Characterization of graded index optical fibers by digital holographic interferometry

Abstract

For the first time to our knowledge, digital holography is used to determine the distribution of parabolic or nonparabolic refractive index fields in graded index optical fibers. The fiber is embedded in an index matching fluid whose refractive index can be varied to a matching and mismatching index with respect to that of the cladding. In experiments for both cases high precision phase-shifting digital holographic interferometry is applied with numerical evaluation employing the multilayer model for recognition of the refraction. Due to the higher redundancy in the multiple phase-shifted holograms better accuracy can be obtained compared to classical two-beam interferometry. Therefore the holographic method is recommended as a nondestructive and noncontacting method for characterizing graded index optical fibers.

Digital Holographic Interferometric Characterization of Optical Waveguides

“…The reference beam reaches the CCD camera at a small incident angle with respect to the propagation direction of the object wave. Therefore, the off axis holographic configuration is used (Wahba & Kreis, 2009a, 2009b, 2009cYassien et al, 2010). In addition, the mirror M2 in the digital holographic setup is mounted on a piezoelectric transducer (PZT), which acts as the phase shifting tool.…”

“…This effect was recognized in holographic interferometric investigations combined with iterative calculations (Sweeney & Vest, 1973) as well as tomographic methods (Cha & Vest, 1981). Recently, digital holographic phase shifting interferometry with the aid of mathematical models, which consider the refraction of the incident rays, were used to investigate some optical parameters of fibrous materials (Wahba & Kreis, 2009a, 2009b, 2009cYassien et al, 2010). The refractive index profile and optical parameters of graded index fibres as well as the refractive index profile of bent optical fibres were determined with accuracy 2.3x10 -4 .…”

Perfect digital holographic imaging with high resolution using a submillimeter-dimension CCD sensor

“…Nevertheless, the resolution and image quality of the most commonly used pre-magnification digital holographic microscopy (Pre-MDHM) and post-magnification digital holographic microscopy (Post-MDHM) are restricted by the photosensitive dimensions and the pixel size of the sensor, which has greatly limited the application of DHM. To improve the resolution and image quality of DHM, many approaches have recently been proposed, such as structured light illumination [20,21], synthetic aperture [22][23][24], superresolution [17,25], interferometric microscopy [26], and vortex light illumination [27]. These methods can improve the resolution theoretically; however, so far, the improvement has not been achieved in microscopic imaging.…”

Measurement of Refractive Index Profile of Optical Fiber Using the Diffraction Phase Microscope

“…이러한 굴절률 프로파일은 광섬유의 광신호 전달특성을 결정하는 광섬유 디자인의 핵심요소로 굴절률 분포의 정확한 측정은 광섬유 및 광섬유 소자의 연구에 유용 한 정보를 제공한다 [1] . [1][2][3][4][5] . 이 가운데 잘 알려진 공초점현미 경 방법(confocal microscopy method) [2,3] 과 굴절근접장 방법 (refractive near-field method: RNF method)은 [4] 수평하게 절 단된 광섬유 단면의 효과를 이용한 방법으로 용이하게 굴절 률분포를 측정할 수 있는 이점이 있으나 비파괴적으로 굴절 률 변화를 측정할 수 없는 단점을 지닌다.…”

“…이 가운데 잘 알려진 공초점현미 경 방법(confocal microscopy method) [2,3] 과 굴절근접장 방법 (refractive near-field method: RNF method)은 [4] 수평하게 절 단된 광섬유 단면의 효과를 이용한 방법으로 용이하게 굴절 률분포를 측정할 수 있는 이점이 있으나 비파괴적으로 굴절 률 변화를 측정할 수 없는 단점을 지닌다. 반면, 간섭현미경 방법(interferometric microscopy method)은 광섬유를 수평하 게 통과하는 빛의 위상변화를 측정하여 굴절률분포의 정보 를 얻는 방법으로 광섬유 길이축 굴절률 변화를 직접 측정할 수 있어 광섬유 뿐 아니라 광섬유 소자의 특성평가에도 활용 성이 높은 장점을 가진다 [1,5] . 년 Michael S. Feld 그룹에 의해 처음 소개되었다 [6] .…”