This thesis describes the design of 10 Gb/s Optical Transmitter using an Electro-Absorption Modulator Integrated Laser (EML) with Temperature Control System using a Proportional Integral Derivative (PID) controller. The experimental results show that the wavelength deviation of the Optical Transmitter is kept within 10 pm according to ITU-T G.692 (Frequency Deviation) standard. The measured 10 Gb/s eye-diagrams of 3 channels in 25-GHz DWDM transmission meet the SONET (OC-192)/SDH (STM-64) specification, without a considering attenuation and chromatic dispersion effects from short fiber patch cord.