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No-Moving-Parts Optical Setups Scan Bar Codes

Photonics Spectra
May 2004
Daniel S. Burgess

Scientists at the University of Central Florida in Orlando have demonstrated a passive-optics no-moving-parts 1-D bar-code scanner. One of several designs for such systems offered by the team, it promises to enable the development of simple, eye-safe scanners with no moving parts for use in a variety of applications.

Nabeel A. Riza, head of the Photonic Information Processing Systems Laboratory at the university's School of Optics, explained that most existing bar-code scanners incorporate a spinning polygonal mirror element that makes the systems rather bulky for portable applications. Moreover, to compensate for beam-positioning inaccuracies and data reading error, the systems incorporate electronic controls that not only increase their bulk, but also add to their expense.

No-Moving-Parts Optical Setups Scan Bar Codes
The bar-code scanner replaces the rotating polygonal mirror with a wavelength-dispersive element. Tuning the wavelength of the laser source directs the infrared radiation to a different point on the bar code to be read. Courtesy of the University of Central Florida.

Riza and Zahid Yaqoob opted to investigate the suitability of a wavelength-multiplexed optical scanner for the reading of bar codes. In such a setup, the output of a tunable laser diode is directed via fiber to a planar wavelength-dispersive element, such as a type of holographic volume Bragg grating called a Dickson grating. The incoming radiation is deflected in a known, wavelength-dependent direction to the bar code to be read. The reflected signal carrying the information from the bar code returns along the same path, where it is dropped using an optical circulator or beamsplitter and directed to a photodetector.

Because each wavelength emitted from the laser is deflected in a different direction from the grating, each reaches a different section of the bar code and returns with information from that spot. Tuning the laser thus scans the read radiation across the code, and the variation in the optical power of the radiation returning at the photoreceiver, expressed as a function of wavelength, corresponds to the series of light and dark features of the bar code. Data acquisition rates depend solely on the speed at which the laser can be tuned, which is on the order of a microsecond for commercial telecom lasers, Riza said. Scanner control is simple, comprising only the electronic selection of the laser's wavelength.

No-Moving-Parts Optical Setups Scan Bar Codes
The experimental setup demonstrated perfect bar-code recovery, with no information lost between the original (left) and the read code (right).

The design lends itself to portable applications, as the components can be integrated onto a single board. It also can utilize any wavelength band, he said, enabling the development of eye-safe systems that prevent injury without the need for additional safety features. In their proof-of-concept system, the scientists employed a laser diode with an 80-nm tunable bandwidth centered at 1560 nm.

The researchers have patented the approach and foresee no technical limitations that might prevent its commercial use. They welcome feedback from the bar-code reader industry to accelerate the commercialization of the design.


GLOSSARY
bar-code scanner
An optical scanning device designed to read information printed in the form of bars of different size by detection and processing of the varying reflectivity of light in the bar code.
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