Planar focusing reflectors based on monolithic high contrast gratings: design procedure and comparison with parabolic mirrors

Abstract

Here, we describe in detail a procedure for the numerical design of planar focusing mirrors based on monolithic high contrast gratings. We put a special emphasis on the reconstruction of the hyperbolic phase of these mirrors and we conclude that the phase does not have to be perfectly mimicked to obtain a focusing reflector. We consider here the grating mirrors that focus light not in the air but in the GaAs substrate and we compare them with conventional parabolic reflectors of corresponding dimensions. The light intensity at the focal point of the focusing grating mirrors was found to be comparable to that of the parabolic reflector. Moreover, the reflectivity of the focusing grating mirrors is almost as high as that of parabolic mirrors covered with an additional reflecting structure, if the ratio of the reflector width to the focal length is less than 0.6. Planar focusing grating mirrors offer a good alternative to parabolic mirrors, especially considering the complexity of fabricating three-dimensional structures compared to planar structures.

Experimental Demonstration of Light Focusing Enabled by Monolithic High-Contrast Grating Mirrors

“…The focusing mirror was designed according to a procedure described in detail elsewhere. 11 The GaAs (single layer) grating is 280 nm thick, and its lateral dimensions are 300 μm × 300 μm. It was manufactured on the surface of a 300 μm thick GaAs substrate (for details on the fabrication procedure, see Section 4.1 ).…”

“…As we have described in ref ( 11 ), we study planar focusing mirrors that reflect light into the high-refractive-index material, instead of the air. Designing this type of mirror is very challenging, as in principle the reflected light may be not only of the zero order but also of unfavorable higher diffraction orders.…”

“…Subwavelength gratings allow for very high power reflectance and simultaneously enable a wide range of variation in the phase of the reflected light. 1,11,12 These two advantages make it possible to There are few reports in the literature on the fabrication of SG focusing mirrors. The first, composed of a silicon grating deposited on a quartz substrate, was demonstrated by Fattal et al 13 This mirror had a focal length of almost 20 mm and a 1/e 2 spot diameter of ∼300 μm.…”

“…Traditionally, this is achieved by covering the curved surface with a metal or multilayer periodic structure. Subwavelength gratings allow for very high power reflectance and simultaneously enable a wide range of variation in the phase of the reflected light. ,, These two advantages make it possible to create highly reflective focusing (or otherwise directing) flat SG mirrors.…”

Impact of Stripe Shape on the Reflectivity of Monolithic High Contrast Gratings

“…MHCGs enable arbitrarily high power reflectance when the grating has a refractive index larger than 1.75 . They facilitate strong polarization discrimination and phase tuning of reflected and transmitted light, even when the thickness of the grating is as little as half of the wavelength in the grating material. In ref , an MHCG used as the top mirror of a vertical resonant cavity in a polariton laser enabled a high quality factor ( Q -factor) cavity and efficient optical pumping through the MHCG.…”