Digital Optical Transmitter

• US 20080063403A1
• Filed: 10/31/2007
• Published: 03/13/2008
• Est. Priority Date: 06/22/1998
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Scientific-Atlanta (Cisco Systems, Inc.)
• Inventors: Gaibazzi, Alberto, Farhan, Forrest
• Granted Patent: US 7,773,879 B2
• Time in Patent Office: Days
• US Class Current: 398/115
• 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 method comprising:

receiving an analog signal;

converting the analog signal to a digital signal;

generating a digital pilot tone;

adding the digital pilot tone to the digital signal to produce a summed signal; and

producing an optical signal in accordance with the summed signal.

2. The method of claim 1, further comprising:

coupling the analog signal to an A/D converter.

3. The method of claim 1, further comprising:

converting the summed signal to a serial signal.

4. The method of claim 1, further comprising:

driving a laser diode to produce the optical signal.

5. The method of claim 3, further comprising:

interleaving bits of the serial signal to the input of a laser diode.

6. The method of claim 5, further comprising:

receiving second analog signal;

converting the second analog signal to a second digital signal;

adding the second digital signal with the digital pilot tone to produce a second summed signal;

serializing the second summed signal to result in a second serial signal; and

interleaving bits of the serial signal with bits of the second serial signal to drive the laser diode.

7. The method of claim 1, further comprising:

transmitting the optical signal from system subscribers in a reverse path of a cable television system 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 signal and transmitting in accordance therewith a digital optical signal representative of the analog signal, the transmitter for interfacing with an optical communication medium for coupling the optical transmitter and an optical receiver.

9. The cable television system of claim 8, wherein the digital optical signal comprises:

a digital representation of the analog signal; and

a digital pilot tone added to the digital representation of the analog signal prior to transmission of 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 signal to a digital 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 signal to produce 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 a second analog signal, converting the second analog signal to a second digital signal, which is summed with the digital pilot tone and serialized to result in a second serial signal, and for providing the second serial signal to the interleaver, wherein the interleaver interleaves bits of the serial signal with bits of the second serial signal to drive the laser diode.

14. The cable television system of claim 8, further comprising:

an optical receiver for receiving the digital optical signal and for recovering therefrom an analog signal representative of the analog signal.

15. The cable television system of claim 8, wherein the optical receiver further recovers a pilot tone level from the digital optical signal.

16. The cable television system of claim 14, 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 a representative analog signal.

17. The cable-television system of claim 8, wherein the optical transmitter is included in a reverse path for receiving information from subscribers in the cable television system.

18. The cable-television system of claim 14, wherein the optical receiver is included in a reverse path for receiving information from subscribers in the cable television system.

19. A cable television system for providing signals, the cable television system comprising:

an optical receiver for receiving a digital optical signal and for recovering therefrom an analog signal, the receiver configured to interface with an F optical communication medium for coupling the optical receiver with an optical transmitter.

20. The cable television system of claim 19, 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 a pilot tone and a representative analog signal.