Coupling Efficiency of LED to Fiber Optic Guide

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Homework Help Overview

The discussion revolves around the coupling efficiency of light from an LED into a cylindrical optical fiber guide, focusing on how this efficiency varies with distance from the fiber's end. The subject area includes optics and photonics, particularly concerning surface mount LEDs and fiber optics.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants discuss the variability of LED types and their light distribution characteristics, questioning the assumptions made about the LED as a point source and the fiber's properties. There are inquiries about the impact of different LED designs and fiber types on coupling efficiency.

Discussion Status

The discussion is ongoing, with some participants providing insights into the complexities of the problem, such as the importance of fiber characteristics and LED configurations. There is a lack of consensus, particularly regarding the need for additional information like datasheets, which has not been provided by the original poster.

Contextual Notes

Participants note the absence of specific details about the LED and fiber types, including their refractive indices and whether lenses or coatings are used, which are critical for evaluating coupling efficiency.

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Homework Statement
Most surface mount types of LED’s have a very nearly cosine distribution of light intensity. If we desire to inject light from an LED to the end of a cylindrical optical guide, what is the coupling efficiency as a function of distance (x) from the end of the guide?

Assume that the LED is a point source and that the fiber has a diameter D
Relevant Equations
I found that the half cone angle let's call it theta=arctan(D/2x)
Now that I know theta, I'm trying to use that to calculate the coupled light.

What unit am I looking for, is it luminous intensity? I'm thinking I have to integrate from 0 to theta but I'm not sure what the integral looks like. Any ideas?
Most surface mount types of LED’s have a very nearly cosine distribution of light intensity. If we desire to inject light from an LED to the end of a cylindrical optical guide, what is the coupling efficiency as a function of distance (x) from the end of the guide?

Assume that the LED is a point source and that the fiber has a diameter D
 
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Pretty vague question, lacks purpose. SMD LEDs come in a variety, some with lenses some wirhout. LED range from infrared to ultraviolet with corresponding changes to LED and interface.

Laser purpose ranges from illumination to indicator to laser diode. Low power diode has small chip and less diff between emitter and fiber diam. High power is larger emmitting area requiring optics to make beam fit in common fiber sizes.

The fiber type (index of refraction, etc.) Is an important variable. Two examples: on circuit board indicators with plastic "rods" from front panel to top of led on circuit board; fiber-optic communication/networking with laser coupled to graduated refractive index fiber that keeps light centered.

Multimode fiber typically uses fiber's internal reflections. Both plug fiber directly into the LED part. Since you don't mention using lenses and antireflective coatings, efficency of energy transfer from LED and fiber is not a concern.
 
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Agreed. I asked the OP via PM to post datasheets and diagrams, but no joy so far...
 
Thanks for the input guys. That's all the information I have hence why I asked for help. but I figured it out after trying a few things
 

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