Abstract:
An optical signal processing circuit including one or more modules. Each module performs a particular optical signal processing function such as filtering, switching, multiplexing/demultiplexing, monitoring or amplifying one or more optical signals. The modules can be combined to form a wide variety of optical signal processing circuits and systems.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of optical networking, in particular to devices for processing optical signals. 
     BACKGROUND OF THE INVENTION 
     In the use of optical signals to convey information in telecommunications networks, there are several optical signal processing functions that are typically performed at various points in a network, such as signal amplification, multiplexing/demultiplexing, filtering and switching. 
     In known optical communications systems, functions such as the aforementioned, are typically performed by specialized hardware arrangements comprised of often large numbers of discrete optical components. In complex systems, large collections of such arrangements can become physically quite large. Furthermore, such systems are subject to substantial signal losses due to long runs of fiber to interconnect the discrete components and due to losses at each of a large number of component interconnections. Other problems include fragility, greater susceptibility to environmental conditions, a greater effort and cost to assemble and difficulty in testing. 
     Moreover, due to the specialized nature of each circuit comprised of discrete components, modification of such circuits and the replacement of failed individual components is often difficult. 
     SUMMARY OF THE INVENTION 
     The present invention provides optical modules for use in optical signal systems which overcome the shortcomings of known optical systems. The present invention also provides an optical signal processing system comprising a plurality of optical modules. 
     In a first exemplary embodiment of an optical module in accordance with the present invention, a plurality of optical channels are each tapped and split into two signals. One signal is used internally in the module for monitoring purposes, and the second signal is provided externally. 
     In a second exemplary embodiment of an optical module in accordance with the present invention, optical pump power is added to each of a plurality of optical channels using wavelength division multiplexing (WDM) couplers and then amplified. 
     In a third exemplary embodiment of an optical module in accordance with the present invention, a plurality of optical channels are passed through a bandpass filter to remove noise and/or other unwanted signals. Each filtered signal is tapped and the plurality of tapped signals are combined and provided externally, as are the filtered signals. 
     The modules of the present invention can be used in a wide variety of arrangements and applications. For example, the same type of module can be used in a downstream circuit as well as an upstream circuit. By thus providing functions which can be used in a wide variety of applications, the modules of the present invention readily lend themselves as building blocks for more complex systems. As such, a small number of module types can be used to build highly complex systems. 
     In an exemplary embodiment of an optical telecommunications arrangement in accordance with the present invention, the aforementioned optical modules are arranged in an optical circuit between client interface (CI) inputs and the backplane of an optical switching system. The exemplary optical circuit provides multiplexing, monitoring, amplification and filtering functions. 
     In a further exemplary embodiment of an optical telecommunications arrangement in accordance with the present invention, the aforementioned optical modules are arranged in an optical circuit between an optical switching system and CI outputs. As with the first embodiment, this circuit performs demultiplexing, monitoring, amplification and filtering functions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a first exemplary arrangement of optical modules in accordance with the present invention. 
     FIG. 2 is a block diagram of a second exemplary arrangement of optical modules in accordance with the present invention. 
     FIGS. 3A and 3B show top and side views of an exemplary package of an optical module in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows an exemplary embodiment of a first optical circuit  1000  in accordance with the present invention. The optical circuit  1000  provides an optical path between client interface (CI) inputs and an optical switching system (not shown). Each CI input can carry optical signals of any one of a plurality (e.g., eight) of distinct, predetermined wavelengths, such as the wavelengths used in a Multiwavelength Optical Network (MONET). The circuit  1000  provides a plurality of outputs (e.g., eight) with each output carrying optical signals of one of the plurality of distinct, predetermined wavelengths. The optical circuit  1000  performs multiplexing, monitoring, switching, amplification and filtering functions which will be described more fully below. 
     FIG. 2 shows an exemplary embodiment of a second optical circuit  2000  in accordance with the present invention. The optical circuit  2000  provides an optical path between an optical switching system (not shown) and CI outputs. The circuit  2000  has a plurality of inputs from the switching system, each input carrying optical signals of one of the plurality of distinct, predetermined wavelengths, and provides the optical signals to the CI outputs. Like the optical circuit  1000 , the optical circuit  2000  performs demultiplexing, monitoring, switching, amplification and filtering functions which will be described more fully below. 
     The optical circuit  1000  comprises a tap-splitter array module  1100 , a 4×8 optical switch  1200 , two splitter-isolator modules  1300 , each coupled to a pump  1400 , a filter array module  1500  and a connector  1700 . 
     In the exemplary embodiment of FIG. 1, the tap-splitter array module  1100  comprises four optical signal inputs each coupled to a tap  1110  which splits the respective input signal into two signals. The input signals are provided via connectors  1115  coupled to the signal inputs of the module  1100 . The connectors  1115  can be angle polished connectors. 10% taps can be used for the taps  1110  (i.e., 90% of the input power is passed through and 10% is tapped-off) although taps with other ratios can be used as well, such as 5% or 4% taps. The main output of each tap  1110  is provided as an output of the module  1100  and the tap output of each tap  1110  is coupled internally to a splitter  1120 . 1×2 3 dB splitters can be used for the splitters  1120 . One output of each splitter  1120  is coupled to an optical connector  1130  on the module  1100 . This provides four optical outputs which can be used to monitor the four CI input signals applied to the module  1100 . The connector  1130  can be a multi-fiber MTP connector available from U.S. Connect, Inc. 
     Another output of each splitter  1120  is coupled to a photodiode  1140  whose output is coupled to an electrical connector or connectors  1145  on the module  1100 . This provides four electrical outputs, in addition to the four optical outputs at the connector  1130 , which can be used to monitor the four optical CI input signals applied to the module  1100 . 
     The main outputs of the taps  1110  are coupled to outputs of the module  1100  and provided to inputs of a 4×8 switch  1200 . Such a switch is available from Lucent Technologies, Inc. The 4×8 switch has four inputs (A through D) and eight outputs (1 through 8) and can route a signal at any input to any output. Each output of the switch  1200  is coupled to an optical path which is adapted to process signals of one of eight predetermined wavelengths, as described below. Each of the four CI inputs may carry optical signals of one of the eight predetermined wavelengths. Depending on the wavelength of the signals that are to be applied to each CI input of the module  1100 , the switch  1200  is configured accordingly to connect each of the corresponding switch inputs (A-D) to the appropriate output ( 1 - 8 ). 
     It should be noted that although in the exemplary embodiment of FIG. 1 a n×2n switch is used, a 2n×2n switch can also be used, e.g., an 8×8 switch. In the latter case, two four-channel modules  1100  can be used on the input side or one eight-channel tap-splitter module (not shown) with similar functionality as the module  1100 , can be used. 
     The eight outputs of the switch  1200  are coupled to two splitter-isolator modules  1300 , with each module handling four optical channels. Each splitter-isolator module  1300  comprises four isolators  1310 , one for each input. Each isolator  1310  is coupled to a WDM coupler  1320 . Each WDM coupler  1320  of each module  1300  is coupled to an output of a 1×4 splitter  1330  which has an input coupled to the output of a pump  1400 . In the exemplary embodiment shown in which the wavelengths of the optical signals processed are approximately 1550 nm, each coupler  1320  can be a 980/1550 WDM coupler and each pump  1400  can be a 125 mW pump emitting light with a wavelength of 980 nm. 
     The WDM couplers  1320  couple the output of each pump into the four optical channels handled by each module  1300 . The isolators  1310  prevent the coupled pump signal from traveling upstream. In the exemplary embodiment described, each isolator typically provides 45 dB of isolation. Each of the four outputs of each module  1300  can be coupled to a length of Erbium Doped Fiber (EDF)  1450  which can be coupled in turn to one of eight inputs of the filter array module  1500 . Each length of fiber  1450  can be comprised of E030 fiber with an approximate length of 25 m. 
     The fibers  1450  in conjunction with the pumps  1400  and WDM couplers  1320  form erbium-doped fiber amplifiers (EDFA) which act to amplify the signals on each of the eight optical channels. The input signals at the CI inputs typically have been attenuated and are further attenuated by the switch  1200  and should be amplified before being provided to the switching system backplane (at the connector  1700 ). In an exemplary application, the input signals typically have a power level of −5 to 0 dBm, whereas the backplane signal level should be approximately 7 dBm. 
     The amplified optical signals are then passed through band pass filters (BPF)  1510  in the module  1500 . The BPFs  1510  can be implemented in a known way using thin-film technology and preferably have a flat pass-band with sharp cut-off characteristics. Each of the eight BPFs  1510  has a different pass-band center wavelength which corresponds to one of the eight wavelengths of the optical signals to be processed (e.g., 1549.315, 1550.918, 1552.524, 1554.134, 1555.747, 1557.363, 1558.983 and 1560.606 nm). The output of each BPF  1510  is coupled to an isolator  1520  which is in turn coupled to a tap  1530 . The isolators  1520  prevent light from propagating upstream from the outputs of the module  1500 . It should be noted that the order of the isolators  1520  and the taps  1530  can be reversed; i.e., the taps  1530  can be arranged between the isolators  1520  and the BPFs  1510 . Each tap  1530  has a tap output which is coupled to an input of an 8×1 combiner  1550 . The 8×1 combiner  1550  has an output which is coupled to a pin of the connector  1700  and thus allows optical monitoring of the signals in all eight of the optical paths after the BPFs  1510 . The main output of each tap  1530  is coupled to a connector  1700 . In the exemplary embodiment of FIG. 1, the connector  1700  is a 12-fiber, MTP backplane connector. 
     The circuit  2000  of FIG. 2 is similar to the circuit of  1000  and includes similar components, although arranged substantially in reverse to the arrangement of the circuit  1000 . The circuit  2000  comprises a connector  2700 , similar to the connector  1700 ; two splitter-isolator modules  2300 , each coupled to a pump  2400 , similar respectively to the modules  1300  and pumps  1400 ; a filter array module  2500 , similar to the filter array module  1500 ; an 8×4 optical switch  2200 ; and a tap-splitter array module  2100 , similar to the module  1100 . 
     As shown in FIG. 2, the connector  2700  has eight pins coupled to inputs of the two splitter-isolator modules  2300 . The outputs of the modules  2300  are coupled via EDF fiber  2450  to the filter inputs of the filter array module  2500 . The signal outputs of the module  2500  are coupled to inputs of the 8×4 switch  2200 . As with the module  1500 , the module  2500  also provides a combined output signal which is coupled to a pin of the connector  2700 . The 8×4 switch  2200  has eight inputs (1 through 8) and four outputs (A through D). Each of the four outputs of the 8×4 switch  2200  is coupled to an input of the tap-splitter array module  2100  which includes four taps  2110  coupled to the inputs of the module  2100 . The main outputs of the taps  2110  are provided as outputs  2115  of the module  2100  while the tap outputs of the taps are coupled internally to photo diodes  2140 . The outputs of the photodiodes  2140  are coupled to a connector or connectors  2145  which allow external electrical monitoring of the optical signals provided to the module  2100 . 
     FIGS. 3A and 3B show top and side views, respectively, of an exemplary package  100  for an optical module in accordance with the present invention. In particular, the packaging shown can be used for the tap-splitter array module  1100  (or  2100 ) and includes a multi-pin electrical connector  500  which provides external connections to the photodiodes  1140  (or  2140 ). The connector  500  can be a 16-pin, 90-degree header-type connector. This configuration allows a signal evaluation circuit pack, or printed wiring board, to be piggy-backed onto the module package. In the case of the switches  1200  and  2200 , for example, electrical connectors may be provided on their packages in order to provide control signals for configuring the switch connections. 
     The package  100  additionally has optical connections  400  for optically coupling to other modules. The optical connections  400  may comprise optical fiber which can be spliced with other optical fiber or may comprise optical connectors. Optionally, the package may also include an MTP connector to provide external connectivity for optical monitoring outputs, as described above. 
     In an exemplary embodiment, the module package  100  has external dimensions of approximately 152 mm×80 mm×12 mm. 
     It should be evident in light of the disclosure provided herein that several variants of the circuits and modules of the present invention are possible. For example, the two laser pumps  1400  and n-channel splitter-isolator modules  1300 ,  2300  of each circuit can be replaced with one laser pump and one 2n-channel splitter-isolator module. Furthermore, each 2n-channel filter module  1500 ,  2500  can be replaced with two n-channel filter modules.