OPTICAL MICROPHONE SUBSTRATE

An optical microphone assembly including a substrate having a first and second substrate portions with the first substrate portion being thinner than the second substrate portion, an interferometic arrangement including a membrane and at least one optical element including a surface of the first substrate portion and/or is disposed on a surface of the first substrate portion, and the at least one optical element does not include a diffractive optical element formed as a plurality of holes through the first substrate portion. The optical microphone assembly further includes a light source 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 and the optical element, and with at least one of the first and second paths passing through the first substrate portion, and at least one photo detector arranged to detect at least part of an interference pattern generated by said first and second portions of light dependent on the optical path difference.