Polarization conversion in specialty soft glass fibers for mid-infrared applications

Mid-infrared (MIR) technologies are crucial for applications ranging from chemical sensing to precision medical surgery. Effective polarization control is essential to enhance the functionality of fiber systems. Current solutions for polarization control in the MIR primarily involve free-space devices and components. In this thesis, we take a step forward and experimentally demonstrate polarization conversion within soft glass fluoride and chalcogenide fibers using a commercially available in-line polarization controller (PC). Our experiments using a single PC show a polarization extinction ratio (PER) of 20.7 dB in a ZBLAN fiber with a coating of urethane acrylic resin. Cascading two PCs enhances the PER to 39.1 dB while reducing the required compressive force and, thus, increasing the fiber lifetime. Chalcogenide fibers (As2Se3, As2S3, Ge20Se60Te20) are coated with polymethyl methacrylate (PMMA) and tested using a single PC. Thanks to the higher strain optic coefficients of chalcogenide glass, these fibers exhibited exceptional PER values, reaching 39.3 dB for As2Se3, 41.4 dB for As2S3, and 38.3 dB for Ge20Se60Te20. The polymer coatings of the ZBLAN and chalcogenide fibers effectively protect them from compressive force and twisting, enabling them to endure more than 30 cycles of compression and decompression without breakage. Stability test conducted over 12 hours with ZBLAN fiber demonstrated that the achieved polarization state remains stable, with maximum deviations due to environmental factors estimated to be less than 2%. This work is the first proof that in-line polarization control using soft glass fibers is achievable, paving the way toward developing all fiber MIR devices and systems.

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Martin Rochette

Professor

McGill University, Montreal, Quebec, Canada

e-mail: martin.rochette@mcgill.ca 

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Surface Plasmon Resonance-based Photonic Crystal Fiber Sensors

To design highly sensitive Surface Plasmon Resonance (SPR) based Photonic Crystal Fiber (PCF) Sensors

The goal of our thesis was to design highly sensitive and fabrication-friendly SPR-based PCF sensors. To achieve that goal, we designed several PCF sensor structures using COMSOL Multiphysics software. The PCF structures were designed by stacking capillaries, ensuring the feasibility of implementing these structures using the standard Stack and Draw method. Therefore, the sensors were made fabrication-friendly. In addition, air holes were placed inside the PCF core to confine the light. The strategic arrangement of air holes allowed enough channels for light to leak from the core and interact with the plasmonic materials. The light-plasmonic metal interaction helped to detect unknown analytes. Lamination of different plasmonic metals (e.g., Gold, Aluminium doped Zinc Oxide, Titanium dioxide) were applied to enact the sensing ability of the PCF structures. The sensing layer was placed just outside the plasmonic layer. The sensing performances of these structures were evaluated in terms of Amplitude Sensitivity (AS), Wavelength Sensitivity (WS), Resolution, Figure of Merit (FOM), and Birefringence. First, performances for different plasmonic metals were evaluated and compared to select the perfect plasmonic metal. Then different geometrical parameters such as air hole diameter, pitch, plasmonic layer thickness were adjusted to find the combination for which maximum sensitivity was achieved. Finally, fabrication tolerance analysis was performed to check the sensor performance alteration due to fabrication errors. Some of these structures were also tested as temperature sensors, strain sensors, and magnetic field strength sensors. These sensors exhibited excellent performance. The AS of the sensors reported previously were around 2000~2500. On the other hand, our designed sensors manifested AS in the range of 3800 to 7000. Moreover, our sensors displayed a higher sensing range compared to the existing sensors. Four of our designs were published in different journals. 

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Mohammad Rakibul Islam

Professor

Islamic University of Technology, Gazipur, Bangladesh

e-mail: rakibultowhid@yahoo.com 

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• Md Moinul Islam Khan

• Fariha Mehjabin

• Jubair Alam Chowdhury

• Mohibul Islam