An ultrafast barcode reader using amplified dispersive Fourier transform

Dispersive Fourier transformation (FT) is a powerful technique in which the spectrum of a pulse is mapped into a time-domain waveform using chromatic dispersion. It replaces a diffraction grating and detector array with a dispersive fiber, single photodetector, and digitizer. This simplifies the system, and more importantly, enables fast real-time spectroscopy . Dispersive FT has also been used for optical coherence tomography. Here we propose and demonstrate a novel imaging method using dispersive FT for ultrafast displacement sensing and barcode reading. This method, which we refer to as chirped wavelength encoding and electronic time domain sampling (CWEETS), exposes a sample to a broadband pulsed probe beam which is spatially dispersed by a diffraction grating so that each separated wavelength of the probe beam is incident on a different part of the sample along a transverse line on the sample. The reflectivity profile of the sample is encoded into the spectrum of the reflected light from the sample. It is then subjected to dispersive FT using group-velocity dispersion to detect the reflectivity profile of the sample in the time domain. To overcome the loss of the dispersive element, we introduce Raman amplification in the same medium, resulting in greatly enhanced resolution.