Tunable fibre Bragg grating based optical cross connects using multi-port optical circulators: structure and crosstalk analyses

Tunable fibre Bragg grating (FBG)-based reconfigureably non-blocking optical cross connect (OXC) using multi-port optical circulators (MOCs) are proposed and presented. In an FBG–MOC-based OXC, system insertion loss, system differential insertion loss together with OXC dimensions have been analysed and compared with FBG–OC-based OXC structure using three-port optical circulators (OCs). Optical crosstalk in a multiwavlength FBG–OC-based OXC is discussed, and two crosstalk mechanisms, intraband and interband are identified. To compare FBG based OXC with other OXC structures, an analytical model of intraband optical crosstalk is presented. Results show that tunable FBGs based OXCs are attractive OXC schemes as crosstalk level is independent of the number of wavelength channel per fibre. For the worst case the coherent crosstalk is the dominant crosstalk, which is about 20–30 dB higher than the incoherent crosstalk, depending on the sitching state of the cascaded 2×2 OXCs. However, in practical applications incoherent crosstalk is usually dominant, since it is highly unlikely that all the same wavelength-channels will originate from the same optical source. And the crosstalk of FBGs is the dominant crosstalk.