Development of Optical MUX/DEMUX on Silicon Optical Bench—Assembly Accuracies

An optical subassembly of MUX/DEMUX where optical devices are hybrid-integrated on a silicon optical bench (SiOB) using a passive alignment method is reported. A tight tolerance of positional and tilting angular accuracy is required for optical devices attachment in order to maximize the coupling efficiency. The critical positioning transverse to the optical axis merely depends on the symmetry, and accuracy of the position and shape of trenches. Any inaccuracy primarily affects the noncritical positioning, i.e., $z$-axis and $theta{ z}$, in the direction along the optical axis; misalignment accumulated and causes undesired insertion loss. All the piece parts, i.e., mirror, thin-film filters (TFFs), ball lens, SiOB, etc., have a defined tolerance in their dimensions and surfaces which increases the challenge in achieving high placement accuracy along the optical axis. The effects from these inherent inaccuracies of the position and shape of trenches and piece parts could be minimized by optimizing the adhesive volume, improve the bottom flatness, proper procedure selection. Misalignment at each axis, e.g., x-, y-, z-, $theta{ x}$, $theta{ y}$, and $theta{ z}$ was characterized and its effect to the coupling efficiency was discussed.