Efficient coupling to slow light photonic crystal waveguide

Abstract

Slow light photonic crystal waveguides (PCWs) have been the subject of intensive study due to their potential for on-chip applications such as optical buffers and the enhancement of nonlinear phenomenon. 1 However, due to high group velocity mismatch between the strip waveguide and the slow light waveguide efficient coupling of light is challenging. The coupling efficiency is also very sensitive to the truncation at the interface between the two waveguides. 2 This sensitivity can be removed and light can efficiently be coupled from the strip waveguide to the slow light waveguide by adding an intermediate photonic crystal waveguide (or coupler) that operates at a group index of ∼ 5. Several designs have been proposed for couplers to obtain higher coupling efficiency within the desired group index range. 3 We have studied uniaxial stretched couplers in which the lattice constant is stretched in the direction of propagation by 10-50 nm in the coupler region. Using a Finite Difference Time Domain (FDTD) Simulation Method that allows the extraction of the group index, 4 we have observed 8.5 dB improvement in the coupling efficiency at the group index of 30. Efficient coupling is dominantly determined by the band edge position of the coupler region and maximum transmission efficiency is limited by the maximum transmission of the coupler PCW. If the band edge of coupler PCW is sufficiently red shifted relative to the band edge of the slow light PCW then higher coupling efficiency can be achieved.

Evolutionary Strategy Algorithm in a Complex Photonic Coupler Device Optimization

“…Os cristais fotônicos são estruturas com periodicidade em uma, duas ou três dimensões e suas constantes dielétricas são devidamente arranjadas de acordo com o interesse da aplicação [12], [13]. No caso de um acoplador com cristais fotônicos, a forma mais usual de projeto considera que os guias de ondas normalmente são os caminhos por onde não existem essas disposições organizadas, ficando apenas com o material do substrato adotado ou qualquer outro.…”

“…Nesse contexto, esses arranjos com os cristais fotônicos podem ser projetados de acordo com a aplicação, mas para se satisfazer a periodicidade da estrutura, leva-se em consideração o tamanho do elemento que compõe o cristal fotônico (r) e a distância entre eles (d), conforme apresentado na Figura 1. Por exemplo, no caso de estruturas cilíndricas, considera-se o raio do cilindro a distância entre eles [12], [13].…”