Hi Daniel,
Thank you for your quick help! I contact with Grintecth and their reply is confusing, could you help to have a look? They said there is no pitch of the prism or "no gradient refractive index within the prism", do you know the meaning? Does it meaning I did not need to cut the lens I used now?
They said: "The pitch length of the lens is about 0.25, the leg length of the prism is 2.0mm. But it makes no sense to define pitch length of the prism, because there is no gradient refractive index within the prism."