This work reports on the fabrication and subsequent supercontinuum generation in a Ge-As-Se-Te/Ge-As-Se core/clad chalcogenide step-index fiber with an elliptical-core and an ultra-high numerical aperture of 1.88 ± 0.02 from 2.5-15 µm wavelength. The fiber has very low transmission loss of < 2 dB/m from 5-11 µm and a minimum loss of 0.72 ± 0.04 dB/m at 8.56 µm. Supercontinuum spanning from 2.1 µm to 11.5 µm with an average power of ∼6.5 mW was achieved by pumping a ∼16 cm fiber with a minor/major axis core diameter of 4.2/5.2 µm with 250 fs pulses at 4.65 µm wavelength and a repetition rate of 20.88 MHz. The effect of the elliptical-core was investigated by means of mechanical rotation of the fiber relative to the linear pump polarization, and it was found to cause a shift in the supercontinuum spectral edges by several hundred nanometers.
CONCLUSIONRadiation pattern and gain measurements on the conformal 6 X 9 slot array indicate that a completely analytic design process is feasible for small slot arrays in waveguide. The measured performance of the conformal array is gratifying, especially for a first trial of a radical design technique.
ACKNOWLEDGMENTThe helpful consultations of R. S. Elliott and L. A. Kurtz are gratefully acknowledged. Appreciation is also expressed to S. W.Lee for his assistance and the timely availability of his referenced report.
REFERENCES[ I ] R. S. Elliott and L. A. Kurtz, "The design of small slot arrays," in
The well-known method presented by Swanepoel can be used to determine the refractive index dispersion of thin films in the near-infrared region from wavelength values at maxima and minima, only, of the transmission interference fringes. In order to extend this method into the mid-infrared spectral region (our measurements are over the wavelength range from 2 to 25 lm), the method is improved by using a two-term Sellmeier model instead of the Cauchy model as the dispersive equation. Chalcogenide thin films of nominal batch composition As 40 Se 60 (at.%) and Ge 16 As 24 Se 15.5 Te 44.5 (at.%) are prepared by a hot-pressing technique. The refractive index dispersion of the chalcogenide thin films is determined by the improved method with a standard deviation of less than 0.0027. The accuracy of the method is shown to be better than 0.4% at a wavelength of 3.1 lm by comparison with a benchmark refractive index value obtained from prism measurements on Ge 16 As 24 Se 15.5 Te 44.5 material taken from the same batch.
A spontaneous emission fiber source operating in the mid-infrared (MIR) wavelength range from 3.5 to 8 µm is demonstrated for the first time at output power levels of at least 1 mW. The source is a Pr3+-doped selenide chalcogenide, multimode, glass fiber pumped with commercially available laser diodes operating at 1.470 µm, 1.511 µm and 1.690 µm. This MIR spontaneous emission fiber source offers a viable alternative to broadband mid-infrared supercontinuum fiber sources, which are comparatively complex and costly. The MIR emission wavelength range is significant for molecular sensing applications across biology and chemistry, and in medicine, agriculture, defense, and environmental monitoring.
In this contribution, a comprehensive experimental study of photoluminescence from Pr 3+ /Dy 3+ co-doped selenide-chalcogenide multimode fiber samples is discussed. The selenidechalcogenide multimode fiber samples co-doped with 500 ppm of Pr 3+ ions and 500 ppm of Dy 3+ ions are prepared using conventional melt-quenching. The main objective of the study is the analysis of the pumping wavelength selection on the shape of the output spectrum. For this purpose, the Pr 3+ /Dy 3+ co-doped selenide-chalcogenide multimode fiber samples are illuminated at one end using pump lasers operating at the wavelengths of 1.32 µm, 1.511 µm and 1.7 µm. The results obtained show that the Pr 3+ /Dy 3+ ion co-doped selenidechalcogenide multimode fiber emits photoluminescence spanning from 2 µm to 6 µm. Also it is demonstrated that, by varying the output power and wavelength of the pump sources, the spectral shape of the emitted luminescence can be modified to either reduce or enhance the contribution of radiation within a particular wavelength band. The presented results confirm that Pr 3+ /Dy 3+ co-doped selenide-chalcogenide multimode fiber is a good candidate for the realization of broadband spontaneous emission fiber sources with shaped output spectrum for the mid-infrared wavelength region.
In the 21 st century, cancer has become a common and feared illness. Early detection is crucial for delivering the most effective treatment of patients, yet current diagnostic tests depend upon the skill of a consultant clinician and histologist for recognition of the cancerous cells. Therefore it is necessary to develop a medical diagnostic system which can analyze and image tissue instantly, removing the margin of human error and with the additional benefit of being minimally invasive. The molecular fingerprint of biological tissue lies within the mid-infrared (IR) region of the electromagnetic spectrum, 3-25µm wavelength. This can be used to determine a tissue spectral map and provide information about the absence or existence of disease, potentially in real-time and in vivo. However, current mid-IR broadband sources are not bright enough to achieve this. One alternative is to develop broadband, mid-IR, supercontinuum generation (SCG). Chalcogenide glass optical fibers have the potential to provide such mid-IR SC light. A popular chalcogenide glass fiber type is based on Ge-As-Se. For biomedical applications it is prudent to avoid the use of arsenic, on account of its toxicity. This paper investigates replacing arsenic with antimony, towards Ge-Sb-Se smallcore optical fibers for SCG. Physical properties of candidate glass pairs are investigated for glass stability via differential thermal analysis etc. and fiber optical loss measurements of associated fibers are assessed. These results are compared to analogous arsenic-containing chalcogenide glasses and optical fibers, and conclusions are drawn focusing on whether there is potential for antimony chalcogenide glass to be used for SCG for mid-infrared medical diagnostics.
Much effort has been devoted to the study of glasses that contain the chalcogen elements (sulfur, selenium and tellurium) for photonics' applications out to MIR wavelengths. In this paper we describe some techniques for determining the refractive index dispersion characteristics of these glasses. Knowledge of material dispersion is critical in delivering step-index fibres including with high numerical aperture for mid-infrared supercontinuum generation.
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