To achieve ultrahigh-density nanoplasmonic integrated circuits, low-loss conventional dielectric waveguides (CDWs) are used to transfer light into and out of the metal–dielectric–metal (MDM) plasmonic waveguides. We show that sandwiching the MDM plasmonic waveguide between two CDWs forms a Fabry–Perot cavity-like structure, which causes oscillations in the transmission coupling efficiency (TCE) into the output CDW as the length of the MDM waveguide is increased. Three types of compact air-gap couplers (AGCs) were used at the interface between those two types of waveguides to enhance the coupling efficiency between them. Our simulation results indicate that tapering CDW before it is connected to AGC not only enhances TCE into the output CDW by 9% over a wide spectrum range but also reduces the need for high-precision fabrication techniques to align AGC at the interface. Moreover, we achieved a TCE into the output CDW of 77% optimized for the optical communications wavelength of 1550 nm when the length of the MDM plasmonic waveguide is 600 nm. In addition, we showed that our proposed design has large fabrication tolerance by investigating the change in its spectrum response as various parameters of the design dimensions differ from that of the targeted optimum dimensions. We found that increasing the dimensions of AGC reduces the width of the spectrum, whereas increasing the width of CDW with its tapered part shifts the spectrum to the right by 100 nm per 40 nm increase in the width. We also found that increasing the refractive index of the MDM plasmonic waveguide with AGC controls the cutoff wavelength, in which TCE is almost zero at wavelengths shorter than the cutoff wavelength, and consequently provides a unique advantage in using our proposed design in sensing applications.
Efficient dielectric–plasmonic interconnect is significant in the design of future electronic–photonic integrated circuits that deal with large data transfer. We propose three designs and analysis of small-footprint couplers that are located at the interface between dielectric and plasmonic waveguides. To the best of our knowledge, our proposed couplers outperform all the works reported in the literature in several aspects including size and coupling efficiency (CE). Our results indicate that the optimum dimensions of the proposed couplers are determined based on whether the coupler is located in the metal side or dielectric side, or the coupler extends equally in both types of materials. The proposed couplers work over a broad frequency range achieving a CE above 88% at the optical communications wavelength 1550 nm. In addition, our results indicate that the CE can be further increased to above 93% by increasing the width of the dielectric waveguide before it is connected to the coupler. Moreover, our proposed designs provide a considerable alignment tolerance, which is needed when aligning the dielectric waveguide to the metal–dielectric–metal waveguide. Our proposed couplers have an impact on the design and miniaturization of nanoscale all-optical devices.
We propose a "slot-to-slot" coupler to convert power between optical and metal-insulator-metal (MIM) plasmonic
modes. Coupling efficiency of larger than 60% is obtained from 2D FDTD simulation. Based on this prototype, a quasi-MIM plasmonic junction is demonstrated using e-beam lithography onto an SOI substrate. The junction is formed by
depositing a thin layer of gold (~20 nm) on part of a dielectric slot. When probed by 1520-nm laser, coupling efficiency
of 36% is achieved for a 500-nm long quasi-MIM junction. Optical modulation is under investigation by pumping the
device using visible light to change the optical property of gold.
In this paper, ultra low cross talk is achieved by using a resonant cavity at the intersection between two strip waveguides
formed in a square lattice photonic crystal structure (PhC). Two PhC structures are studied: one consists of cylindrical
rods and another consists of cubic rods. The Q-Factor of the cavity is changed by increasing the number of rods that form
the cavity and by decreasing the spacing between the waveguide and the cavity. Our two dimensional simulation results
show that the latter method resulted in cross talk reduction of more than 21 dB for both structures. The overall cross talk
was -90.50 dB for the cylindrical rods structure and -105.0 dB for the cubic rods structure. The optimized PhC structures
were fabricated on a silicon-on-insulator platform. The rods were buried in silicon oxide in order to maximize the
photonic band gap and provide index guiding in the vertical direction.
We report a 94% coupling efficiency between silica waveguide (SWG) and planar photonic crystal (PPC). This is achieved using a tapered PPC with a hybrid photonic crystal structure. The hybrid structure combines triangular and rectangular crystals.
In this paper, we designed different structures for PPC tapered waveguide to enhance the coupling between silica waveguide (SWG) and planar photonic crystal (PPC). The designed structures are based on changing the radii of the inner PPC tapered waveguide's crystals before and after adding extra defects. We found that above 88% transmission efficiency is possible by using extra defects followed by radii changes. We also found that changing the operating wavelength from 1.55μm to 1.558μm increases the transmission efficiency to 90% since the field is more confined at the later wavelength.
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