Method and apparatus for transmitting broadband amplitude modulated radio frequency signals over optical links

• US 5,379,141 A
• Filed: 12/30/1992
• Issued: 01/03/1995
• Est. Priority Date: 12/04/1989
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Scientific-Atlanta Incorporated (Cisco Systems, Inc.)
• Inventors: Thompson, Leo, Little, Frank, Pidgeon, Rezin E. Jr.
• Primary Examiner(s): Goldstein, Herbert
• Assistant Examiner(s): NEGASH, KINFE MICHAEL
• Application Number:
  US07/998,208
• Time in Patent Office: 734 Days
• Field of Search: 359/124-125, 359/132-133, 359/188, 359/190-191, 359/195, 358/86, 455/6.1, 455/313
• US Class Current: 398/91
• CPC Class Codes: H04B 10/504 using direct modulation
• CPC Class Codes: H04B 10/506 Multiwavelength transmitters
• CPC Class Codes: H04J 14/0298 with sub-carrier multiplexing [SCM]
• CPC Class Codes: H04N 7/22 Adaptations for optical transmission

Abstract

An optical communications system including a plurality of modulated radio frequency carriers which span more than an octave in bandwidth. In one implementation, the carriers are grouped into ranges which span less than an octave in bandwidth and the individual groups are transmitted over unique optical links. In another implementation, the groups are multiplexed on one optical link by using different wavelengths. In still another implementation, several of the bands are up-converted to the highest band of interest and then transmitted, either over single or multiple links. The resulting optical signals are demodulated and then down-converted before they are recombined into the broadband signal in excess of an octave in bandwidth.

Claims

1. In a system for communicating information signals with a plurality of optical signals, each of which being modulated with a plurality of carrier signals, a method of receiving said optical signals comprising the steps of:

demodulating each of said optical signals into its respective carrier signals, wherein a frequency of one of said carrier signals is substantially equal to a frequency of another of said carrier signals; and

converting the frequency of the one carrier signal to a frequency different than that of the another carrier signal to thereby produce carrier signals having different frequencies.

2. The method of claim 1, wherein said carrier signals having different frequencies have a bandwidth greater than one octave.

3. The method of claim 2, wherein the carrier signals demodulated from each optical signal have a bandwidth of less than one octave.

4. A method for receiving a plurality of optical signals, each of which is modulated with at least one modulated radio frequency carrier signal, said method comprising the steps of:

demodulating each optical signal into its respective modulated radio frequency carrier signals, wherein at least one of said modulated radio frequency carrier signals has a frequency band that overlaps with another of said modulated radio frequency carrier signals;

converting the at least one of said modulated radio frequency carrier signals to a different frequency band of carrier signals which does not overlap with any other modulated radio frequency carrier signal modulating said optical signals; and

combining the resulting modulated radio frequency carrier signals in a single signal path.

5. The method of claim 4 wherein said different frequency band is a lower frequency band.

6. The method of claim 5 further comprising the step of receiving the plurality of optical signals on a plurality of optical fibers.

7. The method of claim 6 wherein each optical signal is modulated with a plurality of modulated radio frequency carrier signals.

8. The method of claim 7, wherein:

a first group of said plurality of modulated radio frequency carrier signals modulates the optical signal received on a first optical fiber of said plurality of optical fibers, and a second group of said plurality of modulated radio frequency carrier signals modulates the optical signal received on a second optical fiber, said first group of modulated radio frequency carrier signals having the same frequency band as said second group of modulated radio frequency carrier signals; and

said step of converting comprises converting each of the first group of modulated radio frequency carrier signals to a different frequency band as the second group of modulated radio frequency carrier signals.

9. The method of claim 7 wherein the plurality of modulated radio frequency carrier signals modulating the optical signal received on each optical fiber have a bandwidth of less than an octave.

10. The method of claim 9 wherein the plurality of modulated radio frequency carrier signals modulating the optical signal received on each optical fiber have a bandwidth of about 300-550 MHz.

11. The method of claim 9, wherein said combined modulated radio frequency carrier signals have a bandwidth of greater than one octave.

12. The method of claim 7 wherein n optical signals are received on n optical fibers and said step of converting comprises converting the modulated radio frequency carrier signals received from n-1 of said optical fibers to a different frequency band of carrier signals which does not overlap with any other radio frequency carrier signal modulating said optical signals or any other converted modulated radio frequency carrier signal.