Post on 13-Jan-2016
End Facet Roughness and Coupling Loss
Hadi Baghsiahi, Kai Wang, David R. Selviah
Photonics Research Group,
Department of Electronic & Electrical Engineering
University College London, UCL, UK
International Electrotechnics Commission IEC Annual International Conference, Charlotte USA 31st October 2013
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Waveguide End Facet Roughness Aims and Motivations:
• To find the relationship between the waveguide end facet roughness and the optical coupling loss.
• Best method to cut a polymer waveguides based on the surface quality, cost and reliability of the method.
• Optimise the cutting parameters of the selected cutting method to reduce the waveguide end facet roughness.
• To find and apply a range of methods for polishing, reducing and minimising the end facet roughness.
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The white rectangles are the cut-out connector sites where the daughter boards are plugged into the backplane
End Facet Roughness
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Schematic diagram of a one flute router and the cutting procedure used for the roughness investigation. (RLG 615 Drill/Router from Ernst
Wessel Machinebau Gmbh).
End Facet Roughness
Milling Router:
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Photomicrograph of the end of the waveguide after cutting with a one-flute router entering the sample from (a) the waveguide and (b) the copper coated FR4 PCB side.
End Facet Roughness
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A sample of the roughnesses of the surfaces cut by router cutters with different numbers of flutes.15000 rpm, cutting speed = 0.25 mm/min
End Facet Roughness
Number of cutting edges on the router:
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End facet roughness for different rotation and feed speeds. Blue indicates low roughness and red high roughness
End Facet Roughness
• One flute router Rotation and translation speed optimization:
300
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300
300
300
300
300
400
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200
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200
400
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Rotation Speed (rpm)
Tra
nsla
tion
Spee
d (m
/min
)
1 2 3 4 5
x 104
0.1
0.2
0.3
0.4
0.5
0.6
0.7
200
250
300
350
400
450Rotation speed
(rpm) 5000 15000 34000 50000
Translation Speed (m/min)
0.10
Roughness (nm)
389 ± 61 310 ± 12 384 ± 10 342 ± 23
Chip load (µm/revolution)
20 6.6 2.9 2
0.25
Roughness (nm)
376 ± 30 183 ± 13 358 ± 12 339 ± 42
Chip load (µm/revolution)
50 16 7.4 5
0.50
Roughness (nm)
474 ± 32 381 ± 18 205 ± 24 410 ± 15
Chip load (µm/revolution)
100 33 15 10
0.75
Roughness (nm)
434 ± 54 386 ± 20 407 ± 43 296 ± 12
Chip load (µm/revolution)
150 50 22 14
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Photomicrograph taken through a Nomarski microscope of a back illuminated waveguide cut at a rotation speed of 34,000 rpm and a translation speed of 0.75 m/min
High Rotation Speed
Cutting speed of 0.50 m/min and A: 60,000 rpm, B: 70,000 rpm. The surface roughness in case A is 395 ±18 nm and case B: 432 ± 21 nm
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• The recommended chip load from the router manufacturer is 8 µm/revolution.
• A minimum on the roughness was observed in the chip load of 8 µm/revolution.
• Minimum roughness was obtained at a chip load of 16 µm/revolution for the best surface quality.
• Stevenage Circuits use this one flute router to cut FR4 glass fibre reinforced epoxy PCBs and they have optimised that to operate at 17 µm/revolution
Chip Load:
10Confidential to the Partners of the IeMRC Flagship OPCB Project
Experiment Configuration:
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Experimental results for the optical input and output coupling loss due to the roughness at the end of the waveguide
End Facet Roughness Measurement Results:
Coupling loss measurements for different magnitude of roughness:
•Optical loss for several samples with different end facet roughness was measured.
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Experimental result of coupling loss due to the roughness at the end of the waveguide.
End Facet Roughness Measurement Results:
Coupling loss measurements for different magnitude of roughness:
13Confidential to the Partners of the IeMRC Flagship OPCB Project
Optical insertion loss plotted versus, σ/T, ratio of RMS roughness to autocorrelation length of the waveguide core end facet roughness.
Theoretical/Statistical Investigation:
14Confidential to the Partners of the IeMRC Flagship OPCB Project
Roughness Comparison:
End Facet Roughness Polishing:
Surface of the waveguide after hand polishing. A: AFM scanned data. B: The scanned surface of the waveguide by Zygo interferometry microscope
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End Facet Roughness Polishing (Future Work):
Schematic diagram of polishing router
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End Facet Roughness Treatment:
New technique for coating the ends of an array of cut waveguides with core polymer and curing to leave a flat smooth surface.
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The improvement of the coupling loss after applying index fluid matching on average is 2.23 ± 1.2 and after applying TruemodeTM acrylate polymer is 2.60 ± 1.3.
End Facet Roughness Treatment Results: