All-optical switch is based on photochromic-doped waveguides

Researchers at Kwangju Institute of Science and Technology (Kwangju, Korea) have developed an all-optical switch comprised of a photochromic-dye-doped Y-branch waveguide and a thick light-blocking metal film. After fabricating the waveguide using spin-coating and oxide-reactive-ion etching, the scientists deposited a 200-nm-thick gold layer on its Y-branch and patterned the gold using photolithography and a wet chemical etching process. A section of coating on one arm of the Y-branch was then removed to allow light exposure. The optical switching occurs because the photochromic dye undergoes a structural change when exposed to both ultraviolet (356 nm) and visible (514 nm) light, which in turn produces a reversible change in the refractive index of the dye-doped polymer film. One benefit of the all-optical switch is its low crosstalk of about -14 dB at 1.55 µm. The response time also decreases exponentially as the intensity of visible light is increased, which, the scientists say indicates that a fast switching time is possible when the device is exposed to high-intensity light. Contact Jang-Joo Kim at jjk@kjist.ac.kr.