Janne Aikio

Single-mode tuning of a 1540-nm diode laser using a Fabry-Pe/spl acute/rot interferometer

We realized a wavelength-tunable laser using a 1540-nm Fabry-Pe/spl acute/rot diode laser and a silicon surface micromachined Fabry-Pe/spl acute/rot interferometer device in the short external cavity configuration. This hybrid-integrated system enables the use of standard laser chips and potentially has a low cost. We obtained single-mode tuning of 13 nm, a sidemode suppression ratio of better than 25 dB, and an average single-mode fiber-coupled power of 100 /spl mu/W. The emitter can be employed in optical communication and fiber-optic sensor applications.

Direct semiconductor laser readout in optical data storage

Extremely small read heads are needed for stacked-disk and small portable optical data storage devices. Our study has revealed several interesting aspects that can be utilized in the design of compact read heads based on direct optical feedback to a laser diode. Experimental confirmation of our theoretical results is in progress.

Simulation of imaging system's performance

In this paper, an imaging system simulation tool is presented. With the tool, it is possible to simulate the performance (quality) of an imaging system. Furthermore, the system allows optimization of the lens system for a given image sensor. Experiments have shown that the tool is useful in actual lens design.

Wavelength tuning of a laser diode by using a micromechanical Fabry-Perot interferometer

We studied the wavelength tuning properties of an edge emitting extended cavity laser diode with a micromechanical Fabry-Perot interferometer as an external reflector. It was seen that this arrangement provides essentially similar tuning range (few nanometers) as traditional system with one external mirror only, but with a much smaller mirror movement. In this letter, the theoretical model and the characteristics of the tuning are explained.

Wavelength-tunable laser module using low-temperature cofired ceramic substrates

We realized a prototype series of the 1550-nm band wavelength-tunable laser module. The edge-emitting Fabry-Perot diode laser operates in the short external cavity configuration and is tuned by a silicon surface micromachined Fabry-Peacuterot interferometer device. Low-temperature cofired ceramic (LTCC) substrate technology was used in the module packaging to enable the passive alignment of the photonic components. Low conductor resistance and dielectric loss, multilayer structures with fine-line capability, compatibility with hermetic sealing, and the ability to integrate passive electrical components (resistors, capacitors, and inductors) into the substrate make LTCC a useful technology for telecommunication applications. In addition, the fair match of the thermal expansion coefficient to optoelectronic chips reduces packaging-induced thermomechanical stresses. The precision three-dimensional (3-D) structures, such as cavities, holes, and channels manufactured in the ceramic parts, ease the packaging process via the passive assembly. The wavelength tuning range of the realized modules ranged from 8 to 19 nm and single-mode fiber-coupled output power was between 100 and 570 muW. The hybrid arrangement uses standard laser chips and, therefore, potentially provides a cost-effective and easily configurable solution for last-mile fiber optic communications

Fabrication and characterization of hybrid-glass-based axicons

We introduce a process for applying directly UV photopattern- able materials and processing methods for the fabrication of binary dif- fractive optical elements. We design and model a binary axicon—an optical element that produces an almost diffraction free beam at a speci- fied distance from the element. We also synthesize sol-gel-based hybrid glass materials and tailor their processing parameters to fit to the de- mands of the axicon design. A grating periodicity of 2 mm, an 850-nm structure depth, and certain morphological properties are required to meet the design parameters. The materials are synthesized using zirco- nium(IV)isopropoxide, methacrylic acid and methacryloxypropyltri- methoxysilane as deposition material precursors. We determine the mor- phological and shape characteristics of the fabricated axicons as a function of the lithographic exposure parameters. The optical character- istics of the axicons are measured in terms of the axial and radial inten- sity profiles. The difference between the modeled and measured results is explained.

Printed hybrid systems

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.

On surface plasmon enhanced near-field transducers

General design principles for near-field transducers that are based on the excitation of surface plasmon polaritons in planar structures are presented. The transmission of normally incident plane waves through thin Ag film containing a very small (sub-wavelength diameter) cylindrical hole that is surrounded by a set of concentric circular grooves is analyzed via the BOR-FDTD method. We find that surface corrugations can substantially enhance light transmission through the central sub-wavelength aperture.

Numerical study of near-field writing on a phase-change optical disk

Absorption in the phase-change layer of an optical disk located in the near field of a Fabry-Perot laser diode is studied with a combination of finite-difference time domain (FDTD) analysis and a phenomenological laser model that predicts the operational characteristics of a laser diode. Some numerical simulations are performed and results are presented. In addition, the combined FDTD/laser-simulation model is described briefly.

Readout Modeling of Super Resolution Disks

We describe 3-dimensional numerical simulations (performed using a finite-difference-time-domain modeling tool) of the readout of very small marks recorded on the data surface of an optical storage medium that incorporates a super resolution (SR) structure comprised of two dielectric thin films which encapsulate a thin AgOx film. We study how different types of light scattering objects, which are dynamically formed in the SR structure during readout of the recorded data surface, affect the characteristics of the reflected optical power modulation.