Youngchun Youk

Simple scanning fibre-optic confocal microscopy for the refractive index profile measurement of an optical fibre

A simple servo-controlled scanning fibre-optic confocal microscope is proposed for determining the refractive index profile of an optical fibre by measuring the reflectance of the end surface of the fibre. Great simplicity has been achieved in confocal microscopy by using a lensed fibre and a 3?dB fibre coupler instead of an objective lens and a beam splitter. A dithering servo control with a phase-locked loop is employed to maintain a constant distance between the lensed fibre and the surface to be measured during the scanning process. The accuracy of the measured refractive index is better than 10-4.

New optical frequency domain differential mode delay measurement method for a multimode optical fiber.

A novel mode analysis method and differential mode delay (DMD) measurement technique for a multimode optical fiber based on optical frequency domain reflectometry has been proposed for the first time. We have used a conventional OFDR with a tunable external cavity laser and a Michelson interferometer. A few-mode optical multimode fiber was prepared to test our proposed measurement technique. We have also compared the OFDR measurement results with those obtained using a traditional time-domain measurement method.

Tightly focused epimicroscope technique for submicrometer-resolved highly sensitive refractive index measurement of an optical waveguide

We introduce a very sensitive new configuration, to the best of our knowledge, in an optical microscope system that utilizes two detectors: one is to measure the power of a low reflected signal from a sample, and the other is only to monitor the confocal geometry of the system. With this new configuration, we could effectively remove measurement noise associated with small perturbation in measurement conditions such as surface curvature, tilt, and vibration in a microscope system. We have obtained a high-resolution relative index precision of 9x10(-5) by employing this novel technique with two detectors.

Guiding Properties of a Tapered Photonic Crystal Fiber Compared with Those of a Tapered Single-Mode Fiber

We have fabricated tapered photonic crystal fibers using a fusion splicer and experimentally observed the near-field mode distribution and the beam divergence of it. We have also compared characteristics of the tapered photonic crystal fiber with those of a tapered standard single-mode fiber. Unlike a tapered standard single-mode fiber, the mode field profile of a tapered photonic crystal fiber shows a good confinement of its field within the core region. The numerical apertures of tapered photonic crystal fibers are increased as the diameter of the fiber is decreased.

Reflection-type Optical Waveguide Index Profiling Technique

We report a new configuration of a reflection-type confocal scanning optical microscope system for measuring the refractive index profile of an optical waveguide. Several improvements on the earlier design are proposed; a light emitting diode (LED) at 650 nm wavelength instead of a laser diode (LD) or He-Ne laser is used as a light source for better index precision, and a simple longitudinal linear scanning and curve fitting techniques are adapted instead of a servo control for maintaining an optical confocal arrangement. We have obtained spatial resolution of 700 nm and an index precision of

Refractive Index Profiling of a Core-Doped Photonic Crystal Fiber

2\times10^{-4}

Mode Analysis and Modal Delay Measurement of a Few-Mode Fiber by Using Optical Frequency Domain Reflectometry

. To verify the systems capability, the refractive index profiles of a conventional multimode fiber and a home-made four-mode fiber were examined with our proposed measurement method.

Novel technique to remove measurement noise generated by pinhole diffraction phenomenon

Direct refractive index profiling for a core-doped photonic crystal fiber with complex and nonsymmetric refractive index structure has been demonstrated for the first time. A new index profiling technique based on a reflectivity measurement technique using a confocal microscope has been employed. This improved, straightforward, and robust method enables us to measure the index structure of a complex structured fiber with high refractive index precision and spatial resolution

Refractive index and geometrical structure measurement of a core- doped photonic crystal fiber

A novel mode analysis method and differential mode delay measurement technique for a multimode optical fiber based on optical frequency domain reflectometry has been proposed for the first time. We have used a conventional OFDR with a tunable external cavity laser and a Michelson interferometer. A few-mode optical multimode fiber was prepared to test our proposed measurement technique. The differential mode delay (DMD) of the sample fiber was measured to be 16.58 ps/m with a resolution of 1.5 ps/m. We have also compared the OFDR measurement results with those obtained using a traditional time-domain measurement method.

Improved Reflection-Method for Refractive Index Measurements of Optical Waveguides

We have developed a novel technique to remove measurement noise generated by pinhole diffraction in confocal microscopy. We compared the refractive index measurement results using our technique with those obtained using a traditional system.