Return-to-Zero Pulse Generators Using Overdriven Amplitude Modulators at One Fourth of the Data Rate

We propose a series of pulse generators based on Mach-Zehnder modulators biased at maximum transmission and overmodulated with a peak-to-peak voltage swing beyond the modulator's point of minimum transmission. In each driving cycle, the modulator output consists of two pairs of different pulses with perfectly timed zero crossings. The pulses are then passively equalized either by use of one-bit-delay interferometers or by a 1/2 Talbot dispersive line. The resulting pulse generators produce the formats 36% return-to-zero (RZ), 50% carrier-suppressed RZ (CSRZ), and 50% CSRZ with low alternate chirp alpha = plusmn0.2. All generators are driven by a single radio-frequency tone at one fourth of the desired bit rate.