Reduplicating one character of a name (杰 → 杰杰) is a standard Chinese pet-name pattern, like English doubling 'JJ'. The Singaporean Mandopop singer 林俊杰 (Lin Junjie / JJ Lin) is widely known by his stage name JJ, often written as 杰杰 in fan circles.
usage
Xinhua dictionary also lists 杰杰 as a literary onomatopoeia for bird cries, but in modern usage it overwhelmingly functions as an affectionate nickname.
