Wideband communication systems using optical signals now commonly employ wavelength division multiplexing (WDM) or dense wavelength division multiplexing (DWDM) to transfer and transmit vast amounts of data at very high data rates. In these multiplexing systems, multiple signal-bearing channels are centered on specified spaced apart wavelengths and sources (e.g. lasers) are set to those wavelengths. Whether combining signals into the multiplex format, or demultiplexing by separating or dropping out signals, the filters and couplers used must have center wavelength stability, with a high degree of precision. This in turn means that temperature variations cannot be permitted to affect operation over a substantial range, such as 0-70.degree. C. For a number of reasons, Bragg grating devices are widely employed in wavelength division multiplex systems because a precise wavelength response can be set by selection of the periodicity of the grating written in a device. Because the periodicity of the grating is affected by temperature, however, due to the temperature coefficient of the waveguide or fiber material, the wavelength selectivity can be unacceptably changed by ambient conditions. For example, without any form of temperature compensation, the center wavelength can vary by as much as +0.01 nm/C. Channel placements and bandwidths for individual signals are such that this amount of variation of length, in a normal temperature environment, would shift the wavelength selectivity such that the coupler or filter is no longer matched to the wavelength of the corresponding laser or other source.
In a prior application, Ser. No. 09/128,476 entitled "Methods of Fabricating Grating Assisted Coupler Devices", filed Aug. 4, 1998 by Anthony S. Kewitsch, et al., and assigned to the assignee of the present invention, this problem is confronted by a disclosed temperature compensation system in which a "prepackage" or support structure is disposed within a cylindrical housing, with the prepackage structure using a number of spaced apart hubs mounted on and/or selectively movable relative to Invar rods. The prepackage structure enables attachment of a span of a fiber-based coupler, and the arrangement provides for the use of thermally dissimilar metal elements (stainless steel) and adjustment means for varying the strain on the critical fiber length which includes a Bragg grating. While this arrangement is fully satisfactory from the operational standpoint, and provides for the needed tensioning of the fiber optic components during the initial writing phase and thereafter despite temperature variations, it is more complex than desirable for high production processes. Further, it is desirable to provide even better temperature compensation, to a level of + or -0.001 nm/.degree. C. center wavelength variation over temperature. In addition, it is desirable to provide means for axial twisting of the fiber optic component, for purposes of achieving polarization independence and reducing polarization mode dispersion (PMD).