Jihyun Hwang

High sensitivity temperature measurement via mask-free hybrid polymer long period fiber grating

Long-period fiber gratings (LPFGs) are useful for environmental sensing under conditions of high corrosiveness and electromagnetic interference. Most LPFGs are fabricated by coherent or high-power UV illumination of an optical fiber under an amplitude mask, resulting in narrow and environmentally-dependent band rejection. We present a hybrid LPFG waveguide fabricated without an amplitude mask through polymer self-assembly under low-power incoherent UV illumination, which demonstrates high-temperature sensitivity in its transmission spectrum compared to LPFG sensors based purely on silica waveguides. A sensitivity of 1.5 nm °C -1 is obtained experimentally for attenuation near 1180 nm, and a sensitivity of 4.5 nm °C -1 with a low random error was obtained with a composite of attenuation bands. Finite element method simulations and coupling mode theory reveal this to be due to a thermo-optic coefficient one order of magnitude greater than that of fused silica. The device has potential for a simple and inexpensive transmission intensity based temperature sensor consisting of an infrared light source, the LPFG, a bandpass filter, and a photodiode.

Highly birefringent V-groove liquid core fiber

We report a new efficient light guidance along a liquid core using an open V-groove. Guiding properties were analyzed using finite element method in terms of the single mode guidance condition, and the corresponding modal birefringence. We experimentally demonstrated a silica V-groove fiber with an opening angle of 40°, which was spliced to single mode fibers at both ends. A liquid with the refractive index of 1.455 was filled to serve as a core along a maximum length of 47cm. We confirmed the single mode guidance and birefringence consistent to theory, which will enable polarimetric liquid sensing.

Fabrication and characterization of V-groove liquid core waveguide

We report development of a new kind of micro-optical waveguide based on liquid core in a V-groove glass and air cladding and a similar finite element method was constructed to investigate the guiding properties such as mode distribution and modal birefringence. Through the detailed modeling, we investigate the role of each parameter such as, refractive index of core and diameter of core of V-groove structure. This work demonstrates numerically and experimentally high birefringence in this optical waveguide and different aspects of the fiber properties related to the fundamental mode and fiber birefringence are revealed. As a result, wave-guide with large birefringence is identified for opening angle of 40 degree and refractive index of 1.472.

Formation of sub pico-liter liquid periodic structure in a hollow optical fiber for photonic device applications

We report a unique technique to generate a liquid periodic structure whose unit volume is as low as a few hundred femto-liter. Liquids such as water, toluene and ethanol were filled in a hollow optical fiber (hole diameter of 8 and 13μm), which were locally heated by a traversing miniature electric furnace. The periods between droplets could be varied flexibly in the range from 14 to 100μm and the volume of individual droplet was in the range from 112 to 845 femto-liter. We also fabricated the periodic liquid droplets with quantum dots, whose fluorescence was successfully measured in each droplet. These periodic liquid droplets could serve as flexible liquid long period fiber grating for the hollow optical fiber, which can be further applied in various mechanical and bio-chemical sensors

Light transmission with self-assembly DNA monolayers through D-shaped optical fiber

Deoxyribonucleic acid (DNA) has been a remarkable material in the development of optoelectronic devices for granted these days. In this research, we report on an optical phenomenon of DNA structures grown by a self-assembly process. Discrete 2D nanocrystal structures of DNA were prepared on a light-guiding substrate. The high evanescent field interaction between the guided light supplied via D-shaped optical fiber and DNA monolayers enabled the systematic investigating of the optical properties of DNA nanocrystal structures. In particular, light guided down the fiber and received by an optical spectrum analyzer enabled spectral analysis, while morphology studies of the self-assembly DNA were performed by atomic force microscopy.