Illuminated and non-illuminated photodiodes for monitoring and controlling AC and DC components of a laser beam

Abstract

Embodiments of the present invention utilize two photodiodes on the same substrate, one illuminated monitor photodiode to monitor an optical beam out of a back facet (or back scattered) of a laser, and one non-illuminated reference photodiode to characterize in real time radio frequency (RF) parameters/performance to control extinction ratio and optical modulation amplitude of the laser beam.

1 . A method, comprising: 
 converting an optical beam emitted by a laser into current proportional to a power in optical beam using a first photodiode on a substrate, the first photodiode being illuminated by the optical beam;    extracting a direct current (DC) bias voltage level for the optical beam using the first photodiode;    deriving a temperature of the laser using a second photodiode on the substrate;    preventing the second photodiode from being illuminated by the optical beam;    adjusting the DC bias voltage level in response to the derived temperature; and    adjusting laser bias voltage in response to the adjusted DC bias voltage level.    
   
   
       2 . The method of  claim 1 , wherein deriving the temperature of the laser comprises correlating a threshold voltage for the second photodiode with a threshold current for the second photodiode.  
   
   
       3 . The method of  claim 2 , wherein deriving the temperature of the laser comprises correlating a temperature of the second photodiode with the threshold current for the second photodiode.  
   
   
       4 . The method of  claim 1 , further comprising adjusting optical signal average optical power based on the derived temperature.  
   
   
       5 . An apparatus, comprising: 
 a laser;    a first photodiode on a substrate, the first photodiode being illuminated by an optical beam emitted by the laser;    a second photodiode on the substrate, the second photodiode being prevented from illumination by the optical beam; and    first circuitry coupled to the first photodiode to adjust direct circuit (DC) components in the optical beam in response to variations in temperature of the second photodiode.    
   
   
       6 . The apparatus of  claim 5 , wherein the first circuitry includes laser bias circuitry coupled to adjust laser bias voltage in response to variations in temperature of the second photodiode.  
   
   
       7 . The apparatus of  claim 6 , wherein the first circuitry is further to adjust average optical power of the optical signal in response to variations in temperature of the second photodiode.  
   
   
       8 . A system, comprising: 
 a transponder having a laser to emit an optical beam, a substrate having a first photodiode and a second photodiode, the first photodiode being illuminated by the optical beam, the second photodiode being prevented from illumination by the optical beam, and first circuitry coupled to the first photodiode to adjust direct circuit (DC) components in the optical beam in response to variations in temperature of the second photodiode; and an erbium-doped fiber amplifier (EDFA) coupled to the transponder.    
   
   
       9 . The system of  claim 8 , further comprising a multiplexer coupled to the EDFA.  
   
   
       10 . The system of  claim 9 , further comprising an add-drop multiplexer coupled to the EDFA.  
   
   
       11 . An article of manufacture article of manufacture, comprising: 
 a machine-accessible medium including data that, when accessed by a machine, cause the machine to perform the operations comprising, 
 converting an optical beam emitted by a laser into current proportional to a power in optical beam using a first photodiode on a substrate, the first photodiode being illuminated by the optical beam; extracting a direct current (DC) bias voltage level for the optical beam using the first photodiode;  
 deriving a temperature of the laser using a second photodiode on the substrate;  
 preventing the second photodiode from being illuminated by the optical beam;  
 adjusting the DC bias voltage level in response to the derived temperature; and  
 adjusting laser bias voltage in response to the adjusted DC bias voltage level.  
   
   
   
       12 . The article of manufacture of  claim 11 , wherein the machine-accessible medium further includes data that cause the machine to perform operations comprising adjusting optical signal average optical power based on the derived temperature.  
   
   
       13 . The article of manufacture of  claim 12 , wherein the machine-accessible medium further includes data that cause the machine to perform operations comprising correlating a threshold voltage for the second photodiode with a threshold current for the second photodiode.