WO2001076022A2

WO2001076022A2 - Optical amplifier

Info

Publication number: WO2001076022A2
Application number: PCT/US2001/007600
Authority: WO
Inventors: Brian R. Gregory
Original assignee: Corona Optical Systems, Inc.
Priority date: 2000-04-03
Filing date: 2001-03-09
Publication date: 2001-10-11
Also published as: WO2001076022A3; AU2001245563A1

Abstract

An optical amplifier is provided including means for receiving a first optical input data signal. A first pump laser is provided for generating a first optical pump signal, and a first optical multiplexer is adapted to receive and combine the first optical input data signal and the first pump signal. The first optical multiplexer thus forms a first composite optical signal that includes the first pump signal and the first optical input data signal. The optical amplifier includes a first substrate having a first doped optical fiber adhered to or embedded within the substrate. The first multiplexer couples the first composite optical signal to an input end of the first doped optical fiber so that the first composite signal is transmitted through the first doped optical fiber. At the opposite end of the first doped optical fiber a first optical demultiplexer is positioned to receive the first composite signal after the first composite signal has been transmitted through the first doped optical fiber. The first demultiplexer removes the first pump signal from the first composite signal and produces a first optical output data signal having increased optical power relative to the first optical input data signal.

Description

OPTICAL AMPLIFIER BACKGROUND OF THE INVENTION

The present invention relates to doped optical fiber amplifiers. Such amplifiers comprise a length of doped optical fiber, typically doped with a rare-earth element such as erbium or some other dopant. The optical input data signal to be amplified is coupled to the doped optical fiber along with an amplifying light signal, or "pump" signal, which is supplied by a "pump" laser. The pump laser will produce light having a wavelength different from that of the optical input data signal. The pump laser radiates optical energy into the doped optical fiber along with the energy of the optical input data signal. The light provided by the pump laser is absorbed by the erbium atoms or other doping elements, in the fiber, exciting the atoms to a higher energy state. When an attenuated optical data signal enters the doped fiber, optical energy is transferred from the excited erbium atoms or other doping elements to the optical input data signal through a process known as stimulated emission. The addition of this optical energy adds to the overall power content of the optical data signal. At the distal end of the doped fiber, the pumping signal is filtered out leaving only the amplified optical data signal. A typical optical amplifier of this type is described in U.S. patent No. 5,374,973 to Maxham et al., the teaching of which is incorporated herein by

reference. Current optical fiber amplifiers such as erbium doped fiber amplifiers (EDFA) tend to be large and expensive. The primary purpose of EDFAs has been to generate as much gain as possible to allow optical data signals to be transmitted over long distances. The gain provided by a particular EDFA is related to the length of the doped fiber and the optical output power, wavelength, and other characteristics of the pump

laser. Since maximum gain is desired in most applications, prior art optical amplifiers often comprise great lengths of doped fibers wound on reels. Such an arrangement is

bulky and takes up an inordinate amount of space within optical networking and routing elements such as optical cross-connects, terabit routers and metropolitan dense wavelength division multiplexed transmission systems. Because of the size and cost of

these amplifiers, they are not particularly well suited for smaller local applications such as fiber optic networks within a single building, or networks linking various sites within a local metropolitan area, or distributed backplane systems in which it is desirable to provide optical amplification between components of a single system. An additional limitation of the prior art EDFA technology is that current

EDFAs are typically dedicated devices configured for particular optical circuits. There is usually little flexibility within the optical assemblies of which EDFAs are a part for rerouting signals, amplifying different or multiple signals, or providing different levels

of gain for different optical data signals under changing operating conditions.

Thus, a need exists for an EDFA or similar optical amplifier that can be more easily integrated with optical assemblies such as optical cross-connects, terabit routers,

and metropolitan dense wavelength division multiplexed transmission systems in order to better serve dense signaling requirements. An improved optical amplifier may be mounted at least partially on the backplane of optical networking and routing elements such as optical cross-connects, terabit routers and metropolitan dense wavelength

division multiplexed transmission systems, or on optical circuit boards mounted within

such networking and routing elements. With such an arrangement, optical data signals originating on, or carried by, various optoelectronic circuit boards could be coupled to the backplane and reconnected to the same or other optoelectronic circuit boards mounted within the networking or routing element. Amplification of various optical data signals could take place either directly on the backplane, or on the removable circuit boards within the networking or routing elements. Further, it is desirable that an assembly be created having a number of such optical amplifiers so that multiple signals could be routed through and amplified within the assembly.

SUMMARY OF THE INVENTION The present invention relates to optical amplifiers and optical amplifier assemblies. An optical amplifier according to the present invention comprises a combination of a doped optical fiber adhered to or embedded within a substrate, a pump signal, an optical multiplexer for combining a pump signal with an optical input data signal to form a composite signal, and an optical demultiplexer for removing the pump signal from the composite signal after the composite signal has been transmitted through the doped optical fiber. Such an arrangement provides an optical output data signal having increased optical power relative to the optical input data signal. An optical amplifier assembly comprises an assembly including at least one optical amplifier. The present invention provides optical amplifiers, such as erbium doped amplifiers (EDFA), that are better suited for applications having dense signaling requirements .

In a first embodiment of the invention, an optical amplifier is provided having a doped optical fiber adhered to or embedded within a substrate. The substrate may form a flexible optical fabric comprising a sheet formed of KAPTON® or MYLAR® produced by DuPont Corporation. A length of doped optical fiber is laminated on or otherwise adhered to a surface of the substrate. Alternatively, the doped optical fiber could be embedded within the substrate as the substrate is formed. The doped optical fiber is doped in a manner which provides amplification of optical data signals through a process known as stimulated emission. Typically, rare-earth dopants such as erbium, ytterbium, neodymium, or prezoidium are used; however, other dopants which are not rare-earth elements, such as fluoride may also be used, as well as composite dopants such as erbium-ytterbium or erbium-fluoride. In the first embodiment of the invention, a substrate such as an optical fabric includes a first conduit for receiving an optical input data signal and a second optical conduit configured to receive an amplification light signal, or "pump" signal. An optical multiplexer which may be either mounted directly on the substrate or positioned remotely is configured to combine the optical input data signal and the pump signal. The combined signal is then coupled to the input end of the doped optical fiber for transmission through the doped optical fiber. At the output end of the doped optical fiber, an optical demultiplexer removes the pump signal from the composite signal that has been transmitted through the doped optical fiber, leaving an amplified data signal having a greater power content than the original optical input data signal. In a second embodiment of the invention, an optical amplifier assembly is provided wherein a plurality of doped optical fibers are adhered to or embedded within a substrate. Each doped optical fiber has a multiplexer coupled to an input end of the doped optical fiber, and a demultiplexer associated with an output end of the doped optical fiber. Separate pump signals and data signals may be applied to the individual multiplexers coupled to the input ends of the doped optical fibers so that a plurality of

optical input data signals associated with the plurality of laminated doped optical fibers are independently amplified.

A third embodiment of the invention is a variation of the second embodiment.

Again, an optical amplifier assembly is provided having a plurality of doped optical

fibers adhered to or embedded within a substrate. In this embodiment, a single pump signal may be provided to excite the dopant atoms embedded within the doped optical fibers on the substrate. An optical splitter is provided to divide the output from a single pump laser into a plurality of lower powered sub-pump signals which are individually applied to the various multiplexers associated with the input end of each of the plurality

of doped optical fibers. Separate optical input data signals are coupled to each of the multiplexers. In this way, a single pump laser may be used to amplify a plurality of different optical input data signals. In a fourth embodiment of the invention, an optical amplifier assembly is

provided having at least two doped optical fibers adhered to or embedded within the

substrate. Separate pump lasers are provided to excite the dopant elements of the individual doped optical fibers, and separate multiplexers and demultiplexers are provided for combining and removing the pump signals from the composite signals transmitted through each of the doped optical fibers. In this embodiment, however, only one optical input data signal is provided. An optical switch is provided to

selectively switch the optical input data signal between the multiplexer associated with the first doped optical fiber and the multiplexer associated with the second doped optical fiber. If desired, the optical input data signal could be switched between a greater number of multiplexers, depending on the number of fibers and multiplexers provided on the substrate. With this arrangement, the optical input data signal can be switched between a first amplifier having a first amount of gain and a second amplifier having a second amount of gain. Alternatively, the amplifiers on the substrate can be configured having equal amounts of gain, but having output connections which lead to different destinations. Thus, the optical switch can be employed to switch the signal between different destinations while maintaining the same or a different level of gain.

In a fifth embodiment of the invention, an optical amplifier assembly is provided including one or more optical amplifiers. One or more doped optical fibers may be adhered to or embedded within a substrate. A multiplexer and demultiplexer are provided at opposite ends of each fiber, as in the previous embodiments. Individual pump lasers are provided to supply pump signals to the individual doped optical fibers. Separate control circuits are provided for exciting the pump lasers. An optical feedback fiber comprising a conventional optical fiber that has not been doped for amplification purposes is provided between the output demultiplexers and the control circuits driving the lasers. The feedback fiber carries a feedback signal which is proportional to the output power of the optical output data signal from the demultiplexers. The control circuits respond to the feedback signal and modify the output power of the pump lasers to achieve a desired amount of gain from each amplifier.

In a sixth embodiment of the invention, an optical amplifier assembly comprises at least two optical amplifiers. At least first and second doped optical fibers are adhered to or embedded within a substrate. Three such doped optical fibers are shown in the embodiment disclosed herein. At least first and second pump signals are

provided by first and second pump lasers. The output signals of the pump lasers are coupled to at least first and second optical multiplexers, each associated with one of the doped optical fibers. An optical splitter is provided which is configured to receive an optical input data signal. The optical splitter splits the optical input data signal into at

least first and second duplicate data signals. The first duplicate signal is coupled to the

first multiplexer and the second duplicate signal is coupled to the second multiplexer and additional duplicate signals may be coupled to additional multiplexers if desired. The first multiplexer combines the first duplicate signal with the first pump signal, and the second multiplexer combines the second duplicate signal with the second pump

signal, and so forth. By splitting the optical input data signal between a plurality of optical amplifiers comprising the optical amplifier assembly, the original data signal may be multiplied, amplified, and then transmitted to a plurality of different locations. In a seventh embodiment of the invention, an amplifier assembly includes at least one optical amplifier comprising a doped optical fiber adhered to or embedded

within a substrate. An optical input data signal and a first laser pump signal are combined by a first optical multiplexer to form a first composite signal that is coupled to the doped optical fiber. In this embodiment, the doped optical fiber is divided into first and second strands rather than being formed as a continuous fiber. The optical amplifier assembly further comprises a second pump laser for generating a second pump signal, and a second optical multiplexer connected between the first and second

strands of the doped optical fiber. The second multiplexer is configured to combine the second pump signal with the first composite signal after the first composite signal has been transmitted through the first strand of the doped optical fiber. The second multiplexer creates a second composite signal that is transmitted through the second strand of the doped optical fiber. An optical demultiplexer is positioned at the output end of the doped optical fiber, and is configured to remove both the first pump signal and the second pump signal from the second composite signal after the second composite signal has been transmitted through the second strand of the doped optical fiber. This arrangement provides additional gain to the optical input data signal by taking full advantage of the amplifying properties of the entire length of the doped optical fiber. With a single pump laser, the pump signal may be significantly attenuated by the time the composite signal reaches the output end of the doped optical fiber. This embodiment compensates for this attenuation by providing additional pumping power to the distal end of the doped fiber so that a significant amount of additional signal gain can be attained.

In an eighth embodiment of the invention, an optical amplifier assembly is provided for use in an optoelectronic assembly such as an optical cross-connect, a terabit router, a metropolitan dense wavelength division multiplexed transmission system, or a distributed backplane system in which optical signals may be routed between various components of a single system. In such an optoelectronic assembly, optical data signals are routed between a plurality of rack mounted removable optoelectronic circuit boards. The optical amplifier assembly is formed in part on an optical backplane. A doped optical fiber is adhered to or embedded within the optical backplane. The optical fiber is doped in a manner which provides optical amplification through stimulated emission. A first pump laser is provided for generating a first pump signal, and a first multiplexer is provided for combining the pump signal with an optical input data signal. The combined signals are then coupled to the first end of the doped optical fiber. At the output end of the doped optical fiber, a demultiplexer is provided for removing the pump signal from the combined pump signal and data signal. The various components of the optical amplifier assembly can be mounted on the backplane or on one of the removable optoelectronic circuit boards. For example, the pump laser

and an optoelectronic transceiver which generates the optical input data signal can each be mounted on one of the removable circuit boards. With this arrangement, the first half of a fiber optic connector may be provided along the rear edge of the removable

optoelectronic circuit board, and a mating half of the fiber optic connector may be mounted to the optical backplane. Preferably, both halves of the fiber optic connector will be configured such that the two connector halves will blind mate as the optoelectronic circuit board is inserted into the rack assembly that supports the removable circuit boards. In this way, signals may be routed from the circuit boards mounted within the optoelectronic assembly, amplified, and transmitted through components mounted on the same circuit board or a different circuit board from which

the signal originated.

In a ninth embodiment of the invention, an optical amplifier assembly is

provided for use in an optoelectronic assembly wherein optical signals are routed through a backplane between a plurality of removable optoelectronic circuit boards. The amplifier assembly is formed at least in part on a removable optoelectronic circuit

board that interfaces with the backplane of the optoelectronic assembly. A doped optical fiber is adhered to or embedded within a surface of the removable optoelectronic circuit board An optical input data signal is provided, either by a transceiver mounted

on the removable optoelectronic circuit board, or from a remote source such as through the optical backplane A pump laser is provided to generate a laser pump signal An optical multiplexer or other means for combining the optical input data signal and the laser pump signal is provided The optical multiplexer forms a composite signal that is coupled to and transmitted through the doped optical fiber At the output end of the

doped optical fiber an optical demultiplexer removes the laser pump signal from the composite signal, leaving an optical output data signal that is substantially the same as the optical input data signal, but having increased signal power Finallv , an optical

connector is provided to connect the optical output data signal to the backplane

BRIEF DESCRIPTION OF THE DRAWINGS

Fig 1 shows an optical amplifier assembly according to a first embodiment of the invention, Fig 2 shows a second embodiment of an optical amplifier assembly including a

plurality of optical amplifiers,

Fig 3 shows a third embodiment of an optical amplifier assembly wherein a single pump laser source excites a plurality of optical amplifiers having doped optical fibers adhered to or embedded within a substrate, Fig 4 shows a fourth embodiment of an optical amplifier assembly wherein an input data signal may be switched between multiple optical amplifiers having doped optical fibers adhered to or embedded within a substrate, Fig. 5 shows a fifth embodiment of an optical amplifier assembly with a plurality of optical fiber amplifiers having doped optical fibers adhered to or embedded

within a substrate, and wherein optical feedback is provided to a control circuit for

adjusting the output power of a pump laser to achieve a particular amount of gain from each optical fiber amplifier;

Fig. 6 shows a sixth embodiment of an optical amplifier assembly wherein a

single optical input data signal is divided between a plurality of optical fiber amplifiers having doped optical fibers adhered to or embedded within a substrate;

Fig. 7 of shows a seventh embodiment of an optical amplifier assembly wherein an optical fiber amplifier includes first and second pump sources, a first pump source having an output which is combined with an input data signal at an input end of a doped

optical fiber amplifier, and a second pump source having an output which is combined with the composite first pump signal and input data signal at an intermediate point along the length of the doped optical fiber; Fig. 8 is a perspective view of an optoelectronic assembly having a portion of an

optical amplifier assembly formed as part of the optical backplane; and

Fig. 9 is a perspective view of an optoelectronic assembly wherein an optical amplifier assembly is formed on a removable circuit board adapted to interface with the optical backplane.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides an optical amplifier assembly conveniently and uniquely presented in whole, or in part, on a substrate. By providing appropriate optical connectors and fibers adhered to or embedded within a substrate, optical amplifier assemblies according to the present invention may be incorporated as part of an optical backplane of networking and routing elements such as optical cross-connects, terabit routers, metropolitan dense wavelength division multiplexed transmission systems, or distributed backplane systems in which it is desirable to provide optical amplification between components of a single system.

In Fig. 1 , a first embodiment of an optical amplifier assembly is shown. The amplifier assembly comprises a substrate 102, preferably formed of a flexible plastic material such as polyimide, commonly marketed under the trademark KAPTON® and produced by DuPont Corporation. The substrate may also be formed of MYLAR®, also produced by DuPont . A length of doped optical fiber 104 is adhered to or embedded within substrate 102. Preferably, the doped optical fiber 104 is laminated to substrate 102, however, other methods of adhering the fiber to the substrate may also be used. For example, the doped optical fiber could be layed out over the substrate, and a quick-hardening emulsion sprayed over the substrate to hold the fiber in place, or the fiber may be dropped into a liquid or semi-liquid bath of encapsulating material that later hardens into a substrate that surrounds the fiber.

Doped optical fiber 104 is preferably doped with erbium, although other rare- earth elements (such as ytterbium, neodymium, or prezoidium), non rare-earth elements (such as fluoride), or composite dopants (such as erbium-ytterbium or erbium-fluoride) may also be used. When doped optical fiber 104 is doped with erbium, the amplifier comprises a laminated EDFA. Fiber 104 may be laminated in a coiled or looping fashion as shown in Fig. 1 in order to increase the length of the fiber and thereby increase the gain of the amplifier while minimizing the space occupied by the fiber. The remaining elements of the amplifier include a pumping laser source 110, an optical multiplexer 106, and an optical demultiplexer 114 at the output end of the doped optical fiber 104. Preferably, pump laser 110 produces an optical output signal having a 1480 nm or 980 nm wavelength, although other wavelengths may also be used, such as 1064nm or 1047nm. Multiplexer 106 may be a fuzed biconic optical multiplexer or a reflective interference filter wavelength division multiplexer, among others. The demultiplexer may be a fiber Bragg grating, a fuzed biconic demultiplexer, or the like. Each of the other embodiments described herein will likewise include components the same as or similar to doped optical fiber 104, pump laser 110, multiplexer 106, and demultiplexer 114.

In the embodiment of Fig. 1, an optical input data signal is coupled to the optical multiplexer 106 via a conventional optical fiber 109 that has not been doped for amplification purposes. Likewise, the pump signal is coupled from the pump laser 110 to the multiplexer 106 via a second conventional optical fiber 111. The output of the multiplexer 106 is coupled directly to the doped optical fiber 104. At the output end of the doped optical fiber 104 a demultiplexer 114 removes the pump signal from the composite signal made up of the pump signal and the optical data signal transmitted through the fiber. The demultiplexer passes only the amplified optical output data signal. The amplified optical output data signal is transmitted from the demultiplexer 114 over an output fiber 116 comprising a length of conventional optical fiber.

As shown in Fig. 1 , the multiplexer and demultiplexer may be mounted directly to the substrate 102. The pump laser, however, as well as the source of the optical input data signal, may be mounted on a printed circuit board separate from the substrate 102. In this arrangement, both the pump laser output signal and the input data signal must be coupled to the substrate via optical connectors or optical fiber jumpers. Similarly, if the output signal of the amplifier is to be transmitted to a separate card or assembly, an output optical connector or jumper must be provided.

Fig. 2 shows a second embodiment of the invention. The embodiment of Fig.2 is the same as that of Fig. 1, except that multiple optical amplifiers are provided on the optical amplifier assembly. Accordingly, a plurality of doped optical fibers 154 are adhered to or embedded in a substrate 152. Multiple pump lasers 160 provide multiple pump signals, one for each optical amplifier formed on substrate 152. The output energy from the pump lasers is input to the optical multiplexers 156, each of which combines one of the pump signals with a separate optical input data signal 151, 153, 155. The combined signals are each transmitted through one of the plurality of doped optical fibers 154. Demultiplexers 164 are provided at the output ends of the doped optical fibers 154 for separating the pump signals from the amplified data signals generated at the output ends of the fibers. Thus, the embodiment shown in Fig. 2 can be used to amplify a plurality of optical data signals.

The embodiment shown in Fig. 2 includes three optical amplifiers. Substrate 152 can be formed having any number of doped optical fibers, depending on the requirements of the particular application. By providing doped optical fibers 154 of different lengths and pump lasers having different output power levels, different levels of signal gain may be obtained for each of the separate optical input data signals. A third embodiment of an optical amplifier assembly is shown in Fig. 3. In the embodiment of Fig. 3, three doped optical fibers 204, 206, 208 are adhered to or embedded within a substrate 202. The doped optical fibers may have identical lengths or different lengths, depending on the amount of gain desired to be achieved from each doped optical fiber. As with the embodiment of Fig. 2, each strand of doped optical fiber has a multiplexer 210, 212, 214 associated with the input end of the fiber and a demultiplexer 220, 222, 224 associated with the output end. In this embodiment, however, a single pump laser 216 generates a pump signal which is input to an optical splitter 218. The optical splitter 218 divides the pump laser output signal and provides a portion of the original pump signal, or a "sub-pump" signal, to each of the multiplexers 210, 212, and 214 which are coupled to the various doped optical fiber strands 204, 206, 208. Separate optical input data signals 226, 228, 230 are also supplied to each of the multiplexers 210, 212, 214. The multiplexers combine the separate sub-pump signals output from the splitter with each of the optical input data signals, and couple the composite signals to the individual doped optical fibers 204, 206, 208. Thus, a single pump laser may be employed to amplify a plurality of different optical input data signals. The amount of gain of each of the separate amplifiers will be diminished somewhat due to the splitting of the optical power of the pump laser. However, by properly selecting the output power of the pump laser 216 and the lengths of the doped optical fibers 204, 206, 208, a desired amount of gain may be obtained from each of the separate doped optical fibers. The optical splitter 218 may be mounted directly to substrate 202, although it could be located remotely if desired. A fourth embodiment of an optical amplifier assembly is shown in Fig. 4. This optical amplifier assembly includes first and second pump lasers 256 and 268, first and second multiplexers 258 and 270, first and second doped optical fibers 260 and 272, and first and second demultiplexers 262 and 274. The doped optical fibers 260, 272 are adhered to or embedded within a substrate 251. In this embodiment, the optical amplifier assembly receives only a single optical input data signal 254. An optical switch 278 directs the optical input data signal to one of the two multiplexers 258 or 270. Thus, an incoming optical data signal 254 can be directed to either one of the doped optical fibers 260 or 272 adhered to or embedded within the substrate. This switching ability can be used to provide continued service if one of the pump lasers fails, to switch between fibers having different gain, or routing signals to different destinations.

A fifth embodiment of an optical amplifier assembly is shown in Fig. 5. In this embodiment a plurality of doped optical fibers 354 are adhered to or embedded within a substrate 352. While the amplifier assembly shown in Fig. 5 has three doped optical fibers, a different number of doped optical fibers could be included depending on the requirements of the particular application. In the embodiment shown, each doped optical fiber 354 relates to an individual optical amplifier. In addition to the doped optical fibers 354, each individual amplifier includes a pump laser 356, a pump laser control circuit 368, a multiplexer 358, a demultiplexer 360 and an optical feedback fiber 370 formed of a conventional optical fiber. The multiplexers 358 receive optical input data signals 364 as well as the output signals from the pump lasers 356. The multiplexers 358 combine the optical input data signals and the pump laser output signals, forming composite signals that are coupled to the doped optical fibers 354. At the output end of the doped optical fibers, the demultiplexers 360 remove the pump signals and couple the amplified optical output data signals to external fibers 372. In addition to removing the pump signals from the composite signals at the output ends of the doped optical fibers 354. the demultiplexers 360 also couple a small portion of the optical output data signals to optical feedback fibers 370 which form optical feedback loops to the pump laser control circuits 368. The signal power of the optical feedback signals is proportional to the output power of the optical output data signals. Thus, the optical feedback loops provide a measure of the output power of the optical output data signals emitted by the amplifiers. Based on the strength of the optical feedback signals, the pump laser control circuits 368 adjust the output power of the pump lasers in order to achieve the exact amount of gain desired from each amplifier.

A sixth embodiment of an optical amplifier assembly is shown in Fig. 6. As with the previous embodiments, the amplifier assembly comprises a substrate 402. A plurality of doped optical fibers 404 are adhered to or embedded within substrate 402. The three separate doped optical fibers 404 each represent part of a separate optical amplifier. Along with the doped optical fiber 404, each optical amplifier includes a pump laser 406, a multiplexer 408, and a demultiplexer 410. In this embodiment, an optical splitter 414 is mounted on the substrate 402 and a single optical input data signal is coupled thereto. The optical splitter 414 divides the optical input data signal among the three optical amplifiers, creating a first optical input data signal 416, a second optical input data signal 418, and a third optical input data signal 420. The separate optical input data signals 416, 418, 420 are each input to a separate one of the multiplexers 408. Each individual optical input data signal is then combined with an individual pump signal and coupled to one of the separate doped optical fibers 404. At the output end of the doped optical fibers 404, the demultiplexers 410 remove the pump signals and couple a plurality of amplified optical output data signals to external conventional optical fibers 412.

This embodiment allows a single optical input data signal to be amplified and broadcast a number of different times. For example, if it is desired to transmit the same signal to a number of different destinations, the data signal may be reproduced any number of times and amplified as necessary to reach each intended destination. The destinations to which the signals are to be transmitted may be located different distances from the optical amplifier. If a data signal is to be transmitted both locally and to points a long distance away, copies of the optical input data signal that are to be broadcast locally can be routed to optical amplifiers having relatively shorter length doped optical fibers which are coupled to relatively lower powered pump lasers. Conversely, data signals that are to be transmitted longer distances can be routed to optical amplifiers having longer length doped optical fibers which are coupled to pump lasers having greater output power. In other words, the signals being transmitted a long distance can be routed to optical amplifiers having higher gain so that these signals will have the power necessary for long distance transmission, while the local signals will be amplified only as much as needed for local transmission.

A seventh embodiment of the invention is shown in Fig. 7. This embodiment is very similar to that shown in Fig 1. In this embodiment, an optical amplifier assembly is provided comprising a doped optical fiber 454 adhered to or embedded within a substrate 452. As with the optical amplifier assembly of Fig. 1, the optical amplifier assembly of the seventh embodiment comprises a pump laser 460, a multiplexer 456, and a demultiplexer 464. In addition to these components, a second pump laser 474 and a second multiplexer 476 are also provided. The two pump lasers 460 and 474 may be of the same or different wavelengths. For example, first pump laser 460 may be a 1480 nm wavelength laser, and the second pump laser 474 may be a 980 nm wavelength laser. The output signal from the pump laser 460 and the optical input data signal 461 are combined by the first multiplexer 456 to form a first composite signal which is coupled to a first strand 453 of the doped optical fiber 454. Approximately mid-way down the length of the doped optical fiber 454, the second multiplexer 476 splits the doped optical fiber 454 to form a second strand 455. The pump signal output from the second pump laser 474 is then combined with the first composite signal transmitted through the first strand 453 to form a second composite signal. The second composite signal is then coupled to the second strand 455 of the doped optical fiber 454 and transmitted to the output end of the fiber. At the output end of the doped optical fiber 454, the demultiplexer 464 removes the output signals from both pump lasers 460, 474. The demultiplexer then outputs an amplified optical data signal.

The embodiment shown in Fig. 7 allows a greater amount of gain to be applied to the optical input data signal. As the combined pump and data signals traverse the length of the doped optical fiber, losses within the doped optical fiber cause the pump signal to be attenuated. Thus, under normal conditions, the amount of gain added at the far end of the doped optical fiber is generally less than that added at the near end of the fiber where the pump signal is coupled to the doped optical fiber. By adding a second pump signal to the doped optical fiber 454 at a point where the original pump signal has been attenuated to a point where it no longer provides sufficient amplification, the overall gain of the amplifier can be increased.

Turning to Fig. 8, which shows an eighth embodiment of the invention, an optoelectronic assembly is shown at 300. The optical assembly 300 may be a networking or routing element such as an optical cross-connect, terabit router, metropolitan dense wavelength division multiplexed system, or part of a distributed backplane system in which it is desirable to provide optical amplification between components of a single system. The assembly comprises a rack 302 which includes a plurality of stacked horizontal tracks 304 configured to receive a plurality of removable optoelectronic circuit boards such as circuit board 307. An optical backplane 308 is oriented vertically in the rear of the assembly. The optical backplane 308 includes one or more doped optical fibers 323 laminated thereon.

In the eighth embodiment shown in Fig. 8, a first circuit board 307 is inserted in the lowest track 305. Circuit board 307 mcludes an optoelectronic transceiver 310 which generates an optical data signal. The circuit board also carries a pump laser 314 which forms a part of an optical amplifier. A first blindmate optical connector 316 is mounted along the rear edge 317 of circuit board 307. A second blind mate optical connector 318 adapted to mate with the first blindmate connector 316 is attached to the optical backplane 308.

The first and second optical connectors 316 and 318 are configured so that as the circuit board 307 is inserted into the track 305, the two optical connectors will mate with one another. The optical connectors 316, 318 are known as blindmate connectors because the structures within the connectors themselves act to align the optical fibers mounted within the connectors as the circuit board 307 is inserted into the rack. No additional effort is required to align the fibers other than inserting the card. The optical connectors 316 and 318 may be configured to hold a plurality of optical fibers so that a number of optical signals may be coupled from the circuit board 307 to the backplane 308. In the embodiment shown in Fig 8, both the pump laser output signal and the optical output data signal from the optical transceiver are coupled from circuit board 307 to the backplane 308.

On the optical backplane 308 itself, conventional optical fibers 319 and 321 carry the optical data signal and the pump signal from the second half of the optical connector 318 to an optical multiplexer 320, also mounted on the backplane. The multiplexer 320 combines the optical data signal and the pump laser output signal. The combined signal is then coupled to the doped optical fiber 323.

At the distal end of the doped optical fiber 323, a demultiplexer 322, also mounted on the backplane 308, removes the pump signal from the composite signal, leaving only the amplified optical output data signal. A short length of conventional optical fiber 325 carries the amplified data signal from the demultiplexer 322 to a first output optical connector 324. A second printed circuit board 338 may be inserted in the uppermost track 339. A mating optical connector 342 is mounted along the rear edge of circuit board 338. As with the connectors 316, 318 described above, connectors 324 and 342 are adapted to blind mate with one another as the printed circuit board 338 is inserted into rack 302. When this second circuit board 338 is fully inserted into the rack, the two output optical connectors 324 and 342 are mated and the amplified optical output data signal is coupled to the components mounted on the second circuit board 338.

As shown in Fig. 8, more than one doped optical fiber may be formed on the optical backplane 308. In the embodiment shown, two such optical amplifiers are provided. The data signals and pump laser signals originate on the lower circuit board 307 and the amplified output signals are coupled to the upper circuit board 338. This particular arrangement is shown as an example only. Both the input and output signals, as well as the pump laser output signal associated with the different optical amplifiers, could be coupled to circuit boards mounted at different vertical levels within the rack 302. Multiple optical paths may be created through the backplane between various circuit boards. Furthermore, the optical signals carried by these various optical paths may be subjected to different levels of power amplification. Any of the various embodiments of the optical amplifier assemblies disclosed in Figs. 1-7 may be incorporated in the backplane of an optoelectronic assembly such as that disclosed in Fig 8.

Fig. 9 shows a ninth embodiment of the invention wherein an optoelectronic assembly similar to that disclosed in Fig. 8 is shown at 500. As with the embodiment of Fig. 8, the optoelectronic assembly 500 may be a networking or routing element such as an optical cross-connect, terabit router, metropolitan dense wavelength division multiplexed system, or part of a distributed backplane system in which it is desirable to interconnect optical signals between various components of a single system.

The assembly 500 comprises a rack 502 which includes a plurality of stacked horizontal tracks 504 configured to receive a plurality of removable optoelectronic circuit boards 506. An optical backplane 508 is oriented vertically in the rear of the assembly. The optical backplane 508 includes one or more optical fibers 523 adhered to or embedded within the backplane 508. The optical fibers 523 route optical signals between the various optoelectronic circuit boards inserted into the tracks 504. The primary difference between the optoelectronic assembly of Fig. 8 and that of Fig. 9 is that in the embodiment of Fig. 9. a doped optical fiber that forms part of an optical amplifier is adhered to the surface, or on a laminated sheet placed over the surface, of a removable circuit board 507 rather than being formed on the backplane 508. Thus, the fibers 523 which are adhered to the backplane 508 may be conventional optical fibers that have not been doped to provide amplification through stimulated emission.

In the embodiment shown in Fig. 9, a doped optical fiber 509 is adhered to a first removable circuit board 507 inserted in the lowest track 505. Circuit board 507 includes an optoelectronic transceiver 510 which generates an optical input data signal. (In alternative embodiments, transceiver 510 can be omitted, and the optical input data signal can be supplied from an alternate source.) The circuit board 507 also carries a pump laser 514 which forms a part of an optical amplifier. The output signal of pump laser 514 as well as the optical input data signal are input to an optical multiplexer 520 which is also mounted on the circuit board 507. The optical multiplexer 520 combines the laser pump signal and the optical input data signal, and couples the composite signal to the doped optical fiber 509. An optical demultiplexer 522 is also mounted to the circuit board 507. The output end of the doped optical fiber 509 is connected to the demultiplexer 522 so that the demultiplexer removes the pump signal from the composite signal after the composite signal has been transmitted through the doped optical fiber. A short length of conventional optical fiber 519 which has not been doped for amplification purposes is connected between the demultiplexer 522 and a first blindmate optical connector 516.

A mating blindmate optical connector 518 is mounted on the optical backplane 508. The first and second blindmate optical connectors 516, 518 are configured so that as the circuit board 507 is inserted into the track 505, the two connectors will mate with one another and the amplified optical data signal output from the demultiplexer 522 will be coupled to an optical fiber 523 formed on the backplane 508. Optical fiber 523 may then route the signal to another matable half of an optical connector, such as 524, so that the signal can be coupled via another mating connector half 542 to components on another circuit board, such as circuit board 538 inserted into the rack 502. The embodiment of Fig. 9 provides an optical amplifier that is integrated within a larger system, but which may be easily removed or changed without affecting the rest of the system. It should be noted that various changes and modifications to the present invention may be made by those of ordinary skill in the art without departing from the spirit and scope of the present invention which is set out in the appended claims. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to be limiting of the invention as described in the appended claims.

Claims

CLAIMSWhat is claimed is:

1. An optical amplifier assembly comprising: a substrate;

a first amplifying optical fiber secured to the substrate, the amplifying optical fiber having a first end and a second end: an optical conduit for receiving a first optical input data signal; an optical conduit for receiving a first optical pump signal; an optical multiplexer configured to combine the first optical input data signal and the first optical pump signal, the multiplexer providing a first composite signal coupled to the first end of the amplifying optical fiber; and a demultiplexer coupled to the second end of the amplifying optical fiber, the demultiplexer removing the pump signal from the first composite signal, and coupling a first optical output data signal to a first output optical conduit.

2. The optical amplifier assembly of claim 1 further comprising:

a second length of amplifying optical fiber secured to the substrate, the second amplifying optical fiber having a first end and a second end;

an optical conduit for receiving a second optical input data signal; an optical conduit for receiving a second optical pump signal; a second optical multiplexer configured to combine the second optical input data

signal and the second optical pump signal, providing a second composite signal coupled to the first end of the second amplifying optical fiber; and

a second demultiplexer coupled to the second end of the second amplifying optical fiber, the second demultiplexer removing the second pump signal from the second composite signal, and coupling a second amplified optical output data signal to a second output optical conduit.

3. The optical amplifier assembly of claim 1 further comprising:

a plurality of amplifying optical fibers secured to the substrate, each of the amplifying optical fibers having a first end and a second end;

a plurality of first optical conduits for receiving a plurality of optical input data signals; a plurality of optical multiplexers for combining the optical input data signals with a plurality of pumping light signals output from at least one pump light source, each multiplexer coupling a composite signal to the first end of one of the plurality of

amplifying optical fibers; and a plurality of demultiplexers, each associated with the second end of one of the plurality of amplifying optical fibers, the demultiplexers configured to remove the

pumping signals from the composite signals and couple a plurality of optical output data signals, each having signal power greater than its respective optical input data signal, to a plurality of output conduits.

. An optical amplifier assembly comprising; means for receiving a first optical input data signal;

a first pump laser for generating a first optical pump signal;

a first optical multiplexer adapted to receive and combine the first optical input data signal and the first pump signal, forming a first composite optical signal;

a substrate having a first doped optical fiber secured to the substrate, the first multiplexer coupling the first composite optical signal to an input end of the first doped optical fiber so that the first composite signal is transmitted through the first doped optical fiber; and

a first optical demultiplexer coupled to an output end of the first doped optical fiber, the first optical demultiplexer adapted to receive the first composite signal after

the first composite signal has been transmitted through the first doped optical fiber, the first demultiplexer removing the first pump signal from the first composite signal to produce a first optical output data signal having increased optical power relative to the

first optical input data signal.

5. The optical amplifier assembly of claim 4 further comprising: means for receiving a second optical input data signal; a second pump laser for generating a second optical pump signal; a second optical multiplexer adapted to receive and combine the second optical input data signal and the second pump signal, forming a second composite optical

signal; a second doped optical fiber secured to the substrate, the second optical multiplexer coupling the second composite optical signal to an input end of the second doped optical fiber so that the second composite signal is transmitted through the second doped optical fiber; and a second optical demultiplexer coupled to an output end of the second doped optical fiber, the second optical demultiplexer adapted to receive the second composite signal after the second composite signal has been transmitted through the second doped optical fiber, and to remove the second pump signal from the second composite signal to produce a second optical output data signal having increased optical power relative to the second optical input data signal.

6. The optical amplifier of claim 4 further comprising: means for receiving a second optical input data signal; a second doped optical fiber secured to the substrate; an optical splitter adapted to receive the first optical pump signal, the optical splitter dividing the first optical pump signal into at least first and second sub-pump signals, the first optical multiplexer adapted to receive and combine the first sub-pump signal and the first optical input signal, forming the first composite signal, the first optical multiplexer coupling the first composite signal to an input end of the first doped fiber so that the first composite signal is transmitted through the first doped fiber; the first demultiplexer adapted to remove the first sub-pump signal from the first composite signal; a second optical multiplexer adapted to receive and combine the second sub- pump signal and the second optical input data signal, forming a second composite signal, the second optical multiplexer coupling the second composite signal to an input end of the second doped optical fiber so that the second composite signal is transmitted through the second doped optical fiber; and

a second optical demultiplexer coupled to an output end of the second doped

optical fiber, the second optical demultiplexer adapted to receive the second composite signal after the second composite signal has been transmitted through the second doped optical fiber and to remove the second sub-pump signal from the second composite signal to produce a second optical output data signal having increased optical power relative to the second optical input data signal.

7. The optical amplifier of claim 4 further comprising: a second doped optical fiber secured to the substrate;

a second pump laser for generating a second optical pump signal;

a second optical multiplexer adapted to receive and combine the first optical input data signal and the second optical pump signal to form a second composite signal, the second optical multiplexer coupling the second composite signal to the second

doped optical fiber; a second optical demultiplexer coupled to an output end of the second doped fiber, the second optical demultiplexer adapted to receive the second composite signal after the second composite signal has been transmitted through the second doped optical fiber and remove the second pump signal from the second composite signal; and an optical switch for selectively directing the first optical input data signal to one of the first and second optical multiplexers so that the first optical input data signal

is combined with one of the first and second pump signals and amplified by one of the first and second doped optical fibers.

8. The optical amplifier of claim 4 further comprising a control circuit configured to control the output power of the first optical pump laser, and a feedback optical fiber coupled between the first demultiplexer and the control circuit, the demultiplexer coupling an optical feedback signal having a power level proportional to the output power of the optical output data signal to the feedback optical fiber, the control circuit adapted to receive the feedback signal and adjust the output power of the pump laser in response to the optical power of the feedback signal so that a desired level of gain is

achieved.

9. The optical amplifier of claim 4 further comprising: a second doped optical fiber secured to the substrate; a second pump laser for generating a second pump signal; a second optical multiplexer associated with an input end of the second doped

optical fiber; a second optical demultiplexer associated with an output end of the second

doped optical fiber; and an optical splitter configured to receive the first optical input data signal and split the first optical input data signal into first and second duplicate input data signals, the first duplicate input data signal being coupled to the first multiplexer and the second duplicate input data signal being coupled to the second multiplexer, the first multiplexer combining the first duplicate input data signal with the first pump signal, and the second multiplexer combining the second duplicate input data signal with the second pump signal, whereby the optical input data signal is reproduced and amplified for transmission to at least two separate destinations.

10. The optical amplifier of claim 4 further comprising a second pump laser for generating a second optical pump signal, and a second optical multiplexer, the first doped optical fiber comprising a first strand and a second strand, the first strand being disposed between the first multiplexer and the second multiplexer, and the second strand being disposed between the second multiplexer and the first demultiplexer, the second multiplexer adapted to combine the second pump signal with the first composite signal to form a second composite signal comprising the first optical input data signal, the first pump signal, and the second pump signal, the second multiplexer transmitting the second composite signal through the second strand of the first doped optical fiber, and the first demultiplexer acting to remove both the first pump signal and the second pump signal from the second composite signal.

11. The optical amplifier of claim 4 further comprising a first control circuit for driving the first pump laser, and a first feedback circuit adapted to measure the optical power of the first optical output data signal, the first control circuit modifying the power of the first pump laser in response to the optical output power measured by the first feedback circuit to achieve a desired amount of gain.

12. The optical amplifier of claim 4 further comprising a plurality of doped optical fibers secured to the substrate, and a plurality of optical connectors for receiving a plurality of optical input data signals, each of the plurality of doped optical fibers having an optical multiplexer associated therewith for combining an optical input data signal with an optical pump signal and coupling the combined signals with the doped optical fibers, and each of the plurality of doped optical fibers having a demultiplexer associated therewith for removing the pump signal from the combined signals at an output end of the doped optical fibers.

13. The optical amplifier of claim 12 further comprising a plurality of pump lasers for providing the plurality of optical pump signals.

14. The optical amplifier of claim 13 further comprising a plurality of control circuits and feedback circuits for driving the plurality of pump lasers to achieve a desired amount of gain for each of the optical input data signals amplified by each of the plurality of doped optical fibers.

15. The optical amplifier of claim 12 further comprising an optical splitter adapted to split a single optical pump signal into a plurality of reduced power optical pump signals, said plurality of reduced power optical pump signals being combined with said plurality of optical input data signals.

16. An optical amplifier assembly for use in an optoelectronic assembly wherein optical data signals are routed between a plurality of rack mounted removable optoelectronic circuit boards, the optical amplifier assembly comprising: an optical backplane having a first optical fiber secured to the backplane, the optical fiber being doped to provide optical amplification through stimulated emission; a first pump laser for generating a first pump signal; a first multiplexer for combining the first pump signal with a first optical data signal, the combined signal being coupled to a first end of the first doped optical fiber; and a first demultiplexer for separating the first pump signal from an amplified optical data signal at a second end of the first doped optical fiber.

17. The optical amplifier of claim 16 further comprising a first optical connector for coupling an optical signal from a first removable circuit board to the backplane, the pump laser and the optical multiplexer being mounted on the first circuit board, the combined pump signal and first optical data signal output from the first multiplexer coupled to the first doped optical fiber through the first optical connector.

18. The optical amplifier of claim 17 wherein the first optical connector comprises a blindmate connector.

19. The optical amplifier of claim 16 further comprising a first circuit board, the pump laser being mounted on the first circuit board, and at least one optical connector for coupling the pump signal and the first optical data signal from the first circuit board to the optical backplane, the first multiplexer being mounted on the optical backplane.

20. The optical amplifier of claim 19 wherein the first optical connector comprises a blindmate connector.

21. An optical amplifier comprising; means for receiving a first optical input data signal; a first pump laser for generating a first optical pump signal; a first optical multiplexer adapted to receive and combine the first optical input data signal and the first pump signal, forming a first composite optical signal; a substrate having a first doped optical fiber secured thereto, the first multiplexer coupling the first composite optical signal to an input end of the first doped optical fiber so that the first composite signal is transmitted through the first doped optical fiber; and a first optical demultiplexer coupled to an output end of the first doped optical fiber, the first optical demultiplexer adapted to receive the first composite signal after the first composite signal has been transmitted through the first doped optical fiber and remove the first pump signal from the first composite signal to produce a first optical output data signal having increased optical power relative to the first optical input data signal.

22. An optical amplifier assembly for use in an optoelectronic assembly wherein optical signals are routed through a backplane between a plurality of removable optoelectronic circuit boards, the optical amplifier comprising: a first removable optoelectronic circuit board; a doped optical fiber secured to said first removable optoelectronic circuit board, said doped optical fiber having an input end and an output end; a first source providing a first optical data signal; a second source providing a laser pump signal; means for combining said first optical data signal and said laser pump signal to form a composite signal coupled to and transmitted through said doped optical fiber; means associated with said output end of said doped optical fiber for removing said laser pump signal from said composite signal after said composite signal has been transmitted through said doped optical fiber, forming a second optical data signal, said second optical data signal being identical to said first optical data signal, but having increased signal power; and means for connecting said second optical data signal to said backplane.

23. The optical amplifier assembly of claim 22 wherein said second source comprises a pump laser. O 01/76022

24. The optical amplifier assembly of claim 23 wherein said pump laser is secured to said first removable optoelectronic circuit board.

25. The optical amplifier assembly of claim 22 wherein said means for connecting said second optical signal to said backplane comprises a blindmate optical connector.