Chip-on-chip 3D optical interconnect with passive alignment

TO-can is commonly used for packaging vertical cavity surface emitting laser (VCSEL) devices, which are wildly used as a laser source in various optoelectronic applications. Non-reworkable laser welding of the TO-can and the tight tolerance of the die placement cause the packaging process of VCSELs expensive and time consuming. Since VCSELs are a surface emitting device, it is relatively difficult to package them with a silicon optical bench (SiOB), which is compatible with V-groove passive alignment. Therefore, active alignment is usually required for coupling VCSELs with optical fibers. In this paper, a chip-on-chip 3D optical interconnect is introduced. The package consists of a SiOB and a flip chip mirror carrier. The light beam is deflected by two pairs of micro-mirrors on both the SiOB and the flip chip mirror carrier. The optical fibers are passively aligned with the pre-defined V-grooves on the SiOB. The mirror pairs on both the SiOB and the flip chip mirror carrier are self-aligned during the reflow of flip chip solder joints. The light is coupled form one optical fiber to another fiber through an "overpass" type of 3D optical path. The prototype shown in this paper is mainly for illustration purpose. In practice, the flip chip mirror carrier may be replaced by other devices such as VCSELs and photo detectors. The presented chip-on-chip 3D optical interconnects are suitable for coupling VCSELs or photo detectors with optical fibers. It is a low cost manufacturing process compared with the TO-can, which requires active alignment. Also, the potential capability to accommodate the small form factor laser array may be another major advantage of the proposed package.