What started as a research project has turned into one of Omega's most unique capabilities- coating the tips of fiber optics with spectrally-complex coatings including broadband antireflection coatings, reflectors and our full-range of filters. We use the same plasma-assisted reactive magnetron sputtering (PARMS) system that produces coatings on flat-glass to provide extremely durable and versatile hard-oxide coatings on fiber tips. 

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Required Specifications for Coated Fiber Tips

Fiber tips are a very unique substrate. Optical fibers come in many shapes and sizes. To ensure that customers get exactly what they want, we prefer that the customer provides the fibers to be coated. In order to properly handle and model the filter performance on the tip, we need information beyond that for a normal flat-glass filter order. 

Ferule- We prefer to coat FC/PC ferrules. FC/APC can be coated as well, though this can complicate the design of the filter.  Other 2.5mm diameter connectors and ferrules can also be easily accommodated.  SMA connectors (3.2mm ferrules) and 1.25mm ferules can also be coated by changing some of our tooling. If you have other connectors or ferrule configurations don't be afraid to ask.

Interface- Will the filter be placed inside a fiber connector so there is intimate contact with both sides of the filter surface, or will the filter have air (or some other material) on one side?

Fiber length and jacketing- Our tooling is a finite size, so we need to know how long the fibers are, the OD of the jacket and bend radius of the fibers to calculate the number of fibers we can accommodate in each coating run.

f/# and modal distribution inside the fiber- The core size and wavelength range determine how many modes are propagated within the fiber. This also affects the f/# and angular distribution within the fiber. Multimode fibers by their nature contain a larger angular distribution within the fiber (lower f/#) than single mode fibers in which the exiting light is close to 0 deg angle of incidence (AOI).

Read how AOI affects filter performance.

In the images below, the filter response mimics the model at AOI=0 (Top figure- in the single-mode, 10 micron fiber) but is shifted to lower wavelengths and distorted in shape in a multimode fiber coating (bottom figure, multimode fiber). The multimode fiber spectral response is integrated over all angles between zero and 12 degrees. 

"coated fiber tip versus the flat glass monitor and model"
Spectral response of a bandpass filter on a single-mode fiber (red) ​​​versus the modelled performance (dashed blue) and flat glass monitor plate (blue)

 

"multimode fiber response versus model"
Spectral response of the same bandpass filter applied to a multimode fiber (red) where the AOI distribution includes all angles +/- 12 degrees

Filter Specifications- please see the pages for each filter type to determine what filter specifications are also required

Types of Coated Fiber Tips

We have demonstrated a number of hard-oxide PARMS coatings on fibertips with thicknesses up to 28 microns. Some examples are below.

"1564nm narrow-band filter on a single-mode fiber"
Narrow-band 1564nm filter on a single-mode fiber

 

"810nm longpass filter on multimode fiber"
810nm longpass filter on a multimode fiber. The spectrum is slightly blue-shifted because of the AOI distribution.

 

810 long pass OD curve
The same 810nm longpass filter plotted in OD. Coating one end of the fiber affords OD 3, but OD 6 can be achieved by coating both ends of the fiber for use in Raman applications.

 

1662 short pass
1662nm shortpass filter on a single mode fiber. There is a slight but reproducible offset in wavelength between the flat glass monitor and the coated fiber tip.

 

Specialty Coated Fiber Tips and Bundles

Specialty reflectors- We have had customers request specific reflectance values at a single wavelength for fiber-laser and other applications. 

Patterned Fiber Tips- Omega is a co-PI on a grant with Nikira Labs to develop fiber bundles that are photolithographically patterned to enable laser delivery through a central fiber and collection through peripheral fibers. Click to read the paper we presented on patterned fiber bundles at SPIE Photonics West, 2022.