Why was Geoffrey Chaucer held captive by the french?

No. He was and remained through all of his life a highly respected public figure, a high public servant as well as a much-admired writer and poet. He only was held captive for a while (but very probably not put in any jail) when as a young man he was fighting in the so-called Hundred Years' War, captured by French forces and held until he was ransomed by the English king's brother.