Patent ID: 8036534

Claim:
An optical transmitter outputting at least two signal light with a preset wavelength span, comprising: at least two optical modules each including, a laser diode directly modulated with an electrical signal with an ON level and an OFF level, said diode emitting said signal light with a first wavelength corresponding to said ON level of said electrical signal and with a second wavelength corresponding to said OFF level of said electrical signal, a thermo-electric controller to control a temperature of said laser diode, and a TEC driver to drive said thermo-electric controller, wherein one of said at least two optical modules outputs one of said at least two signal light and another optical modules outputs another signal light; a multiplexer configured to multiplex said at least two signal light from respective optical modules; an etalon filter with a periodic transmittance with a period substantially coinciding with said preset wavelength span of said two signal light, said etalon filter receiving an output of said multiplexer; and a monitoring unit configured to receive an output of said etalon filter and to output monitored signals each corresponding to said at least two signal light, wherein said TEC driver controls said temperature of said laser diode such that said first wavelength and said second wavelength of said signal light emitted from said laser diode locate in both sides of a critical wavelength of said etalon filter where a variation of said transmittance becomes a maximum.