Spectral discrimination using temporal mapping of light pulses through optical filters

An innovative technique exists for accurately determining the wavelength of a source using optical filters of broad and overlapping bandwidth coupled to various lengths of optical fibers. The input signal is split and passes through several independent filters, each centered at a different wavelength and with distinct spectral transmission characteristics. Time interpolation and resolution is performed through the appropriate selection of filter characteristics and fiber delay lengths. Associated with each selected optical filter are two optical fibers. One fiber is the same length for all filters and is denoted as the start or direct fiber. The second fiber is of unique length for each filter and is denoted as the stop or delay fiber. Incident light is simultaneously transmitted through all optical filters which allow the signal through its unique but broad band-pass. Light from all the filters is collected with no optical delay and summed to one photodetector. Similarly, light from each filter is collected through its unique optical delay and summed to another photodetector. The time difference between the direct and delay channels is affected by the composite shape of the pulse received by the detector in the electronic circuit. The resulting measured time difference is the weighted average of the transmission associated with each time delay. The wavelength of the unknown signal is unique and directly related to the resulting time difference between the direct and delay circuits.