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Single Longitudinal Mode Oscillation of Semiconductor Lasers by Optical Coupling

Spectral behaviour of optically coupled semiconductor lasers is experimentally investigated. The enhancement of a longitudinal mode is found to take place at the wavelength where the difference between the wavelengths of the two lasers is less than 0.3Å. The width of longitudinal modes is found to be broadened by optical coupling as a result of gain reduction induced by the injected light. By using the selective enhancement of longitudinal modes, single longitudinal mode oscillation is realized under CW operation.