1

MY FORTY-YEAR ADVENTURE

IN

THE WONDERFUL WORLD OF FIBER OPTICS! Presented at the 6th International Workshop on Fiber Optics in Access Networks (FOAN)

18 to 20 October 2016, Lisbon, Portugal

Henri Hodara

Symbioptix, Inc

Abstract—. A review of the major technology developments of

last century up to the present that brought about the

Communication and Information revolutions and their fusion

through the use of optical fibers. This is followed by the author’s

recollection of his work in fiber optics over a period of forty

years.

Keywords—Communication, Information, Fiber Optics

I. COMMUNICATION, AND INFORMATION: THE ROLE

OF FIBER OPTICS

My adventure in Fiber Optics can only be described in the context of the two major developments of the last century: The Communication and Information revolution, two major world shaking events that began in the twentieth century, following the Industrial revolution of the nineteenth century. So, I must first describe and review these two astonishing major events with the help of the tables below.

In Table 1, “The Communication and Information Revolution”, I attempt to list the major developments since the 1900s. Observe that technology breakthroughs do occur approximately every decade. It’s interesting to note that nearly at the same time in the 1960s both, Communication and Information took a major leap forward with the development of the laser and the Internet, respectively. By the late 1990s, with the advent of Smartphones, the fusion between communication and information had been accomplished, and would remain a single discipline from then on.

1948 is a key date in Table 1. It marks the birth of Digital Communications, which I refer to as the Third Industrial Revolution. It was brought about by Claude Shannon of MIT and Bell Telephone Laboratories (BTL), who laid out at the same time the principles of digital communications through Boolean Logic (in his MIT Master’s Thesis) and the foundations of Information theory in a seminal BTL paper in May of that year. Why didn’t he get a Nobel Prize is a mystery to me? Richard Feynman, Nobel Laureate stated that in the history of science, only two engineers made a significant contribution to Physics: Sadi Carnot with his second law of thermodynamics, and Claude Shannon with his theory of Information, both disciplines intimately related to the thermodynamics concept of Entropy.

I’d like to add one more remark to the above. To be exact, one could place the birth of the Communication revolution as early as in the eighteenth century, in 1839 when William Cooke and Charles Wheatstone of England inaugurated the first commercial telegraph service. It was followed a few years later by Samuel F. B. Morse in the USA who sent a telegraphic message from Washington DC to Baltimore, MD followed by a reply on 24 May 1844 consisting of the short Biblical quote “What hath God wrought?" Not a very high data rate to speak of, but a major breakthrough.

The ever increasing use of smartphones as shown at the bottom of Table I has engendered a new phenomenon: Social Networks. I have listed the four major social networks and lumped in one row the minor ones. Some have experienced a brief life:.YouTube and Instagram were quickly swallowed by the giants Google and Facebook.

There seems to be no end to the growth of this unique 21st

Century development! In Table II, “Fiberoptic Communications-Historical

Breakthroughs“ I summarize the major developments in Fiber Optics that occurred mostly in the second half of the twentieth century. I emphasize five key technologies that made it possible to wire or rather “fiber” the whole world with unimaginably high data rates: 1) Ultimate low loss single mode fibers, 2) room temperature and low threshold current semiconductor lasers, 3) Erbium doped fiber amplifiers (EDFA), 4) Array Waveguide Gratings (AWG) which in turn led to 5) the implementation of Wavelength Division Multiplexing (WDM). The latter includes Dense WDM (DWDM) with channel separation < 50GHz, which combined with coherent optical transmission and Quadrature Amplitude Modulation (QAM) provides data rates today of 400Gb/s, and climbing higher!

Finally, in Table III below, “Promising Fiberoptic Developments”, I add my own view of what I consider the key promising technologies being pursued at this time, specifically Non-Linear Optical phenomena in fibers (NLF), Integrated Photonic Circuits (IPC), Photonic Crystal Fibers (PCF), and Software Defined Networking (SDN).

I reserve some comments at the end of this paper as to why it seems that our current century has not yielded technological breakthroughs as significant as in the previous century.

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I would like to close this section by mentioning the contributions of two international conferences to the field of Fiber Optics: OFC (Optical Fiber Communications) conference and ECOC (European Conference on Optical Communications). The first OFC conference (known then as Optical Fiber Transmission, OFT) took place in 1975, in Williamsburg, VA with an attendance of 300 participants, We were represented by Dr. Willard Wells, Tetra Tech’s Chief Scientist.The last OFC conference took place in March 2016 in

Anaheim, CA and boasted an attendance exceeding 13,000 people. The field of Fiber Optics is indeed here to stay, and it continues its explosive growth.

A more recent international conference, FOAN specializes as its acronym indicates, in applications of Fiber Optics in Access Networks. We expect that this growing FOAN conference will provide an additional dimension and boost to the growing field of Fiber Optics in the future.

TABLE I THE COMMUNICATION AND INFORMATION REVOLUTION

DECADE

AROUND

BREAKTHROUGH INVENTORS ORGANIZATION OR

COUNTRY

Nobel

Prize

1900 RADIO Marconi/Popov/Tesla Italy/Russia/USA 1909

1910 TRIODE AMPLIFIER De Forest Radio Telephone Co

1920 TV ICONOSCOPE Zworkin RCA

1930 MICROWAVE GUIDES Chu

Barrow

MIT

BTL (Bell Telephone Lab)

1935 Kodachrome Process Godowsky/Mannes Eastman Kodak

1940 RADAR Watson-Watts

Wilkins UK

1944 Polaroid Film Land Polaroid Co.

1948 BIRTH OF INFORMATION THEORY AND DIGITAL

COMMUNICATIONS

Third Industrial Revolution: DIGITAL COMMUNICATIONS

Claude Shannon AT&T BTL/MIT

1950 TRANSISTOR Shockley/Bardeen/

Brattain BTL 1956

1950 MASER Townes

Basov/Prokhorov

Columbia U.

USSR 1964

1960 LASER

Townes/Schawlaw

Gould

Maiman

BTL

Coumbia U.

Hughes Aircraft

1960

INTERNET, TCP/IP

(TCP, Transmission Control Protocol

IP, Internet Protocol)

Kahn/Cerf DARPA

1966 LOW LOSS OPTICAL FIBERS

Feasibility Kao/Hockham ITT STL (UK)

2009

(Kao)

1970 17 dB/Km Optical Fibers

First Production “Low Loss” Fibers Keck/Maurer/Schultz Corning Labs, NY

1970 CW LASER DIODE

Room Temperature Operation

Alferoz

Kroemer

USSR

RCA 2000

1970 MICROPROCESSOR, INTEL 4004

Birth of Integrated Electronics Faggin/Hoff/Mazor INTEL

1980 PC (Personal Computer) LAPTOP Osborne, IBM

Compaq, NEC

1980 CELLULAR NETWORKS

PORTABLE CELL PHONES

AT&T

Motorola

1990 WORLD WIDE WEB

Connects http, Hyper Text Transfer Protocol to TCP/IP Tim Berners-Lee CERN

1990 PDAs (Portable Digital Assistants) PALM/IBM/APPLE

1995 -

Now SMARTPHONES

RMI, Blackberry, APPLE, iPhone

(Total Sales by 2015: $1.0B!)

2000 to

Now SOCIAL NETWORKS: URL and FEATURES CREATORS PEAK MEMBERSHIP

2003 to

now Linkedin.com Adds Business Connections to earlier networks ZUCKERBERG,.. 330 M

2004 to

now Facebook.com Multi-feattured and accepts 3

rd party Apps

HURLEY, CHEN,

KARIM 1.3 B

1006 to

now

Twitter.com Information more than Social Network

Links to pictures/Video -140 SMS Characters DORSEY, GLASS 200 M

2011 to

now Plus.google.com Links to all Google services BRIN, PAGE 540 M

Since 2000 Other players:Youtube (sold to Google), Instagram (sold to

Facebook)

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TABLE II FIBEROPTIC COMMUNICATIONS HISTORICAL BREAKTHROUGHS

~ YEAR BREAKTHROUGH APPLICATION PERFORMANCE INVENTORS ORGANIZATION

1953-1956 Glass Cladded Fibers Endoscopy 1000 dB/Km

Van Heel

O’Brien

Curtiss

U. Delft

American Optical

U. Michigan

1961 Realization

Single Mode (SM)

Fibers

Mostly Imaging!

Snitzer

American Optical

1965 Feasibility

SM Low Loss Fibers Communications 20 dB/Km Kao ITT STL

1970 First Low Loss Fiber Communications 17 dB/Km

Keck

Maurer

Schultz

Corning

1970 CW Laser Diode

Room Temperature Communications

30μm strip

1600 A/cm2

Alferoz

Kroemer

USSR

RCA

1972 Germanium doped

Low Loss SM Fibers Communications 4 dB/Km

Keck

Maurer

Schultz

Corning

1977 “Ultimate”

SM Low Loss Fibers Communications

0.2dB/Km

Theoretical Limit:

Scattering

loss=0.18dB/Km!

NTT (Japan)

1977 SM WDM Communications

C-Band WDM 1530-

1565nm

Today:

20-CWDM Channels-

100GHz

160 DWDM Channels-

12.5GHz

Tomlinson BTL

1987 Ultra Low Threshold

CW DFB Laser Diode

Room Temperature

Communications

100 A/cm2

Electricity-to-Light

η=75%

Yariv et al.

Caltech

1987

Erbium Doped

Optical Amplifier

(EDFA)

at 1550μm

Communications

Gain=20dB

Bandwidth 80nm

Gain Flatness<1.0nm?

Noise Figure<4.5dB

Payne et al.

Desurvire

U. Southampton

AT&T BTL

1991 AWG

Array Waveguide

Grating

WDM

Communications

NxN MUX/DEMUX

Typical today: 80x80 Dragone AT&T BTL

1996 1

st WDM Land

Deployment Communications 8 Wavelengths@2.5Gb/s MCI

~2010 DWDM COHERENT

TRANSMISSION Communications

100Gb/s, 200Gb/s,

400Gb/s All Telecoms

Ultra Low Loss Fiber Communications

<0.18 dB/Km/Disp.<0.18

ps/(nm-Km).

(DFB laser Δν~100KHz)

Brand Name

SMF 28

Corning

NOTE: LONG HAUL COMMUNICATIONS ENABLING TECHNOLOGIES HIGHLIT IN YELLOW

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TABLE III PROMISING FIBEROPTIC DEVELOPMENTS

~YEAR DISCIPLINE BREAKTHROUGH APPLICATIONS INVENTORS ORGANIZATION

1961

NON-LINEAR

FIBER OPTICS

Third Harmonic

Generation in Optical

Fibers

Parametric amplification via

Four-Wave mixing

Raman amplification

Single Photon Very Low

Noise Amplifier

High Speed Data Processing

Peter Franken

U. of Michigan

1962 Complete Theory of Light

Interaction in Dielectrics Nicholas Bloombergen

Harvard U.

(Nobel Prize, 1981)

1969

INTEGRATED

PHOTONIC

CIRCUITS,

IPC

Seminal Publication

proposing integration

with Thin Films

Waveguide

Heterogeneous Materials,

Si, SiO2. InP. GaAs

Integrated in one chip to

provide functions of

Waveguiding, Mux/Demux,

Laser and Detector

Stewart Miller

AT&T BTL

2014

Successful Deposition

of InAs on Si wafers

to create Laser Action

John Bowers

UCSB

1996

PHOTONIC

CRYSTAL

FIBERS

PCF

(Periodic

Structure uses

Silica for

core and

cladding)

BEST PERFORMANCE

TODAY

Index Guiding (solid

core): 0.53dB/Km

ncore>nclad

Photonic Bandgap

(HollowCore):1.2dB/Km

Large Core

Diameter~30μm

ncore<nclad

SHORTCOMINGS

Difficult to draw lengths>

a few Kms

Price/m is ~500xSMF28

DATA CENTERS

Latest Photonic Bandgap

Fiber at 1.55μm:

L=11Km, 5.2dB/Km,

20Gb/s, Latency~1.54μs

NON-LINEAR

INTERACTION

LIGHT/GASES

Interaction length

significantly reduced

100x Reduced Stimulated

Raman Threshold

in Hydrogen filled hollow

cores

Applies to Spectroscopy

Philip RusselL

U. of Southampton

2013

Software

Defined

Networking,

SDN

FIRST PRESENTED at

OPTICAL FIBER

COMMUNICATIONS,

OFC CONFERENCE

2013

SIMPLIFIES NETWORK

OPERATION

BY TRANSEFERING

CONTROL FUNCTION

IN ROUTERS AND

SWITCHES

TO ONE CENTRALIZED

SERVER (CONTROLLER)

Open

Network

Foundation,

ONF

2016

SDN

“WHITE BOX”

PRESENTED At

OFC CONFERENCE

2016

TRANSFERS ROUTING

FUNCTION AS WELL

TO CENTRALIZED

SERVER, THUS

ALLOWING ROUTER TO

BECOME

A SIMPLE NON-

PROPRIETARY SWITCH

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II. MY PERSONAL ADVENTURE IN FIBER OPTICS

My first introduction to Fiber Optics was rather unorthodox, and a presage of what my future involvement and interest in this field would turn out to be in the future.

It was around 1960. I was then living in the suburbs of Chicago, IL, working full time in a communication laboratory as Associate Director of Research for the Hallicrafters Co. I was also working full time on my PhD, after having been prodded by my wife a couple of years earlier to undertake this lofty pursuit of the “sheepskin”. My daytime work dealt with re-entry plasmas, an exciting field in the 60s, at the forefront of space research. I was fortunate (and maybe astute enough) to have chosen a doctoral dissertation in the same field as my daytime work, specifically how to eliminate re-entry blackout, a task at which I eventually succeeded. But it was a backbreaking schedule! An associate of mine who worked on campus at the Illinois Institute of Technology suggested that since I was getting a degree from that school, I should try to get a job at their research center, thus avoiding the commute between job and classes. So, I did go there for an interview and had my first encounter with Fiber Optics.

I met one of the pioneers of Fiber Optics: Narinder Singh Kapany. He was a charming and imposing man, a tall Sikh from Punjab, India who had worked in England with the famous physicist, Harold Hopkins, and together had developed the first fiberscope, a flexible medical endoscope. By the time I met Dr. Kapany in Chicago, he was fully involved in developing fiber optics endoscope for the medical profession using cladded optical fibers with losses on the order of 500dB/Km to 1000dB/km! Although I was impressed by the man and his knowledge, I didn’t relish the idea of spending a career developing devices that would be used to penetrate the various orifices of a human being. Re-entry plasmas was a more exciting field. It gave me the opportunity to interact with renowned physicists in many disciplines, while making my own contributions to this field, based on the fruit of my research in Electromagnetic theory. So, I declined the job offer.

After I received my diploma, I remained in Chicago for a couple of years before I was able to fulfill my dream of eventually settling in California. During this time the laser had appeared on the horizon, and Javan at AT&T BTL had developed the HeNe gas laser that simplified optics forever. It was an exciting development. All the optic experiments of high school and college could now be carried out with coherent light and one could set up in a few minutes a diffraction experiment with coherent light, and marvel at the results without squinting one’s eyes. I quickly forgot about re-entry plasmas, after having made some marks in this field, and instead took a dive in the field of laser and coherent optics.

I finally realized my dream and moved with my family to California. Within two years, in 1966, I co-founded with three other associates a company in Pasadena, Tetra Tech. At that time, the Aerospace business was experiencing a slump, so we concentrated instead on problems of the oceans, solving technical problems for the US Navy. One area of interest I pursued was the use of lasers in Ocean Optics. Javan HeNe red

laser was inexpensive and handy for demonstration purposes, though of the wrong color. (Argon-ion green lasers, with wavelengths around 480nm that match deep sea water minimum transmission loss window were not yet commercially available, at a reasonable price). We showed and demonstrated with the HeNe laser how to eliminate the ambiguity inherent in ill-defined concepts such as underwater imaging contrast. We applied instead concepts of communication theory and coherent optics and specified image quality in terms of signal-to-noise ratio [1]. Another area of interest was laser noise because gas lasers in those days tended to have many unlocked modes beating with each other. I predicted the additional noise that resulted from the beating, which led to the publication of a couple of papers [2], [3]. In addition, Optical communications with increased signal-to-noise ratios through optical heterodyne led me to a patent used later on by NASA, [4].

By 1970, the fiber optic revolution had begun and was spreading! “Low Loss” fibers, 20dB/Km were now available, and could be used for short distance communications. We were thrilled with such fibers though they were extremely brittle. The joke around the lab was that if you stared at them too long, they would shatter! In spite of such drawbacks some branches of the US Government believed that since the light transmitting signals were confined to the fiber core, they were “untappable”. Thus, optical fibers would allow a user to dispense with encryption! I was fortunate to win a contract to look at this possibility, and it became evident that it was very easy to remove some of the light carrying signal transmitted through the fiber and recover the information if it weren’t encrypted. The fibers in those days were so brittle that you could not bend them to induce light leakage without breaking them, so we resorted to heating them with a small torch and inducing multitude of small cracks that let some of the light out of the fiber.

A. INTRUSION DETECTION

Following the failure to prove that optical fibers were secure enough to avoid encryption but not being devoid of imagination, we proposed to develop for the Government “Intrusion Detection” techniques that would reveal any rogue’s attempt to access the information carried by the light signal. There were at the time three other companies developing such intrusion detecting “countermeasures”. As with any countermeasures, this is an endless game. Counter-counter measures can be developed and so on. None of the techniques developed were foolproof. Remember that in those days, the fibers were multimode, had significant absorption and scattering losses (we did not have available commercial single mode fibers that had reached the 0.2 dB/Km attenuation limit shown in Table I), all these factors contributing to limit severely data rates. We did win a major contract to develop and deliver an Intrusion Detection system for the US Army Fort Belvoir Center, but the intrusion detecting sensors were conventional devices, and the role of the optical fiber was relegated to telemetering the information between sensor nodes. A photograph of this early system built at Tetra Tech by Charlie Slemon and his staff in a record time is shown below in Fig. 1.

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Fig. 1. US ARMY FORT BELVOIR INTRUSION DETECTION SYSTEM

With passing years, we became convinced, among many others, that fiberoptic intrusion detection systems were not invulnerable and that the best countermeasure was encryption, and more specifically optical encryption. Optical schemes, as opposed to “algorithmic encryption electronic chips” are agnostic to data rates, only limited by the speed of the photodetectors. Several schemes were invented over the years but their complexity and cost rendered them impractical and they did not lend themselves to commercialization. An added shortcoming of optical schemes is that anytime the security needs to be reinforced, unlike algorithmic chips that often only require a software change, it demands a hardware change. A summary of some of these schemes and their comparison with ongoing developments in Quantum Cryptography through optical fibers is given in Ref. [5] and [8]..

In 1975, a crucial period, single mode optical fibers became commercially available with losses < 4dB/Km. Before the end of this decade, they would reach a loss of around 0.2dB/Km, nearly the theoretical limit of scattering losses! Our company, Tetra Tech was small compared to the Telecommunication giants, and we couldn’t possibly compete with them. So we turned to “niche” markets, which I’ll describe further on.

That meant no more doing research and publishing papers, instead developing and building applications that were unique; and protecting our intellectual property with a series of patents in fiber optics [11].

B. THE NEW TECHNOLOGY APPLICATION PARADIGM:

NO SUBSTITUTIONS!

How we captured these niche markets was a combination of identifying opportunities and timing. It began with a study I was asked to do by Dr. Howard Blood, then Director of the Navy Laboratory (Naval Ocean Systems Center, NOSC) in San Diego. The laboratory staff was engaged actively in developing fiberoptic applications for Undersea Surveillance, and the research engineers being enamored with the new technology were going gung-ho about using optical fibers, often without rhyme or reason. It was such an exciting technology to work with that it was hard to resist the rationale for not taking an existing wire system and converting it to its fiberoptic equivalent. After much thinking we established a criterion as to when optical fibers warranted their use in Naval Undersea systems, and more generally in any system. The answer was simple: “NO SUBSTITUTIONS”. It meant that, fiberoptic

7

technology should not be introduced in a system or mission unless it could solve a problem that current technology was incapable of solving. If optical fibers only brought about an incremental improvement in an existing system or component, conventional technology would always prevail because it was more reliable, easier to install and overall more cost effective.

One of the first systems to be built, based on this criterion was a fiberoptic “distributed acoustic array” that could be laid down covertly on the ocean floor because of its small size. At that time, arrays had to be deployed using telephone coaxial cable laying ships, and the whole world knew where the cables were, so an unfriendly country could destroy them. It took five years and a competitive procurement to have such a system accepted. Tetra Tech was one of the two winning contractors.

The system was “christened” ARIADNE by the government, in reference to Greek mythology’s king Minos of

Crete whose daughter of that name provided Theseus with a fine yarn that he deployed as he walked through the Labyrinth, so that he could find his way back after slaying the Minotaur monster who lived in that labyrinth. The system is described further on. But first, I would like to discuss a terrestrial system based on the same concept where the same criterion was applied: an oil exploration seismic systems.

C. FIBERSEIS: Optical Distributed Network for Seismic

Explorations

Oil exploration seismic systems consist of group of accelerometer (called geophones) sensors that record the sound from explosions into the ground. The sound is picked up by localized groups of sensors and sent to a recording truck for signal processing as shown in Fig.2.

Fig. 2. SEISMIC EXPLORATION PUTS SOUND ENERGY IN THE GROUND AND COLLECTS ECHOS AT GEOPHONES THAT MAP

UNDERGROUND FEATURES.

Before the introduction of optical fiber, it was necessary for the recording truck to receive analog signals from each group of sensors on separate twisted pairs because of their limited bandwidth. As a result, only 64 twisted pairs collecting the data from 64 nodes could be implemented After the introduction of optical fibers, the signals from all the geophones could be combined and transmitted digitally through a multimode fiber. Each group of geophone is a node in a distributed fiberoptic

telemetry system. The collected signal from the first node is sent through the fiber to a second node where both signals are then electronically multiplexed and sent to the next node and so on. The result was the possibility of getting 1024 and eventually 2048 channels instead of 64. The same approach for a distributed system had been used earlier with an electrical coaxial system; but the coaxial cables were very heavy and the system was severely limited in data rate. In our system, a

8

second fiber was used to transmit control signals in the opposite direction. Since cables are always being connected and disconnected in field operation, we patented a module that included the light source and the photodetectors at the ends of

the cables, so that the connections to the nodes were electrical and dirt proof. The system was named FIBERSEIS, and a photograph is shown in Fig. 3.

Fig. 3. OILl EXPLORATION SEISMIC SYSTEM, FIBERSEIS

The development, construction and delivery of the FIBERSEIS system provided Tetra Tech with a learning curve until the US Navy system, ARIADNE was eventually awarded. Steve Braun of Tetra Tech pioneered the development, construction and deliveries of both, FIBERSEIS and ARIADNE. The former transported information at data rates on the order of 10Mb/s while the latter exceeded 50Mb/s, quite an achievement for fiberoptic technology in the early 1980s!

D. UNDERSEA OPTICAL ACOUSTIC DETECTION

SYSTEM

ARIADNE is a much more complex system, but still falls in the category of distributed acoustic array, except that the

telemetry fiber is single mode and the date rates are in tens of Mb/s. The acoustic sensors are conventional hydrophones, highly sensitive, stable, extremely reliable and relatively inexpensive compared to the cost one would have to pay for a fiberoptic acoustic sensor. The nodes are made of heavy titanium capable of withstanding the water pressure encountered at the bottom of the ocean. A sketch of one system node is shown in Fig. 4, and a photograph of the actual hardware that was delivered is shown in Fig. 5. Bear in mind that this system was delivered in the early 1980s before the days of WDM, Low threshold Laser Diodes and EDFAs. (Recall highlit technologies of Table II above).

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Fig. 4. ARIADNE NODE

10

Fig. 5. TETRA TECH UNDERWATER SURVEILLANCE FIBEROPTIC ACOUSTIC ARRAY

Note that none of the distributed systems discussed above

use fiberoptic sensors: Conventional geophones and hydrophones are orders of magnitude less costly than delicate interferometric fiberoptic sensors (intensity fiberoptic systems lack sensitivity), in spite of the fact that optical fibers are ideal for implementing “continuous”, distributed sensors. Distributed fiberoptic sensors have now been demonstrated very successfully in Naval “Towed Arrays”, but few of them are operational at this time, for the reasons given earlier based on the criterion that the best applications of fiber optics are in providing solutions that cannot be solved by conventional technology. To provide an incremental improvement, even reasonable large may not always be sufficient unless the additional cost is justified by a significan performance improvement.

E. FIBEROPTIC INTERFEROMETRIC ACOUSTIC

SENSOR

We built a fiberoptic interferometric sensor in the 80s. A Norwegian oil and gas exploration company that was attending the OFC conference in the early 80s wanted a fireproof underwater sensor (for reasons not worth explaining here) to

detect gas leaks in undersea pipelines. Some of us at Tetra Tech got together and we came to the conclusion that since a leak produces air bubbles, and bubbles rising to the surface make a noise, we should build an acoustic fiberoptic sensor. Ed Miles, of Tetra Tech came up with the idea of using a Polarization maintaining optical fiber that would be deployed from the shore to some point on the gas pipe, would be wound in that area around a resonating mandrel and would return to the shore, where the light signal would interfere coherently with a reference light signal. In the absence of sound, light polarization was maintained through the fiber round trip. The system was balanced so that the “spatial beat” between returned signal and reference signal resulted in a null signal at the photodetector output. If it detected sound, the sound would distort the fiber and change its polarization. The returned signal, with altered polarization, when “beating” against the reference would give a signal whose amplitude was proportional to the sound intensity. We built the system in 3 months and deployed it off shore in Norway, in the middle of the winter, with outstanding results. A photograph with the data sheet is shown in Fig. 6.

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Fig. 6. FIBER GAS LEAK DETECCTION SYSTEM

12

The next step was to build a distributed discrete sensor system but, a year later, the oil glut had set in and oil exploration was greatly curtailed. Whatever little exploration was done, operators reverted to using the old seismic systems in their inventories. In short we had violated the criterion we insisted in applying to justify Fiberoptic applications, “NO SUBSTITUTIONS”. When the Oil industry economics could no longer afford it, the industry reverted to systems available in their inventories that used conventional technologies, which though not as effective and elegant, could still solve the problem, as they did not require new capital investment. If the sensor had been applied to a situation where it was the only available solution, it could have survived!

F. OPTICAL ENCRYPTION

This is not the end of the story. I had begun my adventure in the 70s with the development of Intrusion Detection Systems. Recall that in the mid-70s the best glass fibers one could purchase had losses of 20 dB/Km, and we all thought that was a significant breakthrough! These fibers were very fragile, in fact too fragile to be bent to let the light leak out, so intruders resorted instead to heat the fibers in order to induce micro-cracks that would let the light out readily. Within a few years, single mode fibers with their much longer range and greater bandwidths, and their resistance to bending displaced multimode fibers application thus making Intrusion Detection Systems woefully inadequate. By the 90s, we had abandoned as many others the idea of detecting fiber intrusion, and instead turned to the problem of denying the information to an intruder by encrypting the signal optically. Optical encryption as opposed to the conventional electronic approach known as algorithmic encryption has the advantage that the almost unlimited bandwidth of fibers allows an encryption scheme that is not limited by the signal data rate, for all practical purposes. Additional features of optical encryption were its ability to achieve greater security in key distribution. During the 90s and the first decade of this century, there was great activity in this field. Many papers were published and several patents awarded (References [5] to [10] below}. But optical encryption turned out to be commercially not cost effective, though a limited number of systems were sold to the US government. On the other hand, a single high speed electronic chip with algorithmic encryption is much cheaper to manufacture and takes minimal space compared to the optical schemes that depend on fragile and environmentally unstable interferometers. Finally, it is more difficult to quantify the vulnerability and the reliability of an optical encryption scheme because it depends on hardware. On the other hand, an algorithmic encryption chip is nothing more than millions of identical gates on a silicon substrate for which it is easy to calculate the probability of failure of the whole chip from the failure probability of a single gate. Here again, the NO SUBSTITUTIONS RULE prevails!

Currently, there is significant activity in developing optical encryption schemes using Orthogonal Code Division Multiplexing (OCDM), which combines the wavelength division capability of optical communications with coding algorithms by assigning portions of the message to different wavelengths. Unfortunately, the technique does not solve the problem of secure key distribution

There is light though at the end of the tunnel. Active developments are taking place in Quantum Optical Cryptography that can yield an undecipherable signal by generating an unbreakable key to be distributed to network users. The secure key can then in turn be used to program an electronic algorithmic chip. STAY TUNED!

G. CLOSING REMARKS

A look at Tables I, II and III gives us an uneasy feeling that no significant breakthroughs have occurred in this fledging century. Why? It seems to me that the reason is that long-term research has been abandoned. There is no more a Bell Telephone Laboratory, whose monopoly enabled it to capture the telecommunication business and afford to spend many years in pursuing several avenues of research in the hope that one would pay off. There’s no more a DuPont company that could invest money in long term research and after many years discover Nylon in 1931; neither is there a Kodak company that would allow freedom of research to two professional musicians and amateur chemists, who came up with the Kodachrome process for color photography.

There seems to be an underlying malaise that people cannot wait long enough to achieve significant results. Today everyone expects instant gratification. CEO in large companies are only given two years at the most to make their marks, otherwise they’re out. Same in the government where, with a few exceptions (see next paragraph), civil servants and militaries only stay a couple of years in their posts and are expected to show results before moving to the next position. The only ones that seem to have succeeded in staying long enough in their assignment are our Congressmen and Senators, but look at the results, A DISASTER!

We do need, it seems to me a happy medium between these two extremes: Some short term research (two years) to support ongoing businesses or missions, and an investment in long term research (five years) in the hope that the latter will bring a significant breakthrough, much like what DARPA does. DARPA, the best Government research in the United States, has coined this approach: “High Risk, High Payoff”.

As a closing note, if someone asks me what Fiber Optics breakthroughs we expect in the future, my answer is: No one can predict the future! No one predicted Relativity with Einstein, Quantum Mechanics with Bohr, or Cubism painting with Picasso.

THE FUTURE BELONGS TO THE INVENTORS WHO CREATE IT!

13

REFERENCES

[1] Hodara, H., and Marquedant, R. J., The Signal to Noise Ratio Concept in Underwater Optics. Applied Optics, Vol. 7, No. 3, March 1968.

[2] Hodara, H., Statistics of Thermal and Laser Radiation. Proceedings of

the IEEE, Vol.53, No. 7, July 1965.

[3] Hodara, H. and George, N., Excess photon Noise in Multimode Lasers. IEEE Journal of Quantum Electronics. Vol. QE-2, No. 9, September

1966.

[4] Hodara, H., “Laser Beam Tracking Apparatus”, US Patent #3,489,904 issued 13 January 1970

[5] W. Wells, et al., “Secure communications by optical homodyne,” IEEE J. Sel. Areas Commun. 11, 770–777 (1993)

[6] Eric Udd, "Secure fiber optic communication system based on the Sagnac interferometer", Proc. SPIE 2837, Fiber Optic Gyros: 20th

Anniversary Conference, 172 (November 12, 1996);

[7] J. Menders, et al., “Interferometric generation of random binary keys for secure optical communication”, Proc. SPIE 4471, Algorithms and

Systems for Optical Information Processing V, (13 November 2001)

[8] Wells, W. H., Menders, J., Miles, Ed., Loginov, B., and Hodara, H., Another Alternative to Quantum Cryptography. Inaugural Issue of

Quantum Information Processing, Vol. 1, NO. 1/2, April 2002

[9] H. Hodara, et al., “Secure fiberoptic communications,” Fiber and Integrated Optics 22, 47–61 (2003).

[10] K. Kravtsov et al.,“Physical layer secret key generation for fiber-optical

networks”. OPTICS EXPRESS |Vol. 21, No. 20, October 2013

PATENTS PORTFOLIO IN FIBER OPTICS

PATENT # ISSUED DATE TITLE GRANTED TO

3,489,904 13 January 1970 Laser Beam Tracking Apparatus Hodara

4,367,460 4 January 1983 Intrusion Sensor using Fiber Optics Hodara

4,577,184 18 March 1986 Security System with Randomly Modulated Probe Signal

Hodara/Wells

4,595,839 17January 1986 Bidirectional Optical Electronic Converting Connector with Integral

Preamplification

Braun/Hodara et al.

4,932,004 5 June 1990 Fiber Optic Seismic System Braun/Hodara

5,901,260 4 May 1999 Optical Interface Device Braun/Hodara et al.

5,898,801 27 August 1999 Optical Transport System Braun/Hodara et al.

RE 41247 E 20 April 2010 Re-issued Optical Transport System Braun/Hodara et al.