Polarization maintaining optical fibers with intracore stress mechanisms

A polarization maintaining optical fiber comprising:

• a cladding;
• and
• a core portion disposed in the cladding, the core portion comprising a first core region and a second core region, wherein the second core region comprises at least one down-dopant and at least one up-dopant such that a relative refractive index difference Δcc between the first core region and the second core region is less than 0.1%;
• and
• a birefringence of the polarization maintaining optical fiber is greater than 1×10−5 at wavelengths in a range greater than or equal to 800 nm and less than or equal to 1700 nm.

A polarization maintaining optical fiber comprising:

• a cladding portion;
• and
• a core portion disposed in the cladding portion, the core portion comprising a first core region having a first coefficient of thermal expansion CTE1 and a second core region having a second coefficient of thermal expansion CTE2, wherein:
• a difference between CET1 and CET2 is greater than or equal to 1×10−7/° C.;
• and
• a birefringence of the polarization maintaining optical fiber is greater than 1×10−5 at wavelengths in a range greater than or equal to 800 nm and less than or equal to 1700 nm.