NOEMS devices based on Slot-Waveguides Vilson R. Almeida 1,2 and Roberto R. Panepucci 3 1 – Instituto de Estudos Avancados, Sao Jose dos Campos – SP, BRAZIL 2 – Instituto Tecnologico de Aeronautica, Sao Jose dos Campos – SP, BRAZIL 3 – Florida International University, Miami, FL, USA e-mail address: vilson@ieav.cta.br Abstract: We present device applications for Nano-Opto-Electro-Mechanical System (NOEMS) structures based on the evanescent-wave bonding acting on silicon slot-waveguides. Useful all- optical or electrooptical functionalities include: phase modulation, polarization mode dispersion, near-field probing and reconfigurable optical delay. ©2007 Optical Society of America OCIS codes: (230.7390) Waveguides, planar; (230.4110) Modulators; (130.3120) Integrated optics devices. 1. Introduction Slot-waveguides are channel-type high-index contrast optical structures that present a slot filled with low-index material or even void [1-2], as shown in Fig 1; its unique optical properties depend strongly on the slot width as well as on the refractive index contrast, which ensues a wide variety of applications for slot-based devices. Povinelli et al. have shown that slot-waveguides experience forces between its two sides, which are due to dipole moments induced by the guided light intensity [3]; the force may be either attractive or repulsive, depending on the relative phase of the dipole moments, dictated by the optical properties and the geometrical parameters of the waveguide. A suspended section of a slot-waveguide deprived from cladding thus may experience significant mechanical deformation. For instance, the optical forces lead to useful mechanisms that may be used for novel all-optical control approaches, such as turning the slot-waveguide into a NOEMS device based on all-optical pump-probe method [4]. Cross-sections used in this work are as shown in Fig. 1(a). Ref. 3 shows that the resonance frequency for a 30- μm long cantilever stays around the MHz range. However, for a 1-μm long (L) beam slot-waveguide, our theoretical predictions indicate that mechanical resonance can reach up to 2.2 GHz for a fixed (doubly-clamped) beam seen in Fig. 1(b), and up to 340 MHz for a cantilever (simply-clamped) beam seen in Fig. 1(c). Large on-resonance mechanical amplitudes may be achievable with relatively low optical driving intensities. SiO2 Si substrate SiO2 L SiO2 Si substrate L Fig. 1. (a) Slot-waveguide cross-section. (b) Slot-waveguide fixed beam. (c) Slot-waveguide cantilever beam. We considered a wavelength of λ 0 = 1550 nm, Si (n Si = 3.48) in the high-index core and air (n 0 = 1) in the low- index cladding. The quasi-TE eigenmode exhibits field enhancement effect, as opposed to the quasi-TM counterpart, being more sensitive to the slot width variation [4]. For the quasi-TE case, Fig. 2(a) shows the absolute attractive (negative) forces acting on a slot-waveguide, which can make it yield in its suspended section, thus undergoing deformation, as seen in Fig 2(b); for a beam length of L = 50 μm and an unperturbed slot width of d ini = 50 nm, we predict that deflection collapse occurs for optical power of P 0 = 0.69 W and at a central slot width of d min = 19 nm. The deflection collapse is similar to the critical distance in typical Micro-Electro-Mechanical Systems (MEMS). The slot width at a specific point of the beam is calculated by solving the (static) mechanical differential equation as done in Ref. 3. It is worth noting that experimental research has shown that silicon Young’s modulus decreases as the beam transverse dimensions decrease [5], which prompts even larger deformations for narrow slot-waveguides. 2. Applications Slot-waveguide may also be partially subject to electrostatic forces, bringing full NOEMS capabilities. The combined optical, mechanical, and electrostatic properties of Si/SiO 2 slot-waveguides make them useful for NOEMS devices capable of achieving several functionalities, such as: phase and/or amplitude modulation, polarization mode dispersion (PMD) compensation, group velocity dispersion (GVD) compensation, tunable delay 240 nm 280 nm slot width (a) (b) (c) a1823_1.pdf JThD104.pdf