An unbalanced interferometer comprising a first single mode optical fiber portion, a second single mode optical fiber portion and a multi-mode optical fiber, wherein the multi-mode optical fiber is coupled by a first splicing at one end to the first single mode optical fiber and by a second splicing at another end to the second single mode optical fiber, the first splicing comprising a first offset distance between a longitudinal axis of the multi-mode optical fiber and a longitudinal axis of the first single mode optical fiber.