Infrared Fiber Research Articles

All-optical carbon dioxide remote sensing using rare earth doped chalcogenide fibers

As many fundamental spectroscopic signatures associated to gases of interest are in the 2.5 – 15 µm spectral range (4000–350 cm−1), gases can be detected using efficient infrared (IR) emissions from rare earth (RE) ions embedded into chalcogenide glasses, which are well-known for having low phonon energies. An all-optical IR fiber sensor for in-situ carbon dioxide monitoring was developed. The 4.3 µm mid-IR source probing the gas absorption in this sensor is a Dy3+ doped GaGeSbS fluorescent chalcogenide fiber. Following the 4.3 µm partial absorption by CO2, a wavelength conversion from 4.3 µm to 808 nm is implemented using excited state absorption (ESA) mechanisms in Er3+ doped GaGeSbS bulk glasses or fibers. This wavelength conversion allows the use of silica fibers to transport the 808 nm converted signal. This all-optical sensor with a sensitivity of few hundreds of ppm can be typically deployed over the kilometer range, making this tool suitable for field operations. The photon conversion principle used in this gas sensor could be implemented as a general mean to detect infrared radiations using visible or near-IR detectors instead of mid-infrared detectors.

Dy3+ doped GeGaSbS fluorescent fiber at 4.4 μm for optical gas sensing: Comparison of simulation and experiment

The infrared (IR) fluorescence from Dy3+ doped Ga5Ge20Sb10S65 fibers is investigated in details in order to develop bright IR fiber sources emitting at 4.4 μm for CO2 sensing purposes. Optical sensing requires intense IR radiation to probe with accuracy gas concentrations by measuring the gas absorption. We developed a specific modeling describing the Dy3+ doped GeGaSbS fiber IR output power by simultaneously solving rate equations and propagation equations within the fibers. This modeling allows the determination of the IR fluorescence guided along the fiber as a function of the Dy3+ doping concentration, the propagation losses and the fiber geometry. The results of the simulation are successfully compared with experimental data and are further discussed in order to determine the optimal set of fiber characteristics maximizing the IR fiber output emission.

Improvements on the optical properties of Ge–Sb–Se chalcogenide glasses with iodine incorporation

Decreasing glass network defects and improving optical transmittance are essential work for material researchers. We studied the function of halogen iodine (I) acting as a glass network modifier in Ge–Sb–Se-based chalcogenide glass system. A systematic series of Ge20Sb5Se75−xIx (x=0, 5, 10, 15, 20at.%) infrared (IR) chalcohalide glasses were investigated to decrease the weak absorption tail (WAT) and improve the mid-IR transparency. The mechanisms of the halogen I affecting the physical, thermal, and optical properties of Se-based chalcogenide glasses were reported. The structural evolutions of these glasses were also revealed by Raman spectroscopy and camera imaging. The progressive substitution of I for Se increased the optical bandgap. The WAT and scatting loss significantly decreased corresponding to the progressive decrease in structural defects caused by dangling bands and structure defects in the original Ge20Sb5Se75 glass. The achieved maximum IR transparency of Ge–Sb–Se–I glasses can reach up to 80% with an effective transmission window between 0.94μm and 17μm, whereas the absorption coefficient decreased to 0.029cm−1 at 10.16μm. Thus, these materials are promising candidates for developing low-loss IR fibers.

Crystals based on solid solution of Ag1?xTlxBr1?xIx for the manufacturing of IR fibers

For the development of fiber optics for the range from 0.2 to 50.0 μm, one needs light-stable, nonhygroscopic, ductile crystals that would be transparent within this spectral range and have a lack of cleavage, and from which the flexible infrared (IR) fibers are extruded. The crystals based on solid solutions of silver and monadic thallium halides meet the conditions listed above. Consequently, by differential thermal and x ray analyses, we study the TlBr–TlI phase diagram using the crystals with optimal compositions, which we grow ourselves. We also manufacture light-stable nanocrystalline IR fibers that are transparent at longer wavelengths compared with AgCl–AgBr fibers.

Investigating the properties of infrared PCFs based on AgCl-AgBr, AgBr-TlI, AgCl-AgBr-AgI(TlI) crystals theoretically and experimentally

For operating at the CO2 laser wavelength (10.6 μm), we manufactured single- and double-layered infrared (IR) fibers, as well as those with an enlarged mode field diameter, obtained via extrusion from Ag(Cl)xBr1 − x (0 < x < 1), Ag1 − xTlxBr1 − xIx (0 < x ≤ 0.08), Ag1 − xTlxClyIzBr1 − y − z (0.003 ≤ x ≤ 0.040; 0.066 ≤ y ≤ 0.246; 0.004 ≤ z ≤ 0.048) crystals. We calculated their fundamental characteristics at 10.6 μm and conducted computer simulation of their structure and mode field beforehand. Optical and mechanical characteristics of IR crystals and fibers, such as transmission range, refractive indices, and durability, were also determined, with the dependence of varying monadic thallium iodide content on them being shown as well. In particular, we demonstrated that the increase of thallium iodide content in the initial silver chloride bromide widens the transparency range to 40 μm and improves the rupture strength up to 200 MPa, which is due to the decrease in average fiber grain size up to 95 nm—nanocrystalline size. Using a CCD camera for the far field investigation at 10.6 μm, we showed the single mode of the fibers obtained.

Attenuation measurement of infrared optical fibers by use of a hollow-taper-based coupling method

An alternative method for attenuation measurement of infrared (IR) fibers is described. The method includes a simple technique for direct laser-to-fiber coupling with an uncoated glass hollow taper. The operating principle of the hollow taper is based on the grazing-incidence effect of light reflection. The hollow taper forms a smooth Gaussian-shaped profile of the output laser emission and provides the proper conditions for equilibrium-mode distribution of optical power within the test IR fibers. The experimental hollow-taper-based coupling method is used for measurement of attenuation and bending losses of various kinds of IR fiber, including solid-core (fluoride, chalcogenide, and germanium-doped) and hollow fibers.

Silver halide fiber optic radiometric temperature measurement and control of CO2 laser-irradiated tissues and application to tissue welding.

Tissue heating by laser irradiation has attained importance in many clinical applications. Accurate temperature measurements of laser-irradiated tissues are difficult to achieve, and experiments have produced conflicting results. Fiber optic radiometry allows temperature measurement of laser-irradiated tissues by remote sensing of the emitted infra red (IR) radiation. We have developed an IR fiber optic radiometer capable of accurate tissue temperature measurements (+/- 0.2 degrees C) and utilized it to monitor and control the heating of tissues by CO2 laser irradiation. Tissue temperature control of +/- 2.5 degrees C was achieved. This system was used to control tissue temperature during CO2 laser-assisted welding of urinary bladders in rats. The strength of the welds was recorded for different welding temperatures. A temperature of 55 degrees C was found to be optimal.

Properties of silver halide core-clad fibers and the use of fiber bundle for thermal imaging

Abstract Optical infrared (IR) fibers with core-clad structure are of great importance because they have better qualities than unclad fibers for most IR fiber applications, especially in CO2 laser power delivery and radiometry. We have fabricated core-clad polycrystalline silver halide optical fibers with different compositions and core diameters, and although their loss is still higher than that of unclad fibers, they already have many advantages and new capabilities. The behavior of the scattering loss along these fibers and other optical properties was measured and compared with that of unclad silver halide fibers. We show that the higher loss of clad fibers results mainly from excessive scattering. The improvement in the process of fabricating clad fibers enabled the production of new elements such as single-mode fibers (SMFs) and fiber bundles for thermal imaging.

Liquid Phase Epitaxy of Hg1−xCdxTe from Te Solutions: A Route to IR Detector Structures

The intrinsic semiconductor mercury cadmium telluride (Hg1−xCdxTe), a solid solution of HgTe and CdTe, has assumed an ever increasing role in the fabrication of infrared (IR) detectors because its energy gap (0-1.5 eV) can be tailored to match the specific needs of IR detection and fiber optic systems. In photovoltaic focal plane array (FPA) applications, low power consumption, as well as excellent sensitivity at elevated temperatures, have made Hg1−xCdxTe the material of choice for both the midwave IR (MWIR) and longwave IR (LWIR) region.