Abstract

A guided-wave electrooptic phase modulator, coupled with single-mode fibers, offers great potential in broadband electromagnetic field sensing. The device can be highly sensitive and the use of nonelectrically conducting components guarantees minimum perturbation of the field being measured. A Ti:LiNbO₃ phase modulator consisting of a straight single-mode channel waveguide, 20 mm in length, and of coplanar electrodes has been developed (λ = 0.83 μm). The electrodes were connected to a dipole antenna. An electric field sensor causes a change of the refractive index along orthogonal crystal axes and thus alters the polarization state of an optical carrier propagating along the waveguide. The polarization modulation is transferred into intensity modulation by means of a high birefringent fiber acting as a polarizer. For best sensitivity and linearity the modulator was biased by controlling the input polarization state thus requiring no metallic leads. This was accomplished by a dedicated polarization controller which alters the birefringence of a low birefringent input fiber via the elastooptic effect. The voltage required to switch the light from on to off was 2.9 V.

© 1989 Optical Society of America