Methods and apparatus for optical modulation amplitude measurement

Abstract

Techniques for measuring optical modulation amplitude (OMA) are disclosed. For example, a technique for measuring an OMA value associated with an input signal includes the following steps/operations. The input signal is applied to a photodetector, wherein the photodetector is calibrated to have a given responsivity value R, and further wherein the photodetector generates an output signal in response to the input signal. The output signal from the photodetector is applied to a radio frequency (RF) power meter, wherein the RF power meter measures the root mean squared (RMS) power value of the output signal received from the photodetector. The OMA value associated with the input signal is determined in response to the root mean squared (RMS) power value measured by the RF power meter. The OMA value may be determined as a function of a factor F derived from a relationship between an amplitude of a data signal and the RMS value of the data signal.

1 . A method of measuring an optical modulation amplitude (OMA) value associated with an input signal, comprising the steps of: 
 applying the input signal to a photodetector, wherein the photodetector is calibrated to have a given responsivity value R, and further wherein the photodetector generates an output signal in response to the input signal;    applying the output signal from the photodetector to a radio frequency (RF) power meter, wherein the RF power meter measures the root mean squared (RMS) power value of the output signal received from the photodetector; and    determining the OMA value associated with the input signal in response to the root mean squared (RMS) power value measured by the RF power meter.    
   
   
       2 . The method of  claim 1 , wherein the input signal is applied to the photodetector from a fiber optic link.  
   
   
       3 . The method of  claim 1 , wherein the photodetector generates a photocurrent in response to the input signal.  
   
   
       4 . The method of  claim 3 , wherein the photocurrent is converted to an average optical power value based on the given responsivity value R.  
   
   
       5 . The method of  claim 1 , wherein the determining step further comprises converting the RMS power value to the OMA value.  
   
   
       6 . The method of  claim 5 , wherein the RMS power value is converted to the OMA value through an equation:  
     
       
         
           
             OMA 
             = 
             
               10 
               * 
               log 
               ⁢ 
               
                   
               
               ⁢ 
               10 
               ⁢ 
               
                 
                   ( 
                   
                     
                       F 
                       * 
                       
                         
                           ( 
                           
                             0.001 
                             * 
                             
                               
                                 10 
                                 
                                   ( 
                                   
                                     
                                       RF 
                                       RMS 
                                     
                                     10 
                                   
                                   ) 
                                 
                               
                               / 
                               50 
                             
                           
                           ) 
                         
                       
                     
                     
                       R 
                       * 
                       0.001 
                     
                   
                   ) 
                 
                 . 
               
             
           
         
       
       wherein F represents a predetermined factor and RF RMS  represents the measured RF RMS power in units of dBm.  
     
   
   
       7 . The method of  claim 6 , wherein the portion of the equation under the radical converts the measured RF RMS power, RF RMS , from dBm into the square of the RMS signal current, I RMS   2 , the RMS signal current is then converted to a peak current, I PEAK , by multiplying by a factor F, the peak current is converted to a linear OMA value by dividing by the responsivity R of the photodetector, and the linear OMA is finally converted to the OMA value in units of dBm by dividing by one milliWatt and taking 10-log.  
   
   
       8 . The method of  claim 7 , wherein the factor F is derived from a relationship between an amplitude of a data signal and the RMS value of the data signal and a frequency response of the measuring system.  
   
   
       9 . The method of  claim 1 , wherein the input signal is compatible or desired to be made or verified with at least one of a Fibre Channel (FC) standard and a 10 Gigabit/second Ethernet standard.  
   
   
       10 . The method of  claim 1 , wherein the OMA value is compatible or desired to be made or verified with at least one of a Fibre Channel (FC) standard and a 10 Gigabit/second Ethernet standard.  
   
   
       11 . The method of  claim 1 , wherein the photodetector comprises a photodiode.  
   
   
       12 . The method of  claim 4 , further comprising the step of determining an extinction ratio based on the average optical power value and the OMA value.  
   
   
       13 . The method of  claim 1 , wherein the step of determining the OMA value is performed in accordance with a processor or a look-up table.  
   
   
       14 . Apparatus for measuring an optical modulation amplitude (OMA) value associated with an input signal, comprising: 
 a photodetector for receiving the input signal, wherein the photodetector is calibrated to have a given responsivity value R, and further wherein the photodetector generates an output signal in response to the input signal;    a radio frequency (RF) power meter, operatively coupled to the photodetector, wherein the RF power meter measures the root mean squared (RMS) power value of the output signal received from the photodetector; and    means for determining the OMA value associated with the input signal in response to the root mean squared (RMS) power value measured by the RF power meter.    
   
   
       15 . The apparatus of  claim 14 , wherein the determining means comprises a processor.  
   
   
       16 . The apparatus of  claim 14 , wherein the determining means comprises a look-up table.  
   
   
       17 . The apparatus of  claim 14 , further comprising a portable housing for containing the photodetector, the RF power meter and the determining means.  
   
   
       18 . The apparatus of  claim 14 , wherein the photodetector comprises a photodiode.  
   
   
       19 . An article of manufacture for measuring an optical modulation amplitude (OMA) value associated with an input signal, comprising a machine readable medium containing one or more programs which when executed implement the step of: 
 in response to the application of the input signal to a photodetector, wherein the photodetector is calibrated to have a given responsivity value R, and further wherein the photodetector generates an output signal in response to the input signal, and application of the output signal from the photodetector to a radio frequency (RF) power meter, wherein the RF power meter measures the root mean squared (RMS) power value of the output signal received from the photodetector;    determining the OMA value associated with the input signal in response to the root mean squared (RMS) power value measured by the RF power meter.    
   
   
       20 . A method of measuring an optical modulation amplitude (OMA) value associated with an input signal, comprising the steps of: 
 obtaining the input signal; and    determining the OMA value associated with the input signal by converting a root mean squared (RMS) power value measured from the input signal as a function of a factor F, wherein an optimum value for factor F is a value which when used to convert from RMS power to OMA gives an OMA value that is in substantial agreement with an OMA value that would have been obtained using a standards-specified method.