Estimation of maximum temperature and thermal crosstalk between two active elements in a PIC: development of a thermal equivalent circuit.

The operating temperature plays a key role in the performance and lifetime of photonic integrated circuits (PICs). Miniaturization and increasing heat dissipation promote thermal crosstalk effects and pose additional challenges to the PIC designer. The European Photonics Industry Consortium recommends thermal modeling during design phase. However, a fully numerical optimization of a particular layout requires an unrealistically large number of simulations. Here, we propose a compromise approach: a set of carefully chosen simulations are performed with a multi-physics software. The obtained results are used to derive a linearized equivalent thermal circuit that can be used to maximize the power levels and to minimize the distance between the chosen components while guaranteeing the absence of a thermal crosstalk. For simplification, this model is derived considering a PIC with only two active components. Other parameters are varied, such as the material of the holder (silicon or diamond) and the layer of epoxy that is used to attach the PIC to the holder. The obtained circuit is used to determine the maximum dissipated power or the minimum distance between the components while keeping some predetermined specifications. The model can be extended to contain more elements or to include transient analysis of the temperature distribution.

Measuring Torque and Temperature in a Rotating Shaft Using Commercial SAW Sensors.

Real-time monitoring of torque in a rotating shaft is not easy to implement with technologies such as optic fiber sensors or strain gages. Surface acoustic wave (SAW) sensors are wireless and passive and can be used to monitor strain in moving parts. Commercial solutions (sensors, antennas and interrogation unit) can easily be purchased from some companies; however, they are not customized and may not meet the specificity of the measurements. In order to evaluate the adequacy of commercial off-the-shelf (COTS) solutions, temperature and strain sensors fabricated by SENSeOR (Besançon, France) were mounted on a load cell. The sensors were calibrated using a thermal chamber and a universal testing machine. The load cell was then assembled together with a steel shaft that rotated at different speeds inside an oven. The commercial antennas were replaced with an RF (radio frequency) coupler and the sensors were interrogated with the commercial interrogation unit. The influence of rotation in the accuracy on the measurements, as well as the adequacy of the sensors structure, was evaluated. It can be concluded that SAW sensors can be used to measure temperature or torque in a rotating environment; however, some customization of the components is required in order to overcome the limitations posed by COTS sensing solutions.