Analytical and numerical study of T-shaped plasmonic demultiplexer based on Fano and induced transparency resonances

Abstract

We study analytically and numerically the design of plasmonic demultiplexers based on Fano and plasmonic induced transparency (PIT) resonances. The demultiplexers consist of T-shaped structures with an input waveguide and two output waveguides. Each output contains two waveguide stubs grafted either at the same position or at two different positions far from the input waveguide. We derive closed form analytical expressions of the geometrical parameters allowing a selective transfer of a single mode in one waveguide without affecting the other one. This is performed by implementing the Fano and PIT resonances which are characterized by a resonance placed near an antiresonance or placed between two antiresonances respectively. In particular, we show the possibility of trapped modes, also called bound in continuum (BIC) modes. These modes appear as resonances with zero width in the transmission spectra for appropriate lengths of the stubs. Then, by detuning slightly the stubs, BICs transform to PIT or Fano resonances. The existence of a full transmission besides a transmission zero, enables to filter a given wavelength on one output waveguide, by vanishing both the transmission on the second waveguide as well as the reflection in the input waveguide. The demultiplexer is capable to separate two fundamental optical windows (i.e. 1310 and 1550 nm). The performance of the demultiplexer platform is measured using the crosstalk of the two outputs and quality factor. The lowest value of the crosstalk −96.8 dB with an average of −84.7 dB is achieved and a maximum quality factor 45 is obtained. The maximum transmission reaches a high value of 85% despite the large metallic losses. These values are suitable for integrated photonic circuits in the optical communication. The analytical results are obtained by means of the Green’s function method which enables us to deduce the transmission and reflection coefficients, as well as the delay times and density of states. These results are confirmed by numerical simulations using a 2D finite element method. The analytical analysis developed in this work represent a predictive method to understand deeply different physical phenomena in more complex plasmonic devices.

Friedrich-Wintgen bound states in the continuum and induced resonances in a loop laterally coupled to a waveguide

“…The analytical results are confirmed by the experimental measurements using the coaxial cables in the radio-frequency regime. The results presented in this work can be transposed straightforwardly to mesoscopic systems [11,12,80] as well as plasmonic MIM waveguides operating in the infrared domain by taking properly the geometrical parameters at the nanoscale [22,81]. The structure can be proposed to realize an efficient refractive index sensor.…”

“…This satisfies the FW criterion in Eq. (22). The avoided crossing is due to the strong coupling between the two modes of the cavity.…”

“…To date, BICs represent an ubiquitous phenomenon applying to all domains of wave physics, such as acoustics [3][4][5][6][7][8][9][10], mesoscopics [11,12], photonics [13][14][15], and plasmonics [16][17][18]. There are numerous realizations of BICs in classical systems, leading to a wide variety of different applications such as lasers [19], filters [20,21], demultiplexers [22], and sensors [23,24]. In accordance with the classification presented in * Corresponding author: elboudouti@yahoo.fr review [25], BICs can be categorized into several types based on their physical origin.…”

“…1(a)] that displays FW-type BICs that transform into either EIT, EIR, or ATS resonances when the system deviates from the BICs conditions under a small structural perturbation. The proposed system can be transposed to plasmonic devices based on metal-insulator-metal (MIM waveguides), which are suitable for designing efficient refractive sensor at the nanoscale [22]. The cavity is composed of a loop of length 2d = d 2 + d 3 connected to a wire of length d 1 and a stub of length d 4 ,; the whole cavity is attached vertically to a waveguide at the bottom side of the wire of length d 1 [Fig.…”

Dynamic control of Fano-like interference in the graphene periodic structure

“…Therefore, SPPs are considered to be one of the most advantageous candidates in integrated optical circuit, which has attracted much attentions from researchers. Some devices based on plasma structure have been researched, such as wavelength demultiplexers, slow light systems and filters [7][8][9]. However, the tuning of plasma structure depends mainly on changes in the size of the structure, which is difficult to change once the device is made.…”