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Printed and hybrid integrated electronics produced from recycled and renewable materials can reduce the depletion of limited material resources while obtaining energy savings in small electronic applications and their energy storage. In this work, bio-based poly(lactic acid) (PLA) and recycled polyethylene terephthalate (rPET) were fabricated in film extrusion process and utilized as a substrate in ultra-thin organic photovoltaics (OPV). In the device structure, metals and metal oxides were replaced by printing PEDOT:PSS, carbon and amino acid/heterocycles. Scalable, energy-efficient fabrication of solar cells resulted in efficiencies up to 6.9% under indoor light. Furthermore, virgin-PET was replaced with PLA and rPET in printed and hybrid integrated electronics where surface-mount devices (SMD) were die-bonded onto silver-printed PLA and virgin-PET films to prepare LED foils followed by an overmoulding process using the rPET and PLA. As a result, higher relative adhesion of PLA-PLA interface was obtained in comparison with rPET-PET interface. The obtained results are encouraging from the point of utilization of scalable manufacturing technologies and natural/recycled materials in printed and hybrid integrated electronics. Assessment showed a considerable decrease in carbon footprint, about 10–85%, mainly achieved through replacing of silver, virgin-PET and modifying solar cell structure. In outdoor light, the materials with low carbon footprint can decrease energy payback times (EPBT) from ca. 250 days to under 10 days. In indoor energy harvesting, it is possible to achieve EPBT of less than 1 year. The structures produced and studied herein have a high potential of providing sustainable energy solutions for example in IoT-related technologies.

Understanding the phenomena at interfaces is crucial for producing efficient and stable flexible organic solar cell modules. Minimized energy barriers enable efficient charge transfer, and good adhesion allows mechanical and environmental stability and thus increased lifetime. We utilize here the inverted organic solar module stack and standard photoactive materials (a blend of poly(3-hexylthiophene) and [6,6]-phenyl C61 butyric acid methyl ester) to study the interfaces in a pilot scale large-area roll-to-roll (R2R) process. The results show that the adhesion and work function of the zinc oxide nanoparticle based electron transport layer can be controlled in the R2R process, which allows optimization of performance and lifetime. Plasma treatment of zinc oxide (ZnO) nanoparticles and encapsulation-induced oxygen trapping will increase the absolute value of the ZnO work function, resulting in energy barriers and an S-shaped IV curve. However, light soaking will decrease the zinc oxide work function close to the original value and the S-shape can be recovered, leading to power conversion efficiencies above 3%. We present also an electrical simulation, which supports the results. Finally, we study the effect of plasma treatment in more detail and show that we can effectively remove the organic ligands around the ZnO nanoparticles from the printed layer in a R2R process, resulting in increased adhesion. This postprinting plasma treatment increases the lifetime of the R2R printed modules significantly with modules retaining 80% of their efficiency for ∼3000 h in accelerated conditions. Without plasma treatment, this efficiency level is reached in less than 1000 h.

Indene-C60-bisadduct (ICBA) can represent an excellent choice as an acceptor of organic solar cells due to the, at most, similar cost, higher efficiency, and higher open-circuit voltage (VOC) obtained in small-scale devices compared to phenyl[60]butyrate methyl ester ([60]PCBM). We have investigated ICBA in printed solar cells and assessed the upscale of the printing process to a roll-to-roll (R2R) pilot production. Performances of poly(3-hexylthiophene):ICBA solar cells are confirmed to be superior compared to [60]PCBM. Using large scale 2D R2R printing techniques, with both active material systems excellent processability, reproducibility, and yield are reached. At first, ICBA based large area modules (57 cm2) showed significant loss in efficiency. However, stressing the devices by exposure to sunlight was found to lead high efficiency modules with a VOC of 0.78 V per cell and a PCE of 3.4%. This is among the highest VOC per cell values realized with fully R2R processed organic photovoltaic modules and among the highest PCEs with P3HT based R2R processed modules. Imaging techniques have allowed to identify that stressing with sunlight partially burns shunts and recovers S-shaped behavior in the ICBA-based modules.

We describe the fabrication of roll-to-roll (R2R) printed organic photovoltaic (OPV) modules using gravure printing and rotary screen-printing processes. These two-dimensional printing techniques are differentiating factors from coated OPVs enabling the direct patterning of arbitrarily shaped and sized features into visual shapes and, increasing the freedom to connect the cells in modules. The inverted OPV structures comprise five layers that are either printed or patterned in an R2R printing process. We examined the rheological properties of the inks used and their relationship with the printability, the compatibility between the processed inks, and the morphology of the R2R-printed layers. We also evaluate the dimensional accuracy of the printed pattern, which is an important consideration in designing arbitrarily-shaped OPV structures. The photoactive layer and top electrode exhibited excellent cross-dimensional accuracy corresponding to the designed width. The transparent electron transport layer extended 300 µm beyond the designed values, whereas the hole transport layer shrank 100 µm. We also examined the repeatability of the R2R fabrication process when the active area of the module varied from 32.2 cm(2) to 96.5 cm(2). A thorough layer-by-layer optimization of the R2R printing processes resulted in realization of R2R-printed 96.5 cm(2) sized modules with a maximum power conversion efficiency of 2.1% (mean 1.8%) processed with high functionality.

We present a gravure printing process for zinc oxide (ZnO) nanoparticle ink to be used as a hole-blocking layer in inverted organic solar cells, enabling the production of patterned devices with freedom of design. The printability of the ink is optimized in a pilot-scale roll-to-roll (R2R) process, leading to smooth layers having a thickness of few tens of nanometers. The properties of the printed ZnO film are further optimized using R2R post-printing plasma treatment, which leads to increased adhesion and power conversion efficiency (PCE). The functionality of the printed ZnO layer is demonstrated in fully R2R-printed inverted solar cells showing high performance (2.9 % mean PCE).

Printed electronics and other large area roll-to-roll compatible manufacturing processes are opening up new opportunities for cost efficient mass production of electronics among other functionalities. Several large area and flexible substrates are being pursued such as plastic, paper, metal foils and fabrics as well as on glass. In this chapter different printing processes including flexography, gravure, screen and inkjet printing to deposit different solution-based materials for functional electronic devices on the glass substrate are presented. In addition, several application cases where printing processes are used to manufacture active components on flexible glass are introduced. In addition emerging high resolution printing processes, reverse offset and gravure offset techniques, are presented. Roll-to-roll printed organic photovoltaics cells printed on flexible glass are presented in details. Future trends of printed and hybrid electronics are discussed.

Organic light emitting diodes (OLED) are developing rapidly and provide a huge market potential for signage, lighting and display applications. Cost efficient manufacturing of OLED components on different flexible substrates is under heavy investigation. In this paper focus is on polymer OLEDs and their non-vacuum solution processing using roll-to-roll (R2R) printing techniques. In this paper VTT's R2R manufacturing process capabilities for printed OLED components are presented. Several demonstrator concepts based on printed OLED technology are introduced including; printed OLED elements 1) in a smart package, 2) a 7-segment display integrated in a ID-1 card, 3) an electronics voting card with OLED indicator and 4) a 35 cm2 OLED lighting element printed on glass.

A novel high-durability multifunctional organic–inorganic hybrid coating material is presented in this work as luminescent down-shifting (LDS) host matrix system for flexible organic photovoltaic (OPV) devices. Such new LDS coating is obtained by incorporating a convenient fluorescent organic dye in an appropriately functionalized fluoropolymeric resin that can be readily crosslinked by means of a dual-cure mechanism with a single-step ambient-temperature photo-induced sol–gel process. Due to its peculiar characteristics, the newly proposed system may be readily implemented in heat-sensitive flexible devices. By carefully tuning the amount of organic fluorophore in the hybrid coating material, a maximum increase in power conversion efficiency exceeding 4% is achieved on devices incorporating the new LDS layer with respect to control systems. This represents the highest efficiency enhancement reported to date on flexible OPVs by means of a polymer-based LDS layer. In addition, long-term accelerated weathering tests (>550 h) highlight the excellent stability of LDS-coated OPV devices, which can retain 80% of their initial performance, as opposed to the dramatic efficiency decay experienced by control uncoated devices. The approach presented here opens the way to the straightforward incorporation of versatile multifunctional light-managing layers on flexible OPV systems for improved device efficiency and lifetime.

There is a need for low-cost mass-production circuits on various substrates, possibly performing some simple functions as switches, antennas, displays, and sensors. Also in the field of gas sensors widely used in several applications there is a need for such novel fabrication technologies and materials. In this paper, we present three gas sensor structures fabricated using novel printing techniques. Inkjet and gravure printing techniques were used for fabrication of resistive WO3 nanoparticle gas sensors for detection of NO, and inkjet printing was utilized for fabrication of solid electrolyte (mixture of H3PW12O40 and PVC) in a nanostructured Metal-Electrolyte-Insulator- Semiconductor (MEIS) transistor for detection of H2. The sensor structures were found to be sensitive for detection of NO below 10 ppm, and H2 below 100 ppm concentrations in synthetic air, respectively.

The performance of bulk-heterojunction solar cells made with poly(3-hexylthiophene) (P3HT) as the donor and phenyl-C61-butyric acid methyl ester (PCBM) as the acceptor depends strongly on various factors in fabrication processes. This work studies the effect of the thickness of the P3HT:PCBM layer produced in the spin coating process on photovoltaic performances. Thickness dependent optical absorption in P3HT:PCBM layer is numerically modelled and the results are compared with experimental data. In addition, it is analyzed how degradation of air-exposed P3HT:PCBM blends depends on the storage time in nitrogen atmosphere.

We report on polymer-based solar cells prepared by the high-throughput roll-to-roll gravure printing method. The engravings of the printing plate, along with process parameters like printing speed and ink properties, are studied to optimise the printability of the photoactive as well as the hole transport layer. For the hole transport layer, the focus is on testing different formulations to produce thorough wetting of the indium-tin-oxide (ITO) substrate. The challenge for the photoactive layer is to form a uniform layer with optimal nanomorphology in the poly-3-hexylthiophene (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blend. This results in a power conversion efficiency of 2.8% under simulated AM1.5G solar illumination for a solar cell device with gravure-printed hole transport and a photoactive layer.

This paper presents a novel process chain for fabrication of replication masters for serial manufacture. The proposed process chain is validated for serial fabrication of (large area) organic electronic devices on flexible substrates. The advantages and limitations of the component technologies in the proposed manufacturing route are discussed and their interdependencies in a process chain for producing both 2.5D and 3D nano- and micro-structures are analysed. The proposed master-making route relies on using different technologies for micro-structuring and sub-micron and nano patterning that are applied to the fabrication of Ni shims incorporating different length scale features. In particular, the capabilities of photolithography as a micro-structuring technology were combined with those of FIB machining to add sub-micron and nano-features on micro patterned fused silica templates. Then, by applying UV nanoimprint lithography such templates were validated and their nano and micro-structures were consistently replicated in one step. Finally, the feature transfer of such imprints onto Ni shims was also successfully accomplished with only minor deviations from the target dimensions.

The solution-based deposition of the metal back electrode in inverted polymer solar cells (PSCs) using roll-to-roll (R2R) compatible processing technologies is considered one of the crucial issues towards the upscaling of PSC technology, as it may allow the full exploitation of the high through-put and prospective low-costs envisaged by the R2R fabrication approach. In this work, a water-based solution-processable silver ink formulation with low annealing temperature was developed to be used as precursor for the fabrication of the metallic back-electrode in flexible inverted PSC devices fabricated by means of R2R-compatible printing techniques. In order to investigate the effect of the deposition of such reactive silver ink on the underlying PSC layers, different back-electrode architectures were investigated and thoroughly characterized. In addition, the influence of the thickness of the hole-transporting poly(ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) buffer layer on the functional performance of the PSC devices was also investigated and an optimized combination of back-electrode architecture and PEDOT:PSS thickness was found, that also allowed to obtain semi-transparent PSC devices. The results of this study demonstrate the possibility to employ R2R-compatible processing techniques for the deposition of the metallic back-electrode in flexible inverted PSCs from a solution-processable water-based reactive silver ink formulation characterized by low-annealing temperature, and provide useful insights into the key role played by the hole-transporting buffer layer in the realization of fully functional flexible PSC devices.

Due to the highly light scattering nature of paper, the imaging depth of optical methods such as optical coherence tomography (OCT) is limited. In this work, we study the effect of refractive index matching on improving the imaging depth of OCT in paper. To this end, four different refractive index matching liquids (ethanol, 1-pentanol, glycerol and benzyl alcohol) with a refraction index between 1.359 and 1.538 were used in experiments. Low coherent light transmission was studied in commercial copy paper sheets, and the results indicate that benzyl alcohol offers the best improvement in imaging depth, while also being sufficiently stable for the intended purpose. Constructed cross-sectional images demonstrate visually that the imaging depth of OCT is considerably improved by optical clearing. Both surfaces of paper sheets can be detected along with information about the sheet's inner structure.

Signals of an optical coherence tomograph from paper samples are calculated by the Monte Carlo method before and after the action of different immersion liquids such as ethanol, glycerol, benzyl alcohol, and 1-pentanol. It is shown within the framework of the model used that all these liquids reduce the contrast of the inhomogeneity image in upper layers of the samples, considerably improving, however, the visibility of lower layers, allowing the localisation of the rear boundary of a medium being probed, which is important for precision contactless measuring a paper sheet thickness, for example, during the manufacturing process. The results of calculations are in well agreement with experimental data.

The self-mixing effect in a diode laser and the Doppler technique are used for quantitative measurements of the cardiovascular pulses from radial arteries of human individuals. 738 cardiovascular pulses from 10 healthy volunteers were studied. The Doppler spectrograms reconstructed from the Doppler signal, which is measured from the radial displacement of the radial artery, are compared to the first derivative of the blood pressure signals measured from the middle finger by the Penaz technique. The mean correlation coefficient between the Doppler spectrograms and the first derivative of the blood pressure signals was 0.84, with a standard deviation of 0.05. Pulses with the correlation coefficient less than 0.7 were neglected in the study. Percentage of successfully detected pulses was 95.7%. It is shown that cardiovascular pulse shape from the radial artery can be measured noninvasively by using the self-mixing interferometry.

This paper reports the pilot scale roll-to-roll (R2R) printing of flexible organic solar cell modules with conventional structure. In this module configuration, eight cells are monolithically series connected in order to increase the module output voltage to a desirable level for applications. Indium tin oxide (ITO) used as a hole contact is patterned with screen printing to a rectangular shaped cells with a spacing of 1 mm. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) which acts as an hole injection layer and photoactive layer based on poly-3-hexylthiophene (P3HT) and [6.6]-phenyl-C61-butyric acid methyl ester (PCBM) blend are pre-pared using R2R gravure printing. The sheet evaporated electron contact material of lithium fluoride/aluminium (LiF/Al) is applied for R2R printed modules.

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.

Aerosol jet printing is investigated as a new deposition method for a current collecting grid in indium tin oxide (ITO) free organic solar cells with an inverted layer sequence. In this device configuration, the ITO layer which usually serves as the hole contact is replaced by a transparent highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer in combination with a silver grid deposited by aerosol jet printing. Since the cells are illuminated from the grid side, the optimisation of the grid design is a trade-off between area coverage and conductivity of the grid lines. These factors have been controlled by the printing parameters such as chuck temperature, printing speed and the number of printing passes. In this paper, we demonstrate that continuous, conductive grid lines with a minimum line width of 58 μ m can be processed on the top of the PEDOT:PSS layer. For single pass printing the area coverage varied from 5.8% to 11.9% with corresponding effective sheet resistances ranging from 8.9 Ω to 1.5 Ω . The ITO-free inverted devices with aerosol jet printed grid (an active area of 1.1 cm2) show comparable performance to the cells with an evaporated gold grid. The effective sheet resistance can be further decreased by multiple printing passes without increasing the area coverage proportionally due to an improved aspect ratio. By increasing the conductivity and aspect ratio by multiple line printing, the cell length in the module structures can be significantly extended.

In this paper bottom gate bottom contact organic thin film transistors utilizing R2R-processes for gate manufacturing, application of dielectric, application of imprint resist, and hot-embossing of source-drain patterns are demonstrated. Also the other process steps involved in the manufacturing process i.e. dry etching, evaporation of source-drain electrodes, lift-off, and evaporation of semiconductor can be made in a roll-to-roll fashion, thus making the manufacturing route roll-to-roll compatible. The work presented in this paper demonstrates that roll-to-roll NIL is applicable to create source-drain structures with channel lengths much smaller than achieved by other traditional R2R-printing techniques.

In this letter, organic solar cell modules based on poly-3-hexylthiophene (P3HT) and [6.6]-phenyl-C61-butyric acid methyl ester (PCBM) blend films with a module active area of 15.45 cm2 prepared by roll-to-roll (R2R) compatible gravure printing method are demonstrated. The gravure printed organic photovoltaic modules consist of eight serially connected solar cells in same substrate. Indium-tin-oxide (ITO) is patterned by screen printable etching paste. Hole injection layer and active layer are prepared by gravure printing method. All processing steps excluding cathode evaporation are performed in air. Electrical measurements are done to modules consisting of 5–8 serially connected solar cells. The photovoltaic modules comprising 5, 7 and 8 serially connected cells exhibit an active area power conversion efficiency of 1.92%, 1.79% and 1.68%, respectively (Oriel Sol3A Class AAA, AM1.5G, 100 mW cm−2).

A novel electrode patterning technique by using lift-off a sacrificial black ink layer on thin polymer substrate was performed on a roll-to-roll (reel-to-reel, R2R) printing system. An active-matrix display array was demonstrated by this technique with 2000@mm display pixels with concept of MEMS (micro electro mechanical system) etalon. The resolution of this flexography lift-off system was improved to 100@mm for pattern isolation from gravure printing. Compare to well-developed hot embossing or laser ablation for polymer substrate's patterning, R2R lift-off provides a flat and smooth surface which is a must for multilayer stacking and reliability. This system also provides a high pattern integrity, low cost, large scale, and high throughput solution for electrode patterning on flexible polymer substrate.

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.

A 50% reduction of operation voltage improvement was achieved on a non self-emissive color filter pixels based on MEMS (micro electro mechanical system) Fabry-Perot interference device by minimizing its Newton's rings' size. Newly designed air grooves in spacer layer were proved to be efficient to evacuate air trapped inside pixels which in turn effectively lowered its operation voltage. A seesaw effect was also found if air groove occupied too large area which degrades the operation voltage lowering benefit.

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 Edlen 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 Edlen 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.

In this paper, MEMs solution of the biosensor based on optical feedback interferometry is presented. Optical feedback occurs when part of the emitted laser light is coupled back into the laser cavity. The light interacts with the original laser light producing an interference signal which is detected using a photodetector placed on the opposite side of the laser cavity

In this paper, we investigate possibilities of glucose level monitoring in skin

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.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A self-mixing interferometer is proposed to measure nanometre-scale optical path length changes in the interferometer’s external cavity. As light source, the developed technique uses a blue emitting GaN laser diode. An external reflector, a silicon mirror, driven by a piezo nanopositioner is used to produce an interference signal which is detected with the monitor photodiode of the laser diode. Changing the optical path length of the external cavity introduces a phase difference to the interference signal. This phase difference is detected using a signal processing algorithm based on Pearson’s correlation coefficient and cubic spline interpolation techniques. The results show that the average deviation between the measured and actual displacements of the silicon mirror is 3.1 nm in the 0–110 nm displacement range. Moreover, the measured displacements follow linearly the actual displacement of the silicon mirror. Finally, the paper considers the effects produced by the temperature and current stability of the laser diode as well as dispersion effects in the external cavity of the interferometer. These reduce the sensor’s measurement accuracy especially in long-term measurements.

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.

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 modem noninvasive 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.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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. Keywords: Doppler Optical Coherence Tomography, interference fringes, discrete nonlinear Kalman filtering 1. INTRODUCTION Flow measurements in scattering media with particles with different velocities are important for the biomedicine. For example, optical properties of blood in motion were evaluated 1 . Well known techniques of flow measurements, as Doppler Ultrasound and Laser Doppler Flowmetry are based on the Doppler effect

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 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.