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S. A. Burns, W. Zou, H. Song, Z. Zhong; Wavelength Variable Adaptive Optics Imaging Using a Supercontinuum Light Source. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1053.
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To develop a wavelength variable Adaptive Optics SLO using a supercontinuum light source.
Supercontinuum light sources are capable of producing single mode optical output simultaneously over a very broad wavelength range. This raises the possibility of using such a source to provide variable wavelength composition imaging in a retinal imaging device. These sources typically use a pulsed laser and a nonlinear optical fiber to generate the supercontinuum light. We used a supercontinuum source (Fianium, Inc) that generates 4.7 W of light between 550 nm and 2000 nm using a photonic crystal fiber pumped by a 40 MHz fiber based laser. To eliminate the long wavelengths we implemented a double pass, two prism dispersion system that allowed us to eliminate all wavelengths longer than approximately 1050 nm, by directing them to a beam dump. We then expanded the laser beam and used interference filters to shape the spectrum, and then launched the desired wavelengths into a single mode fiber, which was used to replace our standard SLD light source.
We were able to generate high quality retinal images. The current study used either a relatively narrow bandwidth (for instance a bandpass filter; 840 nm, 20 nm wide) to image the retina, or a broad band illumination (from approximately 700 nm to 900 nm) to image the retina. There were no detectable artifacts arising from an interaction between our 13 MHz pixel clock and the 40 MHz pulse repetition rate, presumably due to dispersion in the fibers and prisms. Wavelength output of the system could be varied from 580 nm to >900 nm (although human retinal images performed human imaging only between 700 and 900 nm). Illumination was sufficient to obtain images of cone photoreceptors, even in a non-dilated eye. The broader band images were very smooth and showed some changes in blood vessel contrast relative to narrower band images, presumable due to the change in absorption spectrum of hemoglobin over this range.
The supercontinuum light source appears to be an excellent source for providing flexible wavelength imaging in scanning confocal retinal imaging systems. This could allow either the use of multiple fixed wavelengths (for instance for two imaging wavelengths and a wavefront sensor beacon) or for tunable multi-spectral imaging.
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