All-optical single-to-dual channel non-return-to-zero to return-to-zero format converter using a periodically poled <inline-formula><math altimg="none" display="inline" overflow="scroll"><mrow><mi mathvariant="normal">Li</mi><mi mathvariant="normal">Nb</mi><msub><mi mathvariant="normal">O</mi><mn>3</mn></msub></mrow></math></inline-formula> and a reflective semiconductor optical amplifier