V.Q. Nguyen

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.

Fabrication of waveguides in sputtered films of GeAsSe glass via photodarkening with above bandgap light

Abstract We have fabricated and characterized waveguides in thin films of Ge 5 As 34 Se 61 glass sputtered onto silicon wafer substrates. The 5-μm width waveguides were fabricated by exposure to 514.5 nm light from an Ar 3+ laser, with a lithographic exposure mask used to provide the lateral patterning for the waveguides. The measured losses of the waveguides ranged from 3.5 to 6.4 dB/cm. From SEM imaging, we concluded that scattering from microcracks at the glass–substrate interface was the dominant source of loss.

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.

Room temperature dielectric properties of the As40S(60-x)Sex glass system

Abstract The relative dielectric constant (e′), relative loss factor (e″), and loss tangent ( tan δ ) of the chalcogenide As40S(60xa0−xa0x)Sex glasses (x=0, 20, 40, and 60 at.% Se) at room temperature have been investigated in the frequency range of 108–1010 Hz. Since the relative dielectric constant is related to polarization, the contribution of electronic and dipolar polarizations can be determined. As the Se content in the glass network increases, electronic polarization contributes up to approximately 78% of the relative dielectric constant for As40Se60 glass. This is mainly attributed to the larger electronic polarizability of the Se atom.

ORMOCHALCs: organically modified chalcogenide polymers for infrared optics

A novel method combining elemental sulfur and selenium was developed, yielding crystalline sulfur-selenium compounds. The compounds were melted, and an organic comonomer added. Once the organic comonomer was consumed, the viscous compound was vitrified and allowed to cool yielding organic-inorganic hybrid polymers that are termed Organically Modified Chalcogenide (ORMOCHALC) polymers.

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.

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.

IR fiber optics development at the Naval Research Laboratory

We report the first technology demonstration of the use of an IR fiber cable in an IRCM system for missile jamming. The IR fiber cable contains sulphide glass fibers which possess low loss, high strength and high threshold to laser damage. The fiber cable was used to transmit the output from a laser operating in the 2 - 5 micrometers atmospheric window to a Jam Head located remote from the laser. The demonstration was successful and fiber cable performed remarkably well and without damage.

Low-temperature deposition of BaCuSF, a visible through mid-infrared p-type transparent conductor.

Barium copper sulfur fluoride (BaCuSF) is a p-type transparent conductor (p-TC) that, when doped with potassium, exhibits exceptionally high conductivity. The results of a detailed optical and electronic characterization of BaCuSF thin films deposited at a substrate temperature of 100 °C are presented. X-ray diffractometry shows the presence of a cubic BaCuSF phase. Spectroscopic measurements demonstrate that the films transmit from the visible through the mid-infrared with a band gap of 1.8 eV. Hall measurements indicate that the material is a degenerate semiconductor. As deposited, the films exhibit conductivity at room temperature of approximately 260 S/cm - among the highest reported room temperature conductivities for p-TCs. After post-deposition treatment in water, their conductivity increases to as high as 800 S/cm, and their band gap is reduced to 1.5 eV. The potential for low temperature deposition of p-type films with high conductivity and optical transmittance makes BaCuSF promising for several applications including flexible electronics and photovoltaics.