Diffraction gratings have attracted considerable interest for their widespread use in many modern optical systems and devices. A multilayer dielectric grating and a dielectric total internal reflection (TIR) grating have been proposed to achieve metal-free reflection, However, both the gratings are difficult to fabricate.

Researchers at Shanghai Institute of Optics and Fines Mechanics (SIOM/China) and Columbia University introduce a rhombic-groove internal reflection (RIR) grating, which not only inherits the advantages of the TIR gratings but also improves the spectral bandwidth.[ OPTICS LETTERS. Vol. 36, No. 8;2011,1431]

Researchers have presented the optimization design of a RIR grating independent on the central wavelength of the incident light, which allows the designing results to have a broader range of applications. An effective method to predict the spectral bandwidth of gratings by the means of efficiency maps has been presented in detail. In fact, the method could also be applied to other grating profiles, such as sinusoidal, trapezoidal, and triangular gratings. The RIR gratings exhibit improved performance over the TIR gratings. Besides inheriting the advantages of high efficiency and simple structure from the TIR gratings, the RIR gratings remove the restriction on the incident angle and have larger spectral bandwidth,which makes them available for potential applications associated with broadband illumination. Fabrication of the rhombic-groove gratings has been reported, and more importantly, the gratings could possibly be replicated for mass production. Therefore, the RIR gratings could be useful in a variety of practical applications.