This paper describes the 10-Gb/s, full C-band (1530 to 1565 nm) operation of 1.55-m electroabsorption modulators (EAMs) designed to eliminate the cost of a back up light source for a 10-Gb/s dense wavelength division multiplexing (DWDM) system. We employ InGaAlAs as the material for the EAM multiple-quantum well (MQW), and design it to achieve a sufficient extinction ratio and a low chirp () parameter over a wide wavelength range. A ridge waveguide buried in benzocyclobutene (BCB) is also introduced for the EAM waveguide. We design the width of the ridge waveguide and the thickness of a core layer that includes an MQW and separate confinement hetero-structure (SCH) layers by calculating the EAM capacitance. 6-well and 12-well based EAMs are fabricated to allow us to compare the wavelength dependence of their static/dynamic extinction ratios (SER/DER), and their small-signal electrical to optical (E/O) responses. We confirm that the 12-well based EAM provides a sufficient DER over the C band. We also determine that the wavelength detuning ( ) between an input light wavelength and an EA absorption peak is 100 nm at an input wavelength of 1530 nm, and evaluate the wavelength dependence of the chirp parameter, and the 40-km SMF transmission characteristics such as eye diagrams and the power penalty (PP). These experiments were conducted using a wavelength tunable laser while maintaining the input power of the EAM at about 13 dBm and changing the input wavelength over the C band. The EAM was also driven with a constant modulation voltage swing (Vpp) of 2.0 V while changing only the EAM bias voltage (Vb). We also measured the input power dependence of the chirp parameter. These results show that the 12-well based InGaAlAs EAM is a promising candidate for an optical modulator that can be used over the C band in a low cost 10-Gb/s optical network system.