A spectrometer comprising: a substrate; a waveguide provided on the substrate and having a first end for receiving electromagnetic radiation and a second end; and a plurality of resonators provided on the substrate and coupled to the waveguide, each of the resonators being resonant at a predetermined wavelength of the electromagnetic radiation; characterised in that the spectrometer comprises: an anti-reflection region provided at the second end of the waveguide on the substrate, the length and the width of the anti-reflection region being optimised to suppress back reflection of radiation that reaches the second end, wherein the waveguide is configured to guide electromagnetic radiation of a predetermined range of wavelengths, and the width of the anti-reflection region is substantially larger than a mean wavelength of the predetermined range of wavelengths of electromagnetic radiation in the anti-reflection region, and the length of the anti-reflection region is substantially longer than the mean wavelength of the predetermined range of wavelengths of electromagnetic radiation in the anti-reflection region, such that electromagnetic radiation entering the anti-reflection region from the waveguide becomes unguided and is absorbed in the anti-reflection region. a substrate; a waveguide provided on the substrate and having a first end for receiving electromagnetic radiation and a second end; and a plurality of resonators provided on the substrate and coupled to the waveguide, each of the resonators being resonant at a predetermined wavelength of the electromagnetic radiation; characterised in that the spectrometer comprises: an anti-reflection region provided at the second end of the waveguide on the substrate, the length and the width of the anti-reflection region being optimised to suppress back reflection of radiation that reaches the second end, wherein the waveguide is configured to guide electromagnetic radiation of a predetermined range of wavelengths, and the width of the anti-reflection region is substantially larger than a mean wavelength of the predetermined range of wavelengths of electromagnetic radiation in the anti-reflection region, and the length of the anti-reflection region is substantially longer than the mean wavelength of the predetermined range of wavelengths of electromagnetic radiation in the anti-reflection region, such that electromagnetic radiation entering the anti-reflection region from the waveguide becomes unguided and is absorbed in the anti-reflection region. an anti-reflection region provided at the second end of the waveguide on the substrate, the length and the width of the anti-reflection region being optimised to suppress back reflection of radiation that reaches the second end, wherein the waveguide is configured to guide electromagnetic radiation of a predetermined range of wavelengths, and the width of the anti-reflection region is substantially larger than a mean wavelength of the predetermined range of wavelengths of electromagnetic radiation in the anti-reflection region, and the length of the anti-reflection region is substantially longer than the mean wavelength of the predetermined range of wavelengths of electromagnetic radiation in the anti-reflection region, such that electromagnetic radiation entering the anti-reflection region from the waveguide becomes unguided and is absorbed in the anti-reflection region.