Mode locking of strip buried heterostructure (AlGa)As lasers using an external cavity

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Abstract
Active and passive mode locking of strip buried heterostructure lasers is observed using an external cavity consisting of a lens and a mirror. Using the second‐harmonic‐generation method to obtain the second‐order autocorrelation function we obtain Gaussian pulses as short as 35.7 psec (FWHM) at a 1.9‐GHz repetition rate. The optical spectrum of the mode locked laser consists of longitudinal modes of the composite cavity spaced by ∼0.05 Å, whose amplitudes are modulated by the 2.09‐Å‐mode spacing of the laser itself, and contained under a Gaussian envelope of 9.5‐Å FWHM. Additional very sharp structure (∼1.6‐psec FWHM) in the autocorrelation is shown to result from the presence of several laser mode groups.