Photoacoustic (PA) imaging offers unique capabilities in studying biological tissue based on optical absorption contrast. The sensitivity and bandwidth in detecting laser-induced ultrasonic signals are crucial for attaining high-quality and high-resolution PA images. Recent studies have shown that optical detection of ultrasound can provide improved detection angle and sensitivity over significantly extended bandwidth. In this review, we provide an overview of recent technological advances in optical methods of ultrasound detection by classifying them based on their implementations in photoacoustic imaging. We further introduce a theoretical framework to generalize sensitivity, bandwidth, and spatial responses of optical ultrasound detection geometries.