I don't know if this is how all fiber optic HDMI cables are made, but all of mine have 4 Fiber cores and the rest are Copper cores. So they are not 100% fiber optic cores. The generic image below shows a pretty typical construction with the optical fiber cores in the middle of the cable.
![61qYa57vxHL._AC_SL1200_.jpg](https://proxy.imagearchive.com/e69/e694633fc6f5b3eef9b7058325a5fba6.jpg)