Wide and continuous dynamic tuning of period, modulation depth and duty cycle of a laminar-flow-based microfluidic grating.

Flexible diffraction gratings that can be dynamically tuned in terms of both diffraction efficiency and diffraction angles are very important components for various applications, and fundamentally can be tuned through varying the modulation depth, duty cycle and grating period. However, dynamic and continuous tuning of a grating in all three aspects is difficult and has never been demonstrated hitherto. We propose and successfully fabricate a laminar-flow-based microfluidic grating in which all the three parameters can be dynamically tuned by simply varying flow rates into several liquid inlets. A 32-period liquid grating is generated by using ethanol and benzyl alcohol as alternate liquid lamellae. The total diffraction efficiency is tuned between 0 and 99%, and the maximum diffraction efficiency of the first order is ∼27%. The duty cycle of the grating is dynamically tuned from 7.6% to 91.5%. The grating period is compressed from more than 22 μm to less than 4 μm, leading to tuning of the first order diffraction angle from 1.7° to 9.2°.