Silicon based mechanic-photonic wavelength converter for infrared photo detection

The development of optical circuits integrated on silicon has been gaining significant momentum in the field of telecommunication. Silicon has for a long time been the major platform for electronics. Silicon is also perfect for photonics owing to its good thermos-dynamical, mechanical, and optical attributes. Above all, an array of semiconductor fabrication methods developed for silicon can be implemented for the fabrication of silicon Nano photonic devices. Moreover, silicon has a high refractive index that allows for the synthesis of high-Q nano cavities as well as low-loss waveguides.

Unfortunately, silicon has its own limitations and is not an effective material with regards to telecom-light detection due to the fact that it does not absorb light at a wavelength above 1µm. A number of methods have been proposed to mitigate this problem such as internal photoemission effect, sub-band gap photo-effect, two-photon absorption, and thermal nonlinear effect. In addition, the quantum efficiency of the above methods is still, low, and most of these methods have high noise levels owing to the generation and recombination of electron-hole pairs.

Researchers led by Professor Zeev Zalevsky at Bar Ilan University in Israel presented a new concept of a mechanical-photonic wavelength converter in silicon that could be implemented as an infrared detector not based on absorption. The device was designed for the conversion of amplitude modulated infrared wavelength of incidence into a different reference wavelength with the same amplitude modulation while the reference wavelength was below 1µm, and hence could be measured by a silicon detector. Their research work is published in peer-reviewed journal, Optics Communications.

The proposed mechanical-photonic wavelength converter uses an optical gradient forced initiated on a silicon Nano rod by electromagnetic field of incident illumination. When an infrared beam is focused on the surface filled with silicon Nano rods, then the photonic gradient force that is laterally directed results in a mechanical bending of the Nano rod. The gradient force is nearly not dependent of the wavelength; therefore, the sensitivity of the mechanical-photonic wavelength converter in nearly all spectral ranges is almost the same.

The proposed concept could realize ultra-wide band silicon photodetector and an ultrasensitive one. This was a significant step towards the development of an ultra-wideband camera. The author modelled and simulated the concept through Comsol and Matlab.

The research team matched the solution obtained from the Comsol Software with the modeling they independently did using Matlab. These two orthogonal methods to the problem confirmed the physics behind the proposed concept. The authors also performed fabrication validation of their designed. This was because the proposed device could not be realistic for practical applications. In their testing, the authors were able to detect a change in electrical attributes of the Nano capacitor versus the applied externa photonic stimulation.