A method for establishing at least two bidirectional communication links using coherent detection, the method comprising the steps of (a) providing, at each of a first and a second side of at least a first and a second optical path, at least two optical transceiver modules, wherein each optical transceiver module comprises an optical modulator and a coherent optical receiver, each optical modulator having an input port, a modulation port and an output port and each coherent optical receiver having a local oscillator port, a receiving port and an output port, wherein an input port of each optical transceiver module is connected by an optical 1x2 power splitter device to the optical modulator input port and the coherent optical receiver input port, (b) creating, at each of the first and second sides of the optical paths, a multiplexed optical CW signal (S CS) comprising at least two optical CW signals (S CWi) having differing wavelengths (λ i), wherein the CW signals (S CWi) created at the first side and the CW signals (S CWi) created at the second side have the same or approximately the same wavelengths (λ i), (c) supplying the multiplexed optical CW signal (S CW) to the input port of each optical transceiver module, (d) creating, at an output port of each optical modulator, which defines an output port of the optical transceiver module, a modulated optical signal (S Mi,l; S Mi,r) which includes information of one or more modulation signals (M i,l; M i,r) that are supplied to the modulation port of the corresponding optical modulator, (e) creating, at each of the first and second sides of the optical paths, at least two first and second optical transmit signals (S TXi,l; S TX,ri) by optically filtering each of the modulated optical signals (S Mi,l; S Mi,r) in such a way that only a single wavelength (λ i) remains, and routing each at least one pair of a dedicated first and second optical transmit signal (S TXi,l; S TXi,r) that is used to establish the at least two bidirectional communication links to a dedicated one of the at least first and second optical paths, wherein the first and second optical transmit signals (S TXi,l; S TXi,r) of each pair have differing wavelengths (λ i) and wherein the first and second optical transmit signals (S TXi,l; S TXi,r) that are transmitted in the same direction over the same optical paths have differing wavelengths (λ i), (f) routing, at each of the first and second sides of the optical paths, each of the at least two first and second optical transmit signals (S TXi,l; S TXi,r) to a receiving port of a dedicated coherent optical receiver, and (g) creating, at the output port of each coherent optical receiver, one or more electrical receive signals (S RXi,l; S RXi,r) by mixing the respective optical transmit signal (S TXi,l; S TXi,r) that is supplied to the receiving port and the multiplexed optical CW signal (S CW). (a) providing, at each of a first and a second side of at least a first and a second optical path, at least two optical transceiver modules, wherein each optical transceiver module comprises an optical modulator and a coherent optical receiver, each optical modulator having an input port, a modulation port and an output port and each coherent optical receiver having a local oscillator port, a receiving port and an output port, wherein an input port of each optical transceiver module is connected by an optical 1x2 power splitter device to the optical modulator input port and the coherent optical receiver input port, (b) creating, at each of the first and second sides of the optical paths, a multiplexed optical CW signal (S CS) comprising at least two optical CW signals (S CWi) having differing wavelengths (λ i), wherein the CW signals (S CWi) created at the first side and the CW signals (S CWi) created at the second side have the same or approximately the same wavelengths (λ i), (c) supplying the multiplexed optical CW signal (S CW) to the input port of each optical transceiver module, (d) creating, at an output port of each optical modulator, which defines an output port of the optical transceiver module, a modulated optical signal (S Mi,l; S Mi,r) which includes information of one or more modulation signals (M i,l; M i,r) that are supplied to the modulation port of the corresponding optical modulator, (e) creating, at each of the first and second sides of the optical paths, at least two first and second optical transmit signals (S TXi,l; S TX,ri) by optically filtering each of the modulated optical signals (S Mi,l; S Mi,r) in such a way that only a single wavelength (λ i) remains, and routing each at least one pair of a dedicated first and second optical transmit signal (S TXi,l; S TXi,r) that is used to establish the at least two bidirectional communication links to a dedicated one of the at least first and second optical paths, wherein the first and second optical transmit signals (S TXi,l; S TXi,r) of each pair have differing wavelengths (λ i) and wherein the first and second optical transmit signals (S TXi,l; S TXi,r) that are transmitted in the same direction over the same optical paths have differing wavelengths (λ i), (f) routing, at each of the first and second sides of the optical paths, each of the at least two first and second optical transmit signals (S TXi,l; S TXi,r) to a receiving port of a dedicated coherent optical receiver, and (g) creating, at the output port of each coherent optical receiver, one or more electrical receive signals (S RXi,l; S RXi,r) by mixing the respective optical transmit signal (S TXi,l; S TXi,r) that is supplied to the receiving port and the multiplexed optical CW signal (S CW).