in an area of 2 u00d7 2 mm 2 and a thickness of 250 u03bcm application_number US 52915500 A description the layout of a first embodiment of an optoelectronic gas sensor based on optodes shown schematically in fig1 contains four equally large transmission branches a b c and d one of the transmission branches namely transmission branch c in this example is designed as a reference segment as indicated by diagonal shading the reference segment three optode segments each made of optode material 5 a 5 d and a photosensitive area 2 a 2 d of a photodiode shown with dotted lines below that are arranged in a star pattern around a central led 3 on a common substrate 1 individual transmission branches a d are separated by barriers 6 a 6 d located in the interspaces between the optode segments the sectional view of the optoelectronic gas sensor based on optodes shown in fig1 as seen along line ii u2014 ii of intersection in fig2 illustrates the integration of the photosensitive areas only areas 2 a and 2 c are shown here of p type si in substrate 1 made of n type si central led 3 is mirrorized on its top and bottom sides with a mirror layer 7 8 made of gold for example so the beams of light emitted by it.