According to string theory, photons are not composed of strings. In string theory, the fundamental building blocks of the universe are tiny, one-dimensional entities called strings. These strings vibrate in different ways, and the different vibrational patterns give rise to different particles with different properties, such as mass and charge.
Photons, which are particles of light and carriers of electromagnetic radiation, are considered elementary particles in the Standard Model of particle physics. They are not composed of anything smaller or more fundamental according to the Standard Model.
String theory proposes that all fundamental particles and forces can be described in terms of the vibrational modes of these tiny strings. However, photons are unique in that they are associated with particles called "gauge bosons," which mediate the electromagnetic force. These gauge bosons, including photons, are not explicitly described as strings but emerge from the underlying framework of string theory.
In summary, while string theory provides a theoretical framework to describe the fundamental particles and forces of the universe, photons are not directly composed of strings according to the current understanding of string theory.