Kun-Wook Chung

A highly sensitive long period grating based tunable filter using a unique double-cladding layer structure

In this paper, we present a highly sensitive long period grating (LPG) with a unique double-cladding layer structure including an ultra-thin inner silica cladding layer and a low refractive index liquid crystal outer cladding layer. By using an ultra-thin cladding layer (28 μm in diameter) reduced by chemical etching, the LPG has a single resonant band over a wide range of wavelength and higher sensitivity to the environmental refractive index change. In addition, the high thermal-optic effect of liquid crystal makes it very easy to tune the resonant wavelength by controlling the temperature of the liquid crystal. Thus, a highly sensitive tunable filter can be made. The experimental results show that a tuning efficiency of 2.1 nm/°C is achieved. To the best of our knowledge, this is the highest tuning efficiency ever reported.

A new design for non-zero dispersion-shifted fiber (NZ-DSF) with a large effective area over 100 μm2 and low bending and splice loss

A new design for large-effective-area non-zero dispersion-shifted fiber (NZ-DSF) for dense wavelength division multiplexing (DWDM) is presented. The Gaussian approximation method is used for calculating electrical field distribution for the designed refractive index profile. The designed fiber has a dispersion about 4 ps/nm/km and dispersion slope about 0.06 ps/nm2/km at 1.55 μm operating wavelength, which can be used to avoid four-wave mixing (FWM). In addition, our calculation also shown that the designed fiber not only has a large effective area over 100 μm2 but also has low bending loss (<1.3×10−3 dB with 30 mm bending radius and 100 turns) and low splice loss (<6.38×10−3 dB) with conventional fiber. The manufacturing tolerance of the fiber is found to be compatible with other types of known profile large-effective-area fibers. Thus, this newly designed fiber may be a good candidate for the long-haul DWDM fiber optic communications.

A novel all-optic tunable long-period grating using a unique double-cladding layer

In this paper, a novel all-optic tunable filter based on long-period grating (LPG) with a unique double-cladding layer structure is implemented. The LPG that has an ultra-thin silica inner cladding layer and a dye-doped liquid crystal outer cladding layer is tuned by photochemical driving liquid-crystal molecular reorientation. The unique feature of this tunable filter is that there is no contact electrodes required, which may make the fabrication of tunable filter easier.

Investigation of the electro-optic properties of electron-irradiated poly(vinylidene fluoride-trifluoroethylene) copolymer

The electro-optic property of electron-irradiated poly- (vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) copolymer is presented. It is found that this special treated polymer not only has a giant electrostriction and relaxor ferroelectric behavior but also has a relatively good electro-optic effect. Thus, this copolymer may be a good candidate for making fast speed electro-optic modulators and switches, which are critical components for information optics.

Wavelength tuning range enhanced single resonant band fiber filter using a long period grating (LPG) with ultra thin cladding layer

A unique fiber filter using a LPG with ultra thin cladding layer (/spl sim/32 /spl mu/m) is presented, which has a single resonant band within 1000 nm to 1700 nm wavelength tuning sensitivity as large as 30 nm shift for a 2/spl times/1O-3 surrounding refractive index change.

SerDes chips for 100Gbps dual-polarization DQPSK

The required features of SerDes chips for 100Gbps Ethernet and OTN optical data transmission are discussed. As a baseline technology for 100Gbps SerDes, 40Gbps DPQSK serializer chip performance is presented.

All-fiber all-optic tunable filter based on the combination of long-period grating and photorefractive cladding layer

In this paper, a broadband tunable long period grating (LPG) with an ultra-thin cladding layer using liquid crystal is presented. By chemical etching the long period grating to a very thin diameter (approximately 30micrometers ), the long period grating becomes extremely sensitive to the surrounding refractive index change so that a wide range tunable filter is realized. By using liquid crystal material (18523) that has a no less than the refractive index of cladding, a resonant band of the LPG is tuned by controlling the temperature of the liquid crystal. We obtained a tuning range of 87nm with a temperature change of only approximately 22 degrees. It is believed that this filter has the largest temperature-dependent tuning effect ever reported. Further experiment will be focused on photo- induced reorientation of the liquid crystal molecules, so that another type of tunable filter via photochemical effect can be realized.

Analysis of volume holographic long period gratings in photonic nanostructured fibers and waveguides

An analysis of volume holographic long period gratings in photonic nanostructured fibers and waveguides is presented. It is found that the unique photonic nanostructure could substantially enhance the tuning capability of the spectral response of the grating, which could result in many practical applications in optical communications and sensors, such as wide tuning range wavelength filters and ultrahigh sensitivity optical sensors.

Accurate hybrid mode analysis of hollow optical fibers

The dispersion relation equation of hybrid modes in hollow optical fiber is derived in the closed form by modeling the fiber in a three-layered structure and by rigorous hybrid mode analysis. The effective refractive indices of hybrid modes as a function of wavelength are accurately calculated. Modal characteristics and transverse field distributions of hollow optical fiber are precisely analyzed by use of the derived hybrid mode dispersion relation equation and the compact 2-D finite difference time domain method. In addition, the effects of the fiber dimension on propagating properties are presented. The number of hybrid modes that can exist in hollow optical fiber is calculated as a function of fiber dimension. We believe that this rigorous analysis is very accurate and provides precise computing methods to design and characterize hollow optical fiber based optical devices.

Analysis of hollow optical fiber couplers using the compact two-dimensional finite-difference time-domain method

The coupling characteristics of newly proposed hollow optical fiber (HOF) couplers are rigorously analyzed using the compact 2-D finite-difference time-domain (FDTD) method. The FDTD-simulated coupling efficiency as a function of the coupling length, and the transverse electric field distributions of the higher-order mode converted by the HOF couplers, are investigated. We propose that the designed HOF couplers can be used for various optical devices such as side-pumping double-clad fibers, mode splitters, and power monitors.