Maurizio Burla Telecommunication Engineering group University of Twente, Enschede, the Netherlands

Telecommunication Engineering group

University of Twente, Enschede, the Netherlands

m.burla@ewi.utwente.nl

University of Twente

Enschede

Telecommunication Engineering

• 6 scientific staff

• 5 postdoctoral researchers

• 14 PhD students

Three main research areas:

Short range radio

Electromagnetic

compatibility

Microwave Photonics

Microwave Photonics Research

Signal distribution

Signal processing Signal generation

• 1 scientific staff

• 2 postdoctoral researcher

• 2 PhD students

• 3 BSc and MSc students

What we do:

Microwave photonics techniques

High performance analog photonic links Optical beamforming, MWP filtering

Pulse generation,

Optical heterodyning

Outline

 Introduction to microwave photonics

 Signal distribution: microwave photonic links

 Signal processing: photonic beamforming, microwave photonic filtering

 RF generation: optical heterodyning, pulse generation

 Discussion

Microwave Photonics

Advantage of photonics

Photonic techniques

Low propagation

loss Flexible

Ultrawide

bandwidth Lightweight

Immunity to EMI

Small size

Meanwhile in the microwave world…

• Very heavy (copper, 567 kg/km)

• Propagation loss scales up pretty fast with signal frequency (190 dB/km @ 6 GHz)

• Rigid and large cross section Coaxial cables

MMIC

• Small size

• Cross-talk problems

• Instantaneous bandwidth limitations

Photonic can perform/assist various microwave functionalities!

Microwave Photonics (MWP)

Microwave signal generation

Microwave signal distribution

Microwave signal processing

Microwave signal measurement

Photonic techniques

• High purity microwave carrier generation

• Arbitrary waveform generation

• Terahertz signal generation

• Photonic analog to digital conversion

• Photonic beamformer

• Filtering, up and down-conversion

• Analog photonic link

• Radio over fiber

• Antenna remoting

• Instantaneous frequency

and phase measurement

Research aspect of MWP

Steady increase in number of publications

Various review articles

Various books and book chapters

Scientific advancement

1999: Melbourne

2008:

Gold coast 1996: Kyoto

1997: Duisburg

1998:

Princeton, NJ

2000: Oxford

2003: Budapest 2005: Seoul 2001:

Long Beach, CA

2004: Maine

2006:

Grenoble 2007:

Victoria, BC

2009:

Valencia 2010: Montreal

2011: Singapore 2012: Noordwijk

The Netherlands

Topical Meeting on MWP regularly held since 1996

User of MWP

Defense/Military Telecom

Avionics

Radio

Astronomy

Business side of MWP: Startups

UPV, Valencia

UCSB, California Jet Propulsion Lab

UCL, London

& Oxford

University of Twente Uni. Melb., Australia

Lincoln Lab, MIT

Syracuse

Summary of part 1

 Microwave photonics is an emerging technology

 MWP covers various aspects, including research, application and commercialization

 Research activity in this field is growing rapidly

 Important functionalities: generation, distribution

and processing of microwave signals

Signal Distribution with

Microwave Photonic Links

Microwave photonic link (MPL)

RF in RF out

Optical fiber

Microwave signal Modulated optical signal Microwave signal

E/O conversion O/E conversion

Two-port

microwave component

 RF in and RF out (two-port system)

 E/O and O/E conversions

 Relatively shot distance (< 1 km)

 Alternative to coaxial cables (not the digital long haul optical links)

Characteristics

Microwave photonic link (MPL)

• MPL is the workhorse of any MWP system

• Conversions losses

• Noise

• Nonlinear distortion

RF in RF out

Optical fiber Functionalities

• filtering

• delay

• frequency conversion…

Input signal Output signal

However…

Two tone test

Input spectrum

Signal

Output spectrum

IMD3

IMD2 HD2

Added noise

IMD: Intermodulation distortion HD: Harmonic distortion

MPL design objective:

to minimize signal loss, added noise and nonlinear distortion

Spurious free dynamic range (SFDR)

= The strongest signal that can be filtered out without distortion

IMD2

IMD3

Important figure of merit (!)

MPL implementation

• Common choice : Intensity modulation +direct detection (IMDD)

• Two types of MPL: Direct modulation and external modulation

• Direct modulation

• Simple

• Cost effective

• Linear

• Frequency chirp

• f < 10 GHz Laser L-I curve

• External modulation

Mach-Zehnder modulator MZM transfer function

• High performance

• Widely used (LiNbO

)

• Chirp-free operation

• f > 110 GHz

• More expensive

• Nonlinear

Direct modulation

• Cost effective relative to external modulation

• Performance is limited by high IMD2

DML spectrum

DML spectrum (sub-octave)

Desired Spectrum (multioctave) Requires a large number

of analog photonic link

Sub-octave = narrow band

Multioctave = broadband

Using direct modulation

is very attractive

Solution: push-pull modulation

 IMD2 is suppressed in the balanced detector (BPD)

 VOA and VODL to match amplitude and phase

 Suppressed IMD2 and enhanced multioctave SFDR

 Commercial-off-the-shelf (COTS) components

Two-tone input Single-arm photonic link Push-pull photonic link

VOA : variable optical attenuator VODL : variable optical delay line

Marpaung et al., IEEE Photon. Technol. Lett., 21(24), 2009.

Link Realization (2.5 GHz)

Single laser

40 dB

Dual laser

Marpaung et al., IEEE MTT-S IMS, 2008, Atlanta.

Wider frequency range

Limited Suppression:

 Fiber paths imbalance

 Different amplitudes and phases of LD1 and LD2 IMD2 components

 LDs with matched

characteristics are required

600 MHz

Marpaung et al., IEEE Photon. Technol. Lett., 21(24), 2009.

SFDR improvement

Marpaung et al., IEEE Photon. Technol. Lett., 21(24), 2009.

Single laser

Push-pull

18 dB

A different point of view

Phase modulation and direct detection

CW laser Phase

modulator PD

RF in

RF out PM to IM

conversion

This work: Phase modulation instead of intensity modulation

• Inherently linear

• Large modulation depth

• No bias

• no coherent detection

• tailoring PM to IM response for:

- noise suppression - linearization

Aim: to demonstrate a high performance photonic link

Approach: ^• to design optical filters as frequency discriminators

• to realize a photonic chip solution

The photonic discriminator

Desired characteristics

The photonic chip

• No 3-dB splitter (no excess loss)

• Five optical ring resonators in add-drop configuration

• Fully programmable with thermo-optical tuning

• Free-spectral range (FSR):

21.5 GHz (Ring 1-3), 10.7 GHz (Ring 4 and 5)

• One input and two outputs

• Responses at the two outputs are mirror images

• Linear slopes (to minimize IMDs)

• Regions with large suppression (to minimize noise)

Marpaung et al. Opt. Express 18(26), 2010.

The device principle ²⁹

Two cascaded rings Three cascaded rings Balanced response

Marpaung et al. IEEE MWP 2010, Montreal

Device realization

Optical waveguide Chip layout

• TriPleX technology

• High index contrast

• Ng = 1.746 (TE pol.)

• Bend radius 150 m

• Circumference 8 mm

Packaging

• Size : 9 x 7 mm

• Wire-bonding to PCBs

• Fiber array units (no spot-size convert.)

Realized chip

Photonic link demonstration

• P = 100 mW

• = 1 MHz

• RIN < -170 dB/Hz

• Freq. detuning : 0.75 GHz/mA

• Used to reduce link loss

• ASE dominates the link noise

• No noise reduction

• Fiber-to-chip coupling loss = 12.5 dB/facet

Marpaung et al. Opt. Express 18(26), 2010.

Link linearity measurement

Drop response

Only one operating point where signal is maximized

Two cascaded rings

Two operating points where IMD2 or IMD3 is minimized

Marpaung et al. Opt. Express 18(26), 2010.

Link linearity measurement

Three cascaded rings Balanced configuration

Single bias point, both IMD2 and IMD3 are suppressed, link linearity is better than MZM with V 1 V

Two operating points and added robustness against bias drifts

Marpaung et al. Opt. Express 18(26), 2010.

SFDR measurement

Marpaung et al. Opt. Express 18(26), 2010.

• High linearity

• Current dynamic range is limited by noise from the EDFA

• Lower fiber to chip coupling and propagation losses will further enhance the dynamic range

• Expected fiber to chip coupling loss with interposer < 0.5 dB/facet

• Expected waveguide propagation loss

< 0.1 dB/cm

Summary of part 2

 Microwave photonic link (MPL) is a workhorse of any MWP system

 The aim of MPL design is to minimize signal loss, noise and nonlinear distortion

 Push pull modulation with two lasers is promising to achieve high broadband dynamic range

 Phase modulation and direct detection scheme

has a lot of potential for a high performance

photonic link

Signal Processing with a

Photonic Beamformer

Motivation: In-flight live satellite TV

Live television channels and

broadband communication at

passenger seats

Aim:

Broadband, continuous and

squint-free beamsteering

Required :

Digital video broadcasting via satellite (DVB-S) signal

To receive : Phased-array

antenna with large number of elements

Antenna tile

Solution :

Photonic beamformer

+

Why phased array antenna?

Conventional solution:

Dish antenna

• Mechanical steering

• Aerodynamic drag

• Increase in fuel consumption

Desired solution:

Phased array antenna

• Electronic steering

• No moving part

• Conformal, less drag, lower fuel con.

http:\\www.skatelescope.org\

SKADS project: for the application of phased array concept in radio astronomy

Desired :

• Wide instantaneous band

• Accurate and continuously tunable beam direction

Total band: 0.1 - 25 GHz

Limited to 40 MHz instantaneous BW

In the mid-band (400 – 1500 MHz) an array antenna has been proposed: EMBRACE demonstrator

RF-photonic solution:

• Beamforming of the complete band (400 – 1500 MHz)

• Continuous tunability

Motivation: wideband aperture arrays

Phased array antenna principle

Case 1: Broadside reception (no delay)

4 antenna elements

Combiner Combiner

Combiner

Delay off

Delay off Delay off

Beam direction Wavefront

Beam

former

Wavefront Beam direction

Antenna elements

Combiner Combiner

Combiner

Delay = T

Delay = 2T Delay = T

Case 2: Angled reception (delay on)

Beam

former

Photonic beamformer

A network of combiners and time delay elements

Beamfomer:

Why photonic beamfomer?

Requirements:

1. Large instantaneous bandwidth (> 2 GHz) 2. Squint free beam

(beam direction independent of frequency) 3. Continuously tunable beam

4. Low sidelobe level (amplitude tapering) f

f

f

& f

(1,2,3)  Broadband and continuously tunable time delay elements

(4)  Continuously tunable combiners

Difficult to achieve with only microwave components

…but photonics can do it!!

Integrated optics chip solution

0 0.2 0.4 0.6 0.8 1.0 0

0.1 0.2 0.3 0.4 0.5 0.6

Normalized frequency

Del ay (n s)

Combiners: Tunable MZI coupler

Delay element: Optical ring resonator

Optical waveguide

Chromium heaters for thermo-optical tuning

If the directional couplers are 50:50, by changing (thermo–optic tuning) the optical power at the

complementary outputs can be tuned from 0 to 100%

Phase shifter to change the resonance frequency

Tunable coupler

Tunable coupler to change the coupling

to the ring

= 0.2

0 0.2 0.4 0.6 0.8 1.0 0

0.1 0.2 0.3 0.4 0.5 0.6

Normalized frequency

D el ay (ns)

= 0.4 = 0.6

Cascaded optical ring resonator

• Single ORR provides tunable delay, but it is band limited

• Trade-off between maximum delay and delay bandwidth

• Solution cascade more than one ORRs

ORR 1

ORR 2

0 0.2 0.4 0.6 0.8 1.0 0

0.1 0.2 0.3 0.4

D e la y (n s)

Normalized frequency ORR 1 ORR 2

Sum Ripple

• More ORRs cascaded  more bandwidth but more ripple

• Trade-off between bandwidth , the number of ORR and the delay ripple

Next step : to arrange the combiners and the ORRs to make a beamformer

Beamformer design and realization

Functional design Chip design

Packaging Chip fabrication TriPleX

High index contrast and low loss optical waveguide technology

FAUs, electrical wires, heatsink, Peltier element

Number of outputs, max delay, number of ORRs, FSR, filter specs

Optical waveguide layout, heater layout, bondpads, and testports

8x1 beamformer

Tunable time delay demonstration

Wavelength (nm)

1549.97 1549.98 1549.99 1550.00 1550.01 1550.02 1550.03

Delay (ns)

0.0 0.2 0.4 0.6 0.8 1.0 1.2

1.4 Out 2

Out 3 Out 4 Out 5 Out 6 Out 7 Out 8

2.5 GHz

Max. ripple 0.1 ns

1 ns ~ 30 cm delay distance in vacuum

5 6 16

5 6

5 6

7 7

out 2 7

8 8 8 15

out 1

out 4 out 3 14

9 10 19

9 10

9 10

11 11

out 6 11

12 12 12 18

out 5

out 8 out 7 3 4 17

3 4

3 4

1 2

1 2

1 2

in 13

stage 1 stage 2 stage 3

Zhuang et al., IEEE Photon. Technol. Lett., 19(15), 2007.

Linearly increasing delay for a 2.5 GHz bandwidth was

demonstrated

Phase response (broadband delay generation)

RF phase shift vs frequency Linear phase characteristic with frequency

True time delay operation was demonstrated

Ripple due to the Fabry-

Perot reflections in the fiber connectors

ideal case measurement

True time delay demonstration

Zhuang et al., J. Lightwave Technol., 28(1), 2010.

Coherent combining demonstration

Power response (coherent combining)

~ 6 dB

~ 6 dB

RF power output vs frequency 6 dB increase of the RF

power each time the number of combined signals is

doubled

Coherent combining was demonstrated

Zhuang et al., J. Lightwave Technol., 28(1), 2010.

Beamforming system

Laser

RF out

Balanced detector

AE LNA

MZM array Optical

splitter

Beamformer

Optical sideband filter

Carrier re-insertion path

Coupler Input signal

10.7-12.75 GHz

f

Optical carrier

2x10.7 GHz

f

DSB-SC

f

True-time delay

f

Sideband filtering

f

Coherent detection

d = 12.5 cm

4 4 antenna array

Photonic beamformer system

Combining the BBBs in a binary-tree structure:

Optical beam forming network (OBFN) for a 4 4 array

Ring resonator delay unit

combiner

Device realization

Low-loss, CMOS-compatible TriPleX ^TM waveguide technology Fully programmable amplitudes and delays

Packaged 16 1 chip with electrical

connections TriPleX

waveguide

(SEM image)

Optical outputs Optical

inputs

70 mm

1 3 mm

RF-photonic system integration

OBFN chip

near-field scanning

probe

OBFN controller

LNAs

4^×1 subarray of Vivaldi antennas RF front-end

VNA

Detector Modulator

bias

MZMs Common DFB

laser source

EDFA

Pol. ctrl

Antenna tile

Integration of antenna and beamformer

Views of back side of the EMBRACE antenna tile modified by adding the photonic components

Modulator

s

Fiber connectors

Integration of antenna and beamformer

OBFN

Antenna measurements

RF-photonic demonstrator in the antenna test range

Integrated demonstrator

Near-field scanning

probe

4 1 array

under test

Squint free beamsteering demonstration

Burla et al., Applied Optics, 2011 (submitted).

1 GHz 0

-11.5

-23.5

1.15 GHz 1.30 GHz 1.50 GHz

1 GHz 1.15 GHz 1.30 GHz 1.50 GHz

1 GHz 1.15 GHz 1.30 GHz 1.50 GHz

The radiation patterns measured for a 4 AEs array show a squint-free beamsteering

with at least 500 MHz instantaneous BW over 23.5 degrees

BW only limited by measurement setup

(the OBFN is capable of over 100% instantaneous BW)

Towards a full antenna system

Demonstration based on DISCRETE components gave promising results

But highly unstable system due to mechanical/thermal fluctuation in the fiber setup

Hybrid integration of the

electronic/photonic components:

no more fibers!

Attractive solution:

Three active projects: Memphis (Dutch), Sandra (FP-7), Satrax (Point-one)

Demonstrators: K

-band fully-steerable array for DVB-S reception

chip modulators

Optical splitters

Why integration is needed

Fiber based system with discrete

components is highly unstable

System integration

(RF and photonics)

brass heat sink

Silicon common base

OBFN controller

Temperature controller

Laser

shaped PCB

Electrical interconnection:

•Wire bonding + PCB From

antenna elements

Modulator drivers

Optical interconnection:

•Butt coupling: splitter – modulators – OBFN – detector

•Fiber: laser - splitter Mechanical

interconnection:

•Silicon common base From

antenna elements

Integrated 1 16 splitter

Optical Beamformer Modulator

array

Detector

PM fiber

Modulator drivers

Photonic integration

Towards a full antenna system

System requirements and specifications Frequency range: 10.7 – 12.75 GHz (K

band) Polarization: 2 linear (H/V)

Scan angle: -60 to +60 degrees Selectivity: << 2 degrees

Element spacing: ~ /2 (~1.2 cm) Maximum delay: ~2 ns

Gain: > 32 dBi No. elements: > 1600

Cannot be achieved with only one beamformer

Two-level OBFNs + MMIC beamforming

Solution:

Hybrid beamforming scheme

Mature and proven Lower risk, higher yield

Gain: > 32 dBi No. elements: > 1600

RF beamforming of 4 AEs (MMIC)

32 of 16x1 beamformer

32x1 beamformer

4-to-1 RF beamforming

16-to-1 optical beamforming

32-to-1 optical

beamforming

Total Antenna:

2048 antenna elements (AEs)

16x1 optical beamformer

Optical modulators array

32 x1 second- stage OBFN

DVB-S receiver

Antenna front-end

32 of 16x1 OBFN

Marpaung et al., EuCAP 2011, Rome (invited)

Important aspects towards the full system

 Accurate modeling and performance analysis of the full system

 Development of the components in the system

 System integration (RF and photonics)

Modulator array (32)

System parameters

G

= 35 dBi T

= 50 K

RF out

Gain, NF

Optical power

Relative intensity noise

Half-wave voltage Insertion loss

Gain

Optical waveguide loss Fiber-to-chip coupling loss

Aim: min 8.1 dB C/N (33 MHz)

at the output (1 transponder)

32 of 16x1 OBFNs

OBFN1 OBFN2

G _a G _front G _OBFN1 G _amp G _OBFN2

P _in

P _out

System modeling

Rec1 Rec2

T _a +T _rec1 +T _rec2 =T _sys

T _rec1 = T _front + T _OBFN1 G _front

T _a

C/N = P _in k _B B _ch G _a

T _sys T _rec2 = T _OBFN2

G _rec1 G _amp T _amp

G _rec1 +

High gain, low NF front-end Low loss and low noise photonic beamformer

• Low optical waveguide loss

• Low E/O conversion loss in the modulators

= T _a +T _front

Meijerink et al., Journal of Lightwave Technology, 2010.

System performance

Key parameters to be determined:

1. Propagation loss in the optical waveguides 2. Gain and noise figure of the front end

3. Half wave voltage (V ) and insertion loss (L

) of the optical modulators

Optical waveguide

Front end

L

≤ 0.2 dB/cm

G ≥ 70 dB ; NF ≤ 2.5 dB

V ≤ 4 V; L

≤ 5 dB

System performance

Corechip Corechip

AE AE

L-band amplifier

NXP Downconverter

LNA 4:1 Combiner

Corechip Corechip

AE AE

Corechip Corechip Ku LNA

L-band amplifier

Down conversion

Image-reject filter

Front-end development

Optical modulator array: MZM

Array of >25 Mach-Zehnder modulators

• A modulator array is absolutely necessary

• MZM array in InP technology from Oclaro

• Performance  V = 3.5 V – 4.5 V  sufficient

= +

Aim: to integrate the modulator array in InP with the beamformer in TriPleX

Samples from Oclaro

Optical modulator array: EAM

• Surface normal electroabsorption modulator

• Different sizes: 125 microns to 25 microns diameter

• Transmission and reflection types

• Potentially low cost

Single modulator on PCB

Ground pad

Signal pad

Modulator Modulator

array

Measurement setup

25 microns aperture

1-5 GHz  bandwidth is OK, but efficiency needs improvement

= 1530 nm P = 9 dBm

EDFA at output

Optical modulator performance

Optical waveguide development

 Waveguide technology optimized for low loss propagation: new geometry defined

“new”

• Due to removal of sidewalls, the new geometry should have lower propagation loss (target: < 0.05 dB/cm) while simultaneously

achieving small bending radius

“old”

Optical waveguide development

Test structures

Waveguide cross section

Red light propagation

Propagation loss 0.1 dB/cm

Waveguide propagation loss

Circumference = 8783 m n

= 1.72

FSR = 20 GHz

Bend radius = 50 to 125 m

Miniaturization

0.8 x 2.2 cm 1.3 x 7 cm 16x1 beamformer, 20 rings

16x1 beamformer, 40 rings Old

New

5 times reduction in chip area!

Current status beamformer chip design

mo d u la tor

2 rows of bond pads

1 cm

2.4 cm

16x1 OBFN

40 ring resonators

Photonic integration: current status

Summary of part 3

 Photonic beamformer based on ring resonators is very promising

 RF-to-RF performance and wideband operation demonstrated (+ measured rad. patterns)

 RF and photonic integration is imperative to yield a reliable beamformer

 Accurate modeling of the system performance has been carried out

 Currently working towards a fully integrated

phased array antenna system

Signal Generation with an

Optical Frequency Locked Loop

LO/clock signal distribution to large antenna arrays from a centralized source

Examples: radio astronomy, large spaceborne arrays

Possible applications

SKA – Square Kilometer Array

Coaxial cables, waveguides: limited by the transmission line losses and bulk size

Optical fibers: low transmission and distribution loss (0.2 dB/km) - it is desirable to generate and distribute the RF signal optically

ESA - SMOS

Very large (~2m) antenna arms deployment in space not possible using coax cables!

(MWP 2010)

 Optical injection locking

 RF generation using external modulation

 Optical phase/frequency-lock loop (OPLL / OFLL)

 …

Yao et al., Journal of Lightwave Technology, 2010.

Photonic generation of RF signals

Optical Frequency Locked Loop (OFLL)

Laser 1

PD Laser 2

Loop Filter

RF Reference

Mixer Amplifier Loop Control

1

2

f

f

f

f

1 2

f f

 Very wide tuning capability

 Robustness vs environmental fluctuations

Photonic generation of RF signals

RF signal at PD output @ f ₁ -f ₂

Local Oscillator Signal Generation

System Demonstrator

RF/electrical PD

Optical distribution network

PD PD

Optical

Phased array antenna

L1

Optical feedback System

Lionix, TNO, TE, IOMS Dual Laser

Optical Heterodyning

L2

[TE]

[NLR]

[TNO]

[IOMS]

Aim: to generate a stable LO signal to downconvert K

band signals

This specific application (DVB-S down-

conversion in standard LNBs) imposes specific requirements in terms of power, phase noise and carrier-to-noise ratio (CNR) of the

generated LO signal

Those LO specifications directly

translate into requirements for the

lasers employed: power, linewidth

and relative intensity noise (RIN)

The specifications for the LO are taken from the datasheet of the standard LNBs

LO parameters for a Ku-band LNB

LO Parameters Values

Frequency 9.75 GHz - 10.6 GHz Single sideband (SSB)

phase noise

-50 dBc/Hz @ 1 kHz -70 dBc/Hz @ 10 kHz -90 dBc/Hz @ 100 kHz -110 dBc/Hz @ 1 MHz

1 Hz bandwidth dBc

SSB phase noise

Frequency

fLO f fLO

How do we translate the specifications for the LO into specifications for the lasers?

Requirements for a std. LO in commercial LNBs

Laser 1

PD Laser 2

1

2

1 2

f f

) (t I

LO generation by optical heterodyning scheme

2 LO

pd L1 L2 2

LO LO

( ) 2 1 /

2( )

1 S

f r P P

f f

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

x 10⁴ -80

-70 -60 -50 -40 -30 -20

Frequency offset from the carrier (Hz)

PSD of PD output (dBW/Hz)

5 kHz 1 kHz 100 Hz

PSD of PD output for various optical LO linewidth

pd L1 L2 pd L1 L2 LO LO

( ) 2 cos 2 ( )

I t r P P r P P f t t

LO 1 2

2

LO phase noise and maximum laser linewidth

SSB phase noise plot for various LO linewidths

0 1 2 3 4 5 6 7 8 9 10

x 10⁵ -120

-100 -80 -60 -40 -20 0

SSB phase noise (dBc/Hz)

Standard LO (Data sheet) Optically generated

LO linewidth

Frequency offset from the carrier (Hz)

A beat linewidth of 125 Hz keeps the phase noise

within that of the standard LO values given

10 kHz 2 kHz 125 Hz

C/N = 1 10 dB /Hz

This imposes a condition of 62.5 Hz linewidth for each of the two lasers

Required extremely narrow (sub kHz) linewidth laser

LO generation by optical heterodyning scheme

 Is a linewidth <1 kHz possible?

 Who knows… but we are going in the right direction 

IOMS-UT

 Calculated RF power spectra show

Lorentzian linewidths of 1.70 0:58 kHz

 Beats the record low 2.7 kHz linewidth (narrowest linewidth of any free-running monolithic laser)

 Standard semiconductor DFB lasers typically have linewidths that are a few orders of magnitude larger

Bernhardi et al., Optics Letters, 2010.

Narrow-linewidth laser development

After all this effort for low phase noise… we don`t want things to be spoiled by additional noise sources!

0 1 2 3 4 5 6 7 8 9 10

x 10⁵ -120

-100 -80 -60 -40 -20 0

SSB phase noise (dBc/Hz)

Standard LO (Data sheet) Optically generated

LO linewidth

Frequency offset from the carrier (Hz) SSB phase noise for various linewidths of the optical LO

10 kHz 2 kHz 125 Hz

C/N…gone 

NOISE

Accurate noise analysis required

Effect of various noise components

Dominant sources :

 Thermal noise (Johnson noise)

Noise generated at the photodetector due to the random arrival of photons, which in turn generate a random fluctuation in the detected photocurrent

i

ⁱ

^{( ) t 2 qI B}

The variance of the shot noise current, , can be written as

q is the electron charge,

I

is the average photocurrent,

 Shot noise

 Relative intensity noise (RIN)

( ) ( )

P t

P P t

Random optical power fluctuations received at the detector

P = average power ( )

P t = random power fluctuation

Effect of various noise components

Average photo current (mA)

Power spectral density (dBm/Hz)

0.01 0.1 1

-220 -200 -180 -160 -140 -120 -100 -80 -60 -40 -20

0.001

LO power (calculate) LO power (measured)

Shot noise RIN (-130 dB/Hz)

2

LO av L

1

P 2 I R

Total noise power =

thermal noise + shot noise + relative intensity noise

RIN 10 2

av L av L

2 10

kTB qI BR I BR

Where,

k is the Boltzmann’s constant, T is the noise temperature,

B is the equivalent noise bandwidth of the receiver,

q is the electron charge, I_av is the average photocurrent, R_L is a load resistance,

RIN is relative intensity noise,

The RF power of the LO

SA+PD

Noise floor (calculated) Noise floor (measured)

Interested in the carrier-to-noise ratio (CNR) change scale

Effect of various noise components

Power spectral density (dBc/Hz)

Average photo-current (mA)

0.001 0.01 0.1 1

-150 -140 -130 -120 -110 -100

At 0.2 mA photo-

current a laser having a

RIN=-123 dB/Hz

keeps the total noise floor at -120 dBc/Hz.

Thermal noise Shot noise

RIN=-110 dB/Hz

Noise floor=-107 dBc/Hz

RIN=-123 dB/Hz

Noise floor=-120 dBc/Hz

RIN=-135 dB/Hz Noise floor=-132 dBc/Hz

Measured Data

125 Hz LO SSB phase noise

Generated LO

Effect of various noise components

Assuming PD

responsivity (r

) as 0.8 A/W…

…the minimum power of each laser is

3

L1

pd

av

0.2 10

0.125 mW

2 2 0.8

P I

r

0.2 mA

 Starting from the RF requirements of the LO for a specific application (DVB-S signal downconversion) …

 Using a complete noise analysis…

 …optical requirements for the lasers have been deduced:

Laser power: 0.125 mW

Laser linewidth: 62.5 Hz

Laser RIN (relative intensity noise) < -123 dB/Hz

Results

Sub-kHz laser… Is it possible?

 Is a linewidth <1 kHz possible?

 Who knows… but we are going in the right direction 

IOMS-UT

 Calculated RF power spectra show

Lorentzian linewidths of 1.70 0:58 kHz

 Beats the record low 2.7 kHz linewidth (narrowest linewidth of any free-running monolithic laser)

 Standard semiconductor DFB lasers typically have linewidths that are a few orders of magnitude larger

Bernhardi et al., Optics Letters, 2010.

Narrow-linewidth laser development

While waiting for the laser… feedback loop test

Summary of part 4

 Optical generation and distribution of RF signals is desirable in several applications

 OFLL system proposed

 Analyzed how desired characteristic of the

generated RF signals translate into requirements for the lasers

 Performed initial demonstration of the feedback

loop

Current works

Laser

Input Gaussian pulse

PM

Instantaneous phase

Instantaneous frequency

RF out PD ^Chip

discriminator

Monocycle generation

Instantaneous frequency

Doublet

generation

Instantaneous frequency

Arbitrary pulse generation / shaping

98

4x4 array

Wavelength multiplexing

(WDM):

4 wavelengths per channel

λ

λ

λ

λ

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

Exploit the frequency periodicity of the ORR to realize a compact MWL system

FSR = 100 GHz

2x1 MUX Asymmetric MZI

1x4 DE-MUX

Asymmetric MZI (FSR: 200 GHz 1^st stage

400 GHz 2^nd stage)

Combiner Symmetric MZI

λ

λ

λ

λ

Reduced

dimensions

& complexity:

8 rings instead of 20 Multi-wavelength OBFN

New OBFN designs

99

Complexity reduction thanks to Wavelength Division Multiplexing

20 rings

15 combiners 15 phase c.

Total: 70 heaters

8 rings

6 combiners 6 phase c.

Total: ~20 heaters

Ring Resonator Combiner Phase corrector Wavelength demux Legenda:

Multi-wavelength OBFN

100

brass heat sink shaped PCB Silicon

common base

Optical detector OBFN

controller

Temperature controller

Lasers + modulators driver

From antenna elements

Mechanical interconnection:

•Silicon common base

Electrical interconnection:

•Wire bonding + PCB Optical interconnection:

•Butt coupling MWL – OBFN

•Fiber OBFN - detector

• Application: phased array antenna for radio astronomy

Multi-wavelength Optical Beamformer

(C4: UT-TE, LioniX) MWL transmitter + fast

integrated modulators (C5: TU/e)

• Components test and integration starting December 2011 (UT-TE, Astron)

OBFN integration scheme

 Multiple wavelength as carriers

-> complicated to do carrier re-insertion

 We need a solution for delay without carrier reinsertion

 Attractive solution: Separate Carrier Tuning (SCT)

 Very recent technique

(many recent publications: Optics Letters, Optics Express)

New delay technique required

technique

Possible solution:

 Separate carrier tuning (SCT) [1-2] consists in using an additional device, with an independently tunable dispersive response, to adjust the phase of the carrier to the desired value (modulus 2π)

)

( Ideal phase

response Real phase

response

“True-time-delay”

bandwidth

[1] P.A. Morton, J.B. Khurgin, IEEE Photon. Technol. Lett. 21(22), 1686-1688 (2009).

[2] S. Chin et al., Opt. Express 18(21), 22599-22613 (2010).

c

RF c

c

RF c

c

RF

?

operation

Proposed solution (submitted to Optics Express):

 Sideband filter, reconfigurable ODL unit and SCT unit integrated on a single CMOS compatible chip

Advantages:

 Compact (single chip), CMOS compatible, fully reconfigurable

 ODL bandwidth + max delay can be increased

just by cascading additional ORRs

operation

 Operation

Experiment

 Measurement setup

 Tuning the optical delay line (ODL unit) we can set different phase slopes (group delays)

 Tuning the phase shift applied to the optical carrier (SCT unit) of the SSB+C signal gives an equal phase shift on the detected RF

signal: 360 degrees (100%) tuning demonstrated

Burla et al. Optics Express (accepted).

Maurizio Burla - Microwave Photonics Activities at the University of Twente

06/09/

M. Burla et al.: On-chip reconfigurable ODL with ¹⁰⁶

Demonstration

 To demonstrate the functionality of the proposed ODL, we build a Microwave photonic filter (MPF) (2-taps, complex coefficients)

 Tap 2 contains the tunable ODL

Tap 2 Tap 1

L = 2.2 m

= T = 10.68 ns FSR = 93.6 MHz

 A single OSBF is used to suppress the LSB for both taps

Demonstration

 The RF-to-RF response displays an interference pattern

 By operating the SCT unit and the ODL, the notch positions and the FSR of the MPF can be tuned independently

T j

j

e

e a a

H ( )

FSR

Maurizio Burla - Microwave Photonics Activities at the University of Twente

06/09/

M. Burla et al.: On-chip reconfigurable ODL with ¹⁰⁸

Demonstration

 A) the phase shift to the optical carrier can be tuned via the SCT unit

 An equivalent RF phase shift is achieved on the detected RF signal

 In this way the notch positions can be tuned

 360 degrees / 100% tunability

T j

j

e

e a a

H ( )

Maurizio Burla - Microwave Photonics Activities at the University of Twente

06/09/

M. Burla et al.: On-chip reconfigurable ODL with ¹⁰⁹

Demonstration

 B) the delay to the passband can be tuned via the ODL unit

 In this way the basic delay (T) of the MPF can be tuned, thus the filter FSR

 FSR: 93.6 MHz to 98.6 MHz (approx. 540 ps)

T j

j

e

e a a

H ( )

Maurizio Burla - Microwave Photonics Activities at the University of Twente

06/09/

M. Burla et al.: On-chip reconfigurable ODL with ¹¹⁰

Demonstration

 C) the ODL unit and the SCT unit can be operated simultaneously

 Operating the carrier tuner does not disrupt the delay response imposed over the sideband by the delay unit

 FSR not affected by the SCT unit operation

T j

j

e

e a a

H ( )

Maurizio Burla - Microwave Photonics Activities at the University of Twente

06/09/

M. Burla et al.: On-chip reconfigurable ODL with ¹¹¹

Conclusions

 We have experimentally demonstrated a reconfigurable ODL based on the SCT technique

 For the first time, all the required components are integrated on a single CMOS compatible photonic chip

 Functionality demonstrated over a bandwidth in excess of 1 GHz

 Scalable delay amount simply by cascading more ORRs

 Work submitted to Optics Express

Maurizio Burla - Microwave Photonics Activities at the University of Twente

06/09/

M. Burla et al.: On-chip reconfigurable ODL with ¹¹²

Current / future work

 Possible applications:

(a) incoherent multitap

microwave photonic filter with complex coefficients on a single chip (no fibers) (b) multi-wavelength optical

beamforming network (OBFN) for phased array antennas

 The ODL is being extended to a multiple-ODL (in production)

Valorization

Innovative Microwave Photonics Circuits

Brussels June 16 2011, ICT Finance Market Place

Enabling Broadband Communication Systems

Manufactured in Nanolab Enschede

 Founded in Enschede December 2009

 Design & Manufacturing of

Innovative microwave photonics components and beam forming networks

 Applications:

communication, observation, security and smart networks

 Chair of Point One R&D Project

Paul van Dijk CEO

Chris Roeloffzen CTO

Management Team

 3 References

 Patents on

manufacturing process

chip modulators

Optical splitters

Fiber based system with discrete components is highly unstable

Proven Technology with

Discrete Components