Effect of Beam-Steering Angle, Operation Wavelength and Mean Inter-Element Distance on the Side-Lobe Levels of Integrated Optical Phased Arrays under Beam-Steering Operation

Round 1

Reviewer 1 Report

In this work, the authors demonstrate the numerical results using the differential evolution method to optimize the side-lobe level for linear integrated optical phase arrays (OPA), and provide design guidelines that can assist in reducing the side-lobe level of integrated linear OPAs.

 

The manuscript is, in general, clearly written. The design and archived results could potentially be beneficial for designing OPAs. However, the reviewer finds some numerical results should be better presented, before it would be considered to be published in Photonics. Below are the points that need to be further addressed:

 

1.      In both Figs. 3 and 4, it seems that SLL changes abruptly around a specific parameter value (i.e., beam steering angle, wavelength) and then stays almost unchanged, which is a bit weird. The review imagines a more continuous change instead of the “step-like” change. Would the authors elaborate more about these figures?

2.      In Sections 3.2 and 3.3, the authors discuss the effects of mean distance (dmean) and number of elements (N) on the SLL, respectively. In the reviewer’s opinion, it would be more meaningful to conduct the discussion on dmean and N with a fixed L, i.e., a fixed device size. Could the authors add this discussion?

3.      It is recommended that the authors summarize the design guidelines more explicitly in the conclusion.

 

Some minor points:

1.      In the abstract, “SLL” should be spelled out upon first mentioning.

2.      Page 1, line 32, “are preferable in applications where the beam steering should be performed in only one direction”. Here it is maybe better to say “in mainly one direction” as techniques such as wavelength scanning can be used to realize beam steering in the other direction.

3.      Page 2, line 65, it is not clear to the reviewer what “structural and operational parameters” are. Could the authors be more specific?

4.      The authors use the term “feeding phase” quite often. Is it a commonly used term?

5.      There is a typo in Line 129, “tree” should be “three”.

 

Mostly fine. Only minor improvement is needed.

Author Response

We thank the careful and constructive feedback from Reviewer 1. Our response is attached in the following pdf document.

Author Response File: Author Response.pdf

Reviewer 2 Report

This paper theoretically optimized the element positions of linear optical phased arrays with different configurations operating by using the differential evolution algorithm. Overall it is interesting and can be accepted provided that some revisions being made.

1. For the differential evolution algorithm, since it is the main method used here, details of the optimization should be presented. And the reason of the chosen 40 polulations and iteration numbers may need to be discussed. Besides, the OPA optimization has aroused much attention recently, more similar works may also need to be cited in the introduction.

2. The guideline in the title seems too broad, it is suggested to be more focused on the presented optimization parameters.

3. Here, only 4, 8, and 16 elements are analyzed. But for the practical application, such a small array element may result in a large divergence angle. And 256 or even 1024 elements have already been reported. So it is suggested to discussed a larger-scale element and it would be more favorable to indicate the significance of this optimization work.

The language may need to be more refined and the some abbreviation should be presented with a full name, such as SLL in the abstract.

Author Response

We thank the careful and constructive feedback from Reviewer 2. Our response is attached in the following pdf document.

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript provides some design guidelines for integrated optical phased arrays under beam-steering operation, in order to overcome the high intensity of the side lobes determined by fabrication constraints limiting the minimum inter element separation. By using a suitable optimization algorithm, the authors optimize the element positions of different configurations of linear arrays, showing that it is necessary to optimize the positions for the broadest beam steering angle and the shortest operation wavelength. Moreover, authors show that when imposing a minimum inter-element distance, there is an optimum mean distance that minimizes the SLL of the array.

The work is interesting, clear, well written and, in my opinion, it is suitable for the publication. In order to increase the quality of the paper, I suggest the authors addressing these points:

1)     The authors should mention at the beginning of Sect. 2 that the proposed approach (pattern multiplication and calculation of the Array Factor as indicated in Eq. 2 is valid only when the elements can be considered as not coupled.

2)     Is there a reason to explain the steps in the curves plotted in Fig. 4? Is this step determined by something related to the existence of Grating Lobes? I’m thinking to this as these steps are in the region of lambda = 1.

3)     The maximum value of the AF as a function of the parameters used for the optimization is not shown except for the plots of Fig. 5. Does |AF| changes with the parameters used for the optimization?

Author Response

We thank the careful and constructive feedback from Reviewer 3. Our response is attached in the following pdf document.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have addressed the reviewer's concern adequately.  Therefore, the reviewer would like to recommend acceptance of the manuscript.