When designing precision lighting systems, basing your optical component selections on single properties like numerical aperture (N.A.) or fiber diameter can backfire on you. To reduce the probability of potential problems, real-world testing and data reveal that relying on them in isolation may undermine system efficiency, beam control, and spectral performance.
This article summarizes a series of controlled tests showcasing the impact of varied fiber-optic formulations on the transmission of broad-spectrum light. By understanding fiber properties and potential pitfalls in their selection, your optical systems engineers will be equipped to make more informed, application-specific decisions.
Test Methodology and Measurement Setup
Several fiber-optic cables were prepared: all had a common length, bundle diameter, sheathing, and ferrules. Our testing looked at transmission (flux), beam angle, and selective absorption; the method of polishing the fiber, the refraction index of the fiber, and the fiber diameters were varied.
All fiber bundles were powered using a 250-watt 4-channel LED fiber-optic illuminator manufactured by Techniquip.
Flux was collected using a Labsphere integrating sphere. All other data were collected by a spectrometer positioned 250 mm from the fiber exit face. Two series of tests were conducted. In the first, the cables were powered directly from the LED illuminator. In the second series of tests, the output of the LED illuminator was sent through a preconditioning patch cable to reduce NA. This was done so that better estimates of the pure transmission losses could be determined.
Two Series of Fiber Optic Transmission Tests
Two separate testing configurations were used to isolate system effects:
Spectral Composition of Light From Source and After Exiting Bundles of Varying N.A.
LED Source Emission
0.22 NA Fiber
0.55 NA Fiber
0.66 NA Fiber
Spectral and Performance Results
The data showed a huge difference in flux between the 0.22 N.A. fiber and the more common 0.55 / 0.66 N.A. fibers. For a system requiring low angles, there are more effective ways to transmit light and block stray light than using 0.22 N.A. fibers.
The data shows a dramatic shift in Corrected Color Temperature (CCT) and a drop in Color Rendering Index (CRI) between the source and the light exiting all the various fibers. You can see here that for a desired CCT / CRI outcome, looking at the source properties is not sufficient to ensure a good design.
The data also showed that relative to other factors, the impact of the polishing method and fiber diameters was negligible.
The above testing helped us complete the development of a high-power OEM darkfield lighting system for semiconductor inspection applications using a quad-LED illuminator and borosilicate fiber optics.
Contact TechniQuip for more information on better techniques and equipment for achieving the best results.