Digital optical transmitter

• US 6,356,374 B1
• Filed: 10/09/1998
• Issued: 03/12/2002
• Est. Priority Date: 10/09/1998
• 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.
• Primary Examiner(s): Chan, Jason
• Assistant Examiner(s): SEDIGHIAN, REZA
• Application Number:
  US09/169,612
• Time in Patent Office: 1,250 Days
• Field of Search: 359/135, 359/140, 359/158, 359/180, 359/123, 359/113, 370/535, 348/1-13, 455/1-12
• US Class Current: 398/191
• CPC Class Codes: H04B 10/504 using direct modulation
• CPC Class Codes: H04B 10/69 Electrical arrangements in the receiver

Abstract

A cable television system (700) includes a clock source (710) for generating a clock signal, an optical receiver (605) coupled to the clock source (710) for recovering the information in accordance with the clock signal, and an optical transmitter (800) that has input ports (720) for receiving first and second information signals and a clock port (760) for receiving the clock signal. An interleaver (745) within the transmitter (800) is coupled to the input ports (720) and to the clock port (760). The interleaver (745) interleaves bits of the information signals in accordance with the clock signal to generate a serial bit stream that is used to modulate a laser diode (750), thereby generating a digital optical signal that is transmitted to the optical receiver (605) over an optical communication medium (110).

Claims

1. A communication system for providing information, the communication system comprising:

a clock source for generating a clock signal having a clock speed;

an optical receiver coupled to the clock source for recovering the information in accordance with the clock signal;

an optical transmitter coupled to the clock source and the optical receiver, the optical transmitter comprising;

first and second input ports for receiving first and second information signals;

a clock port coupled to the clock source for receiving the clock signal;

a clock recovery circuit for filtering the clock signal provided at the clock port;

an analog-to-digital (A/D) converter coupled to the clock recovery circuit for digitizing the clock signal;

an interleaver coupled to the first and second input ports and to the clock port, wherein the interleaver interleaves bits of the first and second information signals in accordance with the clock signal, after it has been digitized, to generate a serial bit stream;

a controller coupled to the A/D converter and the interleaver for clocking the interleaver at a multiple of the clock speed; and

a laser diode coupled to the interleaver and modulated by the serial bit stream to generate a digital optical signal; and

an optical communication channel coupled between the laser diode of the optical transmitter and the optical receiver.

2. The communication system of claim 1, wherein the first information signal and the second information signal are provided to the optical transmitter at a first speed, and wherein the digital optical signal provided by the laser diode is transmitted at a second speed that is a multiple of the first speed.

3. The communication system of claim 1, wherein the communication system comprises a cable television system.

4. The communication system of claim 1, wherein:

the communication system comprises a cable television system including a headend for transmitting forward optical signals in a forward direction, an optical hub for forwarding the forward optical signals over branches of the cable television system, and optical nodes located in branches of the cable television system for converting the forward optical signals to forward electrical signals.

5. The communication system of claim 1, wherein the controller controls the interleaver to generate frames of data according to a signal protocol.

6. The communication system of claim 1, wherein the clock source is included in the headend, from which the clock signal is provided to the optical hub and to the optical nodes.

7. A cable television system for transmitting forward and reverse signals, the cable television system comprising:

a headend for generating forward optical signals and for receiving reverse optical signals, the headend including a clock source for generating a clock signal, having a clock speed;

an optical hub coupled to the headend for receiving the clock signal and for forwarding the forward optical signals throughout the cable television system, the optical hub including a reverse optical transmitter comprising;

first and second input ports for receiving first and second information signals;

first and second analog-to-digital (A/D) converters for respectively receiving the first and second information signals and generating therefrom first and second digital information signals;

first and second serializers coupled respectively to the first and second A/D converters for converting the first and second digital information signals into first and second serial bit streams;

a clock port for receiving the clock signal;

a clock recovery circuit for filtering the clock signal provided at the clock port;

a clock A/D converter coupled to the clock recovery circuit for digitizing the clock signal;

an interleaver coupled to the first and second serializers and to the clock A/D converter,

a controller coupled to the clock A/D converter and the interleaver for clocking the interleaver at a multiple of the clock speed,

wherein the interleaver interleaves bits of the first and second serial bit streams in accordance with the clock signal to generate a serial bit stream; and

a laser diode coupled to the interleaver and modulated by the serial bit stream to generate a digital optical signal for transmission to the headend; and

an optical communication channel coupled between the optical hub and the headend.

8. The cable television system of claim 7, wherein the controller controls the interleaver to generate frames of data according to a signal protocol.