Abstract
In this paper, a Bragg reflector is proposed by placing periodic metallic gratings in the center of a metal-insulator-metal (MIM) waveguide. According to the effective refractive index modulation caused by different waveguide widths in a period, a reflection channel with a large bandwidth is firstly achieved. Besides, the Mach-Zehnder interference (MZI) effect arises by shifting the gratings away from the waveguide center. Owing to different optical paths with unequal indices on both sides of the grating, a narrow MZI band gap will be obtained. It is interesting to find out that the Bragg reflector and Mach-Zehnder interferometer are immune to each other, and their wavelengths can be manipulated by the period and the grating length, respectively. Additionally, we can obtain three MZI channels and one Bragg reflection channel by integrating three different gratings into a large period. The performances are investigated by finite-difference time-domain (FDTD) simulations. In the index range of 1.33–1.36, the maximum sensitivity for the structure is as high as 1 500 nm/RIU, and it is believed that this proposed structure can find widely applications in the chip-scale optical communication and sensing areas.
Highlights
Surface plasmon polaritons (SPPs) are collective oscillations generated by the interaction between the electromagnetic waves and the free electrons on the metal surface [1]
When the periodic metallic gratings (PMGs) are laid in the center of the waveguide, broadband Bragg reflection is achieved owing to the periodic refractive index (RI) modulation
La should not be excessively enlarged to avoid affecting the performance in this structure, finite-difference time-domain (FDTD) simulated spectrum in Fig. 8(b) investigates that three Mach-Zehnder interference (MZI) channels are achieved and their central wavelengths are almost the same as those in since the channels attributed by the Bragg reflection Fig. 6(a), respectively
Summary
Surface plasmon polaritons (SPPs) are collective oscillations generated by the interaction between the electromagnetic waves and the free electrons on the metal surface [1]. Since SPPs can break through optical diffraction limit, they bring the possibility of integration of photonic circuits and electronic circuits. It is no doubt that one would like to integrate those important functional devices into a chip for realizing photonic circuits and electronic circuits. An MIM waveguide with periodic metallic gratings (PMGs) that are used to modulate the refractive index (RI) is proposed. When the PMGs are laid in the center of the waveguide, broadband Bragg reflection is achieved owing to the periodic RI modulation. MZI performance is obtained when the PMGs are moved away from the center, for the reason that two asymmetrical waveguide widths lead to slightly index differences of two optical paths. By cascading different MZI arms, up to three interference band gaps and one Bragg reflection channel are achieved in the proposed structure. The parameters of the proposed structure are fully considered to investigate the performances by using the finitedifference time-domain (FDTD) method
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