Method for bi-directionally transmitting digital optical signals over an optical transmission link, (a) wherein a first optical transmit signal (S1 TX,CHi) at a predetermined optical wavelength is supplied to a first end of the optical transmission link and transmitted in a first transmission direction to a second end of the optical transmission link, (b) wherein a second optical transmit signal (S2 TX,CHi) at said predetermined optical wavelength is supplied to the second end of the optical transmission link and transmitted in a second opposite transmission direction to the first end of the optical transmission link, (c) wherein said first optical transmit signal (S1 TX,CHi) is created according to a non-return-to-zero first binary digital signal (S1 TXi) in such a way that the bit information of the first binary digital signal (S1 TXi) is included in first sections of the symbol intervals of the first optical transmit signal (S1 TX,CHi), (d) wherein said second optical transmit signal (S2 TX,CHi) is created by creating an optical wavelength reuse signal using the first optical transmit signal (S1 TX,CHi) received at the second end of the optical transmission link, the optical wavelength reuse signal being modulated according to a second digital signal in such a way that the bit information of the second digital signal is included in second sections of the symbol intervals of the first optical transmit signal (S1 TX,CHi) received, and (e) wherein the first optical transmit signal (S1 TX,CHi) is an optical bit-interleaved seeding signal having a symbol rate equal to the bit rate of the first binary digital signal (S1 TXi), wherein the symbol intervals of the optical bit-interleaved seeding signal is divided into two equally long first and second sections, the bit information of the first binary digital signal (S1 TXi) being transported in the first sections and the second sections being set to a seeding level with respect to the optical power of the first optical transmit signal, characterized in (f) that the optical bit-interleaved seeding signal is an optical bit-interleaved duobinary coded seeding signal. (a) wherein a first optical transmit signal (S1 TX,CHi) at a predetermined optical wavelength is supplied to a first end of the optical transmission link and transmitted in a first transmission direction to a second end of the optical transmission link, (b) wherein a second optical transmit signal (S2 TX,CHi) at said predetermined optical wavelength is supplied to the second end of the optical transmission link and transmitted in a second opposite transmission direction to the first end of the optical transmission link, (c) wherein said first optical transmit signal (S1 TX,CHi) is created according to a non-return-to-zero first binary digital signal (S1 TXi) in such a way that the bit information of the first binary digital signal (S1 TXi) is included in first sections of the symbol intervals of the first optical transmit signal (S1 TX,CHi), (d) wherein said second optical transmit signal (S2 TX,CHi) is created by creating an optical wavelength reuse signal using the first optical transmit signal (S1 TX,CHi) received at the second end of the optical transmission link, the optical wavelength reuse signal being modulated according to a second digital signal in such a way that the bit information of the second digital signal is included in second sections of the symbol intervals of the first optical transmit signal (S1 TX,CHi) received, and (e) wherein the first optical transmit signal (S1 TX,CHi) is an optical bit-interleaved seeding signal having a symbol rate equal to the bit rate of the first binary digital signal (S1 TXi), wherein the symbol intervals of the optical bit-interleaved seeding signal is divided into two equally long first and second sections, the bit information of the first binary digital signal (S1 TXi) being transported in the first sections and the second sections being set to a seeding level with respect to the optical power of the first optical transmit signal, characterized in (f) that the optical bit-interleaved seeding signal is an optical bit-interleaved duobinary coded seeding signal.