Abstract

The development of fibre optic based sensor systems⁽¹⁾ has created a need for an all fibre tunable frequency shifter in order that efficient heterodyne signal processing can be effected. Several methods have been reported in which an acoustic wave of wavelength equal to the beat length of the fibre is used to couple a guided optical beam from one mode to another for example L_p01 to L_p11 or between the non degenerate L_p01 modes of highly birefringent fibre^(2,3). The acoustic wave being generated either by acoustic horns, acoustic torsional generators or surface acoustic waves^(2,4,5). Although all these devices show promise the fact that they must operate at fixed frequencies will tend to limit their applicability.

© 1992 Optical Society of America