Semiconductor Mode-Locked Laser for High-Speed OTDM Transmission

The aim of this work is to investigate semiconductor mode-locked lasers for their application as a transmitter pulse source in an optical time division multiplexing (OTDM) system with data rates up to 640 Gbit/s and with on-off keying (OOK) or differential phase shift keying (DPSK) modulation formats. Up to the present work there have not been any applications of the semiconductor mode-locked laser at data rates above 160 Gbit/s and in transmission experiments involving the modulation format DPSK. The concept of modular pulse generation was implemented comprising the independent building blocks: pulse source, pulse compressor and pulse shaper. This modular pulse generator was able to generate pulse trains with a pulse widths below 0.4 ps and a pulse peak to pulse pedestal contrast exceeding 40 dB. The timing jitter σrms was lower than 100 fs for an integration interval from 100 Hz to 10 MHz. The generated pulse train was multiplexed up to a 640 Gbit/s single polarization pulse train suitable for OTDM applications. A pulse transmission of compressed pulses over a fiber link of 160 km was demonstrated. The building blocks of the modular pulse generator can be used independently as a pulse source for a 10 or 40 GHz pulse train, as pulse compressor for the reduction of the pulse width from more than 3 ps to less than 0.5 ps and as a pulse shaper for the removal of a pulse pedestal in order to reach signal to background ratios exceeding 40 dB. The application of the modular pulse generator was demonstrated in a transmitter of phase modulated data signals. Error free back-to-back measurements were reported for a 320 Gbit/s DSPK bit sequence in a single polarization and a single wavelength channel. An extension to 640 Gbit/s is possible, however only in combination with forward error correction schemes.