Far-field and wavefront characterization of a high-power semiconductor laser for free-space optical communications

摘要

The far-field intensity and wavefront properties of the laser source are critical in determining the performance of a free-space optical communication system. The Spectra Diode Laboratories Model 5410 semiconductor laser is the laser of choice for NASA's Laser Communications Transceiver (LCT) program. This single-stripe, single quantum well AlGaAs laser is specified to emit 100 mW of continuous-wave (CW) output power in the lowest order spatial mode. The spatial pointing angle and far field beamwidth of this laser is characterized as a function of CW power and also as a function of temperature. In addition, the time-averaged spatial pointing angle and spatial lobe width were measured under intensity-modulated conditions. The measured pointing deviations were determined to be well within the pointing requirements of the LCT program. The wavefront quality of the laser has also been characterized using a computer-controlled Mach-Zehnder phase-shifting interferometer. The rms phase error over the entire pupil was measured as a function of CW output power. In addition, time-averaged measurements of the wavefront quality were also made under intensity-modulated conditions. The measured rms phase errors were determined to be well within the wavefront quality requirements of the LCT program.