Spie Laser Beam2011

8/3/2019 Spie Laser Beam2011

http://slidepdf.com/reader/full/spie-laser-beam2011 1/2

10.1117/2.1201103.003512

All-ber laser generatescylindrical vector beamsLixin Xu, Rui Zheng, Chun Gu, Anting Wang, and Hai Ming

A very simple approach enables fabrication of an all-ber laser withswitchable radial and azimuthal polarization states.

Cylindrical vector (CV) beams are optical beams whose polar-ization states exhibit cylindrical symmetry across their crosssections (see Figure 1). This is different from traditional polariza-tion types, such as linearly, elliptically, and circularly polarized beams, where the polarization state is spatially homogeneousacross the beam’s cross section. 1 CV beams exhibit unique focus-ing properties through high-numerical-aperture lenses. Beamswith radial polarization can be focused onto a smaller spot thantraditionally polarized beams characterized by strong and local-ized longitudinal components. A focal spot as small as 0.16 2

(where is the operational wavelength) has been obtained forradial polarization using an annular aperture. For azimuthallypolarized beams, the focused eld yields a doughnut-shapedspot with a symmetrical polarization distribution. 1 The uniquefocusing properties of CV beams facilitate novel applicationsof cylindrically polarized beams, including particle trapping, 2

material processing, 3 and surface-plasmon excitation. 4

Fiber lasers have attracted signicant interest during themost recent two decades because of their high efciency, com-pact design, and exibility. CV beams can also be generatedin optical bers. According to waveguide theory, the lowest-order transverse-electric (TE 01 ) and transverse-magnetic (TM 01 )modes in step-index bers are characterized by cylindricalpolarization 5 (see Figure 2). To generate a CV beam, we onlyneed to excite TE 01 and TM 01 modes in a few-mode ber.

We present a very simple method to fabricate an all-ber laserthat generates CV beams 6, 7 (see Figure 3). It consist of a sec-tion of ytterbium (Yb) ber, a Sagnac loop mirror, a 980/1060nmwavelength division multiplexing coupler, ber collimators withoperational wavelengths of 1060 and 1550nm, a section of SMF-28 single-mode ber, and a 980nm laser diode. The Yb ber isused as gain medium, while the SMF-28 ber (highlighted inred in Figure 3) acts as few-mode ber for the 1060nm band. We

obtained CV beams by exciting TE 01 or TM 01 modes in the

Figure 1. Polarization distribution of cylindrical vector (CV) beams.(a) Radially polarized. (b) Azimuthally polarized. (c) CV beam asa linear superposition of (a) and (b). Arrows denote polarizationdirections.

Figure 2. Polarization distribution of LP11 linearly polarized modes instep-index bers. TM, TE: Transverse magnetic, electric. HE: Hybridelectric.

Figure 3. Experimental setup for CV-beam generation. WDM: Wave-length division multiplexer. Yb: Ytterbium.

few-mode ber. This was implemented through adjusting theangles and transverse dimensions of the ber collimators. Theradially and azimuthally polarized beams can be switched

Continued on next page

8/3/2019 Spie Laser Beam2011

http://slidepdf.com/reader/full/spie-laser-beam2011 2/2

10.1117/2.1201103.003512 Page 2/2

Figure 4. Intensity distribution of the CV beam.

Figure 5. Radially polarized beam with different polarizationdirections.

conveniently by simply applying twists or pressure to the few-mode ber. Figure 4 shows the doughnut-shaped intensity dis-tribution of the CV beam (recorded on a CCD). To measure thepolarization distribution of the laser beam, we inserted a tunable

linear polarizer in the light path prior to the CCD recorder.In general, when a polarizer is placed in the light path after aCV beam has been generated, two lobes appear in the result-ing intensity prole. Figures 5 and 6 illustrate the radial andazimuthal polarization states, respectively. White arrows indi-cate the polarization directions. Radial polarization is indicated by the dark line between the two lobes orthogonal to the polar-ization direction. Thereverse occurs in the presence of azimuthalpolarization (see Figure 6).

In summary, we obtained CV beams from a new all-ber laserwith two ber collimators as mode lter. Different CV-beamstates, characterized by radial and azimuthal polarization, are

Figure 6. Azimuthally polarized beam with different polarizationdirections.

switchable, while the CV-beam ber laser is also very compactand easy to fabricate. We will further develop our all-ber laserfor practical use.

Author Information

Lixin Xu, Rui Zheng, Chun Gu, Anting Wang, and Hai MingUniversity of Science and Technology of China

Hefei, ChinaReferences1. Q. Zhan, Cylindrical vector beams: from mathematical concepts to applications, Adv.Opt. Photon. 1 , pp. 1–57, 2009.2. Q. Zhan, Trapping metallic Rayleigh particles with radial polarization, Opt. Express12 (15), pp. 3377–3382, 2004.3. M. Meier, H. Glur, E. Wyss, Th. Feurer, and V. Romano, Laser microhole drillingusing Q-switched radially and tangentially polarized beams, Proc. SPIE 6053 , p. 605312,2006. doi:10.1117/12.6604544. A. Bouhelier, F. Ignatovich, A. Bruyant, C. Huang, G. Colas des Francs, J.-C. Weeber, A. Dereux, G. P. Wiederrecht, and L. Novotny, Surface plasmon inter- ference excited by tightly focused laser beams, Opt. Lett. 32 , pp. 2535–2537, 2007.5. A. W. Snyder and J. D. Love, Optical Waveguide Theory , Chapman & Hall,1983.6. R. Zheng, C. Gu, A. Wang, L. Xu, and H. Ming, An all-ber laser generating cylin-drical vector beam, Opt. Express 18 (10), pp. 10834–10838, 2010.7. L. Xu, R.Zhen,C. Gu, A.Wang, and H.Ming, An all-ber laser for cylindrical vectorbeam, Proc. Photon. Asia , pp. 7847–7841, 2010.

c 2011 SPIE