Hak Kyu Lee

Fiber link loss monitoring scheme in bidirectional WDM transmission using ASE-injected FP-LD

We propose and demonstrate a novel fiber link loss monitoring method for a wavelength-division-multiplexed (WDM) passive optical network. This method is based on the optical signal comparison between a reference amplified spontaneous emission signal and its reflection from an optical reflector. Therefore, we can calculate the link loss exactly and also measure the characteristics of upstream optical signals without suspending the in-service channels. Since this scheme does not use narrow-band wavelength-dependent components such as fiber Bragg gratings, it is cost-effective in implementation and maintenance within a real optical network. We experimentally demonstrate that the link quality of upstream signals as well as fiber link faults on all WDM channels can be monitored in real time

Generation of multiorder Stokes and anti-Stokes lines in a Brillouin erbium-fiber laser with a Sagnac loop mirror.

We have demonstrated a novel multiwavelength lasing scheme in which a Brillouin erbium-fiber laser with a Sagnac loop mirror and a metal-coated planar mirror were used. The Sagnac loop permitted the simultaneous presence of a stimulated Brillouin scattering (SBS) pump and Stokes lines within the loop and thus generated high-order Stokes and anti-Stokes waves through a four-wave mixing (FWM) process. A total of 34 lines of Stokes and anti-Stokes waves with 0.08-nm line spacing was generated through the SBS and FWM processes with 1.5-mW SBS pump power at 1561 nm and 80-mW erbium-doped-fiber pump power.

Pulse-amplitude-equalized output from a rational harmonic mode-locked fiber laser

We report, for the first time to our knowledge, the demonstration of amplitude equalization of high-repetition-rate pulses generated from a rational harmonic mode-locked Er-doped fiber laser. The output pulses are injected into another fiber laser with a nonlinear optical loop mirror. This scheme provides pulse-amplitude equalization up to the ninth rational harmonic mode-locked pulse train.

Harmonically mode-locked fiber laser with an acousto-optic modulator in a Sagnac loop and Faraday rotating mirror cavity

Abstract We have demonstrated a new scheme of harmonically mode-locked fiber laser utilizing an all-fiber acousto-optic modulator, which is composed of a two-mode fiber, as an active mode-locker. The harmonically mode-locked lasing occurs when a harmonic frequency of the modulator driven frequency matches with one of the harmonics of the cavity modes at the least common multiple frequency value. The mode-locked laser pulses were obtained at the 7th harmonics of the cavitys fundamental mode frequency.

An electronically wavelength-tunable mode-locked fiber laser using an all-fiber acoustooptic tunable filter

We have demonstrated a novel scheme of a continuously wavelength-tunable and passively mode-locked fiber laser by using the sliding frequency effect of an all-fiber acoustooptic tunable filter. Stable and nearly transform-limited pulses of 800-fs pulsewidth were produced with this laser scheme for a wavelength tuning range of 17 nm at around 1550 nm.We have demonstrated a novel scheme of a continuously wavelength-tunable and passively mode-locked fiber laser by using the sliding frequency effect of an all-fiber acoustooptic tunable filter. Stable and nearly transform-limited pulses of 800-fs pulsewidth were produced with this laser scheme for a wavelength tuning range of 17 nm at around 1550 nm.

A stabilised fibre-optic Mach-Zehnder interferometer filter using an independent stabilisation light source

We have demonstrated a stabilised scheme of fibre-optic Mach-Zehnder interferometer-type optical filter for application in periodic wavelength dividing filters. The stabilised scheme is based on controlling one arm length of the interferometer with electronically fedback fibre stretcher and utilizes an independent control light source and a voltage amplifier. This filter turns out to be useful for optical inputs not only of discrete spectra but also of broadband spectra. The output characteristics including stability, extinction ratio and transmission period are discussed.

Exact solution of two-wave coupling for photorefractive and photochromic gratings in photorefractive materials

Abstract We derive an exact solution of two-wave coupled equations incorporating photorefractive and photochromic gratings in the same photorefractive materials and discuss the effects of the relative magnitude of both gratings.

Phase-matched four-wave mixing between pumps and signals in a copumped Raman amplifier

We observe four-wave mixing (FWM) between copropagating pumps and signals in a Raman amplifier when the zero-dispersion wavelength of the transmission fiber lies symmetrically between the pump and the signal wavelengths. The resultant FWM products, which grow as they experience Raman gain along the fiber, can degrade the signals optical signal-to-noise ratio by as much as 10 dB for a Raman ON-OFF gain of 15 dB.

Multistage access network for bidirectional DWDM transmission using ASE-injected FP-LD

We propose a novel optical distribution network for multistage optical access network with multiple remote nodes (RNs) using 4skip0 filters. The system can be implemented by use of 1/spl times/N arrayed waveguide grating in the central office, cascaded RNs, and a plurality of optical network units (ONUs). It also employs colorless ONUs based on incoherent light injected Fabry-Pe/spl acute/rot laser diodes for low operation and maintenance cost. Experiment shows error-free transmission with simultaneous bidirectional 1.25 Gb/s per channel up to 20 km.

Instability in Raman amplifiers caused by distributed Rayleigh reflection

We observed instability in Raman optical amplifiers caused by the Raman gain and the cavity between two mirrors formed by distributed Rayleigh reflection. Threshold pump power for the instability and limitation imposed on Raman amplifiers are derived and discussed.