Optical drives use 5.25" bays, not 3.5" like a regular HDD. 120mm discs are 4.7" across.
Your Blu-ray drive may only need USB 2.0 - 8x Blu-ray is 36 MB/s, which is barely above the USB 2.0 spec of 35 MB/s.
A USB 2.0 enclosure needs an external power source. So that's an extra cable hanging from your desk, and extra ac adapter brick, and another wall socket used. A USB 3.0 enclosure could in theory be powered entirely over USB. However, I haven't yet seen one which does. I guess just not enough demand so everyone has just been re-using their USB 2.0 designs with a newer USB 3.0 module.
Just search your favorite supplier's website for a 5.25" USB enclosure. (You may not be happy about the price.)...