Optical fiber grating devices having outer coatings of variable thickness metal are highly useful in optical communication systems. In these devices variable thickness thin metal films are used as thin film resistive heaters or strain-relief coatings for altering in controlled ways, the optical properties of the grating. For example, such devices can provide Bragg gratings with adjustable chirp for use as tunable dispersion compensating elements. See U.S. patent application Ser. No. 09/183,048 filed by Eggleton el al. on Oct. 30, 1998 and entitled "Optical Grating Devices With Adjustable Chirp."
The ability to form on-fiber metal coatings with complex but precisely defined variations in thickness is critical to producing these and other types of active grating devices. One method for forming such coatings involves electrodeposition of metal onto a fiber while it is pulled from a planting bath at a controlled rate. Although this technique can form tapered coatings with a range of thicknesses, it has the disadvantages that (i) non-monotonic variations in thickness are not straightfonvard to produce, (ii) a seed layer, typically deposited by electron beam evaporation or electroless planting, is required to initiate electrodeposition, and (iii) formation of ultrathin (&lt;1 .mu.m) coatings with precise variations in thickness is challenging. Accordingly there is a, need for an improved method for providing optical fiber devices with metal coatings of controlled variable thickness.