Yoonseob Jeong

Subwavelength plasmonic lens patterned on a composite optical fiber facet for quasi-one-dimensional Bessel beam generation

We demonstrate a beam shaping method by engraving plasmonic lens consisted of subwavelength slit-metallic groove structure on the cleaved end facet of a composite optical fiber. The fiber consisted of a single mode optical fiber serially concatenated with a coreless silica fiber segment to expand the beam diameter. The subwavelength slit-groove structure on a gold film was fabricated using focused ion beam milling process. Plasmonic interaction in the film generated a quasi-one-dimensional Bessel-like beam with a beam width of 0.8 μm at the focal length of 2 μm. Detailed two- and three-dimensional finite-difference time-domain analyses showed beam characteristics consistent with experimental observations.

Guided Wave Analysis of Hollow Optical Fiber for Mode-Coupling Device Applications

In this paper, optical mode characteristics of hollow optical fibers are thoroughly analyzed using finite element method. The guided modes along the ring core and cladding are identified and their optical properties are investigated. For the core modes, we investigated intensity distribution, higher order mode cutoff, propagation constant, and chromatic dispersion. The mode coupling between the fundamental mode and the excited modes in both core modes and cladding modes are discussed for applications in mode-coupling devices.

Fourier optics along a hybrid optical fiber for Bessel-like beam generation and its applications in multiple-particle trapping

Highly efficient Bessel-like beam generation was achieved based on a new all-fiber method that implements Fourier transformation of a micro annular aperture along a concatenated composite optical fiber. The beam showed unique characteristics of tilted washboard optical potential in the transverse plane and sustained a nondiffracting length over 400 μm along the axial direction. Optical trapping of multiple dielectric particles and living Jurkat cells were successfully demonstrated along the axial direction of the beam in the water.

Crossed fiber optic Bessel beams for curvilinear optofluidic transport of dielectric particles

Due to its unique non-diffracting and self-reconstructing nature, Bessel beams have been successfully adopted to trap multiple particles along the beams axial direction. However, prior bulk-optic based Bessel beams have a fundamental form-factor limitation for in situ, in-vitro, and in-vivo applications. Here we present a novel implementation of Fourier optics along a single strand of hybrid optical fiber in a monolithic manner that can generate pseudo Bessel beam arrays in two-dimensional space. We successfully demonstrate unique optofluidic transport of the trapped dielectric particles along a curvilinear optical route by multiplexing the fiber optic pseudo Bessel beams. The proposed technique can form a new building block to realize reconfigurable optofluidic transportation of particulates that can break the limitations of both prior bulk-optic Bessel beam generation techniques and conventional microfluidic channels.

Wide, tunable band rejection filter based on micro-optical waveguide on microactuating platform covering O, E, S, C, L, and U bands

An ultrawide, tunable band rejection filter was experimentally demonstrated operating from 1060 to 1670 nm seamlessly covering all communication bands (O, E, S, C, L, and U bands). The device consists of a micro-optical waveguide made from fused taper fiber coupler mounted over a microactuating platform that systematically applies a highly localized torsional stress over the coupling region. High-band rejection efficiency of 20-30 dB and very low insertion loss of 0.2 dB were experimentally achieved over the whole operating spectral range.

Fiber fuse effect in hollow optical fibers

We examined nonlinear fiber fuse effect (FFE) in hollow optical fibers (HOFs) that consist of a central air hole surrounded by a high-index ring core and silica cladding. In contrast to conventional solid-core fibers, the HOF with a hole diameter of 4 μm showed high threshold power of 4 W, and resulted in unique tadpole-like voids in periodic arrays after the FFE. As the hole diameter increased to 6 μm, plasma propagation was suppressed within the distance of 1 mm inside of the HOF. Detailed comparisons were made in terms of threshold power, void formation, and penetration length.

A micro-structured aperture made of a hollow triangular-core fiber for novel beam shaping

We demonstrate a micro-structured aperture made of a unique hollow triangular-core fiber (HTCF) that consists of a central air hole, a high-index hollow triangular core, and silica cladding for all-fiber novel beam shaping. Detailed fabrication processes to embed a hollow triangular structure into a cylindrical optical fiber are described and unique diffraction patterns out of the HTCF for monochromatic light are analyzed both experimentally and theoretically. Fourier-optic analysis combined with guided mode calculation was pursued to interpret experimental patterns in terms of the beam propagation distance.

A hybrid fiber-optic photoluminescence measurement system and its application in InGaN/GaN light emitting diode epi-wafer morphology studies.

We report a fiber optic photoluminescence (PL) measurement system using a novel hybrid probe composed of a series of single mode fiber (SMF) and double-clad fiber (DCF) terminated with a coreless silica fiber (CSF) segment and glass micro-lens formed on its cleaved-facet. The fiber probe provided a good guidance and focusing capability for the excitation photon with a focal length of 125 μm and a beam diameter of 13.6 μm. Utilizing a special DCF-to-DCF coupling scheme, the photoluminescence signals were efficiently collected and delivered to a photodetector with a low loss. Utilizing the proposed system, PL morphology was investigated over a 200 × 200 μm(2) area for two types of InGaN/GaN blue light emitting diode (LED) epi-wafers grown on 1) an un-patterned sapphire substrate (UPSS), and 2) a patterned sapphire substrate (PSS). The uniformity in the relative PL intensity and the spectral uniformity in terms of the peak PL wavelength were experimentally compared and analyzed.

Non-phase-matched tunable band rejection in an all-solid photonic bandgap fiber with high-index rods on graded-index pedestals

A new type of an all-solid photonic bandgap fiber for a non-phase-matched tunable band-rejection filter was proposed and fabricated by introducing a hexagonal array of high-index rods surrounded by graded-index pedestals in silica cladding. Due to the graded index and subsequent weak confinement of light, the proposed fiber showed two contrasting transmission spectra: flat transmission for a long fiber segment of ~1 m in contrast to typical bandgap transmission in a short fiber segment of ~10 cm. For the 120-cm-long fiber, we observed unique band-rejection transmission without any requirement of phase-matching conditions, whose rejection strength was tunable by mechanical perturbations such as bending and twisting. Detailed device principles, fiber design, fabrication, and transmission characteristics are discussed in both theory and experiment.

Beam shaping technology based on optical fiber for applications in laser, optical tweezer, and free space interconnects

Various techniques to modify the phase front of the light wave out of an optical fiber facet are reported for beam shaping devices. The principles of beam shaping in the devices and their applications in lasers, optical tweezer, and photonic devices are discussed.