A method for compensating for a difference in optical path length traversed by first and second optical portions of an optical beam which are in orthogonal polarization states, comprising: receiving the optical beam at an input port; directing the optical beam to a first walk-off crystal for spatially separating the optical beam into first and second optical portions that are in first and second polarization states, respectively, the first and second polarization states being orthogonal to one another, the first optical portion being walked-off by the walk-off crystal and the second optical portion passing therethrough without being walked-off; rotating the polarization state of the first and second optical portions; after rotating the polarization state of the first and second optical portions, directing the first and second optical portions to a second walk-off crystal being oriented in an opposite direction from the first walk-off crystal so that the second optical portion is walked-off by the walk-off crystal and the first optical portion passes therethrough without being walked-off, a thickness of the first and second walk-off crystals being selected to adjust the optical path lengths traversed by each of the first and second optical portions, wherein the thickness of the first and second walk-off crystals is further selected to compensate for an optical path difference that arises from one or more downstream optical elements that is traversed by one of the first and second optical portions and not the other of the first and second optical portions, wherein, the thickness of the first and second walk-off crystals , which determine an additional path lengths traversed by the first and second optical portions that respectively pass therethrough, are different from one another. receiving the optical beam at an input port; directing the optical beam to a first walk-off crystal for spatially separating the optical beam into first and second optical portions that are in first and second polarization states, respectively, the first and second polarization states being orthogonal to one another, the first optical portion being walked-off by the walk-off crystal and the second optical portion passing therethrough without being walked-off; rotating the polarization state of the first and second optical portions; after rotating the polarization state of the first and second optical portions, directing the first and second optical portions to a second walk-off crystal being oriented in an opposite direction from the first walk-off crystal so that the second optical portion is walked-off by the walk-off crystal and the first optical portion passes therethrough without being walked-off, a thickness of the first and second walk-off crystals being selected to adjust the optical path lengths traversed by each of the first and second optical portions, wherein the thickness of the first and second walk-off crystals is further selected to compensate for an optical path difference that arises from one or more downstream optical elements that is traversed by one of the first and second optical portions and not the other of the first and second optical portions, wherein, the thickness of the first and second walk-off crystals , which determine an additional path lengths traversed by the first and second optical portions that respectively pass therethrough, are different from one another. <EOS>