P. Pureza

Small-core As-Se fiber for Raman amplification

We have demonstrated Raman small-core As-Se fiber. More than 20-dB of gain was observed in a 1.1-m length of fiber pumped by a nanosecond pulse of approximately 10.8-W peak power at 1.50 microm. The peak of the Raman gain occurred at a shift of approximately 240 cm(-1). The Raman gain coefficient is estimated to be approximately 2.3 x 10(-11) m/W, which is more than 300 times greater than that of silica. The large Raman gain coefficient coupled with the large IR transparency window of these fibers shows promise for development of As-Se Raman fiber lasers and amplifiers in the near-, mid-, and long-IR spectral regions.

Infrared evanescent-absorption spectroscopy with chalcogenide glass fibers

We have used telluride glass fibers fabricated in house to measure the evanescent-absorption spectra of water, methanol, ethanol, isopropanol, acetone, ethanoic acid, hexane, and chloroform. Furthermore, detection limits of less than 2 vol. % solute were obtained for mixtures of water and methanol, ethanol, isopropanol, acetone, and ethanoic acid. Techniques to reduce the detection limits are discussed.

Stimulated Brillouin scattering in single-mode As 2 S 3 and As 2 Se 3 chalcogenide fibers

Stimulated Brillouin scattering was investigated for the first time in As(2)S(3) single-mode fibers, and also in As(2)Se(3). The propagation loss and numerical aperture of the fibers at 1.56 mum, along with the threshold intensity for the stimulated Brillouin scattering process were measured. From the threshold values we estimate the Brillouin gain coefficient and demonstrate record figure of merit for slow-light based applications in chalcogenide fibers.

Characterization of mid-infrared single mode fibers as modal filters

We present a technique for measuring the modal filtering ability of single mode fibers. The ideal modal filter rejects all input field components that have no overlap with the fundamental mode of the filter and does not attenuate the fundamental mode. We define the quality of a nonideal modal filter Q(f) as the ratio of transmittance for the fundamental mode to the transmittance for an input field that has no overlap with the fundamental mode. We demonstrate the technique on a 20 cm long mid-infrared fiber that was produced by the U.S. Naval Research Laboratory. The filter quality Q(f) for this fiber at 10.5 microm wavelength is 1000+/-300. The absorption and scattering losses in the fundamental mode are approximately 8 dB/m. The total transmittance for the fundamental mode, including Fresnel reflections, is 0.428+/-0.002. The application of interest is the search for extrasolar Earthlike planets using nulling interferometry. It requires high rejection ratios to suppress the light of a bright star, so that the faint planet becomes visible. The use of modal filters increases the rejection ratio (or, equivalently, relaxes requirements on the wavefront quality) by reducing the sensitivity to small wavefront errors. We show theoretically that, exclusive of coupling losses, the use of a modal filter leads to the improvement of the rejection ratio in a two-beam interferometer by a factor of Q(f).

Strength and fractographic analysis of chalcogenide As-S-Se and Ge-As-Se-Te glass fibers

Abstract The strengths and Weibull parameters of chalcogenide As–S–Se and Ge–As–Se–Te glass fibers were measured, and the fiber fracture surfaces examined. The sulfide (As–S–Se) fibers have a mean strength of 545 MPa, characteristic strength of 567 MPa, and Weibull slope, m, of 8.5. The weaker telluride (Ge–As–Se–Te) fibers have a mean strength of 427 MPa, characteristic strength of 441 MPa, and a Weibull slope of 11. Fractographic analysis indicates the sources of failure in these glass fibers are inclusions, microbubbles and microcracks. Fracture mirror measurements enabled estimations of fracture toughness and mean critical flaw sizes. The lower strength of the Ge–As–Se–Te glass fibers was determined to be a consequence of a more severe flaw population.

Non-linearity in chalcogenide glasses and fibers, and their applications

High nonlinearity and large IR transparency make chalcogenide fibers well suited for compact Raman amplifiers, supercontinuum generation and other mid-IR sources. As2S3 fiber has record high theoretical gain compared with silica fiber for slow-light applications.

Raman scattering studies of microcrystalline inclusions in fluoride glasses and fibers

Micro-Raman spectroscopy has been successfully used to identify crystalline inclusions in bulk fluoride glasses and optical fibers. The crystalline phases NaF·(2ZrF4·BaF2) and NaF·(HfF4·ZrF4·BaF2) were identified in ZBLAN and HZBLAN glasses, respectively. Also, LaF3 micro-crystallite inclusions were unambiguously identified in the core of a particular optical fiber.

Progress of Chalcogenide Glass Fibers

High nonlinearity and large IR transparency make these fibers well suited for compact Raman amplifiers, supercontinuum generation and other mid-IR sources. As2S3 fiber has record high theoretical gain compared with silica fiber for slow-light applications.

Raman amplification in As-Se fiber

Raman amplification has been demonstrated at 1.56 pm in As-Se fiber. The Raman gain coefficient was measured to be ~300 times that of silica