Dual-quadrature phasemeter for space-based interferometry

This letter presents a dual-quadrature phasemeter, an implementation of a phase-locked loop designed to track the phase of homodyne and heterodyne intersatellite laser links. Dual-quadrature phasemeters use dual-quadrature optical detection to enable an alternate phase readout scheme that operates with wider bandwidths and on signals with carrier-frequency differences down to dc. Analytical modeling demonstrates that dual-quadrature phasemeters overcome the bandwidth limitations of conventional phasemeters. Numerical simulations of noise linearity tests found that the phase-tracking error of the dual-quadrature phasemeter is less than 10 <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>microcycle</a:mi><a:mo>/</a:mo><a:msqrt><a:mi>Hz</a:mi></a:msqrt></a:math> in the presence of nonlinear cyclic errors. The dual-quadrature phasemeter enables exploration of an optical configuration for retroreflector-based space geodesy missions with architecture similar to that implemented in the Gravity Recovery and Climate Experiment Follow-On mission. One such alternate configuration is proposed that is capable of tracking satellite separation without requiring a frequency offset between local and incoming light, eliminating the need for optical frequency shifters.