Y. Jung

Compact three segmented multimode fibre modal interferometer for high sensitivity refractive-index measurement

We experimentally demonstrate a new compact surrounding refractive-index sensor using a MMF-CSF-MMF (MCM) structure. The evanescent waves in the coreless silica fibre (CSF) region can directly interact with the surrounding medium. Due to its distinctive resonant spectral feature, the MCM sensor showed a high sensitivity of 4.37 × 10−4 for a refractive index range of 1.30 to 1.44, suggesting that the proposed device may be suitable for a wide range of biomedical and chemical sensor applications.

Broad-band tunable all-fiber bandpass filter based on hollow optical fiber and long-period grating pair

We report a tunable all-fiber bandpass filter based on a short hollow optical fiber serially concatenated between a pair of long-period fiber gratings. With novel core mode blocking in the hollow core fiber and its optimal design, the device showed a low insertion loss of 1.5 dB and broad-band passband tuning range of 84.3 nm covering both S- and C-band.

Versatile control of geometric birefringence in elliptical hollow optical fiber

A novel optical fiber fabrication technique was developed by converting the symmetry of the silica substrate into the germanosilicate ring core to efficiently introduce geometric birefringence in an elliptical hollow optical fiber. Due to high ellipticity in the hollow ring core, the fiber provides an extremely high group birefringence of 2.35 x 10(-3) at 1550 nm. Single-mode single-polarization guidance was also experimentally confirmed, with a bandwidth of approximately 35 nm. The generic adiabatic mode conversion capability in the taper also provided a stable fusion splice to conventional single-mode fiber with low loss and high tensile strength.

Defect and lattice structure for air-silica index-guiding holey fibers

We propose new design parameters for index-guiding holey fiber that can provide flexibility in defect and lattice design and adiabatic mode transformation capability. The new defect consists of a central air hole and a germanosilicate ring surrounding it, which results in a large-area annulus mode profile, low splice losses to standard fiber, 0.7 dB at 1.55 microm, and chromatic dispersion with a low slope, 0.002 ps/km nm2.

Highly polarization-dependent periodic coupling in mechanically induced long period grating over air-silica fibers

A very flexible and versatile tunable mechanical grating platform is introduced, with which highly polarization-dependent mode coupling is observed for three types of air-silica microstructured fibers: hollow core fiber, hexagonal-boundary holey fiber (HHF), and circular-boundary holey fiber. The resonances of gratings showed highly polarization-dependent broadband coupling compared with conventional single-mode fibers due to their unique beat-length dispersions between the core and the cladding modes, which could find applications in wideband polarization-dependent loss compensation. We further present significance of the spatial symmetry of HHF in distinct mode coupling for different rotation angles around the fiber axis.

New optical frequency domain differential mode delay measurement method for a multimode optical fiber.

A novel mode analysis method and differential mode delay (DMD) measurement technique for a multimode optical fiber based on optical frequency domain reflectometry has been proposed for the first time. We have used a conventional OFDR with a tunable external cavity laser and a Michelson interferometer. A few-mode optical multimode fiber was prepared to test our proposed measurement technique. We have also compared the OFDR measurement results with those obtained using a traditional time-domain measurement method.

Chromatic dispersion measurement for a few-mode fiber using optical frequency-domain reflectometer

Chromatic dispersion measurement for a multimode fiber using optical frequency domain reflectometry (OFDR) is proposed. A few-mode fiber was prepared to directly measure the chromatic dispersions of the excited modes using our proposed measurement technique.

Acousto-optic polarization-dependent mode coupling in a dual-mode hollow optical fiber

We report acousto-optic polarization-dependent coupling in two-mode hollow optical fiber. Local deformation of circular symmetry by traveling acoustic wave results in high birefringence making it suitable for polarization control devices.

Acoustooptic Tunable Gap-Type Bandpass Filter With a Broad Stopband

We demonstrate a novel all-fiber gap-type tunable bandpass filter configuration that consists of a broadband hollow optical fiber (HOF) acoustooptic tunable filter (AOTF) concatenated with a narrowband single-mode fiber (SMF)-AOTF. Owing to the unique mode coupling properties of HOF-AOTF and SMF-AOTF, a narrow passband channel of a full-width at half-maximum (FWHM) of ~4 nm could be formed in a broad stopband platform of a 90-nm FWHM successfully. In this scheme, the center wavelength and rejection efficiency of both passband and stopband were found to be flexibly tunable by adjusting the frequency and the voltage of radio-frequency signals applied to individual acoustic transducers.

Achievement of broadband uniform modal birefrigence in an index-guiding holey fibre using a novel circular hollow ring defect structure

A novel silica index-guiding holey fibre (IGHF) design is proposed utilizing a new defect structure that is composed of a three-layered defect with a central air hole germanosilicate ring and silica clad, based on a hollow optical fibre (HOF). Effects of these parameters on birefringence were numerically analysed using the plane wave expansion method. The proposed IGHF showed unique modal properties such as uniform birefringence and differential group delay in 1.55 µm optical communication windows that have not been achieved in prior arts.