This work reports to the development of a metric system which is able to detect the glottic squamous cell carcinoma tumor and establish its position. It was observed that the images of the glottis, seen through an endoscope, are shaped according to their geometric characteristics and by shades of color and brightness. Thus, by superimposing the metric of a diffractive grid with light spots on images containing the glottic region, the position and attributes of the tumor can be quantified. Thus, by implement computer-aided diagnostic techniques, it is possible to extract features of the pathology, as well as minimize operational costs, compared to empirical experiments. To this end, this study was carried out by analyzing narrow-band endoscope sample images from 10 patients with squamous cell carcinoma-like tumor confirmed on medical diagnosis. The light spot array was generated by a diffractive optical element, designed by an iterative Fourier-transform method. Images segmentation was based on methods of image filtering as well as on active contour region. By employing a 3 x 3 spot array it was possible to obtain ' 97 % tumor detection. The proposed metric system can be considered a powerful tool in order to assist in the prognosis of laryngeal pathologies by detecting attributes and position of laryngeal squamous cell carcinoma tumor.
In this work we present a comparative study of two processes for the fabrication of an array of microchannels for microfluidics applications, based on integrated-circuit technology process steps, such as lithography and dry etching. Two different methods were investigated in order to study the resulting microstructures: wet and dry deep etching of silicon substrate. The typical etching depth necessary to the target application is 50 μm.
Photometers use correction filters to adjust spectral responsivity of sensors so that the combined spectral responsivity approximates the responsivity of the human eye V(λ). However, the combination of these components is hardware based, and the quality of the photometer depends on this combination. We propose a meter that uses an RGB sensor, a LED and an artificial neural network that transforms the output of the sensor into luminous transmittance, without the need of a filter. The ANN was trained and validated with two different spectra datasets and generated results with error values below 3%. The methodology presents an option for a meter with calibration that depends only on a software. This allows the development of a low cost and compact photometer.
Optical sensors based on integrated photonics have experienced impressive advancements in the past few decades and represent one of the main sensing solutions in many areas including environmental sensing and medical diagnostics. In this context, optical microcavities are extensively employed as refractive index (RI) sensors, providing sharp optical resonances that allow the detection of very small variations in the surrounding RI. With increased sensitivity, however, the device is subjected to environmental perturbations that can also change the RI, such as temperature variations, and therefore compromise their reliability. In this work, we present the concept and experimental realization of a photonic sensor based on coupled microcavities or Photonic Molecules (PM) in which only one cavity is exposed to the sensing solution, allowing a differential measurement of the RI change. The device consists of an exposed 5-μm radius microdisk resonator coupled to an external clad microring resonator fabricated on silicon-on-insulator (SOI) platform. This design allows good sensitivity (26 nm/RIU) for transverse electrical mode (TE-mode) in a compact footprint (40 × 40 μm2), representing a good solution for real-life applications in which measurement conditions are not easily controllable.
This work reports the fabrication of a PMMA-based spherical microlens array (MLA), targeting application of Shack-Hartmann wavefront sensor for lens characterization. The array present 10 by 10 elements, with f-number f/# = f/10 (1 mm diameter, 10 mm focal length). The fabrication method employs a computer-controlled mechanical indentation for the fabrication of an insert mold, and subsequent replication by injection molding on PMMA. After replication and de-molding, the PMMA surface containing the negative of the phase profile of the lens array was evaluated by optical profilometry technique, in terms of the surface quality as well as the replication fidelity. The RMS surface roughness level of approximately (λ/10) was found, considering operation in the visible range of spectrum. Optical characterization was based on the evaluation of the sharpness, FWHM, and maximum intensity, IMAX, values associated to the profiles of each of the 100 generated light spots, obtained in the back focal plane of the MLA. An average sharpness of FWHMAVG = 13.9 ± 8% μm, and average maximum intensity of IMAXAVG = 0.72 ± 7% a.u. was obtained.
In this work we report the design and characterization of a Shack-Hartmann wavefront sampling plane based on a microlens array (MLA) composed of 12 X 12 hexagonal contiguous diffractive lenslet, with 355 μm pitch, 4.5 mm focal length, and 4.3 X 4.3 mm lateral dimensions. The device was fabricated by maskless grayscale lithography based on Digital Light Projector (DLP) technology. Optical characterization was performed in order to measure wavefront aberrations in Zernike polynomials terms. Intraocular lenses were used as test elements because they yield well-known optical aberrations, such as defocus and spherical aberration. For the wavefront reconstruction, the modal approach was used, in which the first derivatives of Zernike polynomials are used as the set of orthogonal basis functions. The corresponding polynomial coefficients up to the first 10 Zernike terms were obtained and the resulting reconstructed wavefront presents an RMS reconstruction error compliant to most optical systems of interest.
This work presents the fabrication of a contiguous f/#=f/15 Fresnel microlens array (MLA) by employing a low-cost home-built maskless exposure lithographic system based on a digital light projector technology by using Texas Instruments’ digital micromirror device chip. A continuous diffractive phase relief structure was generated on a photoresist-coated silicon wafer, replicated in polydimethylsiloxane (PDMS) and electrostatically bonded to a glass substrate. The whole exposure time takes 10.8 min to expose a 2.4×2.4 mm MLA, with a resolution of 2.5 μm. This exposure time is relatively short, enabling high throughput or fast prototyping. Optical characterization was carried out using a He-Ne laser source (λ=633 nm ), by evaluating the maximum intensity of each spot generated at the MLA focal plane, Imax, as well as its sharpness by measuring their full width at half maximum (FWHM) intensity values. The resulting FWHM and maximum intensity spot average values were FWHM AVG =20±8% μm and Imax AVG =0.71±7% a.u. , respectively. The quality of replication was evaluated by profile characterization of the resulting mold and replica based on step height measurement along 180 μm. The maximum obtained difference was 32 nm, corresponding to 2.5% of the total mold height or λ/20 . AFM measurements were also carried out to quantify the roughness quality between mold and replica. The resulting RMS roughness was 4.73 nm (λ/130 ) and 6.66 nm (λ/95 ) for mold and replica, respectively. A comparison between theoretical and measured intensity profiles at the MLA focal plane was also carried out. A good correspondence between the results was found. Such an MLA can be applied as a Shack–Hartmann wavefront sensor in optical interconnects and to enhance the efficiency of detector arrays.
This work presents the fabrication of a high fill factor Fresnel microlens array (MLA) by employing a low-cost homebuilt
maskless exposure lithographic system. A phase relief structure was generated on a photoresist-coated silicon
wafer, replicated in Polydimethylsiloxane (PDMS) and electrostatically bonded to a glass substrate. Optical
characterization was based on the evaluation of the maximum intensity of each spot generated at the MLA focal plane as
well as its full width at half maximum (FWHM) intensity values. The resulting FWHM and maximum intensity spot
mean values were 50 ± 8% μm and 0.71 ± 7% a.u , respectively. Such a MLA can be applied as Shack-Hartmann
wavefront sensors, in optical interconnects and to enhance the efficiency of detector arrays.
In certain applications of MOEMS devices, it is often necessary to produce microlens array structures that concentrate
optical power in semiconductor photodetectors. In this work, the design and fabrication of a low f-number cylindrical
microlens array is presented. The lenses were fabricated in thick photo resist - 12 μm thick - using a contact printer
exposure through a mask with a repetitive 6 μm line - 4 μm space pattern. The width of the resulting microlens array was
determined to be 10 μm, with f-number of 0.5. Numerical calculations based on scalar diffraction theory were employed
to model the light propagation inside the resist, determining the aerial image as a function of its thickness. Than the resist
response characteristics, expressed by its contrast curve, and absorption rate were used to obtain a cross section profile.
A good match between numerical and experimental results were found.
A cubic-phase distribution is applied in the design, fabrication and characterization of inexpensive Fresnel lens arrays for
passive infrared motion sensors. The resulting lens array produces a point spread function (PSF) capable of distinguish
the presence of humans from pets by the employment of the so-called wavefront coding method. The cubic phase
distribution used in the design can also reduce the optical aberrations present in the system. This aberration control
allows a high tolerance in the fabrication of the lenses and in the alignment errors of the sensor. In order to proof the
principle, a lens was manufactured on amorphous hydrogenated carbon thin film, by well-known micro fabrication
process steps. The optical results demonstrates
that the optical power falling onto the detector surface is attenuated for
targets that present a mass that is horizontally distributed in space (e.g. pets) while the optical power is enhanced for
targets that present a mass vertically distributed in space (e.g. humans). Then a mould on steel was fabricated by laser
engraving, allowing large-scale production of the lens array in polymeric material. A polymeric lens was injected and its
optical transmittance was characterized by Fourier Transform Infrared Spectrometry technique, which has shown an
adequate optical transmittance in the 8-14 μm wavelength range. Finally the performance of the sensor was measured in
a climate-controlled test laboratory constructed for this purpose. The results show that the sensor operates normally with
a human target, with a 12 meter detection zone and within an angle of 100 degrees. On the other hand, when a small pet
runs through a total of 22 different trajectories no sensor trips are observed. The novelty of this work is the fact that the
so-called pet immunity function was implemented in a purely optical filtering. As a result, this approach allows the
reduction of some hardware parts as well as decreasing the software complexity, once the information about the intruder
is optically processed before it is transduced by the pyroelectric sensor.
The use of diffractive optical elements (DOEs) is increasing for several industrial applications, such as beam shaping and optical filtering. Most elements modulate the phase of the incoming light or its amplitude, but not both. To overcome this limitation, we developed a full complex-amplitude modulation DOE. We employed well-established integrated circuit fabrication steps to fabricate the devices at relatively low cost and with high precision. Using this approach, the new element's optical performances are improved even for near-field operations. With this device it is possible to obtain the total control of the zeroth order transmitted light, resulting in low-noise reconstructed images.
A cubic-phase distribution is applied in the design and fabrication of inexpensive lenses for passive infrared motion sensors. The resulting lenses produce a point spread function (PSF) capable to distinguish the presence of humans from pets by the employment of the so-called wavefront coding method. The cubic phase distribution used in the design can also reduce the optical aberrations present on the system. This aberration control allows a low tolerance in the fabrication of the lenses and in the alignment errors of the sensor. The lens was manufactured on amorphous hydrogenated carbon thin film, by employing well-known micro fabrication process steps. The optical results demonstrates that the optical power falling onto the detector surface is attenuated for targets that present a mass that is horizontally distributed in space (e.g. pets) while the optical power is enhanced for targets that present a mass vertically distributed in space (e.g. humans).
In this work we propose the use of a quadratic phase distribution to implement continuous, full complex amplitude modulation proximity printing masks. The mask is calculated based on the inverse light propagation, determining values of both continuous phase and amplitude modulation. The novelty in this proposition is the use of a quadratic phase distribution in the desired reconstruction pattern in order to achieve a smooth phase and amplitude modulation during the mask calculation. The use of a quadratic phase distribution on the desired reconstruction pattern allows to spread the light of this pattern over a wide region of the calculated proximity-printing mask, generating a magnification of the information to be modulated by the mask. As a consequence, the feature sizes on the mask are larger than in the image reconstruction plane. We believe that this approach will allow the generation of a continuous variation of light in the final required pattern, allowing the generation of arbitrary 3D structures. The smooth phase and amplitude modulation distributions can also minimize the errors caused by using the scalar diffraction to calculate and encode the phase and amplitude modulation of the final mask.
The use of diffractive optical elements (DOEs) is increasing for several industrial applications. Most elements modulate the phase of incoming light or its amplitude, but not both. The phase modulation DOE is the most popular because it has a high diffraction efficiency. However, the phase-only limitation may reduce the freedom in the element design, increasing the design complexity for a desired optimal solution. To overcome this limitation, a novel, full complex-amplitude modulation DOE is presented. This element allows full control over both phase and amplitude modulation of any optical wave front. This flexibility introduces more freedom in the element design and improves the element's optical performance, even in a near-field operation regime. The phase grating of the element was fabricated in an amorphous hydrogenated carbon film. The amplitude modulation was obtained by patterning a reflective aluminum thin film, which was deposited on top of the phase grating. The apertures in the metal film determine the quantity of transmitted light. The use of a reflective layer in the fabrication decreases the risk of laser-induced damage since no absorption is involved in the process. With this device it is possible to obtain extremely efficient spatial filtering and reconstruct low noise images.
A cubic-phase distribution is applied in the design of inexpensive lenses for passive infrared motion sensors. The resulting lenses have the ability to distinguish the presence of humans from pets by the employment of the so-called wavefront coding method. The cubic-phase distribution used in the design can also reduce the optical aberrations present on the system. This aberration control allows a low tolerance in the fabrication of the lenses and in the alignment errors of the sensor.
A hybrid phase and amplitude modulation proximity printing mask was designed, manufactured and tested. The proposed diffractive structure modulates both the phase and the amplitude of a UV exposure beam. In the fused silica substrate a relief is generated in order to modulate the phase and a patterned diamond like carbon layer modulates the amplitude of the UV light. Besides, the diamond like carbon thin film is partially transparent at wavelengths larger than 400 nm, what improves the alignment procedures between different mask levels. The lithographic image was projected onto a resist coated silicon wafer, placed at a distance of 50 micrometer behind the mask, obtaining a resolution better than 1 micrometer, what is impossible with traditional proximity printing techniques.
Novolak type polymers are the basic material for most commercial photoresists used in microelectronic processes, but are not often used for micro-optic applications. In this work, three types of optical devices were implemented in AR P322 novolak-based resist, which can be used as a positive photoresist and a positive electron resist. Gratings of parabolic divergent microlenses with f-number of 0.5 were fabricated using traditional optical lithography, employing the diffraction characteristics of de-focused light during the photolithographic exposure. The contrast curve of the AR P322 used an electron sensitive resist, was determined and yielded a gamma factor of 3.02. This relatively low contrast allows to obtain structures with well controlled curved walls. Direct write electron beam lithography was employed to manufacture gratings of parabolic convergent microlenses with different diameter and focal length, what enables one to control the intensity of the different orders of the diffracted light. This technique was also used to obtain convergent parabolic microlenses, with different diameters and different heights, allowing the control of the focal length of these lenses. These structures have several applications in the fields of pattern recognition, robotic vision and optical sensors.
In order to address an increasing numbers of industrial applications for Diffractive Optical Elements, the development of more efficient ways of designing and fabricating these devices is clearly needed. Among the main applications of these devices are beam shaping, optical interconnects and filtering. In order to reduce the design complexity and increase the performance and robustness, a novel, full complex-amplitude modulation Diffractive Optical Element was designed. This proposed element has the flexibility of allowing full control over both phase and amplitude modulation of whatever optical wave-front. The concept of this element is to bring together the positive characteristics of the high efficient phase modulation Diffractive Optical Element and the characteristics of an amplitude modulation Diffractive Optical Element, to achieve design freedom and fabrication facility, capable of obtaining a high-quality reconstructed image. The phase grating was fabricated in an amorphous hydrogenated carbon thin film, and thereafter an aluminum layer was deposited and patterned to obtain apertures in this reflective film. The use of a reflective layer in the fabrication avoids the risk of laser-induced damage since no absorption is involved in the process. Several devices, such as high-quality holographic displays, can be manufactured with this technique.
Diffractive optical elements are being used in increasing numbers of applications such as beam shaping, optical interconnects and filtering. Their main advantages over traditional refractive optical elements are their reduced size and weight and the possibility of being mass fabricated. In order to reduce the design complexity and increase the performance, a novel, full complex-amplitude modulation diffractive optical element was designed, which allows full control over both phase and amplitude modulation of whatever optical wave front. In this element the wavefront phase modulation is controlled by the variations in the thickness of an optical film and the magnitude modulation is controlled by variations in the area of the apertures in a reflective layer deposited over this film. The use of a reflective layer in this new diffractive element avoids the risk of laser-induced damage when a powerful laser is used with the element since no light absorption is involved in the process.
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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