Optical power transmission in a polygon mirror-based swept source optical coherence tomography system

Swept Source Optical Coherence Tomography (SS-OCT) relies on the rapid tuning of a broadband light source to produce narrow laser linewidths. Imaging speed is governed by the sweeping frequency of the source and the axial resolution is given by the total bandwidth generated. Mechanical, free space methods, employing rotating polygonal mirrors with a pair of telescopically arranged lenses, can achieve tuning speeds in excess of 100 kHz. Their success relies upon maximising the light throughput of the swept spectrum by reducing the effects of aberration and vignetting caused by the lens design and the geometrical properties of the polygon respectively. However, these properties impose constrictions on the spectral filter’s design and care must be taken when building the filter to avoid unnecessarily limiting the performance of the system. This paper presents some of the initial stages of a much larger study into the optimisation of such systems. Theoretical work has been confirmed by experimental observations and compared with ideal simulations for a spectral filter consisting of a dispersive element, a double lens telescope, arranged in a Littman configuration, and a 72-facet, offaxis polygon mirror with end reflector. A non-linear relationship between the linewidth’s location on the telescope in time with the rotation of the polygon was observed and a first approximation for the tuned wavelength with respect to the polygon rotation angle was found. These observations, coupled with ongoing research, will lead to a complete description of polygon based scanners and how their performance can be optimised in future designs.