Hanna Stawska

Application of Negative Curvature Hollow-Core Fiber in an Optical Fiber Sensor Setup for Multiphoton Spectroscopy

In this paper, an application of negative curvature hollow core fiber (NCHCF) in an all-fiber, multiphoton fluorescence sensor setup is presented. The dispersion parameter (D) of this fiber does not exceed the value of 5 ps/nm × km across the optical spectrum of (680–750) nm, making it well suited for the purpose of multiphoton excitation of biological fluorophores. Employing 1.5 m of this fiber in a simple, all-fiber sensor setup allows us to perform multiphoton experiments without any dispersion compensation methods. Multiphoton excitation of nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) with this fiber shows a 6- and 9-fold increase, respectively, in the total fluorescence signal collected when compared with the commercial solution in the form of a hollow-core photonic band gap fiber (HCPBF). To the author’s best knowledge, this is the first time an NCHCF was used in an optical-fiber sensor setup for multiphoton fluorescence experiments.

Dispersion properties of double-clad hollow-core photonic bandgap fibers based on a circular lattice cladding

The major challenges in developing a fiber-optic nonlinear endomicroscope are efficient excitation light delivery and nonlinear optical signals collection, beam scanning, and probe miniaturization [1-4]. Therefore, double-clad PCFs (DCPCF) are used in nonlinear endomicroscope which can play a dual role of ultrashort pulse delivery and efficient collection of nonlinear optical signals [4]. However, due to dispersion of DCPCF, dispersion compensation systems are required. In this paper the dispersion properties and losses of new design of double-clad hollow-core photonic bandgap fibers (DCPBGFs) based on a circular lattice are investigated for the first time, by using a finite difference time domain method.

Anti-Resonant Hollow Core Fibers with Modified Shape of the Core for the Better Optical Performance in the Visible Spectral Region—A Numerical Study

In this paper, we present numerical studies of several different structures of anti-resonant, hollow core optical fibers. The cladding of these fibers is based on the Kagomé lattice concept, with some of the core-surrounding lattice cells removed. This modification, by creating additional, glass-free regions around the core, results in a significant improvement of some important optical fiber parameters, such as confinement loss (CL), bending loss (BL), and dispersion parameter (D). According to the conducted simulations (with fused silica glass being the structure’s material), CL were reduced from ~0.36 dB/m to ~0.16 dB/m (at 760 nm wavelength) in case of the structure with removed cells, and did not exceed the value of 1 dB/m across the 700–850 nm wavelength range. Additionally, proposed structure exhibits a remarkably low value of D—from 1.5 to 2.5 ps/(nm × km) at the 700–800 nm wavelength range, while the BL were estimated to be below 0.25 dB/m for bending radius of ~1.5 cm. CL and D were simulated, additionally, for structures made of acrylic glass polymethylmethacrylate, (PMMA), with similarly good results—DPMMA ∊ [2, 4] ps/(nm × km) and CLPMMA ≈ 0.13 dB/m (down from 0.41 dB/m), for the same spectral regions (700–800 nm bandwidth for D, and 760 nm wavelength for CL).

Multiwavelength erbium ring laser based on multicore fibre

In this contribution a multiwavelength erbium ring laser is presented. The multiwavelength operation isachievedby using a novel in-line Mach-Zehnder (MZ) fibre interferometer based on multicore microstructured fibre (MC-MOF).The MZ interferometer acts as a periodic spectral filter. The modal properties of the MC-MOF are analysed using the finite difference method. Dual wavelength operation is demonstrated with an optical signal-to-noise ratio (OSNR) of 35 dB and a peak separation of 2 nm.

The effect of core shape on the modal properties of the hollow core fiber

In this paper we present the results of numerical simulations of the modal properties of the hollow core fiber with new structure of the core. We show that altering the shape of the core of the hollow core fiber allows an improvement of optical parameters, such as losses or bandwidth.

Fiber fluorescent spectroscopy

The paper presents the way that colour can serve solving the problem of calibration points indexing in a camera geometrical calibration process. We propose a technique in which indexes of calibration points in a black-and-white chessboard are represented as sets of colour regions in the neighbourhood of calibration points. We provide some general rules for designing a colour calibration chessboard and provide a method of calibration image analysis. We show that this approach leads to obtaining better results than in the case of widely used methods employing information about already indexed points to compute indexes. We also report constraints concerning the technique. Nowadays we are witnessing an increasing need for camera geometrical calibration systems. They are vital for such applications as 3D modelling, 3D reconstruction, assembly control systems, etc. Wherever possible, calibration objects placed in the scene are used in a camera geometrical calibration process. This approach significantly increases accuracy of calibration results and makes the calibration data extraction process easier and universal. There are many geometrical camera calibration techniques for a known calibration scene [1]. A great number of them use as an input calibration points which are localised and indexed in the scene. In this paper we propose the technique of calibration points indexing which uses a colour chessboard. The presented technique was developed by solving problems we encountered during experiments with our earlier methods of camera calibration scene analysis [2]-[3]. In particular, the proposed technique increases the number of indexed points points in case of local lack of calibration points detection. At the beginning of the paper we present a way of designing a chessboard pattern. Then we describe a calibration point indexing method, and finally we show experimental results. A black-and-white chessboard is widely used in order to obtain sub-pixel accuracy of calibration points localisation [1]. Calibration points are defined as corners of chessboard squares. Assuming the availability of rough localisation of these points, the points can be indexed. Noting that differences in distances between neighbouring points in calibration scene images differ slightly, one of the local searching methods can be employed (e.g. [2]). Methods of this type search for a calibration point to be indexed, using a window of a certain size. The position of the window is determined by a vector representing the distance between two previously indexed points in the same row or column. However, experiments show that this approach has its disadvantages, as described below. * E-mail: A.Nowakowski@ire.pw.edu.pl Firstly, there is a danger of omitting some points during indexing in case of local lack of calibration points detection in a neighbourhood (e.g. caused by the presence of non-homogeneous light in the calibration scene). A particularly unfavourable situation is when the local lack of detection effects in the appearance of separated regions of detected calibration points. It is worth saying that such situations are likely to happen for calibration points situated near image borders. Such points are very important for the analysis of optical nonlinearities, and a lack of them can significantly influence the accuracy of distortion modelling. Secondly, such methods may give wrong results in the case of optical distortion with strong nonlinearities when getting information about the neighbouring index is not an easy task. Beside this, the methods are very sensitive to a single false localisation of a calibration point. Such a single false localisation can even result in false indexing of a big set of calibration points. To avoid the above-mentioned problems, we propose using a black-and-white chessboard which contains the coded index of a calibration point in the form of colour squares situated in the nearest neighbourhood of each point. The index of a certain calibration point is determined by colours of four nearest neighbouring squares (Fig.1). An order of squares in such foursome is important. Because the size of a colour square is determined only by the possibility of correct colour detection, the size of a colour square can be smaller than the size of a black or white square. The larger size of a black or white square is determined by the requirements of the exact localisation step which follows the indexing of calibration points [3]. In this step, edge information is extracted from a blackand-white chessboard. This edge information needs larger Artur Nowakowski, Wladyslaw Skarbek Institute of Radioelectronics, Warsaw University of Technology, Nowowiejska 15/19, 00-665 Warszawa, A.Nowakowski@ire.pw.edu.pl Received February 10, 2009; accepted March 27, 2009; published March 31, 2009 http://www.photonics.pl/PLP

Detecting cancerous tissues in human body by means of fiber fluorescent spectroscopy

This works purpose is to present a non-invasive optical method of diagnosing cancerous and otherwise pathological tissues. The optical method and devices proposed in this paper can compete with alternative methods presently employed, in that - among other things - they are non-invasive (therefore completely safe to the patient) and they are very sensitive. There is no need to take tissue samples for these methods and devices as they can be performed in vivo. The methods presented in this paper are referred to as those involving fluorescence spectroscopy.

Numerical estimation of ultrafast pulse propagation in double clad hollow core fibers

Hollow core fibers have a lot of applications in domains where delivery of ultrashort pulses is very important. On the other hand, double clad fibers are widely used for delivery and collection of nonlinear optical signals. In this paper we present a new concept of double clad hollow core fibers(DC-HCF) and we investigate the propagation of femtosecond pulses in such fibers. We use split-step Fourier method to estimate the numerical solution of the generalized nonlinear Schrödinger equations (GSNLE).

Temperature dependence analysis of the parameters in double clad hollow core fibers

A double-clad photonic bandgap fiber (DCPBGF) can be used to transmit femtosecond signals. This fiber is supposed to be applied in endoscopy in vivo. In the environment of human body, temperature is higher than ambient temperature. For this reason one should consider influence of temperature rise on properties of ultrafast impulse propagation.