Design of organic 3D microresonators with microfluidics coupled to thin-film processes for photonic applications N. Huby a , D. Pluchon a , N. Coulon b , M. Belloul a , A. Moreac a , E. Gaviot c , P. Panizza a , B. Bêche a,d, * a IPR UMR CNRS 6251, Université de Rennes 1, bât. 11B, 263 avenue Général Leclerc, 35042 Rennes, France b IETR UMR CNRS 6164, Université de Rennes 1, bât. 11B, 263 avenue Général Leclerc CS 74205, 35042 Rennes Cedex, France c LAUM UMR CNRS 6613, Université du Maine, avenue O. Messiaen, 72085 Le Mans Cedex, France d IUF, Institut Universitaire de France, 103 bd Saint-Michel, 75005 Paris, France article info Article history: Received 19 November 2009 Received in revised form 7 December 2009 Accepted 27 January 2010 Keywords: Integrated optics 3D organic microresonators Whispering Gallery Modes Organic compounds Applied complex fluid mechanism abstract We report on the design and realization of photonic integrated devices based on 3D organic microreson- ators (MR) shaped by an applied fluid mechanism technique. Such an interdisciplinary approach has been judiciously achieved by combining microfluidics techniques and thin-film processes, respectively, for the realizations of microfluidic and optical chips. The microfluidic framework with flow rates control allows the fabrication of microresonators with diameters ranging from 30 to 160 lm. The resonance of an iso- lated sphere in air has been demonstrated by way of a modified Raman spectroscopy devoted to the exci- tation of Whispering Gallery Modes (WGM). Then the 3D-MR have been integrated onto an organic chip and positioned either close to the extremity of a taper or alongside a rib waveguide. Both devices have proved efficient evanescent coupling mechanisms leading to the excitation of the WGM confined at the surface of the organic 3D-MR. Finally, a band-stop filter has been used to detect the resonance spectra of organic resonators once being integrated. Such spectral resonances have been observed with an inte- grated configuration and characterized with a Dk = 1.4 nm free spectral range (FSR), appearing as stem- ming from a 78 lm-radius MR structure. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction Optical microresonators deserve a large attention due to their unique optical properties required for a wide range of applica- tions such as filtering/demultiplexing, optical switching and bio- logical sensing [1]. Various 2D and 3D shapes have been reported according to the desired functionality including disks and rings, toroids, and cylinders [2,3]. Last years, silica spheres have attracted a noticeable interest, using various evanescent excitation methods [4–6], due to their specific modes confined by continuous total internal reflection and localized within the surface of the sphere. In addition to such extreme confinement of the field, these so-called Whispering Gallery Modes (WGM) present highly increased photonic lifetimes as a paramount qual- ity for building efficient photonic devices. The surface quality of 3D microresonators (MR) and the lower intrinsic material losses [7] are crucial aspects to obtain high quality Q-factors and long photon lifetimes s = Q/x for ultra-fine bio-sensing applications based on the evanescent probe localization [8]. Regarding WGM excitation in such 3D resonators, specific processes are developed with a view to advantageously coupling and densely packaging photonic MR with other relevant integrated structures and micro- systems such as prisms, fibers, planar waveguides, tapers, sub- wavelength photonic crystal structures. Considering a specific 3D-geometry with relative large radius curvature and lower roughness, such MR will present, respectively, a sufficient surface in contact with the environment and lower optical propagation losses; in that way the development of good quality photonic microresonators is strongly dependent on the structural design of new materials and their fabrication processes. The latter based on polymers present many advantages such as low cost and high speed processing, good mechanical properties and unmatched composition versatility, making them highly attractive for integrated photonic applications [9–11]. Moreover, MR poly- mers materials can be made biocompatible and most proper to the integration onto similar organic waveguides structures. The epoxy-based negative photoresist SU8 (biphenol A ether glycidyl polymer manufactured by MicroChem Corp.) is one of the most studied since it presents appropriate refractive index, optical quality, and chemical stability [12]. This material is now proved most suitable for 2D and 2.5D organic structures such as waveguides, Mach–Zehnder interferometers [13] and disk and ring 0030-4018/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2010.01.065 * Corresponding author. Address: IPR UMR CNRS 6251, Université de Rennes 1, bât. 11B, 263 avenue Général Leclerc, 35042 Rennes, France. Tel.: +33 (0)2 23 23 52 57; fax: +33 (0)2 23 23 61 98. E-mail addresses: nolwenn.huby@univ-rennes1.fr (N. Huby), david.pluchon@ univ-rennes1.fr (D. Pluchon), bruno.beche@univ-rennes1.fr (B. Bêche). Optics Communications 283 (2010) 2451–2456 Contents lists available at ScienceDirect Optics Communications journal homepage: www.elsevier.com/locate/optcom