when traveling down the fiber

  1. Each of these modes takes a different path and thus different length when traveling down the fiber.
  2. Each of these modes takes a different path and thus different length when it travels down the fiber.
    Is #2 correct?
    If it is correct, which one is better?

Neither is very effective in saying what you mean.

Each of these modes takes a different path, and thus traverses a different length of fiber.

Thanks Steve!