Hi aasif bashir dar,
I need to mention one more factor that most widely used optical fiber has refractive index of around 1.4 to 1.5 but most importantly you should maintain the core and cladding refractive index difference as low as possible otherwise the dispersion effect a major concern in that case. moreover going for much higher refractive index material the velocity of light will become lesser and lesser. Thanking you.
Regards,
Dhiman