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RF RETURN OPTICAL TRANSMISSION
CROSS-REFERENCES TO RELATED
APPLICATIONS
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This is a continuation-in-part application of Ser. No. 09/309,717 filed May 11, 1999, and having the same title and the same inventor as the present application.
BACKGROUND OF THE INVENTION 10
1. Field of the Invention
The present invention relates to methods and apparatus for carrying on simultaneous communications over a single optical fiber by using two different operating frequencies, 15 and more specifically to methods and apparatus for use with WDM (wave division multiplexing) at two different wavelengths of light to provide bidirectional telephonic communication using TDM (time division multiplexing) at one wavelength of light and transmitting TV signals in only one 20 direction (downstream) at another wavelength. TV control signals are returned by the telephonic communication path to the TV source by multiplexing the control signals with the telephonic signals.
2. Description of Related Art Including Information Dis- 25 closed Under 37 CFR 1.97 and 1.98
The communications industry is using more and more optical or light fibers in lieu of copper wire. Optical fibers have an extremely high bandwidth thereby allowing significantly more information than can be carried by a copper wire 30 transmission line such as twisted pairs or coaxial cable.
Of course, modern telephone systems require bidirectional communications where each station or user on a communication channel can both transmit and receive. This is true, of course, whether using electrical wiring or optical 35 fibers as the transmission medium. Early telephone communication systems solved this need by simply providing separate copper wires for carrying the communications in each direction, and this approach is still used in part of the transmission path. It is especially used as the signals get 40 closer to the end users. Although twisted pairs and coaxial cables are used in homes and distribution terminals close to the home end user, some modern telecommunication systems now use micro-wave and optic fibers as transmission mediums. In addition TCM (time compression multiplexing) 45 is often used in optical transmission so that a signal optical fiber can carry communications in both direction.
However, because of extremely high band widths available for use by an optical fiber, a single fiber is quite capable of carrying a great number of communications in both 50 directions. One technique of optical transmission is WDM (wavelength divisional multiplexing) and uses different wavelengths for each direction of travel.
Yet another and simpler technique for using a single optical fiber for telephone systems is TCM (time compres- 55 sion multiplexing) and is sometimes referred to as a "pingpong" system. The system operates at a single frequency or wavelength of light and uses a single optical fiber and often even a single diode, for both converting electrical signals to optical signals and converting received optical signals to 60 electrical signals. TCM systems have the obvious advantage of requiring fewer components.
However, as mentioned above, optical fibers have extremely high band widths and use of an optical fiber for a single ping-pong telephone channel is a very ineffective use 65 of the fiber and, in fact, the available bandwidth of an optical fiber makes it possible to use a transmission technique such
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as TCM or ping-pong at one frequency and then by the use of WDM technology to use another technique at a second frequency.
Another area of rapidly growing technology is providing unidirectional TV signals by cable to a multiplicity of subscribers or users. In the past, such signals were and still are typically transmitted by the use of coaxial cables (e.g. cable TV). However, the use of optical fibers for transmission allows broad band transmission to a large numbers of customers and, since substantially all of the transmission of TV signals is one way (i.e. unidirectional), if a single optical fiber were used solely for the TV signals there would be almost no use of the selected wavelength of light for carrying return signal, which are typically control or information signals.
Therefore, a technique for transmitting bidirectional telephony signals and unidirectional TV signals would make efficient use of an optical fiber.
It would also be advantageous to provide return control signals to the TV signal source or station with respect to each customer or subscriber without having to dedicate a frequency or wavelength of light full time to said seldom used or RF Return transmitted signals.
SUMMARY OF THE INVENTION
The above objects and advantages are achieved in the present invention by methods and apparatus which comprise transmitting light at a first wavelength to carry telephony signals between a first telephone-related device and a second telephone-related device, or location and also transmitting light at a second wavelength to carry TV signals from a TV signal source to an end user(s). The wavelengths or light are carried through a single optical fiber from a first-end to a second-end. The first and second wavelengths of light are received at the second-end of the optical fiber, and the signals on the first wavelength of light are detected and converted to first electrical signals at a first frequency band suitable for carrying telephony signals such as voice telephone and computer modem signal, at a frequency band of about 64 KHz or less. The received second wavelength of light is also detected, and the detected light is converted to RF electrical signals, within a second overall frequency band. The overall frequency band typically extends between 5 and 870 MHz, where frequencies between 50 and 870 MHz are representative of TV channel signals and frequencies between 5 and 50 MHz are referred to as return RF signals. The return RF signals may include cable modem signals, set-top box signals and other TV related signals from a subscriber or user. The telephony electrical signals are transmitted to a receiving telephone or other telephonerelated device and the electrical signals representative of TV signals are transmitted to a TV signal receiving device. The return electrical telephony signals are then generated at the receiving telephone-related device at the same frequency band the original telephony signal were transmitted and are representative of return telephone information which could be 56K telephone modem information or voice information. The RF return signals including cable modem signals, TV related electrical signals such as control signals, information signals or TV show ordering signals are generated at a third frequency band. The return electrical telephony signal at the first frequency band of about 64 HKz and the RF return electrical signals generated at about 5 to 50 MHz are combined. The combined electrical signals are converted to light signals at the first wavelength which carries both the return telephony signal and the RF return signals. The light
