| 摘要 |
PURPOSE:To obtain output light in RZ code at a high transmission speed where an LD can not be modulated directly in RZ code by modulating the LD directly in NRZ code and then reconverting light into RZ codes by external modulation. CONSTITUTION:A direct modulation part 3 modulates the LD1 in NRZ code through a driving part 2 corresponding to an input signal in NRZ code. The driving current of the LD1 is converted in NRZ code by a driving part 2 to modulate the projection light 6 of the LD1 in the same NRZ code with the input signal 5 and the light is inputted to an external modulation part 4. The external modulation part 4 imposes external modulation upon the light according to an input clock 7; when the input clock 7 is logic '1', the light is transmitted and when logic '0', the light is cut off. The frequency of the input clock 7 is equal to the transmission speed of the input signal 5, the phase relation between the projection light 6 of the LD1 and input clock 7 is so determined that when the projection light 6 has a constant value, the input clock 7 is logic '1', and the output light 8 of the external modulating part 4 is modulated in RZ code. Namely, the external modulating part 4 has a function of NRZ/RZ conversion for ANDing the projection light 6 of the LD1 with the input clock 7. |
