Covariant optical module

Abstract

An optical module is disclosed wherein the thermal stress induced therein is substantially minimized so as to reduce the interference with the alignment of the optical component(s) enclosed therein. The optical module includes a housing having an assembly platform and sidewalls joined by brazing or soldering. However, because of mechanical, electrical and thermal considerations, the sidewalls and assembly platform are usually made of dissimilar materials. In one embodiment, the optical module includes an assembly platform made of a Cu--W composite, and sidewalls made of Kovar.RTM.. Although nonlinear, the thermal expansion of Kovar.RTM. is substantially linear away from its Curie temperature, with the slope proportional to the thermal expansion coefficient. On the other hand, the thermal expansion profile of Cu--W is substantially linear, with the thermal expansion coefficient determined by the ratio of Cu to W. Thermal stress is substantially reduced by setting the ratio of Cu to W so as to match the thermal expansion of Kovar.RTM. along the region below the Curie temperature of Kovar.RTM.. That is, the thermal expansion coefficient for each material is made substantially the same below the Curie temperature so as to maintain the Cu--W's covariance with Kovar.RTM.. A suitable, rigid braze material, such as Au--Sn, having a melting temperature below Kovaro.RTM.'s Curie temperature, is used to join the assembly platform to the sidewalls of the housing.