Based on the Talbot self-imaging principle, a diffraction-based wavefront sensor, the Z-ViewTM wavefront sensor, has been developed at Ophthonix Inc. According to the Talbot effect, a periodic grating can be self-imaged at certain distances behind the grating, commonly known as Talbot distances, without the aid of any imaging device. The fidelity of the Talbot image to the grating pattern is affected by the wavefront aberration in the illumination beam. Therefore, the wavefront distortion can be retrieved through numerical analysis of the Talbot image. Unlike the well-known Shack-Hartmann wavefront sensor, where a group of pixels on the camera is responsible for only one wavefront data point, each camera pixel in the Z-View wavefront sensor has a corresponding wavefront data. The Z-View wavefront sensor measures the wavefront at 1024 x 1048 data points, and can achieve a dynamic range of wavefront curvature of 20 diopters. The Z-View wavefront sensor has been successfully used for wavefront sensing in ophthalmic aberrometry, adaptive optics, and lensometry at Ophthonix.
A novel wavefront sensor (Z-ViewTM) using a two dimensional diffractive grating has been developed at Ophthonix, Inc. Based on the Talbot self-imaging theory, a CMOS camera is placed behind the grating to capture the first Talbot image of the aberrated wavefront. This captured Talbot image is analyzed to recover the wavefront aberration. The diffractive grating wavefront sensor has been used in Ophthonix's Z-View Aberrometer, an objective refractive vision assessment system which is now commercially used in optometrist's offices/clinics across the United States of America. Coupled with a deformable mirror and other auxiliary optics systems, Z-View wavefront sensor forms the A-View adaptive optic vision correction system at Ophthonix. This A-View system is used to study the effect of complete wavefront correction in human vision, and has potential application in prescribing Ophthonix's wavefront-guided iZonTM lenses. In this paper, the wavefront sensing principle of this novel diffractive wavefront sensor and its applications will be discussed.
High order aberrations in human eye can deteriorate visual acuity and contrast sensitivity. Such aberrations can not be corrected with traditional low-order (defocus and astigmatism) spectacles or contact lenses. A state-of-the-art adaptive optics vision correction system was developed using Ophthonix's Z-View diffractive wavefront sensor and a commercial miniature deformable mirror. While being measured and corrected by this system, the patient can also view a Snellen chart or a Contrast Sensitivity chart through the system in order to experience the vision benefits both in visual acuity and contrast sensitivity. Preliminary study has shown the potential that this system could be used in a doctor's office to provide patients with a subjective feel of the objective high order prescription measured on Z-View.
Common path interferometric microellipsometry based on the Young's interference principle is presented. Interference of the pure p and s reflections at the back focal plane of a microscopic objective takes place by means of Young's interferometry. Therefore, the amplitude ratio, tan (psi) , and the phase different, (Delta) , of the two polarization components are represented as the contrast and the phase shift of the Young's fringe pattern. Hence, the complex refractive index of the sample can be calculated using well- known equations. This technique is particularly applicable in pure topography where the measured optical phase is actually a contribution of both the surface height change and material change as well.
When a low coherence light source is used in a multimode fiber linked interferometer, the level of the modal noise induced by the environmental perturbations on the fibers may be dramatically suppressed, provide the value of the coherence length, Lc, of the light source employed is less than that of the optical path differences (OPD) between the guided modes at the far end of the fiber. In this work, the results of an experimental study on the relationship between the modal noise and the length and diameter of fiber, and the coherence length of the source used are presented, illustrating the major considerations for the use of multimode fiber in a white light interferometer.
When a low coherence light source is used in a multimode fibre linked interferometer, the level of the
modal noise  induced by the environmental variations on the fibres may be dramatically suppressed, provided
the value of the coherence length, Lc, of the light source employed is less than that of the optical path
differences (OPD) between the guided modes at the far end of the fibre [2, 3].
A computer simulation of an in-fiber interferometric hydraulic pressure sensor is carried out by use of a finite element method. Both the interference between the same modes from the two arms of the interferometer and the beat length of the two orthogonal modes in the polarization- maintaining fiber which is used as the working arm of the interferometric hydraulic pressure sensor are examined, for various types of polarization-maintaining fibers under different values of hydraulic pressure. As a result, the design of the in-fiber interferometric hydraulic pressure sensors may be optimized.
A study on the effect of modal noise induced by the modal coupling effect in a graded index multimode fiber, illuminated by a light source with a tunable coherence length was carried out. It has been shown that the value of the signal-to-noise (S/N) ratio in an interferometric system could be reduced by the perturbation-induced modal noise if in the coherence length is in the region of 30 to 80 micrometers . As the coherence length increase, the S/N ratio will reduce correspondingly. However, when the value of the coherence length is in the region of 80 micrometers and upward, the value of the corresponding reduction in S/N ratio was seen to vary only over a very small range.
A method for imaging extended objects using adaptive optics technique is proposed. The wavefront distortion is corrected by using the Fourier transforms of two image intensities obtained with and without a Gaussian amplitude filter at the entrance pupil plane of the imaging system. A one dimensional computer simulation is presented, which shows the effectiveness of the method.