Digital optical transmitter

Abstract

A cable television system ( 100 ) having forward and reverse paths includes, in the reverse path, a digital optical transmitter ( 200 ) for receiving an RF signal, converting it to a digital signal, and adding a digital pilot tone thereto. A laser is driven in accordance with the summed digital signal to generate a digital optical signal representative of the pilot tone and the RF signal. The cable television system ( 100 ) also includes an optical receiver ( 305 )for receiving the digital optical signal and recovering therefrom the RF signal and the pilot tone. The optical transmitter ( 200 ) and receiver ( 305 ) are coupled by fiber optic communication media ( 110 ).

What is claimed is:  
     
         1 . An optical transmitter, comprising: 
 an analog-to-digital (A/D) converter for converting an analog information signal to a digital information signal;    a pilot tone generator for generating a digital pilot tone;    a summer coupled to the A/D converter and the pilot tone generator for adding the digital pilot tone to the digital information signal to result in a summed signal; and    a laser diode coupled to the summer for providing an optical signal in accordance with the summed signal.    
     
     
         2 . The optical transmitter of    claim 1   , further comprising: 
 an input for coupling the analog information signal to the AID converter.    
     
     
         3 . The optical transmitter of    claim 1   , further comprising: 
 a serializer coupled to the summer and the laser diode for converting the summed signal to a serial signal.    
     
     
         4 . The optical transmitter of    claim 3   , further comprising: a driver for driving the laser diode to generate the optical signal.  
     
     
         5 . The optical transmitter of    claim 3   , further comprising: 
 an interleaver coupled to the serializer and the laser diode for interleaving bits of the serial signal.    
     
     
         6 . The optical transmitter of    claim 5   , further comprising: 
 circuitry, coupled to the interleaver, for receiving another analog information signal, converting the other analog information signal to another digital signal, which is summed with the digital pilot tone and serialized to result in another serial signal, and for providing the other serial signal to the interleaver, wherein the interleaver interleaves bits of the serial signal with bits of the other serial signal to drive the laser diode.    
     
     
         7 . The optical transmitter of    claim 1   , wherein the optical transmitter is included in a reverse path of a cable television system for transmitting information from system subscribers to a headend for further processing.  
     
     
         8 . A cable television system for providing signals, the cable television system comprising: 
 an optical transmitter for receiving an analog information signal and transmitting in accordance therewith a digital optical signal representative of the analog information signal;    an optical receiver for receiving the digital optical signal and recovering therefrom an analog signal representative of the analog information signal; and    an optical communication medium for coupling the optical transmitter and the optical receiver.    
     
     
         9 . The cable television system of    claim 8   , wherein the digital optical signal comprises: 
 a digital representation of the analog information signal; and    a digital pilot tone added to the digital representation of the analog information signal prior to transmission of the digital optical signal, wherein the optical receiver further recovers a pilot tone level from the digital optical signal.    
     
     
         10 . The cable television system of    claim 9   , wherein the optical transmitter comprises: 
 an analog-to-digital (A/D) converter for converting the analog information signal to a digital information signal;    a pilot tone generator for generating the digital pilot tone;    a summer coupled to the A/D converter and the pilot tone generator for adding the digital pilot tone to the digital information signal to result in a summed signal; and    a laser diode coupled to the summer for providing the digital optical signal in accordance with the summed signal.    
     
     
         11 . The cable television system of    claim 10   , wherein the optical transmitter further comprises: 
 a serializer coupled to the summer and the laser diode for converting the summed signal to a serial signal.    
     
     
         12 . The cable television system of    claim 11   , wherein the optical transmitter further comprises: 
 an interleaver coupled to the serializer and the laser diode for interleaving bits of the serial signal.    
     
     
         13 . The cable television system of    claim 12   , wherein the optical transmitter further comprises: 
 circuitry, coupled to the interleaver, for receiving another analog information signal, converting the other analog information signal to another digital signal, which is summed with the digital pilot tone and serialized to result in another serial signal, and for providing the other serial signal to the interleaver, wherein the interleaver interleaves bits of the serial signal with bits of the other serial signal to drive the laser diode.    
     
     
         14 . The cable television system of    claim 9   , wherein the optical receiver comprises: 
 a detector for converting the digital optical signal to a digital electrical signal;    a digital-to-analog (D/A) converter for converting the digital electrical signal to an analog electrical signal; and    a filter for processing the analog electrical signal to recover therefrom the pilot tone and the analog signal that is representative of the analog information signal.    
     
     
         15 . The cable television system of    claim 9   , further comprising: 
 a forward path for transmitting information to system subscribers; and    a reverse path for receiving information from system subscribers, wherein the reverse path includes the optical transmitter and the optical receiver.    
     
     
         16 . A cable television system having forward and reverse paths for respectively transmitting forward and reverse signals, the cable television system comprising: 
 first and second distribution systems for providing information to system subscribers located, respectively, in first and second geographic regions;    a headend for generating and transmitting optical signals;    an optical node, remotely located from the headend, for converting the optical signals to electrical signals and for transmitting the electrical signals over the first and second distribution systems, wherein, in the reverse path, the optical node comprises an optical transmitter, including: 
 a first A/D converter for receiving a first analog information signal from subscriber equipment included in the first distribution system and converting the first analog information signal to a first digital information signal;  
 a second A/D converter for receiving a second analog information signal from subscriber equipment included in the second distribution system and converting the second analog information signal to a second digital information signal;  
 a digital pilot tone generator for generating a digital pilot tone;  
 summers coupled to the first and second A/D converters and the digital pilot tone generator for adding the digital pilot tone to the first digital information signal to result in a first summed signal and for adding the digital pilot tone to the second digital information signal to result in a second summed signal;  
 serializers coupled to the summers to convert the first and second summed signals to first and second serial signals;  
 an interleaver coupled to the serializers for interleaving bits of the first summed signal with bits of the second summed signal to generate an interleaved signal; and  
 a laser diode coupled to the interleaver for emitting a digital optical signal in accordance with the interleaved signal.