Single fundamental mode photonic crystal vertical cavity laser with improved output power - Electronics Letters

Introduction: The operation of a laser in a stable single fundamental mode is important for a variety of applications, such as short and midrange optical networks (high quality local area networks and storage area networks). For these purposes, vertical cavity surface-emitting lasers (VCSELs) show more promise in many cases over distributed feedback (DFB) lasers for a variety of reasons: easy array scaling, low power consumption, convenient on-wafer characterisation, easy packaging, and high volume and low-cost commercial manufacturability. Photonic crystal vertical cavity lasers (PhC-VCSELs) have been shown to give reproducible operation in a single fundamental transverse optical mode [1–3]. This method for creating a singlemode VCSEL shows potential improvements over other methods because of its ease in design and reproducibility in fabrication. Unlike in-plane two-dimensional photonic crystal structures where the defect mode often lies within a frequency bandgap, the type of defect mode created in the VCSEL described here is a guided out-of-plane mode confined in a way similar to the case in a solid-core photonic crystal fibre. With the proper selection of hole depths, diameters, and arrangement, this index confinement can be exploited to create singlemode photonic crystal defect VCSELs that have the potential for low threshold currents and high output powers [3, 4]. Other methods not making use of etched holes have also been reported producing high power fundamental [5–7] and higher-order [8] singlemode operation. Owing to the large electrical apertures that have been used previously, only low powers have been achieved in the past because of wasted current passing through an electrical aperture (created from an oxide aperture) but not through the photonic crystal optical aperture. Achieving over 3.1 mW of fundamental singlemode power is reported by allowing an oxide aperture to encroach closer to the photonic crystal lasing aperture. For the first time only focused ion beam milling was used to define the holes.