Multicore fiber imaging

#The present invention relates primarily to multicore fiber imaging, such as used in endoscopy. In preferred forms methods are described for processing images captured with such systems to achieve an improved depth of field image or extract 3D information concerning the images, without requiring the addition of additional optical components.

#Multicore optical fibers (MOFs) are widely used as microendoscopic probes for imaging inside the body. Such MOFs contain thousands of waveguide cores, each 2-3 μm in diameter that relay light from inside the body to an imager that operates as an external detector. The imager generates an image of the distal end of the MOF. The image generated contains a plurality of pixels and includes a plurality of regions within it that each correspond to a waveguide core. Each core will be imaged over a plurality of pixels in the image. The digital image will also include pixels that correspond to interstitial space between said waveguide cores. FIG. 1 illustrates a portion of such an image. In FIG. 1 the contiguous black image portion 2 corresponds to pixels imaging the interstitial space between wave guide cores. The lighter regions (e.g. 4) of varying grey levels correspond to individual waveguide cores, the level of illumination thereof corresponding to the light received at the distal facet of each fiber.

#Developments in MOF techniques have included processing of received data to improve image quality, including filtering techniques to deal with image artefact produced by the interstitial regions between the fiber cores, that can otherwise render as distracting patterns such as visible grids or Moiré effects. U.S. Pat. No. 5,751,340, for example, discloses reducing the contrast of the grid pattern components by suitable filtering, such as the applying a dilation process to interpolate from the brighter center of each fiber into the neighbourhood interstitial regions.

#FIG. 1 represents a portion of a raw image obtained from a MOF by the imager, showing the MOF cores and interstitial areas.

#FIG. 2 is a schematic MOF imaging system, used in capturing images that are can be processed according to an embodiment of the present invention.

#FIG. 3 is a flowchart of a first image processing method according to an embodiment of the present invention.

#FIG. 2 illustrates a schematic of an exemplary optical set up of a MOF in an imaging system 8 arranged to image a prepared sample to illustrate embodiments of the present invention. The imaging system can be an endoscopy system. Preferably it is coupled to, or includes, a data processing system 400 for processing image data from the imaging system 8.

#The proximal facet of an MOF 10 (e.g. a (Fujikura FIGH-30-600S or FIGH-10-350S) is illuminated with incoherent light from a LED 12 (e.g. Thorlabs M565L3 LED, 565 nm center wavelength). Total illumination intensity at the distal end of the MOF is ˜10 μW in this example. Light from the LED 12 is collimated with a collimating lens (CL) via a mirror (M), a 200 mm lens (L), a polarizer (P1), a beam splitter (BS) and a 20× objective lens (OBJ). The illumination source 12 is linearly polarized in order to facilitate rejection of light reflected off of the proximal facet of the MOF. Both ends of the MOF 10 and the sample 14 are affixed to independent 3-axis translation stages (xyz). There is preferably no lens between the distal MOF facet and the sample, although some embodiments of the present invention may use such a lens arrangement.

#Light reaching the distal end of the MOF illuminates the sample 14, after which reflected light couples back into the MOF 10. The back-reflected light couples into a variety of modes depending on its angle of incidence at the distal fiber facet. The output intensity pattern within multiple cores at the proximal end is imaged via a microscope objective (e.g. Olympus Plan Achromat 20× 0.4 NA), the beam splitter (BS), a 200 mm tube lens (TL) and a second polarizer (P2). The polarization axes of P1 and P2 are orthogonal to filter out reflected light at the proximal facet. The image is captured by a camera (CAM) (e.g. monochrome, camera with a 10 ms integration time, Thorlabs DCC3240M). In this example, the core and cladding refractive indices of the MOF are ncore=1.5 and nclad=1.446, respectively, resulting in an NA of 0.398, that roughly matches the 20×, 0.4 NA objective lens (OBJ).