Abstract

The novel technology of distributed optical fiber sensor (DOFS) is very attractive because it can measure the spatial distribution and temporal variation of a mea- surand field along the fiber simultaneously.¹ Many arrangements of a DOFS system are based on the principle of Optical Time-Domain Reflectometry or Polarisation Optical Time-Domain Reflectometry. However, these backscatter DOFS systems have a main disadvantage: very low signal, which leads to a low sensitivity and low spatial resolution. A so-called forwardscatter method can avoid this problem and is being investigated with great interest.^2,3 It is based on the nonlinear interaction between the two counterpropagating pump pulse light and probe light, and for some mechanism the emerging signal is dependent on the external measurand. There are several systems making use of the nonlinear effect between the high intensity pump pulse and the two linearly orthogonal-polarised eigenmodes of probe light in single-mode high birefringence fiber,^4,5 which have complicated system structures. In this paper we present a DOFS system making use of forwardscatter method in elliptical-core two-mode fiber. The optical components and signal detection are relatively simple.

© 1994 IEEE