Digital optical transmitter

• US 6,373,611 B1
• Filed: 06/22/1998
• Issued: 04/16/2002
• Est. Priority Date: 06/22/1998
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Scientific-Atlanta Incorporated (Cisco Systems, Inc.)
• Inventors: Farhan, Forrest M., Gaibazzi, Alberto P.
• Primary Examiner(s): Chan, Jason
• Assistant Examiner(s): SEDIGHIAN, REZA
• Application Number:
  US09/102,344
• Time in Patent Office: 1,394 Days
• Field of Search: 359/135, 359/140, 359/158, 359/180, 359/118, 359/110, 359/142, 375/130-137, 370/535
• US Class Current: 398/182
• CPC Class Codes: H04B 10/0779 Monitoring line transmitter or line receiver equipment
• CPC Class Codes: H04B 10/25751 Optical arrangements for CATV or video distribution adaptations of television systems for optical transmission H04N7/22
• CPC Class Codes: H04B 10/504 using direct modulation

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).

Claims

1. 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 AID 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.

2. In a communications system having forward and reverse paths for respectively transmitting forward and reverse signals from a headend, the communications system including first and second distribution systems for providing information to system subscribers located, respectively, in first and second geographic regions, the reverse path comprising:

an optical transmitter, comprising;

a first analog-to-digital (AID) converter for receiving a first reverse analog signal from subscriber equipment in the first distribution system and for converting the first reverse analog signal to a first reverse digital signal;

a second A/D converter for receiving a second reverse analog signal from subscriber equipment in the second distribution system and for converting the second reverse analog signal to a second reverse digital signal;

a digital pilot tone generator for generating a digital pilot tone;

coupled to the first and second A/D converters and the digital pilot tone generator for adding the digital pilot tone to the first reverse digital signal to result in a first summed signal and for adding the digital pilot tone to the second reverse digital signal to result in a second summed signal;

serializers coupled to the summers for framing the first summed signal and the second summed signal, and for providing a first and second serial reverse digital signal;

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;

a laser diode coupled to the interleaver for emitting a digital optical signal in accordance with the interleaved signal; and

an optical receiver coupled to the optical transmitter via a communication medium, comprising;

a photodiode for converting the digital optical signal to the interleaved signal;

a deinterleaver for deinterleaving the interleaved signal into the first and second reverse digital signal;

deserializers for deserializing the first and second reverse digital signal; and

a first digital-to-analog (D/A) converter for recovering the first reverse analog signal from the first reverse digital signal; and

a second D/A converter for recovering the second reverse analog signal from the second reverse digital signal.

3. The communications system of claim 2, wherein the digital pilot tone provides a reference level for processing in the headend, and wherein the digital pilot tone is not affected by surrounding temperature.