Numerical analysis of the optimal length and profile of a linearly chirped fiber Bragg grating for dispersion compensation.

We propose a theoretical investigation of the length and coupling profile of a linearly chirped fiber Bragg grating for maximum dispersion compensation in a repeaterless optical communication system. The system consists of 100 km of standard optical fiber in which a 1550-nm signal, directly modulated at 2.5 Gbits/s, is launched. We discuss the results obtained with 6-, 4.33-, and 1-cm-long linearly chirped fiber Bragg gratings having Gaussian and uniform coupling profiles. We numerically show that a 4.33-cm-long chirped fiber Bragg grating having a uniform coupling profile is capable of compensating efficiently for the dispersion of our optical communication system.

Time-resolved identification of modes and measurement of intermodal dispersion in optical fibers.

Picosecond pulses from a tunable mode-locked visible dye laser are injected into a 603-m few-mode optical fiber. Measurements of the output power temporal profile with 35-ps resolution show six clearly resolved modes. Time-profile measurements over a two-dimensional array of points in the fiber output far field yield a picture of each mode that identifies it. Measurements as a function of wavelength and fitting to waveguide dispersion calculations are used to model the fiber core refractive-index profile. As a result for the nominal step-index fiber used in this work, the presence of an index dip at the center of the core was detected.

Simple and low-cost method for measuring the coherence time of ultrashort laser pulses.

A simple method for measuring the coherence time of ultrashort pulses is reported. The double reflection off a glass slide produces interference fringes that are used to calculate the coherence time.

Remotely switched hollow-core antiresonant reflecting optical waveguide.

We describe a hollow-core antiresonant reflecting optical waveguide whose transmission can be remotely modulated by the motion of a glass substrate placed at a distance from the light-guiding core that ranges from tens to hundreds of micrometers. A maximum on-off ratio of 17 dB was observed. An analytical mathematical formalism developed to fit the data predicts the possibility of achieving on-off ratios of 30 dB.

Optically pumped ultrashort cavity In(1-x) Ga(x) As(y) P(1-y) lasers: picosecond operation between 0.83 and 1.59 microm.

Ultrashort-cavity, thin-film lasers from In(1-x)Ga(x)As(y)P(1-y) of five different compositions, including InP and In(0.53)Ga(0.47)As, have been made to lase between 0.83 and 1.59 microm. The multitude of lasing wavelengths observed had line-to-line separations of less than 10 nm. The lasers were pumped with 1-psec pulses from a mode-locked dye laser. An output pulse of 6-psec duration was measured at a wavelength of 1.16 microm.

Transmission of 3-D images by means of lens guides.

A simple lens guide can be used to present to an observer a lifelike 3-D image of a distant object. The natural way in which the image is presented suggests the use of lens guides within buildings to look outside from interior rooms and in some applications now served by electronic closed-circuit television.

Soft x-ray gain in the alkali earths.

An unsuccessful attempt was made to observe gain in low pressure sodium vapor at 372 A at an x-ray pumping power level of 0.1 GW/cm(2) . As a result we suggest that high density alkali-earth vapors be used instead. With a system of tunable dye lasers of moderate power, it should be possible to reduce substantially the lower laser level population and achieve gains on the order of 1-3 cm(-1). The calculations reported verify this. The additional outer electron in the alkali-earths is necessary to use the dye laser scheme. The tradeoff is that the upper laser level can Auger decay. Our calculations indicate that this is not too severe a limitation in Ca. Since the calculations may be in error, we further suggest that the dye laser scheme is applicable to alkali-earths which have been preexcited to levels for which Auger decay is forbidden in LS coupling.

Lighting with sunlight using sun tracking concentrators.

The use of controlled beams of sunlight for lighting interior parts of a building is proposed as an economically attractive and practical option in a solar energy context. Sun tracking concentrators introduce beams of sunlight through holes in the roof. Inside, the beams can be relayed throughout the building by means of mirrors and lenses. Ideally cool lighting is obtained by using dielectric mirrors to separate the visible and ir parts of the solar spectrum. The ir can be used to generate electricity and usable heat in solar cells. Results of a preliminary experiment are given.

Ultrahigh speed photography of picosecond light pulses and echoes.

Three new results have been obtained with a recently developed camera of 10-psec framing time: (1) The effect of the finite speed of light in photographing relativistic objects is experimentally demonstrated, by photographing a dumbbell-like entity formed by two packets of light. In contrast to material objects, which, theory predicts, should appear rotated, the light dumbbell appears sheared. (2) Photographs of the mode-locked Nd: glass laser radiation show numerous subsidiary pulses accompanying the main ultrashort pulses in the train. The latter have durations ranging from 7 psec to 15 psec. (3) The technique of gated picture ranging, previously used with nanosecond pulses, is extended to the picosecond range where a resolution of 1 cm is demonstrated. Some potentially useful applications are proposed.