Abstract
A confocal microspectrophotometer is utilized to scan the surface reflectivities of a polished gradient-index (GRIN) rod in the range of 400 to 900 nm. The pure fused silica is used to be a reference standard for deducing the absolute reflectivities of the Ge-doped core. Then, multi-wavelength refractive index profiles of the Ge-doped core can be further determined based on the Fresnel equation. Moreover, this work shows a connection between the material dispersion of the GRIN rod and the Ge-doped concentrations measured by an energy dispersive spectrometer. Finally, the dependence of the refractive index of the Ge-doped core on the doping concentrations at a certain wavelength can be easily expressed as a linear form.
Highlights
Gradient-index (GRIN) rods are widely used to collimate or refocus incident light in applications including sensor, microendoscopy [1,2], and fiber telecommunication [3]
Since the characteristics of a GRIN rod are mainly determined by the refractive-index distribution and material dispersion, it is highly demanded to develop a method for measuring the multiwavelength refractive index profiles (RIPs) and dispersion
The proposed approaches for measuring the RIPs of GRIN rods consist of interferometry [4,5], focusing method [6,7], refracted near-field method [8], ellipsometric technique [9], and reflective scanning method [10,11,12]
Summary
Gradient-index (GRIN) rods are widely used to collimate or refocus incident light in applications including sensor, microendoscopy [1,2], and fiber telecommunication [3]. The proposed approaches for measuring the RIPs of GRIN rods consist of interferometry [4,5], focusing method [6,7], refracted near-field method [8], ellipsometric technique [9], and reflective scanning method [10,11,12] These methods for determining the multiplewavelength RIPs usually require repeated measurements for different wavelengths. A different transverse interferometric method with a Fourier transform spectroscopy was proposed to measure the multi-wavelength RIPs of a 125-μm optical fiber that was inserted into the refractive index matching oil [13] This transverse interferometric method may be extended to measure the multi-wavelength RIPs of the GRIN rod (mm in diameter). We believe that the present method could be applied to GRIN rods and fiber preforms for obtaining the multi-wavelength RIPs and material dispersion
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