This work introduces the experimental results of a temperature sensor device, with doped fiber and LPGs. The device is introduced in a temperature controlled oven, observing a 1 nm shift in wavelength toward longer wavelengths when the temperature increases 3 °C. It is possible to observe the average rate of change in the power related to increased temperature for two and three fiber gratings temperature sensors, and finally it is noted that the channels generated by the interference pattern are dispersed as temperature increases. The experiment was performed for 2 and 3 LPFGs in series where the wavelength displacement, output power and the number of channels were analyzed when the temperature was increased.
In this work we demonstrate the increasing of the trap stiffness (spring constant) constant of an optical trap of particles suspended in water by laser-induced convection currents. These currents are the result of thermal gradients created by a light absorption in a thin layer of hydrogenated amorphous silicon (a:Si-H) deposited at the bottom of cell. Since convection currents (and therefore drag forces) are symmetric around the beam focus particles trapped by the beam are further contained. Around the focus the drag force is directed upwards and partially compensated by radiation pressure depending on the laser power increasing the stiffness of the optical trapping increases significatively so a particle trapped could dragged (by moving the translation stage leaving the beam fixed) at velocities as high as 90μm/s without escaping the trap, whereas with no a:Si-H film, the particle escapes from the trap at lower velocities (30μm/s).
In this work, we present experimental results of a cost-efficient photonic system capable to discriminate Polyvinyl Chloride (PVC) bottles from those made of Polyethylene Terephthalate (PET). The proposed array uses a semiconductor laser emitting at 810 nm, whose output is diverged employing a line lens in order to obtain a line light pattern. Given the lower attenuation coefficient of the PVC in comparison to PET at this wavelength, the received optical power is higher for the PVC than for the PET, which results in higher photogenerated current and, consequently, higher voltage after the transimpedance amplifier. Experiments considering several samples reveal an average voltage difference of 10% between materials, probing its feasibility for future industrial applications.
Recent advances in the acquisition of in-vivo high resolution retinal images through the use of Adaptive Optics (AO) have allowed the identification of cellular structures such as cones and rods, in and out of the fovea, in such a way that their histological characteristics can be studied in-vivo and later compared to data obtained post-mortem. In this work, an algorithm is proposed for the detection of photoreceptors; it consists of two stages: Early Cell Detection (ECD), to detect all candidate cells, and Refinement of Cell Detection (RCD), to reduce over-detection of photoreceptors. The algorithm has been tested using synthetic and real images, the latter acquired with an Adaptive Optics Scanning Light Ophthalmoscope (AOSLO). The proposed algorithm was compared against the one developed by Li and Roorda, and both algorithms were tested on synthetic and real images, yielding similar algorithm performance on both kinds of images when they had only cones; however, the algorithm developed by Li and Roorda, when applied to real images having cones and rods, identifies photoreceptors in vascular tissue, in addition to showing low rod detection.
In this paper, we describe a new method to identify the spots and to obtain the coordinates for the centroids from a Hartmann and Hartmann-Shack screen test when some noise and reflection errors are present using an independent dynamic thresholding method. The proposed algorithm is a robust one, working with almost no interactive operation. It proved to be good for noise removal in the presence of relatively high noise with low and uneven contrast and spot reflections. The process involves the binarization of the image through a thresholding operation. Subsequently, a data segmentation algorithm is used for spot identification. The spot identification and indexing is performed independently. Finally, the coordinates of each centroid are obtained using an appropriate masking for each spot. To test the procedure we used first synthetic images obtained from some specified functions and later we used a Hartmanngram image from a human cornea.
In the current retinal imaging systems, laser cavities or astronomical spectroscopes, there is the need to employ off-axis
reflective systems. These systems often use different configuration where the object or image could be at finite distances
or at infinity with respect to the spherical mirrors. In this work, expressions for the wavefront aberrations in an off-axis
spherical mirror with image point or object point from different cases are presented, analyzed and evaluated. Assuming a
relatively small pupil and a small angle of incidence, these formulas are derived from the optical path difference between
a reference surface (paraboloid, ellipsoid or hyperboloid), and a sphere. They can be used to design and analyze some
off-axis reflective systems.
With the current retinal imaging systems, laser cavities and astronomical spectroscopes, there is the need to employ off-axis reflective systems. These systems, often used in configurations where the object or image are at the infinite with respect to the spherical mirrors, are the most used in this type of instrumentation. Expressions for the wavefront aberrations in an off-axis spherical mirror with image or object at the infinite are presented, analyzed and evaluated. Formulas are derived from the optical path difference between a paroboloid, as reference surface, and a sphere. Exact and approximate expressions, assuming a relative small pupil and a small angle of incidence are presented. They can be used to design and analyze some off-axis reflective systems.
The main constraint of classical off-axis reflecting systems is the primary astigmatism that by long time has been a
research topic of interest. This astigmatism in off-axis spherical reflective imaging systems can be eliminated by one
proper configuration. These configurations could be derived from the marginal ray fan equation and they are valid for
small angles of incidence. The conditions for the astigmatism compensation in configurations with two and three offaxis
mirrors have been derived and analyzed, which has not been reported previously. The expression that defines the
conditions for primary astigmatism compensation in a four-mirror system is presented. This shows that the marginal
ray fan equation can be used to obtain the condition for astigmatism compensation of a reflective system with any
number of mirrors.
The astigmatism in reflective imaging systems can be eliminated by a proper configuration. However, the spherical and
coma are the main residual aberrations in third order theory, but the behavior of all aberrations is not yet fully The main
aberration of classical off-axis reflecting systems is primary astigmatism. The astigmatism in off-axis spherical
understood. Expressions for the wavefront aberrations in an off-axis spherical mirror are presented. These formulas are
derived from the optical path difference between an ellipsoid and a sphere, assuming a relatively small pupil and a small
angle of incidence as it will be described with detail. Using the principle of the optical path difference, we developed the
mathematical expressions that describe the third order wavefront aberrations in a two spherical mirror system when the
object is finite.
Many optical systems need to be evaluated but they cannot be disassembled to test the imaging lens separately. Then,
they have to be tested in a retroreflecting configuration, frequently called double-pass. A typical example of this
procedure is in the optical eye. In this manuscript we will describe the different possibilities that might exist when these
tests are performed. The main differences are due to the different optical properties of the surfaces on which the image is
formed. We will describe the different system conditions and how they can be evaluated and implemented.
The wavefront aberration is the difference between the real wavefront forming an image of an object point and a close
reference sphere, described as an aberration function. This wavefront aberration function has been expressed by different
authors as different polynomial families or polynomial series. This polynomial has their own characteristics and
applications. The physical interpretation is customarily done in terms of Seidel, Zernike, Stephenson and many other
aberrations. We will compare these different representations and will propose a new one.
Scanning laser ophthalmoscopes (SLOs) and optical coherence tomographs are the state-of-the-art retinal imaging
instruments, and are essential for early and reliable diagnosis of eye disease. Recently, with the incorporation of adaptive
optics (AO), these instruments have started to deliver near diffraction-limited performance in both humans and animal
models, enabling the resolution of the retinal ganglion cell bodies, their processes, the cone photoreceptor and the retinal
pigment epithelial cells mosaics. Unfortunately, these novel instruments have not delivered consistent performance
across human subjects and animal models. One of the limitations of current instruments is the astigmatism in the pupil
and imaging planes, which degrades image quality, by preventing the wavefront sensor from measuring aberrations with
high spatial content. This astigmatism is introduced by the sequence of off-axis reflective elements, typically spherical
mirrors, used for relaying pupil and imaging planes. Expressions for minimal astigmatism on the image and pupil planes
in off-axis reflective afocal telescopes formed by pairs of spherical mirrors are presented. The formulas, derived from the
marginal ray fans equation, are valid for small angles of incidence (≤15°), and can be used to design laser cavities,
spectrographs and vision adaptive optics systems. An example related to this last application is discussed.
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.