Woojin Shin

All-optical AND and NAND gates based on cascaded second-order nonlinear processes in a Ti-diffused periodically poled LiNbO(3) waveguide.

All-optical AND and NAND gates have been demonstrated in a Ti-diffused periodically poled LiNbO(3) channel waveguide which has two second-harmonic phase-matching peaks by cascaded sum-frequency-generation/difference-frequency-generation (cSFG/DFG) and sum-frequency-generation (SFG) processes. The conversion efficiency of signal to idler (AND gate signal) was approximately 0 dB in cSFG/DFG process. In the second SFG process, more than 15 dB extinction ratio between signal and dropped signal (NAND gate signal) has been observed.

Novel mode converter based on hollow optical fiber for Gigabit LAN communication

A novel mode converter based on a hollow optical fiber is proposed to reduce the differential modal delay penalty in optical transmission over multimode fibers (MMFs). The device adiabatically converts a fundamental mode in a single-mode fiber to a ring-shaped mode in order to excite selectively a set of higher order modes with a similar group velocity in MMF, maintaining center-launching configuration. The mode converter is composed of serially concatenated concentric segments of a single-mode, hollow, and multimode optical fiber. For 2.5-Gb/s transmission over 500-m-long MMF using a laser diode transmitter, the proposed mode converter shows improvement in bit-error-rate performance at both wavelengths of 1.31 and 1.55 /spl mu/m.

Bandwidth-tunable band-rejection filter based on helicoidal fiber grating pair of opposite helicities

We propose a new type of all-fiber bandwidth tunable rejection filter using cascaded helicoidal long-period fiber gratings in single-mode optical fiber and report controllable broadband rejection characteristic with low insertion loss and polarization dependent loss.

Ultracompact Intrinsic Micro Air-Cavity Fiber Mach–Zehnder Interferometer

A compact intrinsic fiber Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated by incorporating a micro air-cavity ablated by femtosecond laser irradiation. A short cavity of length ~ 10 mum along the single-mode fiber core provided two optical paths: one propagating through the air and the other guided along the ring-shaped silica cladding. A spectral analysis confirmed MZI in a good agreement with experimental results. Temperature-dependent spectral shifts were measured and analyzed.

UV Sensor Based on Photomechanically Functional Polymer-Coated FBG

A simple ultraviolet (UV) sensor based on a photomechanical responsible material (azobenzene moiety) and a typical fiber Bragg grating (FBG) has been proposed and demonstrated for the first time. This sensing device, called the azobenzene-coated FBG sensor, can easily measure the UV light intensity by determination of its center wavelength shift which results from the photoisomerization of the azobenzene moieties. We show that the peak wavelength can be rapidly shifted up to 0.6 nm because of the photomechanical stretching effect of the azobenzene-coated FBG. The strain applied to the FBG under a UV intensity of 208 mW/cm2 was estimated to be 0.054%. We have also confirmed the linearity and stability of our proposed UV sensor.

Fabrication of Micro Fresnel Zone Plate Lens on a Mode-Expanded Hybrid Optical Fiber Using a Femtosecond Laser Ablation System

We present a compact all-fiber zone plate lens directly ablated on the surface of a mode-expanded hybrid fiber end by using a high precision femtosecond laser processing technique. To achieve a sufficiently large beam size and focusing efficiency, a segment of a coreless silica fiber having a 200-mum diameter was adapted. Focusing properties of the zone plate lens were experimentally investigated and compared with numerical simulations.

Compensation of Raman-induced crosstalk using a lumped germanosilicate fiber Raman amplifier in the 1.571-1.591-μm region

A new method to equalize power imbalance caused by Raman-induced crosstalk among optical channels is proposed using a lumped germanosilicate fiber Raman amplifier. Evolution of optical channels through the Raman amplifier was simulated using Raman frequency modeling, which theoretically predicted simultaneous amplification and power equalization. Experimentally, a gain band with negative slope in the range of 1.571-1.591 /spl mu/m was achieved in a lumped Raman amplifier pumped by a broad-band laser diode centered at 1.467 /spl mu/m. We demonstrated compensation of the Raman-induced crosstalk of 5 dB accumulated along 330 km of conventional single-mode fiber.

Tunable Q-switched erbium-doped fiber laser based on digital micro-mirror array

We propose and demonstrate a tunable Q-switched erbium doped fiber laser with a digitally controlled micro-mirror array device. The tunable and pulsed output of the laser was achieved by the pixelated spatial modulation of the micro-mirror array. The wavelength tuning from 1530 nm to 1555 nm was shown with wavelength selectivity of ~0.1 nm and the pulsed operation was accomplished with 130 Hz repetition rate.

Waveguide-Type Wavelength-Tunable Šolc Filter in a Periodically Poled Ti : LiNbO

We have demonstrated the waveguide-type tunable wavelength filtering (Sole filter) characteristics in an 80-mm-long periodically poled Ti: LiNbO3 (Ti: PPLN) channel waveguide which has a domain period of 16.6 mum. At room temperature (25degC), the center wavelength and the full-width at half-maximum of the filter were about 1273.3 and 0.21 nm, respectively. By changing the temperature of the Ti: PPLN waveguide, we have tuned the center wavelength of the filter with a wavelength tuning rate of -0.683 nm/degC. Also, the characteristics of the waveguide-type Sole filter based on a Ti: PPLN waveguide were compared with those of a bulk PPLN device.

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We propose a new type of all-fiber device for inter-band router using a novel hybrid waveguide-MEMS technology. Both continuous and discrete band-routing functions are realized by precise twist control over the fused coupling region, which results in pi phase shift between the output ports. Experimentally we demonstrate inter-band routing functions between O and C-band as well as between E and L-band with a low insertion loss, wide bandwidth of operation, high channel isolation and fast response.