Wavelength-tunable light source and wavelength-division multiplexed transmission system using the source

A wavelength-division multiplexed transmission system, comprising:

• an optical circulator to route a broadband wavelength of light inputted through a first port to a second port and to route an optical signal from N number of Fabry-Perot laser diodes inputted through the second port to a third port;
• an N×1 multiplexer/demultiplexer having a common port and N number of input/output ports to transfer optical signals having different wavelengths between the common port and the N number of input/output ports respectively, wherein N represents the number of subscribers connected to the multiplexer/demultiplexer, the N number of Fabry-Perot laser diodes connect to the N number of input/output ports of the multiplexer/demultiplexer respectively, and the common port of the multiplexer/demultiplexer connects to the second port of the optical circulator;
• an external modulator having an input port and an output port for optical signals, wherein the external modulator to modulate optical signals inputted through the input port according to electrical signals applied thereto and to pass the modulated signals through the output port;
• and
• an external modulator driving device to provide the electrical signals for operating the external modulator, wherein the third port of the optical circulator couples to the input port of the external modulator, and the external modulator driving device connects to the external modulator.