Increasing data throughput in optical fiber transmission systems

• US 7,307,569 B2
• Filed: 11/15/2006
• Issued: 12/11/2007
• Est. Priority Date: 03/29/2001
• Status: Expired due to Fees

• Current Assignee: Quellan, Inc. (Renesas Electronics Corporation)
• Original Assignee: Quellan, Inc. (Renesas Electronics Corporation)
• Inventors: Vrazel, Michael G., Laskar, Joy, Jung, Sungyong, Gebara, Edward, Ralph, Stephen E., Hietala, Vincent Mark
• Primary Examiner(s): Jeanglaude; Jean Bruner
• Application Number:
  US11/599,835
• Publication Number:
  US 20070222654A1
• Time in Patent Office: 391 Days
• Field of Search: 714/704, 341/144, 372/38.02, 372/20, 398/87, 398/9
• US Class Current: 341/144
• CPC Class Codes: H03M 1/08 of noise H03M1/0617 takes precedence
• CPC Class Codes: H03M 1/123 Simultaneous, i.e. using one converter per channel but with common control or reference circuits for multiple converters
• CPC Class Codes: H03M 1/1265 Non-uniform sampling
• CPC Class Codes: H03M 1/745 with weighted currents
• CPC Class Codes: H04B 10/516 Details of coding or modulation

Abstract

Data throughput rates are increased in an optical fiber communication system without requiring replacement of the existing optical fiber in a link. Channel throughput is increased by upgrading the components and circuitry in the head and terminal of an optical fiber communication system link. Aggregate throughput in a fiber optic link is increased beyond the range of conventional Wavelength Division Multiplexed (WDM) upgrades, while precluding the necessity of replacing existing fiber plants. The increase in system throughput is achieved by using advanced modulation techniques to encode greater amounts of data into the transmitted spectrum of a channel, thereby increasing the spectral efficiency of each channel. This novel method of increasing transmission capacity by upgrading the head and terminal of the system to achieve greater spectral efficiency and hence throughput, alleviates the need to replace existing fiber plants. Spectrally efficient complex modulation techniques can be supported by interface circuits with an increased level of signal processing capability in order to both encode multiple bits into a transmitted symbol and decode the original data from the received symbols.

Claims

1. A transmission link for transmitting an optical fiber communication signal for transmission over an optical fiber, the optical transmission link comprising:

a symbolizer for receiving an input data signal comprising a series of pulses, each pulse having one of two distinct pulse levels, wherein the symbolizer is operative to convert n pulses from the input data sign into an error resistant n-bit output word, and further operative to generate an output symbol representing one of 2ⁿ distinct values; and

an optical source for transmitting an output signal comprising a series of the optical symbols over the optical fiber, each optical symbol having one of 2ⁿ intensity levels; and

wherein the symbolizer is further operative to modify a signal property of each optical symbol, according to a signal property of a preceding optical symbol and a signal property of a succeeding optical symbol.

2. The transmission link of claim 1, wherein the input data signal is received from n separate channels, wherein the output signal comprises n-times higher data rate than the n separate channels.

3. The transmission link of claim 1, wherein the digital input signal is received from a single channel.

4. The transmission link of claim 1, wherein the symbolizer further comprises a predistortion circuit.

5. The transmission link of claim 4, wherein the predistortion circuit is further operative to interrogate the output signal to determine the signal property of the first output symbol.

6. The transmission link of claim 4, wherein the predistortion circuit is further operative to interrogate the output signal to determine the signal property of the preceding output symbol.

7. The transmission link of claim 4, wherein the predistortion circuit is further operative to interrogate the output signal to determine the signal property of the succeeding output symbol.

8. The method of claim 4, wherein the predistortion circuit performs the function of accessing a look up table to determine an appropriate modification of the transmitted optical symbol.

9. The transmission link of claim 4, wherein the signal property of the first output symbol is an amplitude of the first output signal and the predistortion circuit is further operative to modify the first output symbol by modifying the amplitude of the first output symbol.

10. The transmission link of claim 9, wherein the predistortion circuit is further operative to modify the amplitude of the first output symbol based on the amplitude of the first output symbol.

11. The transmission link of claim 9, wherein the predistortion circuit is further operative to modify the amplitude of the first output symbol based on the amplitude of the succeeding output symbol.

12. The transmission link of claim 9, wherein the predistortion circuit is further operative to modify the amplitude of the first output symbol based on the amplitude of the preceding output symbol.

13. The transmission link of claim 4, wherein the signal property of the first output symbol is a phase of the first output signal and the predistortion circuit is further operative to modify the first output symbol by modifying the phase of the first output symbol.

14. The transmission link of claim 13, wherein the predistortion circuit is further operative to modify the phase of the first output symbol based on the phase of the first output symbol.

15. The transmission link of claim 13, wherein the predistortion circuit is further operative to modify the phase of the first output symbol based on the phase of the succeeding output symbol.

16. The transmission link of claim 13, wherein the predistortion circuit is further operative to modify the phase of the first output symbol based on the phase of the preceding output symbol.

17. The transmission link of claim 4, wherein the signal property of the first output symbol is a frequency of the first output signal and the predistortion circuit is further operative to modify the first output symbol by modifying the frequency of the find output symbol.

18. The transmission link of claim 17, wherein the predistortion circuit is further operative to modify the frequency of the first output symbol based on the frequency of the first output symbol.

19. The transmission link of claim 17, wherein the predistortion circuit is further operative to modify the frequency of the first output symbol based on the frequency of the preceding output symbol.

20. The transmission link of claim 17, wherein the predistortion circuit is further operative to modify the frequency of the first output symbol based on the frequency of the succeeding output symbol.

21. The transmission link of claim 1, further comprising a desymbolizer comprising a photodetector, a post-compensation circuit, and a decoder.

22. The transmission link of claim 21, wherein the desymbolizer is associated with a receiver functionally connected to the optical fiber, and wherein the desymbolizer is operative to decode the output signal into n output streams, each output stream having a data rate of 1/n of the output signal data rate.

23. An optical transmitter for generating an optical fiber communication signal for transmission over an optical fiber, the optical transmitter comprising:

a symbolizer for receiving an input data signal comprising a series of pulses, each pulse having one of two distinct pulse levels, wherein the symbolizer is operative to convert n pulses from the input data signal into an error resistant n-bit output word, and further operative to generate an output symbol representing one of 2ⁿ distinct values, and

an optical source for transmitting an output signal comprising at least one optical symbol over the optical fiber, each optical symbol represented by one of 2ⁿ optical intensity levels; and

wherein the symbolizer further comprises a linearizer circuit operative to introduce a corrective offset in the output signal to counteract a nonlinear response associated with the optical source.

24. The optical transmitter of claim 23, wherein the input data signal is received from n separate channels, wherein the output signal comprises n-times higher data rate than the n separate channels.

25. The optical transmitter of claim 23, wherein the input data signal is received from a single channel.

26. The optical transmitter of claim 23, wherein a drive current controls the optical source.

27. The optical transmitter of claim 23, wherein the linearizer circuit is further operative to reduce the drive current associated with the output signally an error current.

28. The optical transmitter of claim 23, wherein the linearizer circuit comprises a nonlinear element operative to shunt the error current from the drive current.

29. The optical transmitter of claim 23, wherein the corrective offset comprises a reduction in the drive voltage associated with the output signal by an error voltage.

30. A method for increasing the data throughput of an existing optical fiber communication system without replacing an optical fiber plant associated with the existing optical fiber communication system, the method comprising the steps of:

replacing an existing transmitter with an upgrade transmitter having a symbolizer for receiving an input data signal comprising a series of pulses, each pulse having one of two distinct pulse levels, wherein the symbolizer is operative to convert n pulses from the input data signal into an error resistant n-bit output word, and further operative to generate an output symbol representing one of 2ⁿ distinct values; and

, the output symbol representing the n-bit output word; and

replacing an existing receiver with an upgrade receiver having a desymbolizer operative to receive and decode an output signal generated by the upgrade transmitter, the output signal comprising a series of input symbols.

31. The method claim of 30, wherein the symbolizer is further operative to convert each output symbol to an n-bit error protected symbol using error protection coding, and wherein the transmitted output signal comprises n times higher data rate than a data rate associated with each of the separate input data signals.

32. An optical transmitter for generating an optical fiber communication signal for transmission over an optical fiber while minimizing a bit error rate, the optical transition comprising:

a symbolizer for receiving an input data signal comprising a series of pulses, each pulse having one of two distinct pulse levels, wherein the symbolizer is operatives to convert n pulses from the input data signal into an error resistant n-bit output word, and further operative to generate an output symbol representing one of 2ⁿ distinct values; and

an optical source for transmitting an output signal comprising at least one error resistant output symbol over the optical fiber, each error resistant output symbol corresponding to one of 2ⁿ optical source intensity levels.

33. The optical transmitter of claim 32, wherein the input data signal is received from n separate channels, wherein the output signal comprises n-times higher data rate than the n separate channels.

34. The optical transmitter of claim 32, wherein the input data signal is received from a single channel.

35. The optical transmitter of claim 32, wherein the error resistant output symbol is convolutionally coded.

36. The optical transmitter of claim 32, wherein the error resistant output symbol is encoded with trellis coding.

37. The optical transmitter of claim 32, wherein the error resistant symbol is encoded with block coding.

38. The optical transmitter of claim 32, wherein the error resistant code is a Gray code.

39. The optical transmitter of claim 38, wherein the Gray code is characterized by having adjacent words that are differentiated from each other by a change in only one bit.

40. The optical transmitter of claim 32, wherein the error resistant code is a Q-Gray code.

41. The optical transmitter of claim 40, wherein the Q-Gray code is characterized by having adjacent words that are differentiated from each other by a change in only one bit.

42. A method for increasing the channel data rate throughput in an optical fiber communication system while minimizing a bit error rate, the method comprising the steps of:

receiving a digital input signal, comprising a series of input pulses, each input pulse having one of two pulse levels;

creating a digital input word having n bits from the digital input signal;

converting the digital input word to an error resistant digital input word;

converting each error resistant digital input word to a corresponding error resistant output symbol having one of 2ⁿ distinct values;

generating an output signal comprising a series of error resistant output symbols; and

transmitting each error resistant output symbol to a receiver over a fiber optic link.

43. The method of claim 42, wherein the digital input signal is received from n separate channels, the output signal having n times higher data rate than that of one of the n separate channels.

44. The method of claim 42, wherein the digital input signal is received from a single channel.

45. The method of claim 42, wherein the error resistant output symbol is convolutionally coded.

46. The method claim 42, wherein the error resistant output symbol is encoded with block coding.

47. The method of claim 42, wherein the error resistant output symbol is encoded with trellis coding.

48. The method of claim 42, wherein the error resistant code is a Gray code.

49. The method of Claim 48, wherein the Gray code is characterized by having adjacent words that are differentiated from each other by a change in only one bit.

50. The method of claim 42, wherein the error resistant code is a Q-Gray code.

51. The method of claim 50, wherein the Q-Gray code is characterized by having adjacent words that are differentiated from each other by a change in only one bit.

52. A method for increasing the channel data rate throughput in an optical fiber communication system while minimizing a bit error rate;

the method comprising the steps of;

receiving a digital input word having n bits;

converting the digital input word to an error resistant digital input word;

converting each error resistance digital input word to a corresponding error resistant output symbol representing one of 2ⁿ distinct values; and

transmitting each error resistant output symbol to a receiver over a fiber optic link.