Bong-Ahn Yu

Multiwavelength pulse generation in semiconductor-fiber ring laser using a sampled fiber grating

A novel multiwavelength scheme has been demonstrated using a sampled fiber grating in semiconductor-fiber ring laser. By using semiconductor optical amplifier as an inhomogeneously broadened gain medium, three wavelength channels of 10 GHz are simultaneously generated. The number of the lasing channels can be changed through the polarization state adjustment in the cavity.

Filter characteristics of a chirped volume holographic grating.

We compare and analyze the filter properties of transmission-type volume holographic gratings, especially the dispersion characteristics for uniform and chirped gratings. It is theoretically and experimentally shown that the dispersion characteristics can be controlled by introducing one-dimensional chirping to the volume grating in a photorefractive crystal. The filter response including output power and dispersion comes from a combined effect of the spatial spectra of the grating structure, input beam, and output-coupling fiber mode. Filter responses can be designed by controlling these parameters for optical communication applications.

Phase response design of a polarization-maintaining fiber loop mirror for dispersion compensation

We propose a simple dispersion-compensation filter using a polarization-maintaining fiber loop mirror. Due to the fact that the proposed filter is spectrally periodic and has a relatively large dispersion, it can be used as a multichannel dispersion compensator. The measured delay characteristic agrees with the theory. The delay characteristic can be tuned by changing the power-coupling coefficient of the variable coupler in the loop mirror.

A Compact Diode-Pumped Microchip Green Light Source with a Built-in Thermoelectric Element

A diode-pumped microchip green light source which was based upon a diffusion-bonded Nd:YVO4/KTiOPO4 composite crystal and had a built-in thermoelectric element was developed. The source had the small volume of 0.7 cm3 and showed the average green power of up to 25 mW and the average electrical power consumed in the thermoelectric element of 15 mW at the interior temperature of 51 °C, under the driving condition of the duty ratio of 50%, the average electrical power consumed in pump diode of about 304 mW, and the ambient temperature of 20 °C, which resulted in the electrical-to-optical conversion efficiency of up to 7.8%. The power of the source was so stable with the fluctuation of less than 0.2%. Our source is the smallest green laser with the built-in temperature-controlling unit to our knowledge and thought to be useful in many applications including the portable laser display system.

All-fiber wavelength tunable and mode convertible bandpass filter for optical inter-connections

We report an all-fiber wavelength tunable bandpass filter with multi-mode to single- mode converting property via serially concatenated structure of a helicoidal long-period fiber grating (HLPFG), a hollow optical fiber (HOF), and a multimode fiber (MMF).

Multiwavelength Switchable Erbium-Doped Fiber Ring Laser using Digital Micromirror Device

We demonstrated a multiwavelength switchable erbium-doped fiber ring laser using digital micromirror device. By controlling the tilt states of micromirrors, we achieved some flexible allocations of wavelength channels and multiwavelength switching operations. We generated up to 8 wavelength channels with 0.8 nm spacing at room temperature.

Phase response of polarization maintaining fiber loop mirror with enhanced reflection

A polarization maintaining fiber loop mirror can produce an adjustable dispersion with the tune of couplers power coupling coefficient. In this paper we show the phase response of the filter for a tunable dispersion compensation with the structure that is designed to show quasiall-pass filter characteristic.

Parallel processing optical device using volume holography

By using volume holography characteristics, optical devices having demultiplexer and/or dispersion compensator capabilities are proposed which can control multiple channel wavelengths in the wavelength division multiplexed (WDM) system. Through a specially designed mask system, multiple volume gratings corresponding to the multi-channel components are recorded in a photorefractive crystal. This mask recording scheme simplifies the conventional sequential multiplexing procedure which requires complex mechanical or laser source system. Recording schemes and device characteristics of the above devices are presented in relation with volume diffraction principle and photorefractive crystal properties.

Waveband-switchable semiconductor-optical-amplifier-fiber ring laser using a polarization beam splitter and sampled fiber Bragg gratings

A novel and improved waveband-switchable fiber laser based on a semiconductor optical amplifier and sampled fiber Bragg gratings is proposed using high polarization selectivity of a polarization beam splitter. A multiwavelength-switching operation of five laser lines with 0.8-nm wavelength spacing, whose switching displacement was ∼ 7 nm, has been successfully demonstrated. The switching displacement between wavebands, wavelength channels, and their spacings can be flexibly determined by the selected comb filters.

A fiber Bragg grating sensor demodulation technique using a polarization maintaining fiber loop mirror

A simple, passive, and self-referencing wavelength shift detection scheme, for use with fiber Bragg grating sensing systems, is described. The system is based on the use of a polarization maintaining fiber loop mirror.