Experimental assessment of passive alignment of optical fibers with V-grooves on silicon optical bench

Alignment is one of the most critical issues in optoelectronics packaging. A slight offset in any direction will affect the performance of the photonic devices. Nowadays passive alignment of optical fibers is attracting more attention due to its low manufacturing cost and short processing time when compared with active alignment. The position of the optical fiber in passive alignment is defined by the geometry of a V-groove. The epoxy is usually dispensed in a glob-top manner. However, the optical fiber may be lifted up due to the buoyancy effect. An additional cover plate is usually required to press the fiber against the wall of the V-groove. Although the fibers can be well aligned by the aforementioned method, the applied stress may deform the fibers or damage the cover plate, leading to subsequent reliability issues. In this paper, a new method of dispensing epoxy with self-alignment capability is introduced. An innovative design of V-grooves on a silicon optical bench (SiOB) is developed. A "reservoir" is placed right next to the V-groove. The purpose of this reservoir is to let the epoxy flow into the gap between the optical fiber and the bottom of the V-groove. The excess epoxy may be drained away via the "canal". The reservoir/canal feature is patterned and etched together with the V-grooves so that there is no additional cost and time for fabricating the SiOB. It is observed that, if an appropriate amount of epoxy is flowing in the gap between the optical fiber and the V-groove, the optical fiber will not be lifted up by the buoyancy of the epoxy. On the contrary, the surface tension of running epoxy can pull down the fiber for passive alignment. With this new method, the optical fiber with greater than 60 mu m of initial misalignment can be aligned with the centre of the V-groove within 0.5 mu m of accuracy. In addition, detailed assessments will be made in this paper to evaluate the pros-n-cons of passive alignment of optical fibers with and without the cover plate.