In a method or system for interrogating an optical chip (50), the optical chip (50) is illuminated with input light (30) and a spatially resolved image (50i) of the output light (31,32) is measured from the optical chip (50). The output light (31,32) is imaged together with a reflection of the input light (30). For example, this can be used to establish, improve, or maintain alignment of the input light (30) on a sensor input port (51) of the optical chip (50). The same detector (17) measures the spatially resolved image and a spectral response of the optical chip (50).