Optoelectronic Measurements

Professor Risto Myllylä, Optoelectronics and Measurements Laboratory,
Department of Electrical Engineering, University of Oulu
Professor Harri Kopola, VTT Electronics, Optoelectronics, Oulu
Juha Kalliokoski, Director of the Measurement and Sensor Laboratory (Kajaani),
University of Oulu

risto.myllylaee.oulu.fi, harri.kopolavtt.fi, juha.kalliokoskioulu.fi 

The group comprises an intensive collaboration network of researchers at the Optoelectronics and Measurements Laboratory of the University of Oulu, the Measurement and Sensor Laboratory in Kajaani and VTT Electronics. In accordance with the principles of Infotech Oulu, the group engages in basic research, drawing on the resources of the three organizations as well as their extensive industrial connections and wide experience in technology transfer. Close collaboration partners include the high-speed electronics team of Infotech Oulu along with the analyzer, production technology and microsystems teams of VTT Electronics. At the international level, the Optical Sciences Centre of the University of Arizona (USA) and the Technical University of Gdansk (Poland) are among the primary co-operation partners of the group. In addition, the group participates in several European research and exchange programs.

The group does basic research in optoelectronic measuring techniques with particular emphasis on the practical application of these techniques. In this undertaking, the group focuses on measuring and modelling the propagation of light in turbulent and scattering media such as atmosphere, human tissue, pulp, paper and optical fibres. Interesting properties are for example scattering, reflection, absorption, time-of-flight and the so-called photoacoustic phenomenon. The findings are used in novel applications in medicine and the pulp and paper industry, as well as in smart structures and instrument technology.

Scientific Progress

The research projects of the optoelectronics group have mainly progressed in accordance with the plans and goals stated in the strategy plan

1) The group has exploited several methods to study the properties of both pulp and paper.

A collaboration project called PORO (Optical properties of porous materials) represents real research co-operation between Infotech Optoelectronic Measurements group members and three universities in Eastern Finland (Joensuu, Kuopio and Lappeenranta).

The organizations represent top knowledge in optical research for industry. The research groups, along with Tekes, Valmet and Orion Pharmaceuticals as industry related partners, have lead the PORO-project through one year in order to find new and innovative ways to characterize roughness and porous behaviour of paper and pharmaceutical materials.

Using the optical properties of porous materials, such as paper and pharmaceutical compacts, is a challenging task to increase structural information of the selected substances. The general research issues consisted of using various optical spectroscopies, different light scattering techniques and theoretical study. The actual main techniques developed and now in use are: time-of-flight spectroscopy, applied NIR-spectroscopy, FTIR-PAS (photoacoustic spectroscopy), speckle spectroscopy, systems using novel diffractive optical elements and the advanced scattering technique.

All techniques involved showed their benefits in characterizing different aspects of surfacial and/or porous structure. Through technical meetings, the intermediate research results were shared and used for mutual discussion in order to strengthen the shared goal aiming at new innovations in optical measurement technology. All techniques are to be developed further after this pilot study research period.

The PUPA project is intended for the development of construction techniques in measurement devices for the pulp and paper industry. A new Raman spectrometer prototype was designed and constructed in the project. The principal components of the device construction are a diode laser, a spectrograph and a multi-element CCD detector, placed in a protective housing, and a fiber-optic probe, serving as an interface between the sample and the device. The filtering needed for the measurement of Raman spectra is placed in the head of the fiber-optic probe.

2) Fiber optic sensing technologies have been developed for the determination of residual stresses of composites in cooperation with Engineering Mechanics Laboratory and Department of Chemistry at the University of Oulu. The Finite Element Method has calculated residual stresses building up in microstructure of composite materials during the manufacturing process. The results obtained have been evaluated and verified by time-of-light and Fabry-Perot optical fibre sensors. Fastening methods of the optical fibres to the surrounding material have been investigated and promising chemical procedures developed. Classification of distributed optical fibre sensing methods and their main properties for measuring quantity information continuously from a long sensor fibre have been reported. Also a prototype readout device for interrogation of wavelength multiplexed Bragg grating sensors has been developed.

3) The group has initiated research collaboration on tunable wavelength lasers with the University of Arizona.

It is investigating the possibility of using an external micromechanical Fabry-Perot Interferometer, FPI, as a tuning component in a wavelength tuneable hybrid laser diode. A silicon micromachined electrostatically tuneable Fabry-Perot device was placed in a short distance to the front facet of a laser diode. Together with the front facet of the laser, the FPI formed an extremely short external cavity structure. This structure provided a spectrally adjustable optical feedback to the laser diode cavity. In experiments, a 980-nm single-quantum-well high-power laser diode was used. The FPI device and the front facet of the laser diode formed a ~30-micron external cavity. As a result, a quasi-continuous tuning in a ~4-nm wavelength range was experimentally observed. A theoretical model describing the characteristics of the hybrid laser diode configuration was developed. A Finnish patent application concerning the hybrid arrangement was filed in collaboration with the University of Arizona.

4) With regard to medical applications, the group has evaluated the applicability of the photoacoustic method in non-invasive human tissue measurements. Moreover, the group continues to study methods of measuring blood pressure and pulse on the basis its patented methods.

5) In addition, the group participates in extensive co-operation projects developing, for example, packaging technology for optoelectronic modules, optical spectrometer methods and distributed fibre optic sensors.

Exploitation of Results

Instrumentation within the pulp and paper industry and non-invasive methods for monitoring human health are the main application areas targeted by the optoelectronic measurements group. In addition, distributed fibre-optic sensors enable the development and construction of new, challenging quality control and monitoring systems for large composite, concrete and metal structures. Active interaction with industry ensures the rapid application of research results. The work of the group paves the way for the introduction of a new generation of optoelectronic sensors and instruments based on micro-optics, micromechanics and microelectronics.

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

Future Goals

Reaching an acknowledged position as a top European research unit in its research area forms a key objective for the group. 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 group advances the scientific understanding of optoelectronics and optoelectronic applications and produces high-quality dissertations and publications. Finally, the highly applicable, in-depth, information produced by the group also makes a contribution to product development and the creation of new business opportunities.

In the short term, the research activities of the group will be focused on:

1) promoting current theoretical understanding of multi-scattering in terms of the propagation of light in media such as paper, pulp, process suspensions and human tissue,

2) studying the applicability of time-domain spectroscopy in the characterization of pulp, the analysis of pore structure, and non-invasive measurements of human tissue and blood,

3) developing optoacoustic methods for measuring human blood and tissue and properties of pulp and paper,

4) developing distributed fibre-optic sensors for both quantity and location measurements and applying these sensor systems to such tasks as the monitoring of large composite structures,

5) increasing R&D facilities, promoting companies in the field of photonic sensor technology and improving the competitive edge of Finnish sensor technology-related enterprises.

Personnel

External Funding

Selected Publications

Myllylä R, Marszalec J, Kostamovaara J, Mäntyniemi A & Ulbrich G-J (1998) Imaging distance measurements using TOF lidar. Journal of Optics, Vol. 29: 188-193.

Tenhunen J, Kopola H & Myllylä R (1998) Non-invasive glucose measurement based on selective near infrared absorption; Requirements on instrumentation and spectral range. Measurement, Vol. 24: 173-177.

Räty J, Keränen E & Peiponen K-E (1998) The complex refractive index measurement of liquids by a novel reflectometer apparatus for the UV-visible spectral range. Meas. Sci. Technol, Vol. 9: 1-5.

Nissilä S, Ahola O, Kopola H, Myllylä R, Tenhunen J & Zhao Z (1998) Photoacoustic signal formation in absorbing and scattering liquids. Proceedings of SPIE, Vol. 3199: 2-12.

Suopajärvi P, Pennala R, Heikkinen M, Karioja P, Lyöri V, Myllylä R, Nissilä S, Kopola H & Suni H (1998) Fiber optic sensor for traffic monitoring applications. Proceedings of SPIE, Vol. 3325: 222-229.