Patent ID: 7508519

Claim:
An apparatus for sensing plural gases, comprising: a photogenerator, for emitting a signal light; a planar lightwave circuit having a sensing pathway and a reference pathway, being coupled to the photogenerator by an input port thereof for enabling the sensing pathway and the reference pathway to receive the signal light and thus generate a sensing signal and a reference signal respectively; wherein the sensing pathway and the reference pathway respectively has at least an optic gap and at least an output port; and at least a photodetector, each being disposed at one of the output port selected form the group consisting of the output ports of the reference pathway and the output ports of the sensing pathway, for converting the sensing/reference signal into an electric signal; wherein the sensing pathway and the reference pathway have at least two waveguide branches respectively, and the waveguide branches of the sensing pathway and the waveguide branches of the reference pathway are merged with the input port means for sensing the gas in said optic gap in the sensing pathway using the electric signals from the photodetector in the sensing an reference pathways.