Optical Nyquist pulse train generation by non-auxiliary wavelength selective switch in communication band

We report optical Nyquist pulse train generation by non-auxiliary wavelength selective switch (WSS) in communication band. Nyquist pulses have the attractive feature of tolerance to inter-symbol interference (ISI), which means that densely arranged pulse trains are possible. The typical approach for optical Nyquist pulse train generation uses an auxiliary optical circuit for time division multiplexing as well as a WSS for a single Nyquist pulse generation. The auxiliary use of the optical circuit gives rise to optical losses and inflexibility of pulse-train parameters. The optical loss is estimated as 10 dB even if an ideal optical circuit is used in the case of 10-multiplexing. To resolve these problems, we have recently proposed a new approach for optical Nyquist pulse train generation by non-auxiliary WSS in the near-infrared band, where the WSS combines a single Nyquist pulse generation and time division multiplexing. The key point of the approach is how to design a filter function to minimize the optical loss. We have established the method to design the low-loss filter function, which takes advantage of the ISI-free property of Nyquist pulses. We have experimentally demonstrated Nyquist pulse train generation with the proposed approach in the near-infrared band. In this report, we widen its application range to the optical communication band, and experimental results show that the optical loss for 10- multiplexing is successfully reduced to 1.36 dB. The new approach without an auxiliary optical circuit realizes low-loss, highly flexible and compact optical Nyquist pulse train generator in the optical communication band.