Abstract:We demonstrate evanescent-wave sensing of Cy5-DNA-molecules in an aqueous solution using a photonic crystal fiber. Less than 0.8pL sample volume placed in the holes of the fiber is sufficient for reliable detection.

We address the long-standing unresolved problem concerning the V -parameter in a photonic crystal fiber (PCF). Formulate the parameter appropriate for a core-defect in a periodic structure we argue that the multi-mode cut-off occurs at a wavelength λ * which satisfies VPCF(λ * ) = π. Comparing to numerics and recent cut-off calculations we confirm this result.In photonic crystal fibers (PCFs) an arrangement of air-holes running along the full length of the fiber provides the confinement and guidance of light. The airholes of diameter d are typically arranged in a triangular lattice[1] with a pitch Λ (see insert in Fig. 2), but e.g. honey-comb[2] and kagome [3,4] arrangements are other options. By making a defect in the lattice, light can be confined and guided along the fiber axis. The guidance mechanism depends on the nature of the defect and the air-hole arrangement. For the triangular lattice with a silica-core light is confined by total-internal reflection [1] whereas for an air-core a photonic-bandgap confines light to the defect.[5] For recent reviews we refer to Ref. 6 and references therein.Both type of PCFs have revealed surprising and novel optical properties. In this work we consider the silicacore PCF (see insert in Fig. 2) which was the one first reported.[1] This structure provides the basis of a variety of phenomena including the endlessly single-mode behaviour, [7] large-mode area PCFs,[8] as well as highly non-linear PCF with unique dispersion properties. [9,10,11] Properties of standard fibers are often parametrized by the so-called V -parameter and the entire concept is very close to the heart of the majority of the optical fiber community (see e.g. Refs. 12, 13). The cut-off properties and the endlessly single-mode phenomena of PCFs can also be qualitatively understood within this framework. [1,7,14,15,16] However, the proper choice of the correct length scale for the V -parameter has, until now, remained unsolved as well as the value of V * that marks the second-order cut-off. In this Letter we clarify this problem and also put recent work on multi-mode cut-off [17,18] into the context of the V -parameter.The tradition of parametrizing the optical properties in terms of the V -parameter stems from analysis of the step-index fiber (SIF). The SIF is characterized by the core radius ρ, the core index n c , and the cladding index n cl which all enter into the parameter V SIF given byBecause of its inverse dependence on the wavelength λ, this quantity is often referred to as the normalized frequency. However, in a more general context, this is somewhat misleading (especially if n c and/or n cl has a strong wavelength dependence) and in this Letter we would like to emphasize a more physical interpretation. To do this, we first introduce the numerical aperture NA (or the angle of divergence θ) given bywhich follows from use of Snell's law for critical incidence at the interface between the n c and n cl regions (see e.g. Refs. 12, 13). Next, we introduce the free-space wavenumber k = 2π/λ and its tr...

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.

We numerically study the possibilities for improved large-mode area endlessly single mode photonic crystal fibers for use in high-power delivery applications. By carefully choosing the optimal hole diameter we find that a triangular core formed by three missing neighboring air holes considerably improves the mode area and loss properties compared to the case with a core formed by one missing air hole. In a realized fiber we demonstrate an enhancement of the mode area by ∼ 30 % without a corresponding increase in the attenuation.Applications requiring high-power delivery call for single-mode large-mode area (LMA) optical fibers. While standard-fiber technology has difficulties in meeting these requirements the new class[1] of all-silica photonic crystal fibers (PCF) has a big potential due to their endlessly single-mode properties [2] combined with (in principle) unlimited large effective areas.[3] For recent reviews we refer to Refs. 4, 5.The cladding structure of these PCFs consists of a triangular array of air holes of diameter d and pitch Λ corresponding to an air-filling fraction f = π/(2 √ 3)(d/Λ) 2 . The presence of the air holes results in a strongly wavelength dependent effective index n eff of the cladding and in the short and long wavelength limits we have lim λ≪Λ n eff = n si , lim λ≫Λ n eff = f × n air + (1 − f ) × n si ≡n.

Abstract:We report on a polarization maintaining large mode area photonic crystal fiber. Unlike, previous work on polarization maintaining photonic crystal fibers, birefringence is introduced using stress applying parts. This has allowed us to realize fibers, which are both single mode at any wavelength and have a practically constant birefringence for any wavelength. The fibers presented in this work have mode field diameters from about 4 to 6.5 micron, and exhibit a typical birefringence of 1.510 -4 .

Abstract:We analyze experimentally the polarization properties of highly nonlinear small-core photonic crystal fibers (PCFs) with no intentional birefringence. The properties of recently emerged polarization maintaining PANDA PCFs are also investigated. The wavelength and temperature dependence of phase and group delay of these fibers are examined in the telecommunications wavelength range. Compared to a standard PANDA fiber, the polarization characteristics and temperature dependence are found to be qualitatively different for both types of fibers.

We report on an easy-to-evaluate expression for the prediction of the bend-loss for a large mode area photonic crystal fiber (PCF) with a triangular air-hole lattice. The expression is based on a recently proposed formulation of the V-parameter for a PCF and contains no free parameters. The validity of the expression is verified experimentally for varying fiber parameters as well as bend radius. The typical deviation between the position of the measured and the predicted bend loss edge is within measurement uncertainty.

Abstract-We consider the problem of radiation into free space from the end-facet of a single-mode photonic crystal fiber (PCF). We calculate the numerical aperture NA = sin θ from the half-divergence angle θ ∼ tan −1 (λ/πw) with πw 2 being the effective area of the mode in the PCF. For the fiber first presented by Knight et al. we find a numerical aperture NA ∼ 0.07 which compares to standard fiber technology. We also study the effect of different hole sizes and demonstrate that the PCF technology provides a large freedom for NAengineering. Comparing to experiments we find good agreement.