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Integrated optical bench for a CO2 gas sensor

The reliable, high resolution concentration measurement of carbon dioxide is of critical importance in several life sciences and advanced life support related applications ranging from cabin air quality on extended duration space flights to monitoring and controlling plant growth and efficiency in closed life support systems. The design of a LIGA (German acronym for lithography, electrodeposition and plastic molding) micromachined, integrated optical bench for a carbon dioxide concentration sensor, based on the principle of infrared absorption, is presented in this paper as a compact solution to the need for high resolution CO2 instrumentation. The micromachining approach takes advantage of the superior performance of optical infrared absorption sensing technology. In addition, creating an integral, micro- fabricated optical bench along with the source, detector and other necessary components on the same substrate will eliminate the size and alignment problems of the current designs. The design of the CO2 sensor uses a folded optical system consisting of five parallel micro- mirrors placed 1.6 cm apart. A parametric evaluation of the beam divergence shows that the use of 1000 micrometers mirrors and a laser beam with a spot radius of 300 micrometers would result in a sensor design that can easily be fabricated by the LIGA process.