Polarization controlling optical fiber preform and preform fabrication methods
Methods to fabricate an optical preform for draw into Polarization Maintaining (PM) or Polarizing (PZ) optical fiber are provided. The methods involve assembly of pre-shaped and pieced together bulk glass elements into preforms (“assembled preforms”) for simultaneous fusing and drawing into optical fiber. These preforms form a stress-induced birefringent optical core when drawn to fiber.
1. A method for fabricating an optical fiber preform, comprising:
assembling pre-shaped sections of glass materials surrounding an inner rod having a core and cladding, wherein at least two of the pre-shaped sections, placed diametrically opposed to one another, are made from a material having a relatively higher coefficient of thermal expansion than the other pre-shaped sections, wherein the at least two of the pre-shaped sections comprise doped silica-based glass, wherein the doped silica-based glass comprises at least two dopants, and wherein ratios of the dopants are selected to produce a refractive index of the silica-based glass matched to a refractive index of the cladding; and
surrounding the pre-shaped sections by a glass tube.
2. The method of claim 1 , wherein surrounding the pre-shaped sections results in an optical fiber preform with an outer diameter of at least approximately 50 mm.
3. The method of claim 1 , wherein the dopants comprise two or more of germanium oxide, boron oxide, phosphorous oxide, or fluorine.
4. The method of claim 1 , wherein an overall concentration of the dopants within the silica-based glass is up to 70 mol %.
5. The method of claim 1 , further comprising cutting a tube of glass having the relatively higher coefficient of thermal expansion (CTE) to form the at least two pre-shaped sections.
6. The method of claim 1 , further comprising cutting a tube of glass having a relatively lower coefficient of thermal expansion (CTE) to form the other pre-shaped sections.
7. The method of claim 6 , wherein the tube of glass having the relatively lower CTE comprises high purity silica.
8. The method of claim 6 , wherein the tube of glass having the relatively lower CTE comprises high purity doped silica.
9. The method of claim 6 , wherein the tube of glass having the relatively lower CTE has a refractive index corresponding to a refractive index of the cladding.
10. The method of claim 1 , further comprising fusing at least one end of the optical fiber preform to hold the glass tube and the pre-shaped sections of glass materials together.