Laser diode bitrate datasheet
I guess I'll convert my comments above into an answer: apart from the theoretical signal processing concepts, physical devices are made to be used in real, physical systems. 155 Mbps and 622 Mbps are common data rates used on fiber-optic SONET networks, specifically OC-3 and OC-12 lines. Therefore, the diode that you referenced is specifically designed and manufactured for use on those systems; it would not be common for such a device to be used for some other nonstandard application (not many people would want to go to the expense of designing their own custom fiber-optic networking standard).

With that said, in theory you could potentially use the devices for higher-bandwidth transmission, barring any specific device-related limitations (I haven't read the full datasheet). As long as the carrier frequency is high enough to accommodate the bandwidth of the signal, then it would be possible (e.g. a 1 GHz carrier can't have any larger than 1 GHz one-sided bandwidth).