a fisheye lens for many-point pdv

Vision – Service – Partnership Managed and Operated by National Security Technologies, LLC Nevada National Security Site

6th Annual Photonic Doppler Velocimetry Workshop: Nov 3-4, 2011

A Fisheye Lens for Many-Point PDV

Brent Frogget National Security Technologies, LLC

This work was done by National Security Technologies, LLC, under

Contract No. DE-AC52-06NA25946 with the U.S. Department of Energy.

DOE/NV/25946--1363



AOC 2 in Optical Dome



AOC 2: Fisheye Lens Features

11:19:58

f23crev

Scale:

7.50

BCF 30-Mar-11

3.33 MM

16:02:33

f30k (fisheye lens)

Scale:7.50

Positions: 1-2

BCF 27-Sep-11

3.33 MM

Prototype Build 2 High angular coverage Index matching element to fibers

Hemi 2 lenses Better anti-reflection coatings Cut down lens element diameters Not using highest angles

(View direction in later slide)

Index matching lens element



AOC 2: Fisheye with Reflector Prisms 16:49:38

f30e (NSS hybrid fisheye)

Scale:7.50

Positions: 1-6

BCF 04-Oct-11

3.33 MM

Focus adjustment



AOC 2: Fisheye Fiber Map

Hemi 2 250-micron spacing not fully populated

Index matching lens element



Footprints of Beams

11:50:22


SURFACE18:prism mirror

BCF28-Sep-11

1.50

MM

X=0.000

Y=0.000

Right prism mirror face

Top of fisheye lens element (only half of points shown)

100º 90º

13:42:00


SURFACE15

BCF11-Aug-11

2.50

MM

X=0.000

Y=0.000

Hemi 2 250-micron spacing



AOC 2: Fisheye Rough-Angle Metrology

This measurement inside a dome is vertically flipped compared to the spherical plot from the top (outside) on the next slide.

Symbol key

= rough area blocked

by prism mirror



AOC 2: Used Locations in Spherical Plot with center as ‘up’

Doubled points are both pin measurement machine and rough metrology (uncorrected)

120

90

0 0



AOC 2: Fisheye Lens

•  Disadvantages –  This lens type has some distortion at the edge of the

field-of-view. This causes a change in measurement point spacing with angle―high-angle spots become elliptical and less efficient. Therefore, mirrors were added for better high- angle spots causing some ‘dead’ regions.

–  The fiber plane is larger than standard array connectors and is custom made.



AOC 2: Fisheye Lens

•  Advantages –  A ‘fisheye’ lens can image measurement points over greater

than a hemisphere without ‘dead’ regions.

–  The front fisheye element does not encroach much into the center of the cavity allowing for longer tracking distances.

–  This design uses an index matching element to keep all fibers at the same plane without high return loss.



Data Quality

•  Static back-reflections (minimum, mean, maximum in dB): –  <–70, –58, –46 without target (out of 44 used fibers;

two at –27 not used) –  –58, –45, –33 with target

•  Burn paper spot sizes: –  10 mm away: ~280-micron diameter –  50 mm away: ~320-micron diameter –  90 mm away: ~400-micron diameter

•  Focus adjusted for entire probe at once



Lessons Learned

•  Good 1550-nanometer anti-reflection coatings needed on lenses.

•  Index matching gel works better for us than index matching epoxy.

•  Fiber polishing for coupling to index matching element is sensitive.

•  Focusing to best position is sensitive and best done actively using

an IR camera.

•  Highest angle points are less efficient unless reached using mirrors.

•  Some areas require fibers closer together.

•  We have cut down the lens diameters to fit the small blast tube.

•  We can put the fiber bundle through the blast tube before attaching

it to the lenses so fiber connectors do not need to be cut.



Next Iteration

•  Slightly smaller top fisheye lens element

•  Larger prism mirrors and better prism mounting

•  Different fiber arrangements



AOC 2: Fisheye with Longer Reflector Prisms



AOC 2: Fisheye with Mounting for Longer Reflector Prisms



Example Fisheye Lens Fiber Map

Hemi 4 Some 125-micron cladding close-packed fibers (many other fiber patterns are possible)

Lens axis rotation 1 2

3 4 5

6 7 8

9 10 11 12

13 14

15 16 17 18

19

20 21 22 23

24 25 26

27 28

29 30 31 32

33 34

35 36 37 38

39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56

57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74

75 76 77 78 79 80 81 82

83 84 85 86 87 88 89 90 91

92 93 94 95 96

97 98 99 100 101

102 103 104 105

106 107 108 109 110

111 112 113 114 115 116 117 118 119

120 121 122 123 124 125 126 127

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2 Fiber #

>120 points plotted Points can be added and positions shifted. Close-pack could be 64% tighter with 80-micron cladding fibers.



Footprints of Beams

11:32:25

f30j (NSS hybrid fisheye)

SURFACE18

BCF28-Sep-11

1.50

MM

X=0.000

Y=0.000

Hemi 4 Some 125-micron cladding close-pack fibers 10:55:52

f30j (NSS hybrid fisheye)

SURFACE15

BCF27-Sep-11

1.67

MM

X=0.000

Y=0.000

Right prism mirror face Top of fisheye lens element

100º 90º 80º



S2 Plot

S2 axis lined up to fiber. Points can be added and positions shifted. >120 points plotted.



S2 Plot

Will move points here.

S2 axis lined up to fiber. Points can be added and positions shifted.



S2 Plot




Angular Separation

0 1 2 3 4 5 6 7 8 9

10

0 20 40 60 80 100 120 140 160 180 200

Series1


Polar Angle

Diff

eren

ce in

Pol

ar A

ngle



Ferrule for Fibers



15:45:24

f26b Scale: 7.50 BCF 24-Oct-11

3.33 MM

Lens Design Changes

0

20

40

60

80

100

120

0 1 2 3 4

Anl

ge

fiber R (mm)

f25d

Linear Angle

f26b

Current design

Future reduced distortion design (still in progress)

15:42:55

f25d Scale: 7.50 BCF 24-Oct-11

3.33 MM



Summary for Fisheye Lens Probe

•  Long tracking distance (probe less than 9 mm radius) •  Maximum polar angle coverage: ~ ±100 degrees (dome)

using mirrors •  Rays go to a <3 mm radius common center point near hydro center •  Uses glues and index matching gel (sealed inside) •  Includes many spare fibers (measurement points) •  Point accuracy using aiming can be <1 mm •  Point angular separation:

–  Up: Polar 0.5, azimuth 2.6 degrees (if using 80-micron cladding fibers)

–  Side: 1st–2nd point, polar 2.6 degrees (if using 80-micron cladding fibers)



Acknowledgments

We have an exceptional team. Some team members are:

Brian Cata, Brian Cox, Edward Daykin, Douglas DeVore, David Esquibel, Daniel Frayer, Cenobio Gallegos, Robert Malone,

Morris Kaufman, and Vince Romero (NSTec)

Special thanks to David Holtkamp (LANL) for support and encouragement.

Thank you to everyone who contributed – Great Job!

a fisheye lens for many-point pdv

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