Hello Sanjiv,
Thanks for reaching us!
You can use the white light source component as an optical noise source. If the noise needs to be added in front of the interrogator after the light that is reflected from the FBG, then you still can use a white light source. If the noise to be added after the interrogator (detector), then use the Noise Source component. Please have a look at the help document of white light source to have a better understanding of it. This noise source is a sampled signal not noise bins. You may also check the datasheet of the Set OSNR component to understand this type of noise.
I hope this helps?
Warm Regards,
Saurabh Bedi.