microwave over fiber - linear...

MICROWAVE OVER FIBERApplications and Performance

IEEE North Jersey LEOSNovember 12, 2012

John A. MacDonald

Linear Photonics 1

John A. MacDonaldVice President of Engineering

Linear Photonics, [email protected]

Dr. Allen KatzPresident, Linearizer Technology, Inc.

Professor, The College of New [email protected]

OUTLINE

1. MICROWAVE LINKS: ANALOG / DIGITAL

2. INTENSITY MODULATION & DETECTION

3. PRACTICAL LINK STRUCTURES

– DIRECT MODULATION

– EXTERNAL MODULATION

– PHOTORECEIVERS–

– TRANSMISSION MEDIUM

4. PERFORMANCE LIMITATIONS

– LINEAR EFFECTS

– NONLINEAR EFFECTS

5. NONLINEAR PERFORMANCE IMPROVEMENT/LINEARIZATION

6. SUMMARY

2Linear Photonics

Analog / Digital

• The bulk of fiber optic communications uses digital

modulation

– Fast switching and low pulse distortion determine link fidelity

• Certain applications not suited to digital:

– Bandwidth too high to be digitized– Bandwidth too high to be digitized

– System complexity favors a broad pipe

• Primary distinction between digital and analog is linearity

– Analog/Microwave links depend upon low distortion to achieve high

fidelity

3Linear Photonics

Microwave Fiber Optic Link

Ideally, the output is a linear copy of the input

E to O

transducerRF Input

O to E

transducer RF OutputOptical Fiber

– E/O transducer modulates the RF information onto an optical carrier

– O/E transducer reverses the operation

– Transducers must effectively transfer RF power (information)

• 50 Ω impedance to RF environment

– Modern Microwave Link technology is dominated by:

• Intensity modulation of semiconductor lasers

• Envelope detection using PIN or APD photodiodes

4Linear Photonics

Microwave Link Applications• Radar

– Low weight, complexity

– Beamsteering and Direction-finding

• Antenna and Signal Remoting

– Direct-RF over longer distances (many km)

– Reliable alternative to wireless in fixed services

• Electronic Warfare / SIGINT / ELINT

– Secure Comms (EMI hard)

– Towed Decoys– Towed Decoys

• Space-based

– Mass advantage

– Deployed fiber: can be radiation hard; less thermally sensitive

• Precise Time and Frequency Distribution

• High RF and Magnetic EMI Environments– Fiber is almost completely EMI-proof, and non-metallic

• High Voltage Environments– Fiber will not conduct

5Linear Photonics

Practical Intensity Modulation

• Direct

– Laser diode is modulated directly

• External

– Laser source drives a separate optical – Laser source drives a separate optical

component

6Linear Photonics

Direct Modulation

Bias

Modulating

Signal

SemiconductorLaser

0

2

4

6

8

10

12

0 20 40 60 80 100 120 140 160

Optical Intensity

Mean Offset + Modulation

Slope Efficiency

ηL

IL

im

PDiode Laser

Power vs. Current

7

0 20 40 60 80 100 120 140 160

Laser Modulation Current

DC Bias + RF

ITH

)()( mTHLLm iIIiP +−=η

IL

Linear Photonics

• A CW optical signal is intensity modulated

via a field-dependent optical medium

• µwave / mm-wave modulation speeds can

be achieved with 2 major methods:

External Modulation

be achieved with 2 major methods:

– Electro-Optic Modulation

• Field-dependent change in optical index (electo-

optic effect)

– Electro-Absorption Modulation

• Field-dependent change in optical attenuation

8Linear Photonics

• Mach-Zehnder Interferometer

– Index of refraction is dependent on applied

field (modulating signal)– Electro-Optic effect can be realized in Lithium Niobate (LiNbO3),

InP, and other crystal structures, i.e. KDP (KH2PO4)

Electro-Optic Modulation

InP, and other crystal structures, i.e. KDP (KH2PO4)

9

Vm (RF + Bias)

Optical

Vector • Propagation constant of the beam in

the lower leg is retarded due to applied

electric field – experiences less phase

shift than upper leg.

• Optical intensity (power) is

modulated by the applied RF signal

due to summation of out-of-phase

vectors.Diffused Optical Waveguide

on LiNbO3 substrate

Linear Photonics

0

0.5

1

-15 -10 -5 0 5 10 15

Vm

Inte

nsi

tyMach-Zehnder

Optical Intensity


10

Vm

• Optical Output power follows cos2 function o Vector phase summation

• Vππππ is DC voltage that causes 180° phase rotationo Depends on crystal physics and electrode length o Corresponds to “min” and “max” output powero Digital Modulation: variation between min and max

• Analog Modulation: Bias at Quadrature (shown)o Results in linear intensity modulationo Slope = 1 at quadrature pointo Even order distortions are balanced (zero)

Linear Photonics

Modulation Voltage

DC Bias + RF

• Absorption of optical signal dependent on applied bias

• Transmission follows exponential relationship with applied field

• Generally not as linear as MZM

Electro-Absorption

1

Vm

transmitted

11

0

0.25

0.5

0.75

1

0 0.5 1 1.5 2 2.5 3

)()( Vmf

m eVP−=

N

P

ia

Pin Pout

Linear Photonics

Modulation Voltage

DC Bias + RF

Transmitted Optical Intensity


absorbed

transmitted

• P-I-N diodes are most common

Photodetection

iout

VDC

Iave

PRPI ⋅=)(

R = responsivity (amps/watt)

= ηq / hω

– Intrinsic bandwidth limited by diode capacitance

– Package and launch considerations may also limit

performance

• ~30 GHz bandwidth from lateral PIN

• ~100 GHz from waveguide PIN

12Linear Photonics

Transmission Medium

• Fiber is Optical Waveguide

• Fiber has very low loss

cladcore nn >

< 0.25 dB/km at 1550 nm

• High-fidelity Microwave Links

require Single-Mode fiber

13Linear Photonics

Singlemode

Qualitative Link Measures

E to O

transducer

RF Input

O to E

transducer

RF Output

Optical Fiber

Gain (Loss)

Added Noise

Linear Photonics, LLC 14

• Gain

– Broadband links are lossy

– Gain Slope / Ripple important to system design

• Noise Figure

– Generally higher than the link loss

• Third-Order Intercept

– Intercept of fundamental and 3rd-order IMD curves

• Spur-Free Dynamic Range (SFDR)

– Power Range over which the intermodulation distortion is below the noise floor

– Useful Quality Factor – incorporates Noise and Third-order Distortion

Nonlinear Distortion

Linear Factors affect the Gain and Noise of the output signal

– Microwave Launch– Inherent Bandwidth

• Limited by device and package reactances– Noise– Fiber Medium

• Absorptive Loss• Dispersion (Chromatic, Polarization Mode)

Performance Limits

• Dispersion (Chromatic, Polarization Mode)

Nonlinear Factors affect the shape of the output signal

– Distortion (Harmonic, Intermodulation, …)– Fiber Medium

• Stimulated Brillouin Scattering• Raman Scattering• Four-wave Mixing

15Linear Photonics

Linear Impacts: Microwave Launch

Primary source of microwave loss is input/output matching

DC

10 GHz

RL

RS

C

RS

C

• Narrow band links can be reactively tuned• Limited Bandwdith

• Fano’s rule: (BW)(Reflection Coefficient) < c

• However: Many or Most links require Broadband• Must use lossy matching – affects link gain

RLCL

Forward Biased Laser Diode

• Small real resistance RL

• Junction Capacitance and Ohmic Resistance

Reverse Biased Photo Diode

• Large reactive impedance dominated by junction

capacitance

• Ohmic Resistance adds dissipative loss

CJ

16Linear Photonics

Linear Impacts: Noise

• Laser Relative Intensity Noise (RIN)– Caused by spontaneous emission

• Laser is not a perfect oscillator

• 100 THz carrier is spread over 100’s of GHz

– Receiver detects as microwave noise

– Noise Power follows detection square-law: No ~ I2∙RIN

• Receiver Shot Noise• Receiver Shot Noise– Random arrival of photon quanta

– Output Noise power is white and follows the optical power: No ~ I

• Thermal Noise– Ubiquitous Johnson Noise

– Output Noise Power is constant and white

17Linear Photonics

Noise power delivered to the RF load is the sum of 3 independent sources

Output Noise of F/O Link

-180

-175

-170

-165

-160

-155

-150

-10 -8 -6 -4 -2 0 2 4 6 8 10

Optical Receive Power (dBmo)

No

ise

Po

we

r D

en

sit

y (

dB

m/H

z)

Thermal

Shot

RIN

Total

Gain of F/O Link

-60

-50

-40

-30

-20

-10

0

-10 -8 -6 -4 -2 0 2 4 6 8 10


Ga

in (

dB

)

Noise Figure of F/O Link

0

10

20

30

40

50

60

-10 -8 -6 -4 -2 0 2 4 6 8 10


No

ise

Fig

ure

(d

B)

Noise Figure

• Output noise depends • Gain also depends on • Noise Figure

18

• Output noise depends

on optical power

2:1 in RIN region

1:1 in shot regionconstant in thermal region

• Gain also depends on

optical powerAlways 2:1

• Noise Figure

decreases with optical

powerAsymptotic

Link Noise Figure and Dynamic Range vary with optical power – defined in

conjunction with the operational system

Linear Photonics

Linear Impacts: Fiber Medium

• SM Fiber Attenuation

– Due primarily to Rayleigh (elastic) Scattering

– 0.25 dB/km (1550 nm)

– 0.5 dB/km (1310 nm)

• Chromatic Dispersion

– Wavelength dependent propagation velocity

– Sidebands arrive out-of-phase: gain nulling– Sidebands arrive out-of-phase: gain nulling

• Polarization mode Dispersion

– Orthogonal Polarization Modes different

propagation velocities

– Non-uniform through fiber length• concentricity defects

• mechanical and thermal perturbations

• laser spontaneous emission

– Nondeterministic

– Affects pulsed (digital) systems

– Affects Time/Freq Distribution systems

19

Chromatic Dispersion

Polarization Mode Dispersion

FAST AXIS

SLOW AXIS

Linear Photonics

Nonlinear Impacts:

Modulator Transfer Function

0

2

4

6

8

10

12

0 20 40 60 80 100 120 140 160

Bias Current

Optical Power

Direct Modulation

• Gain Compression• Even and Odd order amplitude distortion

• Phase distortion due to laser chirp (FM to PM)• Laser wavelength = function(drive level, temperature)

Bias Current

0

0.5

1

-15 -10 -5 0 5 10 15

Vm

Inte

nsi

ty

MZM External Modulation

• Gain Compression• Primarily Odd order amplitude distortion

• Very little phase distortion

20Linear Photonics

Linearity Measures

• Third-Order Intercept (IP3)– (Imaginary) point where two-tone third-order intermodulation products (IMD3) are equal to the fundamental

• Spur-Free Dynamic Range– Range of power over which the fundamental is above the noise floor and the IMD3 are below the noise floor

Pout

[ ])()(3)(1743

2)( 3

2

3 dBBWdBmIIPdBNFHzdBSFDR ++−=⋅

21

Pin

Output Noise Floor

IIP3SFDR-3

Linear Photonics

Nonlinear Impacts: Fiber

• Stimulated Brilluoin Scattering (SBS)

– Vibrational/Acoustic oscillations generated by high energy photons

– Forward wave energy is converted to acoustic backward wave (phonons)

– Threshold Effect

– Reduced forward gain; Increased noise floor

• Stimulated Raman Scattering (SRS)

– Inelastic photon scattering Nonlinear fiber effects must be – Inelastic photon scattering

– Wavelength translation

– Reduction in gain

• Self-Phase Modulation

– AM-PM conversion of a single signal

• Cross-Phase Modulation

– AM-PM Transfer from one signal to another (WDM systems)

• 4-Wave Mixing

– Intermodulation Distortion (WDM systems)

22

Nonlinear fiber effects must be

considered during link design phase.

Linear Photonics

Intensity Modulation Summary

TYPE COMPLEXITY SIZE

WEIGHT

POWER

PRACTICAL

MODULATION

FREQUENCY

LINEARITY COST

DIRECT Low: one optical

component

(laser)

Lowest 15 GHz Poor 2nd and

3rd-order

performance

Lowest

ELECTRO- Moderate: Similar to 40 GHz Poorest Higher,

23

ELECTRO-

ABSORPTION

Moderate:

requires separate

source laser and

small modulator

Similar to

direct mod

40 GHz Poorest Higher,

comparable

to EOM

ELECTRO-

OPTIC (MZM)

Highest: requires

source laser,

large modulator,

plus optical and

electrical

controls for bias

locking

Highest > 60 GHz Well-defined

(sin curve).

Operation at

quadrature

provides 2nd-

order null.

Highest

Linear Photonics

Closing the Link

LINK

• Directly Modulated Laser / PIN Receiver

/ Postamplifier

• Reactively Tuned 3.25 – 4.00 GHz

LINK

• E-O Modulator (MZM) / Waveguide

PIN Receiver

• Broadband Response to 40 GHz

PHOTORECEIVER

Broadband O/E Response to 20 GHz

and Output Return Loss

24

Link Type

Centerband

Gain Input IP3 Noise Fig SFDR3

dB dBm dB dB Hz^2/3

4 GHz

Direct Mod-20 32 28 118

20 GHz

MZM-25 31 38 111

30 GHz

EAM-30 18 40 101

40 GHz

MZM-30 25 43 104

“Typical” Link

Gain, Noise, Dynamic Range

Linear Photonics

Trade-Offs, or Why Use Fiber?

• What are the System Engineer’s Tradeoffs?

• Should I consider fiber?

– Tradeoff performance, cost, weight vs. other options

• If fiber, then what do I need to know?

– Direct Mod vs. Ex-Mod (Decision Needed)– Direct Mod vs. Ex-Mod (Decision Needed)

• Direct Mod (usually < 12 GHz)

– Weight, Cost, Loss, Dynamic Range, DC Power

– Often Comparing directly to Coax

• Ex-Mod

– Must evaluate system impact for linearity, G/T, etc

25Linear Photonics

Direct Mod Comparison to Coax

• At Direct Mod frequencies, choice of Fiber vs.

Copper often made on basis of performance as a

function of link length

• Primary System Trades include:

– Attenuation– Attenuation

– Noise Figure

– Weight

– Cost

26Linear Photonics

Direct Mod vs. Coax: Attenuation

25

30

35

40

45

50A

tte

nu

ati

on

(d

B)

Direct Mod Link

27Linear Photonics

0

5

10

15

20

0 200 400 600 800 1000

Att

en

ua

tio

n (

dB

)

Distance (meters) 2000 MHz

Direct Mod vs. Coax: Noise Figure

25

30

35

40

45

50N

ois

e F

igu

re (

dB

)

Direct Mod Link

28Linear Photonics

0

5

10

15

20

0 200 400 600 800 1000

No

ise

Fig

ure

(d

B)

Distance (meters) 2000 MHz

Direct Mod vs. Coax: Weight and Cost

WEIGHT (pounds) 1 m 100 m 1000m

RG8 .32 32 320

LDF6 .21 21 210

Direct Mod Link .14 1.1 10.1

29Linear Photonics

COST 1 m 100 m 1000m

RG8 $3 $300 $3,000

LDF6 $38 $3,800 $38,000

Direct Mod Link $5,000 $5,100 $6,000

Crossover Lengthwhen DM performance exceeds that of coax

Attenuation Noise Figure Weight Cost

RG8 110 m 180 m 30 cm 1800 m

Heliax LDF6 560 m 900 m 50 cm 125 m

Direct Mod Comparison to Coax

• Other factors may influence choice of Fiber vs. Copper:– Linearity (link dynamic range is less than coax)

– EMI immunity (may trump performance)

– Safety, Reliability, etc.

Example: Crossover Lengths at 2 GHz

30Linear Photonics

• Linearization Techniques

– Linearization improves nonlinear distortion, increases dynamic range

– Major techniques under study include optical, electrical, and combinatorial approaches

Performance Improvement

electrical, and combinatorial approaches

• Electrical: aim is to cancel distortion products– Feedforward/Feedback: Inject out-of-phase distortion

products to cancel

– Predistortion: Nonlinear circuits with opposing distortion characteristics

• Optical: generally more complex– Operates in optical domain – inherently wide-band

31Linear Photonics

Electrical Predistortion

• Predistortion Linearization has long history in

Broadcast Power Amplifiers; SSPAs, TWTAs, Space

and Ground Station equipment

– Generally less complex than optical or combinatorial

systemssystems

• Does not rely on sampled waveforms

• Bandwidth is the major challenge

– The aim is to compensate for the gain and phase

compression of the nonlinear system by providing a

cascaded element function that has the opposite gain

and phase characteristic: gain and phase expansion

Electrical Predistortion

• PERFORMANCE OF LINK IS PRIMARILY LIMITED BY THE DISTORTION INTRODUCED BY OPTICAL MODULATION.

• PREDISTORTION (PD) LINEARIZATION ELIMINATES THIS DISTORTION BY GENERATING A FUNCTION WITH OPPOSITE MAGNITUDE AND PHASE OF THE MODULATOR

Predistortion Linearization

-5

-4

-3

-2

-1

0

1

2

3

-5 -4 -3 -2 -1 0 1

1

2

3

4

Input Power

Output Power

Phase

34

• Nonlinear Device exhibits Gain and Phase Compression

-2

-1

0

1

-5 -4 -3 -2 -1 0 1Input Power

Linear Photonics


-5

-4

-3

-2

-1

0

1

2

3

-5 -4 -3 -2 -1 0 1

1

2

3

4

-5

-4

-3

-2

-1

0

1

2

3

4

5

-5 -4 -3 -2 -1 0 1

1

2

3

4

Input Power Input Power

Output Power Output Power

Phase Phase

35


• Precede it with another nonlinear device that exhibits gain and phase expansion, in

conjugate with the device to be linearized (the linearizer)

-2

-1

0

1

-5 -4 -3 -2 -1 0 1

-2

-1

0

1

-5 -4 -3 -2 -1 0 1Input Power Input Power

Linear Photonics


-5

-4

-3

-2

-1

0

1

2

3

-5 -4 -3 -2 -1 0 1

1

2

3

4

-5

-4

-3

-2

-1

0

1

2

3

4

5

-5 -4 -3 -2 -1 0 1

1

2

3

4

-5

-4

-3

-2

-1

0

1

2

-5 -4 -3 -2 -1 0 1

-1

0

1

2

3

Input Power Input Power Input Power

Output Power Output Power Output Power

Phase Phase Phase

36

-2

-1

0

1

-5 -4 -3 -2 -1 0 1

-2

-1

0

1

-5 -4 -3 -2 -1 0 1

-5

-4

-3

-2

-1

-5 -4 -3 -2 -1 0 1Input Power Input Power Input Power


• Precede it with another nonlinear device that exhibits gain and phase expansion, in

conjugate with the device to be linearized (the linearizer)

• The desired outcome is an ideal limiter

– The linearity of an ideal limiter cannot be improved

Linear Photonics

Wideband Predistorter

• Functions from 1.5 to > 20 GHz

• Target: ΔGain = 2.5 dB

• ΔФ < 5 degrees (Ach. to 13 GHz) (Ach. to 13 GHz)

• Flatness ± 0.5 dB (Ach. to 12 GHz)

• Feel can achieve <1GHz to <30GHz

• LPL generic predistorter is very broadband

Linearized Microwave Link

Preamp PredistorterPostamp/

Equalizer

MZM

1550 nm

Source Laser

MPR0020

Photoreceiver

LINEARIZER NONLINEARIZED LINK

RF IN RF OUT

38

• Nonlinearized MZM Link:

– Commercial modulator biased at quadrature

– 20 GHz flat receiver driven at 0 dBmo

• Linearizer:

– Includes broadband gain stages

– Predistorter is single-chip GaAs circuit (proprietary design)

• Signal levels adjusted to match gain expansion of predistorter to gain compression of MZM

– Postamp stage includes slope equalizer to match levels over frequency

LINEARIZER NONLINEARIZED LINK

LINEARIZED LINK

MZM Linearization

• Demonstration of IMD improvement from

predistorting an MZM link

MZM Microwave Link

Linearized IMD Products

120

Non Linearized

Linearized

• Results at 8 GHz

• Measured improvement

0

20

40

60

80

100

0.01 0.10 1.00

Optical Modulation Index

Th

ird

-Ord

er

IMD

(d

Bc

)

21 dB IMD improvement

(yields 5 dB SFDR3)

• Measured improvement

>14 dB (minimum)

from 4 to 12 GHz

Predistortion Linearizer Performance

Pout

• Linearization Results of EAM Link at 14 GHz

• Non-Linearized 4 dB Gain Compression at

Ref. Input Power

0-12

Input Power Backoff (IPBO) in dB

Gain Pout Gain

Pout

Input Power Backoff (IPBO) in dB

0-20

• Linearized Predistortion linearizer

effectively compensates the

gain compression

Predistortion Linearizer Performance

• Intermodulation Distortion Improvement EAM– Measured at 6 dB IPBO

Non-Linearized Linearized

• 15 dB improvement in IMD equates to 5 dB

improvement in SFDR3

THIRD ORDER

AM COMPRESSION TERMS

F1 F2

FOR WB OPERATION (> OCTAVE BW) FOR WB OPERATION (> OCTAVE BW) FOR WB OPERATION (> OCTAVE BW) FOR WB OPERATION (> OCTAVE BW) ---- EVEN & ODD EVEN & ODD EVEN & ODD EVEN & ODD ORDER DISTORTION MUST BE CONSIDEREDORDER DISTORTION MUST BE CONSIDEREDORDER DISTORTION MUST BE CONSIDEREDORDER DISTORTION MUST BE CONSIDERED

Multi-Octave Problem

• IM AND HARMONIC DISTORTION A PROBLEMIM AND HARMONIC DISTORTION A PROBLEMIM AND HARMONIC DISTORTION A PROBLEMIM AND HARMONIC DISTORTION A PROBLEM• 2F1, F22F1, F22F1, F22F1, F2----F1, 2F2F1, 2F2F1, 2F2F1, 2F2----F1 AND 2F1F1 AND 2F1F1 AND 2F1F1 AND 2F1----F2 PRODUCTS OF MOST CONCERNF2 PRODUCTS OF MOST CONCERNF2 PRODUCTS OF MOST CONCERNF2 PRODUCTS OF MOST CONCERN• MOST PREDISTORTERS CORRECT ONLY ODD ORDER DISTORTIONMOST PREDISTORTERS CORRECT ONLY ODD ORDER DISTORTIONMOST PREDISTORTERS CORRECT ONLY ODD ORDER DISTORTIONMOST PREDISTORTERS CORRECT ONLY ODD ORDER DISTORTION

F2-F1 2F1-F2 2F2-F1 2F1

F1 F2

FREQUENCY

EMISSION LIMIT

Multi-Octave Linearization

• MZMs produce minimal 2nd harmonic distortion with bias voltage control

• Predistorters can generate 2nd in addition to 3rd order nonlinearities

43

3 order nonlinearities

– 2nd order terms may worsen performance for > octave bandwidth

– Even terms not in the proper phase to cancel

• Developed predistorters that generate only 3rd-order components and operate over multi-octave bandwidth

Multi-Octave Linearizer

• A multi-octave broadband with even order cancelation

- operating from 1 to 20 GHz

- with single linearizer providing both IM and harmonic

distortion correction using push-pull NLG

Balu

n

NLG

NLG

Pre-Distortion Linearizer Circuitry

NLG

NLG

AttenB

alu

n

Optical & Electro-Optical Linearization

• Dual Series MZM Modulators

– Proper biasing of series MZMs may result in linearization of sinusoidal transfer

• Has been shown to approximate ideal limiter response

• Inherently wideband

• Difficult to tune/align

• Feedforward

– Nonlinear response is sampled (electrically) and re-injected to fundamental path in order to cancel undesired frequency products

• Limited bandwidth due to need for electrical delay in feedforward path

Optical Linearization Example

• Optical Feedforward Coupled linearization of

Mach-Zehnder modulator

– Third-order cancellationOMI

0.2(OMI)^3

split

Vrf

MZMbiased at Vpi/2

AC coupled

-0.5sin(piOMI/2)

a2

MZMbiased at Vpi/2

a1

0.2(a2)(OMI)^3

opticaloutput

delay

Potential for even greater cancelation (> SFDR)

Description

• First MZM generates distortion products

• Amplitudes of distorted detected outputs are:

• 2-tone 3rd-order amplitudes (IMDs) were found by eval. Fourier Series of the output

• Note that Fundamental and IMD products are always out of phase

⋅−=

2sin

2

1 OMIV fund

π 32.0 OMIVIMD ⋅=

• Note that Fundamental and IMD products are always out of phase

• RF signal is delayed and added to the distorted output• Level is set to “just cancel” the carriers of the detected signal, leaving just the

distortion

• Distortion products are re-modulated, and summed with the first modulator

output.• Summation must be noncoherent

• Dual lasers or sufficient delay

• Fiber Optic Links are increasingly being deployed for linear microwave transport applications

– Radar/Antenna remoting where weight and loss are critical

– Sensor Systems

– Precise Time and Frequency Distribution

– High EMI environments

Summary

• Photonic microwave links beneficial alternative to coax or wireless in many applications

– Size, Weight, Cost, Performance, EMI, Safety, …

• Practical intensity modulation links were presented

– Typical Performance, Limitations, and Methods of Improvement

• Linearization can offer dramatic improvement in dynamic range

Linear Photonics 48

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