Gyeong Hun Kim

Linearized Wavelength Interrogation System of Fiber Bragg Grating Strain Sensor Based on Wavelength-Swept Active Mode Locking Fiber Laser

We demonstrated a linearized wavelength interrogation system of fiber Bragg grating (FBG) strain sensors, based on a wavelength-swept active mode locking (AML) fiber laser. Since the wavelength sweeping mechanism of the AML fiber laser does not depend on the wavelength selecting filter, we can easily demonstrate the wavelength-linear sweeping by applying a programmable electrical signal to the laser cavity. Both static and dynamic strain measurements of FBG sensors were characterized with high linearity, which has an R-square value of 0.9999 at a sweep rate of 50 kHz.

Parallel Imaging of 3D Surface Profile with Space-Division Multiplexing

We have developed a modified optical frequency domain imaging (OFDI) system that performs parallel imaging of three-dimensional (3D) surface profiles by using the space division multiplexing (SDM) method with dual-area swept sourced beams. We have also demonstrated that 3D surface information for two different areas could be well obtained in a same time with only one camera by our method. In this study, double field of views (FOVs) of 11.16 mm × 5.92 mm were achieved within 0.5 s. Height range for each FOV was 460 µm and axial and transverse resolutions were 3.6 and 5.52 µm, respectively.

Novel interrogation of the multiple FBGs with same Bragg wavelength by using active mode locking cavity

We proposed a new type of FBG interrogator using active mode locking technique. Since the interrogation mechanism is based on the separated detection of mode-locked frequency of each series FBG, we can interrogate multiple same FBGs.

High speed strain measurement of active mode locking FBG laser sensor using chirped FBG cavity

We propose a high speed strain measurement method using an active mode locking (AML) fiber Bragg grating (FBG) laser sensor with a chirped FBG cavity. The mode-locked frequency of the AML laser depends on both the position and Bragg wavelength of the FBG. Thus, the mode-locked frequency of cascaded FBGs can be detected independently along the cavity length of cascaded FBGs. The strain across FBGs can be interrogated dynamically by monitoring the change in mode-locked frequency. In this respect, the chirped FBG critically improves the frequency sensitivity to Bragg wavelength shift as a function of increasing dispersion in the AML cavity. The strain measurement of the FBG sensor shows a highly linear response, with an R-squared value of 0.9997

Quasi-distributed fiber sensor using active mode locking laser cavity with multiple FBG reflections

We have demonstrated a quasi-distributed sensor using an active mode-locking (AML) laser with multiple fiber Bragg grating (FBG) reflections of the same center wavelength. We found that variations in the multiple cavity segment lengths between FBGs can be measured by simply sweeping the modulation frequency, because the modulation frequency of the AML laser is proportionally affected by cavity length.

Quasi-Distributed active mode locking laser sensor using fiber partial reflectors

We propose a new type of a quasi-distributed optical laser sensor based on an active mode locking fiber cavity. The change of mode locking frequency of lasing peak is experimentally proportional to the fine displacement change.

A MHz speed wavelength sweeping for ultra-high speed FBG interrogation

We demonstrated a MHz speed wavelength-swept fiber laser based on the active mode locking (AML) technique and applied to interrogation system of an array of fiber Bragg grating (FBG) sensors. MHz speed wavelength sweeping of wavelength-swept fiber laser can be obtained by programmable frequency modulation of the semiconductor optical amplifier (SOA) without any wavelength tunable filter. Both static and dynamic strain measurement of FBG sensors were successfully characterized with high linearity of an R-square value of 0.9999 at sweeping speed of 50 kHz.