To reduce the hole pile-up and increase an optical power handling capacity in 40 Gbit/s semiconductor optical modulator, we fabricated three devices whose active layers consist of multi-quantum-well (MQW) having barrier bandgap wavelengths λ{sub}b of 1.18, 1.3, and 1.4 μm. Escape times of holes from active layer were accurately measured to confirm the effect of longer A b on the promotion of carrier escape from well layers. The escape time becomes smaller with increasing A b and reaches a limit determined by the drift time in the active layer. Optical input power dependence of EO response was also measured accurately to quantify the optical power handling capacity. Devices with λ{sub}b = 1.3 and 1.4 μm have larger capabilities by 2-3 dB than the device with λ{sub}b = 1.18 μm.
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