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Method for producing a stable, multi-port fiber optic coupler that is useful for wavelength division multiplexing (WDM). The system response is substantially independent of signal polarization and is reasonably stable against mechanical stresses and elevated temperatures. Contiguous sections of two

Method for producing a stable, multi-port fiber optic coupler that is useful for wavelength division multiplexing (WDM). The system response is substantially independent of signal polarization and is reasonably stable against mechanical stresses and elevated temperatures. Contiguous sections of two or more fiber optic lines are alternatingly heated and elongated and are twisted according to selected process parameters for selected time intervals. The fabrication procedure uses a combination of fiber heating at two or more distinct temperatures, fiber elongation and fiber twisting, applied to two or more contiguous fiber optic lines, to produce a fused fiber optic coupler with controllable wavelength discrimination and controllable signal power coupling into each output branch of the fiber optic coupler. ITU standards for wavelength discrimination and wavelength centering in a fiber optic coupler can be met by adjustment of the process parameters.

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1. A method for producing a stable fiber optic coupler of two or more lines, the method comprising:positioning a selected section, having a selected length d, of at least two fiber optic lines, referred to as "FO lines", contiguous to each other and parallel to a selected alignment axis; heating a s

1. A method for producing a stable fiber optic coupler of two or more lines, the method comprising:positioning a selected section, having a selected length d, of at least two fiber optic lines, referred to as "FO lines", contiguous to each other and parallel to a selected alignment axis; heating a selected central section of the FO lines to a first temperature T1 within a selected first temperature range for a first time interval of selected temporal length .DELTA.t1; elongating the central section of the FO lines to a selected fractional elongation increment f lying in a selected fractional elongation range for a second time interval of a selected temporal length .DELTA.t2, where the first and second time intervals may overlap; providing a selected input signal having at least a first selected wavelength component .lambda.1 and a second wavelength component .lambda.2, and providing a measurement of signal power output in at least one of the FO lines in response to the input signal at each of the wavelengths .lambda.1 and .lambda.2, where .lambda.1 and .lambda.2 are chosen to approximately correspond to two consecutive local minima in signal power output, with .lambda.2>.lambda.1; where .lambda.1 is greater than a selected wavelength value .lambda.1 (ITU), performing at least one of the following processes: elongating the central section of the FO lines to a selected fraction elongation increment f1 for a third time interval of selected temporal length .DELTA.t3; and heating the central section of the FO lines to a selected second temperature T2 within a selected second temperature range for a fourth time interval of selected temporal length .DELTA.t4; where .lambda.1 is less than the selected wavelength value .lambda.1 (ITU), reducing the fractional elongation increment to a selected increment f2