Tunable optical absorption in undoped graphene sandwiched between multilayer dielectric stacks with mirror symmetry

We theoretically investigate the optical absorption of an undoped graphene monolayer when put in a one-dimensional multilayer stack. Using the transfer matrix method, we perform numerical simulations and derive explicit analytical formulas for the optical absorption of the graphene monolayer at the center of the dielectric stack and find that the optical absorption uniquely depends on repetition number (r) and the unit layers structure. When sandwiched between unit layers structure composed of three dielectric materials (referred to as the 'ABC' structure) with even values of r, the graphene monolayer absorbs 2.3% of visible to near-infrared light. This behavior is the same as if graphene were free-standing, not sandwiched between the dielectric stack. In contrast to that situation, in the ABC structure with odd values of r, also when the graphene monolayer is sandwiched between four materials (the 'ABCD' structure) with any values of r, we can obtain optical absorption as large as 50% at particular refractive indices (n) of the constituent dielectric materials. The 50% absorption is, in fact, the maximum optical absorption for any undoped monolayer material in the symmetric dielectric stacks. By varying r and n within the ABC or ABCD structures, we can finely adjust the optical absorption of graphene within the range of 0%-50%, facilitating precise control for various optoelectronic applications.