RF return optical transmission Number:7,103,907 from the United States Patent and Trademark Office (PTO) owispatent

Title: RF return optical transmission

Abstract: A method of transmitting TV signals and bidirectional telephone communication signals on a single optical fiber, existing telephone twisted pair infrastructure, and existing coaxial cable infrastructure. In addition to allowing the downstream transmission of television channels as well as bidirectional telephone communication, the single optical fibers also provides for the upstream travel of television related signals while requiring minimal changes of the existing infrastructure.

Patent Number: 7,103,907 Issued on 09/05/2006 to Buabbud

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Inventors:	Buabbud; George H. (Southlake, TX)
Assignee:	Tellabs Bedford, Inc. (Bedford, TX)
Appl. No.:	09/633,320
Filed:	August 7, 2000

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Current U.S. Class:	725/129 ; 725/121
Current International Class:	H04N 7/173 (20060101)
Field of Search:	725/105,106,118,119,121,122,126,127,129

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Primary Examiner: Srivastava; Vivek
Attorney, Agent or Firm: Baker Botts L.L.P.

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Parent Case Text

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CROSS-REFERENCES TO RELATED APPLICATIONS

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.

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Claims

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I claim:

1. A method of providing first RF signals within a first frequency band from a first location to a multiplicity of second locations, providing bidirectional telephony signals between said first location and at least two of said multiplicity of said second locations, and providing second RF signals within a second frequency band from said at least two second locations to said first location on at least two separate optical paths and comprising: transmitting light at a first wavelength modulated by said first RF signals from said first location to at least two intermediate locations via said at least two separate optical paths and from each of said at least two intermediate locations to said multiplicity of second locations on a multiplicity of first paths, each having at least two electrical conductors; bidirectionally transmitting light at a second wavelength for carrying telephony signals both upstream and downstream on said at least two optical paths between said first location and said at least two intermediate locations and from said at least two intermediate locations to said second locations on a multiplicity of second paths having at least two electrical conductors; transmitting first and second RF signals at selected frequencies within a second frequency band from at least two of said multiplicity of second locations one each to said at least two intermediate locations on at least two of said multiplicity of first paths; further modulating said transmitted light having said second wavelength traveling from said at least two intermediate locations to said first location on said at least two optical paths with said first and second RF signals from said at least two second locations; and receiving said first and second RF signals within said second frequency band at said first location; receiving said light having said second wavelength at said first location traveling from a first one of said at least two intermediate locations on a first one of said at least two optical paths; receiving said light having said second wavelength at said first location traveling from a second one of said at least two intermediate locations on a second one of said at least two optical paths; recovering and attenuating first telephony signals received from light carried by said first one of said at least two optical paths by a first amount such that said first telephony signals are substantially at a preset value; recovering and attenuating second telephony signals received from light carried by said second one of said at least two optical paths by a second amount such that said second telephony signals are also substantially at said preset value; and recovering and attenuating said second RF signals traveling to said first location on said first one and said second one of said at least two optical paths by said first and second amounts respectively such that each of said attenuated second RF signals have substantially the same signal strength.

2. The method of claim 1 and further comprising: comparing the strength of recovered second RF signals within said second RF frequency band to a preset threshold; and inhibiting further transmission of said RF signals within said second RF frequency band if said compared signals are not equal to or greater than said preset threshold.

3. The method of claim 2 wherein recovering said second RF signals from said light waves comprises: receiving light traveling upstream and having said second wavelengths from said at least two optical paths by a photo diode having an anode and a cathode; recovering said second RF signals at one of said anode and cathode of said photo diode; and recovering telephony signals at the other one of said anode and cathode of said photo diode.

4. Communication apparatus comprising: a source for generating first RF signals at a first frequency band and adapted for distribution to a multiplicity of users; at least two transmission paths between a first location having said source and a least two of said multiplicity of users at least two second locations, at least a portion of each at least two transmission paths being optical; a first light generator for generating light at a first wavelength of light, said light being modulated to carry said first RF signals within said first frequency and on said optical portions of said transmission path; at least two pairs of second light generators one each of each pair located at an end of said optical portions of said at least two transmission paths and each second light generators for generating light at a second wavelength modulated to carry bidirectional telephony signals traveling between said first and said at least two second locations on said optical portions of said at least two transmission paths; second and third RF signals within a second frequency band generated at the two second locations and carried to said source one each on said at least two transmission paths by modulating said light having said second wavelength; an attenuator for attenuating first telephony signals recovered from the optical portion of a first one of said at least two transmission paths by a first amount such that said first telephony signals are at a preset value; an attenuator for attenuating second telephony signals recovered from the optical portion of a second one of said at least two transmission paths by a second amount such that said second telephony signals are at said preset value; and attenuators for attenuating said second and third RF signals recovered from the optical portions of said first and second transmission paths respectively such that each of said attenuated second and third RF signals have substantially the same signal strength.

5. The communication apparatus of claim 4 wherein at least one of said photo detectors is a photo diode having a cathode and an anode, and wherein said second RF signals are recovered at one of said anode and a cathode and said telephony signals are recovered at the other one of said anode and cathode.

6. The communication apparatus of claim 4 wherein said RF signals within said first frequency band have a frequency of between about 50 and 870 MHz.

7. The communication apparatus of claim 6 wherein said second and third RF signals within said second frequency band have a frequency of between about 5 and 50 MHz.

8. A method of providing first RF signals within a first frequency band from a first location to a multiplicity of second locations, providing bidirectional telephony signals between said first location and at least two of said multiplicity of said second locations, and providing second RF signals within a second frequency band from said at least two second locations to said first location on at least two separate optical paths and comprising: transmitting light at a first wavelength modulated by said first RF signals from said first location to at least two intermediate locations via said at least two separate optical paths and from each of said at least two intermediate locations to said multiplicity of second locations on a multiplicity of first paths, each having at least two electrical conductors; bidirectionally transmitting light at a second wavelength for carrying telephony signals both upstream and downstream on said at least two optical paths between said first location and said at least two intermediate locations and from said at least two intermediate locations to said second locations on a multiplicity of second paths having at least two electrical conductors; transmitting first and second RF signals at selected frequencies within a second frequency band from at least two of said multiplicity of second locations one each to said at least two intermediate locations on at least two of said multiplicity of first paths; further modulating said transmitted light having said second wavelength traveling from said at least two intermediate locations to said first location on said at least two optical paths with said first and second RF signals from said at least two second locations; and receiving said first and second RF signals within said second frequency band at said first location; amplifying at least one of said first and second RF signals within said second frequency band; amplifying the telephony signals traveling upstream, and amplification of said RF signals and said telephony signals occurring prior to said signals modulating said second wavelength of light; monitoring the signal strength of said amplified upstream telephony signals as a proportion of the modulated light having said second wavelength and generating a control signal therefrom; and adjusting the amplitude level of said RF signals and said upstream telephony signals in response to said generated signal.

9. Communication apparatus comprising: a source for generating first RF signals at a first frequency band and adapted for distribution to a multiplicity of users; at least two transmission paths between a first location having said source and at least two of said multiplicity of users at least two second locations, at least a portion of each of said at least two transmission paths being optical; a first light generator for generating light at a first wavelength of light, said light being modulated to carry said first RF signals within said first frequency and on said optical portions of said transmission path; at least two pairs of second light generators one each of each pair located at an end of said optical portions of said at least two transmission paths and each second light generators for generating light at a second wavelength modulated to carry bidirectional telephony signals traveling between said first and said at least two second locations on said optical portions of said at least two transmission paths; second and third RF signals within a second frequency band generated at the two second locations and carried to said source one each on said at least two transmission paths by modulating said light having said second wavelength; a first amplifier to amplify the upstream telephony signals and a second amplifier to amplify the RF return signals, said first and second amplifier providing electrical signals to modulate light at said second wavelength traveling upstream; a photo diode located at said at least one of said at least two second locations for monitoring the corresponding one of said pair of second light generators; circuitry connected to said photo diode to provide a control signal representative of the upstream telephony signal strength as a proportion of the output power of said one of said pair of second light generators; and said control signal connected to said first and second amplifiers for controlling the output signal strength of said first and second amplifier as a selected proportion of said light output at said second wavelength.

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Description

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BACKGROUND OF THE INVENTION

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, 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 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 Disclosed 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 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 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 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) 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 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 compression multiplexing) and is sometimes referred to as a "ping-pong" 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 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 of the fiber and, in fact, the available bandwidth of an optical fiber makes it possible to use a transmission technique such 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 telephone-related 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 at the first wavelength is transmitted through the single optical fiber from the second end to the first end where it is received and detected such that electrical signals representative of both the return telephony signals and the electrical signal representative of the TV related information or other RF return signals are generated. The return electrical telephony signals are transmitted to the first telephone-related device and the electrical TV related signals are transmitted to the TV signal source.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the present invention will be more fully disclosed when taken in conjunction with the following Detailed Description of the Preferred Embodiment(s) in which like numerals represent like elements and in which:

FIG. 1 is a prior art block diagram showing the present transmission and distribution of a typical coaxial TV and POTS telephone system;

FIG. 2 shows a POTS telephone system and a fiber optic TV distribution system having 1550 nanometer light carrying TV signals in one direction and 1310 nanometers of light carrying telephony signals in both directions;

FIG. 3 shows a block diagram of a preferred embodiment of the present invention incorporating portions of the existing POTS telephone system and the coaxial TV signal distribution system while using a single optical fiber for carrying the TV signals at 1550 nanometers of light downstream and the telephony signals in both directions at 1310 nanometers; and

FIGS. 4A and 4B show detailed block diagram of the invention of FIG. 3.

FIG. 5 illustrates how recovery circuits for different frequency bands can be connected one each to the anode and cathode of a photo diode to achieve high impedance separation.

FIG. 6 is a schematic representation of RF return signals having different optical power loses between "ONU's" (Optical Network Units) at various locations and an HDT distribution terminal.

FIG. 7 is a composite graph of the RF return signal spectrum with signals arriving at a common distribution terminal having different levels of optical power loss, including those shown in FIG. 6.

FIG. 8 is a composite graph of the RF return signal spectrum of FIG. 6 where all of the individual signals have been attenuated so as to have a constant power level.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring now to FIG. 1, there is shown a typical transmission and distribution system for cable TV and normal telephone service, referred to as POTS (plain old telephone service). As shown, cable TV source location 10 has cable TV transmission equipment 12 which may originate from several sources including a satellite receiver 14. The TV equipment 12 would then amplify this signal and send it out typically on a coaxial line such as line 16 to a distribution system which may include several stations such as station 18 where the signal is again amplified and further distributed to an even larger multiplicity of locations. Such re-amplification and further distribution may occur several times but eventually will arrive at a local distribution terminal 20 by means of a coaxial cable 12A from which it is then distributed to a home or building 22 by a coaxial cable 12B. As shown distribution terminal 20 may also provide TV signals to other buildings or homes such as indicated by bracket 24. Once the TV signal is received at building 22, it will then typically be provided to a TV set 26 directly or to a set-top or cable TV box 28. If the signal is first provided to the set-top box 28, it is then directly provided to TV set 26. It should be appreciated that the direction of travel for such signals is primarily unidirectional and downstream. That is, it travels primarily from the cable TV signal source 10 to the set-top box 28 in the building or home 22 at frequencies within a frequency band of between 5 870 MHz, and which TV channels have frequencies of between 50 870 MHz. If information is to be carried upstream or back to source 10, it will typically be at between 50 200 MHz.

Also shown is a typical telephone system or POTS which of course is two-way communication typically carried by means of a twisted pair of wires. In the example shown in FIG. 1, if someone at the cable TV signal source location 10 wishes to talk with someone at building 22, the telephone 30A is used in its normal manner. The two-way conversation is carried on between the person in building 10 using telephone 30A and by a person using telephone 30B in the home or building 22. This communication is typically carried through a pair of twisted wires such as indicated by 32, 32A, and 32B. In recent years, the regular telephone distribution system has also been used to provide communications between computers. This is done by the use of a modem 34 which connects a computer to the telephone line. As was the case with the TV signal distribution, there are typically several stations or substations such as substation 18A between the two telephones 30A and 30B located at the building 10 and the building 22, respectively. Such distribution terminals or stations allow telephone services between all subscribers with which we are all well aware. However, as shown in portion 20A of distribution terminal 20, there may also be several other buildings or homes connected to telephone distribution terminal 20 as indicated by bracket 24A. As was discussed earlier, communications between buildings 10 and 22 were typically accomplished through regular telephone service by individuals talking to each other. However with more efficient automation, telephone lines may also be connected up to the set-top box 28 as indicated by wires 36. In addition, in the distribution terminal 38 at the cable TV signal location, there is also a telephone connection to the TV signal equipment 12, such that it is now possible that movies or information concerning the TV signals and TV equipment can be communicated between the two locations.

As demands increase for more and more TV channels and better and more efficient transmission techniques without disruption and interference, the long runs of coaxial cable are simply becoming inefficient and inadequate. Thus as is shown in FIG. 2, there is an improved system for the transmission of TV signals between the TV signal source location 10 and the building or home 22. In the systems shown in FIG. 2, there is also shown a standard telephone or POTS system as discussed above.

In the improved television transmission system, however, the transmission is achieved by a fiber optical cable as indicated by fiber optical cables 42 and 42A. As shown in FIG. 2, the same coaxial cable 12B exist between the distribution terminal 20 and the home of building 22. However, also as shown distribution terminal 20 includes new equipment 46 which receives the light transmitted on fiber optic 42 and converts it to electrical signals and conversely receives electrical signals from 12B and converts the electrical signals to light signals for transmission on fiber optic 42A. However as will be appreciated by those skilled in the art, the TV signals from the TV signal source building 10 normally travel downstream only and are continuous. Thus, if bidirectional communications between the cable TV signal source 10 and the distribution terminal 20 are to take place, some sort of sharing of the individual fiber optics 42 and 42A as well as the copper wire 12B must be provided. Thus, in the example shown, the TV signals travel in a single direction (i.e., downstream) from the TV signal source at location 10 to the home or building 22 by light waves having a length of at 1550 nanometers. Any return communication traveling on optical fibers 42 and 42A must be carried at a different wavelength of light such as 1310 nanometers which travels upstream to the TV signal source location 10. Likewise, if bidirectional communication is to take place on the single coaxial cable 12B between distribution terminal 20 and home or building 22, the transmission of such bidirectional communication transmission will be at different frequencies. Thus, in the illustrated example, the 1550 nanometer light waves will be converted to electrical signals having a frequency band of between about 50 and 800 MHz which travel in a single direction from distribution terminal 20 to a multitude of homes or buildings 22. The return signals from a cable modem or set-top box at building 22 are then carried at about 5 to 50 MHz back to the distribution terminal 20 and then used to modulate light waves having a wavelength of 1310 nanometers. Thus, it is seen that it is possible by the use of a single fiber optic cable as well as using existing infrastructure copper wiring such as coaxial cable to transmit a broad frequency band of TV signals carrying multiple channels of TV information at one wavelength of light. The individual TV channels are then converted to electrical signals at a specific frequency within a selected frequency band, such as for example, only the 50 800 MHz frequency band. Conversely, electrical control or RF return signals within the 5 50 MHz frequency band are converted to light at a wavelength different from that provided in the downstream mode and transmitted back to the TV signal source location 10. The return wavelength of light in the illustrated example is 1310 nanometers.

Referring now to FIG. 3 there is shown a simplified block diagram of the overall operation of the present invention which takes partial advantage of the existing telephone and coaxial TV distribution systems while also using a single optical fiber. 42A for part of the bidirectional telephone transmission (POTS) as well as part of the transmission path between the TV signal source location 10 and the building or home 22. It should be noted that, although the