Pitch reducing optical fiber array and multicore fiber comprising at least one chiral fiber grating

An optical coupler array for optical coupling of a plurality of optical fibers to an optical device, comprising:

• an elongated optical element having a first end operable to optically couple with said plurality optical fibers and a second end operable to optically couple with said optical device,
• and comprising:
• a common single coupler housing structure;
• a plurality of longitudinal waveguides, including at least one first waveguide and at least one second waveguide, each of said plurality of longitudinal waveguides being positioned at a predetermined spacing from one another, each having a capacity for at least one optical mode of a predetermined mode field profile, and a corresponding predetermined propagation constant, and each being embedded in said common single housing structure, wherein at least one of said plural longitudinal waveguides is a vanishing core waveguide, each said at least one vanishing core waveguide comprising:
• an inner vanishing core, having a first refractive index (N-1), and having a first inner core size (ICS-1) at said first end, and a second inner core size (ICS-2) at said second end;
• an outer core, longitudinally surrounding said inner core, having a second refractive index (N-2), and having a first outer core size (OCS-1) at said first end, and a second outer core size (OCS-2) at said second end, and
• an outer cladding, longitudinally surrounding said outer core, having a third refractive index (N-3), a first cladding size at said first end, and a second cladding size at said second end;
• and
• wherein said common single coupler housing structure comprises a medium having a fourth refractive index (N-4) surrounding said plural longitudinal waveguides, wherein a predetermined relative magnitude relationship between said first, second, third and fourth refractive indices (N-1, N-2, N-3, and N-4, respectively), comprises the following magnitude relationship:
• (N-1>N-2>N-3), wherein a total volume of said medium of said common single coupler housing structure, is greater than a total volume of all said vanishing core waveguides inner cores and said outer cores confined within said common single coupler housing structure, and wherein said first inner vanishing core size (ICS-1), said first outer core size (OCS-1), and said predetermined spacing between said plural longitudinal waveguides, are simultaneously and gradually reduced, in accordance with a predetermined reduction profile, between said first end and said second end along said optical element, until said second inner vanishing core size (ICS-2) and said second outer core size (OCS-2) are reached, wherein said second inner vanishing core size (ICS-2) is selected to be insufficient to guide light therethrough, and said second outer core size (OCS-2) is selected to be sufficient to guide at least one optical mode, such that:
• light traveling from said first end to said second end escapes from said inner vanishing core into said corresponding outer core proximally to said second end,
• light traveling from said second end to said first end moves from said outer core into said corresponding inner vanishing core proximally to said first end,
• and wherein, proximal to said second end, at least a portion of said first waveguide comprises a chiral fiber grating that is configured for controlling light signal coupling in a predetermined wavelength range, having a predetermined pitch and being of a single predetermined handedness, wherein said second outer core size (OCS-2), predetermined pitch and said predetermined propagation constants are configured to couple at least one core mode of said first waveguide with at least one core mode of said second waveguide within said predetermined wavelength range.