Direct measurement of optical phase difference in a 3 × 3 fiber coupler

The precise phase difference in a 3 × 3 coupler is calculated by using Fourier transform based white-light interferometry. The phase relationships between any two of the three outputs are directly measured, and the result is in agreement with the ideal value. The phase difference of two re-constructed signals in a 3 × 3 coupler is also measured. In a passive homodyne system, this technique is helpful in removing the distortion of the demodulated signals, which is caused by imperfect properties of the 3 × 3 coupler.