The low intensity regions existed around the singular point of optical vortex (OV) beams influence the position detection accuracy of phase singular points, especially for OVs of large topological charge. A new method using Shack-Hartmann wavefront sensor (SH-WFS) is proposed to solve this problem. In the method, we combine several phase slopes obtained at individual lenses of a lens array into one to avoid the influence of the low intensity region and use correlation matching with pre-calculated simulation data to get the accurate singular point position. The experimental results show that the position detection precision of this method is maintained less than 0.2 in unit of lens-size for OVs of charges -20 to 20.
We propose a simple method of realizing an accurate position detection of phase singularities in an optical vortex (OV) beam using a Shack–Hartmann wavefront sensor (SH-WFS). The method calculates circulations which are the discrete contour integrals of phase slope vectors measured by the SH-WFS and then determines the accurate positions of the singular points by calculating the centers-of-gravity with a fixed window size around the local peak of the circulation distribution. We use closed paths that connect the centers of eight-connected, instead of 2×2-neighboring lenslet apertures for calculating the circulations. Both the numerical analysis and proof-of-principle experiment were performed to confirm the measurement accuracy. In experiments, the positions of singular points in OV beams generated by a liquid-crystal-on-silicon spatial light modulator were measured. The root-mean-square error of the position measurement was approximately 0.09 in units of the lens size of the lenslet array used in the SH-WFS. We also estimated the topological charges of the singular points being detected based on the peak circulations, and the results agreed well with theoretical ones. The method achieves both rapid implementation and sublens-size spatial resolution detection and is suitable for applications that require real-time control of OV beams.
We propose a new method, based on Shack-Hartmann wavefront sensor (SH-WFS), to achieve high-accuracy position detection of phase singular points of optical vortex (OV) beam. The method calculates evaluation values related to phase slopes of incoming wavefront from Hartmanngram recorded by SH-WFS, and then determines precisely the position of the singular points by calculating the centroid of the 3x3-evaluation-value distribution centered at peak position. A main point is that, in evaluation-value calculation, we use a closed contour connecting the centers of 8-connected, instead of 2x2, lenslet apertures. Theoretical analysis shows that the measurement errors can be greatly reduced in comparison to that of 2x2 closed contour. Proof experiments were performed to confirm its accuracy by measuring singular points of OV beams generated by a liquid crystal on silicon spatial light modulator. The root-mean-square error of the measured position of singular points was approximately 0.052, in units of the lens size of lenslet array used in the SH-WFS. The method achieves fast-speed and sub-lens size spatial resolution detection, is suitable for real-time control applications.
An adaptive optics scanning laser ophthalmoscope (AO-SLO) using a liquid-crystal spatial light modulator was
developed. For routine clinical applications, long-term stability of the AO system is very important because unavoidable
eye movement may degrade the instrument's performance. We studied the long-term performance of the aberration correction with healthy human eyes. Retinal image acquisition and AO data collection were performed simultaneously for periods of several minutes. We confirmed that, for more than 90% of the periods, the root-mean-square errors of residual wavefront were below the Marechal criterion. Drifts and microsaccades of fixational eye movement were examined using retinal images and residual aberrations. The results showed significant correlation between the transverse shift of retinal image and the low-order residual wavefront aberration during the drifts.
We have developed a liquid-crystal-on-silicon spatial light modulator (LCOS-SLM) and examined its performance
capability as a wavefront corrector with an adaptive optics (AO) test system. The LCOS-SLM has a high light-utilization
efficiency so that it is suitable for AO in ophthalmic instruments. Experimental results with a static phase object showed
nearly diffraction-limited performance. The root-mean-square (RMS) value of residual wavefront error was reduced to
0.06 wavelength from 2.09 wavelength. The capability for dynamic aberration correction was also examined. The timevarying
aberration was created by rotating the same phase object. While the RMS wavefront error became slightly larger,
a nearly diffraction-limited performance could be confirmed as same as in the static aberration correction. Effective
stroke and refraction power of the LCOS-SLM were also discussed theoretically. The estimated effective stroke and
refraction power were 40 microns and 2.5D for a beam of 8-mm diameter on the LCOS-SLM, respectively.
We have developed a tabletop adaptive optics wavefront control system used to correct dynamic distortions. The system uses a Shack-Hartmann sensor constructed by using a lenslet array and a high-speed CMOS camera to measure distortion, a high-resolution liquid crystal spatial light modulator to correct distortion, and a personal computer to execute feedback control. A correction refresh rate of 50 cycles per second was achieved as the result of the high-speed vision system. The temporal characteristic measurement was based on the response to periodic signals of patterns, and the measured bandwidth was about 7Hz. We also describe the optical configuration and experimental results of a performance evaluation.
The use of a broad-band interferometer and its fringe analysis method are presented in which the fractional fringe order method for measuring the absolute thickness. An approximate integer part of the fringe order is estimated by mechanical measurements, and the fractional part is determined by interferometric fringe pattern analysis. The fringe patterns are obtained with a Michelson interferometer by illumination of several selected wavelengths, respectively. The use of the fractional fringe order method can determine accurately more than 2(pi) phase jumps. The influence of wavelength and approximate integer part of fringe order on the measurement accuracy is discussed.
A general approach for making up fully parallel optical matrix multiplier is described. The necessary conditions of triple matrix multiplier (TMM) are induced based on Gaussian optics. Two typical configurations of TMM is discussed. 1 .
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