'Cool' Fiber Light Source Inspected

A light source based on fiber-optic technology that could improve the inspection of food, produce, paper, currency, recyclables and other products was the topic of a presentation at OFC/NFOEC 2007.

Industrial processes for inspecting food products and other items now often use "line-scan" cameras, which record images of objects a line at a time, the way fax machines scan documents on a line-by-line basis. Rapid electronic processors then detect any problems and instruct mechanical actuators (such as air jets) to separate out unsatisfactory items.

Current line-scan cameras lack ideal light sources to image objects properly, said Princeton Lightwave of Cranbury, N.J. and OFS Labs -- a Somerset, N.J.-based division of Furukawa Electric. The companies described a fiber-optics-based solution, in which a bright light source, such as a laser, sends light through an optical fiber. Along the length of the fiber is an ultraviolet-light-treated region, or fiber grating, which deflects the light so it exits perpendicularly to the length of the fiber as a long, expanding rectangle of light. This optical rectangle is then collimated by a cylindrical lens so the rectangle illuminates objects of interest at various distances from the source. The bright rectangle allows line-scan cameras to sort products at higher speeds with improved accuracy, the companies said.

They said the new fiber-based light source combines features necessary for accurate and efficient scanning: uniform, intense illumination over a rectangular region; a directional beam that avoids wasting unused light by only illuminating the rectangle; and a "cool" light source that doesn't heat up the objects to be imaged. Typical light sources, such as tungsten halogen lamps or arrays of light-emitting diodes, lack at least one of these features, they said.

According to the researchers, this fiber-based device can be customized for a specific inspection application within four to six weeks, then manufactured for that application in 16 to 20 weeks.

Meeting Paper: G.E. Carver, K.S. Feder, P.S. Westbrook, "FBG Based Distributed Lighting for Sensing Applications," presentated March 29.

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