Multi-span sensing using wavelength / frequency multiplexing, synchronized receiver, and coherent signal processing

A receiver system for distributed acoustic sensing (DAS), comprising:

• a separating component to receive a reflected signal, distributed over a plurality of wavelengths, and to separate the reflected signal according to wavelength into a plurality of optical signals;
• a coherent mixer array comprising a plurality of coherent mixers to mix the plurality of optical signals with a given local oscillator signal at the respective plurality of wavelengths, into a plurality of mixed optical signals;
• a photodetector array comprising a plurality of photodetectors to receive, the plurality of mixed optical signals and convert the plurality of mixed optical signals into a plurality of electrical signals, respectively;
• an analog to digital converter (ADC) assembly comprising a plurality of ADCs, wherein a first ADC of the plurality of ADCs is to sample a first electrical signal of the plurality of electrical signals, and output the electrical signal as a digital signal, wherein the digital signal is associated with a given wavelength of the plurality of wavelengths;
• a clock to send a clock signal to the first ADC to determine a sampling instance for the first ADC, wherein the sampling instance of the first ADC is separated from a sampling instance of a second ADC by a determined delay increment;
• and
• a digital signal processing (DSP) block, wherein the DSP block is configured to process the digital signal, wherein the digital signal, associated with the given wavelength, is rearranged to indicate a location associated with a disturbance that generates a component of the reflected signal.