Speckle reduction in OCT with multimode source fiber

Speckle noise in OCT images originates in the high spatial coherence that allows interference between light backscattered from the tissue specimen. Speckle reduction techniques on which many investigators have reported all rely on averaging independent intensity images of the speckle field. Recently, we completed an experiment to test speckle reduction by averaging independent intensity images formed by incoherent spatial modes emitted from a broadband light source. Broadband light coupled into a multimode optical fiber produces a number of spatial modes that propagate along the waveguide at distinct velocities. When the spatial modes propagate length, modes become mutually incoherent When the multimode fiber is placed in the source path of a Michelson interferometer, each spatial mode produces an intensity image of an independent speckle field. To illustrate speckle averaging using independent spatial modes, we recorded low-coherence interferograms of a scattering metallic surface using single mode and multimode source fiber. The interferogram recorded using a single mod e source fiber is indicative of that observed by conventional OCT. Speckle noise in the interferogram recorded using the multimode source fiber is substantially reduced compared to the single mode case.