Trapping light in a ring resonator using a grating-assisted coupler with asymmetric transmission

Abstract

A recently proposed concept suggests that a matched periodic modulation of both the refractive index and the gain/loss of the media breaks the coupling symmetry of the two co-propagating modes and allows only a unidirectional coupling from the i-th mode to j-the mode but not the opposite. This concept has been used to design a ring resonator coupled through a complex grating composed of both real (index) and imaginary (loss/gain) parts according to Euler relation: n = n0 exp(-jkx) = n0 (cos(kx) - j sin(kx)). Such asymmetrical coupling allows light to be coupled into the ring without letting it out. We present a detailed theoretical analysis of the ring resonator in the linear regime, and we investigate its linear temporal dynamics. Three possible states of the complex grating leads to the possibility of developing a dynamic optical memory cell where, for example, a data modulated train of optical pulses can be stored. This data can be accessed without destroying it, and can also be erased thus permitting the storage of a new bit. Finally, the ring can be used for pulse retiming.

Confinement and optical properties of the plasmonic inverse-rib waveguide

“…Fascinating avenues have been recently opened regarding optical systems with PT symmetry and fields which are symmetry-breaking in these structures [11][12][13][14][15][16][17][18][19][20][21]. Systems with balanced gain and losses with a symmetry plane that exchanges them provide a realization of PT symmetry.…”

“…Photonic systems with balanced gain and losses may show special properties related to their parity-time symmetry (PT symmetry), which may or may not be broken by their field eigenmodes [10]. Symmetry breaking is of high practical interest because it causes exceptional points in the gain dependence of the eigenvalues, with singular trends around them that may inspire novel optical designs, notably those related to "unidirectional" behavior [11][12][13][14][15][16][17][18][19][20][21]. We recently outlined [22] the possibility to get the essential features of perfect PT systems in this respect in cases where losses are fixed, as occurs with metals, and gain variable.…”

Transfer matrix analysis of the unidirectional grating-assisted codirectional coupler

“…Similar to Eq. (5), we define an orthonormality relation for modes p and q in the unperturbed waveguide, 1 4 ͵͵͑ẼpϫHqϩẼqϫHp͒daϭ␦pq, (8) and furthermore introduce the following auxiliary orthonormality relations, which arise from consideration of the real and imaginary perturbations separately:…”

“…We choose to avoid these terms in order to prevent confusion with the common but unrelated concept of Faraday isolation. These unidirectional coupling structures show great promise in optical routing and computing as a lossless add multiplexer [6] and as an optical memory cell [7,8].…”

Parity-time symmetry-broken Bragg grating operating with long-range surface plasmon polaritons

“…Specifically, most of the attention in recent years has been on PT symmetry-broken structures operating near their breaking threshold where many interesting and unusual phenomena are observed [9][10][11][12][13][14]. One example of a structure operating at the breaking threshold of PT symmetry is a Bragg grating with a balanced perturbation of index versus gain/loss and 90°phase shift between these perturbations.…”