An optical coupler device, suitable for monitoring purposes in an optical point-to-point transmission link, comprising: (a) a first, a second and a third optical port; (i) the optical coupler device being configured to transmit a first optical signal (S DS) received at the first optical port to the second optical port and to transmit a second optical signal (S US) received at the second optical port to the first and third optical port according to a monitoring split ratio with respect to the optical power of the second optical signal (S US), the first (S DS) and second (S US) optical signal having a wavelength (λ 1, λ 2) lying in a first optical band; (ii) the optical coupler device being further configured to transmit a third (S mon) and a fourth optical signal (S mon,r) received at the third and the second optical port to the respective other optical port, the third (S mon) and fourth (S mon,r) optical signal having a wavelength (λ 3) lying in a second optical band; characterized in (b) that the optical coupler device is configured to be controllable with respect to the monitoring split ratio and (c) that the optical coupler device further comprises a control means adapted to receive a control signal and configured to control the optical coupler device with respect to the monitoring split ratio in such a way that (i) in a first work mode the second optical signal (S US) is transmitted to the first optical port, only, and (ii) in a second work mode a major portion of the optical power of the second signal (S US) is transmitted to the first optical port and a minor portion of the optical power of the second signal is (S US) transmitted to the third optical port. (a) a first, a second and a third optical port; (i) the optical coupler device being configured to transmit a first optical signal (S DS) received at the first optical port to the second optical port and to transmit a second optical signal (S US) received at the second optical port to the first and third optical port according to a monitoring split ratio with respect to the optical power of the second optical signal (S US), the first (S DS) and second (S US) optical signal having a wavelength (λ 1, λ 2) lying in a first optical band; (ii) the optical coupler device being further configured to transmit a third (S mon) and a fourth optical signal (S mon,r) received at the third and the second optical port to the respective other optical port, the third (S mon) and fourth (S mon,r) optical signal having a wavelength (λ 3) lying in a second optical band; (i) the optical coupler device being configured to transmit a first optical signal (S DS) received at the first optical port to the second optical port and to transmit a second optical signal (S US) received at the second optical port to the first and third optical port according to a monitoring split ratio with respect to the optical power of the second optical signal (S US), the first (S DS) and second (S US) optical signal having a wavelength (λ 1, λ 2) lying in a first optical band; (ii) the optical coupler device being further configured to transmit a third (S mon) and a fourth optical signal (S mon,r) received at the third and the second optical port to the respective other optical port, the third (S mon) and fourth (S mon,r) optical signal having a wavelength (λ 3) lying in a second optical band; (b) that the optical coupler device is configured to be controllable with respect to the monitoring split ratio and (c) that the optical coupler device further comprises a control means adapted to receive a control signal and configured to control the optical coupler device with respect to the monitoring split ratio in such a way that (i) in a first work mode the second optical signal (S US) is transmitted to the first optical port, only, and (ii) in a second work mode a major portion of the optical power of the second signal (S US) is transmitted to the first optical port and a minor portion of the optical power of the second signal is (S US) transmitted to the third optical port. (i) in a first work mode the second optical signal (S US) is transmitted to the first optical port, only, and (ii) in a second work mode a major portion of the optical power of the second signal (S US) is transmitted to the first optical port and a minor portion of the optical power of the second signal is (S US) transmitted to the third optical port.