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Playing guitar with photons (part 2): Optomechanical method


By
Ronghui Lin

April 24, 2017 - Posted in Discussion
Another method to change the frequency of a photon is by optomechanical devices. The concept that wave will change its frequency when reflected by a moving object is widely known as the Doppler Effect. Optomechanical photon frequency shift adopts very similar concept: The frequency of photons will change when introduced into a cavity or waveguide with mechanical vibration.  The frequency shift δω is proportional to the mechanical deformation δx[1]:

1.png

Recently, a group of scientist demonstrated a single-photon frequency shifter by adopting this principle [1]. They fabricated an AlN waveguide which can vibrate when electric field was applied due to the piezoelectric effect of AlN. This vibration caused periodic refractive index change along the optical path that can shift the photon frequency up to 150 GHz. They found that the frequency shift was very sensitive to both the phase of the vibration and the driving power of the vibration which provided a method to control the amount of frequency shift. 

2.png 
Fig.1 Optomechanical photon frequency shifter[1]. 
 
As the author p​ointed out, this method of frequency shift wouldn’t introduce much noise compared to nonlinear optical process because high intensity optical pumping was not necessary. But the drawback was that the range of frequency shift is limited by mechanical vibration frequency, which is relatively low compared to visible light.

It is fascinating to see how optical and mechanical waves, which are seemingly different, to interact with each other. In fact, by combing mechanicalhanica​l and optical resonator, a lot of other applications has been developed [2, 3]. 


Reference
 

[1] Fan, L.R., et al., Integrated optomechanical single-photon frequency shifter. Nature Photonics, 2016. 10(12): p. 766

[2] Bochmann, J., et al., Nanomechanical coupling between microwave and optical photons. Nature Physics, 2013. 9(11): p. 712-716.

[3] ​Ba​lram, K.C., et al., Coherent ​coupling between radiofrequency, optical and acoustic waves in piezo-optomechanical circuits. Nature Photonics, 2016. 10(5): p. 346




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