Generation of optical Nyquist pulses with pre-programmed rectangular-shape spectrum

Nyquist pulses, which are defined as responses of a Nyquist filter, can be used in time-division multiplexing transmission which can simultaneously achieve ultrahigh data rate and spectral efficiency. Generally, the methods of Nyquist pulse generation are based on optical Nyquist filters, optical parametric amplifier effect and electro-optical (EO) modulation. In this paper, we focus on the method of EO modulation. Traditionally the limitation of this method is the complex structure and driven signal synchronization between multiple EO modulators when cascaded EO modulators or special modulator structures are using to generate Nyquist pulses. To address this issue, we proposed a novel setup in which only one EO intensity modulator and an electrical arbitrary waveform generator (AWG) are employed. With this method, it is required less on devices. Furthermore, duty cycles of the ideal Nyquist pulses generated by this new method can be changed by using different tones number to drive the EO modulator. The duty cycles of Nyquist pulses we generated can set at 21%, 16% and 12.5% at the repetition of 2.5 GHz by programming the tones number at 2, 3 and 4 on the AWG. The narrowest pulse full width at half maximum is 50.2 ps, which the measured bandwidth is 22.5 GHz by the optical spectrum analyzer, are generated using only one EO intensity modulator with lower bandwidth down to 10 GHz. This method has a potential benefit to reduce the duty cycle further if we use a modulator with bandwidth more than 10 GHz.