[OPTICAL REVIEW Vol. 8, No. 2 (2001) 101-106]
Development of a Two-Dimensional Bar-Code Detection System Using Multi Laser Diodes with Time-Sharing Light Emission Operation
Hiroo WAKAUMI1 and Chikao NAGASAWA2
1Tokyo Metropolitan College of Technology, 1-10-40, Higashi-Ooi, Shinagawa-ku, Tokyo, 140-0011 Japan, 2Tokyo Metropolitan University, Graduate School of Engineering, 1-1, Minami-Ohsawa, Hachioji, Tokyo, 192-0397 Japan
(Received July 24, 2000; Accepted December 13, 2000)
A new high-speed two-dimensional bar-code detection system using multi laser diodes with time-sharing light emission operation has been developed. A bias current allowing the laser diode to improve the light output rise time was optimized to slightly below the threshold of the diode, so that channel cross-talk among three-line bar-code signals caused by the bias light can be kept small and a high-speed pulse modulation operation can be achieved. The prototype system for a three-line bar code with spatially overlapping laser-diode heads has achieved an effective scanning speed two and nine tenths times that of conventional scanners. It is estimated that the number of time-sharing light emission laser diodes can be increased to at least four when the current photodetection amplifier with a bandwidth of 6.4 MHz is used. This number can be improved to six by using photodetection amplifiers with double the bandwidth of the present ones.
Key words : optical systems, laser diodes, detection, scanner