syntonics aoc rf over-fiber 19 jan 08

7/28/2019 Syntonics AOC RF Over-Fiber 19 Jan 08

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Analog RF-over-Fiber Technology

Association of Old Crows

January 19, 2008

Bruce G. Montgomery, Syntonics LLC

[email protected]


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Agenda

Introduction

Components for analog photonics RF-over-fiber link design

Applications of RF photonics Who is Syntonics LLC?


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1. Introduction

What is RF-over-fiber?


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What is RF-over-Fiber?

RF-over-fiber = Electro-optic components and light usedto transport RF signals over optical fibers [all analog] Radical change from what Mr. Marconi had in mind

RF-over-fiber has certain advantages over coax cable Long, secure, lightweight, easily routed

But RF-over-fiber isnt an engineering silver bullet:

Practical links need gain / attenuation / filtering / closed-loop control Links add thermal and spurious noise and limit SFDR

Link doesnt does not know everything the radio knows


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How does RF-over-fiber work?

RF SourceRF Source

Laser diode

DC bias

PIN diode

DC bias

RF OutRF Out

Amplitude-modulated light

propagates over optical fiber

Bias tee

Transmitter Receiver

The RF Out must be amplified to

provide a useable signal

Any RF signal can be transmitted,

up to many GHz depending on the

laser and its modulation scheme.


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Generic Link Topologies

Different ways to combine lasers, modulators, fibers, detectors

Directly Modulated

Laser at AntennaLaser Detector

RF Out

@ Antenna @ Receiver AM light

Externally Modulated

Laser at Antenna

RF Out

AM or PMlight

@ Antenna @ Receiver

Un-modulatedlight

Laser

External AM or

PM Modulator

Detector (Several designs

to be considered)

Externally Modulated

Laser at ReceiverDetector (Several designs

to be considered)

RF Out

AM or PMlight@ Antenna @ Receiver

Un-modulatedlight

Laser

External AM or PM Modulator


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Optical Communications

1870John Tyndall

1880William Wheeling 1880Alexander Graham Bell


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Mid-Twentieth Century

Early 1950s: Fiberscope & optical fibers with

cladding Snells law: The angle at which light is reflected depends on

the refractive indices of the two materials

Used to inspect inaccessible welds, for laparoscopic

surgery Optical fiber loss ~1,000 dB/km


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1962: First visible laser diode

photographed in its own lightLate 50s to early 70s

1957Gordon Gould at Columbia Universityconceives of laser as an intense light source

Supported by Charles Townes, Arthur Schawlow atBell Labs

1960Ruby laser and helium-neon (HeNe)laser

1962Semiconductor lasers 1966Charles Kao and Charles Hockham at

Standard Telecommunication Laboratory,England

Posit optical fiber communications possible ifattenuation < 20dB/km (1% of light at 1 km)

1970: Robert Maurer, Donald Keck, PeterSchultz at Corning

Achieve glass fiber with < 20 dB/km loss purestglass ever made

1962: IBM scientists observe their

new GaAs direct injection laser.


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2. Components forAnalog Photonics


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EO Components

Lasers

External Modulators Detectors


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Communication LasersButterfly module includes

a Peltier thermoelectric

cooler/heater to maintain

temperature (wave length

control).

TOSA (Transmit Optical

Sub-Assembly) lasersare simpler devices

Metrics: Optical Power & Relative Intensity Noise (RIN)RIN describes the instability in the power level of a laser; usually

presented as relative noise power in db/Hz

Metrics: Optical Power & Relative Intensity Noise (RIN)RIN describes the instability in the power level of a laser; usually

presented as relative noise power in db/Hz


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External Modulators

Oki Semiconductor (www.okisemi.com) 40 Gb/s

EA modulators using GaInAsP semiconductor

Electro-absorption (EA) devicesare intensity modulators Uses Franz-Keldysh effect, i.e., a

change of the absorption spectrumcaused by an applied electric field

Electro-Optic (EO) devices are

phase or intensity modulators Uses Pockels effect, which is small

Most commonly used electro-opticcrystal, lithium niobate (LiNbO3), has

r = 34x10-12 m/V. An electric field of 106 V/m (1V across

electrode gap of 1 m) produces afractional index change of ~ 0.01%.

Most effective with polarized light

n n3

2rE

Where:n = index of refractionr = electro- optic coefficie

E = applied electric field


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Mach-Zehnder Modulator (MZM) Mach-Zehnder interferometer invented ~1900

Measures phase shift ( index of refraction) using two opticalpaths

A MZM is an intensity modulator

Modulation of an electrical data stream using an

external MZM.Schematic cross section through the two arms of a push-pull

MZM (not to scale). Light to be modulated propagates

through core layer along the length of the device (into thepage). Dipoles are aligned anti-parallel in the two arms of

the MZ.


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Optical Detectors

Anode Cathode

Single-ended PIN diode photoreceiver (e.g., ROSA) Absorbed photons generate a mobile electron and electron hole

Carriers are swept from the junction by the built-in field of the

depletion region, producing a photocurrent

Used with reverse bias. Reverse-biased diode has extremely high resistance

Can be used as a photon detector by monitoring the current

running through it

Metrics: Responsivity, Leakage, NEP

Responsivity Ratio of generated photocurrent to incident light power, typicallyexpressed in A/W when used in photoconductive mode

Dark current (Leakage) Current through the photodiode in the absence of any

input optical signal, when it used in photoconductive mode

Noise-equivalent power (NEP) Minimum input optical power to generate

photocurrent equal to the RMS noise current in 1-Hz bandwidth

Metrics: Responsivity, Leakage, NEP

Responsivity Ratio of generated photocurrent to incident light power, typicallyexpressed in A/W when used in photoconductive mode

Dark current (Leakage) Current through the photodiode in the absence of any

input optical signal, when it used in photoconductive mode

Noise-equivalent power (NEP) Minimum input optical power to generatephotocurrent equal to the RMS noise current in 1-Hz bandwidth


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Optical fibers & connectors

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Four Wavelength Regions of

Optical Fibers

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Multi-Mode Optical Fibers

Multimode ~ numerous simultaneous wave modes

related to acceptance angle

Two types: Step-index (left)

Graded-index (right)

Light waves follow serpentine path

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Single-Mode Optical Fibers

Small diameter core precludes

dispersion caused by multiple

mode and achieves lower attenuation losses Early single-mode fiber generally had step-index cladding

Modern single-mode fibers have matched clad, depressed

clad, and other exotic structures

Single-mode fiber presents incremental difficulties Smaller core diameter makes coupling light into core more

difficult

Tolerances for connectors and splices are more demanding

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Optical Connectors

Names reflect 1. connector type/2. end-face polish 1. ST, SC, FC, etc.

2. End polish applied to connectors (i.e., fibers) end face PC = Physical Contact, end face polished and usually convex

APC = Angled Physical Contact at 8 angle

Can also find defined as Angled Polished Contact)

Typically, xx/PC connectors have lowest insertion loss;

xx/APC connectors have lowest return loss

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Wave Division Multiplexing

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Coarse Wave Division

Multiplexing (CWDM) 18 wavelengths specified, 10 used (1430-1610 nm)

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Dense WDM

Dense Wave Division Multiplexing DWDM) 64 wavelengths specified


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RF-over-fiber linkdesign

Loss & Gain & Noise (Noise Figure)

& Linearity SFDR

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RF-over-fiber versus Copper

Advantages {Distance x Bandwidth}

product give better RFperformance for relativelylong links

Easier to route cabling

Reduced weight, diameter,

bend radius Signals are isolated

No cross talk

EMP/EMI isolation of radio

Security regulations Relocates

expensive/sensitive radiosto the user

Can maintain or changereceiver without going to theantenna or changing the fiber

Disadvantages {Distance x Bandwidth}

product give less RFperformance for relatively

short links

Noise figure and SFDR

Requires TX amplifier atantenna

Redundant with HPA in radio

Size-Weight-and-Power

(SWAP) for transmittercomponents

Lasers, current and TEC

control circuits, modulator,

bias controller Higher power LNAs

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Loss versus frequency for coax cablesoss versus frequency for coax cables

0

0.5

1

1.5

2

2.5

0 10 20 30 40

frequecy (GHz)

loss(dB/m)

0.15" OD

0.2" OD

0.3" OD0.3" OD

0.375" OD

0.5" OD

los

sdB

750

600

450

300

150

300 m

Length of

aircraft carrier

50

40

30

20

10

20 m

Cable run

Cable outside

diameter

frequency (GHz)

100

105

110

115

120

125

130

135

15 20 25 30 35 40

1 dB output compression point (dBm)

SFDR(dB-Hz

3rd order dynamic range of typical LNAs

20 dB gain

30 dB gain

40 dB gain

SFDR(

dB-Hz2/3)

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Optical link loss calculations

0.2 dBo / kmSM Optical Fiber

0.1 dBoFusion Splice

0.5 dBoSwitch

3.5 dBoSplitter

0.25 dBoConnector (SC/APC or FC/APC)

Typical LossOptical Component

0.25 + 0.5 + 0.5 + 0.25 + 0.2 1.7 dBo

~0.5 dBo

~0.25 dBo

~0.2 dBo

total

~0.25 dBo ~0.5 dBo

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Optical loss RF loss

RF power loss = 2 x optical power loss

With electrons, RF Power I2

( V2

) Half (RF) Power = 10log(power ratio) = 10log(21)

= 3 dB down

= 70.7% of current (or voltage)

With light, Optical Power number of photons Half (optical) Power = 1/2 number of photons

= 1/2 of current in PIN diode detector RF output Power I2 = 1/4 of RF input power = 6 dB down

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Gain

Gain is required to: Overcome losses in the optical path (TX and RX paths)

2X RF gain to overcome 1X optical loss

Work above the noise floor of the laser (TX and RX paths)

Typically requires 30-40 dB gain in RX path

Reduces SFDR Power the antenna (HPA, TX path)

Coax losses much reduced so less power may be necessary

Many military waveforms require linear amplification Some military waveforms require fast T/R switching

Attenuation is required to:

Survive radio TX power Implement ALC control of HPA

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Noise

Noise results from RIN, Shot Noise, Thermal Noise RIN results from lasers spurious optical emissions (spurious electron

transitions)

Shot noise results from quantum physics of discrete photons striking PINdiode detector

Thermal noise results from resistance in laser diode and PIN diodedetector + noise due to RF amplification

At low optical power,

thermal noise dominates

At high optical power, RIN

dominates

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Noise Figure

Link output noise can be computed directly from specified componentnoise constants and optical loss (OL): Nthermal = cthermal (dBm/Hz)

Nshot = cshot OL (dBm/Hz)

NRIN = cRIN 2OL (dBm/Hz)

Total output noise,

Noise figure (dB) =

where GL is the total link gain,

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Linearity

Linearity refers to second-order, third-order, andhigher order distortion terms

Linearity required by system is function of: Bandwidth, dynamic range, modulation type, number of

carriers

Sources of third-order non-linearities include: Laser diode, fiber, PIN diode detector, RF amps

Sources of second-order non-linearities include: Nonlinear spectral components of sum & difference freqs.

and harmonic freqs.

Not an issue if system bandwidth < 1 octave

Typical RF-over-fiber links operate at low power Only laser diode and RF circuits create non-linearities

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Spur-free dynamic range

SFDR is a consequence of gain, noise, linearity

Usually dominated by third-order SFDR:

Where third-order intercept, IIP3 (dBm) is:

Excellent reference:

Application Note 106-1,

System Design Using

Direct Modulation Fiber

Optic Links

J. A. MacDonald, LinearPhotonics, Hamilton, NJ

http://www.linphotonics.com/technical

_info.htm

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Noise figure and SFDR for MZ quadrature biased link

COTS

NF=18

Po=150mW (fiber laser)

Dual output modulator, V=3Modulator + link loss = 3.8 dBBalanced detector, rd=0.8, Ip=25 mA

NF=29

Po=40mW, RIN=-160dB/Hz (laser

diode)

Dual output modulator, V=5Modulator + link loss = 5 dB

Balanced detector, rd=0.8, Ip=5 mA

NF(V,Ip), balanced link

RIN limited

NF(V,Ip), single detector,(RIN=-160dB/Hz)


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Military CommsApplications for RF-over-Fiber

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Mobile Communications

Radios

below decks

Antennas

on railings

Mobile commandcenter in defilade

Exposed antennas with

good lines of sight

Lightweight

fiber cable

Perimeter Security

Radio Port, typ.

Central antenna


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ATC, Ranges

Moves radios to centralcontrol location yet

antennas can be distant Lowers maintenance costs

Reduces maintenancereaction times

Air Traffic Control

Test & Training Ranges


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Syntonics LLC

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DCAA-approved accountingsystem

ISO 9001:2000 registeredQuality Management System

DSS-supervised facility

clearance (SECRET)

Syntonics LLC

Specializes in RFcommunications

technology for DoD: FORAX communications

systems

Unique antennas

Founded 1999

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Air Force ACOMS,& Comms Sqdrns (multiple units) Air Force NORTHCOM Air Force Office of Scientific Research (AFOSR)

Air Force Pentagon Comms Agency (AFPCA) Army Brigade Combat Teams (multiple units) Army Research Laboratory (ARL) Army Tobyhanna Depot DoD Technical Support Working Group (TSWG) Dwyer Hill Training Center, Ontario

Institute for Defense Analysis Joint Air Defense Operations Center (JADOC) Maryland Procurement Office Missile Defense Agency (MDA) Naval Air Systems Command, Pax River (NAVAIR) Naval Air Warfare Center Weapons Division

(NAWCWD) Naval Special Warfare Groups (multiple units) Naval Surface Warfare Command Carderock Naval Undersea Warfare Center Division Newport Space and Naval Warfare System Command

(SPAWAR)

Special Operations Command (USSOCOM) General Dynamics, Lockheed Martin, BAE,

Brown International, TSE, others

Syntonics Customers


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FORAX RF-over-FiberCommunications

System

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What Is FORAX?

FORAX connects communicationradios to remote antennas usingoptical fibers

FORAX can replace multiplecoaxial cables with single fiberoptic cable

RF-over-fiber is well suited for: Fixed and mobile command centers

Air Traffic Control

Test & Training Ranges

Developed for USSOCOM

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Why Use FORAX? (Warfighters)

FORAX enables a dramatic change in Radio

HillRemoves the radios and crypto equipment to the defilade

safety of the command post

Replaces heavy, short, power wasting coaxial cables one

per radio with a single long, lightweight, secure fiber opticcable

FORAX will change tactical communications

doctrine as it relates to radio/antenna separation:Decrease risk to personnel and costly radio/crypto equipment

Decrease time of CP set-up

Lower maintenance response time


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FORAX RF-over-fiber Users

2008F & M C2HF, LOS, TACSAT, EPLRSVarious(Pending)

2008Fixed C2SINCGARS, EPLRSRT-1523, PRC-117,

EPLRS

CENTCOM

2008Fixed C2TACSAT, GPS, UHF LOSPRC-117, AFTRS, CTIIAl Udeid Air Base

2007Fixed C2GPS L1/L2GPS612th ACOMS Davis-Monthan AFB

2007Fixed C2SINCGARSVRC93, PRC-117CENTCOM

2007Fixed C2TACSATPRC-117NORTHCOM

2007Fixed C2UHF LOS, TACSATPRC-117Army Research Lab

2007Mobile C2TACSATPRC-117Tobyhanna Army Depot

2007Fixed C2TACSATPSC-5DGD/Electric Boat

2007Fixed C2UHF LOS, TACSATPRC-117Pentagon USAFPCA

TACSAT

TACSAT

SINCGARS, VHF & UHF LOS, TACSAT

TACSAT

VHF & UHF LOS

TACSAT

TACSAT

TACSAT

VHF & UHF LOS, TACSAT

VHF & UHF LOS, TACSAT

Application

2005Fixed C2PSC-5, USC-61Pentagon Renovation/GD

2005Mobile C2PRC-117Canadian Forces, DHTC

2004Mobile C2PRC-117DoD/Ft. Bragg

2006Mobile C2PRC-117, PSC-5Army Research Lab

2006Fixed C2VRC91, PRC-117, PSC-5Army JADOC Bolling AFB

2006Fixed C2PRC-117, PSC-5Pentagon USAFPCA

2006Fixed C2PSC-5347th CS Moody AFB

Fixed C2

Fixed C2

Fixed C2

Use

2006PRC-117612th ACOMS Davis-Monthan AFB

2006PRC-117603th ACOMS Ramstein AFB

2006PRC-11756th ACOMS Hickam AFB

SinceRadio(s)User


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FORAX-HARCCommunications

Existing aerostats equipped with

FORAX-HARC (High Antennas forRadio Communications) can extend

radio communications both over the

horizon and into urban canyons.

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HARC C t


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HARC Concept

High antennas improve a CPs line-of-sight(LOS) commsExample: Over-the-horizon comms to distant radiosExample: Local comms into urban canyons

Useful for SINCGARS, VHF, UHF, EPLRS, etc.

Aerostats can carry high antennasFORAX can connect a CPs radios

to multiple high antennas using

the aerostats tether

Rx/Tx

Rx/Tx

FORJ

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FORAX-HARC: Many radios


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FORAX HARC: Many radios

sharing a 5000 antenna tower

Optical fiber

1 @ single-mode

FORAX-HARC AIU (not visible)

Antennas connected via coax cables

Packaged to meet platforms requirements

Coax cables

Four high antennas (not visible)

Separate TX and RX elements

Two types

Aerostat mooring point & FORJs

FORAX-HARC RIU

Radios connected via coax cables

to radios antenna ports

User Radios

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T b f S t i


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To buy from Syntonics

Bruce Montgomery [email protected]

410-884-0500 x201

Ray Madonna [email protected]

410-490-2680 or 410-884-0500 x206

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syntonics aoc rf over-fiber 19 jan 08

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