Digital optical transmitter

• US 6,771,909 B2
• Filed: 10/17/2002
• Issued: 08/03/2004
• 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): SEDIGHIAN, REZA
• Application Number:
  US10/273,240
• Publication Number:
  US 20030063352A1
• Time in Patent Office: 656 Days
• Field of Search: 398/58, 398/66, 398/67, 398/70, 398/71, 398/72, 725/129, 725/119, 725/127, 725/121
• US Class Current: 398/72
• 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. In a cable television (CATV) system having a headend that provides video and data to a plurality of subscriber equipment via hybrid fiber/coax (HFC) network that includes a fiber portion, a first coax portion, a second coax portion, and a node for connecting the fiber portion to the first and second coax portions, a reverse path optical transmitter for use in the node, said reverse path transmitter comprising:

a first input port for receiving a first plurality of reverse RF signals from a first portion of said plurality of subscriber equipment in said first coax portion, said first plurality of reverse RF signals together forming a first combined reverse RF signal;

a first analog-to-digital converter for converting said first combined reverse RF signal into a first reverse parallel digital signal;

a first parallel-to-serial converter for converting said first reverse parallel digital signal into a first reverse serial digital signal;

a second input port for receiving a second plurality of reverse RF signals from a second portion of said plurality of subscriber equipment in said second coax portion, said second plurality of reverse RF signals together forming a second combined reverse RF signal;

a second analog-to-digital converter for converting said second combined reverse RF signal into a second reverse parallel digital signal;

a second parallel-to-serial converter for converting said second reverse parallel digital signal into a second reverse serial digital signal;

an interleaver for interleaving said first and second reverse serial digital signals to form a combined reverse digital signal;

a laser diode for converting said combined reverse serial digital signal into a reverse digital optical signal; and

an output for transmitting said reverse digital optical signal to said headend over said fiber portion of said HFC network.

2. The CATV system of claim 1, wherein the reverse RF signals comprise data, video, or voice signals.

3. The CATV system of claim 1, wherein the subscriber equipment comprises cable television set-top decoders.

4. The CATV system of claim 1, wherein the first and second parallel-to-serial converters include frame encoding circuitry for framing said first and second reverse serial digital signals.

5. In a cable television (CATV) system having a headend that provides video and data to a plurality of subscriber equipment via a hybrid fiber/coax (HFC) network that includes a fiber portion, at least two coax portions, and a node for connecting the fiber portion to the at least two coax portions, a reverse path optical transmitter for use in the node, said reverse path transmitter comprising:

for each of said at least two coax portions of said HFC network,

a single input for receiving from said corresponding coax portion of said HFC network a plurality of reverse RF signals from a portion of said plurality of subscriber equipment in said corresponding coax portion, said plurality of reverse RF signals together forming a combined reverse RF signal;

a single analog-to-digital converter for converting said corresponding combined reverse RF signal into a corresponding reverse parallel digital signal;

a single parallel-to-serial converter for converting said corresponding reverse parallel digital signal into a corresponding reverse serial digital signal;

an interleaver for interleaving said reverse serial digital signals from said at least two coax portions to form a combined reverse digital signal;

a laser diode for converting said combined reverse serial digital signal into a reverse digital optical signal; and

an output for transmitting said reverse digital optical signal to said headend over said fiber portion of said HFC network.

6. The CATV system of claim 5, wherein the subscriber equipment comprises cable television set-top decoders.

7. The CATV system of claim 5, wherein the reverse RF signals comprise data, video, or voice signals.

8. The CATV system of claim 5, wherein the parallel-to-serial converters include frame encoding circuitry for framing said reverse serial digital signals.

9. A method for providing a reverse digital optical signal in a cable television (CATV) system having a headend that provides video and data to a plurality of subscriber equipment via a hybrid fiber/coax (HFC) network that includes a fiber portion, at least two coax portions, and a node for connecting the fiber portion to the at least two coax portions, said method comprising the steps of:

for each of said at least two coax portions of said HFC network,

receiving from said corresponding coax portion of said HFC network a plurality of reverse RF signals from said plurality of subscriber equipment in said corresponding coax portion, said plurality of reverse RF signals together forming a combined reverse RF signal;

converting said corresponding combined reverse RF signal into a corresponding reverse parallel digital signal;

converting said corresponding reverse parallel digital signal into a corresponding reverse serial digital signal;

interleaving said reverse serial digital signals from said at least two coax portions to form a combined reverse digital signal;

converting said combined reverse serial digital signal into a reverse digital optical signal; and

transmitting said reverse digital optical signal to said headend over said fiber portion of said HFC network.