The ability to render objects invisible using a cloak - not detectable by an external observer - for concealing objects has been a tantalizing goal1-6. Here, we demonstrate a cloak operating in the near infrared at a wavelength of 1550 nm. The cloak conceals a deformation on a flat reflecting surface, under which an object can be hidden. The device has an area of 225 um2 and hides a region of 1.6 um2. It is composed of nanometre size silicon structures with spatially varying densities across the cloak. The density variation is defined using transformation optics to define the effective index distribution of the cloak.Comment: 12 pages, 5 figure

Significant effort in optical-fibre research has been put in recent years into realizing mode-division multiplexing (MDM) in conjunction with wavelength-division multiplexing (WDM) to enable further scaling of the communication bandwidth per fibre. In contrast, almost all integrated photonics operate exclusively in the single-mode regime. MDM is rarely considered for integrated photonics because of the difficulty in coupling selectively to high-order modes, which usually results in high inter-modal crosstalk. Here we show the first microring-based demonstration of on-chip WDM-compatible mode-division multiplexing with low modal crosstalk and loss. Our approach can potentially increase the aggregate data rate by many times for on-chip ultrahigh bandwidth communications.

Optical frequency combs are a revolutionary light source for high-precision spectroscopy because of their narrow linewidths and precise frequency spacing. Generation of such combs in the mid-infrared spectral region (2-20 mm) is important for molecular gas detection owing to the presence of a large number of absorption lines in this wavelength regime. Microresonator-based frequency comb sources can provide a compact and robust platform for comb generation that can operate with relatively low optical powers. However, material and dispersion engineering limitations have prevented the realization of an on-chip integrated mid-infrared microresonator comb source. Here we demonstrate a complementary metal-oxide-semiconductor compatible platform for on-chip comb generation using silicon microresonators, and realize a broadband frequency comb spanning from 2.1 to 3.5 mm. This platform is compact and robust and offers the potential to be versatile for use outside the laboratory environment for applications such as real-time monitoring of atmospheric gas conditions.