The influence of heat spreading on the thermal control of Photonics Integrated Circuits

Photonics Integrated Circuits (PICs), a feature of contemporary optical communications technologies, can represent a stringent packaging challenge, particularly in terms of their requirements for thermal control. Devices such as laser arrays can demonstrate tight temperature limits, sub-ambient operating temperatures, moderate heat loads but high devicelevel heat fluxes. A key feature of many hybrid PICs is a multilayer substrate which offers mechanical support, electrical interconnection and heat spreading for the devices that it carries; such substrates are typically mounted on a thermoelectric (TE) module (TEM) to achieve thermal control. The objective of this paper is to examine the influence of heat spreader structures on the thermal behavior of PICs, with particular attention on maximizing TEM efficiency. To this end, closed-form analytical and numerical models are developed for a representative laser array PIC which captures the conductive heat transfer within the spreader, coupled with a constitutive representation of the TEM. A parametric study is conducted to illustrate the influence of the following parameters on the source temperature of the PIC for the application: effective conductivities and dimensions of the heat spreader; thermal interface resistances; and thermal resistance between the TEM and the ambient. The outcome of the paper is an enhanced understanding of the role of heat spreading in the stable and efficient operation of contemporary PICs. This paper represents the initial results of an extensive programme of work on packaging-related aspects of next-generation PICs.