Optical fiber coupler

An optical fiber coupler comprising:

• a pair of elongated optical fibers having central light guiding cores of light-transmitting material, each of said cores having a predetermined cross-section with an end portion characterized by an outer wall surface and an end wall surface;
• an elongated tubular waveguide having a tubular light guiding core of light-transmitting material having a predetermined cross-section with inner and outer wall surfaces surrounding and enclosing said end portions of said central light guiding cores and having recesses at opposite ends;
• said end portions extending coaxially into said opposite recesses;
• each of said end portions having a predetermined coupling length extending into the corresponding recess and being spaced radially inwardly from said inner wall surface a uniform distance along the length thereof to provide a circumferential gap therebetween which has a uniform cross-section along the length thereof;
• a light-transmitting spacer member filling said gap;
• said central and tubular light guiding cores comprising material having the same predetermined refractive index, and said spacer member comprising material having a refractive index less than said predetermined refractive index;
• and
• the cross-sectional dimensions of said central and tubular light guiding cores and each of said coupling lengths having predetermined values chosen according to Equations (3) and (4) enabling maximum transverse optical power transfer through both of said circumferential gaps in series, with minimal, longitudinal optical power transfer between said end wall surfaces of the central light guiding cores.

A method of transferring optical power between a central light guiding core and a tubular light guiding core, both of which cores comprise light-transmitting materials having the same predetermined refractive index, said method including the steps of:

• (a) assembling said central light guiding core within said tubular light guiding core a uniform radial distance along the length thereof with said central and tubular light guiding cores extending along a common axis;
• (b) filling the circumferential gap between said cores with light-transmitting spacer material having a refractive index less than said predetermined refractive index;
• and
• (c) applying optical power to one of said light guiding cores and transferring said power transversely of said axis through said spacer material into the other of said light guiding cores.

A method of transferring optical power from a first central light guiding core to a second central light guiding core, both of said cores comprising light-transmitting material having the same predetermined refractive index, said method including the steps of:

• (a) assembling said first and second central light guiding cores along an axis with adjacent ends facing one another;
• (b) enclosing adjacent end portions of said central light guiding cores coaxially within opposite end recesses of a tubular light guiding core with each of said first and second light guiding cores being spaced a uniform radial distance within the tubular light guiding core along the length thereof, said tubular light guiding core comprising light-transmitting material having a refractive index equal to said predetermined refractive index;
• (c) filling circumferential gaps between said first and second central light guiding cores and said tubular light guiding core with light-transmitting spacer material having a refractive index less than said predetermined refractive index;
• (d) directing optical power longitudinally of said axis along the interior of said first central light guiding core toward said tubular light guiding core;
• (e) transferring said optical power transversely of said axis into said tubular light guiding core;
• and
• (f) re-transferring said optical power transverely of said axis into said second central light guiding core.