The ever-increasing importance in mobile and wearable technology for monitoring, sensing, and processing information demands the development of sophisticated architectures of multifunctional materials. Highly aligned multifunctional carbon nanotube (CNT) fibers combine the specific strength, lightness, and thermal conductivity of carbon fibers with the electrical conductivity of metals and ultrabroadband (ultraviolet to far-infrared) absorption. They are thus promising for flexible optoelectronics, astronomy, sensing, spectroscopy, imaging, defense, and communications applications. We fabricated unique optoelectronic devices based on these fibers for generating, detecting, and polarizing broadband electromagnetic waves. We explored the optoelectronic properties of highly aligned CNT fibers to fabricate photothermoelectric effect-based, polarization-sensitive, flexible, substrate-free, and room-temperature-operating photodetectors that work from the ultraviolet to the terahertz with low noise-equivalent power in the entire range using a novel fabrication technique. We incorporated this CNT-fiber photodetector into textiles by simply stitching it into cloth, crafting smart shirts that can collect sunlight as well as detect light on a mobile person. We will also demonstrate a simple and highly error-tolerant method for fabricating a freestanding terahertz polarizer with nearly ideal performance, reliant on the intrinsically one-dimensional character of conduction electrons in well-aligned CNTs. Finally, CNT fibers have the unique advantage of a high emissivity, nearly close to unity all over the electromagnetic spectrum, which makes them ideal as a source. We will describe a current-driven CNT-fiber-based ultrabroadband thermal light source that emits intense electromagnetic radiation from the visible to the far-infrared wavelength range. Compared to traditional thermal emitters, this emitter is more efficient, faster, more flexible, and more robust, making it a promising source for a variety of mid-infrared applications.