The Effect of Dust on Lensed and non-lensed Connectors. Dr. Michael A. Kadar-Kallen Broadband Network Solutions, TE Connectivity

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1 The Effect of Dust on Lensed and non-lensed Connectors Dr. Michael A. Kadar-Kallen Broadband Network Solutions, TE Connectivity Presentation for inemi at OFC: March 3, 015

2 Outline as discussed with the inemi group 17-Feb-015: Overview of the effect of dust on lensed and non-lensed connectors. A simple dust model Model A only Multimode only Models B (fine dust, same area) and C (more dust) are in the appendix New: Theoretical Foundation Multimode Coupling (singlemode or a few modes) Singlemode

3 Overview This presentation describes a simple model of dust on a fiberoptic connector. The model is used to compare: Lensed vs. non-lensed connectors The effect of dust particles of different sizes with the same total area Single- vs. multi-fiber connectors Lensed connectors are often avoided due to their higher insertion loss (IL), in favor of physical contact (PC) connectors. However, the relative insensitivity of a lensed connector to dust is an advantage when The optical interface may be exposed in a disconnected state The connector is mated many times The connector interface is inaccessible In these cases, the typical IL for an expanded beam connector can be less than a PC connector, particularly in applications with high airflow and a large number of interconnects (ex: Datacenter; Optical Backplane). 3

4 4 Why Choose a Lensed Ferrule?

5 The Effect of Dust on a Lens vs. Fiber 0 µm Dust 9. µm SM Fiber Core 50 µm MM Fiber Core 00 µm Lens Active Area General Features Lens Several particles of dust often land on the lens. The dust obscures a small fraction of the lens area. Fiber Dust often does NOT land on the fiber. When dust obscures the fiber, the loss may be very high. 5

6 A Simple Dust Model Assumptions for this simple model Dust consists of particles which completely obscure light Simplifying assumption: Spherical dust particles with a uniform size. Note: if the dust is significantly smaller than the width of the distribution of light, then the loss depends on the area obscured by a dust particle, and not its shape. The positions of N dust particles are randomly distributed within a rectangular cell surrounding the lens (e.g. 50 µm x 50 µm) The dust particles do not overlap Conservative estimate An array of fibers or lenses is modeled as M independent rectangular cells with N dust particles in each cell. The absorption by a dust particle is a function of the area of the dust particle and the radial distance r from the center of the lens or fiber to the dust particle. This function is specific to each optical design. The optical system in this presentation gives a 4x beam expansion for a 50 µm multimode fiber. 6

7 Multimode Modeling Details Dust is modeled in Zemax as a circular obscuration (0 µm). The non-zero Zemax results are fit to a polynomial (truncated) The fit function is used in the Monte Carlo A = C Cr C4r Fiber: 50 µm wide grid r Lens: 00 µm wide grid Fiber and Lens - Absorption by Dust Lens - Absorption by Dust Absorption (fraction) Fiber Lens Absorption (fraction) Lens r (µm) r (µm) 7

8 Three Configurations (A, B, C) (A) 0 µm, 10 dust particles per 50 µm x 50 µm cell (5% of Area) (B) Fine Dust (equal area) 10 µm, 5% of Area (C) More Dust 0 µm, 10% of Area

9 (A)Monte Carlo Single Lens 0 µm, 10 per 50 x 50 µm area = 5% Area Obscured The use of a lens yields predictable losses. Max loss 0.5 db. 64% with no Dust Loss In the absence of a lens, the losses may be low (frequently zero) but the losses may be high db = max loss for 1 dust particle obscuring a fiber 91% with IL < 1 db : 97% < 0.39 db. Ave = 0.1 db. : 97% < 1.45 db. Ave = 0.4 db. The x-axis is the Dust Loss the additional loss caused by dust. 9

(A)Max IL for a 1 Lens Array 0 µm, 10 per 50 x 50 µm area = 5% Area Obscured The use of a lens yields predictable losses. 0.4% with no Dust Loss It is very likely that one fiber in an array will be obscured by dust.

10 (A)Max IL for a 1 Lens Array 0 µm, 10 per 50 x 50 µm area = 5% Area Obscured The use of a lens yields predictable losses. 0.4% with no Dust Loss It is very likely that one fiber in an array will be obscured by dust db = max loss for 1 dust particle obscuring a fiber : 97% < 0.49 db. Ave = 0.36 db. : 97% <.98 db. Ave = 1.33 db. 30% with IL < 1 db The data and related statistics are for the Maximum IL of the 1 fibers or lenses in an array. 10

11 Theoretical Foundation 11

12 Power Transmission Through Dust In the absence of dust, the power in a beam of light is the integral of the intensity distribution over a surface that is perpendicular to the optical axis. I da= P = I( dxdy We define the dust transmission function for a surface as 0 D( = 1 where dust is otherwise present (We ignore the z-location of the dust on a curved surface.) The fraction of the power that is transmitted through this surface is T Dust I( D( dxdy = I( dxdy 1 = I( D( dxdy P 1

13 Multimode Dust Loss In a low-loss multimode system, all of the power that is transmitted through a plane in the optical system is coupled into the receiving fiber or detector. The additional multimode insertion loss caused by dust is therefore 1 (db) = 10log10T Dust = 10log I( D( dxdy P ILDust, MM 10 In an optical system with few modes (including singlemode) the situation is more complicated, because we must determine how much of the power that is transmitted through the dust will be coupled into the receiving fiber. 13

14 14 Coupling of Electric Fields For an optical system with a source and receiver that have few modes, it is necessary to evaluate the coupling between the field E 1 that source emits and the field E that the receiver accepts. The coupling is given by the overlap integral evaluated in a plane that is perpendicular to the optical axis. For a singlemode source and receiver: The coupling loss in the presence of dust is Therefore transmission due to dust is T C Dust C = Dust, = = C E * 1 E Dust C = E E Edxdy E * 1 1 * 1 * 1 E Edxdy 1 E * 1 dxdy E * D( E E * 1 E E E dxdy dxdy * dxdy D( dxdy E dxdy

15 Coupling of Electric Fields () For a low-loss optical design C 1 This can only occur if the electric fields of the source and receiver are approximately the same: E1( E( It follows that and ( T = I Dust D( P dxdy 1 (db) = 10log10T Dust = 0log I( D( dxdy P ILDust This differs from the MM result by a factor of.

16 Singlemode Dust Loss The output of a singlemode fiber is well-approximated as a Gaussian function. The intensity distribution can be written I P r r, z) = exp πw ( z) w ( z) ( where z is the distance from the beam waist along the propagation direction, and w(z) is the local beam waist (radius at 1/e intensit. It follows that the singlemode dust loss is T Dust = = πw I( D( dxdy P exp r w D( dxdy 16

A Simple Example: Spherical Dust Particle on Axis The dust transmission function for a spherical dust particle located at (0,0) is The dust loss is: T dust 4R =

17 A Simple Example: Spherical Dust Particle on Axis The dust transmission function for a spherical dust particle located at (0,0) is The dust loss is: T dust 4R = exp w 0 D= 1 This result was confirmed using the Zemax FICL operand on the surface of an ideal lens in a 4f configuration. r = exp πw w R if if r r > πrdr R R 17

18 Conclusions 18

19 Conclusions A very simple dust model illustrates the advantage of a lensed connector used in a dusty environment. The model is built upon functions which are fit to data derived from optical modeling and/or analytical calculations. The Theoretical Foundation shows that the loss for an arbitrary distribution of dust can be evaluated if the intensity distribution on that surface is known. Regions of the surfaces of the optical system which have a high intensity of light are more sensitive to dust. The intensity distribution can be shared between competitors without revealing proprietary features of the optical design. It should be possible to define a few typical intensity distributions (such as the Gaussian distribution) which can be used to define a standard for the acceptable level of dust on optical surfaces in lensed systems. 19

20 Thank You 0

21 Models B and C 1

22 (A B) Fine Dust: ½, 4xN, Equal Area 0 µm 10 µm, particles, 5 5% Area Obscured 15 (A) General Features Equal Area Obscured Average loss is approximately unchanged Smaller Dust Less catastrophic effect on fiber loss Larger Number less variation in the number of particles striking the lens or fiber The lens provides less of a benefit if the dust is much smaller than the fiber core (B)

23 (A vs. B) Monte Carlo Single Lens 0 µm vs. 10 µm, 10 vs. 40 particles, 5% Area Obscured Lens (B) Fiber (B) Fiber (B) : 97% < 0.39 db. Ave = 0.1 db. Lens (B): 97% < 0.9 db. Ave = 0.1 db. : 97% < 1.45 db. Ave = 0.4 db. Fiber (B): 97% < 0.73 db. Ave = 0. db. Lens (B) 3

24 (A vs. B) Max IL for an 1 Lens Array 0 µm vs. 10 µm, 10 vs. 40 particles, 5% Area Obscured Lens (B) Fiber (B) Lens (B) Fiber (B) : 97% < 0.49 db. Ave = 0.36 db. Lens (B): 97% < 0.34 db. Ave = 0.8 db. : 97% <.98 db. Ave = 1.33 db. Fiber (B): 97% < 1.1 db. Ave = 0.66 db. 4

25 (A vs. C) More Dust: xn 0 µm, 10 vs. 0 particles, 5 vs. 10% Area Obscured General Features 50 (A) Larger Area Obscured Average loss increases Larger Number less variation in number of particles striking the lens or fiber More dust accentuates the problem (fiber) and solution (lens) (C)

26 (A vs. C) Monte Carlo Single Lens 0 µm, 10 vs. 0 particles, 5 vs. 10% Area Obscured Lens (C) Fiber (C) Fiber (C) : 97% < 0.39 db. Ave = 0.1 db. Lens (C): 97% < 0.68 db. Ave = 0.43 db. : 97% < 1.45 db. Ave = 0.4 db. Fiber (C): 97% <.37 db. Ave = 0.51 db. Lens (C) 6

27 (A vs. C) Max IL for an 1 Lens Array 0 µm, 10 vs. 0 particles, 5 vs. 10% Area Obscured Lens (C) Fiber (C) Lens (C) : 97% < 0.49 db. Ave = 0.36 db. Lens (C): 97% < 0.84 db. Ave = 0.66 db. : 97% <.98 db. Ave = 1.33 db. Fiber (C): 97% < 4.77 db. Ave =.11 db. Fiber (C) 7

28 8 Fiber Array Graphs 8

% with no Dust Loss It is very likely that one fiber in an array will be obscured by dust. 1.

29 (A)Max IL for an 8 Lens Array 0 µm, 10 per 50 x 50 µm area = 5% Area Obscured The use of a lens yields predictable losses. % with no Dust Loss It is very likely that one fiber in an array will be obscured by dust db = max loss for 1 dust particle obscuring a fiber : 97% < 0.47 db. Ave = 0.34 db. : 97% <.74 db. Ave = 1.1 db. 44% with IL < 1 db (56% with IL > 1 db) 9

30 (A vs. B) Max IL for an 8 Lens Array 0 µm vs. 10 µm, 10 vs. 40 particles, 5% Area Obscured Lens (B) Fiber (B) Lens (B) Fiber (B) : 97% < 0.47 db. Ave = 0.34 db. Lens (B): 97% < 0.33 db. Ave = 0.7 db. : 97% <.74 db. Ave = 1.1 db. Fiber (B): 97% < 1.06 db. Ave = 0.59 db. 30

31 (A vs. C) Max IL for an 8 Lens Array 0 µm, 10 vs. 0 particles, 5 vs. 10% Area Obscured Lens (C) Fiber (C) Lens (C) : 97% < 0.47 db. Ave = 0.34 db. Lens (C): 97% < 0.8 db. Ave = 0.63 db. : 97% <.74 db. Ave = 1.1 db. Fiber (C): 97% < 4.15 db. Ave = 1.81 db. Fiber (C) 31

32 Summary of Multimode Results Parameter Model 1 Fiber 1 Lens 8 Fibers 8 Lenses 1 Fibers 1 Lenses B (Fine Dust) % level (db) A C (More Dust) B (Fine Dust) 99% 100% 96% 100% 93% 100% % < 1 db A 91% 100% 44% 100% 30% 100% C (More Dust) 79% 100% 16% 100% 6% 100% B (Fine Dust) Average (db) A C (More Dust) B (Fine Dust) 16.1% 0.00% 0.00% 0.00% 0.00% 0.00% % 0 db A 63.93% 0.1%.44% 0.00% 0.40% 0.00% C (More Dust) 40.67% 0.00% 0.09% 0.00% 0.00% 0.00% 3

21. Propagation of Gaussian beams

21. Propagation of Gaussian beams 1. Propagation of Gaussian beams How to propagate a Gaussian beam Rayleigh range and confocal parameter Transmission through a circular aperture Focusing a Gaussian beam Depth of field Gaussian beams and