Does anyone know what's the difference between LR1 and LR4 optics?
As in 10GBASE-LR versus 40GBASE-LR4?
-L stands for long ~1300 nm wavelength (as opposed to -S for 850 nm and -E for ~1550 nm). -R stands for large block code 64b/66b.
The suffix 4 stands for the number of lanes. With -L, those lanes are multiple wavelengths (CWDM) that are merged by the sender and split again by the receiver. Accordingly, 40GBASE-X requires a QSFP+ optical module with four (Q) 10 Gbit/s (SFP+) lanes. 10GBASE-X uses a narrower, single-lane SFP+ module.
There are other module form factors than (Q)SFP(+) but those are the ones most widely used. The lane scheme applies to all of them since it is required by the PHY standards.