This paper presents the design, simulation, fabrication, and characterization of a thin-film Fabry-Perot resonator composed of titanium dioxide (TiO2) and silicon dioxide (SiO2) thin-films. The optical filter is developed to be integrated with a light emitting diode (LED) for enabling narrow-band imaging (NBI) in endoscopy. The NBI is a high resolution imaging technique that uses spectrally centered blue light (415 nm) and green light (540 nm) to illuminate the target tissue. The light at 415 nm enhances the imaging of superficial veins due to their hemoglobin absorption, while the light at 540 nm penetrates deeper into the mucosa, thus enhances the sub-epithelial vessels imaging. Typically the endoscopes and endoscopic capsules use white light for acquiring images of the gastrointestinal (GI) tract. However, implementing the NBI technique in endoscopic capsules enhances their capabilities for the clinical applications. A commercially available blue LED with a maximum peak intensity at 404 nm and Full Width Half Maximum (FWHM) of 20 nm is integrated with a narrow band blue filter as the NBI light source. The thin film simulations show a maximum spectral transmittance of 36 %, that is centered at 415 nm with FWHM of 13 nm for combined the blue LED and a Fabry Perot resonator system. A custom made deposition scheme was developed for the fabrication of the blue optical filter by RF sputtering. RF powered reactive sputtering at 200 W with the gas flows of argon and oxygen that are controlled for a 5:1 ratio gives the optimum optical conditions for TiO2 thin films. For SiO2 thin films, a non-reactive RF sputtering at 150 W with argon gas flow at 15 sccm results in the best optical performance. The TiO2 and SiO2 thin films were fully characterized by an ellipsometer in the wavelength range between 250 nm to 1600 nm. Finally, the optical performance of the blue optical filter is measured and presented.
This paper presents the design, fabrication and characterization of a linear variable optical filter (LVOF) that operates in the infrared (IR) spectral range. An LVOF-based microspectrometer is a tapered-cavity Fabry-Perot optical filter placed on top of a linear array of detectors. The filter transforms the optical spectrum into a lateral intensity profile, which is recorded by the detectors. The IR LVOF has been fabricated in an IC-compatible process flow using a resist reflow and is followed by the transfer etching of this resist pattern into the optical resonator layer. This technique provides the possibility to fabricate a small, robust and high-resolution micro-spectrometer in the IR spectral range directly on a detector chip. In these designs, the LVOF uses thin-film layers of sputtered Si and SiO2 as the high and low refractive index materials respectively. By tuning the deposition conditions and analyzing the optical properties with a commercial ellipsometer, the refractive index for Si and SiO2 thin-films was measured and optimized for the intended spectral range. Two LVOF microspectrometers, one operating in the 1.8-2.8 μm, and the other in the 3.0-4.5 μm wavelength range, have been designed and fabricated on a silicon wafer. The filters consist of a Fabry-Perot structure combined with a band-pass filter to block the out-of-band transmission. Finally, the filters were fully characterized with an FTIR spectrometer and the transmission curve widening was investigated. The measured transmittance curves were in agreement with theory. The characterization shows a spectral resolution of 35-60 nm for the short wavelength range LVOF and 70 nm for the long wavelength range LVOF, which can be further improved using signal processing algorithms.
An IC-Compatible Linear-Variable Optical Filter (LVOF) for application in the UV spectral range between 310 nm and
400 nm has been fabricated using resist reflow and an optimized dry-etching. The LVOF is mounted on the top of a
commercially available CMOS camera to result in a UV microspectrometer. A special calibration technique has been
employed that is based on an initial spectral measurement on a Xenon lamp. The image recorded on the camera during
calibration is used in a signal processing algorithm to reconstruct the spectrum of the Mercury lamp and the calibration
data is subsequently used in UV spectral measurements. Experiments on fabricated LVOF-based microspectrometer with
this calibration approach implemented reveal a spectral resolution of 0.5 nm.
This paper describes a strategy for the detection of gastrointestinal (GI) dysplasia using a miniaturized system to be
integrated within an endoscopic capsule. This system will be able to perform spectroscopy measurements in specific
spectral bands, which have the potential to provide biological information of normal and diseased tissue. The designed
instrument is based on highly selective thin-film optical filters and silicon photodiodes for the selection and detection of
different spectral bands significant for diagnosis. A thin-film optical interference filter and a silicon photodiode were
designed and fabricated for diffuse reflectance measurements in the green spectral band. A qualitative analysis of GI
spectroscopic data using this specific spectral band is performed. Using a single optical filter, a good sensitivity and
specificity were obtained for the diagnosis of GI dysplasia.
Wearable devices are used to record several physiological signals, providing unobtrusive and continuous monitoring. A
main challenge in these systems is to develop new recording sensors, specially envisioning bioelectric activity detection.
Available devices are difficult to integrate, mainly due to the amount of electrical wires and components needed. This
work proposes a fiber-optic based device, which basis of operation relies on the electro-optic effect. A Lithium Niobate
(LiBnO3) Mach-Zehnder Interferometer (MZI) modulator is used as the core sensing component, followed by a signal
conversion and processing stage. Tests were performed in order to validate the proposed acquisition system in terms of
signal amplification and quality, stability and frequency response. A light source with a wavelength operation of 1530-
1565 nm was used. The modulated intensity is amplified and converted to an output voltage with a high transimpedance
gain. The filtering and electric amplification included a 50Hz notch filter, a bandpass filter with a -3 dB bandwidth from
0.50 to 35 Hz. The obtained system performance on key elements such as sensitivity, frequency content, and signal
quality, have shown that the proposed acquisition system allows the development of new wearable bioelectric monitoring
solutions based on optical technologies.
Optical fiber sensors are increasingly used for monitoring purposes, but flexible smart structures based in this type of
technology have many industrial applications. This paper explores a new approach for integrating optical fiber sensors in
flexible substrates that can be mounted in host structures to monitor. This approach combines two well establish
components, Fiber Bragg grating (FBG) sensors and flexible skin-foils. A three-layer foil construction based on the
spread-coating process was defined, in which the fiber was embedded in the middle layer. Such disposition ensured
protection to the optical fiber element without reducing the sensitivity to external stimulus. The functional prototypes
were subject to thermal and mechanical tests, in which its performance was evaluated. The smart structure behaves
linearly to temperature cycles by 0.01 nm/°C and is able to withstand high strain cycles without affecting the
measurement characteristics. The obtained results validated this approach. In addition, the flexibility of the explored
method allows custom fiber layouts, finishing patterns and colors, enabling this way a range of possible application
This paper reports on the functional and spectral characterization of a microspectrometer based on a CMOS detector
array covered by an IC-Compatible Linear Variable Optical Filter (LVOF). The Fabry-Perot LVOF is composed of 15
dielectric layers with a tapered middle cavity layer, which has been fabricated in an IC-Compatible process using resist
reflow. A pattern of trenches is made in a resist layer by lithography and followed by a reflow step result in a smooth
tapered resist layer. The lithography mask with the required pattern is designed by a simple geometrical model and FEM
simulation of reflow process. The topography of the tapered resist layer is transferred into silicon dioxide layer by an
optimized RIE process. The IC-compatible fabrication technique of such a LVOF, makes fabrication directly on a
CMOS or CCD detector possible and would allow for high volume production of chip-size micro-spectrometers. The
LVOF is designed to cover the 580 nm to 720 spectral range. The dimensions of the fabricated LVOF are 5×5 mm2. The
LVOF is placed in front of detector chip of a commercial camera to enable characterization. An initial calibration is
performed by projecting monochromatic light in the wavelength range of 580 nm to 720 nm on the LVOF and the
camera. The wavelength of the monochromatic light is swept in 1 nm steps. The Illuminated stripe region on the camera
detector moves as the wavelength is swept. Afterwards, a Neon lamp is used to validate the possibility of spectral
measurement. The light from a Neon lamp is collimated and projected on the LVOF on the camera chip. After data
acquisition a special algorithm is used to extract the spectrum of the Neon lamp.
This paper presents a wireless sensor network for smart electronic shirts. This allows the monitoring of individual
biomedical data, such the cardio-respiratory function. The solution chosen to transmit the body's measured signals for
further processing was the use of a wireless link, working at the 2.4 GHz ISM band. A radio-frequency transceiver chip was
designed in a UMC RF 0.18 μm CMOS process. The power supply of the transceiver is 1.8 V. Simulations show a power
consumption of 12.9 mW. Innovative topics concerning efficient power management was taken into account during the
design of the transceiver.
This paper presents a smart suit, water impermeable, containing sensors and electronics for monitoring handicapped people at hydrotherapy sessions in swimming-pools. For integration into textiles, electronic components should be designed in a functional, robust and inexpensive way. Therefore, small-size electronics microsystems are a promising approach. The smart suit allows the monitoring of individual biometric data, such as heart rate, temperature and movement of the body. Two solutions for transmitting the data wirelessly are presented: through a low-voltage (3.0 V), low-power, CMOS RF IC (1.6 mm x 1.5 mm size dimensions) operating at 433 MHz, with ASK modulation and a patch antenna built on lossy substrates compatible with integrated circuits fabrication. Two different substrates were used for antenna implementation: high-resistivity silicon (HRS) and Corning Pyrex #7740 glass. The antenna prototypes were built to operate close to the 5 GHz ISM band. They operate at a center frequency of 5.705 GHz (HRS) and 5.995 GHz (Pyrex). The studied parameters were: substrate thickness, substrate losses, oxide thickness, metal conductivity and thickness. The antenna on HRS uses an area of 8 mm2, providing a 90 MHz bandwidth and ~0.3 dBi of gain. On a glass substrate, the antenna uses 12 mm2, provides 100 MHz bandwidth and ~3 dBi of gain.