Matej Komanec

Multimode Chalcogenide Fibers for Evanescent Wave Sensing in the Mid-IR

Evanescent wave spectroscopy in the mid-infrared (MIR) is a powerful tool for remote real-time sensing. Chalcogenide fibers transparent in MIR are considered as a base for creation of a fiber-optical platform for the MIR sensing. In this paper, a rigorous theoretical approach has been applied for the analysis of evanescent modes propagation in a multimode chalcogenide fiber surrounded by an absorbing medium. A role of particular evanescent mode in power delivering through the fiber has been revealed. Strong absorption of water in this spectral range has been shown to be a main factor limiting sensitivity of the evanescent wave sensor. Possibilities of sensitivity enhancement by using waveguiding properties of the fiber have been discussed. The analysis is supported with an experimental measurement of a [GeSe4]95I5 glass fiber partially immersed in an aqueous acetone solution, in the wavelength range of 2-5 μm.

10 Gbps all-optical relay-assisted FSO system over a turbulence channel

Relay-assisted free space optics (FSO) communications becomes one of the promising solutions to improve the FSO link capabilities by implicitly reducing the transmission distance and exploiting distance-dependent fading variance of turbulence. Highly motivated by the capabilities of the system, this paper presents bit error rate (BER) performance of an all-optical 10-Gbps FSO relay based system using amplify-and-forward signaling is investigated through numerical simulations and experimental implementation. Results show that BER improves up to several orders of magnitudes when using relay based links over the same turbulent distance.

Circular Lattice Photonic Crystal Fiber for Mid-IR Supercontinuum Generation

This letter introduces specific design features of a proposed chalcogenide photonic crystal fiber for ultra-wideband supercontinuum generation in the mid-infrared region. The fiber is optimized to include a circular photonic crystal lattice having tremendous potential in the fields of spectroscopy, food quality control, pulse compression, gas sensing, and various nonlinear applications. By tailoring the zero-dispersion wavelength up to 2 and 2.5 μm, we have reached supercontinuum generation in the anomalous dispersion regime with the entire design hinging upon fibers based on two types of chalcogenide glass-arsenic-selenide and arsenic-sulfide, where supercontinuum broadening from 1.2 to 9.3 μm is made possible.

Multimode fiber tapers for reproducible refractometric liquid detection

This paper describes the refractometric detection of liquids based on silica multimode optical fibers which were tapered to increase the evanescent-wave overlap for higher sensor sensitivity. By precisely monitoring the production process, consistent sample parameters were achieved. More than 200 tapers with a taper waist diameter range from 6.0 to 76.3 μ m were prepared from polymer-clad silica and gradient-index multimode fibers. U-shaped fiber taper sensitivities were analytically compared with straight tapers with resulting intensity sensitivities of over 200%/RIU. Crucial parameters for real sensor applications, such as measurement repeatability, reproducibility, and long-term stability, were further studied for polymer-clad silica straight tapers. Long-term stability was monitored showing stable measurement results over a 6 months long interval. Measurement repeatability and reproducibility with standard deviations of 0.55%/RIU and 2.26%/RIU, respectively, were achieved.

Fiber optic refractometric sensors using a semi-ellipsoidal sensing element.

We present theoretical and experimental results for a fiber optic refractometric sensor employing a semi-ellipsoidal sensing element made of polymethyl methacrylate. The double internal reflection of light inside the element provides sensitivity to the refractive index of the external analyte. We demonstrate that the developed sensor, operating at a wavelength of 632 nm, is capable of measurement within a wide range of refractive indices from n=1.00 to n=1.47 with sensitivity over 500 dB/RIU. A comparison of the developed sensor with two more complex refractometric sensors, one based on tapered optical fiber and the other based on suspended-core microstructure optical fiber, is presented.

High-efficiency coupling to small-core microstructured fibers for broadband dispersion characterization

In this paper we investigate several silica-based suspended core microstructured fibers optical (SC-MOFs) in regards to providing the high efficiency coupling for broadband dispersion measurement. We present free-space optic and butt coupling setup capable of coupling signal from standard single mode fibers (SMF) into SC-MOF with core diameter of less than 4 μm and coupling efficiency over 50%. We then investigate SC-MOF’s effective mode area, nonlinearity coefficient and chromatic dispersion curve, using both modeling of the fibers and measurements. Lastly, we have investigated the effects of the aspheric lens on broadband coupling for the chromatic dispersion measurement.

Detailed analysis of multi-mode optical components for utilization in data centers

Due to the high demands for the reliability of data centers, the determination of properly excited optical field inside the multimode (MM) fiber core belongs to the key parameters while designing such a MM optical system architecture for data centers. Appropriately excited mode field of the MM fiber provides optimal power budget in connections, leads to the decrease of insertion losses (IL) and achieves effective modal bandwidth (EMB), which is essential for high data rates. Crucial is especially the encircled flux (EF) parameter, which should be properly defined for combinations of variable optical sources and MM fiber infrastructure to provide proper mode-field distribution. In this paper, we present detailed investigation and measurements of the mode field distribution for short MM optical data center links with the emphasis on their reliability. Such characterization is essential for the design of large MM networks. Various scenarios were tested in terms of IL and mode-field distribution to reveal potential problematic scenarios. Furthermore, we focused via simulations and experiments on the estimation of particular defects and errors, which can realistically occur like eccentricity or connector misalignment. Their dependence on EF statistics and functionality of data center infrastructure was evaluated. Finally, we provide recommendations for data center systems and networks, using OM3 MM fiber connections.

Development and characterization of highly-nonlinear multicomponent glass photonic crystal fibers for mid-infrared applications

We present a detailed chromatic dispersion characterization of heavy-metal oxide (HMO) glass photonic crystal fibers (PCFs) suitable for mid-infrared applications. Based on previous work with hexagonal and suspended-core fibers the focus was placed on determination of the chromatic dispersion curve to reach precise correlation between simulation model and real fiber based on both a post-draw model correction and broadband chromatic dispersion measurement. The paper covers the fiber design, discusses fiber manufacturing, presents measurements of fiber chromatic dispersion, provides the simulation model correction and finally proposes further applications. Selected fiber designs from simulation model were fabricated by the stack-and-draw technique. The dispersion measurement setup was based on an unbalanced Mach-Zehnder interferometer. The influence of optical elements on the measurement results and broadband coupling is discussed. We have proved that the critical factor represents the accuracy of the refractive index equation of the HMO glass and real fiber structure. By improved technique we reached the zero-dispersion wavelength with a reasonable precision of less than 30 nm.

Optical switching based on arsenic-selenide and lead-silicate fibers

The paper reports our progress on soft-glass fibers for optical switching purposes based on four-wave mixing. Specific development of connectorized nonlinear modules for switching application is presented. For the arsenic-selenide fiber we present a novel solid joint technology, with connection losses of only 0.25 dB, which is the lowest value presented up-to-date. We have carried out conversion efficiency simulations, conversion efficiency of -16.1 dB was obtained with arsenic-selenide fiber of length reduced to 5 m. Finally experimental tests are included employing our developed optical switch testbed. Measurement results with a 26 m and a 4.5 m long arsenic-selenide nonlinear modules are presented.

Suspended-core silica and lead-silicate fibers for nonlinear application and sensing purposes

We report development of suspended-core silica and lead-silicate microstructured optical fibers for detection of liquids and supercontinuum generation. Theoretical analysis of effective mode area, dispersion curve, nonlinear coefficient and mode-field overlap is presented. For a specific lead-silicate fiber we determinated the zero dispersion wavelength at 1113 nm with a nonlinear coefficient of 1321 W-1km-1. For detection of liquids both silica and lead-silicate fibers are found to be suitable in different refractive index ranges 1.38-1.44 and 1.68-1.74 respectively. Coupling efficiency into all studied fibers over 40%; fiber attenuation was measured by the cut-back technique and is approximately 2 dB/m for silica glass fibers and over 3 dB/m for lead-silicate fibers.