Abstract:
Method and apparatus for optical communications. An apparatus for optical communication includes the functionality of both a modulator and an optical transmitter. The modulator receives video data, typically in the digital data form, in the electrical or optical domain and converts it into suitable RF (radio frequency) signals which are then used to modulate a conventional optical (laser) transmitter. The optical transmitter outputs, on optical fiber, a suitable light signal for use in an optical communications network, for instance a cable TV or fiber to the premises system. The modulator and optical transmitter are included in a single apparatus and have a shared controller (e.g., microprocessor or microcontroller) which is suitable programmed so as to allow installation, set up and calibration jointly of the modulator and optical transmitter. Thereby installation/set up/calibration is accomplished more efficiently than if the modulator and optical transmitter were independently calibrated or tuned. By using a common controller and common user interface, intelligence in the controller can set operating parameters of both the modulator and the optical transmitter in some cases via closed loop operation thus substantially simplifying and reducing costs of installation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not applicable.  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not applicable.  
       REFERENCE TO A COMPACT DISK APPENDIX  
       [0003]     Not applicable.  
       FIELD OF THE INVENTION  
       [0004]     This disclosure pertains to optical communications.  
       BACKGROUND OF THE INVENTION  
       [0005]     Optical communications are well known, one particular application being cable television. In many cable television systems, the transmission is a hybrid of transmission in the RF (radio frequency) domain and in the optical domain. The RF type (electrical) signals are typically carried on coaxial cable and the optical signals on optical fiber. For instance, the signals may be transmitted from the head end in the form of RF or data signals of the type used in computer networking which are then converted into optical signals to be transmitted along optical fiber cable to a receiver. Fiber optic networks are the information backbone upon which many network (e.g., cable television) operators deliver broadband interactive services such as high speed internet access, telephony, video and audio streaming and video on demand. There are other well known hybrid optical fiber/coaxial cable networks providing ultimately an electrical signal on the coaxial cable to the home. There is also what is referred to as “fiber to the home” or “fiber to the premises” networks in which the optical fibers extend all the way to the home or business receiver of the subscriber to the network.  
         [0006]     Typically such systems include a component referred to here as a “modulator” which extracts video information from the digital signal input and converts it into a radio frequency signal suitable to modulate a laser. Typically the laser is provided in a second component generally referred to herein as an optical transmitter which outputs suitable optical signals onto an optical fiber for communication.  
         [0007]     An example of such a modulator (also referred to as an “edge QAM” in the field) manufactured and sold by Harmonic Inc. is the “Narrowcast Services Gateway” product. These modulators typically receive standard GbE (Gigabit Ethernet), ASI (asynchronous serial interface) or similar digital electrical (or optical) signals and convert them to radio frequency signals suitable for modulating a laser by using QAM modulators. Typically the input signals contain MPEG-2 data. The modulator typically outputs a radio frequency signal such as a QAM (Quadrature Amplitude Modulated) RF or ASI signal up converted onto an RF carrier signal, as is standard in the field.  
         [0008]     An example of an optical transmitter (also referred to as a “transmitter” in the field) is a product also manufactured and sold by Harmonic Inc. referred to as the HLD MetroLink™ Forward Path Transmitter. This product includes a distributed feedback laser (DFB) and associated components. The laser output optical signal is one of typically 32 wavelengths as defined by the International Telecommunication Union (ITU). This product uses dense wavelength division multiplexing (DWDM), and allows provision of targeted digital “narrowcast” (i.e., to a distinct group of customers) transmissions on a single optical fiber.  
         [0009]     Each of these products, as is typical of those in the field, has its own user (operator) interface. For instance the above described NSG modulator is microprocessor controllable locally or remotely through a variety of user protocols including SNMP (simple network management protocol) XML, HTTP, etc. The MetroLink forward path transmitter similarly includes its own microprocessor for control of key operating parameters to provide consistent and optimum performance and monitoring. Both of these products must be independently set up and calibrated via the user interface when installed. Exemplary parameters to be controlled for the modulator include the number of radio frequency channels (each of which is typically one channel of cable television), a choice of modulation for instance 64 or 256 QAM for each channel, the radio frequency and/or bandwidth of each RF channel, and RF channel output power level. Similarly the parameters to be controlled for the optical transmitter include the amount of RF attenuation (pad), the optical modulation index (OMI) and the optical output power. Since these two products work closely together and typically are serially coupled by a coaxial cable, it is important for the various parameters to be calibrated in a coordinated fashion. Typically this calibration is carried out by a technician when the products are installed in a network. This calibration is relatively expensive and complex and must be accomplished in the field. This cost and difficulty of installation and set up is recognized in the industry as being a drawback, but to date no solutions have been proposed since typically the above mentioned devices are sold as individual components each with its own enclosure, power supply, and user interface.  
         [0010]      FIG. 1A  shows an example of a prior art system of the type referred to above, all of whose components are conventional. A video server  10 , typically maintained at a cable television system head-end, transmits on either copper cable or optical fiber 12 Gigabit Ethernet type signals, typically of the video on demand (VOD) type referred to also as “narrowcast”. These signals are received by the modulator  14  here designated “edge QAM” which has a second GbE interface such that multiple edge QAMs may be “daisy-chained” as is typical in the field. Cable  16  carries data signals. The modulator  14  then transmits the received signals, still in the electrical domain but now in QAM form, to a radio frequency network  18  which in turn is connected via attenuator  20  to a combiner  24 . The broadcast television content (also in RF) is applied at input port  28 . The combined RF signals are then applied to modulate an optical transmitter  26  in this case operating at 1310 nanometers wavelength which is a conventional optical transmitter of the type made and sold by Harmonic Inc. known as the PWR Link directly modulated 1310 nm transmitter. This in turn propagates the optical signal on optical fiber  30  ultimately to the end user.  
         [0011]     Another version of this system is shown in  FIG. 1B  with similar elements identically labeled and having a slightly different optical transmitter  32  here operating in the 1550 to 1560 nanometer wavelength bandwidth. Also provided in the lower portion of  FIG. 1B  is an external modulated video optical transmitter  42  which is also of the type described above which receives the broadcast television signal content on input port  44  and propagates this in optical form along optical fiber  50  to the EDFA (erbium doped fiber amplifier)  52  which turn is connected to an optical splitter  54 , one output port of which is connected to a wavelength division multiplexer (WDM)  36 . The narrowcast optical signal from optical transmitter  32  is connected via optical variable attenuator  34  to a second input port of WDM  36 . In this case a second EDFA  38  is connected between the WDM  36  and the output optical fiber  30 .  
       SUMMARY  
       [0012]     Disclosed here is a combination modulator and optical transmitter capable of receiving input digital data (optical or electrical) signals such as those conforming to Ethernet or other standards and outputting optical signals suitable for propagation on an optical fiber. Hence this apparatus accomplishes both modulating the input digital data signal into a radio frequency signal and using that radio frequency signal to drive a laser outputting the optical signal. In addition to typically being housed in a common enclosure, the modulator and optical transmitter are controlled by a single controller (for instance a microprocessor or microcontroller) having a single user interface, for instance of the SNMP type. This has the significant advantage of not only reducing component count, for instance by having only one power supply and one controller, but also advantageously having a single user interface for setting up and calibrating the apparatus. The interface employs a process to determine the operating parameters of both the modulator and the optical transmitter without requiring independent parameters to be input for each, as done in the prior art. Thus a suitable process is provided, for instance in the form of a computer program executed by the controller, to determine the operating parameters for both the modulator and optical transmitter depending on a single set of user inputs for set up and calibration of the combined modulator and optical transmitter. Hence the controller adjusts the modulator and optical transmitter operating parameters for optimal performance. Thus the single controller and user interface allow significant cost improvements in terms of both hardware components and even more importantly set up and calibration time, thereby reducing the cost of installing an optical communications network. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIGS. 1A, 1B  show prior art systems;  
         [0014]      FIG. 2  shows a system in accordance with this disclosure;  
         [0015]      FIGS. 2-7  show variants of the  FIG. 2  system;  
         [0016]      FIG. 8  shows in a flowchart a process to install and control the systems of  FIGS. 2-7 .  
     
    
     DETAILED DESCRIPTION  
       [0017]      FIG. 2  shows in a block diagram a system in accordance with this disclosure which has a number of elements identical to those of  FIG. 1B , and which are similarly labeled. In  FIG. 2  modulator  14  and optical transmitter  32  may be included in a single housing which may be provided at the factory or installed in the field. Modulator  14  and transmitter  32  share a single digital controller  68 . Controller  68  is typically a conventional circuit board including a microprocessor/microcontroller and associated support circuitry for purposes of control of modulator  14  and transmitter  32  jointly. Controller  68  has a conventional user input/output interface  78  which is typically a connection to an external computer located either locally or remotely. Typically when the computer is provided locally it is only connected temporarily for purposes of calibration/set up of apparatus  60 .  
         [0018]     In the prior art, e.g.  FIGS. 1A and 1B , there are also user input/output interfaces for modulator  14  and transmitter  32  but there each of  14  and  32  has its own individual controller and individual user interface, unlike the shared or common user interface and controller of  FIG. 2 . Also typically in the prior art there is no such single apparatus  60  as shown in  FIG. 2 , but devices  14  and  32  are typically sold separately and may in the field be installed in a common housing but are not so assembled at the factory. Additionally shown in  FIG. 2  is a set of initial (factory) settings  70  provided e.g. at the factory for initially setting up digital controller  68 . The only other element of  FIG. 2  not present in the earlier figures is the adjustable optical attenuator  82  external to apparatus  60 ; this is a conventional component.  
         [0019]      FIG. 3  shows a system with many similar elements to that of  FIG. 2  and similarly labeled again having the common digital controller  68  and user input/output interface  78 . In this case the adjustable optical attenuator  72  is included within the apparatus  86  rather than external thereto as in  FIG. 2 . The attenuator  72  is similarly controlled in conjunction with the modulator and transmitter.  
         [0020]      FIG. 4  shows a system in many ways similar to that of  FIG. 3  but including the WDM  36  within apparatus  90 .  
         [0021]      FIG. 5  shows yet another system in most respects similar to that of  FIG. 4  but further including in apparatus  88  a conventional optical power detector  84  coupled between digital controller  68  and WDM  36  for purposes of conventionally controlling parameters of the modulator, transmitter and optical attenuator as described below.  
         [0022]      FIG. 6  shows another variant of the system where apparatus  94  in addition to the various components similarly connected as in  FIG. 5  also includes further control circuitry  98  in the optical path for closed loop (i.e., feedback) control purposes. Detail of control circuit  98  is shown in  FIG. 7  showing the optical signal input on optical fiber  104  from WDM  36  is connected to an optical tap coupler  106  which propagates 99% of the signal strength to the optical output fiber  108  which connects to the EDFA  38  (not shown) of  FIG. 6 .  
         [0023]     The additional control elements shown in  FIG. 7  include photodiode  110 , filter capacitor  112 , RF amplifier  116 , RF tuner  118  and RF power meter  120 . This  FIG. 7  circuit provides a means of measuring the optical power since 1% of the optical power is diverted from the coupler  106  to photodiode  110 . The RF tuner  118  and RF power meter  120  are connected via digital control lines respectively  122  and  124  to digital controller board  68  for RF and optical signal strength control purposes to create the closed control loop.  
         [0024]     As pointed out above, typically user interface  78  is a connection to an external computer or computing device for providing the desired operating commands to determine the various operating parameters. A technician typically receives information provided by interface  78  for field adjustment of for instance apparatus  60  of  FIG. 2 . User interface  78  may be one of several types. One type is an interface compatible with the SNMP (simplified network management protocol) interface well known in the field. Other types of user interfaces are also suitable. Note that in the apparatus  60 , a single power supply  64  is provided (by conventional connections, not shown) to power all elements in apparatus  60  and a similar shared power supply is provided in  FIGS. 2-6 .  
         [0025]     Operation of controller  68  in  FIGS. 2-6  in one embodiment is as follows. It is to be understood that this is illustrative and not limiting but illustrates that modulator  14  and optical transmitter  32  are to be controlled jointly so that control and especially set up and calibration of both components is substantially simplified. It is understood that components  14 ,  24  are not merely installed and used but instead typically require in the field set up and calibration. However the present inventor has determined that there are relationships between the signal processing in the RF realm and in the optical realm determined by the configuration of the apparatus and also by the nature of electrical and corresponding optical signals. These relationships allow a single set up and calibration which is simpler than performing these tasks separately.  
         [0026]      FIG. 8  shows a generalized flow chart for the process to install and control systems of the type shown in  FIGS. 2-7  in accordance with the invention. Of course this is merely exemplary in terms of both the actual steps and also the particular operating parameters illustrated. Moreover, the various variables shown here of course are purely arbitrary but are the types suitable for use in a suitable computer program to be executed by a microprocessor/microcontroller present in controller  68 .  
         [0027]     In the first step  120 , the apparatus, for instance apparatus  60  of  FIG. 2 , is assembled and calibrated in the factory by conventional methods. Next in step  122 , still typically in the factory or at least prior to installation in the field, certain operating parameters or values (see detail below) for the optical transmitter  32  are set and loaded into the memory portion of controller  68 . This corresponds to setting the factory settings  70  in  FIG. 2 .  
         [0028]     In the next step  130 , the apparatus, for instance  60 , is actually installed in the system as shown in  FIG. 2 , in the field.  
         [0029]     At step  132 , the operator (technician) takes various optical power measurements, depending on the nature of the system. As shown, for  FIGS. 2 and 3 , he measures the output power at splitter  54  and insertion losses at WDM  36 . For  FIG. 4 , he measures only the optical power at splitter  54 . No such measurements are needed for  FIGS. 5 and 6 . These measurements are provided to controller  68  as optical measurement input values, see below.  
         [0030]     In the next step at  134 , certain operating parameters or values such as the number of RF channels and broadcast channels (explained in detail below) pertaining to modulator  14  and broadcast transmitter  42  are set in the field in the memory portion of controller  68  by the operator via the user interface  78 .  
         [0031]     At step  142 , optical measurements pertaining to optical power are made within the apparatus while it is operating as detailed below.  
         [0032]     In the next step  146 , the controller  68  calculates certain output parameters for the RF attenuator  20  and optical attenuator  72 ,  82  using the formulas (pseudo-code) shown below, for calibration purposes.  
         [0033]     In the last step  150 , these calculated parameters and certain calibration instructions requesting the operator to adjust the optical attenuator  72 ,  82  (see  FIGS. 2 and 3 ) to the computed value (see below) are displayed to the operator via user interface  78 . The controller  68  then stops the calibration process until the operator enters a new operating parameter, when the process returns to step  146 .  
         [0034]     The following sets forth, in tabular form and pseudo-code expressed as algebraic formulas, the parameters relating to various factory settings  70  of step  122  and the field settings (not set at the factory) of step  134 . These parameters and settings are collectively referred to below as “Input Values.” Also shown are the optical measurement values of step  132 , and the calculated output parameters (“Output Values”) of step  146 . The tables specify for each parameter/value an algebraic name, the physical unit, where it is set (factory or in the field), and whether that value is common or not for the entire broadcast region (spectrum.) The pseudo-code shows the algebraic relationships of the parameters and the accompanying narrative defines the subsequent activity by controller  68  per  FIG. 8 . This information is provided here for the systems of each of FIGS.  2  to  6 , although there is a high degree of commonality.  
         [0035]     1. FOR THE  FIG. 2  SYSTEM  
                                                                                             Common value                       for entire                   set at   Broadcast           variable   units   factory?   region                                    INPUT VALUES                       Input for Edge QAM 14       #of RF channels (e.g. 1-30)   NncQAM       NO   NO       bandwidth of RF channels (e.g. 6 or 8 MHz)   Be   MHz   NO   NO       # of RF channels with 256-QAM   Nnc256       NO   NO       modulation       #of RF channels with 64-QAM modulation   Nnc64       NO   NO       Input for Narrowcast Transmitter 32       Optimum optical modulation index for 8   mfactory       YES   NO       channel loading (set at factory with 8 RF       QAM channels input channels       RF attenuator setting for such condition.   RFattFACTORY   dB   YES   NO       (set at factory)       Output power (set at factory)   Pncfactory   dBm   YES   NO       Input for Broadcast transmitter 42       # of analog channels   Nanalog       NO   YES       # of 256-QAM ch x dB below analog   Nbc256       NO   YES           x   dB   NO   YES       # of 64-QAM ch y dB below analog   Nbc64       NO   YES           y   dB   NO   YES       assumed OMI of transmitter = 3.6%   mbc       default set   YES                   at 3.6%       Optical measurement       Input optical power of broadcast wavelength   Pbc       NO   NO       Insertion loss of WDM for Narrowcast   LncWDM       NO   NO       wavelength       Insertion loss of WDM for Broadcast   LbcWDM       NO   NO       wavelength       OUTPUT VALUES       adjustment for Ratt*   RFattSETTING   dB   Used for                   internal                   adjustment                   of RF                   attenuator       optical attenuation for NC**   Opt Att   dB   Given to                   operator                  
 
         [0036]     Calculate OMI per analog channel: 
 
 mANALOG=mbc*Sqrt [(6 /Be )(80+33/4)/( Nanalog+Nbc 256/10{circumflex over ( )}( x/ 10)+ Nbc 64/10{circumflex over ( )}( y/ 10)]
 
 Calculate optical power and modulation index of the Narrowcast transmitter  32 : 
 
 mNC 256 =mfactory*Sqrt [(6 /Be )8/( Nnc 256 +Nnc 64/10{circumflex over ( )}(( y−x )/10))]
 
Then the power ratio of Narrowcast/Broadcast 32  10 Log[ mANALOG/mNC 256  Sqrt[ 10{circumflex over ( )}( x/ 10)]]
 
 The interface  78  then displays to the user (operator): 
 
 “The Narrowcast output should be attenuated by”
 
 OptAtt=F 2=10 Log[ mANALOG/mNC 256  Sqrt[ 10{circumflex over ( )}( x/ 10)]]+ Pncfactory−Pbc−LncWDM+LbcWDM  
 
 The digital controller  68  then adjusts the value of RF attenuator  20  from the value of RFattFACTORY to: 
 
 RFattSETTING=Fl=− 20*log[ mANALOG/mNC 256 ]+Rfattfactory  
 
 The digital controller  68  then monitors the changes made to the following parameters by the user: 
    NncQAM, Be, Nnc256, Nnc64, and adjusts the value of RFattSETTING accordingly. 
 
 2. For the  FIGS. 3-5  Systems 
   
 
         [0038]     The  FIGS. 3-5  systems each use substantially similar calculations and display of data to the user as for  FIG. 2  but the control variables are measured internally. This is the (common) calculation for FIGS.  3 - 5 :  
         [0000]     Calculate OMI per analog channel: 
 
 mANALOG=mbc*Sqrt [(6 /Be )(80+33/4)/( Nanalog+Nbc 256/10{circumflex over ( )}( x/ 10)+ Nbc 64/10{circumflex over ( )}( y/ 10)]
 
 Calculate optical power and modulation index of the Narrowcast transmitter  32 : 
 
 mNC 256 =mfactory*Sqrt [(6 /Be )  8 /( Nnc 256 +Nnc 64/10{circumflex over ( )}(( y−x )/10))]
 
Then the power ratio of Narrowcast/Broadcast=10 Log[ mANALOG/mNC 256  Sqrt[ 10{circumflex over ( )}( x/ 10)]]
 
 The digital controller  68  then sets the optical attenuator  72  according to: 
 
 OptAtt= 10 Log[ mANALOG/mNC 256  Sqrt[ 10{circumflex over ( )}( x/ 10)]]+ Pncfactory−Pbc−LncWDM+LbcWDM  
 
 The digital controller board  68  then adjusts the value of RF attenuator  20  from the value of RFattFACTORY to 
 
 RFattSETTING=Fl=− 20*log[ mANALOG/mNC 256 ]+Rfattfactory  
 
 The digital controller board  68  then monitors the changes made to the following parameters by the user: 
    NncQAM, Be, Nnc256, Nnc64, and adjusts the value of RFattSETTING accordingly.    
 
         [0040]     3. Parameters for the  FIG. 3  System  
                                                                           For  FIG. 3  the operating parameters are:                            Common value                       for entire                   set at   Broadcast           variable   units   Factory?   region                        INPUT VALUES                       Input for Edge QAM 14       # of RF channels (e.g. 1-30)   NncQAM       NO   NO       bandwidth of RF channels (e.g. 6 or 8 MHz)   Be   MHz   NO   NO       # of RF channels with 256-QAM modulation   Nnc256       NO   NO       # of RF channels with 64-QAM modulation   Nnc64       NO   NO       Input for Narrowcast Transmitter 32       Optimum optical modulation index for 8   mfactory       YES   NO       channel loading (set at factory) with 8 RF       QAM channels input channels       RF attenuator setting for such condition   RFattFACTORY   dB   YES   NO       (set at Factory)       Output power (set at factory)   Pncfactory   dBm   YES   NO       Input for Broadcast transmitter 42       # of analog channels   Nanalog       NO   YES       # of 256-QAM ch x dB below analog   Nbc256       NO   YES           x   dB   NO   YES       # of 64-QAM ch y dB below analog   Nbc64       NO   YES           y   dB   NO   YES       assumed OMI of transmitter = 3.6%   mbc       default set   YES                   at 3.6%       Optical measurement       Input optical power of broadcast wavelength   Pbc       NO   NO       Insertion loss of WDM for Narrowcast   LncWDM       NO   NO       wavelength       Insertion loss of WDM for Broadcast   LbCWDM       NO   NO       wavelength       OUTPUT VALUES       adjustment for Ratt*   RfattSETTING   dB   Used for                   internal                   adjustment                   or RF                   attenuator       Optical attenuation for NC**   Opt Att   dB   Given to                   operator                  
 
         [0041]     4. Parameters for the  FIG. 4  System  
                                                                           For  FIG. 4  the operating parameters are:                            Common value                       for entire                   set at   Broadcast           variable   units   Factory?   region                        INPUT VALUES                       Input for Edge QAM 14       # of RF channels (e.g. 1-30)   NncQAM       NO   NO       bandwidth of RF channels (e.g. 6 or 8 MHz)   Be   MHz   NO   NO       # of RF channels with 256-QAM modulation   Nnc256       NO   NO       # of RF channels with 64-QAM modulation   Nnc64       NO   NO       Input for Narrowcast Transmitter 32       Optimum optical modulation index for 8   mfactory       YES   NO       channel loading (set at factory) with 8 RF       QAM channels input channels       RF attenuator setting for such condition.   RFattFACTORY   dB   YES   NO       (set at Factory)       Output power (set at factory)   Pncfactory   dBm   YES   NO       Insertion loss of WDM for Narrowcast   LncWDM       YES   NO       wavelength       Insertion loss of WDM for Broadcast   LbcWDM       YES   NO       wavelength       Input for Broadcast transmitter 42       # of analog channels   Nanalog       NO   YES       # of 256-QAM ch x dB below analog   Nbc256       NO   YES           x   dB   NO   YES       # of 64-QAM ch y dB below analog   Nbc64       NO   YES           y   dB   NO   YES       assumed OMI of transmitter = 3.6%   mbc       default set   YES                   at 3.6%       Optical measurement       Input optical power of broadcast wavelength   Pbc       NO   NO       OUTPUT VALUES       adjustment for Ratt*   RFattSETTING   dB   Used for                   internal                   adjustment                   of RF                   attenuator       optical attenuation for NC**   Opt Att   dB   Used for                   internal                   adjustment                   of variable                   optical                   attenuator                  
 
         [0042]     5. Parameters for the  FIG. 5  System  
                                                                           For  FIG. 5  the operating parameters are:                            Common value                       for entire                   set at   Broadcast           variable   units   Factory?   region                        INPUT VALUES                       Input for Edge QAM 14       # of RF channels (e.g. 1-30)   NncQAM       NO   NO       bandwidth of RF channels (e.g. 6 or 8 MHz)   Be   MHz   NO   NO       # of RF channels with 256-QAM modulation   Nnc256       NO   NO       # of RF channels with 64-QAM modulation   Nnc64       NO   NO       Input for Narrowcast Transmitter 32       Optimum optical modulation index for 8   mfactory       YES   NO       channel loading (set at factory) with 8 RF       QAM channels input channels       RF attenuator setting for such condition.   RFattFACTORY   dB   YES   NO       (set at factory)       Output power (set at factory)   Pncfactory   dBm   YES   NO       Insertion loss of WDM for Narrowcast   LncWDM       YES   NO       wavelength       Insertion loss of WDM for Broadcast   LbcWDM       YES   NO       wavelength       Input for Broadcast transmitter 42       # of analog channels   Nanalog       NO   YES       # of 256-QAM ch x dB below analog   Nbc256       NO   YES           x   dB   NO   YES       # of 64-QAM ch y dB below analog   Nbc64       NO   YES           y   dB   NO   YES       assumed OMI of transmitter = 3.6%   mbc       default set   YES                   at 3.6%       Optical measurement       Input optical power of broadcast wavelength   Pbc       NO   NO       OUTPUT VALUES       adjustment for Ratt*   RfattSETTING   dB   Used for                   internal                   adjustment                   of RF                   attenuator       Optical attenuation for NC**   Opt Att   dB   Used for                   internal                   adjustment                   of variable                   optical                   attenuator                  
 
         [0043]     6. For the  FIG. 6  System  
                                                                           For the  FIG. 6  system the parameters are:                            Common value                       for entire                   set at   Broadcast           variable   units   Factory?   region                        INPUT VALUES                       Input for Edge QAM 14       # of RF channels (e.g. 1-30)   NncQAM       NO   NO       bandwidth of RF channels (e.g. 6 or 8 MHz)   Be   MHz   NO   NO       # of RF channels with 256-QAM modulation   Nnc256       NO   NO       # of RF channels with 64-QAM modulation   Nnc64       NO   NO       Reference 256 QAM broadcast channel   ChBC   MHz   NO   YES       frequency       Reference 256 QAM narrowcast channel   ChNC   MHz   NO   NO       frequency       Input for Narrowcast Transmitter 32       Optimum optical modulation index for 8   mfactory       YES   NO       channel loading (set at factory) with 8 RF       QAM channels input channels       RF attenuator setting for such condition.   RFattFACTORY   dB   YES   NO       (set at factory)       Output power (set at factory)   Pncfactory   dBm   YES   NO       Insertion loss of WDM for Narrowcast   LncWDM       YES   NO       wavelength       Insertion loss of WDM for Broadcast   LbcWDM       YES   NO       wavelength       Input for Broadcast transmitter 42       # of analog channels   Nanalog       NO   YES       # of 256-QAM ch x dB below analog   Nbc256       NO   YES           x   dB   NO   YES       # of 64-QAM ch y dB below analog   Nbc64       NO   YES           y   dB   NO   YES       assumed OMI of transmitter = 3.6%   mbc       default set   YES                   at 3.6%       Optical measurement       Input optical power of broadcast wavelength   Pbc       NO   NO       RF measurement made within the device   RF ratio       NO   NO       OUTPUT VALUES       adjustment for Ratt*   RFattSETTING   dB   Used for                   internal                   adjustment                   of RF                   attenuator       Optical attenuation for NC**   Opt Att   dB   Used for                   internal                   adjustment                   of variable                   optical                   attenuator                  
 
         [0044]     The associated calculations for  FIG. 6  are:  
         [0000]     Calculate OMI per analog channel: 
 
 mANALOG=mbc*Sqrt [(6 /Be )(80+33/4)/( Nanalog+Nbc 256/10{circumflex over ( )}( x/ 10)+ Nbc 64/10{circumflex over ( )}( y/ 10)]
 
 Calculate optical power and modulation index of the Narrowcast transmitter  32 : 
 
 mNC 256 =mfactory*Sqrt [(6 /Be )8/( Nnc 256 +Nnc 64/10{circumflex over ( )}(( y−x )/10))]
 
Then the power ratio of Narrowcast/Broadcast=10 Log[ mANALOG/mNC 256  Sqrt[ 10{circumflex over ( )}( x/ 10)]]
 
 The digital controller  68  provides a similar display of data to the user as for  FIGS. 3-5  and then sets the optical attenuator  72  according to 
 
 OptAtt= 10 Log[ mANALOG/mNC 256  Sqrt[ 10{circumflex over ( )}( x/ 10)]]+ Pncfactory−Pbc−LncWDM+LbcWDM  
 
 The digital controller  68  then adjusts the value of RF attenuator  20  from the value of RFattFACTORY to 
 
 RFattSETTING=− 20*log[ mANALOG/mNC 256 ]+Rfattfactory  
 
 After RFattSETTING is set, the apparatus measures the RF power at RF frequencies ChBC and ChNC. Controller  68  then implements a conventional control loop (see  FIG. 7 ) to adjust the values of RFattSETTING and OptAtt in order to make RF power at both channels equivalent, and operates this loop until there is a change (see  FIG. 8  “stop” step) in one of the user inputed values: 
    NncQAM, Be, Nnc256, Nnc64.    
 
         [0046]     It is to be understood that the controller  68  may include any one of a number of well known microprocessors/microcontrollers with suitable internal/external memory of the type commercially available. Programming controller  68  in light of this disclosure to carry out the above described calculations and control and display functions is easily accomplished by one of ordinary skill in the art. The nature of the programming language, etc. is dependent upon the type of microprocessor/microcontroller employed. Moreover, controller  68  need not include a standalone microcontroller/microprocessor, but the controller may be incorporated in some other device or circuitry so long as the requisite intelligence as disclosed here is provided by same.  
         [0047]     This disclosure is illustrative and not limiting; further modifications will be apparent to one skilled in the art in light of this disclosure and are intended to fall within the scope of the appended claims.