I would like to ask, why we can't see objects smaller than wave length of light under traditional microscope.
The wavelength of light is any wavelength. There's visible light (which is what I think you mean) and then there's every possible wavelength above and below that.
Our eyes don't detect light (electromagnetic radiation) outside of the visible region (hence the name :-)) but we can use and do machines to detect these wavelengths and you've probably experienced them : X-ray machines, UV lights for security purpose, infra-red lights for remote controls.
Whatever wavelength you use is going to diffraction limited for resolution. As this detailed article explains, the limit for resolution (and that's assuming everything else is optimal) is about half the wavelength used.
Optical microscopes are designed for the visible wavelengths of light and focus light outside of this region well. You can use special optics designed for that purpose if your interest is outside of visible light.
The development and use of microscopes, not just visible light microscopes, is called Microscopy. That link should provide you with enough information to start with.
I know that there is some way to see them and the scientists who discover this.
Beyond light microscopes, scientists developed the electron microscope and later the scanning tunneling microscope. The principles of these devices are explained at those links.
The 1986 Nobel prize for Physics was shared between three people for their work on these inventions. Another man, Hans Busch, had made a major contribution to the design of the electron microscope but died in 1984 and the Nobel Prize is never awarded posthumously, so even if the committee had thought it appropriate to award him, the rules would have forbidden it.