Project overview

The semiconductor platform is highly versatile and extremely well suited for the realisation of integrated quantum photonic circuits. Key capabilities include the ability to embed single photon emitters such as quantum dots (QDs) within nano-photonic cavities and waveguides in a scalable fashion, and to control their optical properties using local electric and optical fields.

Notably however, the platform is promising from more than simply an optical perspective. For instance, the possibility of mechanical control of nano-photonic devices has recently seen increasing attention. This can be achieved using a number of approaches operating across a wide range of frequencies, from electrostatic displacement (position tuning) of device components to very high frequency strain modulation using surface acoustic waves.

In our group, we are currently investigating the use of cantilevers and comb-drive actuators for in-situ tuning of integrated optical components such as photonic beamsplitters. Such an approach could not only allow fine tuning of fabricated structures to better match design, but also enable the realisation of reconfigurable quantum photonic circuits.

Electro-mechanical control of an on-chip optical beam splitter

The beamsplitter is a fundamental optical element in quantum optics. When miniaturised to the micro-scale, fabrication imperfections can result in a deviation of the final splitting ratio from design (most commonly targeted at 50:50 splitting). In this work, we developed a robust, repeatable technique to tune the splitting ratio in-situ. One arm of the beamsplitter was mounted on a mechanically pliable cantilever, which could be electrostatically displaced towards the substrate upon application of a control bias. This in turn tuned the vertical separation of the two arms of the beamsplitter, therefore controlling the splitting ratio. We used an embedded QD as a light source to demonstrate operation of the device, showing that it is compatible with integration with single photon emitters. Future designs will enable access to the optical output from the displaced arm of the output, therefore allowing cascaded integration in larger photonic circuits. Our technique could also be used to switch the beamsplitter between 50:50 and 67:33 operation, as required for reconfigurable quantum photonic networks.

a) Beamsplitter operation at zero bias. A QD is optically excited in the input arm, and emits light into the beamsplitting region (middle of device). PL emission is evident from both outcouplers (OCs) on the right of the device, indicating that the emitted light emitted is redistributed (split) by the device as expected. PL emission from the input arm OC is unavoidable but of no relevance to the device operation. b) Beamsplitter operation at non-zero bias, with the lower half of the device displaced towards the substrate. The two arms of the beamsplitter are decoupled, and light is no longer detected from the bottom right ‘drop’ OC.

Further reading on this topic: Optics Letters 43(9) 2142 (2018)