Actively Q-switched all-fiber laser with an electrically ... - OSA Publishing

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Abstract: Actively Q-switching of an all-fiber laser system is demonstrated. The active element is a polarization switch with nanosecond risetime based.
Actively Q-switched all-fiber laser with an electrically controlled microstructured fiber Zhangwei Yu1,2, M. Malmström1,2, O. Tarasenko2, W. Margulis1,2* and F. Laurell1 1

Dept. of Applied Physics, Royal Institute of Technology (KTH), Roslagstullbacken 2, SE-106 91 Stockholm, Sweden 2 Department of Fiber Photonics, Acreo, Electrum 236, SE-164 40 Kista, Sweden *[email protected]

Abstract: Actively Q-switching of an all-fiber laser system is demonstrated. The active element is a polarization switch with nanosecond risetime based on a microstructured fiber with electrically driven internal electrodes. Optical feedback between two 100% reflectors is inhibited until a nanosecond current pulse Q-switches the laser. After a short optical pulse develops several roundtrips later, the fiber switch is turned off, removing the short optical pulse from the cavity through a polarization splitter. Pulses of 50 W peak power and ~12 ns duration are obtained with 400 mW pump power at 100 Hz. ©2010 Optical Society of America OCIS codes: (060.2410) Fibers, erbium; (060.4005) Microstructured fibers; (140.3510) Lasers, fiber; (140.3538) Lasers, pulsed.

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#125395 - $15.00 USD Received 12 Mar 2010; revised 30 Apr 2010; accepted 30 Apr 2010; published 11 May 2010

(C) 2010 OSA

24 May 2010 / Vol. 18, No. 11 / OPTICS EXPRESS 11052

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1. Introduction Q-switching of fiber lasers is an established technique to generate short pulses with high peak power and has many applications, such as optical time-domain reflectometry, material processing, remote sensing and nonlinear optical frequency conversion [1,2]. All-fiber devices for Q-switching are advantageous due to their alignment-free characteristics and lower cavity loss. Although passive Q-switching usually involves a simple laser cavity and produces highpower short duration pulses [3–10], the repetition frequency and the pulse timing are often uncontrolled. In contrast, active Q-switching uses external means to determine the loss of the laser cavity and allows for more control over the characteristics of the output pulses. Therefore, actively Q-switched lasers are the usual choice for industrial applications. The most common scheme for producing high power pulses from a fiber laser is the master oscillator power amplifier (MOPA) configuration, where a semiconductor laser pulse seeds a fiber power amplifier [11]. This technique is very powerful and is widely used. However, the MOPA configuration also has its weak points, such as the need for a few amplifying stages and very careful isolation of the seed laser from feedback. This motivates the search for a simpler Q-switching scheme that allows for the direct generation of a high-power short duration pulse by a fiber laser. This could potentially eliminate the need for some of the amplifier stages and a sensitive semiconductor laser diode seed. In the last years, several successful all-fiber approaches based on different modulation techniques have been reported, such as all-fiber intensity modulators [12], all-fiber acousto-optic attenuators [13–15], and a microsphere resonator [16]. Q-switching of all-fiber lasers has been accomplished by tuning fiber Bragg grating (FBG) using acousto-optic modulators [17–19], piezoelectric actuators [20,21], magnetostrictive transducers [22], and temperature controllers [23]. Problems with these methods include mechanical relaxation, hysteresis, slow rise- and falltime and low extinction ratio. In our previous work, a microstructured fiber with electrically driven internal electrodes has been employed to cavity dump an all-fiber erbium-doped ring laser [24]. The internal electrode fiber component allows for polarization rotation of light guided in the core with a risetime