Abstract: A gas sensor of the type having a housing defining a chamber within which light is transmitted from a source to a detector through an optical path, includes internal mirror portions having part ellipsoidal shape. Light is transmitted from a source to a detector via the reflective portions. The detector is arranged to sense light only from a limited range of angles, such that only light transmitted through a defined optical path reflected off the two reflective portions from the source reaches the sensor. This ensures that there is a constant optical path from the source to the detector, which improves the signal to noise ratio of the device.

Abstract: A gas sensor comprises a body on which is mounted an optical source and a detector means sensitive to light from the source. The body further comprises a channel arranged to admit gas, the channel comprising an elongated groove having reflective surfaces defining a folded optical path for light from the source. The groove is arranged as a serpentine shape or spiral shape so that light from the source to detector travels around the groove being internally reflected within the shape.