Can someone help me identify this spiral staircase system?
This isn't a spiral staircase, but rather a helical staircase.  The difference is the lack of the centre pole (As you noticed.  It's otherwise known as a newel) and that it has handrails on both sides, whereas a spiral staircase only has a handrail on the outside.

I was able to find this example of what appears to be a similar design, though it looks wider than your's.