Vertical-cavity surface-emitting lasers (VCSELs) are now key optical sources in optical communications. Their main application is currently in local area networks using multimode optical fibers. VCSELs are also being rapidly commercialized for single-mode fiber metropolitan area and wide area network applications. The advantages of VCSEL include simpler fiber coupling, easier packaging and testing, and the ability to be fabricated in arrays. In addition, VCSELs have an inherent single-wavelength structure that is well suited for wavelength engineering. All these advantages promise to lead to cost-effective wavelength-tunable lasers, which are essential for the future intelligent, all-optical networks. The author reviews the advances on wavelength-tunable VCSELs. She summarizes some of the early breakthroughs in wavelength engineering of VCSELs and then concentrates on the designs and properties of micromechanical tunable VCSEL.
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