An optical transmitter module includes a light source, a first optical circulation unit, a first optical reflector, and an output unit. The light source emits a first light signal with a first wavelength, and a second light signal with a second wavelength. The first optical circulation unit includes three optical couplers and three optical isolators, which are alternately connected to one another to form a loop. The first optical circulation unit includes a first port at a first optical coupler, a second port at a second optical coupler, and a third port at a third optical coupler. The first port is optically coupled to the light source. The first optical reflector is optically coupled to the second port. The first optical reflector reflects the first light signal back to the second port. The output unit is optically coupled to the third port to output the first light signal.