Let's run the numbers...
The cost of just the media for optical drives is just plain not competitive with harddrives.
That would be okay if the longevity of the optical disks was better - but reported experiences with optical disks are not consistent with them having greater longevity (not that harddrives have a sterling record, of course, but when not in use and stored carefully, they rarely fail to work when you fire them up again). Even if optical media is only 2x the cost per gb of spinning rust (I suspect it's worse), i wouldn't feel confident enough to keep only one copy. Whether using spinning rust or optical drives, I'd feel like I need at least 2 copies of the backup.
I think the best solution for you is either tape or high capacity harddrives (maybe configured as RAID array, maybe even in their own second 5 bay NAS that is nominally kept powered down in a secure location)
Let's assume you're backing up 16 TB of data (a 5 bay drobo in raid 5 with the largest HDDs you could find), and let's be assume your data is essentially incompressible (such as video, which is the only way for any normal person to use that kind of space)
I was able to find a quote of like $7k for that optical drive, and the media seems to run a whopping $300 for 1.5TB media. That means your 16TB of data would be $3300, plus $7k for the drive, for $10300 for one copy, and $3300 for each additional copy.
LTO 6 tape seems to run like $80 for 2.5TB. The drives are around $2300, plus 50 for an SAS controller, since you probably don't have one. This would be 7 cartridges for $560, so $2910 plus $560 per extra copy of your data.
LTO Ultrium 5 runs $30 per 1.5TB cartridge. The drives are around $1700, plus 50 for an SAS controller. This would be 11 cartridges for $330, so $2080+330 per extra copy of your data.
A diskless 5 bay NAS can be had for as little as $100, but it seems like reputable brands start at $400-500. 4TB drives can be had for like $180. 5 for $900. So 20 TB of raw storage in 5 bay NAS is $1400 - you'd run it raid 5 like before and get $1400 per copy of your 16GB backup
Spinning rust: $1400 per backup ($1000 if you trust a cheap NAS to house the drives)
Spooling rust (LTO6): $2910 for first backup $560 per extra one
Spooling rust (LTO5 ultrium) $2080 for first backup, $330 for each extra one
Spinning optical dye: $10300 for first backup, $3300 for each extra one.
Looking at even these example numbers is, I think, a good exercise to keep these options in perspective.