Fiber optic digital data transmitting system

• US 4,561,117 A
• Filed: 12/09/1983
• Issued: 12/24/1985
• Est. Priority Date: 07/29/1981
• Status: Expired due to Fees

• Current Assignee: Digital Communications Corp.
• Original Assignee: Digital Communications Corp.
• Inventors: Kuhn, Loughrey R.
• Primary Examiner(s): Coles, Sr., Edward L.
• Application Number:
  US06/595,510
• Time in Patent Office: 746 Days
• Field of Search: 455/608, 455/618, 455/617, 455/619, 370/3, 370/110.4
• US Class Current: 398/190
• CPC Class Codes: H04B 10/54 Intensity modulation
• CPC Class Codes: H04B 10/697 Arrangements for reducing noise and distortion
• CPC Class Codes: H04J 7/00 Multiplex systems in which the amplitudes or durations of the signals in individual channels are characteristic of those channels
• CPC Class Codes: H04L 5/04 the signals being represented by different amplitudes or polarities, e.g. quadriplex

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 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.

Claims

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 occurrence of the non-zero digital amplitudes of the digital signal and other information;

(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.

3. A transmitter in accordance with claims 1 or 2 wherein the means for combining comprises an amplifier.

4. A transmitter in accordance with claim 1 or 2 wherein the time varying signal is a time varying signal of a fixed frequency which is present throughout the entire duration of each non-zero amplitude level of the digital signal to be transmitted.

5. A transmitter in accordance with claim 1 wherein the time varying signal is a digital signal.

6. A transmitter in accordance with claim 1 wherein the means for producing the optical signal is a light emitting diode.

7. A transmitter in accordance with claims 1 or 2 wherein the means for producing the time varying signal comprises means for producing electrical oscillations having an input which is adapted to be coupled to the source of digital data and an output coupled to the means for combining for producing electrical oscillations in response to a digital signal of a non-zero amplitude being present at the input.

2. 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 non-zero amplitude levels of a digital signal having zero and non-zero levels, the time varying signal being used to encode at least the occurrence of the non-zero digital amplitudes of the digital signal;

(b) means for combing 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.

8. A transmitter in accordance with claim 2 wherein the means for modulating is an intensity modulator.

9. A transmitter in accordance with claim 8 wherein the intensity modulator is a BRAGG cell.

10. A transmitter in accordance with claim 8 wherein the intensity modulator is a POCKELS cell.

11. A transmitter in accordance with claim 8 wherein the intensity modulator is a STARK cell.

12. 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.

13. A transmitter in accordance with claim 2 wherein the means for producing a beam of light is a continuous wave laser.

14. 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 and other information;

(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.

15. 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 and other information;

(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 and other information.

16. A digital data transmitting system in accordance with claim 15 further comprising:

(a) means responsive to the means for detecting the time varying signal for producing a pluse each time the presence of a time varying signal is detected to reproduce the transmitted digital signal; and

(b) means for detecting the other information contained within the time varying signal in addition to the presence of a non-zero amplitude of the digital signal in response to each time the means for detecting detects the presence of a time varying signal.

20. A system in accordance with claim 15 or 17 wherein the means for combining comprises an amplifier.

21. A system in accordance with claim 20 wherein the time varying signal is a signal of a fixed frequency which is present throughout the entire duration of each non-zero amplitude level of the digital signal to be transmitted.

22. A system in accordance with claim 20 wherein the time varying signal is a digital signal.

23. A system in accordance with claim 20 wherein the time varying signal is a series of time varying signals of a single frequency which are separated by zero amplitude levels.

24. A system in accordance with claim 20 wherein the means for producing the optical signal is a light emitting diode.

25. A system in accordance with claims 15 and 17 wherein the means for producing the time varying signal comprises means for producing electrical oscillations having an input which is adapted to be coupled to the source of digital data and an output coupled to the means for combining for producing electrical oscillations in response to a digital signal of a non-zero amplitude being present at the input.

17. 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 and other information; and

(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 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

(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 and the other information.

18. A digital data transmitting system in accordance with claim 17 further comprising:

(a) means responsive to the means for detecting the time varying signal for producing a pulse each time the presence of a time varying signal is detected to reproduce the transitted digital signal; and

(b) means for detecting the other information contained within the time varying signal in addition to the presence of a non-zero amplitude of the digital signal in response to each time the means for detecting detects the presence of a time varying signal.

19. The digital transmitting system in accordance with claim 17 wherein:

(a) the means for producing the pulse comprises a one-shot multivibrator and

(b) a means is coupled between the means for detecting the modulated optical signal and the means for detecting the time varying signal for amplifying the time varying signal produced by the detection of the modulated optical signal.

26. A system in accordance with claim 18 wherein the means for modulating is an intensity modulator.

27. A transmitter in accordance with claim 26 wherein the intensity modulator is a STARK cell.

28. A transmitter in accordance with claim 26 wherein the intensity modulator is a BRAGG cell.

29. A transmitter in accordance with claim 26 wherein the intensity modulator is a POCKELS cell.

30. 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 other information; and

(b) means for producing a pulse in response to the detection of each time varying signal.

31. A receiver in accordance with claim 30 wherein the means for detecting the composite signal comprises:

(a) a first channel coupled to the composite signal having low pass filter means for passing the digital signal but rejecting the time varying signal;

(b) a second channel coupled to the composite signal having means responsive to the time varying signal to produce an output signal in response to the time varying signal;

(c) summing means coupled to the low pass filter means and to the output signal of the means responsive to the time varying signal for adding the digital signal and the output signal; and

(d) threshold detection means for detecting the sum of the output signal and the digital signal as the digital signal.

32. A receiver in accordance with claim 31 wherein the means responsive to the time varying signal includes a phase lock loop.

33. A receiver in accordance with claim 31 wherein:

(a) a first amplifier is contained in the first channel with a first gain;

(b) a second amplifier is contained in the second channel with a second gain; and

(c) the ratio of the gains is ##EQU2## wherein m is the modulation depth of the time varying signal with respect to the amplitude of the non-zero level and N₁ and N₂ are the noise levels of the appropriate channels.

34. A receiver in accordance with claim 32 wherein:

(a) a first amplifier is contained in the first channel with a first gain;

(b) a second amplifier is contained in the second channel with a second gain; and

(c) the ratio of the gains is ##EQU3## wherein m is the modulation depth of the time varying signal with respect to the amplitude of the non-zero level and N₁ and N₂ are the noise levels of the appropriate channels.

35. A receiver in accordance with claim 32 further comprising:

means located in the second channel which is coupled to the phase lock loop for detecting an output signal of the phase lock loop to produce the output signal in response to the time varying signal.

36. A receiver in accordance with claim 35 further comprising means for detecting other information which is coupled to the means located in the second channel which is coupled to the phase lock loop.