This research presents an alternative method to represent aberrated wavefronts based on circular Bessel functions. These wavefronts are obtained by means of a Shack-Hartmann wavefront sensor prototype, which was previously statistical validated according to the official Mexican standard. We show experimental results obtained from two wavefronts aberrated by two ophthalmic trial lenses; one of them has a spherical aberration of -1.0 diopter and the other one has a defocus aberration of +1.0 diopter. Both wavefronts are shown in terms of circular Bessel functions and compared with their corresponding representation in Zernike polynomials.
In this paper, we show the results and feasibility of a designed software for obtaining and graphing aberrations in 2D, and the post-processing necessary for the detection of the centroids. This software is designed to be used in low-cost and highly affordable commercial devices such as Raspberry pi and Raspberry pi HQ Camera. Preliminary results will also be presented.
Integration of optical imaging systems with different axial specifications including the maximum measurable range and
the axial resolution expands the axial dynamic range. In this research, an optical time-of-flight and an optical coherence
tomography were integrated, because both methods have a measurable range that overlaps in the submillimeter range. The
integrated optical imaging system has the maximum measurable range of several ten centimeters and the axial resolution
of several micrometers, and also get san inside observation ability derived from the feature of the optical coherence
tomography
We present a demodulation approach for a rotating polarizer-analyzer polarimeter dedicated to retardance measurements.
Through the Mueller matrix approach and the theoretical Fourier transform, we developed a demodulation algorithm
considering the two linear polarizers' initial orientation as calibration. We present experimental results showing the
feasibility of our proposal.
KEYWORDS: Photodetectors, Fourier transforms, Modulation, LabVIEW, Distance measurement, Beam splitters, Signal processing, Signal detection, Light, Control systems
In this manuscript, we present an optical time of flight and a focusing system to measure and track a reflective target, respectively. The time-of-flight and tracking system is based on the reflectance of the targets. This system uses a commercially available variable focal length lens that changes focal planes when current is applied. The optical system is mounted on a motorized stage that moves the system closer to or away from the target to be located; This is to expand the dynamic focal range of the system. The system is controlled by a specially designed LabVIEW program that controls the entire system.
Optical coherence tomography (OCT) is a non-invasive technique in biomedical imaging since it provides high axial and lateral resolutions. OCT requires approaching the measurement probe to the sample within the axial range of several millimeters. If there is an initial condition that the distance is unknown; as expected for automatic measurement. In a distance with longer axial range, the time-of-flight (ToF) becomes is useful. In this research, we integrated ToF with sub-millimeter axial resolution and a meter-order axial range; and OCT with micrometer-order axial resolution and a millimeter-order axial measurable range. A spectral-domain (SD-OCT) system composed of a superluminescent diode, optical fibers, and a spectrometer was implemented. ToF system holds a semiconductor laser which is sinusoidally modulated by an electric signal ranging frequency from 0.1 to 1 GHz, a Si PIN photodetector. The ToF and the SD-OCT systems share a common optical path; the phase difference of the sinusoidal signals returning from the sample and reference arms are measured. The importance of the integrated system is that the accuracy of ToF is smaller than the axial measurable range of SD-OCT. The SLD of the SD-OCT system has a central wavelength of 840 nm and a bandwidth of 80 nm. The axial measurable range was 3.7 mm which was calculated from the specifications of the grating and the LSC system. The ToF system has an experimental accuracy of 0.9 mm operating at a frequency of 0.8 GHz. It is enough for the axial resolution measurable in the range of SD-OCT.
We present a calibration approach for rotating polarizer-analyzer polarimeter dedicated to retardance measurements. The rotating polarizer-analyzer polarimeter is based on retrieving a partial Mueller matrix measurement of a transparent sample to be later associated with its phase retardation properties. Through the Mueller matrix approach, we developed a calibration procedure considering the initial orientation of the two linear polarizers used, and we present experimental results showing the feasibility of our calibration approach.
In this paper, we report an experimental study of the supercontinuum (SC) generated by molecules of solitons (MS) and noise-like pulses (NLP) in two different types of optical fibers: 500m of standard fiber (SMF-28, Corning) and 100m of High-Nonlinearity Fiber with a zero dispersion-slope (HNLF-ZS, Furukawa). We extracted information on the inner structure of SC by using a nonlinear optical loop mirror (NOLM) as an intensity filter. The NOLM suppresses pulses with low peak power, which is especially pronounced for wavelengths longer than ~1750 nm for both fibers, and particularly in the region between 1450 nm and 1640 nm for the High-Nonlinearity fiber. It is worth mentioning that depending on the application, the required properties of SC light can vary considerably. Therefore, it is the main importance to know the properties of the different SC sources.
In this work, we proposed the usage of a rotating polarizer-analyzer polarimeter to retrieve retardance parameters of a sample by treating it as an elliptical retarder that can be characterized by three parameters: total retardance, fast axis orientation and an ellipticity related parameter. By employing the Mueller matrix approach, we developed the demodulation algorithm to retrieve each parameter with the association of the Fourier series analysis. We present experimental results considering dextrose concentrations diluted in distilled water scaling in a range from 30mg/dl to 45mg/dl. For comparison purposes, we employed the method of rotating an analyzer and compare the optical activity variation for both methods.
A less-complex 2.8-mm beam diameter spectral domain optical coherence tomography system with an adaptive optics module presented. In this system a Shack-Hartmann wavefront sensor used for aberration sensing and the Deformable mirror used for aberration correction. We demonstrated the diffraction-limited resolution performance of this system on model retina. On the model, measured speckle size with present system is 2.2 times smaller than a 1.2-mm beam diameter OCT system. Further, on the model eye SNR gain of 6.7 dB was quantified with the present system over a 1.2-mm beam diameter OCT system. Relatively small size of 25 cm by 50 cm, less complexity, large field of view of the present system as compared to the conventional AO-OCT systems, would make it suitable for ophthalmic clinical applications.
A spectrometer design with a multiple line line-scan camera and beam displacer is presented for ultra-high resolution optical coherence tomography measurements of the human retina at 840 nm. The beam displacer offsets the two orthogonal polarization states on the same line-scan camera, which reduces k-space mapping complexity, as data in both polarization channels can be mapped with the same procedure. Its coherence length is 2.8 μm in tissue (n = 1.38). Birefringence values of 1°/μm and higher were found in a circle with a radius of 2.5° eccentricity centered on the fovea, and in the raphe, pointing at a higher packing density of microtubules and a lower concentration of glia. Birefringence measurements may be more helpful in the modeling of individual structure-function maps than thickness measurements, as they are not affected by glial content.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.