Article comprising a multichannel optical amplified transmission system with functional upgrade capabilities and universal modules

Abstract

A universal inline functional module for operation with nonzero average gain G≠0 dB over a bandwidth is provided. The module includes at least one optical functional element producing loss over the bandwidth and at least one rare-earth doped fiber segment. The module produces a flat gain spectrum to within a specified tolerance when made to operate at an average gain of 0 dB over the bandwidth.

1 . A network node for transmitting signals from an input fiber span to an output fiber span operating over a particular bandwidth Δλ with a gain slope S opt  across the particular bandwidth Δλ when operating at an operating average gain level G across the particular bandwidth Δλ comprising:
 at least one broadband optical amplifier that includes at least a first segment of rare-earth doped fiber, an optical source of pump light and an optical coupler for coupling the pump light into the rare-earth doped fiber; 
 at least one inline functional module coupled to an input or output of the optical amplifier in an inline manner to define an inline path, said inline functional module being located at an input or a midstage access point of the optical amplifier, wherein said functional module includes at least one optical functional element producing optical loss within the bandwidth Δλ and at least a second rare-earth doped fiber segment; and 
 wherein the node is configured such that when the functional module is removed from the inline path the network node achieves the gain slope S opt  across the particular bandwidth Δλ when operating at an operating average gain level G across the bandwidth Δλ and without adjustment of optical loss of any element in the node. 
 
     
     
         2 . The network node of  claim 1  wherein the functional module is located at themidstage access point of the optical amplifier. 
     
     
         3 . The network node of  claim 1  wherein the functional module is located at the input of the optical amplifier. 
     
     
         4 . A method of forming a universal inline functional module from at least one optical functional element, comprising:
 coupling a first segment of doped optical fiber having a first length to at least one optical conditioning element to form an inline functional module;   supplying pump power to the doped optical fiber;   adjusting the pump power supplied to the doped optical fiber until an average gain of the inline functional module over an operating bandwidth is equal to 0 dB within a first specifiable tolerance;   measuring a gain slope of the module at the average gain of 0 dB within the specifiable tolerance; and   if the measured gain slope is nonzero, replacing the first segment of doped optical fiber coupled to the optical conditioning element with a second segment of doped optical fiber having a length that results in the measured gain slope being equal to zero at the average gain of 0 dB, thereby forming a universal inline functional module.   
     
     
         5 . The method of  claim 4  wherein the measured gain slope is positive and the replacing step comprises reducing the length of the first segment of doped optical fiber to form the second segment of doped optical fiber. 
     
     
         6 . The method of  claim 4  wherein the measured gain slope is negative and the replacing step comprises replacing the first segment of doped optical fiber with the second segment of doped optical fiber, said second segment having a length greater than the first length. 
     
     
         7 . The method of  claim 4  wherein the doped optical fiber is an erbium fiber. 
     
     
         8 . The method of  claim 4  wherein the optical functional element is an element selected from the group consisting of a DCM, add/drop module, polarization controller, DGEF, and a VOA. 
     
     
         9 . A link in a broadband optical fiber transmission system optically coupling a receiver to a transmitter, said link comprising:
 a plurality of optical fiber spans;   at least one optical amplifier coupling two of the fiber spans and operating over a particular bandwidth Δλ, said optical amplifier including at least one segment of rare-earth doped fiber, an optical source of pump light and an optical coupler for coupling the pump light into the rare-earth doped fiber; and   a first plurality of inline functional modules each coupled in an inline manner with one of the optical fiber spans, wherein said functional modules each include at least one optical functional element that produces optical loss within the particular bandwidth Δλ, and wherein at least a plurality of the first plurality of functional modules each includes at least one rare-earth doped fiber segment and wherein each of the plurality of functional modules that includes at least one rare-earth doped fiber segment is a universal module having a flat gain spectrum to within a specified tolerance at an average gain of 0 dB over the bandwidth Δλ.   
     
     
         10 . A method of upgrading a broadband optical fiber transmission system optically coupling a receiver node to a transmitter node by adding at least one optical functional element at a specified location within the optical fiber transmission system, comprising:
 coupling a first segment of doped optical fiber having a first length to the at least one optical functional element to form a universal inline functional module, said universal module having a flat gain spectrum to within a specified tolerance at an average gain of 0 dB over an operating bandwidth of the transmission system; and   inserting the universal inline functional module in an inline manner with a component of the transmission system situated at the specified location.   
     
     
         11 . The method of  claim 10  wherein said component of the transmission system is an optical fiber span situated between the receiver and the transmitter. 
     
     
         12 . The method of  claim 10  wherein said component of the transmission system is a network node. 
     
     
         13 . The method of  claim 10  wherein the optical functional element is an element selected from the group consisting of a DCM, add/drop module, polarization controller, DGEF, and a VOA. 
     
     
         14 . A universal inline functional module for operation with nonzero average gain G≠0 dB over a bandwidth Δλ comprising;
 at least one optical functional element producing loss over the bandwidth Δλ 
 at least one rare-earth doped fiber segment; and 
 wherein the module produces a flat gain spectrum to within a specified tolerance when made to operate at an average gain of 0 dB over the bandwidth Δλ. 
 
     
     
         15 . The universal inline functional module of  claim 14  wherein the rare-earth doped fiber segment is pumped to produce a gain greater than zero. 
     
     
         16 . The universal inline functional module of  claim 14  wherein the rare-earth doped fiber segment is unpumped, thereby producing a gain less than zero. 
     
     
         17 . The universal inline functional module of  claim 14  further comprising a gain-flattening filter. 
     
     
         18 . The universal inline functional module of  claim 14  wherein the optical functional element and rare-earth doped fiber segment are operationally associated with one another and physically reside in separate housings. 
     
     
         19 . A network node for transmitting signals from an input fiber span to an output fiber span operating over a particular bandwidth Δλ comprising:
 at least one universal inline functional module, wherein said functional module includes at least one optical functional element producing optical loss within the bandwidth Δλ and a rare-earth doped fiber segment, said universal inline functional module producing a flat gain spectrum to within a specified tolerance when made to operate at an average gain of 0 dB over the bandwidth Δλ, 
 wherein, when all universal inline functional modules are removed, the node produces an average gain less than or equal to 0 dB. 
 
     
     
         20 . The network node of  claim 19  wherein said optical functional element and rare-earth doped fiber segment are operationally associated with one another and physically reside in separate housings. 
     
     
         21 . The network node of  claim 19  wherein said universal inline functional module provides signal add/drop capabilities. 
     
     
         22 . The network node of  claim 19  wherein said universal inline functional module provides dispersion compensation.