Bidirectional transmission can reduce the number of hops, the number of wavelengths, and nonlinear effects such as 4-wave mixing(FWM) and cross phase modulation(XPM) compared with unidirectional transmission.
In this thesis, we implemented and demonstrated two-fiber bidirectional ring network with 4 nodes using bidirectional amplifiers and bidirectional add/drop amplifiers(BADAs). The bidirectional amplifiers that are used to compensate loss of the protection fiber share erbium-doped fiber amplifier(EDFA) and mid-stage devices. It has -49 dB low relative intensity noise(RIN) in spite of 18.5 dB high gain because non-reciprocal filter(NRF) is used to suppress the RIN. The NRF is composed of a circulator and an interleaver and has a 20 dB peak isolation. Dispersion compensation fiber(DCF) is used in mid-stage to compensate the dispersion of the single mode fiber(SMF). The BADA module is composed of two unidirectional amplifiers, two bidirectional amplifiers, two interleavers, an arrayed-waveguide grating(AWG), and DCF. The RIN in BADA module is suppressed by the AWG and the interleaver. Because the counter-directionally propagating signals share a single DCF, the dispersion compensation cost can be halved. The capacity is 80 Gb/s and the node spacing is 80 km. Protection time of 17 ms is shorter than SONET standard which is 50 ms.
We assigned the add/drop channels to satisfy the full-mesh connectivity and one additional channel was passed through all nodes to check out the performance of the network. In the working state, the length of the longest path is 320 km and the observed maximum power penalty is about 1 dB. If the network failure outbreaks, the switch control circuits detect the fault and change the state of the ring from the working state to the protection state. In the protection state, the longest path is 480 km and the observed maximum power penalty is less than 2 dB. The protection time is about 17 ms and the retrieval time is about 3.5 ms.
We estimate the scalibility of the two-fiber bidirectional ring network composed of the bidirectional amplifier and the BADA module. If we consider only the RIN, we can accommodate 27 nodes. However, if we consider only the OSNR, we accommodate 6 nodes. Therefore, the implemented bidirectional ring network is limited by OSNR.