Kwang-Hee Kwon

Submersion Sensor with Side-Polished Fiber and Planar Waveguide in Manhole

Experiments are conducted to investigate whether a side-polished fiber sensor can detect submersion without being affected by water impurities when a manhole is submerged. The side-polished fiber sensor is also examined whether it can detect submersion when the overlay of such sensor is covered with impurities.

Variable Optical Fiber Attenuator Using Bending-Sensitive Fiber

A variable optical attenuator with a bending-sensitive fiber (BSF) that can be used in optical networks is developed. The refractive index profile of the BSF is divided into four regions which are inner core, center dip of inner core, outer core and clad. The 3-dimensional finite difference beam propagation method (3D FD-BPM) is utilized to find the characteristics of the BSF, so the mode profile of the BSF and optical power attenuation according to the bending are investigated, and the equivalent model of the BSF is made. By using this equivalent model of the BSF, the BSF is fabricated, and the refractive index profile of the BSF is measured, which is similar to refractive index profile of the proposed BSF. The fabricated variable optical fiber attenuator (VOFA) consists of the BSF in a rectangular rubber ring with a fixed bend radius (BR) in a steady state. The VOFA using the proposed BSF was able to attenuate the optical power by more than about －38 ㏈ at certain wavelengths (1540∼1560 nm) based on adjusting the mechanical pressure applied to the upper surface of the rectangular rubber ring with the bent BSF. In addition, the proposed VOFA produced an insertion loss of 0.68 ㏈, polarization dependent loss (PDL) of about 0.5 ㏈, and return loss of less than －60 ㏈.

Light coupling and propagation in a fiber–dielectric-slab composite with a conductor cladding

A theoretical presentation of evanescent coupling is offered, with consideration of the refractive indices, between a side-polished optical fiber and an infinite planar waveguide with a conductor cladding (PWGCC). The PWG is suspended at a constant distance from an unclad fiber core and coated with a perfect conductor on the far side. The behavior of the distributed coupler is examined using a coupled mode model, which takes account of the two dimensions of the waveguide configuration. The coupling and propagation of light were found to depend on both the relation between the refractive indices of the materials and the configuration of the side-polished fiber used in the PWGCC. The spreading of light in the unconfined direction of the PWGCC is described in terms of a simple geometrical interpretation of the synchronization condition that is in agreement with a previous investigation of the problem based on the coupled mode theory. The power of the light propagated in the fiber decreases exponentially along the fiber axis as power is transferred to the PWGCC, where it is carried away. Then a 3-D finite-difference beam propagation method was applied to the fiber-PWG composite; results of the simulation by this means presented.

The Analysis of tight Coupling and Propagation for a Composite Fiber-Dielectric Slab with a Conductor Cladding

A theoretical presentation of evanescent coupling is offered with respect to the refractive indexes between a side-polished optical fiber and an infinitely planar waveguide with a conductor cladding (PWGCC). The PWG is suspended at a constant distance from an unclad fiber core and attached with the perfect conductor (PEC) on one side. The behavior of the distributed couple. is examined using a coupled mode model, which takes account of the two dimensions of the waveguide configuration. The coupling and propagation of light were found to depend on both the relationship between the refractive index values of each structure and the configuration of the side-polished fiber used in the PWGCC. The spreading of light in the unconfined direction of the PWGCC is described in terms of a simple geometrical interpretation of the synchronization condition that is in agreement with a previous investigation of the problem based on the coupled-mode theory (CMT). The power of the light propagation in the fiber decreased exponentially along the fiber axis as it was transferred to the PWGCC, where it was carried away.

Fabrication and analysis of microbend fiber sensor using bending-sensitive fiber

A bending-sensitive fiber (BSF) is fabricated and analyzed to create a microbend fiber sensor (MFS) with a simple structure. The BSF exhibits a gradual rather than sudden change in the microbend loss, according to a variation in the microbend applied to the BSF. According to the measured refractive index profile of the fabricated BSF, the proposed BSF consists of three different regions: the first core equal to the core of a SMF; the second core that is located around the first core, and whose refractive index is lower than the first core and higher than the cladding; and the cladding. The 3-D finite difference beam propagation method (3-D FD-BPM) is utilized to analyze the characteristics of the BSF. Based on the numerical results using 3-D FD-BPM and the fabricated BSF, a simple MFS with a BSF is created and compared to the MFS with a SMF. In particular, the MFS with the BSF showed a microbend loss from –1 to –20 dB at 1550 nm when the pressure given to the optical fiber is varied from 0 to 0.05 MPa; meanwhile, the MFS with the SMF showed no optical power attenuation.

Bending-Sensitive Fiber for Macrobend Fiber Sensors

A bending-sensitive fiber (BSF) that exhibits a moderate change in bending loss according to the bend conditions is fabricated for application to a macrobend fiber sensor. Simple macrobending experiments are then performed to verify the bending sensitivity of the BSF.

Effect of a Conductor Cladding on a Dielectric Slab for Coupling with a Side-polished Fiber

A theoretical presentation by using a three-dimensional finite difference beam propagating method (3-D FD-BPM) for the evanescent coupling is offered with respect to the refractive indexes between a side-polished optical fiber and an infinitely planar waveguide with a conductor cladding (PWGCC). The PWG is suspended at a constant distance from an unclad fiber core and attached with a perfect conductor (PEC) on one side. The coupling and propagation of light are found to depend on both the relationship between the refractive index values of two structures and the configuration of the side-polished fiber used in the PWGCC. The spreading of light in the unconfined direction of a PWGCC is presented with the distribution of electric fields in xy - plane and the absolute amplitude of electric fields along the x and y axis. The power of the light propagation in a fiber decreases exponentially along the fiber axis as it is transferred to the PWGCC, where it is carried away.

Submersion Sensor Using Bending-Sensitive Fiber

A sensor using bending sensitive fiber (BSF) was studied for real-time long-distance sensing of submersion. The structure of the submersion sensor effectively used the relationship between buoyant force and bending loss of the BSF. A three-dimensional finite-difference beam propagation method (3D FD-BPM) was used to select the bending dimension of the proposed submersion sensor. The operation of the submersion sensor utilizing the BSF was also investigated using 3D FD-BPM. As results of experiments, the submersion sensor fabricated showed a change of optical power from -17 to -1 dB at 1550 nm when the selected sensing region was submerged. In addition, the BSF was easily connected to a single mode fiber (SMF) by fusionsplicing. The BSF exhibited a -1 dB loss when connected to a SMF at both ends.

Influence of Raman effects on propagation of femtosecond pulses in all-optical phase-shift switches

The nonlinear interactions between two ultrashort pulses with temporal widths of less than 100 fsec are numerically studied in all-optical phase-shift switches. Specifically, the influence of self- and cross-Raman scattering on the switching performance is investigated. The energy exchange resulting from cross-Raman scattering during a collision is found to affect the phase-shift resulting from cross-phase modulation. It is also shown that a fiber with a low birefringence can be used in a switching scheme based on a higher-order soliton pulse due to the large self-Raman delay difference between the fundamental soliton pulse and the higher-order soliton pulse.

Design and fabrication of the surface plasmon fiber polarizer

We report theoretical and experimental investigation of a polarizer made of single mode side-polished fiber covered with a metal film. The influence of the metal film thickness and the refractive index of overlay on the device performance has been analyzed in terms of the normal mode theory. Based on the theoretical prediction, a polarizer with 40 ㏈ of polarization extinction ratio and 0.5 ㏈ insertion loss at optical communication wavelength has been realized