| 摘要 |
PURPOSE:To reshape the waveform of a light output pulse and facilitate high speed pulse code modulation by a method wherein an excited=carrier density distribution in a quantum well layer which has the smallest energy band gap is controlled in regard to dimensions and time. CONSTITUTION:For instance, quantum wells 51, 52 and 53 are provided between cladding layers 4 and 7 with barriers 61 and 62 between them. The energy band gap of the center quantum well 52 is the smallest. The first and second energy levels of the electron in this quantum well 52 are V21 and V22 and the first energy levels of the electrons in the left and right quantum wells 51 and 53 are V11 and V31 respectively. The widths of the quantum wells 51, 52 and 53 are W1, W2 and W3 and the widths of the barriers 61 and 62 are B1 and B2 respectively. Inflows and delay times of carriers are controlled by selecting respective levels, widths or number of quantum well layers. The excited-carrier density distribution in the quantum well layer 52 is so controlled as to be synchronized with the growth and attenuation of the oscillation and moreover a relaxation oscillation is suppressed. With this constitution, the waveform of a light output pulse can be reshaped and pulse code modulation with the speed higher than the speed of the conventional method can be realized.
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