Chang-Seok Kim

Highly stable tunable dual-wavelength Q-switched fiber laser for DIAL applications

We demonstrate a stable dual-wavelength Q-switched fiber laser for applications in differential absorption Lidar with tunability in absolute wavelength over several nanometers and discrete tuning in wavelength spacing from 1.1 to 3.3 nm. Single longitudinal-mode operation is also achieved by employing Sagnac loop saturable absorber filter. The delayed self homodyne linewidth measurement of the dual-wavelength continuous-wave laser shows a very narrow spectral linewidth and frequency jitter (<40 kHz). The advantages of tunable wavelengths, narrow linewidth, temperature insensitivity, and high stability in an efficient, cost effective, rugged, compact and light system make it a promising technology for airborne Lidar systems.

Tunable all-fiber birefringence comb filters

We have demonstrated a novel all-fiber comb filter with adjustable channel spacing. The filter can be used as an element in a multi-wavelength laser and provide great flexibility in laser design. Both Lyot and Sagnac-Lyot filters have been demonstrated. The Lyot filter provides a large number of wavelength spacings with only a few fiber segments. (e.g. 40 spacings for 4 segment filter) whereas the Sagnac-Lyot filter provides a tunable filter function that is independent of input polarization. Typical values of measured insertion loss were 4 dB and extinction ratio of 15 dB. The insertion loss values can be improved by using low-loss polarization controllers and improving the fusion splicing of the PM/non-PM fiber splices.

Demonstration of a novel all-fiber bandpass acousto-optic tunable filter

An all-fiber tunable bandpass filter is demonstrated. A dual acousto-optic grating inside a Sagnac loop changes the polarization of the light over a narrow bandwidth which redirects the light from reflection to the transmission port.

FDML wavelength-swept fiber laser based on EDF gain medium

Novel Fourier domain mode locking wavelength-swept laser source is demonstrated based on erbium doped fiber medium. Instead of conventional semiconductor optical amplifier, we use erbium doped fiber amplifier, which can easily generate higher optical power output.

Novel multi-wavelength cascaded-Raman source based on tunable fiber Sagnac loop filter

We have experimentally demonstrated a multiwavelength fiber Raman source based on a tunable high birefringence fiber Sagnac loop filter. Using the novel scheme, we have demonstrated a generation of a broad cascaded Stokes waves with wavelength between 1.12/spl sim/1.57 /spl mu/m and the generation of approximately 20 wavelength channels within the 4th order Stokes waves. By adjusting the pump power and the cavity, the multi-wavelength operation is possible within a particular Stokes waves or all the Stokes waves. Such multi-wavelength laser source is expected to be useful in many applications including the WDM and sensing area.

Linearized interrogation of FDML FBG sensor system using PMF Sagnac interferometer

A novel linearized interrogation method is presented for Fourier-domain mode locked (FDML) fiber Bragg grating (FBG) sensor system. In the ultra high-speed regime over 10 kHz modulation, only sine wave is available to scan a center wavelength of FDML wavelength-swept laser instead of conventional triangular wave. However, sine wave modulation has been suffered an exaggerated nonlinear filter response in demodulating the time-encoded parameter into the absolute wavelength. The linearized demodulation is demonstrated by the third order polynomial conversion of filter between the time-encoded parameter and wavelength-encoded parameter based on the spectral information of polarization maintaining fiber (PMF) Sagnac interferometer.

Incoherent, CW supercontinuum source based on erbium fiber ASE for optical coherence tomography imaging

A novel light source of erbium-fiber ASE-seeded, depolarized, incoherent, CW supercontinuum is proposed for optical coherence tomography imaging. The OCT system using the ∼110-nm bandwidth light source is experimentally demonstrated to enable high quality imaging of human tooth tissues.

Dual-wavelength, all-PM Er/Yb fiber ring laser with wavelength and channel separation tunability

Summary form only given. Tunable multi-wavelength fiber laser sources have numerous applications in optical and RF communications and optical sensing. Specific applications include wavelength division multiplexing, wideband RF signal processing, multielement optical sensors, and optical soliton sources. To date, multi-wavelength operation and tunable single wavelength operation of fiber lasers have been demonstrated. The ability to adjust the channel spacing and tune the absolute frequency in a multi-wavelength laser system can provide many degrees of freedom in the fiber laser design. In this paper, we discuss a method for discretely tuning the channel spacing by using a polarization controller and experimentally demonstrate this concept with a dual-wavelength fiber laser source. We have recently demonstrated the continuous tuning capability of this source.

A novel method of removing optical fiber coating with hot air stream

We discuss a new non-contact technique of removing optical fiber coating in a continuous and uninterrupted manner with hot air stream. The mean breaking stripped optical fiber tensile strength was 4.5 GPa.

Novel wavelength-swept Raman laser for arbitrary gain band OCT

Novel wavelength-swept Raman laser is newly demonstrated to implement an arbitrary gain band for a swept-source optical coherence tomography (SS-OCT). Instead of conventional semiconductor optical amplifier, we adapt optical fiber Raman amplification, which can easily generate an instant femto-second optical gain at arbitrary wavelength region from 1.1 to 1.6 micrometer using a high-power optical pump power. We also experimentally demonstrate OCT images using the novel wavelength-swept Raman laser source.