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Optical System Enables 2-D Scanning

Photonics Spectra
Dec 2001
Gary Boas

In pursuit of new e-book technology, researchers have designed a novel optical system that scans in two dimensions. Although developed for a display in a portable document reader, the designers say that the lens system can be used for any application where a constant focal plane is required for a changing image plane.

techOptical1.jpg

Researchers have developed an optical system that scans both laterally and longitudinally (top) for use in a document reader. They produced versions of the system's lenses in glass (bottom left) and plastic (bottom right). Courtesy of Sergio Vázquez-Montiel.

Hoya Corp. of Tokyo wanted a portable reader for the download and display of electronic versions of books, newspapers and other media. For ease of reading, the company's researchers devised an eye-friendly liquid crystal display (LCD) to simulate the print on paper. It uses an 830-nm laser diode to address the pixels and is erased electronically. At first, the researchers considered the optical systems in laser printers as a model, but the scanners in laser printers write only on one line, with the longitudinal movement of the paper produced mechanically.

In conjunction with the Instituto Nacional de Astrofísica, Optica y Electrónica in Puebla, Mexico, Hoya developed the new optical system, which the researchers dubbed Focoiva for "focal constant and image variable." Focoiva scans in both directions, using a galvanometric mirror to move the beam across the page, like the scanner in a laser printer, and a flat mirror that moves longitudinally under the LCD, reversing the mechanical movement of the page in a printer.

To maintain focus, the system has to account for the continually changing relative position of the LCD to Focoiva's lenses. But when a lens is moved to change the position of the image plane, the effective focal length and the size of the spot change. To overcome this, Focoiva's lenses move simultaneously but at different velocities and even in different directions, so that one lens moves the image while the other maintains a constant effective focal length.

The developers built two versions of Focoiva for the final design of the reader: one with glass lenses and one with plastic. In the glass version, the image can be moved in the longitudinal direction from 300 to 600 mm, vs. 200 to 450 mm in the plastic. The plastic version, lower in production costs, likely will be used in the commercial product.

Potential for 3-D

Sergio Vázquez-Montiel, a researcher at the institute who worked on the project, said that there are many potential applications of Focoiva, including those that require three dimensions, which can be accomplished simply by adding another galvo mirror to the system. He added, however, that Hoya has no commercial plans for the system other than for use in the reader.


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