1. Combine the raspberries, blackberries, passion fruit or pineapple juice, and sugar in a blender and puree until smooth.
2. Strain the mixture into a glass measuring cup, pressing with a rubber spatula to extract as much liquid as possible. Pour the mixture into the popsicle molds.
3. Snap the lids on the molds into place and insert a wooden popsicle stick through the opening in each lid.
4. Freeze overnight. (These can be made in advance and stored in the freezer.)
5. To unmold, unsnap the lid and gently squeeze the bottom and sides of the mold with one hand, while pulling the stick with the other. If the pops don't come out easily, run the molds under warm water for 5 seconds and then remove the pops.Serving Size: 1, 3-ounce popsicle