Fused fiber couplers with asymmetric heating by arc discharge

Temperature measurement using a fused optical fiber coupler in arc environment

“…Normally, K m increases with the increase of Ȝ, however, the rate of increase of K m with Ȝ decreases for higher values of Ȝ. Again, K m increases with the decrease of a eff for lower values of Ȝ but saturates or crosses at higher values of Ȝ [9]. The transmitted and coupled powers of a fused coupler P 1 and P 2 can be expressed from the well known coupled-mode theory, as P 2 = P 0 K m 2 sin 2 (įL) (8) į 2 = [(ȕ 1 -ȕ 2 )/2] 2 + K m 2 (9) P 1 = P 0 -P 2 (10) ȕ 1 -ȕ 2 = Phase mismatch between two fibers = Δβ where P 0 is the input power, ȕ 1 and ȕ 2 are the average propagation constants of the two fibers in the coupling region, K m is the average coupling coefficient and L is the effective coupling length.…”

“…The asymmetry within the coupling region was obtained by two dissimilar fibers [5], or by bending a fused fiber coupler [6], by prepolishing [7], etc. However, a novel method to fabricate fused fiber couplers by using two similar fibers with unequal heating by arc discharge is shown experimentally [8], [9]. A temperature profile forming due to unequal heating in the two identical fibers produces unequal index changes in the cores and claddings of the fibers around the coupling zone.…”