Speckle phase noise in coherent laser ranging: fundamental precision limitations

Published

August 8, 2014

Author(s)

Esther Baumann, Jean-Daniel Deschenes, Fabrizio R. Giorgetta, William C. Swann, Ian R. Coddington, Nathan R. Newbury

Abstract

Frequency-modulated continuous-wave laser detection and ranging (FMCW LADAR) measures the range to a surface through coherent detection of the backscattered light from a frequency-swept laser source. The ultimate limit to the range precision of FMCW LADAR, or any coherent LADAR, to a diffusely scattering surface will be determined by the unavoidable speckle phase noise. Here, we demonstrate the two main manifestations of this limit. First, frequency- dependent speckle phase noise leads to a non-Gaussian range distribution having outliers that approach the system range resolution, regardless of the signal-to-noise ratio. These outliers are reduced only through improved range resolution (i.e., higher optical bandwidths). Second, if the range is measured during a continuous lateral scan across a surface, the spatial pattern of speckle phase is converted to frequency noise, which leads to additional excess range uncertainty. We explore these two effects and show that laboratory results agree with analytical expressions and numerical simulations. We also show that at 1 THz optical bandwidth, range precisions below 10 μm are achievable regardless of these effects.

Citation

Optics Letters

Volume

39

Pub Type

Journals

Download Paper

DOI Link

Keywords

ladar, fmcw, frequency comb, speckle

Citation

Baumann, E. , Deschenes, J. , Giorgetta, F. , Swann, W. , Coddington, I. and Newbury, N. (2014), Speckle phase noise in coherent laser ranging: fundamental precision limitations, Optics Letters, [online], https://doi.org/10.1364/OL.39.004776 (Accessed October 20, 2025)