There are two options that you can pursue after an integrated M.Sc in photonics at CUSAT.

Industry Jobs - The jobs offered by the photonics industry of India are mostly sales. Yes, there are jobs in the telecommunications industry especially in the fiber optics sector which could fetch you some very good technical roles as well.

Research - Photonics is one of the very interesting topics to research upon. The field offers some very good opportunities in India as well as abroad. However, very few educational institutions in India have a photonics department and they also prefer physics students when they hire their professors. So getting a teaching job may also become difficult.

Anyway, if you are really interested in the subject then nothing should come between your choice because opportunities will appear over time.