Spectral width

Abstract: Raman effects cause a continuous downshift of the mean frequency of pulses propagating in optical fibers. For solitons in silica fibers, the effect varies roughly with the inverse fourth power of the pulse width. At 1.5-μm wavelength in a fiber with 15 psec/nm/km time-of-flight dispersion, a soliton of 250-fsec duration is predicted to shift by its own spectral width after about 100m of propagation. The theory agrees well with recent measurements.

Abstract: We present the first ultrahigh-resolution optical coherence tomography (OCT) structural intensity images and movies of the human retina in vivo at 29.3 frames per second with 500 A-lines per frame. Data was acquired at a continuous rate of 29,300 spectra per second with a 98% duty cycle. Two consecutive spectra were coherently summed to improve sensitivity, resulting in an effective rate of 14,600 A-lines per second at an effective integration time of 68 micros. The turn-key source was a combination of two super luminescent diodes with a combined spectral width of more than 150 nm providing 4.5 mW of power. The spectrometer of the spectraldomain OCT (SD-OCT) setup was centered around 885 nm with a bandwidth of 145 nm. The effective bandwidth in the eye was limited to approximately 100 nm due to increased absorption of wavelengths above 920 nm in the vitreous. Comparing the performance of our ultrahighresolution SD-OCT system with a conventional high-resolution time domain OCT system, the A-line rate of the spectral-domain OCT system was 59 times higher at a 5.4 dB lower sensitivity. With use of a software based dispersion compensation scheme, coherence length broadening due to dispersion mismatch between sample and reference arms was minimized. The coherence length measured from a mirror in air was equal to 4.0 microm (n= 1). The coherence length determined from the specular reflection of the foveal umbo in vivo in a healthy human eye was equal to 3.5 microm (n = 1.38). With this new system, two layers at the location of the retinal pigmented epithelium seem to be present, as well as small features in the inner and outer plexiform layers, which are believed to be small blood vessels. ?2004 Optical Society of America.

Abstract: Analysis of the directional spectra of typical sets of surface wave data obtained in the open sea as well asa bay using a cloverleaf buoy system are reported. It is shown that the directional wave spectrum can be approximated by the product of the frequencyspectrum and a unimodal angular distribution with mean direction approximately equal to that of thewind, and that various forms of frequency spectra exist, even in relatively simple wave systems, dependingon their generating conditions. Ocean waves at fairly short dimensionless fetches show spectral forms withvery narrow spectral width, which are similar to those of laboratory wind waves. On the other hand, thespectral forms for ocean waves at very long dimensionless fetches are quite similar to the Pierson-Moskowitzspectra, which are considered, within our present data, to be the wave spectra with the largest spectral width.Finally, there exist many ocean waves at moderate dimensionless fetches, which show spectral forms with interminate spect...

Abstract: The propagation of a Gaussian light pulse through a medium having a positive or negative absorption line is examined. Analytical approximations are obtained for the case where the spectral width of the pulse is much smaller than that of the line. It is shown that the pulse remains substantially Gaussian and unchanged in width for many exponential absorption depths, and that the locus of instants of maximum amplitude follows the classical expression for the group velocity, even if this is greater than the velocity of light, or negative. Numerical calculations have been used to examine what happens beyond the limit of usefulness of the analytical approximations.

Abstract: An efficient multimode quantum memory is a crucial resource for long-distance quantum communication based on quantum repeaters. We propose a quantum memory based on spectral shaping of an inhomogeneously broadened optical transition into an atomic frequency comb (AFC). The spectral width of the AFC allows efficient storage of multiple temporal modes without the need to increase the absorption depth of the storage material, in contrast to previously known quantum memories. Efficient readout is possible thanks to rephasing of the atomic dipoles due to the AFC structure. Long-time storage and on-demand readout is achieved by use of spin states in a lambda-type configuration. We show that an AFC quantum memory realized in solids doped with rare-earth-metal ions could store hundreds of modes or more with close to unit efficiency, for material parameters achievable today.