Method of manufacturing a fiber optic directional coupler

A method of manufacturing a fiber optic directional coupler, comprising:

• removing a portion of the cladding from a clad fiber at a predetermined location intermediate the ends of said fiber;
• introducing light into one end of said fiber for propagation to the other end of said fiber;
• applying an index matching substance having a refractive index slightly different than the fiber core to said predetermined location;
• changing the temperature of said index matching substance after it has been applied to said predetermined location to correspondingly change the refractive index thereof so that this index, at least momentarily, matches the index of the core to cause at least a portion of said light propagating through said fiber to escape from said fiber;
• determining the value of the proportion of the total light introduced at said one end that propagates through said fiber to said second end when the index of said index matching substance is equal to the index of the core;
• performing all of the foregoing steps until said proportion of the total light at said second end is equal to a preselected value, said preselected value corresponding to a first coupling efficiency for said coupler;
• performing all of the foregoing steps for a second fiber;
• and
• accurately positioning said fibers together, with their cores in close spaced relationship at their respective predetermined locations to form a coupler having said first coupling efficiency.

A method of precisely removing cladding material from an optical fiber for an optical coupler having a desired coupling efficiency, said method comprising:

• selecting the desired coupling efficiency from a range of coupling efficiencies;
• removing a portion of the cladding from a finite length of said fiber to form a facing surface;
• measuring the extinction ratio of said fiber;
• utilizing test data which indicates the relationship between extinction ratio and coupling efficiency for said optical fiber to determine the coupling efficiency which will result from superimposing said surface on an identical facing surface of a second fiber having said measured extinction ratio;
• and
• continuing said removing step and said measuring step until said measured extinction ratio corresponds to the desired coupling efficiency.

A method of reproducibly performing an extinction ratio test on an optical fiber, comprising:

• placing an index matching material adjacent said fiber;
• altering the refractive index of said material;
• measuring said extinction ratio to provide a characteristic curve of extinction ratio versus refractive index;
• and
• selecting the extinction ratio at a peak of said curve.

A method of reproducibly removing a precise amount of cladding from optical fibers for optical couplers, comprising:

• testing a first pair of fibers, to determine their extinction ratios, said fibers each having a portion of the cladding removed from one side thereof to provide respective facing surfaces;
• testing said first pair of fibers to determine the coupling therebetween to provide a relationship between the extinction ratio and the corresponding coupled power for said first pair of fibers;
• using said relationship for said first pair of fibers to select an extinction ratio for a second pair of fibers which provides a desired coupled power for said second pair of fibers;
• and
• removing a portion of the cladding from each of said second pair of fibers until said selected extinction ratio is achieved to provide said desired coupled power for said second pair of fibers.

A method of reproducibly manufacturing optical couplers comprising:

• providing a coupler comprising a first pair of fibers;
• testing said first pair of fibers to determine the extinction ratio for each of said fibers and to determine the coupling between said fibers when said fibers are juxtaposed;
• removing a portion of the cladding from one side of each of a second pair of fibers;
• measuring the extinction ratio of each of said second pair of fibers;
• and
• repeating said removing step and said measuring step until said extinction ratio of said second pair of fibers is the same as the extinction ratio of said first pair of fibers to reproduce the coupling of said first pair of fibers in a coupler utilizing said second pair of fibers.

A method of forming a facing surface on the cladding of a fiber optic strand at a distance greater than zero from the core of said strand, said method comprising:

• removing a portion of the cladding from one side of said fiber strand, without affecting the core of said fiber strand, to form said facing surface;
• illuminating said strand to propagate light therethrough;
• determining whether the portion of strand illumination which escapes at said facing surface of said strand has reached a predetermined value to determine whether said facing surface is at said distance from the core of said fiber strand;
• and
• repeating all of the foregoing steps until said strand illumination which escapes at said facing surface reaches said predetermined value.

A method of forming a facing surface on the cladding of a fiber optic strand to provide evanescent penetration at said facing surface, said method comprising:

• removing a portion of the cladding from one side of said fiber strand, to form said facing surface such that said fiber at said facing surface is rotationally non-symmetric;
• illuminating said strand to propagate light therethrough;
• determining the amount of strand illumination which escapes at said facing surface to provide an indication of the evanescent penetration at the facing surface;
• and
• repeating all of the foregoing steps to increase said strand illumination which escapes at said facing surface.

A method comprising:

• introducing optical energy into one end of an optical fiber having an inner core and an outer cladding such that said optical energy propagates along said fiber;
• removing a portion of the cladding from one side of said fiber to form a facing surface;
• providing a material on said facing surface having an index of refraction greater than or substantially equal to the index of refraction of said core;
• detecting the amount of optical energy which escapes from the facing surface;
• and
• removing additional cladding material in accordance with the results of said detection step.

A method for fabricating an optical waveguide evanescent wave coupler, from optical waveguides of the type having a core concentrically surrounded by a cladding material, said method comprising the steps of:

• A. transmitting optical energy through the core of a first optical waveguide thus illuminating the core;
• B. removing a portion of the cladding from said first optical waveguide to form a flat surface on one side of said waveguide;
• C. detecting the amount of light escaping from the illuminated core of said first optical waveguide to provide an indication of the evanescent penetration at said surface;
• D. stopping the removal of the cladding material when said amount of light indicates a desired amount of evanescent penetration;
• E. performing the steps of transmitting, removing, detecting and stopping for a second optical waveguide;
• F. placing said first and second optical waveguides with the removed cladding surfaces in juxtaposition such that evanescent wave coupling occurs.

A method of determining the evanescent field penetration at a surface of an optical fiber having an inner core and an outer cladding comprising:

• introducing optical energy into one end of said optical fiber such that said optical energy propagates along said fiber;
• placing a material on said surface having a first index of refraction;
• altering the refractive index of the material from said first refractive index to a second refractive index closer to the refractive index of said core than said first refractive index;
• and
• detecting the amount of optical energy which escapes from said fiber during said altering step to determine the amount of evanescent field penetration at said surface.