Abstract
The perfect absorption of light in subwavelength thickness layers generally relies on exotic materials, metamaterials, or thick metallic gratings. Here we demonstrate that total light absorption can be achieved in ultrathin gratings composed of conventional materials, including relatively weakly absorbing semiconductors, which are compatible with optoelectronic applications such as photodetectors and optical modulators. We fabricate a 41 nm thick antimony sulphide grating structure that has a measured absorptance of A=99.3% at a visible wavelength of 591 nm, in excellent agreement with theory. We infer that the absorption within the grating is A=98.7%, with only A=0.6% within the silver mirror. A planar reference sample absorbs A=7.7% at this wavelength.
Highlights
Absorbing light within a layer of deeply subwavelength thickness, with zero reflection and zero transmission, is a challenge of both fundamental theoretical interest and of importance for practical applications such as photodetectors [1], optical switches, modulators and transducers [2, 3]
In our experiments we show that Transverse Electrically (TE) polarized light, where the E-field is along the grating rulings (y-axis in Fig. 1), is totally absorbed in gratings composed of relatively weakly-absorbing semiconductors that have a complex refractive index, n = n + in, with n n
We show numerically that Transverse Magnetically (TM) polarized light (H-field along y-axis) can be totally absorbed in ultra-thin gratings, and that this requires metallic materials with n > n (Re(ε) < 0), because it relies on the excitation of Surface Plasmon Polaritons (SPPs)
Summary
Absorbing light within a layer of deeply subwavelength thickness, with zero reflection and zero transmission, is a challenge of both fundamental theoretical interest and of importance for practical applications such as photodetectors [1], optical switches, modulators and transducers [2, 3]. In our experiments we show that Transverse Electrically (TE) polarized light, where the E-field is along the grating rulings (y-axis in Fig. 1), is totally absorbed in gratings composed of relatively weakly-absorbing semiconductors that have a complex refractive index, n = n + in , with n n. Such materials are abundant in nature and are compatible with optoelectronic applications. We show numerically that TM polarized light (H-field along y-axis) can be totally absorbed in ultra-thin gratings, and that this requires metallic materials with n > n (Re(ε) < 0), because it relies on the excitation of Surface Plasmon Polaritons (SPPs).
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