Speedy scanner

Engineers at UCLA have designed a bar code reader that is nearly a thousand times faster than any device currently in use.



The traditional bar code is read by optically scanning the code’s alternating light and dark bars and then using a computer program to convert the resulting image into digital form, essentially ‘decoding’ the information stored within the code.



Conventional bar code readers use one of two approaches to acquire an image of the bar code. In one, a laser beam is scanned over the code to measure the intensity of the light reflected back by the black-and-white pattern. In such devices, the activity of the mechanical scanner limits the image-acquisition speed to less than 1,000 frames per second. In the second type, a digital camera, such as a CCD- or CMOS-based device, takes a picture of the code, which is then recognised by the computer. The frame rate of these devices is limited to about 1,000 frames per second by the refresh rate of the CCD or CMOS image sensor.



The new imaging technique developed by UCLA postdoctoral fellow Keisuke Goda, graduate researcher Kevin K Tsia and electrical engineering professor Bahram Jalali uses an amplified dispersive Fourier transform to read bar codes at a frame rate of 25MHz – about a 1,000 times faster than current technology.



In use, the new CWEETS Scanner (chirped wavelength electronic encoded time domain sampling) amplifies and simultaneously maps a spectrally encoded bar code into a temporal waveform that is then captured with a single optical-to-electrical converter. This is in contrast to typical camera-based bar code readers, which require many optical-to-electrical converters – in other words, an array of pixels – to capture the image.



Dispersive Fourier transformation was originally developed by the UCLA team for ultrafast spectroscopy and has been used to demonstrate real-time spectroscopy with nanosecond time resolution.



The development of a bar code reader using this technology was motivated by the fact that the volume of information in bar codes is increasing and they are becoming integrated into real-time sensor networks. Similarly, there is a need for high-speed scanners for non-contact position and displacement sensing, as used in real-time inspection and monitoring in industrial applications.



Because the new UCLA scanner also amplifies the laser beam that is reflected by the bar code while the signal is still in the optical domain, it achieves a high sensitivity.



This technique prevents the inherent loss that the signal would otherwise experience during spectrum-to-time transformation. It also overcomes the thermal noise of the optical-to-electrical converters, a chronic problem that limits the sensitivity of virtually all scanners.



‘This is more than a fast scanner,’ said Goda. ‘It can detect ultrafast transient phenomena in real time that have not been observed by conventional techniques in the past. Therefore, it is not only useful for industrial applications, but also has much application to basic science.’



‘Eliminating the CCD camera and the mechanically steered mirrors from bar code scanners can prove valuable in applications that demand high-throughput bar code reading, such as industrial monitoring and retail supply line management,’ said Jalali, the principal investigator on the research. ‘The next step is to see whether the new scanner can be produced in a cost-effective manner.’



A more detailed technical description of the system can be found here.



Click here to view an animated film illustrating the concept of amplified dispersive Fourier-transform imaging.