Hi John. Some ultralight pack manufacturers:
Six Moon Designs
Ultralight Adventure Equipment
Gossamer Gear
Mountain Laurel Designs
Z packs
As far as volume goes, 46L could work for 7 days if you have a well refined Ultralight kit. Have you done many multi day trips ? I have a Six Moon Designs Swift which is 56L but also compresses nicely. A few litres extra doesn't add much weight to the pack. Also be aware that many of the UL packs are frameless and may need some adjusting to that style.
For a long trip you could consider an Aarn pack, not Ultralight but ultra comfortable which is the purpose (for me anyway) of having lighter gear.