Narrow bandwidth emission from a mirrorless, far infrared, 13CH3F laser

Frequency tuning and linewidth measurements are reported for a pulsed, mirrorless, kilowatt-power-level, far-infrared (FIR) ¹³ CH₃F laser operating at 245 GHz. The pump laser is an etalon tunable, single-mode CO₂ TEA laser. The FIR frequency spectrum was measured with 2.5-MHz resolution on individual 100-ns laser output pulses using harmonic mixing techniques. The linewidth of the amplified spontaneous emission was found to be surprisingly narrow, about 15 MHz. Frequency tuning of the FIR laser, as the pump laser frequency is tuned, is nonlinear, possibly due to inhomogeneous broadening of the gain by the K-level substructure of the rotational states. These results indicate that heterodyne receivers capable of single-shot frequency measurements can be important tools for investigating the properties of Raman FIR lasers     

Long-distance soliton propagation using lumped amplifiers anddispersion shifted fiber

It is shown both analytically and by numerical simulation, that solitons can traverse great distances through a chain of lumped amplifiers connecting dispersion shifted fiber spans. The fiber spans can also have large fractional variations in D. The resultant pulse distortions and dispersive wave radiation tend to be negligible, as long as the length scale of the variations in energy and dispersion are short relative to the soliton period     

Polarization multiplexing with solitons

It is shown both analytically and with numerical simulation, and confirmed experimentally in transmission over distances up to ~10000 km, that solitons maintain a high degree of polarization over an ultra-long distance transmission system consisting of birefringent dispersion-shifted fiber segments and erbium amplifiers. Based on that fact, the authors propose a polarization/time division multiplexing technique which should allow the single-wavelength bit-rate capacity of an ultra-long distance soliton transmission system to be doubled with little or no significant increase in bit error rate     

Wavelength division multiplexing with solitons in ultra-longdistance transmission using lumped amplifiers

One attractive feature of the all-optical approach to ultra long-distance transmission is that it greatly facilitates wavelength division multiplexing (WDM). It is known that solitons of different velocities are transparent to each other. It is shown, through numerical simulation, that such transparency is also maintained in a system using lumped amplifiers, as long as the length of the collision (the distance the solitons travel down the fiber while passing through each other), is long enough relative to the spacing between amplifiers, or to a possibly longer period of variation in some other parameter, such as the fiber's chromatic dispersion. This result implies the potential for at least several multigigabits-per-second WDM channels spanning just 1 or 2 nm, in a system of transoceanic length (7000-9000 km)     

A fuzzy set approach of an analytical solution of non-steady two-dimensional drainage

A new analytical solution for soil water two-dimensional movement to an orthogonal mesh of parallel drains is presented, as an extended case of the one-dimensional flow problem of the same nature. An equation is provided, that gives the profile of the water surface as well as the volume that has passed through the drains at a given time moment. Non-dimensional profiles of the piezometric surface are given for various values of time and space parameters. The water volume versus time derived from the respective equation is in very good accordance with the volume derived from surface profile integration. We also explore the possibility to solve this problem by using the fuzzy set approach, to cope with the uncertainties of the hydraulic parameters. Triangular fuzzy numbers are used to represent the hydraulic conductivity of the soil as well as the storativity of the aquifer. The drained water volume derived from the fuzzy set after defuzification, approaches the one calculated by the analytical solution, included in the interval of presumption level α = 0.8.     

Propagation of highly chirped pulses in fiber-optic communicationssystems

The propagation of strongly chirped pulses in an amplified fiber-optic communications system is experimentally investigated. Spectral narrowing of the pulses is observed. The narrowing is attributed to interplay between the initial chirp and the nonlinearity in the transmission line. Four-wave mixing (FWM) between wavelength channels is found to be similar to that for unchirped nonreturn-to-zero (NRZ) pulses. Low error rate transmission over 720 km is achieved using these chirped pulses, which are generated by a transmitter based on a mode-locked fiber laser     

A tunable far infrared laser

A continuously tunable far infrared (FIR) laser has been demonstrated; experimental results are presented. A high-pressure (10-12 atm) continuously tunable CO2TE laser is used to pump Raman transitions in CH3F; the generation of continuously tunable radiation in the250-300 mum wavelength range is reported. Accurate frequency and bandwidth measurements have been made and the FIR bandwidth in superradiant emission isapprox4-5GHz. Consequently, the generation of frequency tunable, subnanosecond pulses in the FIR appears feasible. The generation of tunable laser radiation from 150 to 1000 μm by stimulated Raman scattering should be possible using higher pump intensity and/or other gases.     

Energy transfers and frequency shifts from three soliton collisionsin a multiplexed transmission line with periodic amplification

In this paper, we show that there can be four wave mixing between three solitons having different, but equally spaced, frequencies. While this does not happen with solitons in a uniform lossless fiber, we show that in a transmission line with loss and periodically placed amplifiers, it can happen. The spatial periodicity of the transmission line serves to phase match the four wave mixing of the three solitons. This results in permanent frequency shifts for two of the three solitons and energy exchanges between all three solitons