Gilhwan Kim

Lasing wavelength and spacing switchable multiwavelength fiber laser from 1510 to 1620 nm

We experimentally demonstrate a flexibly switchable multiwavelength fiber laser with multiple functionalities like a wide tuning range of lasing wavelength, wavelength spacing, and the number of channels simultaneously. The lasing wavelength is controlled in the range from 1510 to 1620 nm based on the effect of nonlinear gain compression of a semiconductor optical amplifier incorporated with an erbium-doped fiber amplifier. The wavelength spacing and the number of channels in the multiwavelength fiber laser are readily controlled by the effective length of polarization-maintaining fiber (PMF) segments in the intracavity PMF Lyot-Sagnac filter.

Strain and temperature sensitivities of an elliptical hollow-core photonic bandgap fiber based on Sagnac interferometer

We fabricated an elliptical hollow-core photonic bandgap fiber (EC-PBGF) by controlling lateral tension in the hollow core region during the fiber drawing process. The absolute value of group modal birefringence becomes relatively high near the bandgap boundaries. We also experimentally measured the strain and temperature sensitivities of the fabricated EC-PBGF-based Sagnac loop interferometer. The strain and temperature sensitivities were very much dependent upon the wavelength. Moreover this PBGF-based interferometer can be a good sensor of physical parameters such as strain and temperature.

Study on the Fabrication Process of Polarization Maintaining Photonic Crystal Fibers and Their Optical Properties

In this paper, we describe the fabrication process and the characteristics of polarization maintaining photonic crystal fibers (PM-PCFs). The PM-PCF is fabricated by stack-and-draw method, i.e., stacking silica capillary tubes (making a PM-PCF preform) and drawing to optical fiber. Firstly, a PM-PCF preform is formed by stacking two kinds of capillary tubes around a solid silica rod and jacketing these stacked tubes with an outer silica tube (out-jacket tube). Later, the desired preform is drawn to a fiber in a high temperature drawing tower. We also compare the polarization properties such as polarization dependent loss, birefringence, and differential group delay of the fabricated PM-PCF with those of the conventional PANDA PM fiber.

Bending sensitivity of long-period fiber gratings inscribed in holey fibers depending on an axial rotation angle

We discuss bending properties of a long-period fiber grating (LPFG) inscribed into a holey fiber (HF) depending on an axial rotation angle. High quality of the HF-based LPFG with a high extinction ratio of more than 20 dB is achieved. The proposed HF-based LPFG has bending insensitivity under a certain range of the bending curvature. As the bending curvature is higher than 4 m(-1), the center wavelength of the grating is shifted into the shorter wavelength. Bending sensitivity of the HF-based LPFG is changed by an axial rotation angle, which shows its dependence on the rotational orientation. We measure the transmission characteristics of the HF-based LPFG with the ambient index change. The HF-based LPFG has ambient index insensitivity because of the air holes in the inner cladding.

Control of hollow-core photonic bandgap fiber ellipticity by induced lateral tension.

We describe the fabrication of elliptical hollow-core photonic bandgap fibers (EC-PBGFs). It was shown that the aspect ratio of the hollow core can be controlled by tuning the negative pressure in the space between the intermediate preform cane and outer jacketing tube, and by placing this preform assembly off-center in the furnace, resulting in lateral tension during the final draw. Modal birefringences of fabricated PBGFs with different aspect ratio were measured using a Sagnac loop interferometer. For the elliptical hollow core PBGF with aspect ratio of 2.34, the modal birefringence was measured to be about 4.6x10(-2) at 1,550 nm.

Investigation of an Arc-induced Long Period Fiber Grating Inscribed in a Photonic Crystal Fiber with Two Large Air Holes

A photonic crystal fiber with two large air holes outside the holey cladding region is fabricated to induce an effective long periodic grating (LPG) in the core by an electric arc discharge. We believe that the two large air holes lead to the asymmetric perturbation in the core under the electric arc discharge, thereby introducing the coupling to the first higher-order mode. The transmission characteristics of the PCF with the LPG for the external perturbation such as strain, curvature, and temperature are also investigated. It was found that the shift of resonance peak in the transmission spectrum depends on the bending direction. The curvature of 8.55 m-1 results in the center wavelength shifts of 1.8, 4.3, and 11 nm for a vertical, diagonal, and horizontal direction of the curvature to the large air-hole alignment, respectively.

In situ gas sensing using a remotely detectable probe with replaceable insert

We demonstrate a spectroscopic gas sensor using an optical fiber probe with a replaceable insert. The probe consists of a hollow-core photonic bandgap fiber (HC-PBGF) with a core diameter of 10.9 μm and a glass tube where a 2-μm hollow core fiber (HCF) with a gold coated end facet can be inserted. The HCF is designed to function as both a gate where gases can enter the HC-PBGF and a mirror reflecting the guided light back to the HC-PBGF. The opposite distal end of the probe is also designed to be able to regulate the gas pressure within the HC-PBGF for a high gas flow rate, while still transmitting the reflected light to the analysis instrument. The remote sensing probe, we believe, has much potential for detecting gases in hazardous environments.

Wavelength spacing tunable multiwavelength fiber laser with lasing wavelength selectivity

We experimentally demonstrate a flexibly tunable multiwavelength fiber laser with multiple functionalities like the wide tuning range of the wavelength spacing and the lasing wavelength based on the hybrid gain medium.

Probe type gas sensor based on double path absorption using hollow-core photonic band-gap fiber

We demonstrate a reflection type gas sensor which consists of a hollow core photonic band-gap fiber (HC-PBGF) and a 2-μm hollow core fiber (HCF) with a gold coated end facet. Also we present the characteristics of the proposed gas sensor and the results of in situ gas detection with the pressure driven gas filling method.

Highly-birefringent tunable long-period fiber gratings in hollow-core photonic bandgap fiber by use of mechanical pressure

The mode coupling properties of highly-birefringent tuneable LPGs formed in HC-PBGF are presented. The mode coupling from the fundamental core mode to higher-order guided mode of a HC-PBGF is obtained by use of periodic mechanical pressure.