This paper presents research activities carried out at VTT Technical Research Centre of Finland in the field of hybrid
integration of optics, electronics and mechanics. Main focus area in our research is the manufacturing of electronic
modules and product structures with printed electronics, film-over-molding and polymer sheet lamination technologies
and the goal is in the next generation of smart systems utilizing monolithic polymer packages. The combination of
manufacturing technologies such as roll-to-roll -printing, injection molding and traditional component assembly is called
Printed Hybrid Systems (PHS).
Several demonstrator structures have been made, which show the potential of polymer packaging technology. One
demonstrator example is a laminated structure with embedded LED chips. Element thickness is only 0.3mm and the
flexible stack of foils can be bent in two directions after assembly process and was shaped curved using heat and
pressure. The combination of printed flexible circuit boards and injection molding has also been demonstrated with
several functional modules. The demonstrators illustrate the potential of origami electronics, which can be cut and folded
to 3D shapes. It shows that several manufacturing process steps can be eliminated by Printed Hybrid Systems
technology. The main benefits of this combination are small size, ruggedness and conformality. The devices are ideally
suited for medical applications as the sensitive electronic components are well protected inside the plastic and the
structures can be cleaned easily due to the fact that they have no joints or seams that can accumulate dirt or bacteria.
The laser photoacoustic spectroscopy (LPAS) can be applied analytically to determine the concentration of an analyte in
samples and its absorption variation as a function of time. The LPAS has advantages of higher detection sensitivity, pure
absorption measurement and much less interference by background scattering in comparison with traditional optical
spectroscopy. On the other hand, the apparatus is simpler and more generally useful than that of fluorescent
spectroscopy. In this study, we built a photoacoustic setup of a Q-switched Nd:YAG laser excited at the third harmonic
wavelength and a wideband piezoelectric transducer clamped to the side of a cuvette. The samples included NADH
solutions, mitochondrial suspensions and Intralipid-ink mixtures. The experiment results show that the lowest detectable
absorption of the setup is in the order of 10-5 cm-1; the detectable concentration of NADH in a buffer is as low as 1.67
μM. When monitoring mitochondrial suspensions, the minimal concentration that can be detected is lower than 0.1
mg/mL and the absorption variation caused by full reduction of NAD+ to NADH in mitochondria can be detected.
Self-mixing interferometry is a promising technique for a variety of measurement applications. Using a laser diode with
an external cavity as interferometer, the technique offers several advantages over traditional interferometric
configurations. This research used a self-mixing interferometer built in our own laboratory. It is based on a blue emitting
GaN laser diode with a wavelength of 405 nm. Light is directed through an optical fiber from which a 1-cm section of
cladding has been removed, and a cuvette for holding the sample is fixed around this part. Interference patterns, created
in the laser cavity, are acquired with a computer-based data acquisition system and later processed using Matlab
software. Since samples with different refractive indices create interference patterns with different phases, even small
changes in sample concentrations can be measured. However, coupling light into a single-mode optical fiber is a very
challenging task, and the setup is very sensitive to external interference like airflows or vibrations. Experiments with the
device showed that, in stability measurements, the standard deviation of the recorded fringe pattern shifts was only 1.7
nm. In sample measurements, the refractive index change in the sample chamber varied from 1.0029 to 1.33,
corresponding to a fringe pattern shift of 297±4 nm.
This paper presents a novel method for detecting a change in the refractive index of samples. One of its major
applications is sensing molecular interaction in biological samples. In our study a self-mixing interferometer (SMI) was
chosen as the instrument for measuring the refractive index in free -space. A GaN blue laser diode was used as a light-emitting
source. Compared with traditional interferometric configurations, self-mixing interferometry combined with
the laser diode package has the advantage of a compact setup and high sensitivity.
Long-term stability issue was first concerned in our research. The results showed that in 15 minutes the movement of
the fringe pattern formed by the self-interfered laser beam is 13.6 nm. The measurement of the refractive index was
performed by adding a heating element to the external cavity of the SMI. The refractive index of the air in the external
cavity was varied by the atmospheric temperature. The change in the refractive index of the air was calculated using
both a modified Edlén equation and the recorded self-interfered signals. The results showed that the change in the
refractive index observed from the shift in the fringe pattern is compatible with that calculated with the modified Edlén
equation, or about 1×10-6/°C with optical path length of 5 cm. Theoretically, the smallest movement of the fringe pattern
that can be detected with our measurement setup is 1.6 nm, corresponding to a 10-8 change in the refractive index in the
external cavity.
The study concerns the Monte Carlo simulation of the optical coherence tomography (OCT) signal from blood and
Intralipid layers. We show that in the case of the hematocrit values of 5 , 10, and 35%, the rear border of a 0.5-mm-thick
blood layer is clearly distinguishable in the signal. The finding is in line with the fact that the least-scattering component
gives a major contribution to the signal. In the case of Intralipid, the major contribution comes from the multiple-
scattering component, and the signal from the rear border is not visible. The scattering properties of Intralipid, a highly
scattering medium, can be ascertained fiom the slope of the downward slanting part of the signal. As it has been proved,
the change of the detector radius strongly influences the shape of the signal. The larger the radius is, the larger is the
contribution from multiple-scattered photons. On the contrary, the change of the numerical aperture (NA) of the detector
does not change the shape of the signal, as the contributions from diversely scattered photons respond in a similar way.
Hence, to optimize the determination of the properties of the media from the OCT signal slopes, a small detector radius
and large NA should be used.
The problem of fast investigation of the structural properties of paper samples is of great interest nowadays. The existing methods for structural imaging of paper require long time for obtaining the final result or need changing the structure of the studied sample. One of modem high-promising non-invasive techniques for faster examination of paper structure is optical coherence tomography (OCT), based on the principles of low-coherence interferometry of light backscattered from the investigated object. In present paper we simulate OCT signals from different paper samples with planar and non-planar geometry of air-fiber boundaries implementing Monte Carlo method. OCT provides quality images of in-depth scanning for optically transparent low-scattering objects, however for high-scattering media the maximal scanning depth is quite small. In order to increase the scanning depth for such media different clearing agents are used. We consider ethanol, 1-pentanol, glycerol and benzyl alcohol as such agents applied to a paper sample. Obtained results show, that all agents under consideration provide better visualization of rear border of the studied sample, which is very important for precise paper thickness measurement. However, the agents, showing the best results for rear border visualization provide worse visualization of the inner structure of the sample.
In various publications, the values of blood optical parameters reported or used by different authors dffer dramatically.
The aim of the present work is to estimate by means of Monte Carlo simulation the effect of variations of some of these
parameters on the signals measured by different light scattering techniques. The following techniques are considered.
optical coherence tomography, time-of-flight measurements, goniophotometry, and spectrophotometry implementing
the integrating spheres measurements. The base wavelength of 820 mn within the diagnostic window, which is
frequently used when implementing the mentioned techniques was chosen for the simulations. It was shown that both
scattering coefficient and anisotropy factor affect the output signals. which vary significantly in the considered ranges
of the parameters values. The strongest variations are due to varying the anisotropy factor, while varying the scattering
coefficient influences primarily the level of the signal, but preserves its shape.
In the future fast, simple and reliable biosensors will be needed to detect various analytes from different biosamples. This is due to fact that the needs of traditional health care are changing. In the future homecare of patients and peoples' responsibility for their own health will increase. Also, different wellness applications need new parameters to be analysed, reducing costs of traditional health care, which are increasing rapidly.
One fascinating and promising sensor type for these applications is an integrated optical interferometric immunosensor, which is manufactured using organic materials. The use of organic materials opens up enormous possibilities to develop different biochemical functions. In label free biosensors the measurement is based on detecting changes in refractive index, which typically are in the range of 10-6-10-8 [1].
In this research, theoretically generated interferograms are used to compare various signal processing methods. The goal is to develop an efficient method to analyse the interferogram. Different time domain signal processing methods are studied to determine the measuring resolution and efficiency of these methods. A low cost CCD -element is used in detecting the interferogram dynamics.
It was found that in most of the signal processing methods the measuring resolution was mainly limited by pixel size. With calculation of Pearson's correlation coefficient, subpixel resolution was achieved which means that nanometer range optical path differences can be measured. This results in the refractive index resolution of the order of 10-7.
We describe an optical displacement sensor based on optical feedback interferometry in a blue-light emitting GaN laser diode. Also presented are preliminary results from measuring variations in the optical path length (OPL) of an external cavity (EC) in the 0- to 240-nm range. These results show that, within the specified range, the sensor follows linearly the OPL variation of the EC. Moreover, the slope between a reference and the measured OPL is 1.0003, and the average deviation from the linear slope is 5 nm in this range. Finally, we also consider the stability of the interference signal in long-term measurements.
In the present paper the problem of protection of human skin against harmful UV solar rays using nano-sized spherical particles of titanium dioxide and sensing their concentration if embedded into skin is considered. Experimental tape-stripping method was used to reveal the in-depth distribution of the particles within the horny layer up to 20 µm. Computer simulations of optical coherence tomography (OCT) investigations of skin and, in particular, horny layer in vitro with and without titanium dioxide particles added were also performed in order to understand, if this modern non-invasive technique is applicable for skin study and revealing the distribution of nanoparticles within the horny layer. The effect of particles size (25-200 nm) and concentration on simulated OCT signals was analyzed. The increase of scattering in the sample (with increase of particles concentration or size) leads to increase of the OCT signal slope and decrease of rear border peak. We also performed simulations implementing the Monte Carlo technique to evaluate the protecting effect of titanium dioxide nanoparticles of different size. The most effective sizes were revealed. Computations were performed for the wavelength of 290.5 nm as the most harmful one. Dependencies of light intensities absorbed, backscattered, and transmitted through the whole horny layer (20 µm thick) on concentration of titanium dioxide particles (0-5%) were obtained and analyzed.
In this paper, we numerically simulated the signals of an optical coherence tomography (OCT) setup from skin and diluted blood (Hct = 5%) layers in order to reveal the possibilities of OCT application to different biological objects at different wavelengths (820 nm for blood and 633 nm for skin), in particular, in relation to the problems of optical clearing of tissues and increasing of penetration depth of the OCT systems. The chosen model parameters coincide with the parameters of a real OCT setup. The optical parameters of simulated biological media coincide with those published in literature. For a blood layer it was shown that the rare borders of a glass cuvette with diluted blood for in vitro investigations can be clearly detected for layer thicknesses up to 1 photon transport pathlength (around 2.3 mm). To calculate the OCT signals from skin two models were used. The simplest model considers skin as a two-layered medium with optical properties of epidermis and dermis. The other model considers skin as a five-layered structure (epidermis, dermis, dermis with plexus superficialis, dermis, dermis with plexus superficialis). Different values of model optical parameters of the layers were used to take into consideration possible deviations of these parameters in biotissues. Dependences of the signal fringe pattern amplitudes from interlayer borders on optical properties of the media were analysed.
In this paper, optical measurement techniques, which enable non-invasive measurement, are superimposed to glucose sensing in scattering media. Used measurement techniques are Optical Coherence Tomography (OCT), Photoacoustic spectroscopy (PAS) and laser pulse Time-of-Flight (TOF) measurement using a streak camera. In parallel with measurements, a Monte-Carlo (MC) simulation models have been developed. Experimental in vitro measurements were performed using Intralipid fat emulsion as a tissue simulating phantom for OCT and TOF measurements. In PAS measurements, a pork meat was used as a subject but also preliminary in vivo measurements were done. OCT measurement results show that the slope of the OCT signal's envelope changes as a function of glucose content in the scattering media. TOF measurements show that the laser pulse full width of half maximum (FWHM) changes a little as function of glucose content. An agreement with MC-simulations and measurements with Intralipid was also found. Measurement results of PAS technique show that changes in glucose content in the pork meat tissue can be measured. In vivo measurements with a human volunteer show that other factors such as physiological change, blood circulation and body temperature drift may interfere the PA response of glucose.
The Optical Coherence Tomography (OCT) technique proves a subsurface structure investigating along the penetration depth of incident light. The basic principle of this technique is to locate the envelope maximum position of low-coherence interference fringes obtained under the controllable displacement of the reference mirror in interferometer. The obtained OCT image presents a result of convolution of random tissue internal structure presented by a path-length-resolved diffuse reflectance with interferometer response on the ideal change of optical path difference, i.e. with a low-coherence fringe envelope, which has usually known Gaussian form. To increase the OCT image resolution, the deconvolution method can be used. In this paper, the application results of the iterative van Cittert algorithm of deconvolution to the OCT images are presented. Experimental results demonstrate the increase of the envelope peaks after 3 - 5 iterations approximately in 1.5 times with better resolution between them. The tissues tomograms calculated using van Cittert algorithm are presented. Some OCT image details lost in the usual OCT tomograms are visible and more contrast.
Flow velocity of scattering intralipid mixture within the glass capillary is measured using Doppler Optical Coherence Tomography (DOCT) technique. In the DOCT system, interference fringe frequency shift contains information about velocity of mixture. Due to scattering, interference fringe parameters are disturbed and stochastic fringe processing method should be used to evaluate fringe frequency. Interferometric signal frequency and other parameters have been estimated dynamically using discrete nonlinear Kalman filtering method. The stochastic filtering methodology and nonlinear Kalman filtering method are considered with application to experimental DOCT data processing.
In this study, we propose to apply the method optical coherence tomography (OCT) for paper characterization. A PC-controlled experimental measurement system for OCT-imaging of paper is described in detail. A superluminescent diode is used as a light source in a Michelson interferometer. A rapid scanning optical delay line is using a piezo-transducer to modulate the measurement signal for optical heterodyne detection. Amplification, filtering and demodulation are performed by the unit specially designed for this purpose. Experimental measurements include the OCT slice imaging of a paper sample and comparison with a SEM-image. Also some results in surface profilometry are presented briefly. Discussion part gives some ideas of further research that will be carried out in the future.
Peculiarities of light transport in IntralipidTM solutions and the effect of glucose on light scattering properties of the
solution at two different IntralipidTM concentrations were studied with optical coherence tomography (OCT) technique
in vitro. An open air OCT system using a superluminescent light source with center wavelength = 830 nm was used. 5% IntralipidTM
solutions were used to simulate a biological tissue (skin) in our experiment. Glucose concentrations at the
physiologically relevant level were added to IntralipidTM solutions. Increasing IntralipidTM concentration increases the scattering coefficient of the media meanwhile increasing glucose concentration increases the refractive index of the
media and reduces the scattering coefficient of the media. The experimental data were compared to Monte Carlo
simulations. We also made the simulations for 2% IntralipidTM solution. The results indicate that glucose added to 2 and 5% IntralipidTM solutions changes their scattering properties, which is manifested by a decrease in the slope of the OCT signal. This finding shows the ways of using OCT for sensing glucose and monitoring the alterations of its content in
biotissues. Some discrepancies between measurements and simulations were found, which need further investigation.
Interferometers with a low-coherent illumination allow non-contact evaluating random tissues by locating the visibility maxima of interference fringes. The problem is the light scattering by a tissue, it is why interference fringe parameters are randomly varied. Other problem consists in the need to process large amount of data obtained in optical coherence tomography (OCT) systems. We propose to use a stochastic fringe model and Kalman filtering method for noisy low-coherence fringe processing. A fringe signal value is predicted at a next discretization step using full information available before this step and a prediction error is used for dynamic correction of fringe envelope, frequency and phase. The advantages of Kalman filtering method consist in its noise-immunity, high-speed data processing and optimal evaluation of fringe parameters. Specially fabricated random tissues have been measured with a low-coherence interferometer. The obtained data from the tissue internal structure are evaluated using a dynamic stochastic fringe processing algorithm applied to fringe signal samples series. Nonlinear Kalman filtering method was applied to measure scattering liquid velocity profile in the Doppler OCT. The measurement results are in good agreement with the results obtained by the Fourier transform method.
Interferometers with a low-coherent illumination allow non-contact measuring the rough surface relief or multilayer tissues by locating the visibility maxima of interference fringes. The problem is the light scattering by the surface to be evaluated; it is why the interference fringes are often distorted. Other problem consists in the need to process large amount of data obtained in optical coherence tomography (OCT) systems. We propose to use a stochastic fringe model and Kalman filtering method for noisy low-coherent fringe processing. A fringe signal value is predicted at the next discretization step using full information available before this step and the prediction error is used for dynamic correction of fringe envelope and phase. The advantages of Kalman filtering method consist in its noise-immunity, high-speed data processing and optimal evaluation of fringe parameters.
The aim of this study was to measure the velocity and velocity profile of 0.3% Intralipid mixture in a 1.5-mm thick glass capillary using Doppler Optical Coherence Tomography (DOCT). First, while still empty, the dimensions of the capillary were measured. The outer diameter was 1.50 mm ± 0.01 mm while the lumen diameter was 1.01 ± 0.01 mm. Then, having filled the capillary with 0.3% solution, the lumen diameter was measured again. The mean refractive index of the solution was calculated and turned out to be 1.36 ± 0.01 mm. During the next stage, flow measurements were performed at an angle of 88° between the illuminating beam and the velocity vector of the fluid. The velocity profile, based on a set of 10 measurements, was calculated from the DOCT signal using a discrete Fourier transform in 32 sections of the capillary. The maximum velocity, located in the middle part of the capillary, was 0.256 ± 0.035 m/s. The results show that the flow velocity profile of 0.3% Intralipid solution can be obtained from a glass capillary.
This paper investigates the correlation between the shape of the first derivative of a blood pressure pulse and the corresponding Doppler spectrogram, reconstructed from a Doppler signal produced by the movement of the skin above the radial artery in the human wrist. The aim is to study to what extent the arterial pulse shape can be measured using self-mixing interferometry. To obtain a point of reference, a commercial non-invasive blood pressure monitor was first used to measure both blood pressure and pulse shape. Then, a self-mixing interferometer was applied to measure the arterial pulse above the radial artery. Measurements on 10 volunteers yielded a total of 738 pulses for analysis. A cross correlation of 0.84 ± 0.05 was established between the shape of the first derivative of the pressure pulse and the Doppler spectrogram. Using an empirical constant of 0.7 as a limit for successfully detected pulses produced a detection accuracy of 95.7%. The results show that self-mixing interferometry lends itself to the measurement of the arterial pulse shape, and that the thus obtained shape is in good agreement with that produced by a commercial blood pressure monitor.
Interferometers with a low-coherent illumination allow non-contact evaluating random tissues by locating the visibility maxima of interference fringes. The problem is the light scattering by a tissue, it is why interference fringes are often distorted. Other problem consists in the need to process large amount of data obtained in optical coherence tomography (OCT) imaging systems. We propose to use a stochastic fringe model and Kalman filtering method for noisy low-coherence fringe processing. A fringe signal value is predicted at a next discretization step using full information available before this step and a prediction error is used for dynamic correction of fringe envelope and phase. The advantages of Kalman filtering method consist in its noise-immunity, high-speed data processing and optimal evaluation of fringe parameters. Several specially fabricated wood fiber tissues have been measured with a low-coherence interferometer. The obtained data from the tissue internal structure are evaluated using a dynamic stochastic fringe processing algorithm applied to fringe signal samples series. The statistical approach for characterizing wood fiber tissues of different kinds is proposed.
Optical coherence tomography (OCT) is used mainly for noninvasive cross-sectional imaging in biological systems. In this technique, a lateral scanning low-coherence interferometer is employed to produce a two-dimensional image of an object's internal microstructure. This paper presents an experimental OCT measurement system based on a bulk-type Michelson interferometer illuminated by a superluminescent light source. The system was used to provide a visual image of multilayer plastics. In addition, the research team conducted experiments to measure the thickness of varnish on top of plywood and experimented with paper measurements. The system produced two-dimensional pictures of multilayer plastics, showing that it is applicable to transparent media.
In this study, a noninvasive laser Doppler measurement method based on the self-mixing effect of a diode laser was used to measure baroreflex regulation, which is manifest in the blood pressure signal as a 0.1 Hz sinusoidal variation. The laser Doppler measurement system was used to measure the movement of the right radial artery of ten volunteers. Variation in blood pressure caused by the baroreflex affects the elastic properties of the arterial wall. When diastolic blood pressure increases, the elasticity of the arterial wall decreases, causing the wall to lose some of its movability. This decreased elasticity reveals itself in the Doppler signal such that when the blood pressure increases, the Doppler frequency decreases and vice versa. The results show, that the laser Doppler method can be used to measure baroreflex regulation. Finally, baroreflex regulation in the Doppler signal is approximately in the inverse phase with respect to variation in diastolic blood pressure.
The aim of this study was to study the elasticity of the arterial wall using a non-invasive laser Doppler measurement system. The elasticity of the arterial wall is described by its compliance factor, which can be determined when both blood pressure and the radial velocity of the arterial wall are known. To measure radical velocity we used a self- mixing interferometer. The compliance factors were measured from six healthy volunteers, whose ages were varied from 21 to 32. Although a single volunteer's compliance factor is presented as an example, this paper treated the volunteers as a group. First, the elastic modulus, which is inversely proportional to the compliance factor, was determined. Then, an exponential curve was fitted into the measured data and a characteristic equation for the elastic modulus of the arterial wall was determined. The elastic modulus was calculated at different pressures and the results were compared to the static incremental modulus of a dog's femoral artery. The results indicate that there is a correlation between human elastic and canine static incremental modulus for blood pressures varying from 60 to 110 mmHg.
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