Amplified Dispersive Fourier-Transform Imaging for Ultrafast Barcode Reading
The optical source is a mode-locked laser that generates a pulse train. The diffraction grating spatially disperses and separates the incident pulse into many subpulses of different colors, which are projected onto the sample (a test barcode) along a transverse line on the sample. The reflectivity profile of the sample is encoded into the spectrum of the back-reflected light from the sample. The returning subpulses reform a short pulse which travels back and is directed toward a dispresive Fourier transformer which consists of a high dispersive fiber. The dispersive Fourier transformer maps the spectrum of the input pulse into a temporal waveform which is captured by a single photodetector and digitized by a high-speed oscilloscope, performing pulse-by-pulse spectrum analysis. Within the process of the dispresive Fourier transformation, distributed Raman amplification is simultaneously implemented to not only compenstate for the detrimental optical loss in the fiber, but also enhance the detection sensitivity. The oscilloscope displays the spectrally encoded spatial information of the sample (the barcode pattern) in the time domain. Typically, the pulse repetition rate of mode-locked lasers is on the order of 10 MHz, meaning that the test barcode can be read only within 100 ns. Other than barcode reading, the amplified dispersive Fourier-transform imaging technique has numerous industrial applications including displacement sensing and optofluidics.
The animated film was created by Tiffany Lay. A paper that describes the invented imaging technique has been published in
Applied Physics Letters
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