An apparatus includes an optical fiber configured to transport an optical signal. A cross-section of the optical fiber has a longer slow-axis dimension and a shorter fast-axis dimension. The optical fiber includes a core configured to receive and amplify the optical signal, end features optically coupled to the core at opposite ends of the core, and a cladding surrounding the core and end features. The core has a height in the slow-axis dimension and a width in the fast-axis dimension. Each end feature has a height in the slow-axis dimension and a width in the fast-axis dimension. The core has a lower bend loss than the end features. The optical fiber is configured to confine optical power of a fundamental mode in the core and allow optical power of higher-order mode(s) to leak from the core into the end features. Each end feature's height is less than the core's width.