OPTICAL MICROPHONE ASSEMBLY

An optical microphone assembly (38) comprises a rigid substrate (42); an interferometic arrangement, a light source (48), at least one photo detector (50) and an enclosure (74). The interferometric arrangement comprises a membrane (46) and at least one optical element (62) spaced from the membrane (46), wherein the at least one optical element comprises a surface (60) of the substrate (42) and/oris disposed on a surface (60) of the substrate (42). The light source (48) is arranged to provide light to the interferometric arrangement such that a first portion of the light propagates along a first optical path via the interferometric arrangement and a second portion of the light propagates along a second different optical path via the interferometric arrangement, thereby giving rise to an optical path difference between the first and second optical paths which depends on a distance between the membrane (46) and the optical element (62). The photo detector(s) (50) are arranged to detect at least part of an interf