Phase shift keyed systems based on a gain switched laser transmitter.

Area of Science:

• Optical Communications Engineering
• Laser Physics
• Photonics

Background:

• Differential Phase Shift Keying (DPSK) systems, both Return-to-Zero (RZ) and Non-Return-to-Zero (NRZ), necessitate economical and high-performance transmitters for broad adoption.
• Gain-switched lasers are critical components in high-speed optical communication systems.

Purpose of the Study:

• To evaluate a gain-switched Discrete Mode (DM) laser as a cost-effective transmitter for 10.7 Gb/s RZ DPSK systems.
• To compare the performance of the DM laser against a gain-switched Distributed Feed-Back (DFB) laser in RZ DPSK systems.
• To demonstrate the generation of a coherent gain-switched pulse train for use in NRZ DPSK systems.

Main Methods:

• Experimental implementation of a gain-switched DM laser in a 10.7 Gb/s RZ DPSK transmission system.
• Comparative performance analysis against a gain-switched DFB laser under identical RZ DPSK conditions.
• Investigation of laser linewidths to explain performance discrepancies.
• Generation and filtering of sidebands from a coherent gain-switched pulse train for NRZ DPSK applications.

Main Results:

• The gain-switched DM laser achieved error-free performance with a receiver sensitivity of -33.1 dBm in the 10.7 Gb/s RZ DPSK system.
• The standard DFB laser exhibited an error floor at 10⁻¹ in the same RZ DPSK system.
• A highly coherent gain-switched pulse train with approximately 13 sidebands spaced by 10.7 GHz was generated.

Conclusions:

• Gain-switched DM lasers are suitable, cost-efficient transmitters for 10.7 Gb/s RZ DPSK systems, offering superior performance over DFB lasers.
• The spectral characteristics, specifically linewidth, significantly influence the performance of gain-switched lasers in DPSK systems.
• The generated coherent pulse train and its filtered sidebands can serve as narrow linewidth Continuous Wave (CW) sources for 10.7 Gb/s NRZ DPSK systems.