**5. Challenges in fabrication**

The designing of the beam splitter and the mirror requires high precision of fabrication. Any small deviation from the design of the beam splitters leads to a decay of the optical performance. For instance, a beam splitter would present a wrong phase shift, optical loss, unequal splitting or even mirror like operation if its narrow veins are unintentionally narrower or removed. The Silicon rods must be uniform, smooth and vertical at the side wall in order to maintain the collimation effect throughout the device. The optical path length of the interfering signals should be maintained equal otherwise it will lead to additional phase shift.
