Silicon optomechanics

Research Area: Integrated nonlinear optics

Main Researcher: Dries Van Thourhout

The high refractive index contrast and excellent mechanical properties of monocrystalline silicon make SOI a suitable platform for mechanical nanophotonic structures. Typically a part of a nanophotonic waveguide is underetched such that it is able to move. Additionally in a nanophotonic waveguide light is confined in such a way that strong spatial field gradients exist which give rise to strong optical gradient forces. The nature of this force is related to the forces used for free space optical tweezing and trapping of microparticles.

Underetched parallel waveguide pair

On chip however this novel actuation force enables a new class of integrated optomechanical devices (Micro-optomechanical systems = MOMS vs. classical Micro-electro-mechanical systems=MEMS). We demonstrated this on-chip optical force between waveguides in several experiments including attractive force between two nanophotonics waveguides and optical force in a slotted waveguide. Typically these forces are of the gap closing type just like the standard capacitive closing gap actuation found in classical MEMS.

A few years age we were able to demonstrate that with optomechanical actuation an extra degree of freedom is available and that it is possible to tune the sign of the force from attractive to repulsive. For this purpose the structure shown in the picture was designed and fabricated. The region labeled “waveguide string pair” consists of two parallel waveguides.
The rest of the structure is basically a construction which enables us to alter the distribution of light energy between the parallel waveguides when sweeping wavelength. Finally the force arising between the parallel waveguides could be tuned from attractive to repulsive with wavelength. To detect and quantify this ultra-small force also the development of calibration schemes and accurate optical sensing techniques were required. The experiment can be considered a breakthrough of both fundamental and practical importance

Waveguide string pair in an unbalanced Mach Zehnder Interferometer configuration

Currently we are investigating different application of on-chip optomechanical chips, including broadband sensing and parametric amplification

Other people involved:

• Joris Roels
• Alexandre Bazin
• Jesper Hakansson
• Paul Tiebot
• Zhenzhou Tang
• Awanish Pandey
• Khannan Rajendran
• Roel Baets
• Irfan Ansari
• Raphael Van Laer
• Dries Van Thourhout
• Debdutta Basu

PhD thesises