Light from a fibre
Intereference pattern of blue laser light from multiple cores of a bespoke optical fibre. Each core has been acid etched, forming a concave pit. Each concave pit acts somewhat like a lens. The far end of the fibre is illuminated with a laser source over multiple cores. The light exiting the end of the fibre spreads out due to the lensing, and light from multiple cores interferes to form a complex pattern. In the images, when focused on the fibre end (top left) light is seen exiting the cores. When focus is backed away from the fibre (progressing down images and to main image) light is seen to spread out from the cores until the far field interference pattern is observed in the main image.