Nano Lett. 16, 1683–1689 (2016)

Credit: AMERICAN CHEMICAL SOCIETY

Mid-infrared light in the 2–10 μm wavelength range is useful for applications ranging from molecular spectroscopy to guided missile technology. However, the realization of a chip-integrated modulator operating in the mid-infrared regime remains challenging. Now, Charles Lin and colleagues from the University of Toronto, Canada and the University of Minnesota, US, propose, based on theoretical analysis, that a modulator formed from a multilayered black phosphorus thin-film on top of a silicon nanowire may be a viable option. The modulator is formed by a Si waveguide approximately 1,000 nm wide and 310 nm thick, covered by a black phosphorus film and then an Al2O3 passivation layer, and designed for operation at 2.1 μm. An alternative proposal for 3.3-μm-wavelength operation considers a 1,340-nm-wide and 500-nm-thick wire. Various black phosphorus thicknesses were investigated, for example, 6 nm (2.1 μm wavelength) and 20 nm (3.3 μm wavelength). A figure-of-merit, based on extinction ratio divided by insertion loss, yields a value of 5.5 from a single black phosphorus quantum well, compared with 1.6–4 from SiGe modulators (with >10 quantum wells). The researchers also showed that the optical bandgap can be blue-, red-, or bidirectionally-shifted if an out-of-plane electric field is applied.