ABSTRACT
Figure 16.8 (a) Four-wave mixing spectrum obtained after the CNT-deposited PLC waveguide and the corresponding close-up views of (b) converted signal and (c) input signal [22]. Figure 16.9 plots the relation between the conversion efficiency and the S wavelength detuning against the fixed P. A 3 dB tuning range of around 8 nm is observed. One possible reason that limits the tuning range could be due to the response time of around 500 fs for the CNTs [4,5], in which the temporal pulse spreading Δt is corresponding to a bandwidth Δl of few nanometers. The performance of the FWM-based wavelength converter is further investigated by performing BER measurements. Figure 16.10 shows the output BER against the received optical power with the inset showing the 10 Gb/s eye diagrams of the input signal and the converted signal. In this measurement the wavelengths of S and C are the same with those in Figure 16.8. Note that the converted signal is obtained after the
optical filter shown in Figure 16.7 followed by a low noise EDFA with suitable ASE filtering in the receiver. The figure shows the results of a 3 nm down-conversion and the power penalty is measured to be 3 dB at 10-9 BER level. It is worth noting that compared to other CNT devices described in Section 16.3, the power penalty is reduced as a relatively long length of CNT-light interaction can be obtained and the surface smoothness of the PLC waveguide can be well-controlled during the fabrication process. It is believed that if the CNTs are aligned with more evenly deposited on the waveguide to optimize the nonlinear interaction, further reduction of the power penalty can be obtained.
