Post on 13-Jul-2022
rmjenkins@qinetiq.com www.QinetiQ.com© Copyright QinetiQ limited 2007
Hollow Waveguide Optical PCB Technology for Micro-Optical SensorsR Mike Jenkins, Mark E McNie, Ewan D Finlayson, Brian J Perrett and Rhodri R DaviesOptronics Division, QinetiQ Ltd.
Thanks to: Kotska Wallace, Benedikt Guldimann and Bernhard FurchESTEC
11th October 2007
6th ESA Round Table on Micro & Nano Technologies for Space Applications
input beam
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• Optical and laser based systems play an increasingly important role in space missions. In such missions, key requirements are:
• small size• low mass• robustness to optical misalignment• good optical efficiency • low cost
• An optical PCB concept could fulfil these requirements
ESA’s interests in relation to space instrumentation
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beam splitter
reflector
Brewster plate
l /4 plate
lens
detector
hollow multimodewaveguides
polycrystalline alumina substrate
laser
output beaml/2 plate
hollow waveguides
reflector
components inalignment slots
lens
lens
The hollow waveguide optical PCB concept
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• Provides a fundamentally new approach to the manufacture of micro-optical systems
Inherently compact, rugged (optically robust) and low mass
Easy integration of any required discrete component
Easier angular alignment tolerances result in excellent optical performance
Optical guidance means small beam widths allowing increased packingdensity compared with free-space systems
The hollow core waveguides facilitate very broad waveband, high powertransmission characteristics compared with solid core guides
Considerable potential for low cost mass manufacture
Advantages of hollow waveguide optical PCB concept
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Hollow waveguide mode theory
( ){ }( )
( ){ } ⎥⎦
⎤⎢⎣
⎡⎟⎠
⎞⎜⎝
⎛−−
−+⎟
⎠
⎞⎜⎝
⎛−−
−=2/12
2
2
2/12
2
3
2
pq 1ikniknReq
1ikn1Rep
w35.4T
dB
λ
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EH11 EH21 EH33 EH24EH11 EH21 EH33 EH24
w
w
substrate
lidikn − ikn −+w/2− w/2
+w/2− w/2w
w
substrate
lidikn − ikn −
yxz
yxz
yxz
yxz
yxz
yxz
+w/2− w/2
+w/2− w/2
near field
far field
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beam splitter
reflector
Brewster plate
l /4 plate
lens
detector
hollow multimodewaveguides
polycrystalline alumina substrate
laser
output beaml/2 plate
hollow waveguides
reflector
components inalignment slots
lens
lens
The hollow waveguide optical PCB concept
rmjenkins@qinetiq.com
www.QinetiQ.com7© Copyright QinetiQ limited 2007
15w
≤χ
w5λθ ≤
Definition of alignment criteria
angular alignment criteria
lateral alignment criteria
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w
w
λθπθ
λπφ w2w2
==
equates to EH11 coupling ≥ 0.95
equates to EH11 coupling ≥ 0.95
χ
θ
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Angular and lateral alignment tolerances versus guide width
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70
60
50
40
30
20
10
00
hollow waveguide width (microns)
angu
lar a
lignm
ent t
oler
ance
(mra
d )
lateral alignment tolerance (m
icrons)70
60
50
40
30
20
10
00angu
lar a
lignm
ent t
oler
ance
(mra
d )
lateral alignment tolerance (m
icrons)
w5λθ ≤
15w
≤χλ = 1.55 µm λ = 1.55 µm
100 µm
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Attenuation and power handling versus guide width
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1000
750
500
250
0
c.w. (watts)
pulsed(mJ)
300
150
0
1000
750
500
250
0
c.w. (watts)
pulsed(mJ)
300
150
0
hollow waveguide width (microns)
c.w. and pulsed energy thresholds
atte
nuat
ion
in d
B/c
m
Si Cu 1000
750
500
250
0
c.w. (watts)
pulsed(mJ)
300
150
0
1000
750
500
250
0
c.w. (watts)
pulsed(mJ)
300
150
0
Si Cu at 1.55 µmSi: n = 3.478, k ≅ 0, Cu: n = 0.606, k = 8.26
⎟⎠⎞
⎜⎝⎛−≈
3
2
11 wnL35.4T
dBλ
100 µm
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QinetiQ Malvern MEMS processing facility
Leading European provider of custom military & commercial MEMS solutions• Experienced, integrated team of
50 staff
Key Capabilities• MEMS design and modelling
• CMOS Electronic design (PCB / MCM / ASIC)
• Microsystems with embedded processing
• Microstructure fabrication (ISO9001) Advanced characterisation and test
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DRIE Passivation & Etch Cycle
Hollow silicon waveguides for 1.55 µm micro-optical systems
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11-element 90° fold array based on precision alignment slots
20 mm20 mm
20 mm
20 mm20 mm
20 mm
20 mm
Optical PCB test structure with eleven 2 x 2 x 0.5 mm integrated fully reflecting fold mirrors in conjunction with 125 µm wide hollow guides for assessing alignment reproducibility
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fold 1 near field far field
fold 2
fold 3
fold 4
fold 5
fold 6
fold 7
fold 8
fold 9
fold 10
fold 11
20 mm20 mm
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20 mm20 mm
0
20
40
60
80
100
0 0.5 1 1.5 2 2.5 3 3.5 4
Waveguide length (cm)
Tran
smis
sion
(%)
Good transmissionPoor transmissionTheoretical transmissionLinear fit to data
Measurements of attenuation as a function of overall guide length
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1234567891011fold number
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Hollow silicon waveguide Michelson interferometer
fully reflecting mirror on PZT
camera
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Demonstration of hollow silicon waveguide Michelson interferometer
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Characteristics of Michelson interferometer test structure
fully reflecting mirror on PZT
detector
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Hybrid integration of discrete components
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double etch depthdouble etch depth• Passive– Fibres – Lenses - ball/GRIN– Mirrors– Beam Splitters– Gratings– Optical isolators– TFF & AWG (PLC)
• Active– Lasers– Modulators (PLC)– Detectors– VOAs– SOAs
Fibre channel & clips
Ball lens alignment slotBall lens alignment slot
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Monolithic integration of MEMS components
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• Monolithic– Moveable mirrors
• Phase shifters• Beam steering
– VOA / Switch• Shutter-based
• Hybrid– Moveable Mirrors– Tuneable Filters– VOA / Switch– etc.
VOA based on shutter in guideVOA based on shutter in guide
MEMS mirror phase shifterMEMS mirror phase shifter
light beam
light beam
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Horizontal
Demonstration of multimode interference (MMI) splitters
input field
I
λ
2bL =
L
Horizontal
HorizontalHorizontal
LLL
Vertical profile centre
input field
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Proposed HWG 1.55 µm coherent lidar demonstrator
λ/2 plate
95%
5%
λ/2 plate telescope
50%/50% mixer
detector
fully reflecting mirror
return from target laser source
alignment slots
λ/4 plateλ
plate
intensity beam splitter polarising beam
splitter or Brewster plate
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Summary of hollow silicon waveguide optical PCB integration technology
Ease integration of discrete components - no optical interface to bridge
Broad waveband high power transmission characteristics
No beam diffraction - small/fixed beam diameter
Easier angular alignment tolerances c.f. free-space
Easier lateral alignment tolerances c.f. solid-core guides
Predicted attenuation coefficients < 0.01 dB/cm
Integrated 45° fold mirrors provide good fundamental mode propagation fidelity in practice
Hollow waveguide Michelson interferometer demonstrated in practice
With some further development the concept appears set to provide us with compact, low mass, rugged, low cost micro-optical systems
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