In reality, BOTH.
The IVI and the IGD both have Photo-Transistors (Detectors) and Photo-Diodes (LED's)
Over time, any electronic component WILL start to degrade, the Photo-transistors will not be as sensitive to light anymore, just as the Photo-Diodes will not emit as much light power anymore.
Don't worry about 5 - 6 years, in reality, the useable lifespan of the drive (Evironmentally dependant of course) could be anywhere upto 15 years.
For example, we are still upgrading Chassis CU1 systems to CUVC, the power part of the drives are at least 12 years old and still going strong.
The A017 alarm can simply be informing you of the K80 safety relay status (If this is fitted). If you have A017 and no K80 option, then you definately have some hardware problem in the power circuit. IVI, IGD, or IGBT (Could also be a PSU problem, but this is easy to test and disregard).
If you are starting to get optical component degradation (This includes the fibre-optic cable assembly), you will probably suffer F025, F026, and F027's.
There are 10 types of people . . .
Those who understand Binary, and those who don't.