a single step response. Using the compact model, circuit-level analysis of frequency response is carried out. Because of its high computational efficiency, the compact model opens possibilities of simulating thermal tuning algorithms.

In this work a novel methodology is presented for coupled thermo-optical modelling of an electro-absorption modulator (EAM). First, an optical FDTD simulation results in the light absorption map in the EAM waveguide. This absorption is used as a heat source boundary condition in a thermal finite element (FE) simulation in order to calculate the waveguide temperature. The FE model is validated with experimental data. The temperature is averaged over the device length and used as input in a compact, fully coupled thermo-optical model. The model reveals a thermal instability of the device characteristic, which limits the maximum amount of optical power the device can handle. Finally, using the thermal FE model, a self-heating mitigation strategy is proposed. Using process compatible design changes, self-heating can be reduced by up to 40%, greatly increasing the EAM optical power handling capabilities.

Multiscale thermal analysis in integrated systems is required for capturing both device-level and circuit-level dynamics. Traditional analysis with finite element (FE) models can be accelerated by using machine learning (ML) methods. In this article, a performance benchmarking between three ML methods for thermal simulation is carried out: 1) artificial neural networks (ANNs); 2) proper orthogonal decomposition with radial basis functions (POD-RBFs); and 3) finally, POD-RBF-ANN is used as a hybrid ML method. The (dis)advantages of the different methods are demonstrated for the thermal simulation of a multiscale photonic chip. The ML models are trained with FE data for both linear and nonlinear dynamics and are tested for inter- and extra-polation prediction accuracy. A computational speed increase with a factor >7500 compared to FE is obtained. Furthermore, ANNs prove to be the best suited for the simulation of nonlinear dynamics. POD-RBF is the best method for minimizing training time and combining the best of both methods in POD-RBF-ANN creates an ML model with a short training phase and highly accurate predictions.

Ring-based, resonant Si photonic (SiPho) devices are temperature sensitive and require thermal tuning for stable operation, which is accomplished with integrated metallic heaters. This paper investigates the combined electromigration (EM) and thermal performance of tungsten (W) heaters using calibrated electro-thermal finite element models. The current injectors that are used to supply the current to the heater are a known weak spot for electromigration. The presented modelling study shows the conflicting design requirements for optimal thermal performance and optimal EM performance, which results in the need of a careful trade-off, supported by experimental reliability data. Based on modelling results, new device designs are proposed with significant performance increase. Lastly, a new methodology is introduced which allows to predict the lifetime of the W-heaters, given specific operating conditions such as ambient temperature and required phase shift.