Gain-assisted critical coupling for high-performance coherent perfect absorbers

Abstract

Balanced radiation and absorption rates of an optical resonator are necessary for coherent perfect light absorption in many active device applications. This balance is referred to as critical coupling condition. We propose a gain-assisted method for exact access to critical coupling conditions without altering any structure parameters. In a coherent absorber with additional internal gain media, critical coupling with arbitrarily high coherent signal extinction can be obtained by continuously tuning optical pumping density. Assuming a surface-plasmon resonance grating covered by a gain layer as a promising architecture, we numerically demonstrate gain-assisted continuous access to its critical coupling point with experimentally probable settings. In addition, the gain tuning further introduces switching of the coherent-absorber's functionality to a conventional lossless beam splitter.

Coherent perfect absorbers: linear control of light with light

“…[53]. The tuning of the system to the CPA condition can be aided by incorporating a medium with adjustable optical gain [53,62,63] or by varying the temperature (which alters the free-electron collision rate in a metal grating [53]). …”

Coherent control of wave beams via unidirectional evanescent modes excitation

“…Coherent control of propagation of a wave beam by tuning the amplitude and phase of another beam is a very promising approach to realize ultra fast optical devices for optical computing, sensing, and other applications [1][2][3][4][5][6][7][8][9][10][11]. One of the most important effects in coherent control of light is coherent perfect absorption [12][13][14][15][16][17][18][19][20][21][22]. In these devices, the level of absorption of one beam illuminating a thin sheet is controlled by another coherent beam that illuminates the same sheet.…”

“…In Refs. [17,18,23], coherent perfect absorption and scattering for two angularly asymmetric beams are realized by using surface plasmon-polariton (SPP) excitation at silver-based diffraction groove gratings. However, such plasmonic grating designs have limitations.…”

Coherent Control of Wave Beams Via Unidirectional Evanescent Modes Excitation

“…In this decade, the emergence of gradient metasurfaces [20][21][22][23][24][25][26][27] and metagratings [28][29][30][31][32][33][34][35][36][37] has opened a new avenue for manipulation of light for arbitrary incidence angles and versatile functionalities. For periodical metasurfaces or metagratings with the period larger than half of the wavelength, the incident plane wave from one direction will be scattered into multiple directions, and the power carried by the incident wave can be redistributed among a number of diffraction modes.…”