The transversely adjusted gap laser for optical communication systems

If a laser's energy gap is adjusted spatially so that it varies with position in a plane transverse to the direction of light propagation then each position in the transverse plane will amplify a different part of the spectrum. A simple optical technique is shown for dispersing an optical beam so that each frequency component passes through the appropriate part of a transversely adjusted gap (TAG) laser. A TAG laser can be constructed by subjecting a GaAs injection laser to a transverse thermal gradient. Calculations indicate that such a device would have a bandwidth of
20 \times 10^{12}
Hz for a 25-fold increase compared to a conventional GaAs injection laser. An analysis of optical ray angle and spatial-dispersion alignment tolerances is presented. Two TAG-laser subsystems-a multiplex modulator and an amplifier-are proposed and discussed to indicate how the TAG laser's larger bandwidth and spatial dispersion may simplify optical communication systems. A preliminary-test TAG-laser oscillator has been constructed and tested. It verified the basic concept and exhibited a bandwidth of
2.45 \times 10^{12}
Hz as predicted by the model.