Tim Powers definitely is, and the Catholic themes in the last “Pirates of the Caribbean” movie were there because it was based on an earlier novel by Powers, “On Stranger Tides”. I like his stuff.
Other Catholic SF and Fantasy authors:
Walter M. Miller (A Canticle for Leibowitz)
William Shakespeare (A Midsummer Night;s Dream, Hamlet, Macbeth) (maybe)
Anthony Burgess (A Clockwork Orange, the Wanting Seed)
G.K. Chesterton (The Man Who Was Thursday)
Gene Wolfe (a recent convert) (Book of the New Sun series)
Dante Alighieri - The Divine Comedy could be considered fantasy.
Cyrano de Bergerac (author of an early science fiction tale of a trip to the moon)
John C. Ryan
Anne Rice (on again, off again)
Karel Capek (R.U.R., War with the Newts - coined the term “robot”)
Robert Hugh Benson (a Catholic priest)
William Peter Blatty (The Exorcist)
andrew j. offutt
Jerry Pournelle (Lucifer’s Hammer)
Oscar Wilde (The Canterbury Ghost, The Portrait of Dorian Gray) - converted to Catholicism on his deathbed.
Brian Moore (his novella “Catholics” set in a future where the Latin Rite is banned, could be considered Science Fiction)
Pierre Boulle (Planet of the Apes)
Clifford D. Simak