Structural Design and Experimental Investigation of a 1.65 µm Tapered Semiconductor Laser with InGaAlAs MQWs (On InP)
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsYuan Feng et al. present results of a structural and experimental investigation of a 1.65µm tapered semiconductor laser. The content of the manuscript is really interesting and the results are well presented. Thus, in general, it is worth to be published.
Before the manuscript could be published in the MDPI journal Photonics, the authors should consider my following remarks to avoid formulations capable of being misunderstood and to add a few more details to make the mentioned numbers for parameters more clear for the readers.
If the epitaxial layer structure in Table 1 is correct, then the short MQW description in the Abstract (line 12) has to be changed. A form of naming like InGaAlAs/InP MQW implies, that the two mentioned materials are the quantum well and barrier materials. But in your case, InP is the substrate. So I would prefer e.g. “… laser based on an InGaAlAs multiple quantum well structure (grown) on InP.” The title of the paper should be changed accordingly, e.g. “… of a 1.65 µm Tapered Semiconductor Laser with InGaAlAs MQWs (on InP)”.
Reference [6] in line 48 is not from Shi et al. It is listed as [7] in the References at the end of the paper. Either the reference number or the first author have to be corrected.
I don’t like “GaAs-based quantum wells” and “InP-based quantum wells” in line 59. In my opinion, it would be better to use e.g. “semiconductor laser structures on GaAs…” and to note in this sentence, that you generally compare laser structures in different wavelength ranges.
In line 74, you mention far-field divergence angles for the first time in this manuscript. It would be nice to add the meaning of the given number with respect to the profile width or power content: FWHM, 1/e2,… You could add here a statement, that in the following all numbers for far-field divergence angles in this paper are given for FWHM.
In Section 2, you should give a few more geometrical parameters of your laser. I found some information only in the Abstract in line 16: a ridge width of 2 µm and a cavity length of 2 mm. You should add the sizes of LRW, LTap and the overall chip width.
Please cite a paper on standard 1.65 µm semiconductor lasers (e.g. ridge waveguide lasers) and shortly note, why you have chosen an InGaAlAs multiple quantum well structure for the realization of your 1.65 µm tapered laser.
In line 102, I would describe the facet as “outcoupling facet” or “front facet”.
In Fig. 3, I don’t like the linear connecting lines between the data points. If you want to use a line through the data points in this figure, you should smooth it and mention, that it is only a guide for the eye.
ΘP is not described in the text. You could add it e.g. in line 124 "The free diffraction angle ΘP of the..."
Please check Fig. 5 and its description in lines 163-167. In the text, you state a narrow and high bell-shaped curve for a taper angle of 4°, whereas for 6° and 8° the far-field distribution is broadened. But in Fig. 5, the largest slow axis divergence angle is shown for a taper angle of 4° (black line). How does that correlate with each other? Please make clear in its caption, that Fig. 5 is for the horizontal direction.
Please add “for the chosen taper angle of 6°” in the captions of Figs. 7 and 8.
Reference [9] cannot be found using a DOI finder. Following the link in Ref. [13] leads to a failure message in Chinese.
At this point I have to mention, that only 6 of 20 citations are fully available in English for non-Chinese readers in order to get additional information or to verify facts and data used in the manuscript. The MDPI journal Photonics aims at an international readership. So most of the cited papers should be available in English. It is up to the Editors how important they consider this point when deciding whether to publish your manuscript. If possible, please try to increase the number of cited references in English.
Finally, I want to mention some deficiencies with respect to the technical preparation of the manuscript.
When you give the size of a parameter, please write the number and the unit on one line (e.g. see lines 13/14).
Please check the hyphenation of linewidth at the end of line 19.
Please use a space character between two sentences and only one space character between two words within one sentence.
Please enlarge the numbers and axis labels in Figs. 2, 3, and 4.
The References have to be reformatted with respect to the MDPI Citations Style Guide (see https://www.mdpi.com/authors/references) with additional focus on necessary and unneeded space characters.
Following the suggested minor changes and additions, the manuscript of Yuan Feng et al. can be accepted for publication in the MDPI journal Photonics.
Author Response
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Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authors- In the introduction, the authors cited reference [7] and [8]-[12] about the taperd amplifier structures. But reference [7] is Fiber-bulk hybrid Er: YAG laser without taper structure and reference [11] doesn’t mention taper structure either. Other references are not easily accessed.
- In Fig. 1, what material do the different colors represent? What’s the etch depth and ridge waveguide?
- Please describe the simulation methods and waveguide parameters for Fig.2 and Fig.4. What’s the input mode for Fig.4? Also the labels in Fig.2 and Fig.4 are too small to read.
- Is Fig.3 obtained from the simulation or measurement? If it is experimental data, it is suggested to place in section 3.2. Otherwise, please describe how to calculate the laser threshold and also include the mode confinement vs. etching depth.
- Optical images and SEM images should be presented in the paper to verify the actual device dimension.
- Though the laser structure parameters (taper angle, ridge width and cavity length) are mentioned in the abstract, these parameters and etching depth are not clarified in the section 3 Test Results.
- It is noted that the maxim outpower is measured at 100 mA and the far-field pattern is measured at 30 mA. So what are horizontal and vertical FWHM at 100 mA? How does the current degrade the far-field FWHM?
- To highlight the benefits of the tapered 1.65um semiconductor laser, please compare the tapered lasers with regular lasers(such as reference [13]) .
Author Response
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Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThe clarity and readability of this manuscript has been improved after the revision. Minor revisions are still required before accepted for publication.
（1）Please add details of material growth and device fabrication.
（2）Please provide some SEM or TEM images of the real device.
Author Response
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