Demonstration of Two-Dimensional Beam Steering through Wavelength Tuning with One-Dimensional Silicon Optical Phased Array

Round 1

Reviewer 1 Report

This paper is about the 2D beam steering by wavelength tuning with the silicon OPA. The paper is well organized and well written.

There are some questions and comments for authors to consider.

Eq(1): I couldn't drive the last part of eq(1) from the second part of it. Using the definition of lambda_m, it should be (lambda_m - lambda) instead of 'just' lambda. 

Eq(2): Lambda_2pi is smaller than lambda_m from this equation (m is integer), is it right?

Line 78: Lambda_0 should be defined. I think it might be a typo.

* I suggest authors to re-check from 68~78.

Figure 1: Delta_L1 should be considered at the top postion y-direction. For the x-direction, all the paths experience the same path length. The path difference(delta_L1) occurs in y-direction at the left part of the grating radiators.

Figure2(b) and Figure5(e): It would be better to use the same range.

Line 144: I think phase initialization is one of important points in this paper, so including brief explanation of this part(algorithm and/or how to do it) woul help readers follow the manuscript.

Line 223: 'as least a harp of' might be a typo.

Line 235: Shoud check the m_i part. 

For the experimental results: Main lobe uniformity during the steering is important for many applications, I suggest including this data, cause SLL cannot show exact main lobe uniformity.

 

Overall, I recommend accepting the paper. I think authors can reflect above comments to the revised version.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

 

In this work, the authors propose and experimentally demonstrate two-dimensional beam steering by wavelength tuning in a one-dimensional silicon optical phased array (OPA). The authors have experience in the design and characterization of different optical phased arrays. In this case, electro-optic p-i-n phase shifters were employed for phase initialization to compensate for intrinsic deviations of the waveguide geometry that often arise from fabrication process. The research topic may be of interest for the photonics community, and results presented are robust. The proposed OPA exhibits a transversal steering near 46° (wavelength tuning of 7 nm) and a longitudinal steering near 12° (wavelength tuning of 90 nm), while the side-lobe level is below 8 dB. In addition, the effect of fabrication errors on beam steering has been studied. I have some comments below, which could help improve this manuscript:

1.    In the introduction, I suggest the authors distinguish between on-chip and off-chip optical wireless transmission (line 30) as well as expand a little more the discussion about OPAs based on the silicon-on-insulator (SOI) platform and their different architectures and performances (please include more references on this regard).

2.   I have found that the references do not follow a sequential order (see Refs. [10], [15] and [13]), and that some acronyms are not defined, e.g., SOI. In line 182, there is a typo of a hyphen crossing out a comma.

3.    In Section 2, it is not clear to me some of the equations. For example, in line 68, is not π missing to calculate the phase difference? It would be highly appreciated if the authors could include the references from which the expressions used in this manuscript have been obtained or a more detailed mathematical development.

4.   After Eq. (3), I believe that “n_eff^gra” refers to the effective index of the Floquet-Bloch mode in the grating and “clad” to cladding.

5.     For the design of the OPA (grating couplers, MMIs, phase shifters, etc.), at least physical parameters should be mentioned in order to be able to reproduce the results presented and not only refer to other previous papers from authors.

6.      The path difference ΔL₁ is only 2 µm. I wonder if the waveguides are not placed too close to each other so that some interference occurs (e.g., power coupling between adjacent waveguides?)

 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

This manuscript demonstrated two-dimensional beam steering through wavelength tuning in a Si 1-D OPA. The manuscript is well organized and presented and can publish in the current version.

Author Response

Dear Reviewer,

 

Coauthors and I very much appreciated your patient review and recommendation of publication.

 

Kind regards,
Hyeonho Yoon