Polarization-maintaining photonic crystal fiber

A polarization-maintaining photonic crystal fiber comprising:

• an elongated guiding core;
• and
• an elongated photonic crystal cladding surrounding the core;
• wherein:
• a cross-sectional area of the fiber taken orthogonally to a fiber longitudinal axis of the fiber characterized by an x-axis and a y-axis, the x-axis orthogonal to the y-axis, the x-axis and the y-axis orthogonal to the fiber longitudinal axis;
• the cross-sectional area of the fiber defines a collection of groups of elongated holes located in the cladding, each hole in the collection having a hole longitudinal axis that is parallel to the fiber longitudinal axis, the collection of groups comprising a first group [1], a second group [2], a third group [3], and a fourth group [4], the first group [1] and third group [3] defining an opposing first pair, the second group [2] and fourth group [4] defining an opposing second pair;
• the first group [1] and the third group [3] are symmetrical with each other with respect to the x-axis or the y-axis;
• a first plurality [1A] of the holes in the first group [1] have a first adjacent-hole centerpoint distance [1AP] and a first common dimension [1AD];
• the second group [2] and the fourth group [4] are symmetrical with each other with respect to the x-axis or the y-axis;
• a first plurality [2A] of the holes in the second group [2] have a first adjacent-hole centerpoint distance [2AP] and a first common dimension [2AD];
• and
• a difference in the first adjacent-hole centerpoint distance [1AP] and the first dimension [1AD] of the first plurality [1A] of the holes in the first group [1] with respect to the first adjacent-hole centerpoint distance [2AP] and the first common dimension [2AD] of the first plurality [2A] of the holes in the second group [2] is configured to generate a predetermined birefringence in the polarization-maintaining photonic crystal fiber.