A method of manufacturing a Fabry-Perot interference filter includes a forming step of forming a first thinned region, a first mirror layer, a sacrificial layer, and a second mirror layer are formed on a first main surface of a wafer, and the first thinned region in which at least one of the first mirror layer, the sacrificial layer, and the second mirror layer is partially thinned along each of a plurality of lines is formed; a cutting step of cutting the wafer into a plurality of substrates along each of the plurality of lines by forming a modified region within the wafer along each of the plurality of lines through irradiation of a laser light, after the forming step; and a removing step of removing a portion from the sacrificial layer through etching, between the forming step and the cutting step or after the cutting step.

An optical system (230) comprises an image sensor (231), a reference sensor (232), and an optical multiplexer (300). The optical multiplexer defines a first area for receiving a first portion of incoming light and a second area (320) for receiving a second portion of the incoming light. The second area radially surrounds the first area. The optical multiplexer is arranged to direct the first portion of the incoming light to the image sensor (231) and the second portion of the incoming light to the reference sensor (232). The optical multiplexer may take the form of a pinhole minor (300).