Modal decomposition of light is essential to study its propagation properties in waveguides and photonic devices. Modal analysis can be carried out by implementing a computer-generated hologram acting as a match filter in a spatial light modulator. In this work, a series of aspects to be taken into account in order to get the most out of this method are presented, aiming to provide useful operational procedures. First of all, a method for filter size adjustment based on the standard fiber LP-mode symmetry is presented. The influence of the mode normalization in the complex amplitude encoding-inherent noise is then investigated. Finally, a robust method to measure the phase difference between modes is proposed. These procedures are tested by wavefront reconstruction in a conventional few-mode fiber.
A new methodology to completely characterize active 5 multicore waveguides is proposed. The method is applied to two-6 core waveguides written in an Er 3+ /Yb 3+ co-doped phosphate glass 7 by femtosecond laser inscription. Determination of the core diame-8 ter and refractive index variation is based on asymmetric excitation 9 of the dual core waveguide and measurements of the intensity 10 output distribution. Moreover, a single core waveguide has also 11 been written for characterization purposes and signal enhancement 12 measurements carried out on it have allowed the determination of 13 the glass active properties. Finally, enhancement measurements on 14 the two-core waveguides for different pump powers and core-to-15 core separations have been performed, together with simulations of 16 the experiments using the parameters determined in the character-17 ization procedure. The good agreement between measurements and 18 simulations supports the validity of the characterization method 19 presented. The proposed characterization technique is suitable 20 for any multicore symmetric structure regardless the fabrication 21 method and the number of cores, allowing the benefits of multi-core 22 fibre designs to be transferred to integrated active structures. 23 Index Terms-Erbium/ytterbium codoping, femtosecond laser 24 inscription, integrated optical amplifiers, multicore waveguides. 25 I. INTRODUCTION 26 M ULTICORE fibres (MCF) have been proposed as good 27 candidates for enhancing the capacity of optical trans-28 mission systems [1], both through spatial division multiplex-29 ing (SDM) [2] and modal division multiplexing (MDM) [3]. 30 Moreover, strongly coupled MCF can be designed to have both 31 large mode area (LMA) and low numerical aperture [4], being 32
Keywords:Multicore waveguide Er 3+ -doping Modal interferometer Bending sensor
A B S T R A C TWe present a study of the feasibility of transforming the multicore fiber in a supermode-interference based bending sensor into an active stage. By compensating the antisymmetric supermode losses for high curvatures, fringe visibility is improved and the sensor operating range can be extended. For a given multicore fibre length and Er 3+ -ion concentration sensor calibration curves allow assessing the bending radius by measuring the visibility as a function of the input pump power. The Er 3+ -ion concentration, available input pump power and multicore fiber length set the minimum bending radius that could be measured. (J.A. Vallés).Optical Materials xxx (xxxx) xxx-xxx 0925-3467/
We present a modal analysis of coupled two-core integrated waveguides fabricated by femtosecond laser writing as a function of the core-to-core distance, illuminating position and input light wavelength. In order to do that we use the correlation filter method, implementing the computer generated holograms in a phase-only spatial light modulator. Due to the two-core waveguide symmetry, we prove it is not necessary to encode the complex amplitude in a phase-only device as long as the cores are not strongly coupled. A comparison between experimental and numerical modal weights is presented, showing that simple phase-only match filters allow the modal decomposition of two-core waveguides output beams.
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