Atomic layer deposition of optical coatings inside microchannels

An air wedge was created, between 2 square wafers of silicon approximately 7 cm on a side, with the air gap varying in thickness linearly from 0-1650 mum over 7 cm. A Fabry-Perot optical cavity composed of an atomic layer deposition (ALD) Al
₂
O
₃
/HfO
₂
multilayer was deposited inside the wedge, and the measured resonant wavelength only shifted by -10.3% over a distance of 6 cm along the gas flow direction and over a 118-1533 mum range of gap thickness.The first experiments to test optical coatings inside microchannels were performed using 12 cm long glass capillary tubes with an interior dimension defined by a square 500 mum opening, a 240:1 aspect ratio.