Fiber-optics imaging

(optics) The formation of optical images by transmission through precisely aligned bundles of optical fibers; each fiber transmits one element of the image.

The use of fiber optics in image transmission, based on the ability of a precisely aligned bundle of optical fibers to transmit an image from one end of the bundle to the other. Each fiber transmits one element of the image so that the complete image is made up of a matrix of dots (pixels) which blend into a recognizable image like a halftone picture on a printed page.

Light is transmitted through individual fibers by means of total internal reflection from the fiber walls. For efficient transmission, each fiber has a highly transparent core (usually glass) coated with a layer (cladding) of lower refractive index (also usually glass). This cladding prevents light from leaking into neighboring fibers (crosstalk) and protects the core from contamination and wear. Fiber bundles may be either flexible or rigid. See also Crosstalk; Optical materials; Refraction of waves.

Flexible image bundles are used in a wide variety of industrial and medical fiberscopes or endoscopes to transmit the image from an objective lens at the distal end to an eyepiece in the control handle. Industrial fiberscopes ranging in length from 3 to 8 ft (1 to 2.5 m) are used in aircraft engine inspection, for example, examination of turbine blades. Longer industrial fiberscopes are used for pipe and weld inspection, including those in nuclear power plants.

Medical endoscopes range in size from less than 0.08 in. (2 mm) for viewing inside the arteries (cardioscope) to 0.6 in. (15 mm) for examining the colon (colonoscope). The latter has an operating channel large enough to perform surgery via remotely controlled forceps or electrosurgical snares. Intermediate-sized endoscopes are used to view the bronchi (bronchoscope), the kidneys (nephroscope), the bladder (cystoscope), the throat (laryngoscope), and the stomach (gastroscope).

Fused-fiber boules are the starting point for various image-transmitting components, including faceplates (windows) for image-intensifier tubes and cathode-ray tubes, image inverters (twisters), magnifiers, and rigid conduits. Image intensifier tubes are used in military night-vision devices, low-light television cameras, and astronomical telescopes. In a cathode-ray tube the fiber-optic faceplate is used to transmit the image on the phosphor screen to the exit face for printing directly onto photographic material. See also Cathode-ray tube; Light amplifier; Optical fibers.