Design of widely tunable semiconductor three-branch lasers

We describe the design and operating principles of the new, widely tunable, three-branch semiconductor Y3-lasers, which we have demonstrated recently. This multibranch tunable laser structure is formed by a cascade of Y-junctions and uses a geometrical tuning leverage to achieve wide-range discrete frequency tuning. Y3-lasers have demonstrated experimentally a tuning range of 45 nm (5.6 THz) and access to 50 frequency channels, with potential access to more than a 100 channels. Among the important issues discussed in this paper are the Y3-laser structure, mode selection of the Y3-laser filter, laser side-mode suppression, number of accessible channels, tuning range, and the tuning mechanism of the Y3-laser. A specific design example is also presented. The simplicity of Y3-laser fabrication and the powerful digital channel-access control make these lasers important electronically-tunable sources for multichannel wavelength-division-multiplexed (WDM) optical communication networks