What do you understand by secular literature ?
The word "secular" generally refers to worldly, rather than spiritual. In prehistoric India, there were many kinds of literature which were non-religious in nature. The law books of ancient India was known as 'Dharmasutras' and 'Smritis'. These literary books were known as secular literature. Secular literature is one which comprises of worldly things and not pertaining to religious rituals or beliefs.This literature is rather more rational, scientific in its approach.
These books used to have the code of duties for kings, administrators, and the public. They also had rulebooks regarding property and prescribed punishments for murder, theft and other crimes. Kautilya's (Popularly known as Chanakya) 'Arthashastra' is the best example of secular literature. 'Indica', written by Megasthenes is one more example of this type of work. More examples include biographies of important historical characters like ‘Harshacharitra’ by Banabhatta, dramas, and poems like Kalidasa’s ‘Abhijnanasakuntalam’ and ‘Meghaduta’, folk tales like ‘Panchatantra’, books on the law like ‘Manusmriti’.
Accounts of foreign travellers are also important sources of information.
Panini and Patanjali, though they had written on Sanskrit Grammar, also described some political events, are also good examples of secular literature.