NASA / TM--2000-209776

On-Board Fiber-Optic Network Architectures

for Radar and Avionics Signal Distribution

Mohammad F. Alam, Mohammed Atiquzzaman, and Bradley B. Duncan

University of Dayton, Dayton, Ohio

Hung Nguyen and Richard KunathGlenn Research Center, Cleveland, Ohio

March 2000

https://ntrs.nasa.gov/search.jsp?R=20000034016 2018-07-09T15:29:16+00:00Z

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NASA / TM--2000-209776

On-Board Fiber-Optic Network Architectures

for Radar and Avionics Signal Distribution

Mohammad F. Alam, Mohammed Atiquzzaman, and Bradley B. Duncan

University of Dayton, Dayton, Ohio

Hung Nguyen and Richard Kunath

Glenn Research Center, Cleveland, Ohio

Prepared for theInternational Radar Conference

sponsored by the Institute of Electrical and Electronics Engineers

Alexandria, Virginia, May 7-12, 2000

National Aeronautics and

Space Administration

Glenn Research Center

March 2000

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On-board Fiber-optic Network Architectures for

Radar and Avionics Signal Distribution

Mohammad F. Alam, Mohammed Atiquzzaman, Bradley B. Duncan

Department of Electrical and Computer Engineering

University of Dayton

Dayton, Ohio 45469

Hung Nguyen and Richard Kunath

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

ABSTRACT

Continued progress in both civil and military avionics applications is

overstressing the capabilities of existing radio-frequency (RF) communication networks

based on coaxial cables on board modem aircrafts. Future avionics systems will require

high-bandwidth on-board communication links that are lightweight, immune to

electromagnetic interference, and highly reliable. Fiber optic communication technology

can meet all these challenges in a cost-effective manner. Recently, digital fiber-optic

communication systems, where a fiber-optic network acts like a local area network

(LAN) for digital data communications, have become a topic of extensive research and

development. Although a fiber-optic system can be designed to transport radio-frequency

(RF) signals, the digital fiber-optic systems under development today are not capable of

transporting microwave and millimeter-wave RF signals used in radar and avionics systems

on board an aircraft. Recent advances in fiber optic technology, especially wavelength

division multiplexing (WDM), has opened a number of possibilities for designing on-

board fiber optic networks, including all-optical networks for radar and avionics RF

signal distribution. In this paper, we investigate a number of different novel approaches

for fiber-optic transmission of on-board VHF and UHF RF signals using commercial off-

the-shelf (COTS) components. The relative merits and demerits of each architecture are

discussed, and the suitability of each architecture for particular applications is pointed

out. All-optical approaches show better performance than other traditional approaches in

terms of signal-to-noise ratio, power consumption, and weight requirements.

1._TRODUCTION

Recent advances in avionics applications in both civil and military aircrafts

require high-bandwidth on-board microwave and millimeter-wave radio-frequency (RF)

communication networks. A number of RF systems with their interconnection network

based on coaxial cables and waveguides increase the complexity of the RF

communication network on board modem-Civil and military aircrafts with increasing

problems related to electromagnetic interference (EMI). A simple, reliable, and lightweight

communication system that is free from the effects of EMI, and capable of supporting the

NASA/TM--2000-209776 1

broadband RF communications needs of the future on-board avionics systems can not

implemented by existing coaxial cable based systems easily. Fiber-optic communication

systems can meet all the challenges of modern avionics applications in an efficient and

cost-effective manner where a single fiber has the potential to replace dozens of RF

cables [1]. In addition, a number of optical fibers can be bundled in a single fiber-optic

cable, which has the potential to reduce the weight of the fiber-optic cable network

significantly. In addition, fiber-optic components for airbome applications which are

capable of withstanding the adverse environmental conditions on-board an aircraft are

already under development [2-6].

Presently, two different optical wavelength regions are used for modem optical

communication in optical fiber. These wavelength regions are around 1.31 and

1.55 micron (1310 and 1550 nm, respectively). For both of these wavelengths two

methods can be used for fiber-optic transmission: analog and digital. Analog signals are

continuously varying signals where the exact waveform of the RF signal needs to be

preserved when transmitted over a fiber optic link. This requires the analog fiber-optic

transmitter and the analog fiber-optic receiver to be extremely stable, linear, and to have a

large dynamic range. These stringent requirements increase the cost of analog fiber optic

transmitters and receivers considerably. On the other hand, digital signals are composed

of ones and zeros as in computers. The digital signal does not require preserving the exact

wavefoma of the transmitted signal as long as the transmitted signal is not distorted to the

extent that ones and zeroes can not be distinguished from each other. For these reasons,

digital fiber-optic communication equipment can perform well even when noise and

distortion of the optical signal is present.

Fiber-optic communication networks onboard aircrafts for digital data

communication has recently become an active area of research and development [7-11 ].

However, the systems under development today are digital fiber-optic communication

systems which are capable of carrying digital data only, but are not capable of

transporting radar and avionics RF signals from one place to another on board an aircraft.

Analog fiber-optic links can be employed to transport microwave and millimeter-wave

RF signals from one place to another on board an aircraft. These analog fiber-optic links

take as input an RF signal, transports it over fiber, and reproduces at the output an exact

replica of the RF waveform fed to it at the input end. The RF signal itself may be

modulated by a baseband signal by any of the analog or digital modulation techniques,

but an analog fiber-optic link transmits the RF signal in the same manner irrespective of

the method of modulation used for modulating the RF signal by the baseband signal.

Figure 1 shows a typical RF signal (modulated by analog or digital modulation

techniques) being transported by an analog fiber-optic link.

An optical transmitter launches the optical signal into an optical fiber. At the other

end of the fiber, we need an optical receiver that converts the optical signal to RF again.

Usually a single fiber can carry information in one direction only (simplex) which means

that we usually require two fibers for bi-directional (duplex) communication. However,

recent advances in wavelength division multiplexing make it possible to use the same

fiber for duplex communication using different wavelengths.

In this paper, we will discuss a number of architectures for RF signal distribution

with traditional hybrid RF-optical as well as modern all-optical approaches using

commercial off-the-shelf (COTS) components. The rest of the paper is organized as

NAS A/TM---2000-209776 2

follows. In Section 2, we introduce the principles of some of the novel fiber-optic

communication techniques based on recent advances in fiber optic systems. Section 3

discusses some generalized fiber-optic distribution networks including all-optical

solutions, whereas Section 4 describes fiber-optic architectures for multiple-source

multiple-destination networks. We conclude this paper in Section 5

Analog __

signal

%

Digital __

data

101010...

IAnalog I A nalog

modulator I demodulator

_1 'F_;:'2itPl:; _"_ Firbeer;;petlc _

T 1 Analog fiber-optic link __I_

I DigitalDigital demodulator

modulator

Pow er

Combiner

A natogsignal

%

Digital data101010...

Fimare 1: An analog fiber-optic link transports RF signals where the RF signal may be modulated by an

analog or a digital modulation techniques.

2. TRADITIONAL AND MODERN FIBER-OPTIC SYSTEMS

We first show how a simple system can be implemented using both traditional

and modern all-optical approaches. Figure 2 shows such a simple system where an on-

board VHF system communicates with a VHF antenna, and an on-board UHF systemcommunicates with a UHF antenna.

4 channels

(VHF Antenna 2)

100 150

I xl24 channels 24 channels

(UHF Svste 1) .L Optic Fiber (UHF Antenna 1)

AIIIIIIIK ................................... A I IIN950 1450 -- _ _ 950 1450 MHz

i,,xt4 channels

(VHF System 2)

__LJL- MHz

100 150

Fimare 2: A simple fiber-optic communication system. The VHF antenna communicates with the VHF

system, and the UHF antenna communicates with the UHF system.

NASA/TM--2000-209776 3

2.1 Traditional Approach:

In the traditional fiber-optic approach, separate optical fibers are used for each

point-to-point link. Thus, one pair of fibers connects UHF antenna 1 with UHF system 1,

and another pair connects VHF system 2 with VHF antenna 2. Each point-to-point link

requires a fiber-optic transmitter (Tx), a fiber-optic receiver (Rx), and a continuous fiber-

optic light path from each transmitter to the corresponding receiver. This system requires

three cable segments: the left segment requires a cable with two fibers, the middle

segment requires a cable with four fibers, and the right segment requires two fibers. For

the two fibers connecting the UHF antenna 1 with UHF system i, splicing is required at

every cable junction: once at the junction between the left and the central cable segments,

and again at the junction between the central and the right cable segments.

VI-FAntenna 2

UHF Systom 1 100 150 bl--Iz .... I ._.................... _.. ...... i I UHF Antenna 1

..............{............--=-==::::==:======II.......'° / - \

100 150 MHz

Figure 3: Traditional fiber-optic network solution to the interconnection problem of Fig. 2. Rx representsfiber-optic transmitters, and Tx represents fiber-optic receivers.

This architecture is simple, economical and easy to implement when few systems

need to be interconnected. However, as the number of systems that need to be connected

becomes higher and complex, it becomes almost impossible to use fiber cables with

multiple fibers. If cables with multiple fibers are used, then they have to be spliced at

many locations, making the system lossy and unreliable. On the other hand, using many

single-fiber or twin-fiber cables reduces the advantage of weight reduction which could

be obtained if fiber cables with multiple fibers could be used. One solution to the

problem, which addresses signal'loss at each splice, can be solved by using a fiber-optic

receiver and a transmitter at each node where a fiber has to be spliced. This solution,

which we call the hybrid RF-optical approach is discussed in Section 2.2. Another

modem approach, where a number of different wavelengths are carried by the same

optical fiber using the wavelength division multiplexing (WDM) technology is discussedin Section 2.3.

NASA/TM--2000-209776 4

2.2 Hybrid RF-Optical Approach:

In this approach, one fiber carries all the RF signals from left to right, and another

fiber carries all the RF signals in the opposite direction. These fibers are, however, split at

every node where an RF channel needs to be added to the fiber, or a node where an RF

channel needs to be dropped from the fiber. In addition to fiber-optic transmitters and

receivers, we also need RF power combiners and RF demultiplexers for this approach.

RF power combiners multiplex a number of different RF channels onto a single RF

transmission line, while the RF demultiplexer separates an RF channel from a band of RF

frequencies. Each transmitting/receiving node must have a channel add-drop subsystem,

which, for the simple network of Fig. 2, requires only two add-drop subsystems for VHF

antenna 2 and VHF system 2.

Channel add/drop

subsystem

_ ---_---t

/ \950 --- b}-tz --- 1450

VII= Antenna 2

/ \

........... .......H:H,xt

Vtf Svstern 2

/ \

........... ........

UHF System 1 ',

n7 n.............._,.............................., ...............

/ \ / \100 150 tvHz 100 150 MHz

VHF A nter'ma 2 VHF System 2

/ \950 --- MI-Iz -- 1450

UPF Antenna 1

Fi_,ure 4: Hybrid RF-optical approach for Fig. 2. MUX represents RF power combiner (or multiplexer).

DMX represents RF demultiplexer.

The advantage of this system is that only a single pair of fibers running from the

nose section to the tail section of the aircraft acts as the fiber-optic trunk line. At any

point in the aircraft, if a new channel need to be added to the fiber optic trunk line, the

channels coming from the upstream fiber are converted to RF by an optical receiver, the

local RF signal is multiplexed with the channels from upstream, and the multiplexed RF

signal is again sent out to the downstream Optical fiber using an optical transmitter.

Although this approach saves some fiber as compared to the traditional approach

discussed in Section 2.1, additional fiber-optic transmitters and receivers, as well as RF

power combiners and demultiplexers increase weight and power consumption of the

system.

NASA/TM--2000-209776 5

vCi

fi1280 nm

I WAVELENGTH

LiHF System 1 ! POWERCOMBINER DEMUX

1280 nm

OF

l&qt3nm

UHF Antenna 1

• I---'--7 1280+1330 nm _ OF

|OF WAVELENGTH i

DEMUX POWE OMBiNER !

j12eon_ 112B°_'

VHF Antenna 2 VHF Syslern 2

Figure 5: All-optical solution to the problem of Fig. 2 using wavelength division multiplexing

2.3 All-Optical Approach:

The method of sending more than one wavelengths through an optical fiber is

called wavelength-division multiplexing (WDM), which is a new and evolving

technology. Using WDM technology, it is possible to share a single fiber for carrying two

or more optical channels at different optical wavelengths simultaneously. Thus, a single

fiber carries a number of optical wavelengths, and each of the wavelengths carry a

number of multiplexed RF channels. In this approach, we need optical power splitters,

optical power combiners, and optical wavelength demultiplexers. Optical power splitters

split the optical power received from an incoming optical fiber into two or more equal or

unequal fractions, and each fraction is transmitted to a new outgoing fiber.

In order to implement the system in Fig. 2, we can choose the wavelength

1330 nm for the UHF system, while the VHF system will communicate on 1280 nm.

(Both a splitter and a combiner have the same physical construction. So, a single

component can work either as a combiner or as a splitter depending on the way it is

connected). We still require two fibers, one for transmission in each direction. However,

we do not need four fibers in the central segment as in Fig. 2. For the fiber carrying signal

from left to fight, optical signals from two transmitters, one from the UHF system 1 and

the other from the VHF antenna 2, are combined by an optical power combiner. One of

the transmitters transmit at the wavelength 1280 nm, while the other transmitter operates

at the wavelength 1330 nm. The combiner at the VHF antenna 2 combines the two

wavelengths and launches the combined power onto a single fiber, which runs up to the

point where the VHF system 2 is located. At that point, a power splitter splits the total

power into two equal halves. The receiver for the VHF system 2 at 1280 nm will receive

its channel from VHF antenna 2 via one of the ports of the splitter. The other port of the

splitter transmits half of the signal which is received by the UHF antenna 1. The receiver

at UHF antenna 1 receives its channel from the UHF system 1 on 1330 nm. Both of these

receivers (VHF system 2 and UHF antenna 1) should have the capability to choose the

fight wavelength from the two wavelengths (1280 and 1330 nm). The fight wavelength

can be easily separated by an optical wavelength demultiplexer at the receiver. For

NASA/TM--2000-209776 6

communication in the reverse direction, we need another fiber running in the opposite

direction, and two more combiners/splitters.

The advantage of this method is that it is an all-optical solution where an optical

signal injected into the system by an optical transmitter remains in optical form until the

optical signal is received by the corresponding optical receiver. Thus, a complete light-

path exists between an optical transmitter and an optical receiver for every wavelength

that is present in the system, and there is no optical-to-RF and RF-to-optical conversion

(as in the solution of Section 2.2) which may degrade the signal-to-noise ratio of the RF

signal being carried by the optical signal. Also, the ability to carry many RF signals on

different wavelengths over the same fiber means savings in weight. In addition, the use of

wavelength multiplexers and demultiplexers, which are passive components requiring no

power supply, reduces the power consumption compared to hybrid RF-optical systems.

3. FIBER-OPTIC SIGNAL DISTRIBUTION SYSTEMS

In this section, we discuss the problem of designing a fiber-optic signal

distribution network which distributes an RF signal originating from a single source (e.g.,

an antenna) and distributes it to a number of points on an aircraft. Figure 6 shows the

distribution system design problem in detail. Here, a single VHF antenna receives RF

signals which need to be distributed to a number of on-board systems (1, 2, 3 etc.). We

can adopt either a hybrid RF-optical approach as in Section 2.2, or an all-optical approach

as in Section 2.3. Both these approaches to implement the system in Fig. 6 are discussed

next.

4 channels

(VHF Antenna)

_LJ_-[_ MH z

! 00 | 50

Optical Fiber

4 channels 4 channels 4 channels

tSystem 1) (System 2) (Syste 3)

..../hill I11 AI 111 All Ih,100 150 1O0 150 IO0 150

Figure 6: A fiber-optic Signal distribution system.

3.1 Hybrid RF-Optical Approach:

In this method we extend the idea of Section 2.2 to multiple nodes. There is only

one pair of fibers running from the nose to the tail of an aircraft. At each point (called a

node) the incoming optical signal coming from the left side is converted to RF, the local

NASA/TM--2000-209776 7

RF channel is extracted, and a new optical signal is transmitted by a fiber-optic

transmitter to the outgoing fiber-optic link. Figure 7 shows the implementation details of

this approach, where each node is a receiving node. The details of each node are

described in Figure 8.

VHF A ntenna

(4 channels)

System 1

( 4 channels)

iii:ii!'!i_ii_ii!ii!i_ii!:il,i!iiiiii_iiiiiiiiiiiiii!iiiiiiii_i_i!_:_i_:,i!i;;!_! !51_iiiiiiiiUiii_;ili_ilii_iiililiii...............

? i2i ; i

System 2

(4 channels)

,,'?'i_i"i'_'i'iiii_!iii'i:ii_!'_i_i_'i_i'ii'i!'iiii'ii_!_ii'.ii,'_ii,,_--iiiiii,li:iiii_i,li,_ii_i_,ii'iiiiiiiiii_ii_iiiii!iiiii_iiiiiii_iiiiiiiiii!ili

System 3

( 4 channels)

Figure ?: Schematic diagram of hybrid RF-optical so!ution of the problem in Fig. 6.

Other

Systems

From

Tx

TO

To R_senger

Fimare 8: Detailed schematic of a receiving node in Fig. 7.

This solution is simple and requires only a single fiber running over the length of

the aircraft. However, each node requires a fiber-optic transmitter as well as a receiver in

this approach.

3.2 All-Optical Approach

A fiber-optical splitter is a device which splits the optical power received from a

single fiber into a number of fractions and then transmits each fraction to a separate fiber.

It is usually a passive device which is simple and light-weight in construction. Using one

or more levels of splitters, it is possible to generate a distribution tree from a single

source of fiber-optic signal.

Figure 9 shows the all-optical solution to the signal distribution problem of Fig. 6.

In this approach, we first convert the RF signal into an optical signal using a fiber-optic

transmitter. Then it is split into eight by a one-to-eight optical splitter. Each of the split

optical signals may go through repeaters (where the weak optical signal is first converted

to RF, and then re-transmitted by a fiber-optic transmitter, as in Fig. 10). Each of these

optical signals is then again split into eight by another level of optical power splitters. If

repeaters are not used, then each receiver receives only 1/64 of the optical power

transmitted by the optical transmitter at the antenna.

NASA/TM--2000-209776 8

This system is highly advantageous because the optical signal is distributed by an

all-optical network (except for repeaters, if needed) and the overall design of the system

is simple and easy to implement.

Vlf Antenna

(4 channels)

l-. 1i i i i ii i i ! i

G --1 E

[--:Si i i

Figure 9: Schematic diagram of all-optical solution to the problem of Fig. 6. Rp represents optionalrepeaters which may or may not be required depending on the signal strength at the final receivers.

r

Figure 10: Detailed schematic of a Repeater (Rp)

4. SYSTEMS WITH MULTIPLE TRANSMITTERS AND RECEIVERS

Finally, we describe the design methodology for an on-board system where

multiple nodes are transmitting, and each of the systems on board the aircraft must be

capable of receiving the transmission from any one of the transmitters.

Figure 11 shows a communications architecture with three antennas from where

optical signals are transmitted, and these signals should be transported to any of the on-

board systems (three shown in Fig. 1 I). As in the earlier sections, we can take either the

hybrid RF-optical approach, or the all-optical approach.

NASA/TM--2000-209776 9

VHF Antenna 1 VHF Antenna 2 VHF Antenna 3

100 150 100 150 100 I50

System 1 System 2 Syste 3

/111 II1[, /11 1111\ /qlll Iit[.100 150 100 150 100 150

Figure 11" A fiber-optic communication network architecture with multiple transmitters and receivers.

4.1 Hybrid RF-Optical Approach

In this approach, we use two fibers running in opposite directions throughout the

length of an aircraft. At the location of each (transmitting) antenna or (receiving) system,

the optical signal is first converted to RF, and then either a new RF channel is added in

case of a transmitting node, or the received signal is retransmitted in case of a receiving

node. Figure 12 shows the block diagram of such a multiple-transmitter multiple-receiver

system. The antenna nodes are transmitting (Tx) nodes, while the system nodes are

receiving (Rx) nodes. The details of each of the transmitting and receiving nodes are

shown in Figs. 13 and 14, respectively. At each of the transmitting and receiving nodes,

the optical signal is converted to RF, an RF channel is added or extracted, and then a new

optical signal is transmitted from the RF signal.

LLLTx Tx

N0C_I r,t_3 I

ANt1

---f-I

Fk

N0t_2

i

FW Tx

Ngde4 Nbde5

4_1_" V_F WI-- _ ] VH:ANt2 I 2

-*-T

L_

N_6

3

Figure 12: Hybrid RF-optical solution to multiple-source multiple-destination problem.

NASA/TM--2000-209776 10

I

I

Figure 13" Detailed schematic of a Transmitting (Tx) node in Fig. 12.

r

Fi_,ure 14: Detailed schematic of a receiving(Rx) node in Fig. 12.

This solution has the advantage that the optical signal is being amplified at each

of the nodes, so signal loss at connectors is not a problem. In addition, this system utilizes

only two counter-running fibers. However, this system has the disadvantage that many

fiber-optic transmitters and receivers are required. Also, a signal which was injected to

the fiber at the leftmost end reaches the rightmost end after a large number of optical-to-

RF and RF-to-optical conversions, which may cause the RF signal to degrade

considerably, and the RF signal may have an unacceptable signal-to-noise ratio.

4.2 All-Optical Approach

In this approach, we use dense wavelength division multiplexing (DWDM)

technology, where a number of wavelengths, which are separated by only a few

nanometers, are transmitted over the same fiber, Different transmitters transmit optical

signals at different wavelengths. Just like earlier solutions, we need two counter-running

fibers for carrying optical signals in two directions. From each antenna, two separate

transmitters are used to transmit the optical signals into the two fibers carrying signals

into two (opposite) directions. Each receiving system receives optical signals from an

antenna either from the upper fiber or the lower fiber, but not from both fibers from the

same antenna (whether the receiving system is located to the left or to the right of the

NASA/TM--2000-209776 11

antenna determines whether the signal is received via the upper fiber or the lower fiber).

Figure 15 shows the block diagram of an all-optical multiple-transmitter multiple-

receiver system.

Each of the transmitting nodes adds a new wavelength (W_, W2 etc.) to the set of

wavelengths being carried by the optical fiber with the help of an optical power

combiner. Each receiving node uses a optical splitter to split the incoming signal and take

out a fraction of the optical signal being transmitted through the optical fiber. Each of the

receiving systems receives more than one wavelengths. By using wavelength

demultiplexers, each of the wavelengths (WI, W2, W3 etc.) can be separated. From each

of the separated wavelengths, separate receivers can retrieve the separate RF signals

transmitted by different transmitting nodes (antennas). For clarity, the fiber-optic

transmitters, fiber-optic receivers and the wavelength demultiplexers are not shown in

Fig. 15.

This system has the advantage that the system uses only two fibers to interconnect

a large number of transmitting and receiving nodes. The solution is all-optical, and a

light-path is established between every optical transmitter and receiver. Since there are no

optical-to-RF and RF-to-optical conversion, the problem of signal-to-noise ratio

degradation is eliminated which is a substantial problem in the hybrid RF-optical solution

of Section 4.1. Also, by choosing proper power-splitting ratios at the power splitters, the

signal strength may be kept at a high level at each point despite the losses at the

connectors.

" '' ,J ,"1 Wl +W2+

p,'-, , w', --- _""_. _"ql +W2 ]W3+W4r ,_.____ _1+_ ___./] w3 [ ,_p.___ _w!+w2 Jb._I ,, ] w4[ ,, _ql+W2+ "1---<',,I w3,+.w4 ._"l ",,I+vl++v= I "1 ....W1 +W3

(From previous (To more

TWRX) "rX/RX)

Wl+W2+ ,dWl+W2 .,aWl+W2 .,d Wl

V_3+W4 • • • - "_n • _- "q •

[---_.. /_- ..... _ ,/_- ..... _ W2 /_ - -- evious

i,or,o, _____h.C_L_____j .... _____h ._____._ ..- L_h ._r-_---_TX/RX) VHFAntl IT System1 VHFAnt2 [ V System2 VHFAnt3 j • System3

Figure 15: All-optical solution using dense wavelength division multiplexing for implementation ofmultiple-source multiple-receiver network architecture.

5. CONCLUSION

In this paper, we investigate a number of different novel approaches for fiber-

optic transmission of on-board VHF and UHF RF avionics and radar signals using

commercial off-the-shelf (COTS) components. In almost all cases we can either take a

hybrid RF-optical approach or an all-optical approach.

The hybrid RF-optical approach has the advantage of low signal loss due to

repeated re-generation of the RF signal, and requires less number of fibers. However, the

use of too many fiber-optic transmitters and receivers increases the weight and cost of the

hybrid system,and-also increaSes E-ML :

The all-optical approach, on the other hand overcomes all these difficulties by

ensuring a continuous light-path from a fiber-optic transmitter to one or more fiber-optic

receivers while sustaining a strong optical signal. Also, an all-optical approach has the

NASA/TM--2000-209776 12

potential for replacingmultiple-fiber cablesby carrying a number of RF signals ondifferentwavelengthson a single fiber simultaneously,therebyreducingthe weight. Inaddition,all-opticalsolutionsusea numberof passivecomponentslike powercombiners,powersplittersandwavelengthdemultiplexers,all of which arepassivedevicesrequiringno power supply. Hence, an all-optical solution requires lesspower than hybrid RF-opticalsolutions.

REFERENCES

[1] C.A. Bedoya, "Fly-by-Light Advanced Systems Hardware (FLASH) program",

"Fly-by-Light: Technology Transfer," Proc. SPIE, vol. 2467, pp. 2-13, 1995.

[2] M.W. Beranek, E.Y. Chan, H.E. Hager, Q.N. Le, and J.S. Wilgus, "Emerging

opportunities for applying COTS optoelectronics in avionics fiber-optic networks,"

Microprocessors and Microsystems, vol. 22, no. 8, pp. 439-451, 1999.

[3] M.W. Beranek, E.Y. Chan, H.E. Hager, and Q.N. Le, "Status of optoelectronic

module packaging for avionics/aerospace applications," 1998 llth Annual Meeting,

IEEE Lasers and Electro-Optics Society, Orlando, FL, USA, pp. 329-330,

December 1-4, 1998.

[4] D. Horwitz, "COTS fiber optic interconnect solutions for mobile platforms," 1998

48th Electronic Components & Technology Conference, Seattle, WA, USA,

pp. 395-403, May 25-28, 1998.

[5] A.G. Lubowe, T.P. Million, E.G. Sayegh, and F. Baumann, "Multifiber optical

connectors for avionics," Proc. SPIE, vol. 2840, pp. 14-22, 1996.

[6] E.Y. Chan, M.W. Beranek, K.W. Davido, H.E. Hager, C.S. Hong, R L. St. Pierre,

"Challenges for developing low-cost avionics/aerospace-grade optoelectronic

modules," Proc. Electronic Components & Technology Conference, pp. 1122-1129,1996.

[7] J. Zhang, "High-speed avionic optical fiber CDMA networks," IEEE Aerospace &

Electronic Systems Mag., vol. 14, no. 6, pp. 15-21, 1999.

[8] J. Zhang, "Optical fiber data bus modulation techniques for military avionics,"

IEEEAerospace & Electronic Systems Mag., vol. 14, no. 4, pp. 31-37, 1999.

[9] G.L. Nelson, N. M. Rao, J.A. Krawczak, and R.C. Stevens, "Design process for a

photonic network for military platforms," Proc. SPIE, vol. 3541, pp. 179-190,1999.

[10] E.M. Drogin, and A.M. Leopardi, "High speed data link concepts for military

aircraft," National Aerospace Electronics Conference, Dayton, OH, USA,

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[11] D. Halski, "Fly-by-light flight control systems," Aerospace Engineering, vol. 16,

no. 9, pp. 11-18, 1996.

NASA/TM--2000-209776 13

REPORT DOCUMENTATION PAGE FormApprovedOMB No. 0704-0188

Public reporling burden for this collection of information is estimated to average 1 hour per response, including the time for revlewfng instructions, searching existing data sources,

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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

March 2000 Technical Memorandum

4. TITLE AND SUBTITLE

On-Board Fiber-Optic Network Architectures for Radar and AvionicsSignal Distribution

6. AUTHOR(S)

Mohammad F. Alam, Mohammed Atiquzzaman, Bradley B. Duncan,Hung Nguyen, and Richard Kunath

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Aeronautics and Space AdministrationJohn H. Glenn Research Center at Lewis Field

Cleveland, Ohio 44135-3191

I9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space AdministrationWashington, DC 20546-0001

5. FUNDING NUMBERS

WU-576--01-21-00

8. PERFORMING ORGANIZATIONREPORT NUMBER

E-12056

10. SPONSORING/MONITORINGAGENCY REPORT NUMBER

NASA TM--2000-209776

11. SUPPLEMENTARY NOTES

Prepared for the International Radar Conference sponsored by the Institute of Electrical and Electronics Engineers,Alexandria, Virginia, May 7-12, 2000. Mohammad F. Alam, Mohammed Atiquzzaman, and Bradley B. Duncan,University of Dayton, Department of Electrical and Computer Engineering, Dayton, Ohio 45469; Hung Nguyen andRichard Kunath, NASA Glenn Research Center. Responsible person, Hung Nguyen, organization code 5640,(216) 433-6590.

12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE

Unclassified -Unlimited

Subject Category: 32 Distribution: Nonstandard

This publication is available from the NASA Center for AeroSpace Information, (301) 621_3390.

13. ABSTRACT (Maximurn 2OOworda)

Continued progress in both civil and military avionics applications is overstressing the capabilities of existing radio-frequency (RF)

communication networks based on coaxial cables on board modem aircrafts. Future avionics systems will require high-bandwidth on-

board communication links that are lightweight, immune to electromagnetic interference, and highly reliable. Fiber optic communica-

tion technology can meet all these challenges in a cost-effective manner. Recently, digital fiber-optic communication systems, where a

fiber-optic network acts like a local area network (LAN) for digital data communications, have become a topic of extensive research

and development. Although a fiber-optic system can be designed to transport radio-frequency (RF) signals, the digital fiber-optic

systems under development today are not capable of transporting microwave and millimeter-wave RF signals used in radar and avionics

systems on board an aircraft. Recent advances in fiber optic technology, especially wavelength division multiplexing (WDM), has

opened a number of possibilities for designing on-board fiber optic networks, including all-optical networks for radar and avionics RF

signal distribution. In this paper, we investigate a number of different novel approaches for fiber-optic transmission of on-board VHF

and UHF RF signals using commercial off-the-shelf (COTS) components. The relative merits and demerits of each architecture are

discussed, and the suitability of each architecture for particular applications is pointed out. All-optical approaches show better perfor-

mance than other traditional approaches in terms of signal-to-noise ratio, power consumption, and weight requirements.

14. SUBJECT TERMS

Emerging technologies; Photonics; Optical signal

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Unclassified

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Unclassified

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Unclassified

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Standard Form 298 (Rev. 2-89)Prescribed by ANSI Std, Z39-18291]-102