Wavelength-Swept VCSELs

Abstract

The ability to continuously tune the wavelength of a laser is of critical importance and is a fundamental building block for many optical systems, including wavelength division multiplexed optical fiber communication systems. Vertical cavity surface emitting laser (VCSEL) structure offers a unique advantage to engineer the lasing wavelength because of its ultrashort cavity length, inherently supporting a single Fabry–Perot mode. Hence, a continuous change in VCSEL cavity thickness leads to a continuous sweep of VCSEL wavelength. Wavelength-tunable VCSELs have been a subject of intense interest for the last two decades. Incorporating part or entire top mirror of a VCSEL in an optical microelectromechanical structure (MEMS), continuous wavelength sweeps have been reported. The monolithic integration brings together the best of both technologies and leads to an unprecedented performance in the continuously swept wavelength range. In addition, with the advances of ultrathin high contrast gratings and metastructures (HCG/HCM), the wavelength tuning speed of MEMS-VCSELs has been increased to 1–10 MHz range. Such lasers, now referred as wavelength-swept lasers, are enabling new applications in optical coherent tomography and light detection and ranging systems. In this paper, we review various structures and recent progress of MEMS-VCSELs. We summarize some of the early breakthroughs in designs and properties of micromechanical tunable VCSELs, including advances in HCG/HCM-based MEMS-VCSELs emitting at 850, 1060, and 1550 nm wavelength regimes. In addition, we report a brand new design leading to a record high Δλ/λo = 6.9% tuning ratio with 600 kHz speed at center wavelength of 1060 nm.