Power Loss Reduction of Angled Metallic Wedge Plasmonic Waveguides via the Interplay between Near-Field Optical Coupling and Modal Coupling
, Ram Prakash Dwivedi 4 and Sheng Hsiung Chang 2,3,*
Round 1
Reviewer 1 Report
Report on Manuscript No. 1895847
The authors study the power loss of SPP waves supported in the CWP waveguides. In such a coupling waveguide system, the interplay between the near-field optical coupling and the modal coupling is demonstrated. They find that the power loss in the CWP waveguides can be effectively modulated by varying the wedge angle of the CWP waveguides, and give a brief theoretical explanation.
I recommend this paper to be published after they will explain my concerns below:
l The authors claimed that it can be observed the interference beats in the instantaneous Ex distributions, however the interference beats become not obvious with the increase of propagation distance (Fig. 2 (d)-(f)). These results seems to indicate that the coupling between the fundamental mode and higher order modes become weaker during the propagation, in other words, whether the higher order modes could propagate stably over long distances in CPW waveguides when the wedge angle of the CWP waveguide is lower than 45°ï¼Ÿ
l This work only investigated several specific wedge angles of the CWP waveguide (the angles are all multiples of 15), so how can conclude that 60° is the transition wedge angle for the generation of the higher order modes in the CWP waveguide, it should be clarified.
l The authors showed that the modal fields are more concentrated at the top corners with the decrease of wedge angle. I would like to ask the authors whether this CWP waveguide structure could achieve an effective localization of modal fields at the corners (such as SPPs’ nano-focusing) when a very small wedge angle is used or it will generate the spatial distortion and radiative loss due to the instability of higher order modes?
l There are several symbol mistakes in the manuscript, such as line 49 on page 2.
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Reviewer 2 Report
Coupled metallic-wedge nano-plasmonic (CWP) waveguides plays important role in ultra-compact and broadband integrated optical circuits design. Minimizing the power loss and improving its performance is always the goal in this field. In this manuscript, the authors proposed a new method to reduce power loss which is by manipulating the near-field distribution and the near-field modal coupling in the CWP waveguide. Their results show the lowest power loss of the CWP waveguide can be achieved at a wedge angle of 60° due to the lowest modal index. In my view, this manuscript could be published in Photonics after minor revision.
1. In Figure 1, the authors should mention yellow and blue part of their schematic represents what kind of materials, xyz coordinates should also be included. The same issue in Figure 4 and Figure 5, the authors should mark the type of the materials on the field distribution. xyz coordinates and scale bar should also be included.
2. In Figure 2, if the xyz coordinates is the normal case in most previous publications. The plotting should be Ex-Y axis plot instead of Ex-Z?
3. From the electric field distribution (Figure 4), the intensity of the field looks similar as the wedge angle changing from 60o to 15o. However, in Figure 3a, 60o is a critical point where the loss starts to increase. Can the authors explain why this is a critical point? How do the hybrid mode and fundamental mode represent in the field distribution plot?
4. The authors used near-field simulation in this manuscript, can the authors comment on does the results remain correct if the SPP mode is not excited via dipole excitation, such as port excitation?
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Reviewer 3 Report
In this manuscript, Liao et al, provided a simulation study on the near-field distribution and the near-field coupling in CWP. The paper is well-prepared and the conclusions are well supported.
Author Response
We thank the reviewer for the positive comment.
Reviewer 4 Report
The authors investigate numerically a plasmonic wavegguide composed of a trapzoid shaped trench into a metallic substrate. The modal properties including the modal index, propagation loss and the mode confinement are analyzed. Although the topic of modal confinement using plasmonic waveguide used to attract a lot of research interests, I have to say that unless new solutions to circumvent the intrinsic losses of metals, this topic is not as appealing as it used to be now. Furthermore, I am against the publication of this manuscript due to the following additional reasons.
1. There is no new physics reported. To use the coupled plasmonic mode to reduce the mode distribution inside the metals is a commonly used approach to for a longer propagation length. One famous example is the long-range surface plasmon modes supported by a thin metal film, where the coupling between the surface plasmon modes on the upper and lower metal surfaces determines the loss.
2. The authors present that 60 degrees is the optimal angle. However, there is no analysis on the reason. A calculation of the modal overlap between the wedge plasmon modes at different angles should be presented and analyzed.
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Round 2
Reviewer 4 Report
I persist that the results provided by the authors in this manuscript are of no significant interest to the current nanophotonics community. Unless new developments have been made to circumvent the problem of intrinsic loss of metals, the plasmonic waveguide is not attractive any more. This can be reflected by the very few number of publications on this topic now. Actually, even in the nanoantenna area, the interest on plasmoic nanoantennas have been replaced by that in all-dielectric counterparts nowadays.
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