Patent Publication Number: US-2003223683-A1

Title: Modular optical amplifier assembly

Description:
[0001] This application claims the benefit of U.S. Provisional Patent Application No. 60/368,460, filed Mar. 27, 2002, which is incorporated herein by reference. 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0002] 1. Field of the Invention  
       [0003] The present invention relates to optical fiber telecommunication systems and, in particular, the modular optical amplifiers employed in such systems.  
       [0004] 2. Technical Background  
       [0005] Presently, optical amplifiers for telecommunication networks are uniquely designed to meet specific customer needs in specific customer applications, according to the amplifier&#39;s role in each customer&#39;s proprietary system. There is very little commonality of either the optical designs or the physical embodiments between different amplifiers manufactured for either different customers and or different applications.  
       [0006] Custom design efforts add significant time and cost to the development of each amplifier. In addition, custom designs prevent achievement of efficient manufacturing scale, because only relatively few amplifiers of the same design are sold to each customer. The custom design approach also creates an inventory risk, as unsold product for one customer/application cannot be sold to another. Finally, custom designed amplifiers hinder future upgrade capability and hardware reuse.  
       [0007] U.S. Pat. No. 5,778,132 discloses a three “cassette” modular approach to assembly of optical amplifiers. The first cassette (first module) contains a first coil of rare earth doped optical fiber, an optical tap, an optical isolator and a wavelength division multiplexer (WDM). The second cassette (second module) contains an isolator and a WDM. The third cassette contains a second coil of rare earth doped optical fiber, a WDM, an isolator, and an optical tap. The laser sources are provided externally. The modular design approach disclosed in this patent has several shortcomings.  
       [0008] While this partitioning into three cassettes allows the disclosed optical amplifier to be manufactured, the three cassettes are of limited use in that they cannot be recombined to create many of today&#39;s more complex amplifiers. The disclosed partitioning of the amplifier into three cassettes does not constitute fundamental building blocks that would have wide commercial use. Furthermore, the specific cassette content does not include other components necessary for many currently available amplifier designs. For example: (a) the inclusion of the rare earth doped optical fiber in with the first and third cassettes does not allow for the manufacture of a complete, single coil amplifier; (b) the cassettes do not allow for gain flattening filters (GFFs) or variable optical attenuators (VOAs); and (c) the number and location of the bandsplitters are constrained, yet they are not always present or always present in the same configuration in commercial optical amplifiers.  
       [0009] Second, the cassettes are not designed to be effectively integrated. For example, the laser sources are provided externally, with no allowance for cost-effective integration of the laser sources into the cassettes.  
       SUMMARY OF THE INVENTION  
       [0010] According to the present invention modular optical amplifier assembly, comprises at least one first module and at least one second module. The first and second modules are optically connected to one another. The first module is an Optical Power Supply module. The first module comprises an optical circuit including: (i) at least two optical ports, (ii) at least a one light source having a first wavelength known to cause amplification in rare earth doped optical fiber located between said optical ports; (iii) at least one bidirectional light combiner/separator optically coupled to the light source, and (iv) at least one position for a directional optical attenuator, located between the two optical ports. The second module is an amplification module. The second module comprises an optical circuit including (i) at least two optical ports, and (ii) at least one amplification medium.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0011] The drawings provided illustrate, schematically, numerous embodiments of the present invention. The drawings are provided for further understanding, and are meant to be exemplary in nature, and not exhaustive.  
     [0012]FIGS. 1 a - 1   n  illustrate schematically a plurality of amplifier modules. More specifically, FIGS. 1 a ,  1   b ,  1   c  illustrate, schematically, three embodiments of an Optical Power Supply module. FIG. 1 d  illustrates, schematically, an embodiment of an Amplification module. FIGS. 1 e  and  1   f  illustrate, schematically, embodiments of Monitoring and Access modules. FIGS. 1 g ,  1   h , and  1   i  illustrate, schematically, three embodiments of an Optical Processing module. FIG. 1 j  illustrates, schematically, an embodiment of a Telemetry Add/Drop module. FIGS. 1 k ,  1   l ,  1   m,    1   n  illustrate, schematically, additional embodiments of an Optical Power Supply module.  
     [0013]FIG. 2 illustrates, schematically, a first embodiment of a first optical amplifier, comprised of a first Optical Power Supply module, optically connected to a first Amplification module  20 .  
     [0014]FIG. 3 illustrates, schematically, a second embodiment of a second optical amplifier. The optical amplifier of the second embodiment comprises a first Optical Power Supply first module, optically connected to a first Amplification module, further optically connected to a first Monitoring and Access module.  
     [0015]FIGS. 4 through 14 illustrate, schematically, other embodiments of optical amplifiers, each comprised of unique combinations of configurable amplifier modules.  
     [0016]FIGS. 15 a - 15   r  illustrate, schematically, examples of several configurations of optical circuits  10 ′ and  11 ′ within three embodiments of the Optical Power Supply modules shown in FIGS. 1 a - 1   c.    
     [0017]FIGS. 16 a - 16   r  illustrate, schematically, some examples of several configurations of the optical circuits  30 ′ and  31 ′ within the two embodiments of the Monitoring and Access modules illustrated in FIGS. 1 e  and  1   f.    
     [0018]FIGS. 17 a - 17   q  illustrate, schematically, some examples of configurations of the optical circuits  40 ′ and  41 ′ within the three embodiments of the Optical Processing modules illustrated in FIGS. 1 g ,  1   h , and  1   i.    
     [0019]FIG. 18 illustrates, schematically, yet another embodiment of an optical amplifier of the present invention.  
     [0020]FIGS. 19 a - 19   l  illustrate, schematically, nine embodiments of optical connections between modules.  
     [0021]FIGS. 20 a - 20   i  illustrate, schematically, nine embodiments of multiple optical circuits provided within various amplifier modules, each optical circuit comprising it&#39;s own independent optical ports and optical components.  
     [0022]FIGS. 21 a - 21   i  illustrate, schematically, eight embodiments of multiple optical circuits provided within various amplifier modules, each optical circuit possessing it&#39;s own independent optical ports, but sharing at least one optical component.  
     [0023]FIGS. 22 a - 22   d  illustrates, schematically, examples of the configurations of selected modules shown in FIGS. 20 a - 20   i  and  21   a - 21   i.    
     [0024]FIGS. 23 a - 23   c  illustrates, schematically, examples of the novel integration of the Optical Power Supply module.  
     [0025]FIGS. 24 a - 24   c  illustrates, schematically, examples of the novel integration of the Monitoring and Access module.  
     [0026]FIGS. 25 a - 25   g  illustrates, schematically, alternative embodiments of the Amplification modules.  
     [0027]FIGS. 26 a - 26   b  illustrates, schematically, two embodiments of an optical amplifier that includes an optional dispersion compensation module.  
     [0028]FIG. 27 a  illustrates, schematically, an embodiment of an optical amplifier that includes an optional interface module.  
     [0029]FIG. 27 b  illustrates, schematically, an embodiment of an optical amplifier that includes an optional interface module that is utilized as a support base for other modules.  
     [0030]FIG. 28 a  illustrates, schematically, an embodiment of an optical amplifier that includes color coding of modules by module type to facilitate identification.  
     [0031]FIG. 28 b  illustrates, schematically, an embodiment of an optical amplifier that includes passive (readable) encoding of information regarding the manufactured modules to facilitate identification.  
     [0032]FIG. 28 c  illustrates, schematically, an embodiment of an optical amplifier that includes an active (read/writeable) encoding of information regarding the manufactured modules to facilitate identification.  
     [0033]FIGS. 29 a - 29   c  illustrate, schematically, several embodiments of an optical amplifier modules that include mechanical registration to facilitate alignment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0034] Optical amplifiers for telecommunication networks are typically uniquely designed to meet specific customer needs in specific customer applications, according to the amplifier&#39;s role in each customer&#39;s proprietary system. There is very little commonality of either the optical designs or the physical embodiments between different amplifiers manufactured for either different customers and or different applications. Custom design efforts add significant time and cost to the development of each product, and prevent efficient manufacturing scale from being achieved. Custom designs also create inventory risk, as unsold product for one customer/application cannot be sold to another. Finally, custom designed amplifiers hinder future upgrade capability and hardware reuse.  
     [0035] It is therefore desirable to simplify the design and manufacture of optical amplifiers by identifying the minimum, common “building blocks”, that could be used to make a wide variety of optical amplifiers  1 . As used herein, the term “modules” means the building blocks. Several examples of such building blocks or modules are illustrated in FIGS. 1 a - 1   j . According to an embodiment of the present invention, this approach requires the definition of a top level, fully operable total optical amplifier circuit which includes all the desired amplifier features. An optical amplifier circuit is defined as a collection of optical and electro-optic components and light paths traversing between and through, to, and from these optical and electro-optic components. This total optical amplifier circuit is subsequently partitioned into commonly utilized, smaller optical circuits  10 ′,  11 ′,  20 ′,  30 ′,  31 ′,  40 ′,  41 ′,  50 ′, that can be incorporated into amplifier modules  10 ,  11 ,  12 ,  20 ,  30 ,  31 ,  40 ,  41 ,  42  and  50 , shown in FIGS. 1 a - 1   j . These modules can be efficiently manufactured and combined to create a variety amplifiers  1 , as shown in FIGS.  2 - 14   b . Each amplifier module performs a specific function, or set of functions, and can interact with other modules.  
     [0036] Variety in features within each module is accomplished by selective configuration of the modules. That is, each module is designed to be configurable. That is, the modules have optical circuits that are designed to optionally allow the inclusion or exclusion of certain optical, opto-electrical, and electronic components during manufacturing, without design changes. The manufactured modules are operable with or without the optional components. Examples of how the modules  10 ,  11 ,  12 ,  20 ,  30 ,  31 ,  40 ,  41 ,  42 ,  50  can be selectively configured in order to achieve specific module and optical circuit features are shown schematically In FIGS.  15 - 17 , and are described in detail below.  
     [0037] Used together, unique combination of common, yet configurable, optical amplifier modules allows for the manufacture of a wide variety of commercially available optical amplifiers as illustrated schematically in FIGS.  5 - 14 , and described in detail below.  
     [0038]FIG. 1 a  illustrates, schematically, a first embodiment of an Optical Power Supply module  10 , including a Optical Power Supply optical circuit  10 ′. This optical circuit  10 ′ includes a first light source  101 ′ having a first wavelength λ 1 , a first bidirectional light combiner/separator  102 ′ optically connected to the light source  101 ′, and a directional optical attenuator  103 ′ optically connected to the bidirectional light combiner/separator  102 ′. A light source  101 ′ is an electro-optical device that generates optical radiation, that radiation having a wavelength known to cause amplification in rare earth doped optical medium, such as optical fiber. A bidirectional light combiner/separator  102 ′ is an optical device that combines two or more light paths. Conversely, the same device, allowing light to pass in the reverse direction, can separate light into two or more light paths. Such separation can be according to wavelength, as in a wavelength division multiplexer, or according to polarization, as in a polarization combiner. An example of such an optical device is wavelength division multiplexer (WDM)  102 . A directional optical attenuator  103 ′ is an optical device that can function only as a one-way optical filter. An example of such an optical device is an optical isolator  103 . In this and all other illustrations, the direction of passing-through light is indicated by the pointed end of the figure symbolizing the optical isolator  103 . Furthermore, it is understood that the orientation of this optical component may be optionally reversed in the optical circuit in order to accomplish the same function in the opposite direction.  
     [0039] In this embodiment, the first light source  101 ′ is a laser source  101 , having a wavelength of approximately 960 nm, 980 nm or 1480 nm. Such pump laser sources are available, for example, from Corning Lasertron, located in Bedford, Mass. Optical laser sources of other wavelengths may also be utilized. In this embodiment, the first bidirectional light combiner/separator  102 ′ is wavelength division multiplexer  102  (WDM), and the directional optical attenuator  103 ′ is optical isolator  103 . Other optical components with the same or similar function can be substituted for laser source  101 , wavelength division multiplexer  102  (WDM), and optical isolator  103 . WDMs are available, for example, from Corning Incorporated, located in Corning, N.Y.  
     [0040] The isolator  103  is optically connected to optical port  10   a , and the wavelength division multiplexer  102  is connected to optical port  10   b . An optical port provides a connection path for optical communication. More specifically, an optical port in a module provides external optical access to the optical circuit of the module. Such optical access allows for connection between optical circuits of two connected modules. Examples of optical ports include the input/output surface of a waveguide, such as end faces of optical fiber pigtails. Other optical ports may include apertures, input/output surfaces of a planar waveguide, lenses or mirrors facing the outside of the module.  
     [0041]FIG. 1 b  illustrates a second embodiment of an Optical Power Supply module  11 . The second embodiment of the Optical Power Supply module is similar to the Optical Power Supply module  10  described in FIG. 1 a , but has an optical circuit  11 ′ that includes two laser sources  101  optically connected to a second wavelength division multiplexer  102 . The second wavelength division multiplexer  102  is optically connected to the first wavelength division multiplexer  102 , and to optical port  11   b . Both laser sources are of a wavelength known to cause amplification in rare-earth doped optical fiber, and may provide a laser source wavelength of, for example, approximately 980 nm or 1480 nm. It is known that the laser source wavelength may vary, due to manufacturing tolerances, by ±5 nm, and preferably by less than ±1 nm, and most preferably by ±0.5 nm or less. The first wavelength division multiplexer  102 , is optically connected to the isolator  103 . The isolator  103  is optically connected to optical port  1   a.    
     [0042]FIG. 1 c  illustrates a third embodiment of an Optical Power Supply module  12 . The Optical Power Supply module  12  is similar to the Optical Power Supply modules  10  and  11  shown in FIGS. 1 a  and  1   b . Optical Power Supply module  12  includes the optical circuits  10 ′ and  11 ′ shown in FIGS. 1 a  and  1   b . The optical circuit  10 ′ possesses independent optical ports  10   a  and  10   b  from the optical circuit  11 ′, yet both are contained in the same module  12 .  
     [0043]FIG. 1 d  illustrates, schematically, one embodiment of Amplification module  20 . The optical circuit  20 ′ includes an amplification medium  104 ′ optically connected to two optical ports  20   a ,  20   b . In this embodiment, the amplification medium  104 ′ is a coil of rare earth doped fiber  104 . More specifically, in this embodiment, the optical fiber is doped with erbium. Other optical components with the same or similar function can be substituted for the optical fiber  104 . For example, a planar waveguide gain medium may also be utilized.  
     [0044]FIG. 1 e  illustrates, schematically, a first embodiment of a Monitoring and Access module  30 , including a Monitoring and Access optical circuit  30 ′, including a wavelength division multiplexer  102 , optically connected to two optical ports  30   a ,  30   b . The wavelength division multiplexer  102  is further optically connected to a first optical tap  105 ′. The optical tap  105 ′ is further optically connected to an optical isolator  103 , and to a second, optical tap  105 ′. In this embodiment, the first optical tap  105 ′ is a three port optical tap coupler  105 , and the second optical tap  105 ′ is a four port optical tap coupler  105 , which are each, in turn, connected to an associated optical sensor  107 ′. The three port optical tap  105  is further optically connected to an optical port  30   c , and the isolator  102  is optically connected to an optical port  30   d.    
     [0045] An optical tap  105 ′ is an optical device whose function is to separate light according to predetermined optical power ratios, predominantly independent of wavelength or polarization. An example of such a device is a multiclad or fused biconic taper coupler. These couplers are available, for example, from Corning Incorporated, of Corning N.Y.  
     [0046] An optical sensor  107 ′ is an opto-electronic device with a light sensitive material that provides electrical signal output that indicates the power of the light incident on this device. An example of an optical sensor is a photodiode, or a photodiode with further electronic signal modification.  
     [0047] In this embodiment, the optical sensor  107 ′ is a photodiode  107 . Other optical components with the same or similar function can be substituted for the taps  105 , and photodiode  107 . For example, the taps could be micro-optic taps or planar waveguide taps, available, for example, from JDS Uniphase Corporation, of San Jose, Calif. The photodiode  107  may include a photodiode with a integrated electronics for electronic signal processing. Such photodiodes are available, for example, from Epitaxx Inc, West Trenton, N.J. Integrated optical taps, incorporating a photodiode, are available, for example, from DiCon Fiberoptics Inc, Berkeley, Calif.  
     [0048]FIG. 1 f  illustrates a second embodiment of a Monitoring and Access module  30 . This second embodiment of a Monitoring and Access module  30  includes an optical circuit  31 ′ similar to the optical circuit  30 ′ described in FIG. 1 e , but configured to include an additional photodiode  107  instead of an optical port  30   c.    
     [0049]FIG. 1 g  illustrates, schematically, one embodiment of an Optical Processing module  40 , including the Optical Processing optical circuit  40 ′, comprising an optical isolator  103 , optically connected to a first optical port  40   a  and a light filter  108 ′. The light filter  108 ′ is further optically connected to a second optical port  40   b.    
     [0050] A light filter  108 ′,  109 ′ is an optical device that provides light attenuation in at least one direction—i.e., it attenuates light that passes from the filter input to the filter output. The filtering strength, and the wavelength dependence and/or or polarization dependence of the filtering effect is determined by the type of filter employed. The filter may alternatively be a wavelength dependent filter, or predominantly wavelength independent filter. The light filter, whether of a wavelength dependent nature, or of a wavelength independent nature, may also be of a fixed nature, a settable nature, or of a dynamically adjustable nature. A wavelength dependent filter is a filter that transmits and/or reflects light based on light&#39;s wavelength. A predominately wavelength independent filter is a filter that reduces the intensity of incident light substantially equally across the wavelengths of interest. An example of such a filter is a VOA or a neutral density filter.  
     [0051] A filter of a fixed nature is a filter that has pre-determined, known, and non-adjustable filtering characteristics. These include, for example, a fixed gain flattening filter.  
     [0052] A slope adjusting filter is a filter with a wavelength dependent attenuation that can provide adjustment of the slope of the wavelength dependence of attenuation with wavelength (dL(λ)/dλ, where L(λ) is Loss as a function of wavelength, and λ is wavelength).  
     [0053] An example of a fixed, predominantly wavelength independent light filter device is a neutral density filter, or a fixed attenuator, available, for example, from RIFOCS Corp, of Camarillo, Calif.  
     [0054] A filter of a settable nature has adjustable filtering characteristics, but is implemented in such a way as to allow final adjustment at the time of manufacture, and is not intended for dynamic adjustment following manufacture. An example of a settable, predominantly wavelength independent light filter device is a mechanically tuned variable optical attenuator, tuned with a set-screw, available, for example, from JDS Uniphase Corporation of San Jose, Calif. as model number MV 50.  
     [0055] A filter of a dynamically adjustable nature has adjustable filtering characteristics, and is implemented in such a way as to allow active modulation of the filtering characteristics in situ based on a dynamically changing control system. An example of a dynamically adjustable, wavelength dependent light filter device is a dynamic gain flattening filter. Such a filter is available, for example, from Corning Incorporated, of Corning, N.Y. Such a filter may also be a dynamic slope-adjusting filter driven by a control circuit. Such dynamic slope adjusting filters are available, for example, from Coadna Photonics Inc., of San Jose, Calif. An example of a dynamically adjustable, predominantly wavelength independent light filter device is a variable optical attenuator driven by a control circuit. Such a variable optical attenuator is available, for example, from Corning Incorporated, of Corning, N.Y.  
     [0056] In this embodiment, the light filter  108 ′ is gain flattening filter (GFF)  108 . Other optical components with the same or similar function can be substituted for the gain flattening filter  108 . For example, the light filter  108 ′ could be a thin film dielectric filter-based gain flattening filter operating in transmission or reflection. Such a filter could also be a fiber Bragg grating-based gain flattening filter operating in transmission or reflection available. Alternatively, a long period fiber Bragg grating-based gain flattening filter may also be utilized. Alternatively, fiber evanescent coupler-based gain flattening filter may also be used. Such filters are available, for example, ITF Optical Technologies of Montreal, Canada.  
     [0057]FIG. 1 h  illustrates, schematically, a second embodiment of an Optical Processing module  41 . This second embodiment of an Optical Processing module  41  includes the optical circuits  40 ′ and  42 ′, as illustrated in FIGS. 1 g  and  1   i . However, the optical circuit  40 ′ is optically connected to the optical circuit  42 ′ between the gain flattening filter  108  and the first three port optical tap  105 . This first optical tap  105  is connected directly to the GFF  108 .  
     [0058]FIG. 1 i  illustrates, schematically, a third embodiment of an Optical Processing module  42 , including the Optical Processing optical circuit  42 ′. The Optical Processing optical circuit  42 ′ comprises a first, three port optical tap  105  optically connected to optical port  42   a , a first photodiode  107 , and a light filter  109 ′. In this embodiment, the light filter  109 ′ is a variable optical attenuator (VOA)  109 . The VOA  109  is further optically connected to a second, three port optical tap  105 . The second three port optical tap  105  is further optically connected to a second photodiode  107  and a second optical port  42   b . Other optical components with the same or similar function can be substituted for the variable optical attenuator  109 . The optical amplifier may also utilize a Telemetry Drop/Add module  50 . The exemplary Telemetry Drop/Add module  50  is illustrated schematically in FIG. 1 j  and includes two locations  102   a  for wavelength division multiplexer (WDM) components. Either one or both of these locations  102   a  may be receive a WDM at the manufacturing stage. For example, the Telemetry Add/Drop module  50  of FIG. 1 j  comprises two wavelength division multiplexers  102 , each optically connected to three optical ports  50   a - c  and  50   d - f.    
     [0059]FIG. 1 k  illustrates, schematically, a fourth embodiment of an Optical Power Supply module  13 , including a Optical Power Supply optical circuit  12 ′. Optical Power Supply module  13 , is similar to the Optical Power Supply module illustrated in FIG. 1 a , except that Optical Power Supply module  15  utilizes one external pump laser source  101 , instead of an internal laser source  101 . Thus, optical circuit  12 ′ includes an optical signal port  12   a  that provides a connection to an external optical pump source  101  that forms a part of the optical circuit  13 ′ of the additional pump module  14 . The optical circuit  12 ′ of the an Optical Power Supply module  13  also includes a bidirectional light combiner/separator such as a wavelength division multiplexer WDM  102  optically connected to the light source  101  via optical ports  12   c  and  13   a , and a directional optical attenuator such as an isolator  103  optically connected to the wavelength division multiplexer (WDM)  102 . The wavelength division multiplexer WDM  102  combines optical signal power and optical pump power received through the optical ports  12   a  and  12   c , respectively and provides it to the optical port  12   b.    
     [0060] A fifth embodiment of the Optical Power Supply module  15  is shown in FIG. 11. Optical Power Supply module  15 , is similar to the Optical Power Supply module illustrated in FIG. 1 b , except that Optical Power Supply module  15  utilizes one external pump laser source  101 , in addition to the internal laser source  101 . In this embodiment, the external laser source  101  is provided in additional pump module  14 .  
     [0061]FIG. 1 m  illustrates an Optical Power Supply module  16 . This Optical Power Supply module contains a laser source  101 , a first and a second wavelength division multiplexer (WDM)  102 , and two optical isolators  103 . The first wavelength division multiplexer (WDM)  102  is optically coupled to the optical port  15   b . The second wavelength division multiplexer (WDM)  102  is optically coupled to the optical port  15   d . The laser source  101  is connected to the optical tap  105  which splits the optical pump power provided by the laser source  101  into two directions. One portion of the optical pump power is provided to the first wavelength division multiplexer WDM  102  and another portion of the optical pump power is provided to the second a wavelength division multiplexer WDM  102 . It is noted that optical isolators  103 , may be present in the locations  103   a , but in a reverse orientation. Finally, the optical isolator  103  which is located between the second WDM  102  and the optical port  15   c  may also be moved so as to be positioned between the optical port  15   d  and the second WDM  102 .  
     [0062]FIG. 1 n  illustrates another embodiment of the Optical Power Supply module. The Optical Power Supply module  17  of figure in includes two optical circuits, i.e.—optical circuits  15 ′ and  12 ′. The Optical circuit  15 ′ is identical to the optical circuit of Optical Power Supply module  16  of FIG. 1 m . The Optical circuit  12 ′ is similar to the optical circuit  12 ′ of the Optical Power Supply module  13  illustrated in FIG. 1 k , but has the optical isolator  103  oriented in an opposite direction.  
     [0063]FIG. 2 illustrates, schematically, one embodiment of a first optical amplifier  1 A of the present invention. The optical amplifier  1 A of the first embodiment includes at least one Optical Power Supply module  10  and at least one Amplification module  20 . The first and second modules  10 ,  20  are optically connected to one another.  
     [0064] Optical Power Supply module  10  includes optical circuit  10 ′ that comprises: (i) at least one optical port  10   a  and at least one optical port  10   b , (ii) at least a first light source  101 ′ having a first wavelength known to cause amplification in rare earth doped optical fiber  104 , such as a laser source  101  for example; (iii) at least one a bidirectional light combiner/separator  102 ′, such as a wavelength division multiplexer (WDM)  102  for example, and (iv) at least one position  103   a  for a directional optical attenuator  103 ′, such as an optical isolator  103  for example. In this embodiment, the optical isolator position  103   a  does not include optional optical isolator  103 , and the wavelength division multiplexer  102  is optically connected to optical port  10   a.    
     [0065] As illustrated here and in subsequent figures, a position that contains an associated optical or electro-optic component is shown as an outline of the component, which is filled with dark gray (or black in the case of optical ports). A position that does not contain the associated component is shown as a transparent outline of this component.  
     [0066] The optical circuit  10 ′ of the Optical Power Supply module  10  in FIG. 2 does not include the isolator  103  and, therefore, does not provide optional optical isolation feature. However, the optical circuit  10 ′ of the Optical Power Supply module  10  in FIG. 2 is fully operable without the directional optical attenuator  103 ′. The design of this module allows for the optional addition of this optical component during manufacture, without design changes, to upgrade the capability of the optical supply module  10  to include the optical isolation feature. Thus, the Optical Power Supply module  10  is configurable at the manufacturing stage.  
     [0067] The light source  101 ′ may be a laser source  101  operable at approximately 980 nm, or 1480 nm for example. If non-erbium doped amplification medium is used, for example Thulium doped fiber, the appropriate laser source wavelengths are approximately 1050 nm, 1400 nm, or 1550 nm. If Neodymium, or Holmium-doped amplification medium is used, the laser source wavelengths are approximately 800 nm, or 1300 nm, respectively. If Raman amplification is utilized, optical laser sources in wavelength range of 1425 nm to 1510 nm may be used. As stated above, the term “approximately” means that laser source wavelength variation is within ±5 nm of the above specified wavelengths. It is preferable that it is within ±2 nm, and more preferably within ±1 nm of the above specified wavelengths. It is most preferable that they be within ±0.5 nm of their specified wavelengths. Multiple laser sources of the same or different wavelengths may be utilized.  
     [0068] Amplification module  20  includes optical circuit  20 ′ comprising (i) at least one optical port  20   a  and at least one optical port  20   b , (ii) and at least one amplification medium  104 ′. The amplification medium  104 ′ in this embodiment is an erbium doped optical fiber coil  104 . However, other rare-earth dopants may also be utilized. Furthermore, a planar waveguide amplification medium may also be utilized.  
     [0069] The modules  10  and  20  are mounted to either a common support structure or to each other. A support structure is a mechanical support, such as a support board, base module, rack, frame, rod, chassis, or shelf. In one embodiment, modules may take a form of optical circuit boards that plug into a “mother board” and are then placed into the amplifier housing. In another embodiment, these modules may be stacked together mechanically, interconnecting to each other&#39;s housing, in a manner of Lego™ blocks, for example. In yet another embodiment, these modules may be located independently within a larger frame, yet optically and electrically connected so as to form the desired optical and electrical circuits.  
     [0070] An optical amplifier of the present invention may also include at least one, third, Monitoring and Access module  30 . As an example, FIG. 3 illustrates, schematically, a second embodiment of an optical amplifier  1 B, comprised of a first Optical Power Supply first module  10 , optically connected to a first Amplification module  20 , further optically connected to a first Monitoring and Access module  30 .  
     [0071] The Monitoring and Access module  30  shown in FIG. 3 includes an optical circuit  30 ′ comprising: (i) at least one optical port  30   a  and at least one optical port  30   b , (ii) at least one, first optical tap  105 ′ (such as four port optical tap coupler  105 ), (iii) at least one optical sensor  107 ′ (such as photodiode  107 ) associated with each tap, and (iv) at least one location with a capacity to accept an optical component such as a WDM  102 , isolator  103 , or tap coupler  105 , in order to provide at least one additional optical function. More specifically, this optical function is provided by inclusion of least one additional optical component that forms part of the optical circuit and is connected to the first optical tap  105 ′. The optical sensor  107 ′ is preferably an opto-electronic device with a light sensitive material connected to an electrical apparatus for the purposes of sensing the power of the incident light and converting it to an electrical signal. The electrical signal output is dependent on the power of the incident light. For example, optical sensor  107 ′ could be photodiode  107 . The optical sensor  107 ′ may also include further electronic signal modification. The additional optical function may be bidirectional light combination/separation, optical tap coupling, or directional optical attenuation, provided for example, by a WDM  102 , a tap coupler  105 , or optical isolator  103 , respectively.  
     [0072] In this embodiment, the optical circuit  30 ′ of the Monitoring and Access module  30  is minimally configured, i.e. it includes only the minimum filled positions. Specifically, the isolator position  105   a , the WDM position  102   a , the three port optical tap position  105   a , and one of the photodiode positions  107   a , do not contain the associated isolator  103 , wavelength division multiplexer  102 , tap  105 , and photodiode  107  as described above. This is illustrated in the figures by transparent outlines of these associated optical and electro-optic components. Consequently, the four port optical tap  105  is optically connected to the photodiode  107 , optical ports  30   c , and  30   d . The last optical connection from the four port optical tap  105  may optionally be optically connected to optical port  30   a  or  30   b . However, alternative configurations of the Monitoring and Access module may also be utilized and are shown in FIGS. 1 e  and  1   f . These figures illustrate that the positions  102   a ,  105   a , and  103   a  have been filled by the appropriate optical components, such as taps  105 , WDMs  102 , and isolators  103 .  
     [0073] The first, second, and third modules are optically connected so as to complete the overall optical circuit of the optical amplifier  1 B. These modules are mounted to either a common support structure, or to each other, as described previously.  
     [0074] According to additional embodiments of the present invention, an optical amplifier further includes at least one, fourth module  40 ,  41 ,  42 . These modules  40 ,  41 ,  42  are illustrated in FIGS. 1 g - 1   i . The modules  40 ,  41 ,  42 , are referred to as Optical Processing modules, and include at least one of the optical circuits  40 ′,  42 ′. The optical circuits  40 ′,  42 ′ include: (i) at least one first optical port  40   a ,  42   a , and at least one second optical port  40   b ,  42   b , (ii) at least one light filter  108 ′,  109 ′, and (iii) a location with the capacity to include an optical and/or opto-electronic component that provides at least one additional optical and/or opto-electronic function. This additional optical component, when present, forms a part of the optical circuit  40 ′,  41 ′ and is connected to the light filter  108 ,  109 . The additional optical function may be, for example, optical tap coupling, directional optical attenuation, or sensing.  
     [0075] Two embodiments of an optical amplifier  1 C,  1 C′ utilizing one or more Optical Processing modules are shown in FIGS. 4 a  and  4   b . All of the amplifier modules are optically connected so as to complete the overall optical circuit of the optical amplifier  1 C,  1 C′. These modules are mounted to either a common support structure, or to each other, as described previously.  
     [0076] Furthermore, the optical amplifier may include more than one of each type of module. For example, the optical amplifier  1 C depicted in FIG. 4 a  includes two Monitoring and Access modules  30 , two Optical Power Supply modules  12 , two Amplification modules  20 , and one optical processing module  41 . The optical amplifier  1 C depicted in FIG. 4 b  includes two Monitoring and Access modules  30 , two Optical Power Supply modules  12 , two Amplification modules  20 , and two optical processing modules  40  and  42 .  
     [0077] The optical amplifier embodiments of FIGS. 4 a  and  4   b  are functionally similar to each other, and will serve as a reference for comparison with other, similar amplifiers illustrated in FIGS.  5 - 14 , and discussed below.  
     [0078] As illustrated in FIG. 4 a , Optical Power Supply module  12  comprises optical circuits  10 ′ and  11 ′, each with respective independent optical ports  10   a ,  10   b  and  11   a ,  11   b . This Optical Power Supply module  12  is optically connected to a first Amplification module  20 , a first Monitoring and Access module  30 , and a first Optical Processing module  41 . Optical port  10   a  of the optical circuit  10 ′ of the first Optical Power Supply module  12  is optically connected to optical port  30   d  of the first Monitoring and Access module  30 . Optical port  10   b  of the first Optical Power Supply module  12  is optically connected to optical port  20   a  of the of the first Amplification module  20 . Optical port  11   b  of the first Optical Power Supply module  12  is optically connected to optical port  20   b  of the of the first Amplification module  20 . Optical port  11   a  of the first Optical Power Supply module  12  is optically connected to optical port  40   a  of the first Optical Processing module  41 . Furthermore, a second Optical Power Supply module  12  includes optical circuits  10 ′ and  11 ′, each with independent optical ports  10   a ,  10   b  and  11   a ,  11   b , is optically connected to the first Optical Processing module  41  and a second Amplification module  20 , and a second Monitoring and Access module  30 . Optical port  10   a  of the optical circuit  10 ′ of the first Optical Power Supply module  12  is optically connected to optical port  42   b  of the first Optical Processing module  41 . Optical port  10   b  of the second Optical Power Supply module  12  is optically connected to optical port  20   a  of the of the second Amplification module  20 . Optical port  11   b  of the second Optical Power Supply module  12  is optically connected to optical port  20   b  of the of the second Amplification module  20 . Optical port  11   b  of the first Optical Power Supply module  12  is optically connected to optical port  30   d  of the second Monitoring and Access module  30 . In this embodiment, all optical positions in circuits  10 ′,  11 ′,  20 ′,  40 ′, and  42 ′ are filled.  
     [0079] Monitoring and Access module  30  of the optical amplifiers  1 C,  1 C′ shown in FIGS. 4 a  and  4   b  provides band-splitting of telemetry channels, and provides bidirectional signal power monitoring of the input and output optical power. For example, in Monitoring and Access module  30  on the left side of FIG. 4 b , optical Port  30   a  is the optical input to the device for signal and telemetry supervisory channel. From WDM  102 , the telemetry supervisory channel is output at optical Port  30   b . The optical signal quality is monitored electrically and optically via the photodiodes  107  and the optical output at optical port  30   c . For example, photodiodes  107  connected to the 4 port optical tap  105  measures input optical signal power, and photodiode  107  connected to the 3 port optical tap  105  measures optical back-reflectance.  
     [0080] Optical Processing module  41  includes an isolator  103  that optically isolates the first rare-earth-doped fiber of the first Amplification module  20  coil from the second coil of the second Amplification module  20  with respect to the backwards traveling amplified spontaneous emission and signal power. This leads to amplifiers with lower noise figure and superior multi-path interference properties. The GFF  108  of the Optical Processing module  41  (FIG. 4 a ) flattens the resultant gain spectrum provided by the two coils. It is understood that other amplification media may also be used. They are, for example, Thulium-, Neodymium-, or Holmium-doped fibers. Furthermore, the amplification medium may be present in a planar waveguide, instead of fiber waveguide form. Finally, if an amplifier is Raman amplifier, amplification medium is transmission fiber and the optical laser sources of Optical Power Supply module  10 ,  11 ,  12  utilize optical laser sources  101  in wavelength range of 1425 nm to 1510 nm.  
     [0081] Optical Processing module  41  of FIG. 4 b  includes VOA  109  that adjusts the overall gain of the amplifier to maintain amplifier gain spectrum flatness as the input power to the amplifier changes. The photodiodes  107  in module  42  allow the monitoring of signal power in front of and behind of the VOA  109  to allow for the adjustment of the VOA  109 .  
     [0082] The optical processing modules  40 ,  41 ,  42  are optically and functionally located between the amplification modules  20  so as to optimize optical performance of the amplifier assembly, by minimizing their impact on noise figure NF and on amplifier output power conversion efficiency. The amplifier output power conversion efficiency is defined by how much output power is provided by an amplifier given a certain amount of pump power.  
     [0083] In FIG. 4 b  a first Optical Power Supply module  10  (with optical ports  10   a ,  10   b ), is optically connected to a first Amplification module  20  via optical connection  113  between optical ports  10   b  and  20   a , and to a first Monitoring and Access module  30  via second optical connection  113  between optical ports  10   a  and  30   d . The first Amplification module  20  is further optically connected to a second Optical Power Supply module  11  via optical connection  113  between optical ports  20   b  and  11   b . The second Optical Power Supply module  11  is optically connected to a first Optical Processing module  40  via optical connection  113  between optical ports  11   a  and  40   a . The first Optical Processing module  40  is optically connected to a second Optical Processing module  42  via optical connection  113  between optical ports  40   b  and  42   a . The second Optical Processing module  42  is optically connected to a third Optical Power Supply module  10  via optical connection  113  between optical ports  42   b  and  10   a . The third Optical Power Supply module  10  is optically connected to a second Amplification module  20  via optical connection  113  between optical ports  10   b  and  20   a . The second Amplification module  20  is optically connected to a fourth Optical Power Supply module  11  via optical connection  113  between optical ports  20   b  and  11   b . The fourth Optical Power Supply  11  is optically connected to a second Monitoring and Access module  30  via optical connection  113  between optical ports  11   a  and  30   b . The Optical Processing modules  40 ,  42  in FIG. 4 b  perform the same function as Optical Processing module  41  of FIG. 4 a.    
     [0084] In both embodiments of FIGS. 4 a  and  4   b , only the isolator positions  103   a  in the Monitoring and Access modules  30  are vacant.  
     [0085] In both embodiments, the optical signal enters through port  30   a  of the module  30  and is routed through port  30   d  to the module  10 , through its input port  10   a . The optical signal is then routed through the isolator  103 , which prevents laser source light and amplified spontaneous emission from leaking backwards into the monitoring photodiodes,  107 , and transmission fiber, and is combined within the WDM  102  with the laser source light output by the laser source  101 . The combined signal/laser source light is routed toward the first Amplification module  20 . The optical signal (and laser source light from module  10 ) then enters, through the input port  20   a , the first amplification module  20  and the amplified optical signal exits the first amplification module  20  through the output port  20   b . The amplified signal is routed through module  12  (FIG. 4 a ) or  11  (FIG. 4 b ), where it is separated by a WDM  102 , and provided to one or more Optical processing modules  40 ,  41 ,  42 , through optical port(s)  40   a ,  42   a . The Optical processing modules  40 ,  41 ,  42  are configured to process the amplified signal and to adjust the gain magnitude and the shape of gain spectrum, by adjusting gain, at different wavelengths, by an appropriate amount. The processed, amplified signal exits Optical processing modules,  41  (FIG. 4 a ),  42  (FIG. 4 b ) through the optical ports  42   b  and is routed, through module  12  (FIG. 4 a ),  10  (FIG. 4 b ) to the second amplification module  20 , for further amplification. The signal enters the second amplification module  20  through port  20   a , is further amplified by the rare-earth doped fiber coil  104  and exits the second amplification module  20  through port  20   b . The signal light than is routed through modules  12  and  30  (FIG. 4 a ) or modules  11  and  30  (FIG. 4 b ) and exits the module  30  either through port  30   a  or  30   c . The amplified signal is then ideally disposed for coupling to a transmission fiber, for transmission over a large distance, or for coupling to an additional optical component or module before it is coupled into a transmission fiber or another downstream optical network element.  
     Amplifier Variety  
     [0086] The amplifier modules described herein are used as building blocks to provide a large variety of customized amplifiers. However, because each of the amplifiers is made of common blocks, they can be manufactured quickly and inexpensively, and if a purchase order is canceled, the modules can be re-used to manufacture other amplifiers. Furthermore, the modules themselves are configurable, as needed at the time of manufacture and may or may not utilize optional optical components.  
     [0087] All of the modules may be mounted to either a common support structure or to each other, as described previously.  
     [0088] Thus, according to the present invention, the unique combination of common, yet configurable, optical amplifier modules  10 ,  11 ,  12 ,  20 ,  30 ,  31 ,  40 ,  41 ,  42 ,  50  allows for the manufacture of a wide variety of commercially available optical amplifiers. This is illustrated schematically in FIGS.  5 - 14 , which depict the embodiments of alternate optical amplifiers similar to the optical amplifier embodiments  1 C,  1 C′ illustrated schematically in FIGS. 4 a  and  4   b  and described in detail above. The amplifiers of FIGS.  5 - 14  show variation in the presence or absence of optical amplifier modules  10 ,  11 ,  12 ,  20 ,  30 ,  31 ,  40 ,  41 ,  42 ,  50 , and in the selective configuration (presence or absence of electro-optic and optical components) of the module optical circuits  10 ′,  11 ′,  12 ′,  20 ′,  30 ′,  31 ′,  40 ′,  41 ′,  42 ′,  50 ′, as described previously. The embodiments of the optical amplifiers in each of FIGS.  5 - 14  are similar in functionality to each other, and are compared to the two embodiments of the optical amplifiers  1 C and  1 C′ shown schematically in FIGS. 4 a  and  4   b , respectively, and described in detail above.  
     [0089] For example, in comparison to the optical amplifier  1 C of FIG. 4 a , optical amplifier  1 D of FIG. 5 a  includes a first Optical Power Supply module  12 , a first Amplification module  20 , and a first and second Monitoring and Access modules  30 . The optical circuits included in each module are configured as in FIG. 4 a , except as indicated in the figures. For example, optical circuit  11 ′ of Optical Power Supply module  12  does not contain any optical components. Furthermore, optical circuit  30 ′ in the first Monitoring and Access module  30  does not contain WDM  102 , isolator  103 , three port optical tap  105  with associated photodiode  107 . Furthermore, the second Monitoring and Access module  30  includes optional isolator  103 . Finally, FIG. 5 a  illustrates an alternative connection between optical ports  20   b  and  30   b  which bypasses the Optical Power Supply module  12  entirely in order to minimize connection losses. Likewise, in comparison to FIG. 4 b , amplifier  1 D′ of FIG. 5 b  is comprised of a first Optical Power Supply module  10 , a first Amplification module  20 , and a first and second Monitoring and Access module  30 . Modules  20  and  30  are configured as described for FIG. 5 a . As one can see from the illustration, the amplifier  1 E′ of FIG. 5 b  utilizes a simpler and smaller Optical Power Supply module  10  than that of the amplifier of FIG. 5 a . However, because the configuration of Optical Power Supply module  12  of FIG. 5 a  includes the same optical components as the Optical Power Supply module  10  depicted in FIG. 5 b , it performs the same function and operates identically.  
     [0090]FIGS. 6 a  and  6   b  illustrate, schematically, two alternative embodiments of optical amplifier  1 E,  1 E′.  
     [0091] Amplifier  1 E of FIG. 6 a  is similar to the optical amplifier of FIG. 4 a  because it includes the same modules—i.e., first and second Optical Power Supply modules  12 , first and second Amplification modules  20 , first and second Monitoring and Access modules  30 , and a first Optical Processing module  41 . However, the modules  12 ,  30 , and  41  depicted in FIG. 6 a , are configured differently than those of FIG. 4 a . For example, optical circuit  11 ′ of the first Optical Power Supply module  12  of FIG. 6 a  does not contain any optical components. Furthermore, optical circuit  11 ′ of the second Optical Power Supply module  12  of FIG. 6 a  contains a WDM  102 . In addition the optical circuit  30 ′ in the first Monitoring and Access module  30  of FIG. 6 a  does not contain WDM  102 , isolator  103 , three port optical tap  105  with associated photodiode  107 . Furthermore, the second Monitoring and Access module  30  includes optional isolator  103 . Finally, optical circuit  42 ′ of the first Optical Processing module  41  of FIG. 6 a  does not contain any optical components.  
     [0092] Likewise, in comparison to FIG. 4 b , amplifier  1 E′ of FIG. 6 b  includes a first, second and third Optical Power Supply module  10 , a first and second Amplification module  20 , a first and second Monitoring and Access module  30 , and only a first Optical Processing module  40 . Modules  20  and  30  are configured as illustrated in FIG. 6 a . The third Optical Power Supply module  10  of FIG. 6 b  contains only a WDM  102 .  
     [0093]FIGS. 7 a  and  7   b  illustrate, schematically, two alternative embodiments of optical amplifier  1 F,  1 F′.  
     [0094] Optical amplifier  1 F of FIG. 7 a  is similar to the optical amplifier depicted in FIG. 4 a . The amplifier  1 F illustrated in FIG. 7 a  includes a first and second Optical Power Supply module  12 , a first and second Amplification module  20 , and a first and second Monitoring and Access module  30 , and a first Optical Processing module  41 . The optical circuits included in each module are configured similar to those of FIG. 4 a , except for the differences illustrated in the figure. For example, optical circuit  11 ′ of the first Optical Power Supply module  12  provides for the inclusion of optical components but does not contain a complete set of optical components. Furthermore, optical circuit  30 ′ in the first Monitoring and Access module  30  does not contain WDM  102 , isolator  103 , three port optical tap  105  with associated photodiode  107 . Finally, the second Monitoring and Access module  30  does not contain three port optical tap  105  with associated photodiode  107 .  
     [0095] Amplifier  1 F′ of FIG. 7 b  is similar to the amplifier depicted in FIG. 4 b . The amplifier  1 F′ illustrated in FIG. 7 b  includes a first and second Optical Power Supply module  10 , and a first Optical Power Supply module  11 , a first and second Amplification module  20 , and a first and second Monitoring and Access module  30 , and a first Optical Processing module  40  with a second Optical Processing module  42 . Modules  20  and  30  of the amplifier  1 F′ of FIG. 7 b  are configured as described for FIG. 7 a.    
     [0096]FIGS. 8 a  and  8   b  illustrate, schematically, two alternative embodiments of optical amplifier  1 G,  1 G′.  
     [0097] Optical amplifier  1 G of FIG. 8 a  is similar to the optical amplifier depicted in FIG. 4 a . The amplifier  1 G illustrated in FIG. 8 a  includes a first and second Optical Power Supply module  12 , a first and second Amplification module  20 , a first and second Monitoring and Access module  30 , and a first Optical Processing module  41 . The optical circuits included in each module are similar to those in FIG. 4 a , except for the differences illustrated in the figure. For example, optical circuit  11 ′ of the first Optical Power Supply module  12  provides for the inclusion of optical components but does not contain a complete set of optical components. Optical circuit  11 ′ of the second Optical Power Supply module  12  contains a only first laser source  101 , WDM  102  and isolator  103 . Optical circuit  30 ′ in the first Monitoring and Access module  30  does not contain WDM  102 , isolator  103 , and a three port optical tap  105  with associated photodiode  107 . Finally, the optical circuit  42 ′ of the first Optical Processing module  41  does not contain a first three port optical tap  105  with associated photodiode  107 . As stated above, the included optical and electro-optic components are illustrated using dark blocks, while the unpopulated positions for optical components are shown as outlines of the associated components.  
     [0098] Optical Amplifier  1 G′ of FIG. 8 b  is similar to the amplifier depicted in FIG. 4 b . The amplifier  1 G′ illustrated in FIG. 8 b  includes a first, second and third Optical Power Supply module  10 , a first and second Amplification module  20 , a first and second Monitoring and Access module  30 , a first Optical Processing module  40 , and a second Optical Processing module  42 . Modules  20  and  30  are configured as described for FIG. 8 a . However, the third Optical Power Supply module  10  contains a laser source  101 , a WDM  102 , and an isolator  103  and optical circuit  42 ′ of the second Optical Processing module  42  is configured as described for FIG. 8 a , but the optical circuit  10 ′ for the Optical Power Supply module  10  does not provide for the inclusion of the additional optical components (i.e., additional laser sources, isolators, etc.) as does the Optical Power Supply module  12  of FIG. 8 a.    
     [0099]FIGS. 9 a  and  9   b  illustrate, schematically, two alternative embodiments of optical amplifier  1 H,  1 H′.  
     [0100] Amplifier  1 H of FIG. 9 a  is similar to the optical amplifier depicted in FIG. 4 a . The amplifier  1 H illustrated in FIG. 9 a  includes a first and second Optical Power Supply module  12 , a first and second Amplification module  20 , and a first and second Monitoring and Access module  30 , and a first Optical Processing module  41 . The optical circuits included in each module are configured as in FIG. 4 a , except as indicated. For example, optical circuit  11 ′ of the first Optical Power Supply module  12  and optical circuit  10 ′ of the second Optical Power Supply module  12  provides for the inclusion of optical components but does not contain a complete set of optical components. Furthermore, optical circuit  11 ′ of the second Optical Power Supply module  12  contains a laser source  101 , WDM  102 , and an isolator  103 . Finally, optical circuit  30 ′ in the first Monitoring and Access module  30  does not contain WDM  102 , isolator  103 , or three port optical tap  105  with associated photodiode  107 .  
     [0101] Amplifier  1 H′ of FIG. 9 b  is similar to the optical amplifier depicted in FIG. 4 b . The amplifier  1 I illustrated in FIG. 9 b  includes a first and second Optical Power Supply module  10 , a first and second Amplification module  20 , and a first and second Monitoring and Access module  30 , a first Optical Processing module  40 , and a second Optical Processing module  42 . Modules  20  and  30  are configured as described for FIG. 9 a . The second Optical Power Supply module  10  contains an isolator  103  in the reverse orientation, and is optically connected between optical port  20   a  of the second Amplification module  20  and optical port  30   b  of the second Monitoring and Access module  30 .  
     [0102]FIGS. 10 a  and  10   b  illustrate, schematically, two alternative embodiments of optical amplifier  1 I,  1 I′.  
     [0103] Amplifier  1 I of FIG. 10 a  is similar to the amplifier depicted in FIG. 4 a . The amplifier  1 I illustrated in FIG. 10 a  includes a first and second Optical Power Supply module  12 , a first and second Amplification module  20 , and a first and second Monitoring and Access module  30 , and a first Optical Processing module  41 . The optical circuits included in each module are configured as in FIG. 4 a , except as indicated. For example, optical circuit  11 ′ of the first Optical Power Supply module  12  provides for the inclusion of optical components but does not contain a complete set of optical components. Furthermore, optical circuit  10 ′ of the second Optical Power Supply module  12  does not contain isolator  103 . Furthermore, optical circuit  11 ′ of the second Optical Power Supply module  12  contains a only first laser source  101 , WDM  102  and isolator  103 . Finally, optical circuit  30 ′ in the first Monitoring and Access module  30  does not contain WDM  102 , isolator  103 , three port optical tap  105  with associated photodiode  107 .  
     [0104] Amplifier  1 I′ of FIG. 10 b  is similar to the amplifier depicted in FIG. 4 b . The amplifier  1 J′ illustrated in FIG. 10 b  is comprised of a first, second and third Optical Power Supply module  10 , a first and second Amplification module  20 , a first and second Monitoring and Access module  30 , a first Optical Processing module  40 , and a second Optical Processing module  42 . Modules  20  and  30  are configured as described for FIG. 10 a . The second Optical Power Supply module  10  does not contain isolator  103 . The third Optical Power Supply module  10  contains isolator  103  in the reverse orientation, and is optically connected between optical port  20   a  of the second Amplification module  20  and optical port  30   b  of the second Monitoring and Access module  30 .  
     [0105]FIGS. 11 a  and  11   b  illustrate, schematically, two alternative embodiments of optical amplifier  1 J, J′.  
     [0106] Amplifier  1 J of FIG. 11 a  is similar to the amplifier depicted in FIG. 4 a . The amplifier  1 J illustrated in FIG. 11 a  includes a first Optical Power Supply module  12 , a first Amplification module  20 , and a first and second Monitoring and Access module  30 . The optical circuits included in each module are configured as in FIG. 4 a , except as indicated. For example, optical circuit  11 ′ of Optical Power Supply module  12  provides for the inclusion of optical components but does not contain a complete set of optical components. Furthermore, optical circuit  30 ′ in the first Monitoring and Access module  30  does not contain WDM  102 , isolator  103 , or three port optical tap  105  with associated photodiode  107 . Finally, the second Monitoring and Access module  30  does not contain WDM  102 .  
     [0107] Amplifier  1 J′ of FIG. 11 b  is similar to the amplifier depicted in FIG. 4 b . The amplifier  1 J′ illustrated in FIG. 11 b  includes a first Optical Power Supply module  10 , a first Amplification module  20 , and a first and second Monitoring and Access module  30 . Modules  20  and  30  are configured as described for FIG. 11 a.    
     [0108]FIGS. 12 a  and  12   b  illustrate, schematically two alternative embodiments of optical amplifier  1 K,  1 K′.  
     [0109] Amplifier  1 K of FIG. 12 a  is similar to the amplifier depicted in FIG. 4 a . The amplifier  1 K illustrated in FIG. 12 a  includes a first and second Optical Power Supply module  12 , a first and second Amplification module  20 , and a first and second Monitoring and Access module  30 , and a first Optical Processing module  41 . The optical circuits included in each module are configured as in FIG. 4 a , except as indicated. For example, optical circuit  11 ′ of the first Optical Power Supply module  12  provides for the inclusion of optical components but does not contain a complete set of optical components; and optical circuit  30 ′ in the first Monitoring and Access module  30  does not contain WDM  102 , isolator  103 , three port optical tap  105  with associated photodiode  107 .  
     [0110] Amplifier  1 K′ of FIG. 12 b  is similar to the amplifier depicted in FIG. 4 b . The amplifier  1 K′ illustrated in FIG. 12 b  includes a first and second Optical Power Supply module  10  and a first Optical Power Supply module  11 , a first and second Amplification module  20 , and a first and second Monitoring and Access module  30 , and a first Optical Processing module  40  with a second Optical Processing module  42 . Modules  20  and  30  are configured as described for FIG. 7 a.    
     [0111]FIGS. 13 a  and  13   b  illustrates, schematically, two alternative embodiments of optical amplifier  1 L,  1 L′.  
     [0112] Amplifier  1 L of FIG. 13 a  is similar to the amplifier depicted in FIG. 4 a . The amplifier  1 L illustrated in FIG. 13 a  includes a first and second Optical Power Supply module  12 , a first and second Amplification module  20 , and a first and second Monitoring and Access module  30 , and a first Optical Processing module  41 . The optical circuits included in each module are configured as in FIG. 4 a , except as indicated. For example, optical circuit  11 ′ of the first Optical Power Supply module  12  provides for the inclusion of optical components but does not contain a complete set of optical components. Furthermore, optical circuit  10 ′ of the second Optical Power Supply module  12  does not contain isolator  103 . Optical circuit  11 ′ of the second Optical Power Supply module  12  contains a only first laser source  101 , WDM  102  and isolator  103 . Optical circuit  30 ′ in the first Monitoring and Access module  30  does not contain WDM  102 , isolator  103 , three port optical tap  105  with associated photodiode  107 . Finally, optical circuit  30 ′ of the second Monitoring and Access module  30  does not contain WDM  102  or isolator  103 .  
     [0113] Amplifier  1 L′ of FIG. 13 b  is similar to the amplifier depicted in FIG. 4 b . The amplifier  1 L′ illustrated in FIG. 13 b  includes a first, second and third Optical Power Supply module  10 , a first and second Amplification module  20 , a first and second Monitoring and Access module  30 , a first Optical Processing module  40 , and a second Optical Processing module  42 . Modules  20  and  30  are configured as described for FIG. 10 a . The third Optical Power Supply module  10  contains an isolator  103  in the reverse orientation, and is optically connected between optical port  20   b  of the second Amplification module  20  and optical port  30   d  of the second Monitoring and Access module  30 .  
     [0114]FIGS. 14 a  and  14   b  illustrate, schematically, two alternative embodiments of optical amplifier  1 M,  1 M′. These embodiments illustrate that an optical amplifier may further include at least one, sixth module  50 . The sixth module  50  is referred to as the Telemetry Add/drop module and includes at least one optical circuit  50 ′. The Telemetry Add/drop module  50  comprises: (i) at least three optical ports  50   a - 50   f , (ii) at least two positions for bidirectional light combiner/separators  102 , either one or both of which may contain the bidirectional light combiner/separators  102 . The bidirectional light combiner/separators  102  may be, for example, wavelength division multiplexers WDMs.  
     [0115] In comparison the optical amplifier of FIG. 4 a , optical amplifier  1 M of FIG. 14 a  includes one Telemetry Add/drop module  50 , optically connected between the two Optical Power Supply modules  12  and the Optical Processing module  41  via optical port connections  113  connecting ports  50   a  to  40   a ,  50   c  to  11   a ,  50   d  to  10   a , and  50   f  to  42   b . The module  50  provides the same telemetry access provided by the Monitoring and Access modules  30  of FIG. 4 a . Consequently, the first and second Monitoring and Access modules  30  of FIG. 14 a  do not contain WDM  102 , as illustrated by the transparent outlines in that figure.  
     [0116] Likewise, in comparison to FIG. 4 b , amplifier  1 M′ of FIG. 14 b  includes one Telemetry Add/drop module  50 , optically connected between the first Optical Processing module  40  and the second Optical Processing module  42  via optical connections  113  connecting optical ports  50   a  to  42   a ,  50   c  to  40   b ,  50   d  to  10   a , and  50   f  to  42   b . Modules  20  and  30  are configured as described for FIG. 10 a.    
     Module Configuration  
     [0117] As described above, the amplifier modules may be configured in a variety of ways. Such configurations are shown, for example, in FIGS. 15 a - 17   q . All of the modules are configured to interact and/or communicate optically and/or electronically with at least one other module. All of the modules have optical, electronic, electrical and/or mechanical ports that are configured to connect or interact with the corresponding port of at least one other module. As stated above, the modules are upgradable because additional optical components may be added to their optical circuit(s). Each of the modules is made so as to be detachable from the other modules, so that another, upgraded module can be substituted in its place. Thus, the amplifiers are upgradable because additional optical components may be added to their optical circuit(s) by way of module upgrade.  
     [0118] The modules contain various optical and electrical components that may be coupled to one another, for example, through fiber splices, fused connections, mechanical fiber connections or through other mechanical couplers, or via free space optical communication.  
     [0119]FIGS. 15 a  through  15   c  illustrate the configurable nature of the optical circuit  10 ′ of the embodiment of the Optical Power Supply module  10  described above and illustrated in FIG. 1 a.    
     [0120] As a specific example, an Optical Power Supply module  10  as shown in FIG. 15 a , contains a laser source  101 , a wavelength division multiplexer (WDM)  102 , and an optical isolator  103 . The optical isolator  103  is in the optical circuit  10 ′ between the optical port  10   a  and the wavelength division multiplexer  102 . That is, the output of isolator  103  and laser source  101  are multiplexed by WDM  102  and provided to the output port  10   b . Module  10  of FIG. 15 a  is configurable during manufacture. For example, in FIG. 15 b , the same module is constructed without the isolator  103 , with the optical circuit  10 ′ bypassing the vacant isolator position  103   a . The laser source output (i.e., the output from the laser source  101  is provided to the wavelength division multiplexer  102  which is directly connected to the optical port  10   b . Likewise, the Optical Power Supply module illustrated in FIG. 15 c  contains the same laser source  101 , wavelength division multiplexer  102 , and optical isolator  103 , as FIG. 15 a , with the optical isolator  103  present in the same location  103   a , but in a reverse orientation. Thus, the Optical Power Supply module  10 , can be configured, as needed, for example in three different ways, but can be manufactured efficiently using the same production line. The optical circuit  10 ′ functions with isolator  103  absent or present, and if present, with isolator  103  in two different orientations. Thus, the Optical Power Supply module  10  is upgradable because its optical circuit contains position(s) and/or connection(s) to a at least one optional optical component such as, for ISO  103 , WDM  102  and/or laser source(s)  101 .  
     [0121] More specifically, as shown in FIG. 15 a , if the construction of the Optical Power Supply module  10  uses conventional, pigtailed components, the optical circuit  10 ′ would include a pigtailed isolator  103  spliced on the input end to an optical port connector  10   a , and on the output end to one of the WDM  102  pigtail inputs. A pigtailed laser source  101  is spliced to the other optical port of the pigtailed WDM  102 . The WDM output pigtail is spliced to the optical port connector  10   b . In order to accomplish the configuration illustrated in FIG. 15 b , the location  103   a  for isolator  103  is left vacant, and the WDM  102  input is spliced to the optical port connector  10   a . To accomplish the configuration of FIG. 15 c , the pigtailed isolator  103  is installed into the designated location  103   a , with the input end spliced to the WDM  102  and the output end spliced to the input port  10   a.    
     [0122] Alternatively, if the construction of the Optical Power Supply module  10  in FIG. 15 a  uses micro-optic components, the optical circuit would include an micro-optic isolator  103  in the path between the optical port connector  10   a  and one of the optical ports on a micro-optic WDM  102 . A laser source diode  101  provides a laser source power that is coupled into the path through the other optical port of the micro-optic WDM  102 . The micro-optic WDM  102  output is directed to the optical port connector  10   b . In order to accomplish the configuration illustrated in FIG. 15 b , the isolator  103  is absent from its position  103   a , and the WDM  102  input is coupled to the optical port connector  10   a . As described above, to accomplish the configuration in FIG. 15 c , the isolator  103  is installed into the designated location  103   a , but in a reverse orientation.  
     [0123] Alternatively, if the construction of the Optical Power Supply module  10  in FIG. 15 a  uses planar waveguides, certain optical components providing specific functions could be optionally produced in the optical path at predetermined locations by the application of electrical, optical, electromagnetic or thermal energy. For example, a grating could be optionally written into an optical fiber that forms a part of the optical circuit of the module.  
     [0124]FIGS. 15 d  through  15   g  illustrate the configurable nature of the optical circuit  11 ′ of the embodiment of the Optical Power Supply module  11  illustrated in FIG. 1 b . Similarly, FIGS. 15 h  through  15   r  illustrate the configurable nature of the optical circuits  10 ′,  11 ′ of the embodiment of the Optical Power Supply module  12  described above and illustrated in FIG. 1 c . As shown in these figures, the Optical Power Supply Module  11  may utilize a plurality of laser sources  101 . These laser sources may be of approximately the same, or alternatively, of different wavelengths.  
     [0125]FIGS. 16 a  through  16   i  illustrate the configurable nature of the optical circuit  30 ′ of the embodiment of the Monitoring and Access module  30  illustrated in FIG. 1 e . FIGS. 16 j  through  16   r  illustrate the configurable nature of the optical circuit  31 ′ of the embodiment of the Monitoring and Access module  31  illustrated in FIG. 1 f.    
     [0126] As a specific example, an Monitoring and Access module  30  as shown in FIG. 16 a , contains a wavelength division multiplexer (WDM)  102  (located in a position  102   a ), a first optical tap  105  (in a first position  105   a ) and connected to the WDM  102 . The first optical tap  105  is further connected to an optical isolator  103  (located in a position  103   a ), to a second optical tap  105  (located in a second position  105   a ), and to a first photodiode  107  (located in a first position  107   a ). The second optical tap  105  is connected to the optical port  30   c  and the second photodiode  107  located in the second position  107   a.    
     [0127] Module  30  of FIG. 16 a  is configurable during manufacture. For example, in FIG. 16 b , the same module is constructed without the isolator  103 , with the optical circuit  30 ′ bypassing the vacant isolator position  103   a . Likewise, the Monitoring and Access module illustrated in FIG. 16 c  contains the same wavelength division multiplexer  102 , and optical tap  105  with associated photodiode  107 , as the module of FIG. 16 a . However, it does not contain the second optical tap  105 , and associated second photodiode  107 .  
     [0128]FIGS. 16 d - 16   f  illustrate other configurations of the Monitoring and Access modules  30 . These embodiments of the module  30  do not contain the WDM  102  present in the modules illustrated in FIGS. 16 a - 16   c . Therefore, the modules illustrated in FIGS. 16 d - 16   f  do not contain an open optical port  30   b . Optical port  30   b  may be plugged to prevent contaminants from entering the module. Other, non-utilized ports, are also shown as a transparent outline.  
     [0129] Furthermore, the Monitoring and Access modules  30  of FIG. 16 f  utilizes only a second optical tap  105  and its associated photodiode  107 , leaving the locations of the isolator  103   a , first optical tap  105   a  and its associated first photodiode  107   a  vacant.  
     [0130] Thus, the Monitoring and Access module  30 , can be configured, as needed, but can be manufactured efficiently using the same production line. The optical circuit  30  functions with the optional components absent or present, and if present, with isolator  103  in two different orientations. The Monitoring and Access modules shown in FIGS. 16 g - 16   i  are similar to the previously described modules  30 , but include isolator  103  in its associated position  103   a.    
     [0131] The Monitoring and Access modules shown in FIGS. 16 j - 16   r  are similar to the previously described modules  30 , but include a position  107   a  for a third photodiode  107  associated with the second tap  105 . In some of these figures, the module includes a third photodiode  107  situated in that position. Thus, as described above, Monitoring and Access modules can be upgraded to include additional, optional components.  
     [0132] The construction of the Monitoring and Access module may utilize conventional, pigtailed components, or micro-optic components, or planar waveguide components. Above.  
     [0133]FIGS. 17 a  through  17   c  illustrate the configurable nature of the optical circuit  40 ′ of the Optical Processing module  40  illustrated in FIG. 1 g . This module includes positions  103   a  and  108   a  for and isolator  103  and GFF  108 , respectively, that may be located between the ports  40   a  and  40   b . As shown in FIGS. 17 a - 17   c , either one, or both, of these positions many be occupied by the associated optical component.  
     [0134]FIGS. 17 d  through  17   h  illustrate the configurable nature of the optical circuit  42 ′ of the Optical Processing module  42  illustrated in FIG. 1 i . This module includes first and second positions  105   a  and  107   a  for first and second optical taps  105  and associated photodiodes  107 , and a VOA  109  located between the first and second optical tap positions  105   a . As shown in FIGS. 17 d - 17   h , either one or both of the optical taps  107  and associated photodiodes  107 , with the VOA  109 , may be present in the module between ports  40   a  and  40   b.    
     [0135]FIGS. 17 i  through  17   q  illustrate the configurable nature of the Optical Processing module  41 , comprised of optical circuit  41 ′ and  42 ′, illustrated in FIG. 1 h . More specifically, FIGS. 17 i - 17   q  illustrate that one or more of the optical or electro-optical components may be absent from its designated position(s). However, as shown above, Optical Processing modules can be upgraded to include these additional optional components.  
     [0136] In another example a Mach-Zehnder interferometer could be optionally written into the optical path within the Optical Processing module where, by thermal tuning for example, control could be exerted over the attenuation of the optical signal. This would provide filtering function similar to that provided by the VOA, while resulting in smaller optical losses and a more compact design.  
     [0137]FIG. 18 illustrates, schematically, a further embodiment of the present invention includes at least one Controller module  60 . The controller module  60  electrically communicates with the electrical and opto-electronic devices contained within the configuration of modules comprising the amplifier, so as to provide necessary power, command, control, alarming, and communication within the amplifier and within the network system. The Controller module  60  may include analog electronic components, digital electronic components, or a combination of both types of components. The Controller module  60  may also implement one or more different control algorithms. Although such algorithms are not described herein they are known to those skilled in the art. The control electronics and other components may be provided as a single module within an amplifier, or as a separate module, or several modules, in a distributed control network system. The controller module  60  is configured to interact with other modules and has input and output ports that correspond to output and input ports of other modules.  
     [0138] Furthermore, FIG. 18 illustrates an optical amplifier  10  comprised of the described modules, wherein at least one selected module includes at least one temperature sensor  110 . An example of such a temperature sensor is a thermistor, for example, from OMEGA Engineering, INC., of Stamford, Conn.  
     [0139] A further embodiment of the present invention includes an optical amplifier further comprised of the described modules, wherein at least one selected module includes at least one (vi) passive or electrically driven heat transfer device  111 . An example of such an electrically driven heat transfer device is a thermo-electric cooler (TEC) with heat convection fins (either heat dissipation or heat application fins). Such heat transfer device is available, for example, from Melcor Thermal Solutions of Trenton, N.J. A resistive heating element such as a thin flexible resistance heating circuit made of Dupont Kapton®, is available for example, from OMEGA Engineering, INC., Stamford, Conn. Alternatively, a heat transfer device may include convection cooling fins augmented by heat pipes, available for example, from Thermacore Inc. of Lancaster, Pa. Finally, any amplifier modules that include electrical or opto-electronic components are provided, as needed, with appropriate electrical connections  112  to communicate electrically with power sources and controllers. The heat transfer device may also be a heat sink that routes excess thermal energy away from the amplifier assembly. Such a heat sink is available, for example, from Aavid Inc. of One Kool Path, Laconia, N.H.  
     [0140] According to an embodiment of the present invention, where a plurality of amplifiers are to be co-located within a network system installation, the amplifier modules utilized in the individual amplifiers may be grouped according to module type. Amplifier modules are mounted to each other or to a common support structure, while being optically and electrically connected to the other modules within the amplifier&#39;s optical circuit.  
     [0141] As shown, for example in FIGS. 19 a - 19   l , according to an embodiment of the present invention, the optical connections  113  between amplifier modules are comprised of at least one of the following types of connections: optical fiber connections, free-space optic connections, or direct contact of optical elements such as planar waveguide devices, lenses, or optical waveguides.  
     [0142]FIGS. 19 a - 19   d  illustrate, schematically, examples of alternative embodiments of optical fiber connections that may be used to optically connect amplifier modules  10 ,  11 ,  12 ,  20 ,  30 ,  31 ,  40 ,  41 ,  42  and  50 . FIG. 19 a  generally illustrates an optically connected first and second module. Specifically, FIG. 19 b  illustrates, schematically, one fiber pigtail  114  from each of any two first and second amplifier modules  10 ,  11 ,  12 ,  20 ,  30 ,  31 ,  40 ,  41 ,  42 ,  50  that are optically connected with a fusion splice  115 . FIG. 19 c  illustrates, schematically, that one fiber pigtail  114  from each of any two amplifier modules  10 ,  11 ,  12 ,  20 ,  30 ,  31 ,  40 ,  41 ,  42 ,  50  is terminated with a mechanical connector  116 . Such mechanical connectors  116  may be male connectors, available, for example, from Diamond USA Inc., of Chelmsford, Mass. The two pigtails are optically connected via a second mechanical mating adapter  117 . Such second mechanical mating adapter  117  may be a female-female mating adapter, available from, for example, Diamond USA Inc. of Chelmsford, Mass. FIG. 19 d  illustrates, schematically, two amplifier modules  10 ,  11 ,  12 ,  20 ,  30 ,  31 ,  40 ,  41 ,  42 ,  50  optically connected via a fiber optic jumper  118 , between fiber optic bulkhead fittings  119  on each of the two modules. Such bulkhead fittings may be in the form of male connectors attached to the modules. Fiber optic jumper  118  are available, for example, from Corning Cable Systems LLC of Hickory, N.C., while fiber optic bulkhead fittings  119  are available from, for example, from Diamond USA Inc., Chelmsford, Mass.  
     [0143] Alternatively, FIGS. 19 e - 19   h  illustrate, schematically, examples of free-space optical connections that may be used to optically connect amplifier modules  10 ,  11 ,  12 ,  20 ,  30 ,  31 ,  40 ,  41 ,  42  and  50 . FIG. 19 e  generally illustrates an optically connected first and second module using free-space optics. Specifically, FIG. 19 f  illustrates, schematically, one focusing/alignment element  120  from each of any two first and second amplifier modules  10 ,  11 ,  12 ,  20 ,  30 ,  31 ,  40 ,  41 ,  42 ,  50  that optically communicate with each other without physical contact. Such a focusing/alignment element may include lenses, collimators, or mirrors. FIG. 19 g  illustrates, schematically, one fiber pigtail  114  from each of any two amplifier modules  10 ,  11 ,  12 ,  20 ,  30 ,  31 ,  40 ,  41 ,  42 ,  50  that are mechanically located so as to optically communicate with each other without physical contact. More specifically, the two facing ports  114  of the two adjacent modules, are located no more than 1 mm apart, and preferably, in order to minimize optical power loss, 0.1 mm apart or less. This may be facilitated, for example, by thermally expanding the core of each fiber to expand the waveguide mode field diameter and thereby reduce the numerical aperture of each fiber to an extent that enables the distance between the fibers to be substantially increased without incurring a significant communication loss penalty between the two fibers when they are spaced by more than 1 mm. Such approaches are disclosed, for example, in U.S. Pat. No. 6,275,627, incorporated by reference herein. FIG. 19 h  illustrates, schematically, two amplifier modules  10 ,  11 ,  12 ,  20 ,  30 ,  31 ,  40 ,  41 ,  42 ,  50  optically connected via planar waveguide ports  121  (available from Corning Cable Systems GmbH &amp; Co., of Munich, Germany), that optically communicate with each other without physical contact.  
     [0144] Alternatively, FIGS. 19 i - 19   l  illustrate, schematically, examples of alternative embodiments of direct mechanical optical connections that may be used to optically connect amplifier modules  10 ,  11 ,  12 ,  20 ,  30 ,  31 ,  40 ,  41 ,  42  and  50 . FIG. 19 i  generally illustrates an optically connected first and second module using free-space optics. Specifically, FIG. 19 j  illustrates, schematically, one focusing/alignment element  120  from each of any two amplifier modules  10 ,  11 ,  12 ,  20 ,  30 ,  31 ,  40 ,  41 ,  42 ,  50  that optically communicate with each other while in intimate physical contact. Such a focusing/alignment element may include lenses, collimators, or mirrors. FIG. 19 k  illustrates, schematically, one fiber pigtail  114  from each of any two amplifier modules  10 ,  11 ,  12 ,  20 ,  30 ,  31 ,  40 ,  41 ,  42 ,  50  that are mechanically located so as to optically communicate with each other with intimate physical contact. This can be achieved, for example, by aligning and attaching the two fibers with a mechanical fiber splice. FIG. 19 l  illustrates, schematically, two amplifier modules  10 ,  11 ,  12 ,  20 ,  30 ,  31 ,  40 ,  41 ,  42 ,  50  optically connected via a planar waveguide ports  121  that optically communicate with each other with intimate physical contact. This can be achieved, for example, by aligning two planar waveguides, abutting them together, and mechanically fixing them in their relative positions with respect to one another.  
     [0145] Although mechanical connections between fibers may be somewhat more expensive than fusion spliced fiber connections, mechanical connectors are preferable for use between some of the modules in some applications. Mechanical connectors allow for easy detaching and connection of modules, when upgrades (preferably in-service upgrades) of the modules are required. For example, if a different, upgraded optical power supply module is required, the original optical power supply module is detached and an upgraded optical power supply module is re-connected in its place. Other modules may also be upgraded as needed or desired by the end user. The upgrades would usually consist of replacing only those modules or components necessary to upgrade capability, not the replacement of the entire amplifier.  
     [0146] According to further embodiments of the present invention, the optical circuits according to module type may be replicated within a selected module to further reduce manufacturing cost. Using a “ganged” method, similar circuits are replicated as individual circuits with individual optical paths, and grouped, or “ganged”, within a common module, as shown, for example, in FIGS. 20 a - 20   j . Alternatively, a “parallel” method may be used, where like circuits are replicated as individual circuits with individual optical paths within a common module, but with portions of the optical path shared within common optical elements, as shown, for example, in FIGS. 21 a - 21   i . The “ganged” and “parallel” module types may be configurable, as shown in the examples in FIGS. 22 a - 22   d.    
     [0147] The “ganged” approach is illustrated schematically in FIGS. 20 a - 20   i  where, for example, in FIG. 20 a , two optical circuits  10 ′ from FIG. 1 a , are provided in the same optical power supply module. FIG. 20 b  illustrates that the optical circuit  10 ′ from FIG. 1 a  and the optical circuit  11 ′ of FIG. 1 b  are provided in the same optical power supply module.  
     [0148]FIG. 20 c  illustrates, schematically, ganged amplification module  21 . More specifically, this figure illustrates two optical circuits  20 ′ of FIG. 1 d , contained in the single amplification module  21 . FIG. 20 d  illustrates a further embodiment of Amplification module. This module includes two optical circuits  20 ′, co-joined to an optical isolator  103  (forming a single circuit  21 ′). The optical circuit  21 ′ is connected to optical ports  21   a  and  21   b . This configuration provides optical isolation between the two amplification media and prevents leakage of back-propagating light. The Amplification module of FIG. 20 d  eliminates the need for additional optical ports  20   b  and  20   a , (located between the two amplification medium coils) shown in FIG. 20 c  and eliminates optical losses associated with these ports.  
     [0149]FIG. 20 e  illustrates, schematically, two identical optical circuits  30 ′ from FIG. 1 e , provided in the same Monitoring and Access module. Although the Monitoring and Access module of FIG. 20 e  contains all optical and electro-optical components in their designated positions, depending on particular application, not all of the component positions need to be occupied.  
     [0150]FIGS. 20 f  and  20   g  illustrate two ganged examples of the Optical Processing modules. More specifically, FIG. 20 f  illustrates, schematically, a single Optical Processing module containing two optical circuits  40 ′ of FIG. 1 g . FIG. 20 g  illustrates, schematically, a single Optical Processing module containing two optical circuits  42 ′ of FIG. 1 i.    
     [0151]FIG. 20 h  illustrates a single Optical Processing module containing two optical circuits  41 ′ of FIG. 1 h.    
     [0152]FIG. 20 i  illustrates, schematically, a Telemetry Add/drop module containing two optical circuits  50 ′ of FIG. 1 j.    
     [0153] The “parallel” approach is illustrated schematically in FIGS. 21 a - 21   i . FIG. 21 a , illustrates, schematically, an Optical Power Supply module that includes two optical circuits  10 ′,  11 ′ of FIGS. 1 a ,  1   b , but with the optical isolator  103  element shared by both optical circuits  10 ′,  11 ′. Therefore, this Optical Power Supply module eliminated the need for an additional isolator, present for example, in the Optical Power Supply module of FIG. 20 b.    
     [0154]FIG. 21 b  illustrates, schematically, an exemplary Amplification Module that utilizes two optical circuits  21 ′, similar to the optical circuits illustrated in FIG. 20 d , but with the optical isolator  103  element shared by both circuits  21 ′. This configuration eliminates the need for an extra isolator and is very compact.  
     [0155]FIG. 21 c  illustrates, schematically, an exemplary Monitoring and Access Module that utilizes two optical circuits  30 ′, similar to the optical circuits illustrated in FIG. 1 e , but with the optical tap elements  105  and wavelength division multiplexer element  102  shared by two optical paths within the circuits. This Monitoring and Access module may be used for bidirectional optical signal monitoring. This Monitoring and Access module may also be simultaneously utilized by more than one optical amplifier. More specifically, the Monitoring and Access Module in FIG. 21 c  includes two isolators  103  that are coupled to, and share, a single optical tap  105 . This tap is connected to two photodiodes  107  and to another tap  105 . The second tap  105  is also connected to two photodiodes  107 .  
     [0156]FIG. 21 d  illustrates another Monitoring and Access module similar the one illustrated in FIG. 21 c , but is again doubled, with four optical circuits  30 ′. The optical tap elements  105  and wavelength division multiplexer element  102  of FIG. 21 d  are shared by four optical paths within the circuits. Each of the isolators  103  is shared by two optical circuits.  
     [0157]FIGS. 21 e - 21   h  illustrate, schematically, several embodiments of Optical Processing modules. The module of FIG. 21 e  includes two optical circuits  40 ′, similar to those shown in FIG. 1 g , but with the optical isolator  103  and gain flattening filter  108  shared by two optical circuits within the module.  
     [0158]FIG. 21 f  is similar to that of FIG. 21 e , except only the optical isolator  103  is shared by the two optical circuits  40 ′. FIG. 21 g  is similar to that of FIG. 21 e , except only the gain flattening filter  108  is shared by the two optical circuits  40 ′.  
     [0159] The Optical Processing module of FIG. 21 h  is similar to the module illustrated in FIG. 1 i , but with the optical tap elements  105  shared by two optical circuits  42 ′.  
     [0160] The Telemetry Add/Drop module of FIG. 21 i  is similar to that of FIG. 1 j , except two optical circuits  50 ′ share a single wavelength division multiplexer element  102 .  
     “Ganged” and “Parallel” Configurations  
     [0161]FIGS. 22 a - 22   d  illustrate, schematically, further examples of “ganged” and “parallel” modules described in FIGS. 20 a  through  21   i.    
     [0162] For example, FIG. 22 a  illustrates, schematically, the “ganged” Monitoring and Access module  30  from FIG. 20 e , including a first optical circuit  30 ′ configured to include only the four port optical tap  105  and the associated photodiode  107 , and a second optical circuit  30 ′ configured to include all circuit components except for the isolator  103 .  
     [0163]FIG. 22 b  illustrates, schematically, an Optical Power Supply module similar to the one illustrated in FIG. 21 a . The Optical Power Supply module of FIG. 22 b  is configured to include all circuit components except for the second laser source  101  and third WDM  102 .  
     [0164]FIG. 22 c  illustrates, schematically, a Monitoring and Access module similar to the one illustrated in FIG. 21 c , but configured to include all circuit components except for the shared WDM  102 , one isolator  103 , and one photodiode  107 .  
     [0165]FIG. 22 d  illustrates, schematically, a Monitoring and Access module similar to the one illustrated in FIG. 21 d , but configured without the shared WDM  102 , one isolator  103 , and two photodiodes  107 .  
     [0166] Amplifier modules may, preferably, be reduced in size and cost through-integration of the internal components that make up the optical circuits. Integration of optical components includes combining optical and opto-electronic materials within the same component packages to provide more than one function. This allows a reduction in packaging costs compared to individually packaged components. Additionally, the optical connections between the materials may be substantially reduced in size, for example, by replacing the conventional spliced optical fiber connections with precise placement and/or direct abutment of the materials. Optical losses associated with the fiber interconnections may therefore be minimized. This allows for the overall reduction in size of the modules. Finally, integration of components to eliminate fiber interconnections would enable automation of the manufacturing processes. Therefore, a fully integrated component is a single component that provides several optical or opto-electronic functions. Such a component may be a monolithic component.  
     [0167]FIGS. 23 a - 23   c  and FIGS. 24 a - 24   c  illustrate, schematically, examples of the novel integration of the Optical Power Supply module  11  and the Monitoring and Access module  30 , respectively. More specifically, FIG. 23 a  illustrates, schematically, an embodiment of an Optical Power Supply module  11 , similar to the configuration variant of the Optical Power Supply illustrated in FIG. 15 d . This Optical Power Supply optical module  11  includes two light sources  101 ′ that provide optical pump power (for example, laser sources  101 ), a first and second bidirectional light combiner/separator  102 ′ (for example two WDMs  102 ) optically connected to the light source  101 ′, and a directional optical attenuator  103 ′ (for example, an isolator  103 ), optically connected to one of the bidirectional light combiner/separators.  
     [0168]FIG. 23 b  illustrates another embodiment of the Optical Power Supply module  11 . This embodiment of the Optical Power Supply module provides a similar function to the Optical Power Supply module  11  shown in FIG. 23 a , but includes a novel, single, component that provides the component functions of the WDM  102 , isolator  103 , and laser sources  101 . The highly integrated, novel, single component of this module is shown in more detail in FIG. 23 c . This single component includes at least one light source  101 ′, (for example, in the form of a pump chip  101 ), at least one bidirectional light combiner/separator  102 ′, and a directional optical attenuator  103 . This results in a very compact Optical Power Supply module. The optical alignment tolerance requirements to allow for efficient optical coupling between the pump chip(s), the WDM(s), and isolator are known to those skilled in the art of opto-mechanical engineering. Tolerances can be achieved in manufacturing using a combination of passive alignment, active alignment, or a combination of both passive and active alignment. Examples of passive alignment manufacturing processes include the use of, for example, passive solder bump technology, computer aided vision technology with associated fiduciary marks, mechanical passive alignment stops or mechanical v-grooves etched into a substrate material onto which the optical components are assembled by, for example, an automated pick and place assembly machine. The typical alignment tolerances associated with passive alignment machines range from a precision of +/−10 microns to less than +/−0.3 microns, depending on the complexity of the alignment machine.  
     [0169] Higher levels of alignment precision can be attained with “active” alignment, i.e., with automated assembly machines that seek out the optimal alignment using a power peaking or hill climbing algorithm during the alignment process. This, “active” alignment technique, results in more optimal alignment and better optical coupling between adjacent components and reduced optical losses.  
     [0170] Similarly, FIGS. 24 a - 24   c  illustrates, schematically, an example of the novel integration of the Monitoring and Access module  30 . More specifically, FIG. 24 a  illustrates, schematically, an embodiment of Monitoring and Access module  30 . This Monitoring and Access module  30  includes two optical taps  105 , a photodiode associated with each tap  107 , a WDM  102  and an isolator  103 .  
     [0171]FIG. 24 b  illustrates another embodiment of the Monitoring and Access module  30 . This embodiment of the Monitoring and Access module provides a similar function to the Monitoring and Access module shown in FIG. 24 a , but includes a novel, single, component that provides the component functions of the optical taps, photodiodes, WDM, and isolator. The highly integrated, novel, single component of this module is shown in more detail in FIG. 24 c . This single component includes at least one optical tap  105 , at least one associated detector chip  107 , a WDM  102 , and a directional optical attenuator  103 . This results in a very compact Monitoring and Access module.  
     Amplification Module Variants  
     [0172]FIGS. 25 a - 25   g  illustrates, schematically, alternate embodiments of the Amplification Module. In FIGS. 25 a - 25   c , the Amplification Modules  24 ,  25 ,  26  are comprised of optical circuits  22 ′,  23 ′, and  24 ′, respectively, optically connected to the associated optical ports  21   a ,  21   b ,  22   a ,  22   b ,  23   a , and  23   b . Optical circuits  22 ′,  23 ′, and  24 ′ differ from optical circuit  20 ′, described previously, in that they include at least one additional optical component providing an additional optical function. For example, optical circuit  22 ′ of Amplification Module  24 , as illustrated schematically in FIG. 25 a , includes amplification medium  104 ′ and a light filter  108 ′. In this embodiment, the amplification medium is erbium doped optical fiber  104  and the light filter is a gain flattening filter  108 . In another example, optical circuit  23 ′ of Amplification Module  25 , as illustrated schematically in FIG. 25 b , includes amplification medium  104 ′ and a bidirectional light combiner/separator  102 ′. In this embodiment, the amplification medium  104 ′ is erbium doped optical fiber  104  and the bidirectional light combiner/separator  102 ′ is a wavelength division multiplexer  102 . The WDM  102  of circuit  23 ′ is positioned to accept only one input, optical power and signal light from Er doped fiber  104 . The WDM  102  separates excess pump power from the amplified signal power, and provides optical signal power to optical port  22   b . The excess pump light is routed to an optical absorber located within the module where it is dissipated. Such an optical absorber may be, for example, part of the WDM component (as in a ball-terminated fiber) or as a separate component. The optical circuit  24 ′ of Amplification Module  26 , as illustrated schematically in FIG. 25 c , includes amplification medium  104 ′ and both a light filter  109 ′ and bidirectional light combiner/separator  102 ′. In this embodiment, the amplification medium  104 ′ is erbium doped optical fiber  104 , the bidirectional light combiner/separator  102 ′ is a wavelength division multiplexer  102 , and the light filter  108 ′ is a gain flattening filter  108 . The WDM  102  functions similarly to the one described in conjunction with FIG. 25 b . These embodiments provide the amplifier designer with added flexibility to form unique combinations of modules.  
     [0173] As discussed previously, optical circuits may be combined within larger modules using “ganged” or “parallel” approaches. FIGS. 25 d  and  25   e  illustrate two embodiments of a “ganged” approach to optical circuits  20 ′,  22 ′,  23 ′, and  24 ′. Specifically, FIG. 25 d  illustrates, schematically, the Amplification module  27 , comprised of optical circuits  20 ′ and  22 ′, optically connected to the associated optical ports  20   a ,  20   b ,  21   a , and  21   b , respectively. Likewise, FIG. 25 e  illustrates, schematically, the Amplification module  28 . This Amplification module  28  is comprised of optical circuits  23 ′ and  24 ′, optically connected to the associated optical ports  22   a ,  22   b ,  23   a , and  23   b , respectively. In this embodiment, the wavelength division multiplexers  102  in each optical circuit  23 ′ and  24 ′, are optically connected. In this embodiment, the WDM  102  of circuit  24 ′ separates pump power from the amplified signal power provided by the Er doped coil of circuit  24 ′, and provides optical signal power to the gain flattening filter  108 . The pump power is routed to a second WDM  104  within the module  28 , for recombination with signal light (or signal and pump light) provided by the optical port  22   a.    
     [0174] In an alternative embodiment, an isolator  103  may be provided between the gain flattening filter  108  and the associated Er doped fiber coil  104 . This is shown, for example, in FIGS. 25 f  and  25   g.    
     [0175] Certain optical functions could be optionally produced in the optical circuit of the Amplification Module at predetermined locations by the application of electrical, optical, electromagnetic or thermal energy. For example, a diffraction grating could be optionally written into an optical fiber or planar waveguide that forms a part of the optical circuit of an Amplification module. More specifically, a diffraction grating (fiber Bragg grating FBG) can be written into the gain medium to replace the function provided by the dielectric GFF. Alternatively, a GFF in the form of a Lattice filter or cascaded Mach-Zehnder interferometer may be written within the waveguide, as taught U.S. Pat. No. 5,295,205. This would result in smaller optical losses and a more compact design.  
     [0176] One advantage of a modular approach to optical amplifiers is that the architecture can accommodate expansion and change. Other modules, with features other than those described above, may be added to the optical amplifier to create new products. For example, FIGS. 26 a  and  26   b  illustrate, schematically, two amplifier embodiments similar to those of FIGS. 4 a  and  4   b , which include an additional module that provides dispersion compensation. Such a module may include, for example, dispersion compensating fiber, diffraction gratings, or other dispersion compensating components.  
     [0177] Additionally, users of optical amplifiers need to have the optical amplifier interact with the other parts or devices of the network systems. This requires a customer and application specific interface between the optical amplifier and the devices associated with the network systems. This interface includes at least one of the following: optical ports, electrical ports, mechanical or thermal connections necessary to operate the amplifier. For example, the Customer Interface module may include a heat transfer device  111  connected to at least one of the other modules. This heat transfer device  111  may be a heat sink that routes excess thermal energy away from the amplifier assembly. Therefore, a modular Customer Interface module  70 ,  71  would include internal connection ports  70   a ,  70   b ,  71   a ,  71   b  to connect to other amplifier modules within the amplifier. Other internal connection ports may also be utilized. The internal ports  70   a ,  70   b ,  71   a ,  71   b  are preferably oriented so as to facilitate connection of the amplifier modules to the Customer Interface module  70 ,  71  during manufacturing. The internal connection ports  70   a ,  70   b ,  71   a ,  71   b  are routed within the Customer Interface module to the user-specified ports  70   c ,  70   d ,  71   c ,  71   d  or connections on the external customer interface. The inclusion of a highly configurable Customer Interface module  70 ,  71  in the design architecture of the optical amplifier aids in simplifying the complexity of the remainder of the optical amplifier modules. As an example, FIG. 27 a  illustrates a Customer Interface module  70  that would provide predetermined connections within the amplifier, yet have a custom, customer-specified, external electrical and optical interface  70   e ,  71   e . In addition to providing the customer-specified, external electrical and optical interface  70   e ,  71   e , the Customer Interface module (module  71 ) may also be utilized as a support structure, base, or motherboard for other modules. This is illustrated schematically in FIG. 27 b . The connections illustrated may be accomplished using known methods and techniques.  
     [0178] Other modules, providing other optical functions, may also be developed and combined with the amplifier modules in a similar way.  
     [0179] In general, modules to be used for a plurality of optical amplifiers are defined based on their functionality using the following partitioning method steps:  
     [0180] i. identifying a plurality of common functions required in each one of the plurality of optical amplifier types;  
     [0181] ii. identifying which groups of optical components are capable of providing this plurality of functions;  
     [0182] iii. selecting components to be grouped together in discrete modules, each module having at least one optical circuit, each of the components being coupled to at least another one of the components in this optical circuit, wherein each module provides one of the plurality of functions.  
     [0183] Thus, when manufacturing such modules it is preferred to:  
     [0184] i. identify a plurality of common functions required in each one of the plurality of optical amplifier types;  
     [0185] ii. identify which optical components, as a group, are capable of providing the required function(s);  
     [0186] iii. group the components together, such that each group of components is capable of providing one of the plurality of functions;  
     [0187] iv. place these optical components into modules, such that each of the modules performs one the plurality of functions. The modules may be then assembled together into an optical amplifier assembly. It is noted that optical connection between various components (and modules) may be accomplished, for example, via splicing of optical fibers. In a fusion splice, the connection is accomplished by the application of localized heat sufficient to fuse or melt the ends of two optical fibers, forming a continuous single fiber. In a connector splice, two mating pieces of hardware, i.e. connectors, are mechanically coupled to ends of respective fibers to be spliced and the connectors are mated to one another to position the ends of the fibers in opposition to one another. The connector splicing offers more flexibility because the splices can be easily undone and redone. Other optical connections may also be utilized.  
     [0188] Thus, a method of assembling an optical amplifier comprises the steps of:  
     [0189] i. selecting a plurality of modules required in the optical amplifier; the plurality of modules being selected from at least types: Optical power supply module, Amplification module and at least one additional module; and  
     [0190] ii. assembling the modules into an amplifier assembly.  
     [0191] Thus, a method of assembling an optical amplifier would typically include the following steps:  
     [0192] i. selecting a plurality of modules required in the optical amplifier; the plurality of modules being selected from at least three of the following types: Optical power supply, Amplification, Monitoring and Access; Optical Processing, Customer Interface, or Telemetry Add/drop; and  
     [0193] ii. assembling the modules into an amplifier assembly.  
     [0194] Furthermore, a method of assembling an optical amplifier thus may includes the steps of:  
     [0195] i. identifying a plurality of functions required in the optical amplifier; the plurality of functions being selected from at least three of the following types: Optical power supply, Amplification, Monitoring and Access; Optical Processing, Customer Interface, or Telemetry Add/drop;  
     [0196] ii. identifying which optical components, separately or in combination with other components are capable of providing this plurality functions; and  
     [0197] iii. identifying which of the components are to be grouped together to provide each of a the plurality of functions; placing the groups of optical components into modules, such that each of the modules performs one of the plurality of functions; and assembling the modules into an amplifier assembly.  
     Module Self-Identification  
     [0198] In the manufacture of optical amplifiers from the configurable amplifier modules described above, it is advantageous to easily determine a module&#39;s type, module&#39;s configuration, to determine manufacturing history of the module and other results and parameters associated with the finished modules. Several methods to accomplish this are shown in FIGS. 28 a - 28   c . For example, FIG. 28 a  illustrates a series of amplifier modules, color coded by module type to aide in visual identification. As an example, Amplification modules  20  are coded red, Monitoring and Access modules  30  are coded green, and an Optical Processing module  41  is coded blue. This aids in identification of the modules in the manufacturing facility.  
     [0199] For the needed detailed understanding of a module&#39;s background, a module may be passively or actively labeled. Passive labeling may include visual, tactile, magnetic, or other markings imposed on a module that may be interpreted by man or machine to determine information such as a reference model number and serial number, configuration information (how the module is configured), processing instructions, manufacturing data, testing protocols, or manufacturing results. Processing instructions, for example, may include whether or not a module is to be subjected to certain optional processing conditions, such as a bum-in step, or what software to load. Manufacturing data may include, for example, the date, time and location of manufacture. Testing protocols may include, for example, information regarding the type of testing required for each module. Manufacturing results may include, for example, data resulting from the specified testing protocol for the module, or performance data for the actual components used. The reference serial number may be utilized to retrieve manufacturing data from other sources or databases regarding the specific module. Examples of a passive label include a printed label, a bar code or, alternatively, a magnetic stripe. Passive labeling is illustrated schematically in FIG. 28 b.    
     [0200] Active labeling includes electronically interactive markings that may be interpreted by, modified or added to, by a computer or similar device connected to the module. The active labeling may include information such as a reference model number and serial number, configuration information (how the module is configured) processing instructions, manufacturing data, testing protocols, manufacturing results, or field history. As described above, the reference serial number is used to retrieve manufacturing data from other sources regarding the specific module. However, the active labeling may electronically acquire information developed during the manufacturing process that will be used subsequently. For example, the exact component configuration, with component serial numbers and component data could be present within the active label. Such information could be used by a measurement device to compare the performance of the completely configured module, to that of the individual components, as an aid to troubleshooting. The active labeling may include processing and testing protocols specific to a module&#39;s configuration and customer that will be interpreted and used by downstream processing and testing equipment. Manufacturing dates, times, locations, test results, and calibration information may also be indicated by the active labeling. Field history information may include data useful for troubleshooting amplifier problems that occurred in the field. For example, this information may be pump drive current (for an Optical Power Supply module), or thermal or other environmental history information (for any module), maximum optical power to which the assembly was subjected (for any module). The primary advantage of this approach is that automated assembly and test equipment will be able to determine, without intervention, the processing and testing requirements as the modules and the finished amplifiers are manufactured. An example of an active label is an internal read/write memory chip, with external computer connections. Active labeling is illustrated schematically in FIG. 28 c.    
     [0201] In the mechanical design of the amplifier, consideration is given to the overall mechanical architecture. More specifically, the individual module form factors must be derived so as to allow the resulting, assembled amplifier to achieve an overall size and shape required by the customer. Furthermore, it is advantageous in manufacture to design the three-dimensional form factors such that, when combined, they are compact, and fit together in a correct manner. FIGS. 29 a - 29   c  illustrate a method of mechanical registration used between modules in order to ensure correct orientation and fit. Modules may be connected by mating mechanical compression fit or spring-loaded connections, with or without electronic/electrical and/or thermal connections. Furthermore, modules may be connected by snap-fit mechanical connectors, mating guides and rails, mating pins and apertures, or mating non-planar surfaces. Mating non-planar surfaces are illustrated schematically in FIG. 29 a , mating pins and apertures are illustrated schematically in FIG. 29 b , and a combination of mating guides and rails (between modules  20 ) and mating pins and apertures (between modules  20  and the substrate/motherboard) are illustrated schematically in FIG. 29 c.    
     [0202] The modules may also be assembled as optical/electrical circuit chips on a common motherboard, where the chips may be upgraded as needed.  
     [0203] The present invention provides for novel segmentation of the design of an optical amplifier into configurable modules, based on functional requirements and technical and manufacturing advantage. It is an advantage of this invention that a minimal number of configurable modules can be utilized to create a wide variety of custom-made amplifiers at minimum cost. It is a specific additional benefit that amplifiers implemented in this way could be provided with additional or improved modules in order to change and/or upgrade the amplifier functionality.  
     [0204] In manufacturing, the manufactured volumes of commonly used modules will typically be higher than for any individual custom amplifier. Higher volumes of more commonly used modules will reduce the manufacturing costs of modules as well as that of the resulting amplifiers. Furthermore, manufacturing costs can be subsequently reduced by novel integration, automation and manufacturing optimization of each module.  
     [0205] In development, new amplifier designs can incorporate previously designed, tested, and available module designs, significantly reducing amplifier design and development costs, as well as reducing development time-to-market.  
     [0206] Furthermore, as another advantage of the present invention, inventory risks can be reduced due to the ability to create a wide variety of amplifiers from the same modules.  
     [0207] Finally, it is an advantage of the present invention that the modules themselves are configurable. That is, the optical circuits employed in the modules are designed to optionally allow the inclusion or exclusion of certain optical, opto-electrical, and electronic functions during manufacturing, without design changes. This is accomplished, in such a way as to ensure that allowable combinations of options result in modules that can become part of a variety of commercial amplifiers designed to meet differing customer needs. In one embodiment of the present invention, optical, opto-electrical, and electronic functions components may be included or not included in the optical circuit. As an example, the optical circuit of the third, monitoring and access module, may or may not include an optical tap with an optical sensor with dependent electrical output, by way of presence or absence of the component function. The design of the module is such as to allow the component to be present or absent from the module, and present or absent from the optical path that makes up the optical circuit. In another embodiment of the present invention, optical components may be present within or accessible to the optical circuit but be disabled. As an example, the optical circuit of the first, Optical Power Supply module, may include a light source that is present, but not activated. Such a design would allow for manufacturing an amplifier with upgrade capability resident within the amplifier, accessible by the customer only after the purchase of, for example a software key, or optionally activated by the customer only following failure of a system component. Finally, in another embodiment of the present invention, a predetermined location may be reserved in a material within the optical circuit to allow the selective creation of an optical function directly within the light path. As an example, a grating may optionally be written into a section of optical fiber provided within the optical circuit to create a light filter. As a second example, in a planar waveguide implementation of the third Monitoring and Access module, the present invention would allow for a predetermined space in the optical path within the planar waveguide component within which to create an optical tap or bidirectional light combiner/separator function.  
     [0208] For a more complete understanding of the invention, its objects and advantages refer to the following specification and to the accompanying drawings. Additional features and advantages of the invention are set forth in the detailed description, which follows.  
     [0209] It should be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various features and embodiments of the invention, and together with the description serve to explain the principles and operation of the invention. It is intended that the present invention cover the modifications and adaptations of the disclosed embodiments, as defined by the appended claims and their equivalents.  
     [0210] Accordingly, it will be apparent to those skilled in the art that various modifications and adaptations can be made to the present invention without departing from the spirit and scope of the invention.