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Quantifying Back Reflections in Zemax for Optical Fiber Endoscope

  • May 8, 2025
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Hi,

This is Oliver. I’m currently working on an optical fiber endoscope project, where minimizing back reflections is critical for our application in optical coherence tomography (OCT).

In particular, I’m looking to quantify the back reflections from specific lens surfaces—such as the ball lens-air interface highlighted in the attached figure. The system involves a single-mode fiber launching light through a segment of coreless fiber and a ball lens. The majority of the back reflections appear to originate from the ball lens-air interface.

My goal is to use Zemax to estimate the amount of power reflected back into the single-mode fiber. For example, if the input power is 10 mW, is it possible to calculate the power reflected back toward the source in Zemax?

Ultimately, I plan to optimize the material and geometry of the ball lens to minimize these reflections. I’ve attached the Zemax file for your reference, and I would appreciate any guidance or suggestions on how best to approach this analysis.

Thank you for your help.

Best regards,
Oliver

 

Best answer by Rishab

Hi Oliver,

To see the power from the back reflection you need to model the setup in non-sequential mode.

You can place a detector at the focal plane and another detector facing the ball lens such that it can intercept rays getting reflected from the ball lens - air interface.

In the source give a smaller number of analysis rays (e.g.: - 10 or 20 otherwise you’ll be saving a very large file) and while ray trace you can save the ray file. Once you run the ray trace open the detector viewer and choose your saved ray file in ray database and apply the filter mentioned you will be able to see the power incident on the detector surface which is getting reflected from your concerned surface. I am attaching the ZEMAX NSQ model for your reference.

 

Regards,

Rishab.

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  • May 13, 2025

Hi Oliver,

To see the power from the back reflection you need to model the setup in non-sequential mode.

You can place a detector at the focal plane and another detector facing the ball lens such that it can intercept rays getting reflected from the ball lens - air interface.

In the source give a smaller number of analysis rays (e.g.: - 10 or 20 otherwise you’ll be saving a very large file) and while ray trace you can save the ray file. Once you run the ray trace open the detector viewer and choose your saved ray file in ray database and apply the filter mentioned you will be able to see the power incident on the detector surface which is getting reflected from your concerned surface. I am attaching the ZEMAX NSQ model for your reference.

 

Regards,

Rishab.

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