Spectral discrimination using temporal mapping of light pulses through optical filters

An apparatus for determining the wavelength spectrum of an incident optical signal comprising:

• an array of apertures which capture the incident optical signal;
• a plurality of filters, each filter in the plurality of filters connected by an optical fiber to each aperture in the array of apertures, said plurality of filters having overlapping band pass regions;
• a plurality of optical delay lines, an optical delay line in the plurality of optical delay lines connected to a respective filter in the plurality of filters, the optical delay line imposing a time delay on light received from its respective filter dependent on wavelength, each optical delay line in the plurality of optical delay lines having an incrementally increasing fiber length to add an additional time delay to distinguish each filter in the plurality of filters;
• a plurality of separate optical lines, each separate optical line in the plurality of separate optical lines connected to an aperture in the array of apertures and each separate optical line in the plurality of separate optical lines having a uniform filter length different from the length of the plurality of optical delay lines;
• a first photo detector connected to the plurality of separate optical lines, said first photo detector generating a first electrical pulse upon receipt of the incident optical signal from any of the plurality of separate optical delay lines;
• a second photo detector connected to the plurality of optical delay lines, said second photo detector generating a second electrical pulse upon receipt of the optical signal from any of the plurality of optical delay lines;
• a parallel RLC circuit connected to the first photo detector and the second photo detector, said RLC circuit producing a first decaying sinusoidal signal upon receiving the first electrical pulse and a second decaying sinusoidal signal upon receiving the second electrical pulse;
• a zero crossing detector connected to the RLC circuit, the zero crossing detector generating a first zero crossing signal upon receiving the first decaying sinusoidal signal and generating a second zero crossing signal upon receiving the second decaying sinusoidal signal;
• a counter connected to the zero crossing detector, said counter generating a time delay count signal, said time delay count signal starting upon receiving the first zero crossing signal and stopping upon receiving the second zero crossing signal;
• and
• a microprocessor connected to said counter, the microprocessor programmed to convert the time delay count signal into a wavelength measurement.

A method for determining a wavelength spectrum of an incident optical signal comprising:

• receiving the incident optical signal;
• filtering the incident optical signal into separate wavelength bandwidth optical signals;
• imposing a time delay in the separate wavelength bandwidth optical signals, the time delay dependent upon wavelength of the separate wavelength bandwidth optical signals;
• measuring the time delay;
• and
• converting the time delay measurement into a wavelength measurement.

An apparatus for distinguishing incident light transmitted by a particular enemy transmitter in a group of enemy transmitters which transmit a spectrum of wavelength ranges, each enemy transmitter transmitting a distinguishable wavelength range in a spectrum of wavelength ranges, said apparatus comprising:

• a set of optical bandpass filters substantially fewer in number than the group of enemy transmitters, the set of optical bandpass filters receiving the incident light and separating the incident light into separate wavelength components spanning the spectrum of wavelength ranges of the group of enemy transmitters;
• means for generating a separate optical time delay for each optical band pass filter, said time delay distinguishing individual filters in the set of optical band pass filters and said time delay dependent on wavelength of light received from each bandpass filter in the set of optical band pass filters;
• and
• means for converting said time delay into a wavelength measurement, said wavelength measurement separating the distinguishable wavelength ranges enabling determination of which enemy transmitter in the group of enemy transmitters transmitted the incident light.