Image Number 5 for United States Patent #4881817.
A fiber optic rotation sensor using birefringent optical fiber includes an uncorrelating element, an equalizing element and a polarizer in the common input and output fiber portions of the sensor to reduce or eliminate the intensity type phase errors caused by interference between lightwaves originally in the same polarization mode on entry to the sensor loop that cross couple into another polarization mode. In the preferred embodiment, the uncorrelating element comprises a birefringence modulator and a length of birefringent fiber. The equalizing element comprises a birefringent fiber having a splice at which the axes of birefringence of the spliced portions of the fiber are positioned at 45.degree. relative to each other. The preferred embodiment also advantageously includes a birefringence modulator that introduces a time-varying birefringence into the optical fiber to introduce a deterministic phase error that reduces or eliminates amplitude type phase error caused by coherent interference between field components of light that are orthogonally polarized at the input of the sensor loop and that couple to the same polarization mode within the loop.