Dora Juan Juan Hu

Holey fiber design for single-polarization single-mode guidance

We propose a holey fiber design to achieve single-polarization single-mode (SPSM) guidance. The photonic crystal fiber (PCF) has a triangular-lattice with elliptical airholes in the microstructured cladding and circular airholes in the core. The SPSM guidance can be obtained by designing the PCF structure such that the fundamental space-filling mode (FSM) of the core region is positioned between the indices of the two nondegenerate orthogonally polarized FSMs of the microstructured cladding.

A Compact and Temperature-Sensitive Directional Coupler Based on Photonic Crystal Fiber Filled With Liquid Crystal 6CHBT

A directional coupler structure formed by a nematic liquid crystal (NLC)-filled photonic crystal fiber (PCF) represents a promising configuration in sensing applications. Because of large refractive index difference between the NLC and silica material, the mode coupling between the NLC waveguide and the silica core is more complicated than the situation of coupling between two fundamental modes of the waveguides. Therefore, it is necessary to perform a theoretical investigation of the mode properties associated with the experimental studies of the coupling characteristics. In this paper, we present a thorough analysis, both theoretically and experimentally, of the directional coupler structure, including the mode properties, coupling characteristics, and thermal sensing properties. The temperature response of the device is experimentally measured, showing a polynomial curve in nematic phase and a linear curve in isotropic phase. The nonlinearity of the temperature response of the device in nematic phase and the linearity in isotropic phase are attributed to the temperature dependence of the refractive index of the NLC. Specifically, the sensitivity is -3.86 nm/°C in isotropic phase of the 6CHBT with good linearity and shows good agreement with simulation results.

Hole-assisted lightguide fibers with small negative dispersion and low dispersion slope

A nonzero dispersion shifted fiber design based on hole-assisted lightguide fiber is presented. The proposed fiber has low dispersion slope around -0.01 ps/nm(2)-km and small negative dispersion values over the wavelength range from 1530 to 1620 nm. It can be used as a transmission medium for a long-haul dense wavelength-division-multiplexed system.

Fiber-integrated second harmonic generation modules for visible and near-visible picosecond pulse generation

Second harmonic generation (SHG) is a ubiquitous technique for extending the spectral coverage of laser sources into regions that would otherwise be technologically challenging to access. SHG schemes typically rely on the use of bulk optical components, resulting in systems with large footprints requiring precise optical alignment. Integration of the SHG components into a single unit facilitates the implementation of compact, robust and turn-key sources, suitable for applications in biophotonic imaging, amongst others. We report on the development of fiber-coupled frequency doubling modules and their application to novel fiberintegrated picosecond pulse sources in the visible and near-visible. The modules employ a simple, single-pass configuration using a periodically-poled lithium niobate (PPLN) crystal as the nonlinear conversion medium. They are readily adaptable for different fiber pump laser configurations and are configurable with either fiber-coupled or collimated free-space outputs. Two sources using the modules are presented, operating at 780 nm and 560 nm. The 780 nm source utilizes an erbium master oscillator power fiber amplifier (MOPFA) scheme. SHG was performed in a 35 mm long crystal, generating 3.5 W of 780 nm radiation with a pulse duration of 410 ps at 50 MHz and conversion efficiencies exceeding 20%. Results of this source being used for parametric wavelength conversion in photonic crystal fiber are discussed. The 560 nm source was based on SHG of a Raman amplified CW diode pumped by a pulsed ytterbium-fiber MOPFA. This source generated 450 mW of average power with conversion efficiencies greater than 20%.

Design and fabrication of a holey fiber microfluidic device with transverse micro-channel

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

Hybrid photonic crystal fiber coupler infiltrated with liquid crystals

We theoretically investigate the thermally tunable photonic crystal fiber (PCF) coupler infiltrated with nematic liquid crystals. The thermo-optical responsive NLC offers thermal tunability of the fiber coupler. The proposed design can find promising sensor applications.

Hole-assisted lightguide fiber for dispersion tailoring

The exploitations of air holes in optical fiber design have been receiving growing research interest since the first photonic crystal fiber (PCF) was demonstrated. Many peculiar optical properties are achievable with the flexible control of the geometry of the air holes in the microstructured cladding. Different from the complex geometry of microstructured cladding in the holey PCF, hole-assisted lightguide fiber (HALF) is based on conventional optical fiber design and therefore guides light by total internal reflection. The existence of the assisting air holes in the cladding helps to tailor the optical properties of the fiber. In this work, the dispersion tailoring is demonstrated by varying the structural parameters and material properties of the fiber. Additional tunability is achieved by infiltrating substance with tunable refractive index into the assisting holes.