A conventional approach for beam steering is using tunable phased arrays, which typically consist of tens or even hundreds of emitters. In optics, phased arrays can be made extremely small by using integrated photonics, but the tuning of each element of the array, which is typically achieved thermally or electrooptically, results in high power consumption. To solve this issue, Carlos Errando-Herranz and coworkes have conceived a device that revolutionizes the way of steering the light. In their idea, the array of phase-controlled emitters is replaced by just a single element, consisting of a suspended micro-electromechanically actuated waveguide grating. The grating is fabricated on a silicon photonic platform and radiates the light coming from an optical waveguide to free space. Pulling and stretching the grating through a voltage control signal, the spacing between the teeth of the grating can be modified on demand, in such a way that the direction of the out-of-plane angular emission is steered. The power consumption required for the steering is remarkably low, in the sub-μW range, which means more than 5 orders of magnitude lower than that of thermo-optic tuning methods and 10 times lower than electro-optic devices. The steering angle of this first proof-of-concept device is still rather limited, about 5.6 degrees with 20 V actuation, but the authors are confident that further optimizations in the fabrication process can widen the steering angle to 30 degrees or more with 40 V actuation.
After that, can we conclude that phased arrays are obsolete? Not at all, I would say. The good news is that now we have another available option for optical beam steering and, given the large number of applications requiring these features, this new concept is likely to find its place, especially in applications where low cost and low power consumption are key requirements.
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