University of Oulu
INFOTECH OULU

Optoelectronics and Measurement Unit (OPME)

Professor Risto Myllylä and Professor Markku Moilanen, Optoelectronics and Measurement Techniques Laboratory, Department of Electrical and Information Engineering, University of Oulu
Dr. Jouni Tornberg and Research Professor Harri Kopola, VTT, Oulu
Juha Kalliokoski, Research Director of the Measurement and Sensor Laboratory (Kajaani), University of Oulu

risto.myllyla(at)ee.oulu.fi, markku.moilanen(at)ee.oulu.fi, jouni.tornberg(at)vtt.fi, harri.kopola(at)vtt.fi, juha.kalliokoski(at)oulu.fi

http://www.infotech.oulu.fi/opme

Background and Mission

The Optoelectronics and Measurements Unit (OPME) comprises an intensive collaboration network of researchers at the Optoelectronics and Measurement Techniques Laboratory (OEM) at the University of Oulu, the Measurement and Sensor Laboratory (MILA) in Kajaani and VTT Oulu. The unit consists of 79 researchers and students who engage in high-level research in optoelectronics and measurements techniques, electronic testing techniques, wireless instrumentation with particular emphasis on the practical applications of these techniques, material techniques, photonics integration and testing needed in advanced sensors. A new technology field, printed intelligence, is integrated into the Optoelectronics and Measurements unit to bring together professionals from all above mentioned fields for close collaboration with a view to improving the know-how and education possibilities in this area.

The practical research and work activities in which the OPME unit is involved include, but are not limited to:

  • theoretical simulation and measurement of light propagation in turbulent and scattering media such as bio-tissues, bio-fluid, pulp and paper;
  • developing various optoelectronic measuring instruments based on optical coherence tomography, time resolved spectroscopy, photoacoustic spectroscopy and imaging ellipsometry for material characteristics;
  • exploring optically non-invasive biomedical measurement and paper evaluation, short and ultra-short optical pulse interactions with biological structures at tissue, cellular and molecular levels, and nano-particles in biomedical application;
  • building optical tweezers for trapping single micro-particles and studying their optical scattering and scattering phase function;
  • electronics testing techniques such as embedded testing, RF testing and EMC testing and measurement methods;
  • developing wireless sensors and sensor networks for healthcare applications; for example, using ZigBee and UWB technologies to measure and monitor various signals and parameters, such as ECG, heart rate, respiration, blood pressure, and other parameters as location and position of patients in a ubiquitous environment;
  • integration of optical interconnects on circuit boards;
  • optical and micro- sensors produced with MEMS technology, camera and machine vision in optical measurement;
  • advanced optical, ultrasonic, and microwave techniques specially applied in wood processing;
  • printable optics and optoelectronics which integrate traditionally optoelectronic devices to polymer platforms (OLED, OSC, etc.).

As a member of the Infotech Oulu Graduate School, the OPME unit also arranges lecture series and graduate school courses for graduate students. During 2008, the unit organized the traditional 8th Infotech Oulu Workshop on Optoelectronic Devices and Instrumentation, concentrating this time on "Nano-photonics and related applications".

In 2008, there were 20 new projects opened in the OPME unit, taking the total project number up to 35. The unit published 40 journal articles, 47 international conference papers and 16 other scientific papers. Research collaboration has been active with 17 domestic partners located in Finnish universities and VTT, and 24 international partners coming from universities and institutes in the USA, Canada, Japan, Korea, China, Russia, UK, Ireland, Poland, Germany, Sweden, and many other countries. The international visits for research activities, each of a duration of one month or more, involve 10 foreign visits coming to the OPME unit and also 10 visits from the unit going to aboard.

It is worthy of mention that in 2008 Professor Risto Myllylä was promoted to Fellow Status of SPIE - the International Society for Optical Engineering - for his specific achievements in laser pulse range finding and optical coherence tomography.

Scientific Progress

The following research examples illustrate the scientific progress of the OPME unit. These research projects have been carried out in active collaboration between both domestic and international research institutions and industrial partners.

Fiber Optic Self-Mixing Interferometry

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. It can be used in many kinds of sample concentration change studies in different fields. Research used a self-mixing interferometer built in our own laboratory which is based on a blue emitting GaN laser diode with a wavelength of 405 nm.

Light was directed through an optical fiber from which a 1 cm section of cladding had been removed, and a cuvette for holding the sample was fixed around this part. Interference patterns, created in the laser cavity, were 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 could be measured. However, coupling light into a single-mode optical fiber was a very challenging task, and the setup was 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 up to 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.

Sensor part of the measurement setup.

 

Optical Coherence Tomography (OCT) and Advanced OCT

Doppler OCT in Flow Velocity Profile Measurements

In recent years, the technique of Doppler Optical Coherence Tomography (DOCT) has been rapidly developed due to major advances in imaging speed and manufacturing new light sources with a broader spectrum. The DOCT technique as well as the ordinary OCT technique is based on the interference of low coherent light. By using wide spectrum light sources, it is possible to achieve spatial resolution of 1-5 µm which is over ten times better than a resolution of an ultrasound. We developed DOCT and applied it on the measurements of the flow velocity profiles of different kinds of suspensions from cellular protoplasm to industrial pigments and printed electronic inks. The flow velocity profile is important for determining rheological characteristics such as a viscosity and a shear rate of non-Newtonian suspensions. We also studied the effect of the light scattering on the measured velocity profile of the suspension flow embedded into the scattering medium. The result shows that the specificity of the flow profile reconstruction in the case of the flow embedded into the scattering medium is the "non-zero" level of the detected frequencies at the rear border of the capillary.

 

OCT image of a glass capillary with the inner diameter of 0.5 mm filled with the 1% Intralipid solution in flow and embedded at the depth of 185 µm into 1% Intralipid solution (the capillary walls are two similar dark blue stripes, right one corresponds to the deeper wall and has lower contrast).

 

 

Intralipid flow profile for the case of the figure above. Pumping speed is 50 ml per hour.

 

 

Ordinary OCT and DOCT are also used to image of cytoplasm shuttle flow in strands of Physarum Polycephalum. Slime mould Physarum is a unicellular organism representing a non-stationary system of cylindrical strands which connect frontal zones of organism to the main body. Physarum shows the complex autowave amoeboid type of the cellular motility, including the contraction of the gel-like walls of the strands. These contractions generate the gradients of pressure which cause shuttle flow of the internal part of cytoplasm along the strands. The typical period of the oscillation of the strand with a diameter of about several hundred micrometers at room temperature is about 1 min.

OCT image (a) and time resolved DOCT image (b) of Physarum strand. In both images one can well see the contractions of upper border of strand wall.

 

Spectral Domain OCT for Ophthalmic Imaging

The development of spectral domain optical coherence tomography (SD-OCT) with a 1 µm probing band has been continued. This work has been performed in collaboration with the Computational Optics Group (COG) from the University of Tsukuba, Japan. The imaging speed of the SD-OCT system has improved to be 47 000 depth scans / sec. The spectrometer of that system is also modified to achieve a better signal to noise ratio (SNR). In addition to system development, some data processing methods have been implemented, including a Doppler signal based blood flow velocity determination method, and a retinal and choroidal vessel structure characterization method with artifact compensation. Several patient measurements have been performed to evaluate our system's suitability for diagnosing ophthalmic diseases.

Volume rendering image of the optic nerve head. The measurement was performed for a healthy human volunteer. The measured area covers 5x5 mm2.

 

UHR-OCT for Paper Imaging with Sub-Micron Resolution

An Ultra High Resolution Optical Coherence Tomography (UHR-OCT) system has been developed. Sub-micron resolution has been achieved by a device based on a Ti-sapphire femtosecond laser and nonlinear optics. The femtosecond laser generates 50 fs pulses with a pulse repetition rate of 86 MHz. The available spectral range is 750 - 850 nm and the average pulse power reaches 400 - 500 mW at 800 nm. These pulses are guided into a highly nonlinear, polarization maintaining photonic crystal fiber (PCF, Crystal Fibre Femtowhite 800). Introduction of high energy pulses, and interaction between the nonlinear effects in the PCF produce a phenomenon known as supercontinuum generation (SG). In SG, nonlinear effects generate new frequency components, and the narrow bandwidth light literally explodes in a wide range of new colors. When this broadband light is guided to the interferometer, sub-micron resolution in optical coherence tomography can be achieved, the resolution being much higher than with ordinary OCT devices based on a conventional SLD technique.

Schematic diagram of OCT device capable of sub-micron resolution. Po = polarizer, PS-BS = polarization sensitive beam splitter, FR = Faraday rotator, P = prism, M = mirror, O = objective, BS = beam splitter, L = lens, F = filter and D = detector.

 

 

Images of Pergamin paper with UHR-OCT (resolution 0.85 µm) (up) and OCT (resolution 8 µm, based on conventional SLD technique) (down).

 

Optical Tweezers for Trapping Micro-Particles

Optical tweezers offer a sophisticated and contactless way of studying small particles. A light beam is tightly focused with a high NA microscope objective to a small spot. The light beam intensity gradients generate forces and trap small particles under this illumination. The trapped objects may be manipulated by moving a sample stage or by changing different parameters of the trapping beam. The performance of the trap can be evaluated by calculating the trapping efficiency. It is dependent on the optical power after the objective, as well as the forces generated by the focused light. Trapping forces can be measured for example by using a viscous drag method.

The trapping efficiency of the system was evaluated using polystyrene microspheres with diameters of 3.1 µm and 6.0 µm and with red blood cells. The optical power of the trapping laser was measured simultaneously. The trapping efficiency can be calculated when the optical power and the trapping force are know.

Basic principle of the optical tweezers. A tightly focused Gaussian laser beam is used to create a strong axial and radial gradient force. A dielectric particle in the laser beam experiences a force towards the centre of the beam, where the light gradient is stronger.

 

Schematic of optical tweezers. Laser light is guided via a beam splitter and mirrors through microscope objective to trap the particles in the sample. White LED:s are used to show the image of the particles at the CCD camera. Polystyrene microspheres (diameter 6.0 µm), Bangs Laboratories, Inc. and human red blood cells (RBC) (diameter ~7.4 µm) are shown as examples of trapped objects.

 

Electronic Testing Techniques

The research was done in the REMTEST project (Remote Access Testing Platform). The goal of the REMTEST project, which is carried out in the Optoelectronics and Measurement Techniques, Electronics, and Microelectronics and Materials Physics Laboratories at the University of Oulu, was to evaluate the performance and cost benefits of embedded and remote testing in a real-life product context. Therefore, two generations of the same device - a Linux-based home media server - were designed and built; one with traditional electronics with conventional production and testing plan, and another loaded with several embedded test capabilities. The following subjects were developed during the two-year project.

A prototype of a product with embedded test techniques

  • embedded test structures including RF-test
  • automatic scheduled or remote controlled self-testing
  • implemented BIST methods
  • monitoring cell for proactive fault detection
  • wireless test access
  • controlled and in advance simulated defects

A prototype of a product with conventional design for

  • estimating the test structure impact on performance
  • comparing the developed testing process with conventional testing

Testing through a network with

  • remote service centre or control room
  • testing access and testing commands
  • test data files and post processing
  • preliminary tool for MTTF prediction

One of the most interesting novelties included in the REMTEST device is the capability to monitor BGA solder joint quality during normal operation of the product, and to predict the time of failure of these joints. This capability is made possible by bridge-based online measurement of solder ball resistance built in a test access ASIC, use of ceramic sockets with embedded corner balls under measurement, and the required prognostic mathematical and computer algorithms. In this method, the resistance of the corner balls is measured, and by detecting the increase of the resistance as the solder joints degrade over time, one can predict the actual time of critical failure.

 

Embedded BGA solder joint prognostics in the REMTEST device.

 

 

The remote user interface (UI) is built around the results received from the remote platform - i.e. the UI program sends requests to the remote server using an in-house (UTCS) format and then processes the results to a more human readable form such as that shown. The UI allows the user to select the tests he or she wants to run in the remote device, to run the selected tests, and to see the results in a tabular form or as highlighted component values in the schematic window on the left. It is worth emphasizing that the UI above described runs inside a normal web browser. Thus, the developed software is cross-platform and runs automatically in Windows PCs, UNIX workstations, web enabled smart phones, PDAs etc.

 

Remote REMTEST user interface in a web browser.

 

 

The HW of the REMTEST device with its embedded Linux computer, audio add-on card with wired and wireless communication capabilities mimics well the common structure of a modern IT product, thus making the findings of the project highly relevant to modern testing of electrical products. Therefore, the on-going analysis of the material created during the project will produce valuable information on the pros and cons of both the performance and cost of embedded life-cycle testing of future electrical products.

Non-Invasive Blood Pressure Measurement

This project is focused on designing and implementing a non-invasive blood pressure measuring device capable of being used during magnetic resonance imaging. This device is based on measuring pulse wave velocity in arterial blood and using the obtained result to estimate diastolic blood pressure. Pulse transit times are measured by two fibre optical accelerometers placed over the chest and carotid artery.

The fabricated accelerometer contains two static fibres and a cantilever beam. The free end of the beam is angled at 90 degrees to act as a reflecting surface. Optical fibres are used for both illuminating the surface and receiving the reflected light. Acceleration applied to the sensor causes deflection of the beam, whereupon the amount of reflected light changes. The sensor output voltage is proportional to the intensity of the reflected light.

Tests conducted on the electronics and sensors inside an MRI room during scanning proved that the device is MR conditional. No artifacts or distortions were detected.

Made with LabView, the measurement software automatically recognizes pulses and calculates their transit times and the patient's heart rate. The calculated data is saved and plotted in real time.

MR images of the tests.

 

 

Calculated pulse transit time (red line) and heart rate (green line) during an MRI scan. Before the scan, the patient was hyperventilating for two minutes, which causes an increase in the blood pressure (decrease in the pulse transit time) in the carotid artery.

 

TiO2 Nanoparticles as Inorganic UV Filter in Sunscreens

The main purpose of sunscreen use is to support additional protection to human skin while sunbathing. Protective properties of sunscreens are caused by absorption and scattering by their ingredients, chemical and physical compounds. Chemical compounds are organic molecules absorbing UV light. Physical compounds are nanoparticles of titanium dioxide (TiO2) and zinc oxide (ZnO) having both absorbing and scattering properties.

In the experiments, carried out in frames of collaboration with Prof. Lademann's group (Charité Hospital, Berlin, Germany) transmittance of UV light through a layer of o/w emulsion (L'Oréal, France) with nanoparticles UV-TITAN M 160 (Kemira, Finland) was measured with the spectrophotometer Lambda 20 (Perkin Elmer, Germany). In the corresponding simulations and experiments, 100 nm TiO2 nanoparticles with a volume fraction of 0.2% embedded into a 20 µm layer of the transparent medium with a refractive index 1.4 were considered. The maximal extinction is achieved at a wavelength of 360 nm. By using the Mie theory and taking into account the optical parameters of TiO2 particles at 360 nm wavelength, a combination of absorption (Qa) and scattering cross-sections (Qs) of particles, as well as scattering anisotropy factor (g) and particle diameter (d), [Qa + Qs*(1-g)]/d, is calculated for the particle diameters from 35 nm to 200 nm; the corresponding particle size, 98 nm in this case, of the maximal value of the quantity indicates the size which generates maximal attenuation. The maxima of the experiment and simulation curves clearly coincide, which means the size of nanoparticles embedded in the emulsion is about 100 nm.

Experimental and simulation attenuation curves resulting from TiO2 nanoparticles with average size of 100 nm (left) and dependence of quantity [Qa + Qs*(1-g)] / d on a particle diameter for 360 nm wavelength calculated using the Mie theory (right).

 

Photoacoustics in Measurement of Pulp Suspensions

Backward Scattering Model for Determination of Fiber and Fine Consistencies

Developing online techniques for simultaneously determining consistencies of long fibers and fine particles in a pulp suspension is a challenge work, which paper pulp mill is looking forward to it. It has been actively launched in the OEM laboratory based on an innovative method - scattering photoacoustic technique - which can simultaneously measure optical and acoustic parameters using a wide bandwidth, low ringing piezoelectric transducer. Long wood fibres and fine particles have different properties in optical scattering and acoustic attenuation. Therefore, the technique has a potential ability to determine the consistencies of suspensions with the two fractions. To improve the use efficiency of optical energy and reduce the cost in final instruments, the technique is further innovated as a backward model and a specific transducer has been developed in the OEM laboratory. Moreover, current results of online experiments show some other advantages, such as higher signal amplitude, larger measurement range (for high consistency), better linearity, and less effect of fibre flocks in suspension compared with the former sideward model. However, micro-air bubbles produced by entrained air or released by suspension still strongly interfere with the measurement results.

The self-made transducer assembled on a measurement chamber (left) and the online system in the experiments.

 

Simultaneous Measurement of the Kappa Number and Consistency

The Kappa number is a measure of lignin content in pulp fibers. In existing process measurement of Kappa number, pulp consistency is swept from a low level to a higher one. The optical signal is measured during this consistency sweep, and some of its consistency points are calibrated against laboratory data. Because of pulp scattering, the technique is incapable of separating optical absorption from scattering components, and therefore requires calibration of the measurement points. To save the calibration and seek a more convenient method for process measurement, a photoacoustic technique based on time-resolved stress reconstruction is originally applied to measure the optical parameters of pulp suspensions in the OEM laboratory. Reconstructing stress distribution along the direction of the incident laser light allows determining the effective attenuation coefficient of these suspensions. Simultaneously, by determining the total diffuse reflectance from the suspensions at the same wavelength, 355 nm, at which lignin exhibits definite optical absorption but wood cellulose and aqueous matrixes do not, the reduced scattering coefficient and absorption coefficient can be split up. The preliminary experiment demonstrates that a reduced scattering coefficient of the suspension has a linear relationship with fiber consistency, no matter what Kappa number the suspension has. Knowing the absorption coefficient and the consistency, the kappa number can be determined. Therefore, the technique has an ability to simultaneously measure both the fiber consistency and Kappa number of the pulp suspension.

On the left, the diamond, triangle and square marks correspond to samples with a kappa number of 2, 13, and 16, respectively; the solid marks represent absorption coefficients, and the empty marks reduced scattering coefficients. On the right, the triangle and square marks correspond to samples with a fiber consistency of 4% and 3%, respectively; the solid marks represent absorption coefficients and the empty marks reduced scattering coefficients. The lines show a linear relationship.

 

Refractive Index Matched Paper Testing Using a Microscope

The research at this early point is focused on basics. During 2008 we investigated the extent to which optical refractive index matching improves microscope's visibility. Different paper grades were transparentized with a different transparentizing agent and transparency was measured. The residual ink analysis of the de-inking process and de-inked pulp is expected to improve in accuracy as the techniques are ready.

A clear difference in transparency can be seen with a sample without a transparentizing agent on the left and with benzyl alcohol as a transparentizing agent on the right. The sample is 84 g/m2 and 122 µm newsprint.

 

Printed Electronics

The Optoelectronics and Measurement Techniques Laboratory has close co-operation with a group led by the FiDiPro Professor Ghassan E. Jabbour, a director of the Advanced Photovoltaics Center at Arizona State University. His group is involved in state-of-the-art research and development of a wide spectrum of rigid and flexible (including organic and hybrid) photovoltaics, OLEDs, organic thin film transistors, sensors, transparent conductors, encapsulation coatings, and smart textile, from the nano to the mega scale. Professor Jabbour has invited graduate students and post-doctoral scholars from Finland to visit his state-of-the-art laboratories and conduct research in the area of optoelectronics and printed electronics. The new printed electronics laboratory "The center for printing of nano-to-mega photonics, electronics, and bioinformatics" built-up by FiDiPro Prof. Jabbour will be ready for research and teaching in the spring of 2009 at University of Oulu.

First Demonstration of Electroluminescence from Inkjet Printed Quantum Dots

Quantum dots are nano-sized (from a few nanometers to tens of nanometers in diameter) inorganic particles with a crystalline atomic structure. Emission color can be simply tuned by varying the diameter of the dot: the bigger the dot becomes, the smaller the band gap is. Furthermore, emission spectra is extremely narrow compared to organic emitters (FWHM ~ 40 nm typically), resulting in purer colors, thus for example making them superior emitters for high definition displays.

Quantum dot light emitting diodes resemble organic LED; only the light emitting media is now inorganic nanoparticles. CdSe/ZnS quantum dots were inkjet printed in ambient conditions onto spin coated hole transport material poly(9-vinylcarbazole) PVK and finalized with thermally evaporated small molecule electron transport material TPBi (1,3,5-tris(2-N-phenylbenzimidazolyl) benzene) and a lithium fluoride/aluminum cathode. Indium Tin Oxide (ITO) worked as a transparent cathode. In this experiment, 200 µm quantum dot lines with 150 µm spacing were printed on a 1" by 1" substrate and the actual pixel was defined by a patterning cathode through a shadow mask; here one pixel was a 0.14 cm2 circle. Under positive bias (typically ~ 10 V), the device emitted only from the dots, indicating efficient quantum dot coverage (e.g. no pin holes) as well as complete energy transfer from the surrounding organic materials.

These results are remarkable from the manufacturing and actual product realization point of view due to a fast and low material consumption technique which allows direct patterning without masks or lithography steps. Thus far, similar devices have been made using spin coating or mist deposition, both undesirable candidates for low cost manufacturing of these devices.

An emission spectrum of an active device shows pure emission from the dots (around 600 nm) indicating perfect energy transfer as well as good coverage of dots. Insert: Photograph of printed lines in one pixel, pixel area ~0.14 cm2. The energy diagram explains charge transport in the device.

 

Device structure for inkjet an printed QD-LED. Simple structure contains printed QD layer sandwiched between organic charge transport layers. Typical drive voltage for such devices varies between 5 - 10 V.

 

 

Organic Solar Cells

The study of organic solar cells will have an increasingly important role in the development of carbon-free energy technologies. Organic solar cells are cheap to manufacture, flexible and environmentally friendly. As a disadvantage, organic solar cells suffer from relatively low energy conversion efficiency, which is currently about 5%.

Ghassan Jabbour's Optoelectronics group is concentrating on researching the important materials issues and how to optimize a printed solar cell device structure to enhance its efficiency and reliability. In manufacturing of tandem organic solar cells our approach employs ink-jet printing, spin coating, thermal deposition and hot embossing of a nano-thick layer on top of rigid and flexible substrates which already have the ITO electrode.

These methods require detailed understanding of the interactions of materials in solution, and the interaction of chemical solutions with the printing medium (e.g. nozzle and cartridge in inkjet printing). Moreover, understanding the interactions between the solar cell solution surface tension and the surface energy of the substrate, and the transition from hard surfaces to flexible ones are the primary goals.

The outcome of this research will allow the setting of some of the guidelines needed for the fabrication of printed flexible solar cells with acceptable efficiency and reliability. The materials used in this study are based on molecular, polymeric, and nanoparticles active chemicals having broad absorption in the solar spectrum. The main target of our research is to demonstrate low cost, flexible organic solar cells having more than 10% in conversion efficiency using AM1.5 illumination.

 

 

Two tandem organic solar cells connected in series (above) and Flexible solar cell (left).

 

Infrared Temperature Sensing System for Mobile Devices

An infrared (IR) temperature measurement system provides non-contact temperature measurement for mobile devices. The sensing system consists of not only a detector module and electronics, but also an optomechanical system that guides IR radiation onto the sensor.

In IR temperature sensing, the target temperature measurement is based on the measurement of the emitted IR radiation from the object. The main advantages compared to thermistor based measurement are as follows. The thermal signal from the target can be amplified by optics and the thermal signal from the device itself can be attenuated by an advantageous optical and thermal design and implementation. Since the field of view of the sensor has to be restricted in a practical mobile application the sensor also sees a surface which typically is not at the same temperature as the surface to be measured. In idealized conditions, this so called Narcissus effect can be calibrated away using an internal compensation circuit that measures the temperature of the sensor element itself.

Traditional optomechanical design for IR sensing, showing the Narcissus effect.

 

It is clear that the Narcissus effect of the cover, lens and tube in the measurement has to be minimized. This is achieved by increasing the transmittance of optics and decreasing the relative amount of the optical signal from the optomechanics. The field-of-view (FOV) of a Perkin-Elmer thermopile detector model TPS 333 for example is 100 degrees defined at the 50% relative response points. The wide FOV causes the optomechanics of the measurement system to be easily seen by the detector. Use of reflective optics instead of refractive optics can provide higher optical transmittances through very high reflectivity surfaces. In addition, the reflective optics can be designed in such a way that there are only high reflectivity optical surfaces within the FOV of the detector. The high reflectivity of the surface corresponds to low emissivity, which means that a relatively low Narcissus effect originates from a high reflectivity surface.

A parabolic reflector was designed on top of the TPS 333 thermopile detector to fulfil the FOV requirement of 1:6. The parabolic shape was chosen because the shape was able to limit the sensor field of view to a sufficiently narrow acceptance cone.

The designed optical system (parabolic reflector) and its dimensions.

 

The parabolic reflector surface is 9 mm long. The input aperture diameter is 4.9 mm and output aperture diameter is 1.56 mm. The output aperture is designed in such a way that it does not obscure any rays originating from inside the FOV.

The designed optics performance was modelled and verified by measurement sensor prototyping. The two measured analog signals from the TPS 333 thermopile detector, namely a thermistor signal and thermopile signal, were amplified and coupled to a measurement card (National Instruments 6210) USB bus version equipped with 8 differential channels with 16-bit AD converters. Labview based user interface and measurement software were implemented in a PC environment. Calibration of the sensor system was performed by varying the temperature of the black painted aluminum plate placed on top of a Peltier element from -10 to +100 °C in a room temperature. The temperature reference of the aluminum target was measured with a thermistor (Shibaura PSB-S7 (PB7-43)) attached to the measurement plate. A calibration procedure noticing operational temperature variations was applied. The repeatability of the implemented IR temperature sensor usage on a correct transferred calibration curve was better than ±0.5 °C in an operational temperature range from +12.6 to +49.3 °C and target range from +10 to +90 °C.

Continuous Measurement of Water and Waste Water Quality Using Direct Optical Methods

Water quality research was started at the Measurement and Sensor Laboratory in 2004. At that time, we noticed that continuous monitoring of water and waste water quality at most treatment plants is infrequent. One of the reasons is the cost and the time required to complete most tests, but also because of uncertainty regarding the reproducibility of the current techniques. Our aim is to use direct optical (reagent free) online methods for water quality measurements.

Optical techniques have been widely used in analyses of liquids and monitoring of various industrial processes, but online applications are rare. The advantages of these techniques lie in their rapidity, simplicity, relatively low running costs and versatility. Moreover, several parameters can be measured simultaneously. The optical sensors are based on the interaction of light (UV-Vis, infrared (IR)) with the sample. The characteristic transmission, absorption, fluorescence spectrum or vibrational properties of chemical species in waste water is measured in order to determine its concentration.

Our previous results were promising regarding the essential water quality parameters. Multivariate analysis, such as principal component analysis (PCA) and partial least squares (PLS) analysis were fitted to the spectroscopic data. Calibrations were based on the PLS-1 model correlating the values of the chosen water quality parameters to UV-Vis-NIR spectra.

 

Calibration correction factors obtained with partial least squares (PLS) analysis of UV/Vis or NIR spectra correlating to water quality parameters. q2 corresponds to cross-validated correlation coefficient, SEP to standard error of prediction, r2 correlation coefficient of model, PC number of principal components, N to number of analyzed samples, Max and Min to minimum and maximum value of water quality parameter.

 

The next step was to build in the Measurement and Sensor Laboratory a reagent free and field capable online monitoring device using commercial spectrometers. This unit measures continuous UV-Vis-NIR-spectra (190 - 2500 nm) and fluorescence. Different measurement geometries, detector solutions, flow cells and fiber optics were applied to achieve the best measurement results in current measurement circumstance. The fluorescence unit is PMT based, and measures three wavelength band channels simultaneously. At present, we are still using commercial spectrometers in our optical applications (UV-Vis-NIR), but we have developed our own PMT based and highly versatile fluorometer. In the future, our aim is to incorporate power source, optical and certain conventional measurement units in the single multipurpose unit, and use wireless data transfer for measurement data. This will need research concerning power harvesting, and low power consuming electronic and optical components.

Online water quality monitoring system and test setup of sample line.

 

Exploitation of the Results

The research results of the unit have been presented at scientific conferences and published in professional journals. In projects funded by Tekes, the acquired knowledge has been directly transferred to the participating enterprises. Also commissioned research has been directly reported to the enterprises concerned, and several senior and junior researchers have taken up employment with them.

Numerous international visits to and from the unit establish an important channel for access to the latest research areas and results from abroad.

Future Goals

Achieving an acknowledged position as a top European research unit in its own field forms a key objective for the unit. Another important goal involves becoming a central cooperation partner for Finnish industry in the development and application of measuring techniques and instrument technology. In addition, the unit advances the scientific understanding of optoelectronics and measurement applications, and produces high-quality dissertations and publications. Moreover, the highly applicable, in-depth, information produced by the unit also makes a contribution to product development and the creation of new business activities, for example, in medicine, pharmaceutical, pulp and paper and mechanical wood industries as well as wireless sensing and instrumentation.

As a participant in Infotech Oulu Graduate School, the unit will continue effective education of graduate students. The aim is to continue the traditional workshop series on Optoelectronics Devices and Instrumentation. In addition, internationally renowned scientists will continuously be invited to give lectures to the students.

Personnel

professors & doctors

22

graduate students

38

others

19

total

79

person years (univ. 68%, VTT 27%)

58

External Funding

Source

EUR

Academy of Finland

321 000

Ministry of Education

146 000

Tekes

1 711 000

other domestic public

1 773 000

domestic private

367 000

international

634 000

total

4 952 000

Doctoral Theses

Kirillin M (2008) Optical coherence tomography of strongly scattering media. Acta Universitatis Ouluensis C 295.

Popov A (2008) TiO2 nanoparticles as UV protectors in skin. Acta Universitatis Ouluensis C 304.

Niskanen I (2008) Measurement and analysis of optical properties of turbid media. University of Joensuu, Department of Physics and Mathematics, Dissertations 58.

Keränen K (2008) Photonic module integration based on silicon, ceramic and plastic technologies. VTT Publications 692.

Karppinen M (2008) High bit-rate optical interconnects on printed wiring board. Micro-optics and hybrid integration. VTT Publications 698.

Selected Publications

Bykov A, Indukaev A, Priezzhev A & Myllylä R (2008) Study of the influence of glucose on diffuse reflection of ultrashort laser pulses from a medium simulating a biological tissue. Quantum electron 38(5): 491-496.

Bykov A, Kirillin M & Priezzhev A (2008) Monte Carlo simulation of light propagation in human tissues and noninvasive glucose sensing. Chapter 3, Handbook of Optical Sensing of Glucose in Biological Fluids and Tissues (Series in Medical Physics and Biomedical Engineering), Tuchin V, editor, CRC Press, Taylor & Francis Group.

Hattuniemi J & Mäkynen A (2008) Thickness measurement of thin wood material by differential laser triangulation method. Proceedings of SPIE 7022: 70220R.

Järvinen T, Malinen J, Teppola P, Virtanen A, Kalvas T & Tiitta M (2008) Puun kosteuden jatkuvatoiminen mittaus. Paperi ja Puu - Paper and timber 90(3): 28-33.

Kinnunen M & Myllylä R (2008) Application of optical coherence tomography, pulsed photoacoustic technique and time-of-flight technique to detect changes in the scattering properties of a tissue-simulating phantom. Journal of Biomedical Optics 13(2): 024005.

Kinnunen M, Myllylä R & Vainio S (2008) Detecting glucose-induced changes in in vitro and in vivo experiments with optical coherence tomography. Journal of Biomedical Optics 13(2): 021111.

Kirillin M, Priezzhev A & Myllylä R (2008) Role of multiple scattering in formation of OCT images of skin. Quantum Electronics 38(6): 570-575.

Lauri J, Wang M, Kinnunen M & Myllylä R (2008) Measurement of microfluidic flow velocity profile with two Doppler optical coherence tomography systems. Optical diagnostics and sensing VIII, Proceedings of SPIE 6863: 68630F.

Li F, Dhagat P, Haverinen H, McCulloch I, Heeney M, Jabbour G & Nathan A (2008) Polymer thin film transistor without surface pretreatment on silicon nitride gate dielectric. Applied Physics Letters 93: 073305.

Määttälä M, Lauri J, Kinnunen M, Hast J & Myllylä R (2008) Fiber-optic biosensor based on self-mixing interferometry. Sixth International Conference on Advanced Optical Materials and Devices (AOMD-6), Proceedings of SPIE 7142: 71420I.

Makita S, Fabritius T & Yasuno Y (2008) Full-range, high-speed, high-resolution 1 µm spectral-domain optical coherence tomography using BM-scan for volumetric imaging of the human posterior eye. Optics Express 16: 8406-8420.

Makita S, Fabritius T & Yasuno Y (2008) Quantitative retinal blood flow measurement with three-dimensional vessel geometry determination using ultrahigh-resolution Doppler optical coherence angiography. Optics Letters 33(8): 836-838.

Meglinski I, Kirillin M, Kuzmin V & Myllylä R (2008) Simulation of polarization-sensitive optical coherence tomography images by Monte Carlo method. Optics Letters 33(14): 1581-1583.

Mondal R, Wex B, Shah B, Kaafarani B, Danilov E, Jabbour G & Neckers D (2008) Photoluminescent and electroluminescent properties and ultra-fast spectrometric studies of dihydroheptacenes. Organic Electronics 9: 227-233.

Myllylä R, Zhao Z & Kinnunen M (2008) Pulsed photoacoustic techniques and glucose determination in human blood and tissue. Chapter 14, Handbook of Optical Sensing of Glucose in Biological Fluids and Tissues (Series in Medical Physics and Biomedical Engineering), Tuchin V, editor, CRC Press, Taylor & Francis Group.

Niskanen I, Mutanen J, Lehtonen P, Räty J, Yamaguchi, M, Peiponen K-E & Jääskeläinen T (2008) Multifunction spectrometer for optical inspection of red wine. Sens. & Instrumen. Food Qual. 2: 58-65.

Niskanen I, Räty J & Peiponen K-E (2008) Estimation of effective refractive index of birefringent particles using a combination of the immersion liquid method and light scattering. Applied Spectroscopy 62(4): 7-9.

Olkkonen H & Olkkonen J (2008) Measurement and Reconstruction of Impulse train by parallel exponential filters. IEEE Signal Processing Letters, IEEE 15: 241-244.

Olkkonen H & Olkkonen J (2008) Simplified biorthogonal discrete wavelet transform for VLSI architecture design. Signal, Image and Video Processing 2(2): 101-105.

Park S, Karppinen M, Le Q & Yoon B-Y (2008) Burst-mode optical transmitter with DC-coupled burst-enable signal for 2.5-Gb/s GPON system. Microelectronics Journal 39(1): 112-116.

Park S, Park C, Karppinen M, Tanskanen A, Kautio K & Karioja P (2008) Interchannel crosstalk analysis in parallel optical receiver up to 10 GHz. IEEE Transactions on Advanced Packaging 31(4): 783-793.

Peiponen K-E, Kontturi V, Niskanen I, Juuti M, Räty J, Koivula H & Toivakka M (2008) On estimation of complex refractive index and colour of dry black and cyan offset inks by a multi-function spectrophotometer. Measurement Science and Technology 19: 115601.

Prykäri T, Alarousu E, Kuivaniemi J, Czajkowski J & Myllylä R (2008) Ultra-high resolution optical coherence tomography in paper characterization. The 2nd International Topical Meeting on Optical Sensing and Artificial Vision (OSAV´2008), Saint Petersburg, Russia.

Saarela J, Heikkinen S, Fabritius T, Haapala A & Myllylä R (2008) Refractive index matching improves optical object detection in paper. Measurement Science and Technology 19: 055710.

Voutilainen J, Putaala J, Moilanen M & Jantunen H (2008) Proactive diagnostics of solder interconnection failures with embedded precursor monitoring. IEEE European Test Symposium, Verbania, Italy.

Yang X, Wang Z, Madakuni S, Li J & Jabbour G (2008) Efficient blue- and white-emitting electrophosphorescent devices based on platinum(II) Chloride. Adv. Mater. 2008: 2405-2409.

Zhao Z, Hast J, Myllylä R & Känsäkoski M (2008) Pulsed photoacoustic measurements of suspensions: in case study of mitochnodrial NADH and its phantom. Sixth International Conference on Advanced Optical Materials and Devices (AOMD-6), Proceedings of SPIE 7142: 714213.

Zhao Z, Törmänen M & Myllylä R (2008) Pulsed laser photoacoustic monitoring of paper pulp suspensions. Proceedings of SPIE 7022: 70220D.