![]() ![]() ![]() The main goal of multiplexer is to combine the light into one port. The number of outputs can be increased further by increasing the number of cascading steps. 7.17(A)), where two MZIs have been connected to outputs of the first MZI. To enable multiple output ports, a cascaded formation is created (as shown in Fig. Due to reciprocity, if all these wavelengths enter from the same port on right-hand side, all these wavelengths will be combined to the same output at the left-hand side: working as a multiplexer. For an asymmetric MZI, the optical path length difference between these two waveguides (delay length ΔL) can be written as:įrom 7.16 (A), it is clear that a 2×2 MZI works as a demultiplexer when the light travels from left to right separating λ 1, λ 3 into top output and λ 2, λ 4 into bottom output. The extinction ratio depends on the splitting ratio of the splitter/combiner and the loss mismatch between the two waveguides. 7.16(A) and (B) shows the schematic and expected spectral representation of an asymmetric 2×2 MZI. Therefore, the requirement of an application and use of material platform will determine an appropriate splitter/combiner. All these splitters/combiners have advantages and disadvantages. There are various components used as a splitter/combiner: DC, MMI, y-junction, and adiabatic coupler. If two symmetric waveguides are used, the MZI is known as balanced MZI. The splitter splits the input light into two symmetric/asymmetric waveguides and the outputs of these two waveguides are combined by a combiner. A MZI consists of one splitter, one combiner, and two symmetric/asymmetric waveguides. MZI can work as a modulator, switch, isolator, wavelength multiplexer, demultiplexer, etc. The MZI is a basic building block of integrated phonics, as it can play many roles with an engineering adaptation. This MZI switch was later integrated into an InGaAsP/InP SLA-MZI for 20 Gbit s − 1 all-optical add-drop multiplexer for optical time division multiplexing (OTDM) systems ( Jahn et al., 1996). Therefore, the switching window is governed by the asymmetry of the two SOAs. the time interval between the control signal arrival at the two nonlinear media. The input signal is switched out only when the signals in the two MZI arms have different nonlinear phase shifts, i.e. ![]() Due to the asymmetry, the times when the control signal arrives at the nonlinear media in the upper arm and the lower arm are different. ![]() The two SOAs are placed asymmetrically in the upper and lower arms. The control signal is launched from the left coupler (C 1), while the input signal is launched from the right coupler (C 2), such that the control signal and input signal do not have to be separated by wavelength or by polarization. the time interval between the arrival of control signal at the upper arm in the nonlinear medium and that at the lower arm.Īs mentioned earlier, optical switching based on the MZI configuration can also be achieved using just one control signal while having the nonlinear media in the MZI placed asymmetrically in the two branches, as shown in Fig. 7.9. The MZI is biased such that the input signal is switched out only when there is a phase difference between the two MZI arms, i.e. Thus, the control signal arrives at the nonlinear medium in the upper arm of the MZI earlier than at the lower arm, resulting in a temporal offset between the nonlinear phase shifts induced in the two MZI arms. The control signal going to the upper arm has a shorter path length than the one going to the lower arm, and the path difference (Δ t) is adjustable for controlling the width of the switching window. A CW signal is split into two branches at the input coupler, C 1 of the MZI, while the control signal is split into two copies using a polarization beam splitter (PBS) and is injected into the two MZI arms separately through optical couplers (C 2 and C 3). The MZI is built using two optical couplers (C 1 and C 4) and two nonlinear media in each of the arms of the interferometer. The configuration of the MZI switch with two control signals is shown in Fig. 7.8. ![]()
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