Fiber optic digital data transmitting system

Abstract

A fiber optic digital data transmitting system is disclosed which has the capability of transmitting and accurately reproducing digital data signals at the receiver even when the optical signal is attenuated in the fiber optic transmitting medium. A composite signal is produced at the transmitter which is the time coincident sum of the non-zero amplitude of the digital data signal to be transmitted and a time varying signal which encodes each non-zero amplitude of the digital signal and other information. The composite signal modulates an optical carrier signal which is coupled to a fiber optic transmission medium which couples the transmitter to the receiver. At the receiver, the presence of each time varying signal is detected as a non-zero amplitude of the digital signal. Circuitry is are provided in the receiver for producing a pulse in response to the detection of each time varying signal for reproducing the transmitted digital signal and for detecting any information in addition to the non-zero amplitude of the digital signal which has been encoded in the time varying signal. The present invention is compatible with existing PCM systems which utilize threshold detection.

I claim: 
     
       1. A transmitter for use in a digital data transmitting system having a transmitter, an optical transmission medium and a receiver comprising: (a) means for producing a time varying signal which is time coincident with the non-zero amplitude levels of a digital signal having zero and non-zero amplitudes, the time varying signal being used to encode the occurence of the non-zero digital amplitudes of the digital signal;   (b) means for combining two input signals into a time coincident composite output signal, the first input signal being from a source of a digital signal which is to be transmitted, and the second input signal being from the means for producing the time varying signal; and   (c) means coupled to the means for combining for producing an optical signal varying in amplitude in accordance with the composite signal.   
     
     
       2. A transmitter for uase in a digital data transmitting system having a transmitter, an optical transmission medium and a receiver comprising: (a) means for producing a time varying signal which is time coincident with non-zero amplitude levels of a digital signal having zero and non-zero levels, the time varying signal being used to encode the occurence of the non-zero digital amplitudes of the digital signal;   (b) means for combining two input signals into a composite output signal, the first input signal being from a source of a digital signal which is to be transmitted and the second input being coupled to the means for producing the time varying signal;   (c) means for producing a beam of an optical carrier signal which is adapted to be coupled to the optical transmission medium used for transmitting the digital signal; and   (d) means disposed within the beam which is responsive to the means for combining for modulating the beam with the composite signal.   
     
     
       3. A transmitter in accordance with claim 2 wherein the means for modulating is an intensity modulator. 
     
     
       4. A transmitter in accordance with claim 3 wherein the intensity modulator is a STARK cell. 
     
     
       5. A transmitter in accordance with claim 2 wherein the modulator varies the polarization of the coherent electromagnetic energy in accordance with the amplitude of the composite signal. 
     
     
       6. A transmitter in accordance with claim 2 wherein the means for producing a beam of light is a continuous wave laser. 
     
     
       7. A transmitter for use in a digital data transmitting system having a transmitter, a transmission medium and a receiver comprising: (a) means for producing a time varying signal which is time coincident with non-zero amplitude levels of a digital signal having zero and non-zero levels, the time varying signal being used to encode the occurrence of the non-zero digital amplitudes of the digital signal;   (b) means for combining two input signals into a time coincident composite output signal, the first input signal being from a source of a digital signal and the second input being coupled to the means for producing the time varying signal; and   (c) means coupled to the means for combining for modulating a carrier signal in accordance with the composite signal.   
     
     
       8. A digital data transmitting system comprising: (a) means for producing a time varying signal which is time coincident with non-zero amplitude levels of a digital signal having zero and non-zero amplitude levels, the time varying signal being used to encode the occurrence of the non-zero digital amplitudes of the digital signal;   (b) means for combining two input signals into a time coincident composite output signal, the first input signal being from a source of a digital signal and the second input being coupled to the means for producing the time varying signal;   (c) means coupled to the means for combining for producing a modulated optical carrier signal varying in amplitude in accordance with the composite signal;   (d) an optical transmission medium having an input and an output, the input being coupled to the means for producing a modulated optical carrier signal;   (e) means for detecting the modulated optical signal to produce a time varying signal which varies in accordance with the composite signal, the means for detecting being coupled to the output of the optical transmission medium; and   (f) means for detecting the time varying signal, the detection of the time varying signal indicating reception of a digital signal of non-zero amplitude.   
     
     
       9. A digital data transmitting system comprising: (a) means for producing a time varying signal which is time coincident with non-zero amplitude levels of a digital signal having zero and non-zero levels, the time varying signal being used to encode the occurrence of the non-zero digital amplitudes of the digital signal;   (b) means for combining two input signals into a time coincident composite output signal, the first input signal being from a source of a digital signal and the second input signal being coupled to the means for producing the time varying signal;   (c) means for producing a beam of an optical carrier signal which is used for transmitting the digital signal;   (d) means disposed within the beam which is responsive to the means for combining for modulating the beam of coherent electromagnetic energy with the composite signal;   (e) an optical transmission medium having an input and an output, the input being coupled to the means for producing a modulated optical carrier signal;   (f) means for detecting the modulated optical carrier signal for producing a time varying signal which varies in accordance with the composite signal, the means for detecting being coupled to the output of the optical transmission medium; and   (g) means for detecting the time varying signal, the detection of the time varying signal indicating the reception of a digital signal of a non-zero amplitude.   
     
     
       10. A receiver for use in a digital data transmission system having a transmitter, an optical transmission medium and a receiver comprising: (a) means for detecting a composite signal which has been modulated upon a received optical carrier signal, the composite signal comprising a time coincident non-zero amplitude digital signal and a time varying signal which encodes the non-zero digital amplitude of the digital signal; and   (b) means for producing a pulse in response to the detection of each time varying signal. .Iadd.   
     
     
       11.  A digital data system comprising: a source of digital data;   a source of additional information, responsive to non-zero levels of the digital data, for outputting additional information only within a time interval coincident with the non-zero levels of the digital data; and   a composite signal generator, responsive to the source of digital data and the source of additional information for combining the digital data and the outputted additional information into a composite signal which is a function of the digital data non-zero levels and the outputted additional information. .Iaddend. .Iadd.12. A digital data system in accordance with claim 11 wherein:   the composite signal generator adds the outputted additional information to the digital data non-zero levels to produce the composite signal. .Iaddend. .Iadd.13. A digital data system in accordance with claim 11 wherein:   
     
     
       the outputted additional information is a single tone. .Iaddend. .Iadd.14. A digital data system in accordance with claim 12 wherein: the outputted additional information is a single tone. .Iaddend. .Iadd.15. A digital data system in accordance with claim 11 wherein:   the outputted additional information is a plurality of single frequency tones. .Iaddend. .Iadd.16. A digital data system in accordance with claim 12 wherein:   the outputted additional information is a plurality of single frequency tones. .Iaddend. .Iadd.17. A digital data system in accordance with claim 11 wherein:   the outputted additional information is a plurality of tones having different frequencies. .Iaddend. .Iadd.18. A digital data system in accordance with claim 12 wherein:   the outputted additional information is a plurality of tones having   
     
     
        different frequencies. .Iaddend. .Iadd.19.  A digital data system in accordance with claim 11 wherein: the outputted additional information is a PCM signal. .Iaddend. .Iadd.20. A digital data system in accordance with claim 12 wherein:   the outputted additional information is a PCM signal. .Iaddend. .Iadd.21. A digital system in accordance with claim 11 further comprising:   a receiver, responsive to the composite signal, for outputting the additional information. .Iaddend. .Iadd.22. A digital system in accordance with claim 21 further comprising:   a light source, responsive to the outputted composite signal, for modulating an optical carrier with the additional information;   an optical carrier medium for transmitting the modulated carrier from the light source to the receiver; and wherein   the receiver includes a light detector, responsive to the modulated carrier received by the receiver, for outputting the composite signal including the additional information which is outputted by the receiver. .Iaddend. .Iadd.23. A digital system in accordance with claim 12 further comprising:   a receiver, responsive to the composite signal, for outputting the additional information. .Iaddend. .Iadd.24. A digital system in accordance with claim 23 further comprising:   a light source, responsive to the outputted composite signal, for modulating an optical carrier with the additional information;   an optical carrier medium for transmitting the modulated carrier from the light source to the receiver; and wherein   the receiver includes a light detector, responsive to the modulated carrier received by the receiver, for outputting the composite signal including the additional information which is outputted by the receiver. .Iaddend. .Iadd.25. A digital system in accordance with claim 13 further comprising:   a receiver, responsive to the composite signal, for outputting the   
     
     
        additional information. .Iaddend. .Iadd.26.  A digital system in accordance with claim 25 further comprising: a light source, responsive to the outputted composite signal, for modulating an optical carrier with the additional information;   an optical carrier medium for transmitting the modulated carrier from the light source to the receiver; and wherein   the receiver includes a light detector, responsive to the modulated carrier received by the receiver, for outputting the composite signal including the additional information which is outputted by the receiver. .Iaddend. .Iadd.27. A digital system in accordance with claim 14 further comprising:   a receiver, responsive to the composite signal, for outputting the additional information. .Iaddend. .Iadd.28. A digital system in accordance with claim 27 further comprising:   a light source, responsive to the outputted composite signal, for modulating an optical carrier with the additional information;   an optical carrier medium for transmitting the modulated carrier from the light source to the receiver; and wherein   the receiver includes a light detector, responsive to the modulated carrier received by the receiver, for outputting the composite signal including the additional information which is outputted by the receiver. .Iaddend.   
     
     
        .Iadd.29.  A digital system in accordance with claim 15 further comprising: a receiver, responsive to the composite signal, for outputting the additional information. .Iaddend. .Iadd.30. A digital system in accordance with claim 29 further comprising:   a light source, responsive to the outputted composite signal, for modulating an optical carrier with the additional information;   an optical carrier medium for transmitting the modulated carrier from the light source to the receiver; and wherein   the receiver includes a light detector, responsive to the modulated carrier received by the receiver, for outputting the composite signal including the additional information which is outputted by the receiver. .Iaddend.   
     
     
        .Iadd.31.  A digital system in accordance with claim 16 further comprising: a receiver, responsive to the composite signal, for outputting the additional information. .Iaddend. .Iadd.32. A digital system in accordance with claim 31 further comprising:   a light source, responsive to the outputted composite signal, for modulating an optical carrier with the additional information;   an optical carrier medium for transmitting the modulated carrier from the light source to the receiver; and wherein   the receiver includes a light detector, responsive to the modulated carrier received by the receiver, for outputting the composite signal including the additional information which is outputted by the receiver. .Iaddend. .Iadd.33. A digital system in accordance with claim 17 further comprising:   a receiver, responsive to the composite signal, for outputting the   
     
     
        additional information. .Iaddend. .Iadd.34.  A digital system in accordance with claim 33 further comprising: a light source, responsive to the outputted composite signal, for modulating an optical carrier with the additional information;   an optical carrier medium for transmitting the modulated carrier from the light source to the receiver; and wherein   the receiver includes a light detector, responsive to the modulated carrier received by the receiver, for outputting the composite signal including the additional information which is outputted by the receiver. .Iaddend. .Iadd.35. A digital system in accordance with claim 18 further comprising:   a receiver, responsive to the composite signal, for outputting the additional information. .Iaddend. .Iadd.36. A digital system in accordance with claim 35 further comprising:   a light source, responsive to the outputted composite signal, for modulating an optical carrier with the additional information;   an optical carrier medium for transmitting the modulated carrier from the light source to the receiver; and wherein   the receiver includes a light detector, responsive to the modulated carrier received by the receiver, for outputting the composite signal including the additional information which is outputted by the receiver. .Iaddend.   
     
     
        .Iadd.37.  A digital system in accordance with claim 19 further comprising: a receiver, responsive to the composite signal, for outputting the additional information. .Iaddend. .Iadd.38. A digital system in accordance with claim 37 further comprising:   a light source, responsive to the outputted composite signal, for modulating an optical carrier with the additional information;   an optical carrier medium for transmitting the modulated carrier from the light source to the receiver; and wherein   the receiver includes a light detector, responsive to the modulated carrier received by the receiver, for outputting the composite signal including the additional information which is outputted by the receiver. .Iaddend.   
     
     
        .Iadd.39.  A digital system in accordance with claim 20 further comprising: a receiver, responsive to the composite signal, for outputting the additional information. .Iaddend. .Iadd.40. A digital system in accordance with claim 39 further comprising:   a light source, responsive to the outputted composite signal, for modulating an optical carrier with the additional information;   an optical carrier medium for transmitting the modulated carrier from the light source to the receiver; and wherein   the receiver includes a light detector, responsive to the modulated carrier received by the receiver, for outputting the composite signal including the additional information which is outputted by the receiver. .Iaddend.