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Integrated photonic beamformer employing continuously tunable ring resonator-based delays in CMOS-compatible LPCVD waveguide technology. C. G. H. Roeloffzen* a , A. Meijerink a , L. Zhuang a , D. A. I. Marpaung a , R. G. Heideman b , A. Leinse b , M. Hoekman b , W. van Etten a .

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slide1

Integrated photonic beamformer employing

continuously tunable ring resonator-based delays in CMOS-compatible LPCVD waveguide technology

C. G. H. Roeloffzen*a, A. Meijerinka, L. Zhuanga, D. A. I. Marpaunga, R. G. Heidemanb, A. Leinseb, M. Hoekmanb, W. van Ettena.

aUniversity of Twente, Faculty of Electrical Engineering, Mathematics and Computer Science, Telecommunication Engineering Group, P.O. Box 217, 7500 AE Enschede, The Netherlands

bLioniX B.V., P.O. Box 456, 7500 AH Enschede, The Netherlands

contents
Contents

1. Introduction;

  • System overview & requirements;
  • Optical beamformer- Ring resonator-based delays;- OBFN structure;- Chip fabrication;- OBFN control block;- E/O & O/E conversion;- System performance.
  • Conclusions

MWP » MWP in PAAs » SMART » Conclusions » Questions

1 introduction what is beamforming
1. Introduction: What is beamforming

Smart Antenna systems:

Switched beam: finite number of fixed predefined patterns

Adaptive array: Infinite number of (real time) adjustable patterns

MWP » MWP in PAAs » SMART » Conclusions » Questions»

1 introduction smart antenna
1. Introduction: Smart antenna

Smart Antenna systems:

Using a variety of new signal-processing algorithms, the adaptive system takes advantage of its ability to effectively locate and track various types of signals to dynamically minimize interference and maximize intended signal reception.

Beamforming: spatial filtering

MWP » MWP in PAAs » SMART » Conclusions » Questions»

1 beamforming uniform line array
1. Beamforming: Uniform line array

s(t)

x0(t)

d

x1(t)

x2(t)

xM(t)

(M-1)

MWP » MWP in PAAs » SMART » Conclusions » Questions»

1 beamforminh delay sum
1. Beamforminh: Delay-sum
  • When T=, the channels are all time aligned
  • wm are beamformer weights
  • Gain in direction  is wm. Less in other directions due to incoherent addition.

Timed array

(t-[M-1]T)

x

w0

(t-[M-2]T)

x

+

w1

(t)

x

wM-1

MWP » MWP in PAAs » SMART » Conclusions » Questions»

1 beamforming similar to fir filter
1. Beamforming: Similar to FIR filter

br

  • Let T=0 (broadside)
  • Represent signal delay across array as a delay line
  • Sample: x[n]=x0 (nT)
  • Looks like an FIR filter!
  • x[n]*w[n]
  • Design w with FIR methods

x

(t-)

w0

x

+

y(t)

w1

(t-)

x

wM-1

MWP » MWP in PAAs » SMART » Conclusions » Questions»

1 beamforming narrowband
1. Beamforming: Narrowband
  • Narrowband assumption: Let s(t) be bandpass with BW << c / (M-1)dHz.
  • This means the phase difference between upper and lower band edges for propagation across the entire array is small, e.g. < /10 radian.
  • Most communication signals fit this model.
  • If signal is not narrowband, bandpass filter it and build a new beamformer for each subband.
  • Sample the array x[n]=x(nT),
  • We can now eliminate time delays and use complex weights, w= [w0, …, wM-1] , to both steer (phase align) and weight (control beam shape)

MWP » MWP in PAAs » SMART » Conclusions » Questions»

1 beamforming narrowband phased array
1. Beamforming: Narrowband phased array

x0[n]

x

w0

x1[n]

x

+

w1

xM-1[n]

x

wM-1

m = amplitude weight for sensor m,

f0 = bandpass center frequency, Hz,

0 = direction of max response

MWP » MWP in PAAs » SMART » Conclusions » Questions»

1 beamforming fft implementation
1. Beamforming: FFT implementation

Suppose you want to for many beams at once, in different directions.

If beam k steered to k , has strongest signal, we assume sources is in that direction.

MWP » MWP in PAAs » SMART » Conclusions » Questions»

1 beamforming fft implementation1
1. Beamforming: FFT implementation

many beams at once

x0[n]

Amplitude

Taper

(multiply by )

FFT

y0[n]

x1[n]

y1[n]

xM-1[n]

y(M-1)[n]

MWP » MWP in PAAs » SMART » Conclusions » Questions»

1 beamforming examples
1. Beamforming: Examples

Beamforming:

Electronic

Digital

Optical

MWP » MWP in PAAs » SMART » Conclusions » Questions»

1 examples electronic beamforming
1. Examples: Electronic beamforming

SiGe

H. Hashemi, IEEE Communications magazine, Sept 2008

MWP » MWP in PAAs » SMART » Conclusions » Questions»

1 examples electronic beamforming1
1. Examples: Electronic beamforming

CMOS

MWP » MWP in PAAs » SMART » Conclusions » Questions»

1 examples electronic beamforming2
1. Examples: Electronic beamforming
  • MMIC (CMOS & SiGe)
  • + very small chip
  • + TTD & phase shifters
  • Switched delay
  • + Large bandwidth
  • + low power consumption
  • - Large coupling between channels

MWP » MWP in PAAs » SMART » Conclusions » Questions»

1 examples digital beamforming
1. Examples: Digital beamforming

Digital beamforming:

MWP » MWP in PAAs » SMART » Conclusions » Questions»

1 examples digital beamforming1
1. Examples: Digital beamforming

Frequency domain beamforming

Narrowband decomposition

MWP » MWP in PAAs » SMART » Conclusions » Questions»

1 examples digital beamforming2
1. Examples: Digital beamforming
  • Digital beamforming:
  • +Easy implementation of time delays
  • Multiple data converters required
  • Large sampling rate
  • Large number of bits (large dynamic range)
  • Large power consumption

MWP » MWP in PAAs » SMART » Conclusions » Questions»

1 examples optical beamforming
1. Examples: Optical beamforming

Optical beamforming:

+Easy

MWP » MWP in PAAs » SMART » Conclusions » Questions»

1 int aose
1. Int: aose

Smart

MWP » MWP in PAAs » SMART » Conclusions » Questions»

1 introduction aim and purpose
1. Introduction: aim and purpose

Aim:

Development of a novel Ku-band antenna for airborne reception of satellite signals

, using a broadband conformal phased array

  • Purpose:
  • Live weather reports;
  • High-speed Internet access;
  • Live television through Digital VideoBroadcasting via satellite (DVB-s)

MWP » MWP in PAAs » SMART » Conclusions » Questions»

1 introduction specific targets
1. Introduction: specific targets
  • Specific targets:
  • Conformal phased array structure definition;
  • Broadband stacked patch antenna elements;
  • Broadband integrated optical beamformerbased on optical ring resonatorsin CMOS-compatible waveguide technology;
  • Experimental demonstrator.

MWP » MWP in PAAs » SMART » Conclusions » Questions»

2 system overview requirements
2. System overview & requirements

8x8

8x1

gain

40x40

optical

beam width

Antenna

array

RF

front-end

beamformer

to receiver(s)

with amplitude tapering

scan angle

Frequency range: 10.7 – 12.75 GHz (Ku band)

Polarization: 2 linear (H/V)

Scan angle: -60 to +60 degrees

Gain: > 32 dB

Selectivity: << 2 degrees

No. elements: ~1600

Element spacing: ~/2 (~1.5 cm, or ~50 ps)

Maximum delay: ~2 ns

Delay compensation by phase shifters?  beam squint at outer frequencies!

 (Broadband) time delay compensation required !

1

 Continuous delay tuning required !

MWP » MWP in PAAs » SMART » Conclusions » Questions»

3 optical beamformer overview

controlblock

3. Optical beamformer: overview

plane position & angle

antenna viewing angle

feedbackloop

Antenna

elements

RFfront-end

OBFN chip

E/O

O/E

to receiver(s)

?

?

?

tunable broadband delays& amplitude weights.

MWP » MWP in PAAs » SMART » Conclusions » Questions»

3 optical beamformer orr based delays
Periodic transfer function;

Flat magnitude response.

Phase transition aroundresonance frequency;

Bell-shaped group delay response;

Trade-off: delay vs. bandwidth

 f

3. Optical beamformer: ORR-based delays

Single ring resonator:

 Phase

T : Round trip time;

: Power coupling coefficient;

 : Additional phase.

 Group delay

 f

MWP » MWP in PAAs » SMART » Conclusions » Questions»

3 optical beamformer orr based delays1
Rippled group delay response;

Enhanced bandwidth;

Trade-off: delay vs. bandwidth vs. delay ripple vs. no. rings;

bandwidth

ripple

3. Optical beamformer: ORR-based delays

Cascaded ring resonators:

 Group delay

 f

Or in other words: for given delay ripple requirements:

Required no. rings is roughly proportional to product of required optical bandwidth and maximum delay

MWP » MWP in PAAs » SMART » Conclusions » Questions»

3 optical beamformer 8x1 obfn
3. Optical beamformer: 8x1 OBFN

8x1 Optical beam forming network (OBFN)

combining networkwith tunable combiners(for amplitude tapering)

8 inputswithtunabledelays

1 output

12 rings

7 combiners

 31 tuning elements

MWP » MWP in PAAs » SMART » Conclusions » Questions»

3 optical beamformer chip fabrication
3. Optical beamformer: chip fabrication

Fabrication process of TriPleX Technology

MWP » MWP in PAAs » SMART » Conclusions » Questions»

3 optical beamformer chip fabrication1
3. Optical beamformer: chip fabrication

TriPleXTM results

1: chip length 3 cm

2: here, small core fibers were used (MFD of 3.5 µm)

3: minimal bend radius ~400 µm

MWP » MWP in PAAs » SMART » Conclusions » Questions»

3 optical beamformer 8x1 obfn chip
3. Optical beamformer: 8x1 OBFN chip

Single-chip 8x1 OBFN realized inCMOS-compatible optical waveguide technology

TriPleX Technology

1 cm

4.85 cm x 0.95 cm

Heater bondpad

MWP » MWP in PAAs » SMART » Conclusions » Questions»

3 optical beamformer obfn control block
3. Optical beamformer: OBFN control block

beam angle

delays + amplitudes

ARM7microprocessor

chip parameters (isand is)

DA conversion & amplification

heater voltages

MWP » MWP in PAAs » SMART » Conclusions » Questions»

3 optical beamformer obfn measurements
3. Optical beamformer: OBFN measurements

OBFN Measurement results

L. Zhuang et al., IEEE Photonics Technology Letters, vol. 19,no. 15, Aug. 2007

1 ns ~ 30 cm delay distance in vacuum

MWP » MWP in PAAs » SMART » Conclusions » Questions»

3 optical beamformer e o and o e conversion
3. Optical beamformer: E/O and O/E conversion
  • E/O and O/E conversions?
  • low optical bandwidth;
  • high linearity;
  • low noise

RF front-end

LNA

photo-diode

DM laser

OBFN

chirp!

TIA

electrical » optical

optical » electrical

MWP » MWP in PAAs » SMART » Conclusions » Questions»

3 optical beamformer e o and o e conversion1
3. Optical beamformer: E/O and O/E conversion
  • E/O and O/E conversions?
  • low optical bandwidth;
  • high linearity;
  • low noise

RF front-end

LNA

photo-diode

CW laser

mod.

OBFN

beat noise!

TIA

electrical » optical

optical » electrical

MWP » MWP in PAAs » SMART » Conclusions » Questions»

3 optical beamformer e o and o e conversion2
3. Optical beamformer: E/O and O/E conversion
  • E/O and O/E conversions?
  • low optical bandwidth;
  • high linearity;
  • low noise

RF front-end

LNA

photo-diode

mod.

OBFN

CW laser

TIA

electrical » optical

optical » electrical

MWP » MWP in PAAs » SMART » Conclusions » Questions»

3 optical beamformer e o and o e conversion3

spectrum

frequency

3. Optical beamformer: E/O and O/E conversion

2 x 12.75 = 25.5 GHz

12.75 GHz

RF front-end

10.7 GHz

LNA

photo-diode

mod.

OBFN

CW laser

TIA

electrical » optical

optical » electrical

MWP » MWP in PAAs » SMART » Conclusions » Questions»

3 optical beamformer e o and o e conversion4

spectrum

frequency

3. Optical beamformer: E/O and O/E conversion

2 x 2.15 = 4.3 GHz

2150 MHz

RF front-end

950 MHz

LNB

LNA

photo-diode

mod.

OBFN

CW laser

TIA

electrical » optical

optical » electrical

MWP » MWP in PAAs » SMART » Conclusions » Questions»

3 optical beamformer e o and o e conversion5

spectrum

frequency

3. Optical beamformer: E/O and O/E conversion

single-sideband modulation withsuppressed carrier (SSB-SC)

  • Implementation of optical SSB modulation?
  • Optical heterodyning;
  • Phase shift method;
  • Filter-based method.

RF front-end

1.2 GHz

LNB

photo-diode

  • Balanced optical detection:
  • cancels individual intensity terms;
  • mixing term remains;
  • reduces laser intensity noise;
  • enhances dynamic range.

SSB-SC

mod.

filter

OBFN

CW laser

filter

TIA

electrical » optical

optical » electrical

MWP » MWP in PAAs » SMART » Conclusions » Questions»

3 optical beamformer e o and o e conversion6

spectrum

frequency

3. Optical beamformer: E/O and O/E conversion

single-sideband modulation withsuppressed carrier (SSB-SC)

  • Filter requirements:
  • Broad pass band and stop band (1.2 GHz);
  • 1.9 GHz guard band;
  • High stop band suppression;
  • Low pass band ripple and dispersion;
  • Low loss;
  • Compact;
  • Same technology as OBFN.

RF front-end

1.2 GHz

LNB

mod.

OBFN

CW laser

filter

TIA

electrical » optical

1 chip !

optical » electrical

MWP » MWP in PAAs » SMART » Conclusions » Questions»

3 optical beamformer e o and o e conversion7
3. Optical beamformer: E/O and O/E conversion

Optical sideband filter chip in the same technology as the OBFN

5 mm

MZI + Ring

MWP » MWP in PAAs » SMART » Conclusions » Questions»

3 optical beamformer e o and o e conversion8
3. Optical beamformer: E/O and O/E conversion

Measured filter response

3 GHz

Bandwidth—Suppression Tradeoff

14 GHz

20 GHz

25 dB

FSR 40 GHz

MWP » MWP in PAAs » SMART » Conclusions » Questions»

3 optical beamformer e o and o e conversion9

f1

f2

f1

 f

 f

 f

MZM

OSBF

SA

fiber coupler

 f

RF

f1 – f2

f2

 f

 f

 f

3. Optical beamformer: E/O and O/E conversion

Spectrum measurement of modulated optical signal

Optical heterodyning technique:

MWP » MWP in PAAs » SMART » Conclusions » Questions»

3 optical beamformer e o and o e conversion10
3. Optical beamformer: E/O and O/E conversion

Spectrum measurement of modulated optical signal

Measured filter response, and measured spectrum of modulated optical signal, with and without sideband-filtering

MWP » MWP in PAAs » SMART » Conclusions » Questions»

3 optical beamformer e o and o e conversion11
3. Optical beamformer: E/O and O/E conversion

RF phase response measurements

RF output

RF input 1-2 GHz

Measured RF phase response of one beamformer channel, for different delay values.

MWP » MWP in PAAs » SMART » Conclusions » Questions»

3 optical beamformer e o and o e conversion12
3. Optical beamformer: E/O and O/E conversion

Signal combination measurements

RF input 0-1 GHz

CH 1

CH 2

Output

CH 3

CH 4

Measured output RF power of beamformer with intensity modulation and direct detection, for - 1 channel, - 2 combined channels, - 4 combined channels

MWP » MWP in PAAs » SMART » Conclusions » Questions»

3 optical beamformer conclusions
3. Optical beamformer: Conclusions

Conclusions

  • A novel squint-free, continuously tunable beamformer mechanism for a phased array antenna system has been described and partly demonstrated. It is based on filter-based optical SSB-SC modulation, and ORR-based OBFN, and balanced coherent detection.
  • This scheme minimizes the bandwidth requirements on OBFN and enhances the dynamic range.
  • Different measurements on optical beamformer chip successfully verify the feasibility of the proposed system.

MWP » MWP in PAAs » SMART » Conclusions » Questions»