CATV distribution networks using light wave transmission lines

• US 5,153,763 A
• Filed: 12/01/1989
• Issued: 10/06/1992
• Est. Priority Date: 12/01/1989
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Scientific-Atlanta Incorporated (Cisco Systems, Inc.)
• Inventors: Pidgeon, Rezin
• Primary Examiner(s): Coles, Sr., Edward L.
• Assistant Examiner(s): NEGASH, KINFE MICHAEL
• Application Number:
  US07/444,598
• Time in Patent Office: 1,040 Days
• Field of Search: 370/3, 358/86, 455/612, 455/5, 455/617, 359/124, 359/125, 359/127, 359/133
• US Class Current: 398/71
• CPC Class Codes: H04B 10/2507 for the reduction or elimination of distortion or dispersion
• CPC Class Codes: H04N 7/22 Adaptations for optical transmission

Abstract

Light wave communication over optical fiber networks for the distribution of broadband, multiple channel CATV (Cable Televison) signals uses fibers which carry amplitude modulated broadband signals over a considerable distance (6-30 km) to a fiber node. Electrical to optical transmitters at the head end and optical to electrical receivers at the fiber node launch and receive the optical signals corresponding to the broadband CATV electrical signals. Distribution from the fiber node to subscribers is obtained by transmitting the electrical signals from the receivers at the node through a limited cascade of amplifiers along an electrical transmission line (coax cable). The limited cascade is much shorter than the fiber span and includes trunk amplifiers which are insufficient in number to add significant losses or distortion. Line extender amplifiers may be connected to output couplers located off the subscribers premises and then via electrical cables to the subscribers. In order to reduce distortion (second order distortion) which may be due to nonlinearities and interactions of signals in the transmitter, fiber and receiver, all or a portion of the spectrum which contains the lower channels is translated (block converted) to a frequency range which covers less than an octave. The converted signal is applied as an RF modulating signal to the transmitter which may contain a laser diode, and provides an amplitude modulated output. The signals are received at the output end of the fibers (at the fiber node), retranslated to the original band and filtered so that second order distortion components are removed. The broadband CATV signal is then distributed to the subscribers. Only those channels which extend over more than an octave need be combined, translated to a band which does not extend more than an octave and then transmitted as an amplitude modulated optical signal over a fiber. One or more additional fibers are used for the channels in the upper portion of the band which is not converted. The optical signals from the fibers are received, the converted portion is retranslated back to its original frequency range and combined with the other band limited portions to provide a broadband signal for distribution to the subscribers.

Claims

1. A CATV network for distributing broadband, multi-channel CATV signals from a head end or hub to subscribers, having means for frequency multiplexing individual TV channel signals into broadband electrical signals, which comprises:

a) means at said head end or hub for providing light wave signals corresponding to said broadband electrical signals,

b) a fiber node with optical electrical signal receiver means for converting said light wave signals to said broadband electrical signals,

c) a fiber optic cable with opposite ends, one of said ends being supplied with light wave signals from said head end or hub, the other of said ends delivering said light wave signals to said fiber node,

d) a cell to which a multiplicity of subscribers are connected,

e) a transmission line of length much less than said optical cable, being the input of said cell, a cascade of amplifiers in said transmission line, one end of said transmission line receiving said broadband electrical signals from said fiber node, the other end of said transmission line being connected to an output coupler means, said output coupler means connecting said transmission line to said subscribers.

2. The network according to claim 1 wherein said fiber cable is at least 6 km in length and said cell has a limited cascade including at least one trunk amplifier connected to said node, which limited cascade provides a portion of said line which itself is much less than said 6 km in length.

3. The network according to claim 2 wherein said cell includes a bridger, said limited cascade being connected between said bridger and said node.

4. The network according to claim 3 wherein said cell further comprises an electrical transmission line with line extender amplifiers connected to said bridger for distributing said electrical broadband signal transmitted by said limited cascade, and an output coupler off the subscriber'"'"'s premises connected to said line having said line extender amplifiers, said subscribers being connected to said output coupler.