Bong Wan Lee

Dynamic erbium-doped fiber amplifier based on active gain flattening with fiber acoustooptic tunable filters

We describe the first demonstration of a dynamic erbium-doped fiber amplifier (EDFA) based on automatic feedback control of active gain equalizing filters. The filters are all-fiber acoustooptic tunable filters capable of generating controllable filter shapes. Wide dynamic-range gain/power control is achieved with <0.6-dB signal ripple over 30 nm in various operating conditions. We also show, by numerical simulation, an important advantage of the dynamic EDFA over a conventional EDFA in cascaded structures.

High-sensitivity mode-locked fiber laser gyroscope

We report significant performance improvement of a mode-locked fiber laser gyroscope. A Fabry-Perot cavity GaAlAs laser diode whose front facet was antireflection coated was used as a gain medium. The rms noise equivalent rotation rate measured with a time-interval counter was improved to 0.06deg/ radicalh. The long-term drift of the gyroscope signal was reduced to 100deg/ radicalh after a polarizer was inserted into the laser cavity formed with a polarization-maintaining fiber.

Dynamic erbium-doped fiber amplifier with automatic gain flattening

We demonstrate, for the first time to our knowledge, a dynamic EDFA based on automatic active gain flattening. Wide-dynamic-range gain/power control is achieved with <0.6 dB signal ripple over 30 nm in various operating conditions. We also show a significant advantage of the dynamic EDFA over conventional one in cascaded structures.

Phase sensitive detection for mode-locked fiber laser gyroscope

We demonstrate a significant improvement in the performance of a mode-locked fiber laser gyroscope by using a lock-in amplifier. We show that the direct output of the lock-in amplifier has a desirable linear dependence on the rotation rate and is insensitive to the intensity difference between two pulses that causes phase error in the time interval measurement. Two orders of magnitude improvement is demonstrated in the long-term stability compared to that from previously reported time interval measurement.

Mode-locked fiber laser gyroscope based on a distributed-feedback semiconductor laser amplifier.

A mode-locked fiber laser gyroscope is reported that uses a distributed-feedback semiconductor laser amplif ier as the gain medium. Stable mode-locked optical pulses were obtained without gain competition, and the pulse interval could be measured with much-improved accuracy as a function of rotation rate. The rms noise equivalent rotation rate was measured to be 0.4 deg/ radicalh.

Analysis of polarization properties of a mode-locked fiber laser gyroscope

We investigated the polarization characteristics of a mode-locked fiber laser gyroscope (MLPLG) formed with a Nd-doped fiber as an optical gain medium and a Sagnac loop mirror. The output pulse patterns and the polarization states were found to be determined by fiber birefringence in the different sections of the MLPLG. We describe the conditions for the MLPLG to operate with automatic reciprocity leading to the possibility of phase-error-free operation.

Measurement of Effective Refractive Index of Nematic Liquid Crystal in Fabry-Perot Etalon

We report a measurement of effective refractive index of a nematic liquid crystal Fabry-Perot etalon according to the applied static electric field intensity. The effective refractive index decreases from 1.67 to 1.51 as the applied electric field intensity is increased.

Polarization characteristics of mode-locked fiber laser gyroscope

A mode locked fiber laser gyroscope (MLFLG) [1] has a laser cavity formed with a fiber amplifier with a planar mirror at one end and a Sagnac loop interferometer at the other end, as shown in figure 1. The Sagnac interferometer functions as a loop mirror, and a phase modulator in the interferometer is used to modulate the reflectivity of the loop mirror.

Electric field sensor based on cholesteric liquid crystal Fabry-Perot etalon

We propose an electric field sensor using a cholesteric liquid crystal (CLC) Fabry-Perot etalon and a broadband optical source. The CLC cell consists of glass substrates, polyimide layers, electrodes, and CLC layer. There is a threshold behavior for CLC cell and no change in the transmitted wavelength occurs until a threshold value. The threshold value is 0.8 V/μm for fabricated CLC cell in this experiment. The transmitted or reflected wavelength from the CLC Fabry-Perot etalon depends on the applied electric field. The valley wavelengths of the transmitted light from the CLC device are linearly increased from 1303 nm to 1317 nm as the applied electric field to the CLC device is increased from 0.8 V/μm to 1.9 V/μm.

Characteristics of a Wavelength-swept Laser with a Polygon-based Wavelength Scanning Filter

We report the characterization of a wavelength-swept laser (WSL) using a polygon-based wavelength scanning filter and two semiconductor optical amplifiers (SOAs). The output intensity and scanning bandwidth of the WSL depend on the position of the two SOAs in the laser cavity and the coupling ratio of the output fiber coupler. The outputs of the WSL are characterized for coupling ratios of 10%, 30%, 50%, 70%, and 90% for the output fiber coupler. In the setup in which the output fiber coupler is located between the two SOAs, high output power and wide scanning bandwidth can be achieved with an optimized configuration. Using the optimized configuration of the WSL, the intensity increases with the coupling ratio. These results can be used to construct an optimized WSL using the polygon-based wavelength scanning filter.