In recent years, the optical networks employing the wavelength-divisionmultiplexing (WDM) technology have attracted great attenuation to keep up with the explosive growth of bandwidth demand. The bidirectional WDM transmission over a single optical fiber is considered as a one of the promising candidate to realize future high-capacity optical networks since it increases the spectral efficiency and reduces the use of fiber infrastructure by a factor of two. The bidirectional point-to-point transmission systems have been commercialized and deployed over the world. However, there have been arguments on the feasibility of the bidirectional WDM networks and it still remains a challenge to implement high-capacity networks employing the bidirectional WDM transmission technology. In this dissertation, we have demonstrated bidirectional WDM networks, i.e., the bidirectional self-healing ring network and the bidirectional interconnected ring network, and verify the reality of the bidirectional WDM networks. We have also analyzed the ultimate capacity of the WDM networks and demonstrated an access network employing WDM transmission technology.
In bidirectional networks, the relative intensity noise (RIN) caused by the Rayleigh back scattering and/or optical reflections limits the network performance. Thus, it is essential to suppress the effect of the RIN to implement bidirectional WDM networks. We have proposed and implemented novel network elements such as bidirectional optical amplifiers, a bidirectional add/drop amplifier module and a bidirectional optical cross-connect (BOXC). All the network elements were designed to suppress the RIN and to support dynamic reconfiguration. In addition to that, the bidirectional dispersion compensation technique was applied to the network elements to save the dispersion compensation cost.
Two different bidirectional WDM networks, a bidirectional optical multiplex section shared protection ring (OMS-Spring) network and a bidirectional interconnected ring network were demonstrated by using the realized network elements. The bidirectional OMS-Spring network was composed of four bidirectional add/drop multiplexer (BADM) nodes. Each of them connected to adjacent nodes with two 80-km of conventional single mode fibers (SMFs). The bidirectional interconnected ring network was realized by inteconnecting two 2-fiber bidirectional ring netwoks with the BOXC. Each ring network consists of two BADM nodes spaced by 80 km and a BOXC that was shared by two ring networks. We have implemented the network control system that includes supervisory channels, an analytic routing and wavelength assignment (RWA) algorithm, a fault-detection system, a graphic user interface (GUI) and so on. By using the network control systems, we have demonstrated the automatic protection switching and the automatic retrieval in the networks within 12 ms.
To investigate the scalability of the WDM networks, we have analyzed the ultimate capacities of the WDM transmission systems and WDM networks. We derive analytic expressions of the ultimate capacity-length-product (CLP) of the WDM transmission systems and the ultimate node throughput-length-product (NTLP) of the WDM networks limited by the stimulated Raman scattering (SRS). The CLP and the NTLP are proportional to the square root of the system capacity and the node throughput, respectively. However, they are independent of the system capacity and the node throughput when we compensate for the SRS induced power depletion. The CLP increases as we decrease the amplifier spacing. However, there exists an optimum amplifier spacing that maximizes the NTLP. We confirmed the results of the analytic calculations with those of the numerical simulations.
To accommodate the bandwidth demand in subscriber loops, the WDM technology will be penetrating into access network. A low-cost WDM source is key component in cost-sensitive WDM passive optical network (PON). We have proposed and demonstrated a wavelength-locked Fabry-Perot laser diode (F-P LD) as a low cost WDM source. We achieved a single mode output from an uncooled and unisolated F-P LD by injecting a narrow-band ASE and transmit successfully 155 Mb/s data through 120 km of conventional SMF with the proposed light source. We have also demonstated upstream transmission in WDM-PON with the proposed WDM sources.
