Microsoft HoloLens: A Review of Architecture, Applications and Challenges in Untethered Mixed Reality

Microsoft HoloLens is one of the first commercially available, fully untethered optical see-through head-mounted displays (HMDs) for mixed reality (MR). Since the release of the first generation in 2016 and HoloLens 2 in 2019, the device has been adopted in healthcare, manufacturing, education, defense and remote collaboration. This paper reviews the hardware and software architecture of both generations, including the waveguide display, depth sensing, spatial mapping, the Holographic Processing Unit and the interaction model. It then surveys the main application domains and summarizes reported strengths and limitations, such as field of view, tracking accuracy, ergonomics, battery life and cost. Finally, it discusses open research problems and the future of head-worn MR following the discontinuation of HoloLens 2 hardware production. The review aims to help researchers and practitioners choose, evaluate and design MR systems for real-world use.