Near-field to far-field transition of photonic crystal fibers: symmetries and interference phenomena

The transition from the near to the far field of the fundamental mode radiating out of a photonic crystal fiber is investigated experimentally and theoretically. It is observed that the hexagonal shape of the near field rotates two times by pi/6 when moving into the far field, and eventually six satellites form around a nearly gaussian far-field pattern. A semi-empirical model is proposed, based on describing the near field as a sum of seven gaussian distributions, which qualitatively explains all the observed phenomena and quantitatively predicts the relative intensity of the six satellites in the far field.Comment: 7 pages including 6 figures. Animated version of Fig. 5 is available at http://www.crystal-fibre.com/technology/movie.gi

Reduced micro-deformation attenuation in large-mode area photonic crystal fibers for visible applications

We consider large-mode area photonic crystal fibers for visible applications where micro-deformation induced attenuation becomes a potential problem when the effective area A_eff is sufficiently large compared to lambda^2. We argue how a slight increase in fiber diameter D can be used in screening the high-frequency components of the micro-deformation spectrum mechanically and we confirm this experimentally for both 15 and 20 micron core fibers. For typical bending-radii (R~16 cm) the operating band-width increases by ~3-400 nm to the low-wavelength side.Comment: Accepted for Optics Letter

Experimental investigation of cut-off phenomena in non-linear photonic crystal fibers

The modal cut-off is investigated experimentally in a series of high quality non-linear photonic crystal fibers. We demonstrate a suitable measurement technique to determine the cut-off wavelength and verify it by inspecting the near field of the modes that may be excited below and above the cut-off. We observe a double peak structure in the cut-off spectra, which is attributed to a splitting of the higher order modes. The cut-off is measured for seven different fiber geometries with different pitches and relative hole size, and a very good agreement with recent theoretical work is found.Comment: 3 pages including 1 table and 4 figures. Accepted for Optics Letter

Low-loss criterion and effective area considerations for photonic crystal fibers

We study the class of endlessly single-mode all-silica photonic crystal fibers with a triangular air-hole cladding. We consider the sensibility to longitudinal nonuniformities and the consequences and limitations for realizing low-loss large-mode area photonic crystal fibers. We also discuss the dominating scattering mechanism and experimentally we confirm that both macro and micro-bending can be the limiting factor.Comment: Accepted for Journal of Optics A - Pure and Applied Optic

Label-free somatic cell cytometry in raw milk using acoustophoresis.

A microfluidic system for cell enumeration in raw milk was developed. The new method, preconditions the milk sample using acoustophoresis that removes lipid particles which are larger than a few micrometers. The acoustophoretic preprocessing eliminates the need for conventional sample preparation techniques, which include chemical solvents, cell labeling and centrifugation, and facilitates rapid cell enumeration using microscopy or coulter counter measurements. By introducing an acoustic standing wave with three pressure nodes in a microchannel at the same time as the milk sample is laminated to the channel center, lipids are acoustically driven to the closest pressure antinode at each side of the channel center and the cells in the milk sample are focused in the central pressure node. The extracted center fraction with cells becomes sufficiently clean from lipid vesicles to enable enumeration of somatic cells without any labeling step either by direct light microscopy or by coulter counting. Obtained lipid free milk fractions clearly revealed the cell fraction when analyzed by Coulter Counting. Cell counting as measured by a Coulter Counter after acoustophoretic lipid depletion aligned with the corresponding data obtained by reference measurements based on fluorescence staining and subsequent flow cytometer analysis. © 2012 International Society for Advancement of Cytometry

Harmonic microchip acoustophoresis: a route to online raw milk sample precondition in protein and lipid content quality control

A microfluidic approach for raw milk sample preconditioning prior to protein and lipid content analysis has been developed. The system utilizes microchip acoustophoresis and is a further extension of our previously reported multiple node ultrasonic standing wave focusing platform ( Grenvall , C. , Augustsson , P. , Matsuoka , H. and Laurell , T. Proc. Micro Total Anal. Syst. 2008 , 1, 161-163 ). The microfluidic approach offers a method for rapid raw milk quality control using Fourier transform infrared spectroscopy (FT-IR). Two acoustophoresis modes are explored, 2 lambda/2 and 3 lambda/2, offering lipid content enrichment or depletion, respectively. Lipid content depletion above 90% was accomplished. FT-IR data on microchip-processed raw milk samples, enabling direct lipid and protein content analysis, are reported. Most importantly, the harmonic operational modes bypass the problem of lipid aggregation and subsequent clogging, inherent in lambda/2 acoustophoresis systems

Emulsio- ja putkipanostuksen aiheuttama rikkoutumisvyöhyke tunnelilouhinnassa

Tavoitteena on määrittää tunnelilouhinnan seinälinjassa käytetyn 17 mm F-putkipanoksen ja emulsioräjähde Kemiitti 810:n 350 g/m rannun aiheuttamat rikkoutumisvyöhykkeet. Kummallakin räjäytysaineella tehdyn tunneliosuuden seinään sahatuista poikkileikkauksista mitataan rakojen pituudet, joista määritetään rikkoutumisvyöhykkeen syvyys. Rikkoutumisvyöhykkeen syvyyteen vaikuttavaa räjähdysnopeutta porareiässä mitataan edellisten räjähdysaineiden lisäksi Kemiitti 810:n 600 g/m rannusta. Vuosaaren salaman tunneliurakassa 5 (YIT Rakennus Oy) tehdyissä tutkimuksissa Kemiitti 810:n 350 g/m rantu aiheutti keskimäärin 25 cm ja 17 mm F-putkipanos keskimäärin 34 cm syvän rikkoutumisvyöhykkeen. Valmistaja (Oy Forcit Ab) ilmoittaa F-putkipanokselle laskennalliseksi teoreettiseksi rikkoutumisvyöhykkeen syvyydeksi 40 cm. Rikkoutumisvyöhykkeen syvyyttä tunnelin seinästä ei ole mitattu Kemiitti 810:ilä aikaisemmin. Rakojen mittaus tunkeumanesteellä sahatuista pinnoista ei jätä mitään arvailujen varaan ja on siten suositeltava menetelmä jatkotutkimuksissa selvittää eri räjähdysaineiden rikkoutumisvyöhyke. Tutkimus osoittaa lisäksi, että räjähdysaineen panostusasteen (kg/m) ohella räjähdysnopeudella (m/s tai km/s) on suuri merkitys räjäytyksessä kallioon kohdistuvaan paineeseen ja rakoilun muodostumiseen, vertailtaessa rakoilun ulottuvuutta eri räjähdysaineilla. Voima/painoyksikkö s-arvon merkitys ns. silolouhinta räjähdysaineilla lienee usein rakojen syntyä tarkasteltaessa vähäinen. S-arvo on 1980 - 1990 -luvun tutkimuksissa ollut yleinen "rakoiluvyöhyke" kriteeri ja se on (ollut) käytössä vertailtaessa eri räjähdysaineiden tehoa massalouhinnassa ja massiivisessa kiven irrotuksessa. S-arvon merkitystä tulisi tutkia edelleen