Lynda E. Busse

Reduced Fresnel losses in chalcogenide fibers by using anti-reflective surface structures on fiber end faces.

We demonstrate microstructuring of chalcogenide fiber end faces in order to obtain enhanced transmission due to the antireflective properties of the microstructured surfaces. A variety of molding approaches have been investigated for As(2)S(3) and As(2)Se(3) fibers. Transmission as high as 97% per facet was obtained in the case of As(2)S(3) fiber, compared to the native, Fresnel-loss limited, transmission of 83%. The potential for hydrophobic character was also demonstrated by increasing the contact angle of water droplets to greater than 120°.

Effect of scattering centers on the optical loss of As2S3 glass fibers in the infrared

Scattering theory has been used to determine the effect of various defects on the scattering loss of As2S3 glass fibers. The scattering is related to the particle shape, size, relative refractive index, and wavelength of light. Bubbles possess the highest relative refractive index and therefore the highest scattering factor. For a given particle size and wavelength, the scattering decreases in the order bubbles≳carbon≳SiO2≳Al2O3≳As2S3. The calculations have been used to predict the maximum tolerable number of defects to obtain low attenuation equal to 10 dB/km at 5.0 μm.

Development of low-loss IR transmitting chalcogenide glass fibers

We have fabricated long lengths of low loss sulphide and telluride glass fibers for the 1 - 6 and 3 - 12 micrometers regions, respectively. Minimum losses for core/clad fibers are approximately 0.6 and 0.7 dB/m, respectively, while core-only fibers have exhibited losses of about 0.1 dB/m. The measurements have been performed on long lengths, typically 7 - 50 meters. Fiber strengths are reasonable for many short length applications, but improved processing will lead to stronger fibers for long length applications. These fibers are candidates for chemical sensors and for IR laser power delivery.

Anti-reflective surface structures for spinel ceramics and fused silica windows, lenses and optical fibers

Anti-reflective surfaces structures (ARSS) have been successfully fabricated on fused silica windows, lenses and fibers, and spinel ceramics. The reflection loss for spinel was reduced from 7% per surface to 0.9%. For fused silica with ARSS, the reflection loss was reduced to 0.02% near 1 µm. Pulsed laser damage thresholds at 1.06 µm were measured and thresholds as high as 100 J/cm2 were obtained for fused silica windows of up to 10 cm in diameter with ARSS and 850 J/cm2 for silica fibers with ARSS on the end faces. Spinel samples with ARSS showed damage thresholds more than two times higher than that of spinel with traditional AR coatings.

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).

Infrared transmitting fiber optics for biomedical applications

The availability of low loss and high strength chalcogenide fibers is enabling many applications, including biomedical. We report the fabrication and use of chalcogenide fibers for biomedical spectroscopy, scanning near field IR microscopy (SNIM) and laser power delivery. For example, lateral resolution of 20 nm and optical resolution of about 100 nm have been demonstrated for SNIM. The preliminary results are very encouraging and more work is being performed in lowering the losses and improving the performance of the fibers in the appropriate applications.

Reduced Fresnel losses in chalcogenide fibers obtained through fiber-end microstructuring

We demonstrate microstructuring of chalcogenide fiber facets in order to obtain enhanced transmission due to the antireflective properties of the microstructured surfaces. A variety of molding approaches have been investigated for As(2)S(3) and As(3)Se(3) fibers. Transmission as high as 97% per facet was obtained in the case of As(2)S(3) fiber, compared to the native, Fresnel-loss limited, transmission of 83%.

Wavelength dependence of the scattering loss in fluoride optical fibers.

Scattering losses as low as 0.025 dB/km at 2.55 microm have been measured in short lengths of fluoride-glass optical fiber.These measurements were made on several 5-7-cm lengths of fiber. Measurements were also made at various wavelengths to determine the wavelength dependence of the optical loss.

Optical properties of BaO-Ga2O3-GeO2 glasses for fiber and bulk optical applications

Barium gallogermanate glasses are a relatively new family of glasses with tremendous potential for both fiber and bulk optical applications. This ternary system has a broad region of glass forming ability, excellent stability with respect to crystallization, and transmission beyond 5 micrometers . This paper reports the effects of composition and processing on properties critical to both fiber and bulk optical applications of these glasses.

Design parameters for fluoride multimode fibers

Numerical calculations of losses due to polymer coatings and macrobending have been made for step-index multimode fluoride fibers. To minimize such losses, fiber parameters must be chosen to give a large value for V, the normalized frequency. Due to the long propagation wavelength (2.5 mu m) for fluoride fiber, the parameters needed are very different from those of silica fiber. Using the criterion that >or=90% of the modes have losses >