For a stylish modern curtain rod, the 3/4" square Zen collection from Urban Decors is a great option. The sleek black finish matches well with any design style. Square end caps or stylized finial completes the design. Coordinating square rings with liners are available for operable treatments.
Creating a double layer treatment is easy with Urban Decors Zen drapery hardware. Both single and double brackets are available. You may to use the outermost rod for a valance or decorative fabric and the back rod for sheers. If you have a valance with a rod pocket, make sure that the pocket depth is at least two inches. While the square rod is only about 3/4", it's not flat and thin like a regular curtain rod, so your pocket needs to be able to expand to fit the square shape.
You can use rings one or both of the rods. The spacing between the two layers is far enough apart for both panels to operate. Just remember, the rings won't be able to move past the support brackets, so if your span is wide, you'll need to consider split draw curtains.
For a double-treatment, you might want to consider using the finial on the outermost rod and the end caps on the rear rod.