Single and multiple optical switches that use freestanding silicon nanowire waveguide couplers

Abstract

Silicon photonic devices consisting of nanowire waveguides are a promising technology for on-chip integration in future optical telecommunication and interconnection systems based on silicon-large scale integration fabrication. However, the accommodation of variable optical components on a chip remains challenging due to the small size of microchips. In this study, we investigated the characteristics of a microelectromechanical silicon nanowire waveguide switch with a gap-variable coupler. Due to its capacitive operation, the proposed waveguide switch consumed negligible power relative to switches that use a thermo-optical effect and carrier injection. The proposed switch was characterized using analyses based on coupled-mode theory for rectangular waveguides, as well as a simulation using the finite difference time domain method. A 232 single switch with an improved configuration and a 236 multiple switch composed of the 232 switches was designed and fabricated by a combination of electron beam lithography, fast-atom beam etching and hydrofluoric acid vapor sacrificial etching. The properties of the switches were measured and evaluated at a wavelength of 1.55 mm. 1 The monolithic fabrication of silicon waveguides and silicon electronics is useful for future integration in opto-electronic systems. Due to the high refractive index of silicon (,3.5 at a wavelength of 1.5 mm), silicon waveguide circuits can be miniaturized to be several orders of magnitude smaller than silica waveguide circuits. Several types of circuits that employ submicron-scale silicon waveguides, such as waveguide splitters/couplers and micro-rings, 2-4 have been reported. In addition, a waveguide switch that uses a thermo-optical effect 5 and an ultra-fast silicon waveguide light modulator based on changes in the refractive index of silicon by carrier injection 6 have been reported. Recently, submicron-scale waveguide switches for optical path changes using the nano-mechanical motions of electrostatic actuators have been reported. 7 Due to the very low power consumption associated with capacitive operation, this technology suits the large-scale integration and reduced energy consumption requirements of telecommunication systems. [8][9][10][11][12][13][14][15][16] Among these waveguide circuits, coupler switches have attracted interest due to the use of non-contact low-loss mechanisms.13,15 A coupler switch using InP waveguides was operated by applying electrostatic forces between the freestanding waveguides. 13 In the case of a parallel-electrode actuator, a coupler gap smaller than two-thirds of the initial gap is not consistently controllable due to force instability. Using an in-plane comb-drive actuator, stable low-voltage operation has been realized for silicon waveguides.

Design of dual-core optical fibers with NEMS functionality

“…Our system is thus the fiber equivalent of chip-based optical MEMS switches based on two evanescently coupled waveguides as demonstrated recently for example in silicon [12] and InP [13]. Comb actuators are usually used for moving sub-micron sized guiding beams and waveguides on chips [14].…”

Nano-opto-electro-mechanical switch based on a four-waveguide directional coupler

“…of the cantilever. The proposed switch has a switching actuation displacement of only 55 nm, which is one order of magnitude smaller than the previous designs [16,[18][19][20]. For crosstalk below −20 dB, the displacement tolerance is −3 nm /+4 nm and the corresponding voltage tolerance is −6 mV/+7 mV, according to the simulations.…”

“…One can control this transfer simply by tuning the coupling rate between the waveguides (e.g. by varying their distance), which is the principle of most micro/nano electromechanical switches based on directional couplers [18][19][20][21]. From the optical point of view, as most waveguides have a height/width aspect ratio lower than one, vertical actuation is more efficient because of larger mode overlap, compared to horizontal one.…”

“…Micro-electromechanical optical switches are mostly based on mechanically displaceable mirrors [12,15], which are power-efficient but are difficult to integrate and therefore difficult to scale. Recently, micro-/nano-electromechanical optical switches based on movable waveguides have been reported [16,[18][19][20][21][22], which are more compact and can be integrated in photonic integrated circuits. However, most designs require a displacement of several hundreds of nanometers for switching operation, resulting in a high actuation voltage [16,[18][19][20][21][22], which limits their practical application.…”

Silicon-based on-chip multiplexing technologies and devices for Peta-bit optical interconnects

“…of a nano-slot can be realized by using e.g., optical forces [71], or electrostatic comb-drive actuators [72].…”