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Abstract

A waveguide spectrum analyser comprises an input waveguide (10) for receiving a beam of electromagnetic radiation to be spectrally analysed, a plurality of output waveguides (14, 16) which are single mode for wavelengths longer than a certain minimum, a substantially wavelength independent splitter (18) for splitting the input radiation between the single-mode output waveguides, and an array (24) of radiation-sensitive detector elements (30). Each output waveguide has a respective exit port (20, 22) facing the detector array so that radiation from the exit port is diffracted onto the array. The separation of the exit ports and the distance to the detector array is selected such that at least for a range of wavelengths longer than the certain minimum a plurality of interference fringes are produced at the array each extending across sufficient detector elements to allow spatial sampling of the fringes above the Nyquist rate. Data processing means (26) is provided for sampling the detector array to capture an image of the fringes and transforming the captured image data to the frequency domain, preferably using HTP and/or DFTS processing techniques.

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First Claim