Since fiber optics work just dandy, clearly getting your source to switch on and off at the requisite rate is not the trick. But if you're not shining down a fiber optic cable, you have the problem that intensity decreases as the square(?) of distance from the emitter; and that your multipath problems become a lot more pronounced.
These 2 things are created in different semiconductor technology (materials) that have quite different properties. Most communications are either in GaAs for NIR or in InGaAS/InP for mid IR. Visible stuff here is generally a large GaN die pumping a phosphor material. As the size of the die increases so does its capacitance which ultimately limits the rate at which the signal can be modulated or the brightness of the source. Additionally in the visible you use Si detectors which are slow due also to their large capacitance. So I think it's unlikely you could ever realize 224Gb/s unless you were using WDM (wavelength multiplexing).
