3d printed switch for plastic optical...
TRANSCRIPT
POSTER 2017, PRAGUE MAY 23 1
3D Printed Switch for Plastic Optical Fibres
Martin KOŠŤÁL1
1 Dept. of Microelectronics, Czech Technical University, Technická 2, 166 27 Praha, Czech Republic
Abstract. This paper concerns the possibilities of3D printing for switch for plastic optical fibres. Achievableprecision of nowadays consumer 3D printers is sufficientfor such a switch. I achieved similar insertion loss tocommercially available POF switches.
In this paper I describe the design of the switch,fabrication with concern of suitable materials forFDM printer. I further present measured insertion losswith comparison to calculated insertion loss according totheory.
I discuss comparison of the measured insertion loss withthe insertion loss of commercial switches.
KeywordsFibre, optics, POF, switch, 3D print, FDM
1. IntroductionIn this paper I present a possible switch for plastic
optical fibres using a cost-effective filament 3D printer.
Plastic optical fibres (POF) are broadly used incommunications, measurements and other applications.Those applications are driven by various types of activeand passive optical components. One of the basic passivecomponents is optical switch. For low loss switchingMEMS switches are available, this paper concerns onlyopto-mechanical switches.
The crucial parameter of optical switches is insertionloss, which describes the attenuation caused by acomponent in an optical circuit. The attenuation is mostlygiven by the misalignment of the introduced fibres. Thusmechanical accuracy of the fabrication makes impact onthe attenuation due to misalignment.
In the recent years 3D printing technologies havedeveloped to a point, where low volume production is moreprofitable using 3D printing, than any other technology.Two mostly used approaches to 3D printing is printingfrom solid string of plastics – fused deposition modelling(FDM). And printing from liquid photopolymer -stereolithography (SLA).[1]
FDM printers became widely spread because ofopen source design and self replicating. Those printers areknown as RepRap.
2. Design of the switchThe POF switch presented in this paper is designed to
switch between five branches. It is manually controlled andthe overall design has minimal material footprint.
The switch consists of two main parts. One is staticand the other is moving. The static part forms supportstructure of the whole switch and holds output fibres atdefined positions. The output fibres are mounted intogrooves and secured in place with overlay cover plate.To increase the mechanical security of the fibre mountsI propose using a glue. For such a scenario would benecessary to find a glue with refraction index smaller thanthe fibre core, otherwise the glue can introduce additionalattenuation to the system.
The input fibre is mounted into a groove onthe moving part of the switch, which I will call slider.The slider is secured in desired place with overlay plate,which also secures the input fibre in the groove. The slideris designed to move perpendicularly to the axis of the fibre.Precise positioning is dependant on single screw andspring.
Switching mechanism is enabled by the screw. Eachrotation corresponds to a defined shift of the slider, thus theinput fibre can be moved to a desired alignment with one ofthe output fibres. The shift is given by the formula
(1)where Δx is the shift, n is the number of rotations and l isthe thread lead.
The total loss on the switch is given by many factors.The first one is Fresnel reflection due to air gap betweenthe two fibres. I assume the Fresnel reflection of 0,32dB.[2][5]
M. KOŠŤÁL, 3D PRINTED SWITCH FOR PLASTIC OPTICAL FIBRES
The second one is loss due to spacing between theinput and output fibres.
L=10log(1−2 s⋅AN3 n⋅d ) (2)
Where L is loss, s is distance between the ends of thefibres, d is the fibre diameter AN is numerical aperture ofthe fibre and n is refractive index of the fibre core.[3]
The third one is loss due to misalignment of thefibres.
L=10log(π
π−2arcsin( xd)−2(xd )⋅√1−( xd )) (3)
Where L is loss, x is deviation from the ideal fibrealignment and, d is the fibre diameter.[3]
The last one is loss due to rough surfaces. I estimatethe loss of 0,1dB as ATM Forum specifies for polishedsurfaces.[4]
Loss through the angle between fibre axis is omitted,because the angle is close to 0 degrees.
2.1 Fabrication
I have chosen the most common 3D printingtechnology available today – the fused depositionmodelling. This technology uses a plastic string of usualdiameter of 1,75mm or 3mm. The string is heated withinthe extruder and thin layer of plastic is laid through thenozzle on the print bed. The whole model is build layer bylayer. Precision of the 3D printer is given by the nozzlediameter, in my case I use 0,4mm nozzle. Printingresolution is given by the stepper motors usedin 3D printer, 0,05mm is well achievable.
Printing parameters of the tested POF switch aregiven in the Tab. 1. Resolution XY means the resolutionin horizontal plane and resolution Z means resolution invertical direction thus the layer thickness.
Nozzle diameter 0,4
Resolution XY 0,4
Resolution Z 0,2
Tab. 1. Printer parameters in mm
Choice of material is important, due to the fact, thatnot every material has suitable thermo-mechanicalproperties for precise 3D models. The filament is depositedto the model while heated up to the 220°C for ABS and theswitch is used in room temperature of 23°C. That meansalmost 200°C difference. Thermal expansion coefficient ofABS is 88·10-6mm-1K-1 and PET is only 59·10-6mm-1K-1
which means shrinking for 1mm for 5cm long designprinted from ABS.[7] Thus I suggest using PET ormaterials with lower thermal expansion coefficient orcompensate the design for thermal expansion duringprinting. My design is using 0,75mm fibres and manual
slider, so the thermal expansion is negligible in comparisonwith inaccuracy of the manual control.
Requirements for mechanical properties are little.Basic resistance against forces originating from useroperating the switch is needed, thus I recommend infilldensity of minimal 10% together with square infill patternto ensure mechanical reliability while in use.
Choice of material is important for possibleapplications in extreme temperatures, which causes meltingof the printed structure. Also chemical properties shall bestudied for some applications. For purpose of this paper Ichose PLA for its availability.
Fig. 1. Generated G-code visualization for 3D printer. PrintablePOF switch components
The printed components are connected together withthe use of metal M2 screws. The holes for the screws areprinted without threads, because it is under the printresolution. Hardness of the PLA allows for cutting threadswith the screw, hence no metal nuts are needed.
Fig. 2. Fabricated POF switch with fibres, side view underconstruction, top view
POSTER 2017, PRAGUE MAY 23 3
The slider movement is enabled by the control screw.Steel M2 screw together with spring coil is used.The spring coil serves as protection from randommovement of the slider and helps with reverse sliding.The slider deviation per one rotation of the control screwequals thread lead of 0,4mm.
Total dimensions of the switch are : 39mm x 15mm x23mm. Print time of the switch was 25minutes and required1,8m of the filament.
2.2 Adjustments of POFs
POFs has to be mounted into the grooves to finish theswitch. End surfaces of the POFs has to be polished tominimise losses due to surface roughness. Polishing is donewith polishing puck on diamond polishing pads with 3 μmgrit, then 1 μm and finally 0,3 μm grit. Distilled water wasused as polishing grease.
Fig. 3. POF polishing; from left top: unpolished, 3μm, 1μm and0,3μm polishing pad grit size
Parameters of used POF is shown Tab. 2.
ncore 1,49
AN 0,5
dcore [μm] 735
dfibre [μm] 750
Tab. 2. POF parameters [6]
3. Results and DiscussionTo evaluate the fabricated switch I conducted the
following measurement. I used a hand-held optical powermeter. First I measured the total loss on all connectedcomponents including the switch. The loss is measureddependent on the fibre misalignment in all five branches ofthe switch. Than I measured loss of the components wherethe switch was replaced by an uninterrupted fibre, which Iassume has 0 loss. Switch attenuation is obtained from
subtraction of those values. Wavelength of 650 nm wasused for the experiment.
The results for all five branches are nearly identical asexpected, thus results are merged.
-0,4 -0,3 -0,2 -0,1 0 0,1 0,2 0,3 0,4
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
measured theoretical z = 0 mm
theoretical z = 0,15 mm
Deviation from alignent [mm]
Atte
nuat
ion
[dB
]
Fig. 4. Graph of switch loss
The theoretical data were calculated for estimatedworst case fibre spacing of 1mm. Measured loss for fibrealignment is (2,27 ± 0,34) dB. The theoretical result foraligned fibres is far from measured result, I added anothercalculations for misalignment of 0,15 mm in verticaldirection.
Aligned fibres have higher attenuation than calculatedvalue of 0,56 dB, 1,82dB respectively. The difference is(0,45 ± 0,34) dB. This is most presumably given by dustparticles in the fibre spacing. Deviation in verticalalignment is source of considerable loss, which could belowered by better calibration of the fabrication process.
Device switch Li [dB]
3D printed 2,27 ± 0,34
Automatic switch 1,00 ± 0,30
Manual switch 2,00 ± 0,50
Adjustable splitter 4,00 ± 0,30
Tab. 3. Comparison of insertion loss with commercial devices.3D printed – switch evaluated in this paper. Automaticswitch – Velickov POF switch. Manual switch – BauerEngineering switch manual. Adjustble splitter – Velickovvariable Y splitter / combiner [8][9][10]
Tab. 3 shows the comparison of 3D printed POFswitch with similar commercial products. In compare
M. KOŠŤÁL, 3D PRINTED SWITCH FOR PLASTIC OPTICAL FIBRES
especially with Bauer Engineering manual switch theresults are very satisfying.
The fibre misalignment in vertical direction isconsiderable source of losses and can be improved by moreaccurate mounting of the fibres on the switch. Increasedaccuracy of layer thickness can have positive impact on thefabricated switch.
4. ConclusionIn this paper I have shown, that fused deposition
modelling technology available today at the consumermarket is precise enough for the manufacturing needs offibre optics components.
The presented 3D printed switch for plastic opticalfibres is capable of its purpose with insertion losscomparable with commercial products. Measured loss is(2,27 ± 0,34) dB which is in range of the commercialmanual switch. Further increase in accuracy of thefabrication process can lower the insertion loss.
AcknowledgementsResearch described in the paper was supervised by
doc. Ing. Václav Prajzler, Ph.D., FEE CTU in Prague and
This work was supported by the research program ofCzech Technical University in Prague by projectno. SGS17/188/OHK3/3T/13.
References[1] PRŮŠA J., PRŮŠA M.: Základy 3D tisku, Prusa Research s.r.o.,2014
[2] WEINERT A.: „Kunststofflichtwellenleiter“, Publicis MCD Verlag,Erlangen, Munich, 1998
[3] MARCOU J.,WILEY J. & SONS, Club des Fibres OptiquesPlastiques (CFOP) France: „Plastic Optical Fibres - PracticalApplications“, Masson, 1997
[4] ZIEMANN O., KRAUSER J., ZAMZOW P. E., DAUM W.: POFHandbook Optical Short Range Transmission Systems, 2nd, Springer,2008
[5] CISCO: Introduction to Optical Fibres, Attenuation andMeasurements, Cisco, 2005
[6] ESKA Polyethylene Jacketed Optical Fiber Cord SH3001,Mitsubishi Int., 2010
[7] PART SNAP: ABS Thermoplastic – FDM 3D printing material,online: http://www.partsnap.com/3d-printing/fdm/abs/, 2017
[8] BAUER ENGINEERING: POF-SWM: Manual Optical Switch,online: www.bauer-eng.de, 2007
[9] VELICKOV ENGINEERING: POF-VYSC: Variable Y-Splitter/Combiner, online: www.velickov.eu, 2010
[10] BAUER ENGINEERINGVELICKOV ENGINEERING: POF-SW:Optical Switch, online: www.velickov.eu, 2010About Authors...
Martin KOŠŤÁL was born in Prague. He has finished hisbachelor degree in Communications Multimedia andElectronics at FEE, CTU in Prague in 2016.