Patent ID: 7030994

Claim:
A method comprising: using a fiber optic pickup comprising an input coupler and a fiber to couple two input beams derived from a common source into the fiber to produce an output beam, wherein the output beam comprises information about an optical path length difference between the two input beams, wherein imperfections in the fiber optic pickup cause a measurable interferometric test phase derived from the output beam to deviate from the expression Φ=pknL, where p is an integer, k is the wavenumber of the output beam, and nL corresponds to the optical path length difference, wherein the deviation comprises a non-cyclic error term that varies as a function of a separation of one or both of the input beams from an axis of the input coupler; measuring the test phase while varying the separation of at least one of the input beams from the axis; comparing the measured test phase to a reference phase indicative of the optical path difference; and determining a representation indicative of the non-cyclic error term for the fiber optic pickup based on the comparison.