Linearly polarized, Q-switched Er-doped fiber laser based on reduced graphene oxide saturable absorber

Abstract

We demonstrate generation of linearly polarized pulses from a passively Q-switched Erbiumdoped fiber laser. The cavity was designed using only polarization maintaining (PM) fibers and components, resulting in linearly polarized output beam with degree of polarization (DOP) at the level of 97.6%. Reduced graphene oxide (rGO) was used as a saturable absorber for Q-switched operation. The laser was capable of delivering 1.85 µs pulses with 125 nJ pulse energy at 115 kHz repetition rate.Graphene, due to its unique nonlinear optical properties, has been widely used as a saturable absorber (SA) for various types of lasers. Since the demonstration of a mode-locked fiber laser [1], many setups were presented, utilizing erbium-[1-4], ytterbium- [5,6] and thulium-doped fibers [7]. Thanks to the high modulation depth, broad operation range and ultrafast recovery time, graphene may be used to generate ultrashort pulses (e.g. 174 fs [4]) from passively mode-locked lasers. Recently, also passive Q-switching with graphene-SA has been demonstrated [8][9][10][11]. In a passively Q-switched laser, the cavity losses are automatically modulated by the saturable absorber, so there is no need of placing an active component (e.g. acoustooptic modulator) inside the resonator. The repetition rates of such lasers are lower and the pulses are longer in comparison to mode-locked lasers, but the achieved pulse energies usually exceed those which are achievable from mode-locked oscillators. Recent reports have shown the possibility of achieving 40 nJ pulses from graphene Q-switched Er-doped lasers [8]. Nevertheless, all previous reports on graphene Q-switched lasers were related to non-polarization maintaining cavities. Therefore, the polarization state of the output beam was undetermined. Such setups require polarization controllers (PC) placed in the laser cavity in order to induce the pulsed operation. In many practical applications (industrial or scientific) it is extremely important to maintain the linear polarization state of the laser output. In general, the saturable absorption in graphene is a polarization-independent process, which was verified experimentally by Zhang et al. [12]. It means, that graphene-based saturable absorbers may be used in PM cavities with only one, well-defined polarization state, without affecting the saturable absorption. This opens a possibility to generate scalar solitons in mode-locked lasers [13,14] or linearly polarized pulses from Q-switched lasers, with the DOP near to 100%.Up till now, many various methods were used to fabricate graphene saturable absorbers. For example, Bao et. al and Zhang et. al [1,2] demonstrated the usage of chemical vapor deposition (CVD) to synthetize graphene on Ni films. Also mechanical exfoliation of graphene from bulk graphite may lead to efficient fiber laser mode-locking [15]. Wet chemistry offers a wide spectrum of techniques of preparing flake graphene and its derivatives. Among them two methods are most attractive and efficient. The first is direct exfoliation of gra...

Influence of pump fiber laser conditions at 1550 nm on broadband infrared supercontinuum generation in all-solid all-normal dispersion photonic crystal fibers

“…Normal dispersion covers range up to 3 μm, which from the point of view of obtainable numerically supercontinuum bandwidth, enables to consider the fiber as allnormal dispersion. Another source demonstrated by this group was a polarization maintaining Er-doped laser 16 , passively Q-switched by a saturable absorber. The laser was capable of generating 1.85 μs pulses with 125 nJ energy at 115 kHz repetition rate.…”

Dual-wavelength fiber mode-locked laser based on graphene saturable absorber

“…Since the first demonstrations of graphene mode-locked laser [10,13] a lot of works on graphene based lasers have been presented [10,[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. The Q-switched operation of graphene-based lasers has been also presented [29,30]. Thanks to wavelength independent absorption characteristic of high quality graphene, the mode-locked operation based on such SA was demonstrated in the spectral range from 800 nm [28] to 2500 nm [27].…”

“…SESAM technology based on quantum well structures involves also complicated molecular beam epitaxy (MBE). These weaknesses cause that the new class of materials like carbon nanotubes [5][6][7][8][9][10], graphene [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] and topological insulators [31][32][33] have been recently considered as broadband and cost effective SAs. First, single-walled carbon nanotubes (SWCNT) have been used as an effective SA [5].…”

Passively Q-switched fibre laser based on interaction of evanescent field in optical microfibre with graphene-oxide saturable absorber

“…1a shows the Raman spectrum of the GO solution. The spectrum indicates two peaks, D and G. The D peak measured at 1355 cm -1 originates from a C-C bond, whereas that referred to as G is located at 1606 cm -1 and arises from the first scattering of E 2g phonon at SP 2 C atoms [19,20]. Fig.…”