Abstract
Purpose: :
Adaptive optics is a technique to correct wavefront aberrations in real time and widely used in retinal imaging modalities. Liquid crystal spatial light modulators (LC-SLMs) have many advantages as an alternative to deformable mirror devices from the viewpoint of compactness, low cost, low power consumption and high resolution. However, wavelength dependency of the phase modulation of LC-SLMs restrains applications of liquid crystal adaptive optics to multi-spectral imaging. In order to circumvent the problem, we propose an open-loop adaptive optics system with an LC-SLM as a wavefront corrector.
Methods: :
We developed a retinal imaging system of flood-illumination type by using adaptive optics with a liquid crystal on silicon spatial light modulator (LCOS-SLM, Hamamatsu). Fiber coupled laser with a broad spectrum was used for illumination and a highly sensitive electron multiplication CCD camera was used for retinal imaging. Ocular aberrations were measured by using a Shack-Hartmann sensor as the detector and a super luminescent diode (SLD) at a wavelength of 780 nm as the optical beacon. Measured aberrations were calibrated with the look-up-table of wavelength dependency of the LCOS-SLM and the LCOS-SLM was operated according to the calibrated compensation pattern. The system was operated with open-loop control, instead of feedback control.
Results: :
High-resolution retinal imaging was achieved at different wavelengths by operating the open-loop adaptive optics system. However, the linewidth of the imaging light is limited to relatively narrow region (less than 40 nm) for high-resolution imaging.
Keywords: retina • aberrations • macula/fovea