Generation of femto-second pulses from self mode-locked by yrf69717


									  Generation of femto-second pulses from self mode-locked Yb-doped fiber laser

                          Young-Won Kim, Sung-Ki Hong, Min-Suk Kim, Kwanghoon Ko and Changhwan Lim
                                 Lab. for Quantum Optics, Korea Atomic Energy Research Institute
                                           P.O. Box 105 Yusong, Daejeon 305-600, Korea

                                                         Jae-jin Goo and Young-suk Seo
                                             Technology research laboratory, WonTechnology Co., Ltd.
                                  No. 538, Deadeok Techno Vally, Yongsan-dong, Yusong, Daejeon 305-600, Korea


   Recently, the fiber lasers have received vast attention as an oscillator of Master Oscillator Power Amplifier
(MOPA) system due to their excellent output power stability. Especially, all-fiber splicing connection-type fiber
lasers offer several advantages over conventional bulk-type fiber lasers, including greater stability, compactness,
and ease of management. This type of fiber laser does not need the adjustment of its spatially coupled
components because it consists of only optical fibers, whereas the conventional fiber lasers using focus lenses
and air gaps need the adjustment of spatially coupled components. In addition, the direct splicing of fiber
components is very robust to thermal effects and mechanical disturbances because it does not need much optical
   We have been demonstrated the self mode-locked Yb-doped fiber laser by Nonlinear Polarization Rotation
(NRT)[2] which consist of all-fiber splicing connection-type and only PM Single-mode fiber due to their
structures are similar. Since no polarization instability or polarization mode-beating, a highly polarized cavity
can generate highly stable pulses. We have fiber ring resonator without air gap of connection between fibers, the
active element as laser amplifier was PM-YDF which has two air-channels located in parallel to the core in order
to maintain linear polarization, and we used a PANDA fiber that high internal birefringence loss maintaining
linear polarization against external perturbation as shown Fig.1. When pump power was weak, unstable noisy
pulses were observed. As the Pump power gradually increased, the operation mode change to the mode-locked
pulse generation from noisy pulse trains. We obtain the detail pulse waveform that measuring spectrum FWHM
of 70 nm by digital spectrum analyzer, measuring pulse train repetition rate of 25 MHz and measuring pulse
width of 44 fs by SHG FROG method as shown Fig 2.
   The self mode-locked Yb-doped fiber laser system can be widely tunable from 1020 nm to 1080 nm by using
a fiber-type band-pass filter. This type of fiber laser will be useful as an oscillator stage for the amplification
using various materials such as Nd:YAG, Nd:Silica, Nd;phosphate, Nd:glass, Yb:YAG, and also Bi:Silica.
                                                                                Mi r r o r 3

                                                                                                            Mo d e- l o c k ed
                                                                                                                p u l es

                                                            Mi r r o r 1
                                                                                                           Co l l i ma t o r 1

                                                                                               hwp   qwp
     Gr a t i n g 1

                                                                                                                                 Yb d o p ed
                                                                                                                                  f i b er
                                                            Isol a t o r

         Mi r r o r 2                    Gr a t i n g 2

                                                                                                       WDM c o u p l er

                                                          Co l l i ma t o r 2

                                                                                                           980 n m LD

           Op t i c a l s p ec t r u m                                          Pa n d a
                  a n a l y zer                                                 f i b er

   Fig 1. Schematic diagram of mode-locked Yb fiber laser                                                                                      Fig 2. Measuring Pulse train & Pulse width

[1] K. Sumimura et al., Environmentally Stable Ytterbium-Doped Fiber Pulse Laser Composed of All-
Polarization-Maintaining Fiber System with a Broad Tuning Range, Jpn. J. Appl. Phys. Vol. 45. No. 8A (2006)
[2] M. Hoger et al., Mode locking with cross-phase and self-phase modulation, Opt. Lett.Vol 16. No.7

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