Anthony M. Johnson

New approach to the measurement of the nonlinear refractive index of short (<25 m) lengths of silica and erbium-doped fibers

The nonlinear refractive index n 2 of silica fiber (24 m) and erbium-doped fiber (10 m) is measured to within an accuracy of 5% by use of time-delayed photorefractive beam coupling of intense 53-ps, 1.064-μm pulses that experience self-phase modulation in the fibers. The resultant induced grating autocorrelation response yields a value of n 2 /A eff and a calibration standard for the fiber. A phase shift of the order of 0.19π can be detected and is limited only by laser amplitude fluctuations. A unique advantage of this technique is its ability to measure n 2 accurately in short lengths (z≤25 m) of fiber, whereas other approaches typically use much longer lengths of fiber (z≥100 m) .

Linear and nonlinear optical properties of single-walled carbon nanotubes within an ordered array of nanosized silica spheres

The linear and nonlinear optical properties of well-separated, single-walled carbon nanotubes were measured. The tubes were grown into the voids of an ordered array of silica spheres. Transmission of light through these tubes increased with the incident laser intensity. The nonlinear decay time of a λ=800-nm probe was measured at 320 fs when the sample was pumped with 400-nm light. Current–voltage characteristics changed upon illumination with a laser beam. Raman scattering decreased as electrical biasing increased.

Measurement of the nonlinear coefficient of telecommunication fibers as a function of Er, Al, and Ge doping profiles by using the photorefractive beam-coupling technique

We have used the photorefractive two-beam-coupling technique to measure the nonlinear coefficient (n_2/A_eff) of several telecommunication fibers and investigated the dependence of n_2/A_eff on Er, Al, and Ge doping profiles in single-mode fibers, where n_2 is the nonlinear refractive index and A_eff is the effective area of the LP_01 mode. A semiempirical relation is derived for predicting the value of n_2/A_eff as a function of Er, Al, and Ge content in optical fibers. We have further examined the wavelength dependence of A_eff in pure and doped silica fibers between 1064 and 1552 nm and found that the A_eff value of doped fibers changes more markedly with wavelength than that of pure-silica fibers.

Femtosecond non-degenerate pump-probe measurements of single-wall carbon nanotubes (SWCNTs) within an ordered array of nanosize silica spheres

We present preliminary lifetime data of single-wall carbon nanotubes (SWCNTs) grown within the voids of an ordered array of silica spheres. Non-degenerate pump-probe measurements with /spl lambda//sub pump/ = 400 nm and /spl lambda//sub probe/ = 800 run indicate a decay of 319 /spl plusmn/ 25 fs.

Hands-On Optics (HOO) – Making an Impact with Light

Hands-On Optics (HOO) is a collaborative three-year program to create and sustain a unique, national, informal science education program to excite students about science by actively engaging them in optics activities. It will reach underrepresented middle school cohorts in science and technology, and connect with their parents, teachers, school districts and communities.