INFOTECH OULU Annual Report 2005 51

OPTOELECTRONICS AND MEASUREMENTS GROUP (OPME)

Professor Risto Myllylä and Professor Markku Moilanen, Optoelectronics and MeasurementTechniques Laboratory, Department of Electrical and Information Engineering, University of Oulu

Dr. Jouni Tornberg, Professor Harri Kopola and Professor Aarne Mämmelä, VTT Electronics, OuluJuha Kalliokoski, Research Director of the Measurement and Sensor Laboratory (Kajaani),

University of Ouluristo.myllyla@ee.oulu.fi,markku.moilanen@ee.oulu.fi, jouni.tornberg@vtt.fi,

harri.kopola@vtt.fi, aarne.mammela@vtt.fi, juha.kalliokoski@oulu.fihttp://www.infotech.oulu.fi/opme

Background and Mission

The Optoelectronics and Measurements Group(OPME) comprises an intensive collaboration networkof researchers at the Optoelectronics and Measure-ment Techniques Laboratory at the University of Oulu,the Measurement and Sensor Laboratory (MILA) inKajaani and VTT Electronics. OPME employs 38postgraduate students and 38 other persons in the re-search work. The main research activities are in thefields of optoelectronic measuring and electronics test-ing techniques and communication systems, with par-ticular emphasis on the practical applications of thesetechniques. The group work includes pursuing newmethodologies in sensing and measurement, develop-ing new devices and instruments for basic researchpurpose, and helping companies and enterprises toimprove their designing and process controlling.

In these undertaking, the group focuses on measuringand modeling the propagation of light in turbulent andscattering media such as the atmosphere, human tis-sues, pulp and paper. Interesting basic properties oflight are, for example, scattering, absorption, reflec-tion, refraction, diffraction and polarization when lightpropagates through non-homogenous media. The tech-niques developed for measuring these optical proper-ties are absorption spectroscopy, diffuse-reflectionspectroscopy, Raman spectroscopy, photon time-of-flight, a scattering photoacoustic approach, and highand low coherent interferometry. Optical and micro-sensors including MEMS technology, and camera andmachine vision in optical measurement are the focusesof the group research. Looking for new materials, tech-nologies, integration of the systems and customizedmicro-optical devices, optoelectronic devices andnovel packaging technologies are still activities in theOPME group. All this work and achievements arebeing applied in biomedicine, and in the pharmaceu-tical, paper, pulp and mechanical wood industries, aswell as in wireless communication and instrumenta-tion.

As a participant in the Infotech Oulu graduate school,

the group also focuses its efforts on arranging lectureseries and graduate school courses for graduate stu-dents. During 2005, the group organized the traditionalInfotech Oulu Workshop on Optoelectronic Devicesand Instrumentation for the fifth time, concentratingthis time on ‘MEMS, NEMS and Optical Micro-systems’. The group also organized the IEEE/LEOSInternational Conference on Optical MEMS and TheirApplications, and the 2nd Finnish-Russian Meeting:Photonics and Laser Symposium. In addition, threeinternational lectures and courses were held in thegroup, ‘the development of wireless sensor networkplatform in Korea and some basic research results onubiquitous health care’, ‘Mechanical properties ofgreat arteries of cardiovascular system: a) theoreticalinvestigation, b) clinical applications’ and ‘Laser mea-surements’.

It is worth noting that optical and electrical compo-nents used in low end products like disposable sen-sors, product packages, flexible displays etc. will bebased more and more on organic materials in the nearfuture. These so called ‘polytronics’ can be manufac-tured using roll-to-roll and printable techniques likegravure, offset, screen and inkjet printing, which re-duces remarkably the manufacturing period and costs.Integration of traditional optoelectronic measurementtechniques to polymer platforms is a great challenge,but it opens up a lot of new solutions in different bio-medical and industrial measurement applications. Oneexample of this may be different biosensor applica-tions where a biomolecular recognition process couldbe performed using polymer waveguides. The sub-group of VTT Electronics has engaged in this workand the achievement thus far is encouraging.

Scientific Progress

The following research examples illustrate the scien-tific progress of the OPME group. These researchprojects have been carried out in active collaborationwith both domestic and international research institu-tions and industrial partners.

52 INFOTECH OULU Annual Report 2005

Miniature Michelson Interferometer Based onan LTCC PlatformA miniature Michelson interferometer based on a lowthermal co-fired ceramics (LTCC) platform was dem-onstrated. The interferometer was implemented on a25 mm × 25 mm ceramic optical table, which a thick-ness of 0.5 mm. The interferometer can be used inhigh-precision displacement measurements. An imag-ing lens was used to image a laser diode facet on thesurface of a measurement mirror and a reference mir-ror. Controlled displacement of the measurement mir-ror was achieved by attaching the measurement mir-ror on top of a piezo actuator. Driving the laser diodein a LED mode, the optical path difference (OPD)between optical arms was adjusted to zero by movingthe second mirror along the optical axis and simulta-neously monitoring the interference pattern. The mir-ror was then attached to an LTCC substrate with ep-oxy. The OPD after the reference mirror attachmentwas smaller than 200 nm.

A 128-element CMOS detector, pixel size 62.5 µm ×200 µm, was used to detect interferogram modulationdue to measurement mirror displacement. Measuredanalog pixel values were digitized by 16-bit and thecorresponding displacement was calculated using alaptop. The displacement of the mirror as a functionof piezo driving voltage was characterized using anatomic force microscope (AFM). When using a 100Hz sinusoidal piezo driving signal introducing a 1 nmpeak-to-peak mirror movement and using 1 s integra-tion time, a displacement resolution of 20 pm wasachieved. Theoretical investigations based on the cal-culated SNR achieved by FFT measurements suggestthat displacement resolution below 5 pm should bepossible to attain via increasing integration time to100 s.

Biosensor Based on Young InterferometerPrincipleConventional biochemical analyses are carried out inchemical laboratories with relatively large and expen-sive equipment; they are also time consuming. Theobjective of this project was to develop a miniatur-ized biosensor, which is cheap to produce and quickto use. The sensor should also have sufficient sensi-tivity. Because interferometric methods can be ex-tremely sensitive and such sensors are very well suitedto compact sizes, a Young interferometer structure waschosen for the sensor.

The integrated Young interferometer sensor is basedon confining light in a waveguide structure. Thiswaveguide structure guides the light inside the sensorand divides the light to go through a sample area anda reference area. Although light is confined inside thewaveguide layer, a small part of it, called an evanes-cent wave, reaches through the physical boundary ofthe waveguide into the sample/reference area. Thisinteraction between the light and the sample causes aphase change in the propagating light, because the re-fractive index of the sample area differs from the re-fractive index of the reference area. When the lightleaves the sensor, it is superimposed on an observa-tion screen or a detector, where it creates an interfer-ence pattern. The shift of this interference pattern isdirectly proportional to the change in the phase of thelight, and thus we can observe changes happening inthe sample area. For example, an antibody-antigenbinding event on the sample area can be detected fromthe interferogram shift.

The waveguide chip in this project was fabricated fromsiloxane material, which can be processed by UV-li-thography to have a channel like waveguide structure.The sensitivity of the integrated Young interferom-eter was studied and found to be in the order of 10-6

refractive index unit.

Electronics Testing TechniquesMiniaturization and new manufacturing technologieswill make testing of electronic products difficult inthe future. Access to certain locations in the devicewill be impossible with traditional measurement tech-niques, or the access will require new, possibly ex-pensive, and time consuming methods.

Miniature interferometer schematic and Implemented inter-ferometer.

Principle of the Young interferometer sensor and waveguidestructure.

INFOTECH OULU Annual Report 2005 53

One way to address these concerns is to incorporatemeasurement capabilities into the product itself. Inthis, so-called embedded testing, new test-specific cir-cuit structures and existing parts of the product areused together to perform parameter, functional, inter-connect and component self-tests on different partsof the product.

Basic concepts for such embedded testing have beendeveloped in the research group. Principles of com-ponent and interconnect testing via analogue bound-ary scan test architecture have been developed, thefrequency range of the test bus has been extended toRF with the use of simple integrated radio-frequencydetectors, and the basic phenomena related to thebreaking-up of solder joints of ball grid arrays havebeen studied.

Embedded testing forms one of the cornerstones onwhich the concurrently developed ideas on tests serv-ing the entire life-cycle of products from developmentto field repair are laid upon. Since in this kind of sce-nario, test instruments and measurement equipmentare embedded as part of the product, a method to re-motely initiate and control the tests, and to access themeasurement results is needed. Groundwork leadingtowards standardized ways of performing such remotetesting and data telemetry is being done by the on-going effort in the Wireless Test Standard (WTS)workgroups. This work will provide the network pro-tocols and infrastructure for communication betweenthe embedded test enabling circuitry, the software in-side the device under test, and the remote user.

Optical Measurements for Steering a Surgi-cal, Interactive Robot in an MRI-EnvironmentA surgical robot will take biopsy samples of soft tis-sue or bone, and works on the basis of MRI-imageand ordinary camera information. The purpose is todesign miniaturized optical angle and position sen-sors for measuring the robot’s arm position accuratelyinside arm joints. Also, a three dimensional force sen-sor for a robot head to sense biopsy needle forces isone of the main research topics. In addition, aim is totransmit measurement data out to the controller unitoptically by using fibre optical link or using UWB(Ultra Wide Band)-technology. The whole robot sys-tem will be tested in the EMC-laboratory to ensureelectromagnetic compatibility.

Theories and different measurement setup possibili-ties for developing fiber optic 3D-sensors were pre-sented. One of them, based on the strain of the Bragggratings, was used to make a demonstration. In addi-tion, the mechanical structure (POM-material) forsense needle forces was machined. At that point, re-search was refocused to sense forces in the handle,

which will be used for manual steering of the robothead. With the help of personnel at the Mechatronicsand Machine Diagnostics Laboratory of the Depart-ment of Machine Engineering, the handle design wasmodeled, but then it proved to be too complex to solveby using only Bragg gratings: the solution was thenfocused on 1-dimensional needle force sensor (Bragg-grating) and an optical joystick. Commercial MRI-compatible angle encoders were charted. Developmentof our own solution based on a high precision fiberoptical displacement sensor with an eccentric cam-shaft (spiral) was started. The availability of a smallsized, MRI-compatible video camera was charted. Oneof them was ordered for further evaluation. Prelimi-nary tests within an MR-imaging room were carriedout.

Scattering Photoacoustic Measurement inTurbid SuspensionsThe scattering photoacoustic (SPA) method is basedon the photoacoustic (PA) effect produced in the stud-ied medium and external absorbers. A light beam isused to illuminate a scattering medium and then a partof the optical energy is absorbed at an incident pointto generate a PA source. When the scattering sampleis weakly absorbed, another part of light energy is scat-tered outside the illuminated region.

Measurement setup and sensitivity curves of the fiber opticdisplacement sensor.

Electronics for measuring displacement differentially. Onefiber is transmitting light and two fibers are collecting re-flected light. The difference of the amplitude is amplified.

54 INFOTECH OULU Annual Report 2005

The SPA method uses absorbers with a high absorp-tion coefficient at the irradiation wavelength, locatedoutside of the sample, to accept the scattering light.Therefore, other PA sources are produced at the re-ception surfaces of the absorbers, whose intensitiesare strongly dependent upon the scattering propertyof the sample with low absorption. All PA sources emitacoustic waves and can be detected by an ultrasonictransducer which acoustically contacts with an ab-sorber. Analyzing these wave amplitudes may sensethe sample change or its optical properties. Moreover,SPA detection can also be used to simultaneously studyacoustic properties, such as acoustic speed and attenu-ation, on the basis of acoustic waves propagatingthrough the sample. In this case, two absorbers, lo-cated symmetrically at the same distance from the in-cident light beam, will generate two photoacousticsources with an equal intensity. The ratio of both sig-nal amplitudes received is proportional to the acous-tic attenuation of the sample, because one wave goesdirectly through the sample, while the other one doesnot, before being received by the ultrasonic transducer.

Apparently, an advantage of SPA is that it can studyoptical and acoustic properties of scattering materialssimultaneously, merely by applying an ultrasonic trans-ducer to fulfil optical and acoustic measurements. Theapparatus is convenient for practical application andhas high ratio between function and price. Currently,we are using it in measuring optical parameters ofintralipid suspension, in determining fibre and fineconsistencies in paper pulp, in monitoring the lipidcontent in milk, and in sensing the glucose effect onthe scattering properties of milk, intralipid and poly-styrene micro-sphere suspensions. The results showthat currently the SPA approach is effective in nearinfrared wavelengths for aqueous suspensions wherereduced scattering coefficients are in the range of 0.2mm-1 to 3 mm-1.

Paper Research Using Optical CoherenceTomographyThe growth of the paper making industry has triggereda continuous search for improved methods for diag-nosing and characterizing paper properties. By andlarge, testing tends to be focused on the goal of ensur-ing that the paper produced meets end-user specifica-tions at the lowest possible cost. On the macroscopiclevel, paper can be characterized by numerous param-eters, including, for example, density, bulk, porosity,thickness, roughness and gloss. All these parametershave an effect on paper quality, and can be used toclassify different types of paper as suitable for par-ticular purposes.

Surface analysis, including roughness, porosity andgloss estimation, is particularly important in printingpapers, because parameters like roughness and sur-face porosity affect such optical properties of paperas gloss and ink absorption. There are several ap-proaches for non-contact surface analysis of paper,but the need to see through a paper surface calls formore sophisticated methods. Current measurementmethods for structural analysis of paper tend to beeither slow, labor-intensive, expensive or invasive.

The latest Optical Coherence Tomography - OCT de-vices are fast and have a resolution which competeswith conventional laboratory structural analysis meth-ods of paper. The advantage is the non-contact andnon-invasive approach. A resolution of 1 - 2 µm canbe reached by the new Nd:YAG pumped Ti:Sapphiresource based OCT-system shown in the figure below.Such a high resolution enables the imaging of singlefibers, coating paste and color layers.

In OCT-imaging of paper, there is a need for knowl-edge of many areas such as paper physics, photonmigration in paper, paper chemistry, signal process-ing and automation control of the imaging device,which means that the collaboration between severalscientists and research groups has to be active. In ad-dition to the imaging of paper, the technique has beenapplied to fluid mechanics evaluation by using theability of the method to determine the velocity pro-files of flowing suspensions like pulp and coating pastesuspensions.Scheme of an SPA measurement and a typical signal re-

ceived by an acoustic detector.

TISSA-50 Ti:Sapphire laser.

INFOTECH OULU Annual Report 2005 55

Pulp and Paper ResearchResearch on a new imaging technology utilizingdiodelaserstroboscopy, the DILA-project was a jointeffort with Tampere University of Technology’s Op-tics laboratory. During the project, this technology wastested in four case studies with industrial partners.Diodelaserstroboscopy is an efficient technology forimaging very fast phenomena. In the case studies, thelight pulses used were between 0.1 - 10 ms. The caseswere

• Measuring the speed profile of fibers in a high speedsteam flow

• Measuring the speeds and sizes of air bubbles in anAOD converter

• Visualization of the collapse of cavitation bubblesin an ultrasonic washer

• Visualization of wood fibers in a wood fiber-air flow

The technique proved to be very effective in all ofthese case studies.

Mechanical Wood ResearchDuring 2005, the research on wood properties tooksome notable steps forward. Data-analysis techniqueswere studied in the METRI project, and in August alarge development project called PLOMMI wasstarted. PLOMMI utilizes the results from earlierprojects and aims to further develop our competencein non-destructive testing and measurements of woodand microwave measurement techniques. ThePLOMMI project aims to detect accurately the knotsand decayed parts in trunks, utilizing microwaves andinfrared spectroscopy. During the project, a prototypeof a measurement device will be built for measuringknots and decay from spruce and pine in the longitu-dinal direction.

Wireless InstrumentationIn the System-on-Chip project, our Wireless instru-mentation team has applied the latest SoC-technolo-gies in different environments in research and industry.SoC, System-on-Chip, is a circuit where a large em-bedded system has been integrated into one single chip.The increased capacity of FPGA’s has made it pos-sible to use them as SoC’s. This technology enablesus to develop more complicated measurement solu-tions, where calculations can be effectively executedwith SoC’s.

Sports Technology MeasurementsThe Meibi project aims to apply the SPR method forbio-measurements of human physiology. In this projectwe focus on developing the required optical solutionsfor a measurement device that is being developed to-gether with the Laboratory of Biotechnology inSotkamo. The goal is to develop a prototype of a fullyoperational SPR device for laboratory conditions. Thedeveloped measurement method is non-invasive, andit will be used to measure different factors of humanphysiology using sweat and saliva as the source ofinformation. The long term vision is to develop a por-table, multi channel on-line measurement device thatcan be applied in health care as well as in environ-mental measurements.

Exploitation of the Results

Active interaction with industry ensures the rapid ap-plication of research results. The work of the grouppaves the way for the introduction of a new genera-tion of optoelectronic sensors and instruments basedon micro-optics, micromechanics and microelectron-ics, and polymer-based manufacturing technology.

The research results of the group have been presentedat scientific conferences and published in professionaljournals. In projects funded by TEKES, the acquiredknowledge has been directly transferred to the par-ticipating enterprises. Also commissioned research has

The light source used in the DILA project.

On the left is the 3D-model of alog and on the right a cross sec-tion from the same log. A is aphotograph of the cross section,B represents a calculated densityestimate, C shows the moisturedistribution measured with near-infrared spectroscopy, D the mi-crowave absorption and E the mi-crowave reflectance map of thecross section.

56 INFOTECH OULU Annual Report 2005

been directly reported to the enterprises concerned,and several senior and junior researchers have takenup employment with them.

Future Goals

Attaining an acknowledged position as a top Euro-pean research unit in its own field forms a key objec-tive for the group. Another important goal involvesbecoming a central cooperation partner for Finnishindustry in the development and application of mea-suring techniques and instrument technology. In ad-dition, the group advances the scientific understandingof optoelectronics and measurement applications, andproduces high-quality dissertations and publications.Finally, the highly applicable, in-depth, informationproduced by the group also makes a contribution toproduct development and the creation of new busi-ness opportunities.

The research activities are still focusing or will befocused on:

1) modeling and simulating of the propagation of lightin turbulent and scattering media, especially in pa-per, pulp, process suspension and human tissue,

2) pursuing new measuring and testing techniques orcombining them with traditional ones to new ap-plications,

3) improving the OCT for industrial application, es-pecially in measuring paper thickness and internalstructure,

4) continuing the scattering photoacoustic measure-ment in paper pulp and other turbid suspensionsand following biomedical imaging based onphotoacoustics,

5) developing optical high and low coherent interfer-ometry for trace detection and particle behavior ina turbid medium,

6) applying pico-second and femto-second lasers tostudy the impulse response of paper and bio-materials in the time domain,

7) combining customized photonic devices, and ad-vanced materials and packaging technologies fortheir implementation in novel systems for opticalcommunications, wireless instrumentation, machineautomation, and biomedicine,

8) continuing to develop polymer devices and bio-sensors to be used in low end products like dispos-able sensors, product package, flexible display, etc.,and

9) developing non-destructive testing and measure-ments of wood to detect accurately the knots anddecayed parts in trunks, utilizing microwaves andinfrared spectroscopy.

As a participant of the Infotech Oulu graduate school,the group will continue effective education of gradu-ate students. The aim is to continue the traditionalworkshop series on Optoelectronics Devices and In-strumentation. In addition, internationally well knownscientists will continuously be invited to give lecturesto the students.

Personnel

srotcod&srosseforp 22

stnedutsetaudarg 93

srehto 51

latot 67

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External Funding

ecruoS RUE

dnalniFfoymedacA 000171

noitacudEfoyrtsiniM 000032

sekeT 0002851

cilbupcitsemodrehto 0002551

etavirpcitsemod 000636

lanoitanretnirehto+UE 000968

latot 0000405

Doctoral Theses

Kataja K (2005) Numerical modelling of near field opticaldata storage. VTT Publications 570.

Selected Publications

Olkkonen J, Kataja K & Howe D (2005) Light transmis-sion through a high index dielectric-filled sub-wavelengthhole in a metal film. Optics Express 13: 6980-6989.

Heikkinen V, Heikkinen M, Keränen K, Mitikka R, PutilaVP & Tukkiniemi K (2005) Laser profilometer modulebased on a low-temperature cofired ceramic substrate, Op-tical Engineering 44: 093603, 7 p.

Keränen K, Karppinen M, Lenkkeri J, Mäkinen JT, Ollila J& Karioja P (2005) LTCC technology for photonic andmillimeter wave module integration. International Journalof Software Engineering and Knowledge Engineering15:215-224.

Heikkinen V, Aikio J, Alajoki Y, Kautio K, Ollila J & KariojaP (2005) Wavelength-tunable laser module using low-tem-

INFOTECH OULU Annual Report 2005 57

perature cofired ceramic substrates. IEEE Transactions onAdvanced Packaging 28:121-127.

Kinnunen M, and Myllylä R (2005) Effect of glucose onphotoacoustic signals at the wavelengths of 1064 and 532nm in pig blood and Intralipid. Journal of Physics D: Ap-plied Physics 38:2654-2661.

Popov AP, Priezzhev AV, Lademann J & Myllylä R (2005)TiO

2 nanoparticles as effective UV-B radiation skin-pro-

tective compound in sunscreens. Journal of Physics D: Ap-plied Physics 38:2564-2570.

Kirillin YM, Priezzhev AV, Tuchin VV, Wang RK & MyllyläR (2005) Effect of red blood cell aggregation and sedimen-tation on optical coherence tomography signals from bloodsamples. Journal of Physics D: Applied Physics 38:2582-2589.

Hast J, Krehut L & Myllylä R (2005) A displacement sen-sor based on optical feedback interferometry in a GaN di-ode laser. Optical Engineering, 44(8):080504.

Zhao Z & Myllylä R (2005) Measuring the optical param-eters of weakly absorbing, highly turbid suspensions by anew technique: photoacoustic detection of scattered light.Applied Optics 44: 7845-7852.

Alarousu E, Krehut L, Prykäri T & Myllylä R (2005) Studyon the use of optical coherence tomography in measure-ments of paper properties. Measurement Science and Tech-nology 16:1131-1137.

Popov AP, Priezzhev AV & Myllylä R (2005) Effect of glu-cose concentration in model light-scattering suspension onpropagation of ultrashort laser pulses. Quantum Electron-ics 35:1075-1078.

Popov AP, Lademann J, Priezzhev AV & Myllylä R (2005)Effect of size of TiO

2 nanoparticles embedded into stratum

corneum on UVA and UVB sun-blocking properties of theskin. Journal of Biomedical Optics 10:064037-(1-9).

Sorvoja H, Kokko VM, Myllylä R & Miettinen J (2005)Use of EMFi as a blood pressure pulse transducer. IEEETransactions on Instrumentation and Measurement 54: 2505-2512.

Sarén M-P, Peura M & Serimaa R (2005) Interpretation ofmicrofibril angle distributions in wood using micro-diffraction experiments on single cells. Journal of X-RayScience and Technology 13:191-197.

Peura M, Müller M, Serimaa R, Vainio U, Sarén M-P,Saranpää P & Burghammer B (2005) Structural studies ofsigle wood cell walls by synchrotron, X-ray microdiffractionand polarised light microscopy. Nuclear Instruments andMethods in Physics Research B 238:16-20.

Jaakkola T, Mäkinen H, Sarén M-P & Saranpää P (2005)Does thinning intensity affect the tracheid dimensions ofNorway spruce. Canadian Journal of Forest Research 35:2685-2697.

Suhonen R, Tuomikoski M, Maaninen A & Kopola H (2005)Roll-to-roll manufacturing technologies of OLEDs forsignage and lighting. Printed Electronics USA 2005 Con-ference Proceedings.

Känsäkoski M, Kivimäki L, Maaninen A, Leinonen M,Kopola H, Takkinen K & Pulli T (2005) Bioactivenanoparticulate hybrid materials for diagnostic applications.New trends in research and development in the areasmedicine-biotechnology-nanotechnology. Biotechnica,Hannover.