A receiver system for extracting data from a plurality of electromagnetic data signals collectively encoding the data, the system comprising: a phase modulator for receiving an electromagnetic beam , and generating an electromagnetic primary reference beam with a defined phase; one or more mixing units , each mixing unit being arranged to receive a respective one of the data signals and a reference beam, and to generate two mixed signals , the one or more mixing units including a first mixing unit for which the reference beam is the electromagnetic primary reference beam ; a plurality of detection units , each detection unit being arranged to receive a respective one of the data signals and a respective mixed signal from one of the mixing units , and to obtain a difference measurement indicative of a difference between the respective data signal and the respective mixed signal ; and a summation unit , arranged to receive the difference measurements generated by the detection units , and to obtain a summed difference value indicative of the sum of the difference measurements ; there being a plurality of mixing units , the mixing units being composed of the first mixing unit and one or more additional mixing units , the additional mixing units being arranged to receive, in addition to the respective data signal , a mixed signal generated by another of the mixing units : the mixing units being arranged in a hierarchical array having at least two successive layers , the first layer comprising the first mixing unit , and each other layer of the array comprising, for each mixing unit of the preceding layer, a corresponding pair of mixing units which each receive a respective mixed signal generated by that mixing unit of the preceding layer. a phase modulator for receiving an electromagnetic beam , and generating an electromagnetic primary reference beam with a defined phase; one or more mixing units , each mixing unit being arranged to receive a respective one of the data signals and a reference beam, and to generate two mixed signals , the one or more mixing units including a first mixing unit for which the reference beam is the electromagnetic primary reference beam ; a plurality of detection units , each detection unit being arranged to receive a respective one of the data signals and a respective mixed signal from one of the mixing units , and to obtain a difference measurement indicative of a difference between the respective data signal and the respective mixed signal ; and a summation unit , arranged to receive the difference measurements generated by the detection units , and to obtain a summed difference value indicative of the sum of the difference measurements ; there being a plurality of mixing units , the mixing units being composed of the first mixing unit and one or more additional mixing units , the additional mixing units being arranged to receive, in addition to the respective data signal , a mixed signal generated by another of the mixing units : the mixing units being arranged in a hierarchical array having at least two successive layers , the first layer comprising the first mixing unit , and the mixing units being arranged in a hierarchical array having at least two successive layers , the first layer comprising the first mixing unit , and each other layer of the array comprising, for each mixing unit of the preceding layer, a corresponding pair of mixing units which each receive a respective mixed signal generated by that mixing unit of the preceding layer. <EOS>