Fiber bundle imaging

We've put to use an under-appreciated property of the optical fiber bundles used in endoscopy. Fiber bundles are optical waveguides and as such they support discrete optical modes. Incoming light couples into these modes in a way that depends on the orientation of the incoming light. When light emerges at the output of the bundle, its spatial pattern within each fiber core depends on the orientation of the input light.

Generally, light that arrives at oblique angles (large angle of incidence) tends to exit close to the core/cladding interface (see left). On the other hand, normally incident input light exits near the center of the output core. The result of this observation is that we can use the modal patterns as a proxy for angular information. We use this approach to digitally modify the collection aperture of a bare fiber bundle in post processing. This is interesting because (1) fiber bundles have no physically adjustable collection aperture, and (2) we can use a constructed aperture to increase the depth of field (eDOF) and imaging quality (see below).

Antony Orth, Martin Ploschner, Ivan S. Maksymov, and Brant C. Gibson, "Extended depth of field imaging through multicore optical fibers," Opt. Express 26, 6407-6419 (2018)