Abstract:
A system for configuring an optical amplifier in a fiber optic communications network including a safety shutdown input, includes a non-volatile memory for storing optical amplifier parameters. Circuitry is provided for inputting amplifier parameters into the memory and for changing previously stored amplifier parameters. Configuration of the optical amplifier parameters cannot be changed until a hardware control input is actuated. The system also provides for an indication of a mismatch between newly input parameters and previously stored optical amplifier parameters.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to fiber optic communications networks, and more particularly to a configurable safety shutdown for an optical amplifier using non-volatile storage for system configuration for reliably controlling a safety shutdown function in the event of a fiber optic transmission line disconnect or cut. 
     BACKGROUND OF THE INVENTION 
     The demand for communications capacity on fiber optic communications networks has resulted in increased use of wavelength-division multiplex (WDM) systems. WDM systems provide another level of multiplexing to individual or already multiplexed channels. In WDM systems, the individual transmission channels are carried on separate optical wavelengths and are combined in a single fiber at the optical link layer. WDM systems are generally used when the number of fibers in a transmission link is inadequate for the capacity or becomes a critical cost item. 
     The distances between WDM optical equipment and the signal transmission rates may be attenuation and/or dispersion limited. As a result, amplifiers are employed to boost signal strength to overcome these limitations due to losses from WDM devices, dispersion compensating fibers/gratings, connectors, splices, and fiber. As amplifier designs and WDM systems have evolved, so has the need for increased power grown. Optical power levels generated by fiber optic transmission systems can therefore be high enough to be hazardous to the human eye. If the transmission fiber is disconnected or accidentally cut or broken, the open end of the fiber can be emitting hazardous power, and this emission can possible be pointed into a person&#39;s eye. This power is higher when multiple optical channels are transmitted over a single fiber, as in WDM systems. Even higher power levels are generated when optical amplifiers are used. 
     Fiber optic transmission systems may employ a safety shutdown function which will shut down the optical output when the fiber is disconnected, cut, or broken. Such existing safety shutdown systems are based on the detection of input loss of power, which is then used to shut down the optical output. The operation of an optical amplifier is controlled by various parameters including, for example, shutdown, restart off period, restart on period, and loss of signal threshold. These parameters allow optical amplifiers within the optical transmission system to be configurable, depending upon the specific application and location within the system. Configuration and reconfiguration of such parameters within an optical amplifier may be accomplished by utilizing system software to configure logic gates within an optical amplifier module. However, due to the use of volatile software configurable logic gates, there exists the possibility that the gates may be accidentally reprogrammed to a configuration which makes the optic transmission system unsafe. Such undesirable changes may occur when a module is removed from the system and reinserted in a different location or plugged back into a same location. Furthermore, internal system software changes may occur to reconfigure an optical amplifier without knowledge of a system operator. 
     A need has thus arisen for a system for reliably configuring an optical amplifier safety shut down function in a fiber optic transmission network where the network may utilize configurable optical amplifiers such as, for example, erbium-doped fiber amplifiers (EDFAs) and other remote pumped EDFAs for boosting signal strength in WDM systems to ensure proper amplifier configuration. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, in a fiber optic communications network having an optical amplifier including a safety shutdown input, a system for configuring the optical amplifier is provided. The system includes a non-volatile memory for storing optical amplifier parameters. Circuitry is provided for inputting amplifier parameters into the memory and for changing previously stored amplifier parameters. Configuration of the optical amplifier parameters cannot be changed until a hardware control input is actuated via manual intervention. The system also provides for an indication of a mismatch between newly input parameters and previously stored optical amplifier parameters. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention and for further advantages thereof, reference is now made to the following Description of the Preferred Embodiments taken in conjunction with the accompanying Drawings in which: 
     FIG. 1 is a block diagram of a fiber optic communications network utilizing the present configurable optical amplifier safety shutdown function; and 
     FIG. 2 is a logic block diagram of an embodiment of the present amplifier. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, an optical fiber transmission communications network is illustrated, and is generally identified by the numeral  10 . Optical fiber transmission network  10  interconnects a site  12  to a site  14 . Each site  12  and  14  includes a group of transmitters  16  and a group of receivers  18 . Transmitters  16  of site  12  communicate with receivers  18  of site  14  via an optical fiber transmission line, generally identified by the numeral  20 . Transmitters  16  of site  14  communicate with receivers  18  of site  12  via an optical fiber transmission line, generally identified by the numeral  22 . Whereas network  10  has been illustrated utilizing two lines  20  and  22 , the present invention can also be utilized in a bi-directional fiber transmission system. 
     Transmitters  16  located at sites  12  and  14  are similarly configured, and like numerals will be utilized for like and corresponding components. Similarly, receivers  18  located at sites  12  and  14  are similarly configured, and like numerals will be utilized for like and corresponding components of receivers  18 . Transmitters  16  and receivers  18  are part of external terminal equipment devices or other transmission systems. As used herein, terminal equipment will include equipment as well as additional networks. Each transmitter input signal is applied to a transmit wavelength adapter (TWA)  30 . Each TWA  30  is a transponder module which is used as an input interface device for each data channel as data enters network  10 . The transponder module performs a series of functions: it receives and detects the incoming transmitter signal, and it regenerates the input signal, and transmits the data signal with a modulator and a wavelength-stabilized single-mode CW laser. 
     The output of each TWA  30  is an individual wavelength that is applied to a WDM multiplexer  32  which combines the multiple  1 -N wavelength channels into a composite multi-wavelength (multi-channel) signal for transmission. The output of multiplexer  32  is applied to an amplifier, such as, for example, an erbium doped fiber amplifier (EDFA) transmit optical fiber amplifier  34  whose output is applied to optical fiber transmission line  20 . Transmit optical fiber amplifier  34  also includes a shutdown control  42 . 
     Receiver  18  at site  14  includes a EDF amplifier  60 . A photodetector  62  is connected at the input of EDF amplifier  60 . Detection of loss of input power by photodetector  62  actuates a shutdown-restart control  82  which includes shutdown logic and a fail-safe restart timer to actuate shutdown control  42  and thereby terminate operation of transmit optical fiber amplifier  34  in transmitter  16  of site  14 . Additionally, after shutdown, shutdown-restart control  82  functions to turn the associated amplifier back on after the fiber has been repaired. Shutdown-restart control  82  operates to turn an amplifier on for a predetermined time period and then off for a predetermined time period. This on/off cycle is repeated until the fiber is repaired. The on and off periods are configurable parameters of the amplifier as well as the shutdown provisioning and loss of signal threshold provisioning of the amplifier. These parameters are set by system software. 
     The output of amplifier  60  is applied to a WDM demultiplexer  66 . The multiple outputs of demultiplexer  66  are each applied to the multiple receive wavelength adapters (RWA)  68 . Receive wavelength adapter  68  includes a transponder module used as an output interface device for each data channel as data exits from the WDM system at site  14  via channels  1 -N to terminal equipment receivers  18  at site  14 . RWA  68  uses a high performance receiver to detect and recover the received signal, monitors the quality of the received signal, monitors the signal trace code, and regenerates the optical signal for sending signals out of WDM network site  14  to terminal equipment receivers  18  at site  14 . 
     An important aspect of the present invention is the use of the present shutdown-restart control  82  utilizing a non-volatile storage to store the configuration parameters that are provided by the system software. The configuration is placed into a temporary location by the system software once the desired configuration has been entered via a system interface, and then the operator manually stores this configuration in the non-volatile memory via a switch. The parameter configurations cannot be changed until the switch is operated again so that the shutdown operation is under hardware control thereby improving the reliability due to hardware circuitry. 
     Referring now to FIG. 2, a portion of shutdown-restart control  82  is illustrated. Amplifier configuration parameters are input to shutdown-restart control  82  via an internal data bus. Information is stored in input registers  90 ,  92 , and  94  for such configurable parameters as the on and off periods of an optical amplifier and the loss of signal threshold. Registers  90 ,  92 , and  94  temporarily store these parameters. These parameters are then stored in a non-volatile storage memory such as, for example, an electronically erasable, programmable read-only memory (EEPROM)  98 . Data input to EEPROM  98  is accomplished through a write signal and a signal generated by closure of a pushbutton switch  100 . These signals are applied to an OR gate  102  which enables the write function of EEPROM  98 . It is only through operation of switch  100  that parameters stored in registers  90 ,  92 , and  94  are transferred to EEPROM  98 . The configuration parameters stored in EEPROM  98  are input to the system and associated optical amplifier via output registers  104 ,  106 , and  108 . Register  104  provides shutdown provisioning, register  106  provides restart off period, and register  108  provides for restart on period and loss of signal threshold. 
     The output of EEPROM  98  is also applied to a register compare logic  110  which also receives as an input the output of registers  90 ,  92 , and  94 . Compare logic  110  compares the contents of register  90  to register  104 , the contents of register  92  to register  106 , and the contents of register  94  to register  108 . In this manner, the operator is alerted as to whether any new configuration parameters which have been input into registers  90 ,  92 , and  94  are different from the previously stored configuration parameters in EEPROM  98 . Parameter mismatch is indicated by a visible indicator, such as, for example, illumination of a light emitting diode  112 . In this manner, any inadvertent or accidental change in configuration parameters input via the internal data bus will be detected when compared to previously stored configuration parameters through the operation of compare logic  110 , and a visual indication will be provided to the system operator that the system desires to change configuration parameters. If, in fact, the configuration parameters are to be changed, the system operator then actuates switch  100  to load new configuration parameters into EEPROM  98  for a new system configuration. Therefore, a positive action is required by the system operator to reconfigure the parameters of the shutdown-restart control  82  of an optical amplifier in network  10 . The present system thereby confirms whether the same parameter configuration exists when a module is unplugged and replugged back into the system, or when a module is replaced by a new module. 
     It therefore can be seen that the present invention provides for a reliable control for a safety shutdown of an optical amplifier of a fiber optic communications network in which configuration parameters are reliably set and which require a hardware action for reset. 
     Whereas the present invention has been described with respect to specific embodiments thereof, it will be understood that various changes and modifications will be suggested to one skilled in the art and it is intended to encompass such changes and modifications as fall within the scope of the appended claims and is not limited to specific components and features, individually or in combination which have been disclosed. Such components and features are not the only types of systems components and features that can create signal degredations that are resolved by the use of the present invention.