Kramers-Kronig Anomalous Dispersion on Single-Mode Fiber-Optic Couplers and Tapers

The Kramers-Kronig relations couple the real and imaginary part of the dielectric constant of a medium, namely the refractive index n(ω) and the extinction coefficient κ(ω). Changes in n(ω) due to normal and anomalous dispersion (Kramers-Kronig effect) are investigated for the first time using fiber optic couplers and tapers. Kramers-Kronig effect is induced by evanescent wave absorption in these devices. Couplers and tapers have oscillatory spectral outputs that are highly sensitive to the refractive index of the surrounding medium. Theoretical modeling of the Kramers-Kronig effect on couplers and tapers shows two distinct effects. First, the spectral outputs of these devices show a decrease in intensity due to evanescent wave absorption. Second, the spectral maxima and minima are shifted in wavelength due to Kramers-Kronig effect. Experimental studies clearly demonstrate Kramers-Kronig anomalous dispersion on fiber optic couplers and tapers. These devices are shown to be useful as chemical sensors

Thermal Effects on Y\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e:Eu\u3csup\u3e3+\u3c/sup\u3e for Fiber Optic Temperature Sensing

Fiber optic methods have gained acceptance in the past several years as non­ intrusive optical techniques of measuring environmental variables, particularly under hostile conditions. Fiber optic temperature sensors are required for many applications which have a large operating range. One way to implement this sensor is to introduce rare earth-doped materials into a fiber showing temperature-dependent optical emission characteristics. The thermal effects on optical emission characteristics of Y2O3:Eu3+ were studied. The thermal broadening and temperature dependence of the lifetime (τ) of the 611.4 nm emission due to the 5D0 ➔ 7F2 transition were studied in detail in the range of 20 to 850° C. τ was found to be independent of temperature from 20 to 600° C, whereas line broadening depends on temperature in this range. From 600 to 850° C, τ was found to decrease with temperature. This was shown to be due to non-radiative multiphonon emission processes. This result can be applied towards high temperature sensing using an optical fiber containing Y2O3:Eu3+ powder

Microwave Plasma Chemical Vapor Deposited Diamond Tips for Scanning Tunneling Microscopy

Diamond microparticles were grown on etched tungsten wires using a microwave plasma-assisted chemical vapor deposition process. The apexes on cubo-octahedral particles bound by {100} and {111} facets were effectively used as tunneling tips for scanning tunneling microscopy. The atomically resolved surface image of highly oriented pyrolytic graphite was acquired. Tunneling characteristics revealed a higher electron emission from the diamond tips than that from the platinum–iridium tips. The same diamond tips were used to produce surface indentation and its image. © 1997 American Institute of Physics