Immersionless single-mode preform index profiling.

Area of Science:

• Materials Science
• Optical Engineering
• Photonics

Background:

• Traditional focusing methods for refractive-index profiling of optical fibers and preforms require immersion in index-matching fluid.
• Immersion in index-matching fluid can be undesirable, potentially damaging preform surfaces and affecting fiber tensile strength.

Purpose of the Study:

• To develop and validate a dry focusing method for measuring refractive-index profiles of optical fiber preforms.
• To eliminate the need for index-matching fluid, thereby preventing preform surface damage and expanding material compatibility.

Main Methods:

• A novel technique employing a dry, cylindrical matching lens (homogeneous glass rod) to achieve collimated light incidence on the preform.
• Comparison of refractive-index profiles obtained using the new dry method with those from the conventional index-matching fluid focusing method.
• Evaluation of the technique's applicability to single-mode and multimode preforms.

Main Results:

• Excellent agreement was achieved between refractive-index profiles measured by the new dry focusing method and the conventional fluid-immersion method.
• The dry technique is effective for single-mode preforms.
• Limitations exist for multimode preforms due to light collimation constraints and lens aberrations, restricting accessible profiling regions to approximately half the preform's cross-section.

Conclusions:

• The dry focusing method with a cylindrical matching lens is a viable alternative to fluid immersion for refractive-index profiling of optical preforms.
• This technique enhances preform handling safety and is beneficial for materials requiring high refractive indices or long operating wavelengths.
• The method's applicability is currently limited to single-mode preforms, with further research needed for multimode profiling.