Flowline Optical Simulation to Refractive/Reflective 3D Systems: Optical Path Length Correction

Round 1

Reviewer 1 Report

The manuscript applies a new conserved quantity 'Optical Path Length' in teh problem  as an  a topical problem and the work appears to be well executed, with flowline calculations benchmarked against raytrace results.  Agreement between irradiance maps derived in the axially aligned system without refractive elements is reasonable. Slight discrepancies or noise seem readily explained by the resolution of the raytrace calculation.   Some benchmarking of the raytrace itself would be welcome, maybe comparing results against a second raytrace code.  The authors motivate their study suggesting imrpoved computational efficiency but this is not quantified, maybe a sentence or two could be added to provide quantitative detail on this point. 

The methodology is outlined, but the paper could be improved with a little more detail on how the calculation of OPL since it is not what the correct OPL path should be.  The irradiance at any one place on the detector is composed of the image of light that has arrived from all parts of the source, travelling via different optical paths through the refractive element. For this reason it seems unclear how a single optical path length value at the detector could capture all of that complexity. Perhaps the correct 'net' optical path would be one that follows the flowline from the point on the detector back to the source? 

It is not clear to me why there is a difference between the  raytrace and flowline methods, is there a physical reason for this?  It seems unlikely that an arbitrary and system dependent path-length constant ʎ is necessary  be required to make the flowline results match.  Can the authors elucidate this point?

Finally, the paper is clearly presented but would be improved with some light editing, for example on page 1 there are at least three typographical errors.  

p1 line 28 should read "Such a concept..." not "Such concept.."

p1 line 30, the word Module should be replaced with Modulus.

p1 line 45, "academicals results" should be replaced with "academic results"

 

 

Author Response

Please see attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

In the manuscript "Flowline optical simulation to refractive/reflective 3D 2 systems: Optical Path Length correction", Garcia-Botella and co-workers discuss an extension to the well-developed flowline approach to Nonimaging Optics to the 3D case.

The manuscript is well-written and interesting and I certainly consider it worth publishing after a few remarks have been addressed. Note that, however, the previous publications concerning the 2D case from the authors (Refs 9,12) are published behind a paywall and could not be assessed while preparing this report.

--Technical comments--

1) One of the main claims of the manuscript is the introduction of an ad-hoc correction factor to the Optical Path length. This by itself seems quite interesting, and it requires further studies to assess its theoretical/physical meaning. However, the original article (Ref 12) introducing the gauge invariance is placed behind a paywall. For the sake of completeness and to strengthen their case, I would suggest the authors to include the useful parts of the discussion included in Ref 12 in this work.

2) In the various examples of asymmetric refractive elements, the boundaries of the spatial domain seem to differ significantly from the ray-tracing computations (see, e.g. Figure 12). This applies both for the corrected and the corrected path-length calculations. Where is this discrepancy coming from?

--Minor comments--

* Across the different figures, the axes labels and tick labels are very small and hard to read. Could the authors increase the font size to enhance readability?

* Since the journal does not apply any extra charge to publish coloured pictures, I'd suggest that the surface plots illustrating the irradiance profile using a full-colour colourmap, which would be more useful to appreciate any difference in profile between the ray-tracing case and the flowline methods.

Author Response

Please see attachment

Author Response File: Author Response.pdf