Off-axis coupled etalon interferometers

Abstract

Methods and apparatus are employed to enhance the efficiency and applicability of Fabry-Perot interferometers. In existing devices, light introduced at a first off-axis point on the image plane is partially transmitted through the interferometer to the detector and partially reflected to a second off-axis point on the image plane. Broadly, the invention re-uses the light reflected to the second off-axis point rather than discarding it. As one example, the reflected light is guided to a third off-axis point on the image plane for retransmission back through the interferometer to a different point on the detector. A plurality of optical fibers are employed, each having one end to receive light at an off-axis point of the image plane, and another end to re-direct the light back through the etalon from a different off-axis point of the image plane. Alternatively, the reflected light is guided to a second detector, which may, in fact, form a portion of a second interferometer. As a further alternative, a mirror or other reflective element may be used to redirect the light back to the same point on the detector. In each case, the angular coherence of the light is preferably randomized prior to the subsequent detection. A multi-mode optical fiber is preferably used to carry the redirected light, which conveniently acts to randomize the angular coherence of the light during its travel.