(I DID do a search for 'Soul Cairn' and NOTHING came up)
Yes. And no need to either be a Vampire. It is said that when you entered, "a part of you" stayed there, making travel "safe" within
Actually, AIBQuirky isn't entirely correct. If you chose to have a part of your soul trapped, then you are linked to the Cairn...but if you choose to become a vampire and have since been cured, it has been my experience that you are barred from going back and would have to become a vamp again to re-enter. This has been my experience, at least.
And just so you know, the search function here hasn't been functional since 2014.... so that's not on you, that's on the devs.
If you give Serana a part of your soul, you do what you have to do in the cairn.
There should be a speech-option with Valerica. She will tell you that the black soul gem with you soul is somewhere in the cairn. You search for it and take it.
The next time you will enter the cairn, no further preparations should be necessary.