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Single-frequency l.5μm semiconductor lasers, formed by butt-coupling of a regular Fabry—Perot laser to an external waveguide Bragg reflector, are shown to have very uniform frequency modulation characteristics under direct current modulation. The laser's frequency modulation characteristics, together with its narrow linewidth (̃ 1 MHz), make coherent transmission possible without external modulators. The laser performance was evaluated in a 417Mbit/s, 102 km, frequency-shift-keying coherent transmission experiment.
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Olsson et al. (1987) studied this question.
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