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

• US 5,500,758 A
• Filed: 10/11/1994
• Issued: 03/19/1996
• 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, Pidgeon, Rezin E. Jr., Little, Frank
• Primary Examiner(s): Boudreau, Leo
• Assistant Examiner(s): NEGASH, KINFE MICHAEL
• Application Number:
  US08/321,234
• Time in Patent Office: 525 Days
• Field of Search: 359/189, 359/193, 359/161, 359/154, 359/132, 359/133, 359/125, 359/131
• US Class Current: 398/202
• 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. A method of receiving intensity-modulated optical signals over optical links to produce a plurality of radiofrequency channels covering more than one octave of bandwidth, comprising:

receiving at least three intensity-modulated optical signals over optical links;

demodulating each received intensity-modulated optical signal to produce a corresponding group of modulated radiofrequency carrier signals;

filtering each said group of modulated radiofrequency carrier signals to roll off noise and distortion products, thereby producing respective groups of modulated radiofrequency carrier signals, each group of modulated radiofrequency carrier signals having a bandwidth of contiguous radiofrequency channels covering less than one octave; and

combining the groups of modulated radiofrequency carrier signals to produce a single signal having a plurality of radiofrequency channels covering more than one octave of bandwidth.

2. An optical receiver for receiving intensity-modulated optical signals over optical links to produce a plurality of radiofrequency channels covering more than one octave of bandwidth, comprising:

at least three optoelectronic receivers for receiving at least three intensity-modulated optical signals over optical links and for demodulating each received intensity-modulated optical signal to produce a corresponding group of modulated radiofrequency carrier signals;

at least three filters, each said filter corresponding to one of said optoelectronic receivers, for filtering the group of modulated radiofrequency carrier signals produced by its corresponding optoelectronic receiver to roll off noise and distortion products thereby producing respective groups of modulated radiofrequency carrier signals, each group of modulated radiofrequency carrier signals having a bandwidth of contiguous radiofrequency channels covering less than one octave; and

a signal combiner, coupled to said filters, for combining the groups of modulated radiofrequency carrier signals to produce a single signal having a plurality of radiofrequency channels covering more than one octave of bandwidth.

3. The optical receiver of claim 2, wherein said at least three filter comprise a high pass filter, at least one bandpass filter, and a low pass filter.

4. The optical receiver of claim 3, wherein said at least three filters comprise plug-in filters for plugging into a circuit board.

5. The optical receiver of claim 4 further comprising:

a hybrid amplifier coupled to the output of said signal combiner for amplifying the single signal output by said signal combiner to produce an amplified signal.

6. The optical receiver of claim 5, further comprising:

trim adjustment circuitry coupled to an output of said hybrid amplifier;

a selectable Pad circuit, coupled to an output of said trim adjustment circuitry, for adjusting the level of the amplified signal; and

an equalizer, coupled to an output of said selectable Pad circuit, for adjusting for tilt in signal response.