Atmospheric methane trends over the last few years have been increasing at a rate of 7-12 parts per billion (ppb) per year after brief a pause in the first decade of this century. The reasons for the pause and subsequent increase remains unclear. Thus, there is a critical need for additional, precise and accurate methane observations to understand the natural and anthropogenic processes that drive the trends in atmospheric methane and to constrain its sources, and sinks. At NASA Goddard Space Flight Center (GSFC), in collaboration with Freedom Photonics Inc., we have been developing a lidar to measure atmospheric methane using Integrated Path Differential Absorption (IPDA) from an airborne platform as a precursor to a future space mission. In this paper we present the design of a laser transmitter operating at ~1651 nm based on a newly developed Distributed Bragg Grating (DBR) seed laser and an Optical parametric oscillator (OPO). The DBR is rapidly step-tuned over the methane absorption at several discrete wavelengths. This multi-wavelength approach enables us to sample the entire methane lineshape and reduce systematic errors.
Freedom Photonics and the University of Virginia have developed high power, wide-bandwidth balanced photodetectors based on vertically-illuminated modified uni-traveling carrier (MUTC) photodiode technology. These balanced pairs are based on single photodiodes which achieve 3-dB bandwidths of 25 GHz, coupled with output powers above 23 dBm, as well as 35 GHz photodiodes with output powers greater than 19 dBm. A balanced configuration of these devices offers advantages in common-mode noise reduction, increasing the signal-to-noise ratio. In a photonic link, high-power, balanced photodiodes support high link gain and large bandwidths, while the high linearity of these devices maximizes spurious-free dynamic range (SFDR).