hollow waveguide optical pcb technology for micro-optical

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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

www.QinetiQ.com2© Copyright QinetiQ limited 2007

• 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


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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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


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


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


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


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


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


Horizontal

Demonstration of multimode interference (MMI) splitters

input field

I

λ

2bL =

L

Horizontal

HorizontalHorizontal

LLL

Vertical profile centre

input field


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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hollow waveguide optical pcb technology for micro-optical

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