enhances absorption as the light is reflected gt 100 times within the resonant cavity between the top and bottom distributed bragg reflectors dbrs during operation the lasing power can be monitored remotely via transmission through an optical fiber or directly via an integrated detector fig1 b shows the refractive index profile and electric field intensity generated with a transmission matrix model of an embodiment of the mems tunable ec vcsel of fig1 a note that the composition grading is continuous but is represented as discrete steps in order to simplify the simulation in order to efficiently and selectively detect the signature absorption lines of the gas of interest an appropriate tunable optical cavity is designed the absorption cross section of o 2 around 760 nm is shown in fig2 a in one embodiment the laser linewidth u03b4 u03bb of a tunable vcsel is designed to be lt 1 pm within a full scanning range of at least 10 nm the actuation voltage is designed to be lt 10 v and the power consumption is designed to be on the order of tens of mws as shown in fig2 b the threshold gain vs wavelength is calculated showing the capability of continuous tuning over 20 nm within the wavelength range of interest dynamic mode hop free tuning is inherent in mems tunable vcsels due to the extremely short axial cavity length thus the wavelength resolution of the tunable laser is limited by the voltage source driving the electrostatic actuator the stability of the micromechanical system and the resolution of the read out system the presence of gases in the vcsel air gap affects the amplification factor or round trip enhancement of the power.