The purpose of this paper is to present the optical system developed for the Wide Field imaging Camera - WFI that will be integrated to the CBERS 3 and 4 satellites (China Brazil Earth resources Satellite). This camera will be used for remote sensing of the Earth and it is aimed to work at an altitude of 778 km. The optical system is designed for four spectral bands covering the range of wavelengths from blue to near infrared and its field of view is ±28.63°, which covers 866 km, with a ground resolution of 64 m at nadir. WFI has been developed through a consortium formed by Opto Electrônica S. A. and Equatorial Sistemas. In particular, we will present the optical analysis based on the Modulation Transfer Function (MTF) obtained during the Engineering Model phase (EM) and the optical tests performed to evaluate the requirements. Measurements of the optical system MTF have been performed using an interferometer at the wavelength of 632.8nm and global MTF tests (including the CCD and signal processing electronic) have been performed by using a collimator with a slit target. The obtained results showed that the performance of the optical system meets the requirements of project.
The first Brazilian remote sensing multispectral camera (MUX) is currently under development at Opto Eletronica S.A. It consists of a four-spectral-band sensor covering a 450nm to 890nm wavelength range. This camera will provide images within a 20m ground resolution at nadir. The MUX camera is part of the payload of the upcoming Sino-Brazilian satellites CBERS 3&4 (China-Brazil Earth Resource Satellite). The preliminary alignment between the optical system and the CCD sensor, which is located at the focal plane assembly, was obtained in air condition, clean room environment. A collimator was used for the performance evaluation of the camera. The preliminary performance evaluation of the optical channel was registered by compensating the collimator focus position due to changes in the test environment, as an air-to-vacuum environment transition leads to a defocus process in this camera. Therefore, it is necessary to confirm that the alignment of the camera must always be attained ensuring that its best performance is reached for an orbital vacuum condition. For this reason and as a further step on the development process, the MUX camera Qualification Model was tested and evaluated inside a thermo-vacuum chamber and submitted to an as-orbit vacuum environment. In this study, the influence of temperature fields was neglected. This paper reports on the performance evaluation and discusses the results for this camera when operating within those mentioned test conditions. The overall optical tests and results show that the "in air" adjustment method was suitable to be performed, as a critical activity, to guarantee the equipment according to its design requirements.
In this work, the development of a laser scanning system for ophthalmology with micrometric positioning precision is presented. It is a semi-automatic scanning system for retina photocoagulation and laser trabeculoplasty. The equipment is a solid state laser fully integrated to the slit lamp. An optical system is responsible for producing different laser spot sizes on the image plane and a pair of galvanometer mirrors generates the scanning patterns.
Jose Augusto Stuchi, Elisa Signoreto Barbarini, Flavio Pascoal Vieira, Daniel dos Santos, Mário Antonio Stefani, Fatima Maria Mitsue Yasuoka, Jarbas Castro Neto, Evandro Luis Linhari Rodrigues
The need of methods and tools that assist in determining the performance of optical systems is actually increasing. One
of the most used methods to perform analysis of optical systems is to measure the Modulation Transfer Function (MTF).
The MTF represents a direct and quantitative verification of the image quality. This paper presents the implementation of
the software, in order to calculate the MTF of electro-optical systems. The software was used for calculating the MTF of
Digital Fundus Camera, Thermal Imager and Ophthalmologic Surgery Microscope. The MTF information aids the
analysis of alignment and measurement of optical quality, and also defines the limit resolution of optical systems. The
results obtained with the Fundus Camera and Thermal Imager was compared with the theoretical values. For the
Microscope, the results were compared with MTF measured of Microscope Zeiss model, which is the quality standard of
ophthalmological microscope.
One of the widely used methods for performance analysis of an optical system is the determination of the
Modulation Transfer Function (MTF). The MTF represents a quantitative and direct measure of image
quality, and, besides being an objective test, it can be used on concatenated optical system. This paper
presents the application of software called SMTF (software modulation transfer function), built in C++ and
Open CV platforms for MTF calculation on electro-optical system. Through this technique, it is possible to
develop specific method to measure the real time performance of a digital fundus camera, an infrared sensor
and an ophthalmological surgery microscope. Each optical instrument mentioned has a particular device to
measure the MTF response, which is being developed. Then the MTF information assists the analysis of the
optical system alignment, and also defines its resolution limit by the MTF graphic. The result obtained from
the implemented software is compared with the theoretical MTF curve from the analyzed systems.
This work presents the mechanisms adopted for the design of micro-second pulsed laser mode for a CW Self-Raman
laser cavity in 586nm and 4W output power. The new technique for retina disease treatment discharges laser pulses on
the retina tissue, in laser sequences of 200 μs pulse duration at each 2ms. This operation mode requires the laser to
discharge fast electric pulses, making the system control velocity of the electronic system cavity vital. The control
procedures to keep the laser output power stable and the laser head behavior in micro-second pulse mode are presented.
The treatment of keratoconus and corneal ulcers by collagen cross-linking using ultraviolet type A irradiation, combined
with photo-sensitizer Riboflavin (vitamin B2), is a promising technique. The standard protocol suggests instilling
Riboflavin in the pre-scratched cornea every 5min for 30min, during the UVA irradiation of the cornea at 3mW/cm2 for
30 min. This process leads to an increase of the biomechanical strength of the cornea, stopping the progression, or
sometimes, even reversing Keratoconus. The collagen cross-linking can be achieved by many methods, but the
utilization of UVA light, for this purpose, is ideal because of its possibility of a homogeneous treatment leading to an
equal result along the treated area. We have developed a system, to be clinically used for treatment of unhealthy corneas
using the cross-linking technique, which consists of an UVA emitting delivery device controlled by a closed loop system
with high homogeneity. The system is tunable and delivers 3-5 mW/cm2, at 365nm, for three spots (6mm, 8mm and
10mm in diameter). The electronics close loop presents 1% of precision, leading to an overall error, after the calibration,
of less than 10% and approximately 96% of homogeneity.
Tiago Ortega, Alessandro Mota, Giuliano Rossi, Guilherme C. de Castro, Yuri Fontes, Glauco Costal, Fatima M. Yasuoka, Mario Stefani, Andrew Lee, Helen Pask, Jarbas C. de Castro N.
In this work, we present a continuous-wave yellow laser operating at 586.5nm based on self-Raman conversion in
Nd:GdVO4. We report more than 4.2W CW and 5.5W instantaneous output at a 50% duty cycle regime. This is the
highest CW power of a self-Raman laser to be reported so far. We also demonstrate the integration of this laser cavity
into a console for applications in ophthalmology, and more specifically for retinal photocoagulation therapies.
According to recent studies, an increase in corneal stiffness is a promising alternative for avoiding ectasias and for
stagnating keratoconus of grades 1 and 2. The clinical treatment consists essentially of instilling Riboflavin (vitamin
B2), in the cornea and then irradiating the corneal tissue, with UVA (365nm) radiation at 3mW/cm2 for 30min. This
procedure provides collagen cross-linking in the corneal surface, increasing its stiffness. This work presents a system for
UVA irradiation of the corneas at a peak wavelength of 365nm with adjustable power up to 5mW. The system has closed
loop electronics to control the emitted power with 20% precision from the sated power output. The system is a prototype
for performing corneal cross-linking and has been clinically tested. The closed loop electronics is a differential from the
equipments available on the market.
High image quality and complex, refractive optical systems, as those used in remote sensing applications, are, in general, very difficult to be manufactured with the required performance. This can be charged to the high sensitivity of such systems to the fabrication tolerances, mainly concerning the relative alignment of the optical components with respect to each other. When the system does not achieve the expected quality, the puzzle is to identify where the problems lies. This is even worsened when the number of optical elements becomes high. Due to these facts, some misalignment characterization and estimation techniques based on Bayesian estimators and wavefront measurements have been proposed in the literature. This paper is the result of a deep study and investigation of these techniques, with emphasis on an application to an intentionally simple system for the sake of illustration that highlights conceptual issues that could be extended to more realistic, complex optical systems. With this purpose, the sensitivity of the wavefront Zernike coefficients to the misalignment parameters, its use in a parameter estimator design that includes nonlinear terms, the study of the system observability, and a statistical analysis of the estimator performance considering the observation noise are addressed in details. Numerical simulation results for the simple system are shown. We also present insights on how to apply the technique to the alignment of a 11-lens optical system used in the Brazilian remote sensing camera MUX, that will fly on-board the upcoming Sino-Brazilian satellites CBERS 3&4.
A laser triangulation range finder based on a chaotic and detection scheme is presented. An elementary non-linear electronic oscillator composed by two operation amplifiers with feedback current form two antiparallel diodes generates a chaotic signal that is used to generate a chaotic clock modulation with a well-defined broad band spectrum. This chaotic clock modulates a laser beam that is transmitted and received by a collecting optics in a laser triangulation range finder scheme. A band limited phase delay equalized amplifier sends the received signal to a balanced demodulator using the same chaotic generated signal as 'local oscillator'. A low pass filter is tuned to assure good compromise against noise immunity and the desired response speed. This modulator scheme allows several laser stations to operate in same working area, avoiding carefully adjusted field-of-view screening and cross-detection false alarm due to the interference of other laser stations. The chaotic modulator can be used as an alternative for microprocessor based pseudo random sequence generator when board space or cost is a critical system specification. The laser triangulation range finder has a range of 0.5m to 2m using a 3mW class IIIa visible laser, with precision of 5 mm.
A hybrid diffractive optical element capable of splitting a monochromatic laser beam into an arbitrary number of lines over high angle is presented. The element is formed by a continuous parabolic surface-relief phase grating and a binary surface-relief computer generated phase hologram. The parabolic profile was generated into a thick photo resist and the binary surface-relief was generated into a quartz substrate.
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