Patent attributes
An annular optical spacer includes a first side portion, a second side portion, an outer annular portion, an inner annular portion and an anti-reflective layer. The second side portion is opposite to the first side portion. The outer annular portion connects the first side portion with the second side portion. The inner annular portion connects the first side portion with the second side portion. A vertical distance between the inner annular portion and a central axis of the annular optical spacer is shorter than a vertical distance between the outer annular portion and the central axis of the annular optical spacer. The inner annular portion includes at least one rugged surface. The rugged surface includes a plurality of annular protruding structures, and the annular protruding structures are coaxially arranged around the central axis. The anti-reflective layer is on top of the rugged surface.