United States Patent (19)
`Braun et al.
`
`54) OPTICAL TRANSPORT SYSTEM
`75 Inventors: Steve W. Braun, Leucadia; Henri
`Hodara, Dana Point, both of Calif.;
`John J. Soderberg, Acworth; G. Allan
`Whittaker, Alpharetta, both of Ga.
`73 Assignee: Lockheed Martin Corporation,
`Bethesda, Md.
`
`21 Appl. No.: 09/014,079
`22 Filed:
`Jan. 29, 1998
`51
`Int. Cl. .............................. G02B 6/28; H04B 10/20
`52 U.S. Cl. ............................ 385724; 359/119; 359/127;
`359/134
`58 Field of Search .................................. 385/24, 27, 31,
`385/45, 47, 37, 17; 372/6; 359/115, 119,
`127, 134, 143,125, 137
`
`56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`... 385/24
`5,572,612 11/1996 Delavaux et al. .......
`... 385/24
`5,712.932
`1/1998 Alexander et al. ..
`... 385/24
`5,764,821
`6/1998 Glance .................
`5,796,890 8/1998 Tsuji et al. ................................ 385/24
`
`Primary Examiner Hemang Sanghavi
`Attorney, Agent, or Firm-Eric R. Katz
`
`
`
`USOO58988O1A
`Patent Number:
`11
`(45) Date of Patent:
`
`5,898,801
`Apr. 27, 1999
`
`ABSTRACT
`57
`A bi-directional, redundant, optical transport System is con
`figured to provide a non-blocking, bi-directional, multi
`channel, protocol independent optical transport System for
`the Simultaneous transfer of digital, analog, and discrete data
`between a plurality data terminal equipment. The optical
`transport System includes a light transmission line for trans
`mitting light bi-directionally and a plurality of nodes, con
`nected in Series by the light transmission line for receiving,
`extracting and passing Signal light. Each node comprises:
`data terminal equipment for issuing and receiving electrical
`Signals, an electro-optical interface device, associated the
`data terminal equipment, for converting electrical signals
`issued by the associated data terminal to Signal light for
`insertion onto the light transmission light and for converting
`Signal light, extracted from the light transmission line into
`electrical Signals to be received by the associated data
`terminal; a translation logic device connected between the
`optical interface device and the data terminal equipment, for
`performing required protocol translation for the data termi
`nal equipment and an optical interface device, connected to
`the electro-optical interface device and the light transmis
`Sion line, for extracting Signal light from the light transmis
`Sion line to be converted into electrical Signals by the
`electro-optical interface device for receipt by the data ter
`minal equipment, for inserting, onto the light transmission
`line, Signal light received from the electro-optical interface
`device and for passing Signal light bi-directionally on the
`light transmission line.
`18 Claims, 16 Drawing Sheets
`
`Ex.1029
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`U.S. Patent
`
`Apr. 27, 1999
`
`Sheet 1 of 16
`
`5,898,801
`
`
`
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`CISCO SYSTEMS, INC. / Page 2 of 25
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`

`U.S. Patent
`
`5,898,801
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`Ex.1029
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`U.S. Patent
`
`Apr. 27, 1999
`
`Sheet 3 of 16
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`5,898,801
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`Ex.1029
`CISCO SYSTEMS, INC. / Page 4 of 25
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`U.S. Patent
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`Apr. 27, 1999
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`Sheet 4 of 16
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`Apr. 27, 1999
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`Ex.1029
`CISCO SYSTEMS, INC. / Page 6 of 25
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`Apr. 27, 1999
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`CISCO SYSTEMS, INC. / Page 7 of 25
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`Apr. 27, 1999
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`Ex.1029
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`U.S. Patent
`
`Apr. 27, 1999
`
`Sheet 8 of 16
`
`5,898,801
`
`ARINC AVIONICSELEMENT
`
`
`
`TRANSMITTER
`SECTION
`
`1450
`
`CLEAR TO SEND (CTS)--TWP
`
`SENSORS 147a
`
`149
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`SECTION
`
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`U.S. Patent
`
`Apr. 27, 1999
`
`Sheet 9 of 16
`
`5,898,801
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`ARINC AVIONICSELEMENT
`
`TRANSMITTER
`SECTION
`
`
`
`
`
`
`
`CLEAR TO SEND (CTS) -- X=635mm
`AVIONICS
`ELEMENTS
`
`RECEIVER
`SECTION
`
`FIG. 4E
`
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`U.S. Patent
`
`Apr. 27, 1999
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`Sheet 10 of 16
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`5,898,801
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`U.S. Patent
`
`Apr. 27, 1999
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`Sheet 11 of 16
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`5,898,801
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`U.S. Patent
`
`Apr. 27, 1999
`
`Sheet 12 of 16
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`5,898,801
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`U.S. Patent
`
`Apr. 27, 1999
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`Sheet 13 of 16
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`5,898,801
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`U.S. Patent
`
`Apr. 27, 1999
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`Sheet 14 of 16
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`5,898,801
`
`1.00
`0.90
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`0.70
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`
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`
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`U.S. Patent
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`Apr. 27, 1999
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`Sheet 15 of 16
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`5,898,801
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`U.S. Patent
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`Apr. 27, 1999
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`Sheet 16 of 16
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`5,898,801
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`LASER DRIVER &
`TEMP CONTROL
`
`FIG. 8A
`
`
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`
`FIG. 8B
`
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`

`

`1
`OPTICAL TRANSPORT SYSTEM
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`The present invention generally relates to an optical
`transport System for transmitting, extracting, and inserting
`light bi-directionally on a light transmission line, and more
`particularly to a redundant, non-blocking, bidirectional,
`multi-channel, protocol independent optical transport Sys
`tem for the Simultaneous transfer of multiple, optically
`encoded signals.
`2. Background Discussion
`A variety of different topologies are employed to manage
`the transmission of data on an electrical data bus. Known
`network topologies include: 1) broadcast, Such as utilized on
`a data bus; 2) point-to-point electrical and optical repeater
`links, such as seen with the ring configuration; 3) and logical
`Star, where all data is transmitted to and from a central
`location for retransmission to an intended recipient.
`One particular problem with these known network topolo
`gies is that they cannot be easily integrated with one another.
`In essence, once a particular topology and protocol are
`chosen for managing the transmission and receipt of data on
`a given network, that topology and protocol must always be
`used by the network. This lack of adaptability is a particular
`detrimental problem when new or more useful topologies
`are developed but cannot be applied to existing data trans
`mission networks which are locked into archaic, less effi
`cient topologies.
`Recent advances in data transmission technology have
`been directed to increasing the bandwidth or data capacity of
`the network, i.e., increasing the amount of data that can be
`transmitted by the network.
`Physics imposes data rates limits on Standard optical
`networks which encode data in pulses of laser light and
`dispatch them through wires made of glass. Very fast data
`rates require very short pulses, which tend to Smear into one
`another as they travel through kilometers of fiber. Electronic
`devices Staggered along the path can clean up the Signal, but
`they are expensive and can work on at most 50 billion bits
`per Second using current technology.
`To increase the data capacity, researchers have transmitted
`many signals simultaneously over a single fiber by encoding
`them in different wavelengths or channels. Transmission
`networks that use this technique, known as wavelength
`division multiplexing (WDM), have boosted the capacity of
`existing fiber twenty fold or more.
`
`SUMMARY OF THE INVENTION
`Accordingly, it is an object of the present invention to
`provide an optical transport System which overcomes the
`disadvantages of the prior art and takes advantage of the
`recent advances in wavelength division multiplexing.
`Accordingly, it is another object of the present invention
`to provide a novel, bi-directional, redundant optical trans
`port System configured to provide a non-blocking,
`bidirectional, multi-channel, protocol independent optical
`transport System for the Simultaneous transmission of mul
`tiple optical Signals.
`It is a further object of the present invention to provide an
`optical transport System using an unique optical amplifica
`tion arrangement whereby through-fiber between nodes of
`the System are doped with a rare earth, Such as, for example,
`erbium to provide Sufficient amplification to compensate for
`coupler splitting losses, Splice and connector losses.
`One particularly advantageous feature of the present
`invention is that it provides an advanced bus Structure which
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`readily Supports the bandwidth and channel capacity
`requirements of present and future avionics data buses while
`providing physical redundancy to enhance network Surviv
`ability.
`Another particular advantageous feature of the present
`invention is that it provides the ability to Simultaneously
`transmit a plurality of information as analog, digital and
`discrete signals over a single wavelength using a single fiber.
`In this regard, the invention is capable of the Simultaneous,
`non-interfering transmission over multiple topologies of
`multiple co-existing protocols each running at independent
`data rates. Additionally, it features the Simultaneous, non
`interfering transmission over multiple co-existing topologies
`of analog, digital and discrete Signals.
`The present invention relates to an optical transport
`System that permits one, two or a plurality of different
`network topologies to be respectively connected by one, two
`or a plurality of fiber optic transmission lines that each
`transmit light bi-directionally over each of the one, two or
`plurality of fiber optic lines. Each fiber optic transmission
`line is capable of carrying one, two or a plurality of
`wavelengths and each wavelength can contain one, two or a
`plurality of analog, digital and discrete Signals that are
`encoded using one, two or a plurality of encoding tech
`niques.
`The heart of the present invention is an ingenuous
`arrangement of passive fiber optic couplers, which when
`combined with wavelength division multiplexing (WDM)
`Selectively route optical Signals in and out of the System at
`each node thereof as discloses by Applicants co-pending
`U.S. patent application entitled An Optical Interface Device,
`Ser. No. 08/831,375, filed Apr. 1, 1997, (the entire disclosure
`of which is herein incorporated by reference for all
`purposes). This optical interface device, also Sometime
`referred to as an optical bus interface module (OBIM), is
`capable of inserting, extracting and transmitting light
`bi-directionally over one, two or a plurality of fiber optic
`transmission lines carrying one, two or a plurality of wave
`lengths over each fiber optic transmission line and each
`wavelength contains one, two or a plurality of analog, digital
`or discrete Signals that are encoded using one, two or a
`plurality of encoding techniques.
`These and other objects, advantages and features of the
`present invention are achieved, according to one embodi
`ment of the present invention by a redundant, optical trans
`port System which is configured to provide a non-blocking,
`bi-directional, multi-channel, protocol independent optical
`transport System for the Simultaneous transfer of multiple
`optical Signals between a plurality data terminal equipment.
`The optical transport System includes a light transmission
`line for transmitting light bi-directionally and a plurality of
`nodes, connected linearly by the light transmission line for
`receiving, extracting and passing Signal light. Each node
`comprises: data terminal equipment for issuing and receiv
`ing electrical Signals, an electro-optical interface device,
`asSociated the data terminal equipment, for converting elec
`trical Signals issued by the associated data terminal to light
`Signals for insertion onto the light transmission light and for
`converting Signal light, extracted from the light transmission
`line into electrical Signals to be received by the associated
`data terminal; a translation logic device connected between
`the optical interface device and the data terminal equipment,
`if required, for performing required protocol translation for
`the data terminal equipment and an optical interface device,
`connected to the electro-optical interface device and the
`light transmission line, for extracting light Signals from the
`light transmission line to be converted into electrical signals
`by the electro-optical interface device for receipt by the data
`terminal equipment, for inserting, onto the light transmission
`line, Signal light received from the electro-optical interface
`
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`

`3
`device and for passing Signal light bi-directionally on the
`light transmission line.
`The transport System further includes a pumping
`arrangement, for example, an optical pump Source, for
`inserting excitation light onto the light transmission line; an
`optical amplifier connector fiber connecting the each of the
`optical interface devices linearly to one another, wherein the
`optical amplifier connector fiber is doped with a material
`which is excited by the excitation light and which emits light
`having a same wavelength as the light Signals when radiated
`with light Signals transmitted bi-directionally by the at least
`one fiber optic line.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1A is a block diagram which schematically illus
`trates the optical transport System of the present invention;
`FIG. 1B is a pictorial representation of the elements
`comprising the optical transport System of FIG. 1A,
`FIGS. 2 and 3 illustrate arrangements for providing opti
`cal amplification within the optical transport System of the
`present invention;
`FIG. 4A illustrates the configuration of an E/O Interface
`card in use with yet another embodiment of the optical
`transport System of the present invention wherein the optical
`Signal is inserted, extracted and passed on two separated but
`redundant fiber optic lines,
`FIG. 4B, illustrates an EOIC configuration for Mil-Std
`1553 avionics element;
`FIG. 4C illustrates an EOIC 117 for ARINC 429 avionic
`element;
`FIG. 4-D illustrates a typical, known ARINC network
`configuration;
`FIG. 4E illustrates an optical arrangement wherein dif
`ferent optical wavelengths are assigned for each equivalent
`electrical transmission path;
`FIG. 4F, illustrates an optical arrangement which relies on
`Time Division Multiplexing (TDM) techniques to eliminate
`the plethora of optical wavelengths required by the arrange
`ment of FIG. 4E;
`FIG. 4G illustrates the structure for an EOIC adapted to
`Support Video;
`FIG. 4H illustrates an arrangement wherein different
`wavelengths are assigned to different nodes to provide a
`topology equivalent to a non-blocking Star configuration
`using MUX/DEMUXes;
`FIG. 4I illustrates an arrangement where, by using dich
`roic couplers, the resulting topology for these nodes is that
`of a Point-to-Point Repeatered Link;
`FIG. 5 illustrated an optimum bus interface topology with
`the specific coupler ratios 80/20 on-line and 50/50 off-line;
`FIG. 6 is a plot showing the optimum in-line coupling c
`opt
`VS n, where n is the number of nodes,
`FIG. 7 is a perspective View illustrating a Small rugged
`enclosure complete with moisture Seals for ensures a benign
`mechanical environment for OBIMs; and
`FIG. 8 illustrates component placement for a Mil Std
`1553 type card.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT(S)
`The Optical Transport System-General Description
`Referring to FIG. 1A, a block diagram of a first embodi
`ment of an optical transport System in accordance with the
`present invention, generally indicated at 111, is illustrated
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`for extracting, inserting and passing light bi-directionally on
`a light transmission line, generally indicated at 113, which
`comprises at least one fiber optical fiber. The system 111 is
`designed to permit communication between different elec
`trical devices having differing communication protocols and
`requirements. The optical transport System 111 preferably
`forms a broken ring, as shown in FIG. 1A, to prevent the
`recirculation of light.
`The system 111 comprises a plurality of optical bus
`interface modules (OBIM's) or optical interface devices
`115, as discloses by Applicants co-pending U.S. patent
`application entitled An Optical Interface Device, Ser. No.
`08/831,375, filed Apr. 1, 1997, (the entire disclosure of
`which is herein incorporated by reference for all purposes).
`Each OBIM 115 is an arrangement of passive fiber optic
`couplers, as will be more fully explained with particular
`reference to FIG. 4A, which wavelength selectively route
`optical Signals in and out of the network at each node,
`generally indicated at A.
`The primary purpose of the OBIM's 115 is to facilitate
`bi-directional data transmission and reception over fiber
`light transmission line 113 comprising one, two or a plurality
`of fiber optic lines as will be more fully described herein
`after. The configuration achieving this function is shown in
`FIG. 4A. The OBIM's 115 are interconnected, linearly, by
`the transmission line 113 and constitute a totally optical
`interface to the system 111.
`The optical signals that are fed in or out of the systems 111
`are then processed within the node A through the use of an
`electro-optical interface card (EOIC) 117 which includes
`wavelength Selective filters, photoreceivers and a laser trans
`mitter or light emitting diode photo-transmitter as will be
`more fully described hereinafter.
`Each EOIC 117 is a device which performs an impedance
`match between the light and electrical domains. The input
`and the output of each of the EOIC's 117 are connected to
`a translation logic card (TLC) 119 which performs the
`required protocol translation for the data terminal equipment
`(DTE) 121, which comprise, for example, a computer, Video
`or telephone device, which each have, for example, different
`protocol requirements. However, a TLC 119 is not required
`and the EOIC 117 can interface directly with the memory of
`each of the DTE 121. This eliminates approximately two
`thirds of the interface electronics presently employed for the
`purpose of transmitting information from one DTE to other
`DTES.
`Each EOIC 117 is provided for converting the optical
`Signals transported over the transmission line 113 to elec
`trical Signals which will be eventually read by the associated
`DTE 121 and for converting the electrical signals issued by
`the associated DTE 121 to optical Signals for transmission
`over the optical transmission line 113.
`The EOIC 117, in addition to performing the electrical
`to-optical and optical-to-electrical function, provides the
`means for Signal transfer between bus elements and the work
`stations through TLC's 119 (intermediate interface cards). A
`TLC is a device which performs protocol impedance match
`ing between the DTE's and the EOIC's. The protocol can be
`either the preferred direct digital memory interface, the
`direct analog Sensor interface or a legacy protocol. The TLC
`119 is capable of receiving or transmitting and converting
`one or more protocols. For example, two Such cards provide
`standardized avionics communication protocols for ARINC
`429 and Mil Std 1553. Two PC based workstations (DTE's
`121) provide data display capability using a multi-window
`display format for the Simultaneous viewing of multiple
`Signals and man-machine interface.
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`S
`The optical transport System 111 incorporates optical
`amplification which is powered using a laser pump 123,
`emitting light having a wavelength of about 980 nm as will
`be more fully described with particular reference to FIG. 2.
`The transmission line 113 of the general configuration of
`the optical transport system 111 illustrated by FIG. 1A,
`comprises two optical fibers 113", 113" (one serving as a
`redundant fiber) laid out in a “broken ring” to avoid recir
`culation of the optical signals. The through fibers at 114 (as
`best seen in FIG. 4f) between each node A are a few meters
`long and doped with a rare earth, Such as, for example,
`erbium to provide amplification to compensate for all optical
`losses encountered by an optical Signal passing through an
`OBIM 115 as will be explained hereinbelow. Optical ampli
`fication in the erbium doped through fibers is obtained by a
`“pump' signal provided by laser pump 123 transmitted
`through the entire system 111.
`FIG. 1B is a pictorial representation of the optical trans
`port system 111 of the present invention illustrated by FIG.
`1A.
`Arrangement For Pumping The Optical Transport System
`Referring to FIG. 2, a first embodiment of the arrange
`ment for optically pumping the system 111 is shown at 19.
`For the sake of simplicity, the OBIM at 11 is shown
`configured for use with a Single fiber optic line 13.
`The arrangement 19 comprises a pump Source 21 for
`inserting excitation light (about 980 nm) onto the transmis
`Sion line 113 which as noted above, comprises a Single fiber
`optic line 13, however, the present invention is not limited
`to a single line 13 and envisions use with two or more fiber
`optic lines as will be more fully discussed hereinafter.
`An optical amplifier 27 for amplifying Signal light is also
`provided which comprises, for example, a connector fiber
`optic line having a length 1, for connecting the OBIM 11
`with other devices as well as between OBIM's of the system
`111. The connector fiber optic line of the optical amplifier 27
`is doped with a material that is excited by the excitation light
`and that emits light having a same wavelength as the light
`Signals when radiated with light signals.
`Erbium is a suitable material for doping the fiber optic line
`of the optical amplifier 27 because 980 nm excitation light
`excites erbium atoms in the fiber Such that when the excited
`erbium atoms collapse, 1550 nm light (the same wavelength
`as the signal light) is emitted. Therefore, when a photon of
`1550 nm signal light collides with the excited erbium atoms,
`one photon of 1550 nm signal light becomes two photons of
`1550 nm signal light.
`According to the preferred embodiment of FIG. 2, the
`pump Source 21 is a pump laser which emits excitation light
`having a wavelength of about 980 nm. As noted above, the
`signal light has a wavelength of about 1550 nm. The length
`1 of the optical amplifier connector fiber is Set as a function
`of the amount of amplification required and in the preferred
`embodiment of FIG. 2, the length of the connector fiber of
`the optical amplifier 27 is about two meters.
`The connector fiber of the optical amplifier 27 is used to
`connect the OBIM 11 to an other device, including, but not
`limited to another OBIM 11 and can be provided both prior
`to and subsequent to the OBIM 11. Further, the connector
`fiber of the optical amplifier 27 can also be connected to at
`least one of the extraction port 29 or the insertion port 31 of
`the OBIM 11.
`Referring to FIG. 3, a further embodiment of the arrange
`ment 19 for optically pumping an OBIM 11 is illustrated
`wherein each OBIM 11 is provided with a pump source 21
`for emitting excitation light. A coupler 33, Such as, for
`example, a wave division multiplexer is provided for insert
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`ing the excitation light from the pump Source 21 onto the at
`least one fiber optic line 13 to one side of the pair of fiber
`optic-line, optical couplers 17, 17 of the OBIM 11.
`An optical amplifier 27 for amplifying Signal light is also
`provided for receiving excitation light from the pump Source
`21 as well as Signal light transmitted in both directions A or
`B on the at least one fiber optic line 13. As described above,
`the optical amplifier 27 comprises, for example, a connector
`fiber optic line having a length 1, for connecting the OBIM
`11 with other devices. The connector fiber optic line of the
`optical amplifier 27 is doped with a material, Such as, for
`example, erbium, that is excited by the excitation light and
`that emits light having a Same wavelength as the light signals
`when radiated with light signals.
`According to the preferred embodiment of FIG. 3, the
`pump Source 21 is a pump laser which emits excitation light
`having a wavelength of about 980 nm. As noted above, the
`signal light has a wavelength of about 1550 nm. The length
`1 of the optical amplifier connector fiber is Set as a function
`of the amount of amplification required and in the preferred
`embodiment of FIG. 3, the length of the connector fiber of
`the optical amplifier 27 is about two meters.
`The connector fiber of the optical amplifier 27 is used to
`connect the OBIM 11 to another device, including, but not
`limited to another OBIM 11 and can be provided both prior
`to and Subsequent to the OBIM 11. Further, the connector
`fiber of the optical amplifier can also be connected to at least
`one of the extraction port 29 or the insertion port 31 of the
`OBIM.
`In lieu of the OBIM 11 of FIG. 2, it is understood that
`other OBIM configurations, as disclosed by Applicants
`co-pending application noted above, wherein the at least one
`fiber optic line 13 comprises two or more fiber optic lines,
`are envisioned for use with present invention.
`In order to provide redundancy, the light transmission line
`113 of the optical transport system 111 of the present
`invention preferably comprises a pair of fiber optic lines as
`best seen in FIG. 4A. Therefore, if one of the fiber optic lines
`is broken, the remaining fiber optic line will transmit the
`Signal light.
`DETAILED DISCLOSURE OF OBIM
`STRUCTURE
`Referring to FIG. 4A, a preferred arrangement of an
`OBIM 115 is illustrated for the insertion and removal of light
`from the transmission line 113, which in this case, comprises
`a pair of fiber optic lines 113', 113", to implement the desired
`fail-safe operation, (if one line fails, the other line is avail
`able to provide the signal light). The OBIM 115 of FIG. 4A
`comprises first and second 50/50 couplers 125, 125", one
`provided for each of the pair of fiber optic lines 113', 113".
`The 50/50 couplers 125, 125' are provided for receiving light
`from the EOIC 117 to be inserted onto one of the fiber optic
`lines 113', 113" or for providing signal light extracted from
`the lines 113', 113" to the EOIC 117.
`The OBIM 115 also comprises a pair of 80/20 fiber
`optic-line, optical couplers 126, 126", each coupled directly
`to one of the fiber optic lines 113', 113" and to one of the pair
`of 50/50 optical couplers 125, 125", for respectively passing
`light on the associated fiber optic line 113' or 113", for
`receiving light from the associated 50/50 optical coupler 125
`or 125' to be inserted onto the associated fiber optic line 113'
`or 113" and for transmitting Said received light in opposite
`directions on the one associated fiber optic line 113' or 113",
`and for extracting light from opposite directions on the one
`associated fiber optic line 113' or 113" and transmitting said
`extracted light to the associated 50/50 optical coupler 125 or
`
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`125". An additional 50/50 optical coupler 127 is included for
`receiving light outputed by the EOIC 117 and providing the
`received light to the pair of 50/50 optical couplers 125, 125'
`for insertion bi-directionally on both of the fiber optic lines
`113' and 113".
`To understand the optical routing achieved by OBIM 115,
`the following discussion is provided. A signal exiting from
`the upper left fiber (labeled fiber 113') traveling toward
`80/20 coupler 126 is split such that 80% of the signal is
`passed on fiber 113' to the next node and the remaining 20%
`is directed toward the EOIC 117. The remaining 20% of
`light, by action of the associated 50/50 coupler 125 is split
`equally and routed towards optical filter/receiver combina
`tion 129, 131. In a similar fashion, tracing the signal from
`the EOIC 117, light is split equally by 50/50 coupler 127 and
`provided to both 50/50 couplers 125, 125' where it is split
`equally and routed to each bus fiber 113', 113" for insertion
`thereon in opposite directions simultaneously one each of
`the fibers 113', 113".
`Because two parallel optical paths now exist, optical
`Signals for each will be slightly delayed with respect to each
`other as a function of path length difference between respec
`tive transmitting and receiving nodes. For high frequency
`operation, these signals must be treated independently, for
`example, by employing two optical receivers, one dedicated
`to each path.
`Generic EOIC Structure
`Located between the OBIM and the DTE 121, the EOIC
`117 enables communication between like DTE's 121 located
`at different nodes of the system 111. As shown in FIG. 4A,
`the EOIC 117 comprises a pair of optical filters 129, 129 for
`respectively receiving light Signals extracted from the pair of
`fiber optic lines 113',113". These optical filter, 129, 129",
`which have, for example a 4 nm passband, precede optical
`receivers 131, 131', respectively, and pass only the desig
`nated wavelength of the corresponding network element
`(DTE 121 not shown in FIG. 4A) and reject all others.
`Optical receivers 131, 131' convert the received optical
`Signals into electrical Signals. Switch 133 Selects one of the
`electrical outputs from receivers 131, 131' which is then
`provide to the TLC 119 for processing in order to be
`compatible with associated DTE 121 as will be more fully
`explained hereinbelow. Electrical outputs from the DTE 121
`are converted to optical signals by the EOIC 117 which are
`inserted onto the fiber optic lines 113', 113" using the optical
`amplifier 135.
`In a fully operational mode of the system 111, the output
`of either receiver 131, 131' is valid and the choice as to
`which to use is arbitrary. However, in the event of a fiber
`break, the alternative receiver is automatically Selected.
`Each receiver 131, 131' detects and measures the incident
`input Signal and outputs a corresponding digital Signal
`indicating whether or not a minimum input optical power
`threshold is exceeded. Control logic then monitors these
`Signals and Selects the appropriate receiver.
`Instead of continuous data transmissions, the System 111,
`particularly when applied to avionics data bus requires,
`deals with bursty transmission (high density, clusters or
`packets of data). Most optical receivers designed for digital
`transmission incorporate automatic gain control for extend
`ing optical input dynamic range. These AGC loops have
`Settling times in excess of many bit periods thereby causing
`loSS of leading bits in a data packet. For continuous data this
`is generally not a problem, but in discontinuous data
`transmission, the Situation is unacceptable. To get around
`this problem, the receivers 131, 131' operating on the
`principle of edge detection, although a penalty is incurred in
`terms of loSS of optical Sensitivity.
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`The details of the optical and electro-optical System for
`implementing Simultaneous multi-network operation using
`multiple optical carriers over a Single fiber implementation
`are also shown in FIG. 4A. The technical approach exploits
`the two low attenuation windows of Step indeX single mode
`optical fiber, 1310 nm and 1550 nm. By means of narrow
`bandwidth optical Sources, temperature controlled distrib
`uted feedback lasers, and complementary narrow band opti
`cal filters, multiple interfering optical carriers are realized in
`the 1550 nm operating band.
`Therefore, it is possible to provide four channels within
`the 1550 nm operating band which each have center wave
`lengths at, for example, 1536 nm, 1543 nm, 1550 nm, and
`1557 nm, each channel being capable of carrying different
`Signal light