Femtosecond laser fabrication of waveguides in DR13-doped PMMA P.H.D. Ferreira n , R. Stefanutti, F.J. Pavinatto, C.R. Mendonça Instituto de Física de São Carlos, Universidade de São Paulo, Caixa Postal 369, 13560-970 São Carlos, SP, Brazil article info Article history: Received 9 September 2013 Received in revised form 17 December 2013 Accepted 21 December 2013 Available online 7 January 2014 Keywords: Microfabrication Waveguides Femtosecond lasers Polymers absctract This work demonstrated the fabrication of tubular waveguides in bulk samples of PMMA doped with Disperse Red 13 (DR13) by oscillator only fs-laser micromachining. We studied the influence of the incident pulse energy on the diameter and quality of the fabricated waveguides by analyzing optical microscopy images. HeNe laser (632.8 nm) was coupled into the fabricated waveguides, revealing an annular intensity distribution resulting from the superposition of propagation modes with azimuthal symmetry. The averaged total loss of the fabricated waveguides was estimated as 0.8 dB/mm. Residual birefringence was observed in the produced waveguides, probably generated during the fabrication process, which prevented determining optically induced birefringence owing to the presence of the azochromophore DR13. & 2014 Elsevier B.V. All rights reserved. 1. Introduction In the last decade years, femtosecond lasers have been largely used for the production of microstructures such as interferometers, waveguide couplers and decouplers, gratings, switches, and ampli- fiers [1–8]. The use of fs-laser micromachining has some advantages in relation to other techniques employed for waveguide fabrication, such as photolithography, high-energy ion implantation and reactive ion etching [9]. The latter methods often need prior design and fabrication of masks, being inherently planar technologies that require numerous processing steps. On the contrary, fs-laser fabrica- tion allows single-step, maskless and direct processing [9–12]. Furthermore, micromachining with fs-laser pulses allows the pro- duction of 3D micro- and nano-structures [13]. The interest on developing polymer-based optical technologies has grown in the last years because they present some advantages over glass, such as easiness of processing and fabrication and low cost of production. Moreover, polymeric materials can be engi- neered to present certain properties such as, for instance, electro- optic coefficient, nonlinear optical response and enhanced photo- sensitivity aiming at applications [14], such as optical storage and electro-optic modulators. In particular, poly(methyl methacrylate) (PMMA), whose monomer molecular structure is shown in Fig. 1(a), is an inexpensive and widely used polymer for the production of optical components due to its high transmission in the visible and near-infrared, and the similarity of its refractive index to that of standard optical fibers, which favors coupling to existing fiber technologies. For example, the first demonstration of tubular waveguides in PMMA was reported by Zoubir et al. [15]. Further- more, organic chromophores or inorganic compounds, such as rare-earth ions [16], can be incorporated into its polymeric matrix to develop devices aiming at specific applications [17]. In this paper we demonstrate the fabrication of waveguides by femtosecond laser micromachining in PMMA doped with the chro- mophore Disperse Red 13 (DR13) [18,19]. DR13 is an azoaromatic chromophore, also known as azochromophore, whose molecular structure is presented in Fig. 1(b). Azochromophores possesses interesting linear and nonlinear optical properties, which can be exploited for electro-optic modulators [20], second-harmonic gen- eration [21] and birefringent devices [22,23]. After studying the experimental conditions for waveguides fabrication in the PMMA/ DR13, which presented tubular structure, they were characterized by optical microscopy. We demonstrated the functionality of the fabri- cated waveguides by measuring the near-field intensity distribution at the waveguide output, as well as its guiding efficiency. Because the produced waveguides presented residual birefringence, generated during fs-laser fabrication, we have not been able to observe any optically induced birefringence, although it was observed in bulk PMMA/DR13. 2. Experimental The PMMA/DR13 sample was prepared by bulk polymerization. [4 0 [[2-(methacryloyloxy) ethyl] ethylamino]-2-chloro-4-nitroazo- benzene methacrylate] DR13Ma (Aldrich) was used as obtained. Methyl methacrylate (MMA) (Aldrich) was distilled before use. The bulk polymerization was carried out in a glass ampoule in which 18.72 g (0.1872 mol) of MMA, 0.021 g (5.037  10 6 mol) of DR13Ma and 0.0032 g of 2,2-azobisisobutyronitrile (AIBN) were added. The ampoule was cooled in liquid nitrogen and placed in a vacuum before Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/optcom Optics Communications 0030-4018/$ - see front matter & 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.optcom.2013.12.066 n Corresponding author. Tel.: þ55 16 3373 8085x211. E-mail addresses: paulohdf@gmail.com, paulohdf@ursa.ifsc.usp.br (P.H.D. Ferreira). Optics Communications 318 (2014) 53–56