Modulated optical source and methods of its operation

1. A modulated optical source comprising a light source, an optical modulator, and a control circuit operatively coupled to the light source and the optical modulator, wherein:

(a) the control circuit is arranged and connected so as to receive an electrical modulating signal that includes alternating active and idle temporal segments, wherein each one of the active temporal segments of the electrical modulating signal encodes corresponding information;

(b) the modulated optical source is arranged and connected so as to produce, in response to the electrical modulating signal, an output optical signal (i) that is characterized by an output optical frequency and an output optical spectral width and (ii) that includes alternating active and idle temporal segments corresponding to the active and idle temporal segments of the electrical modulating signal;

(c) the light source and the optical modulator are arranged so that at least a portion of a source optical signal produced by the light source is received by the optical modulator, and the output optical signal comprises one or more portions of the source optical signal that are transmitted by the optical modulator;

(d) the control circuit is arranged and connected (i) to the light source so as to cause the light source to produce the source optical signal at a non-zero source idle power level during each idle temporal segment, and (ii) to the optical modulator so as to cause the optical modulator to transmit the source optical signal at a substantially constant idle transmission level during each idle temporal segment;

(e) the control circuit is arranged and connected (i) to the light source so as to cause the light source to produce the source optical signal at a non-zero source average active power level during each active temporal segment, and (ii) to the optical modulator so as to cause the optical modulator to transmit the source optical signal at an average active transmission level during each active temporal segment, the average active transmission level being higher than the idle transmission level; and

(f) the control circuit is arranged and connected to the light source or the optical modulator so as to result in modulation, during each active temporal segment, of the output optical signal in accordance with the electrical modulating signal, so that each active temporal segment of the output optical signal encodes the information of the corresponding active temporal segment of the electrical modulating signal.

2. The modulated optical source of claim 1 wherein the control circuit is arranged so that the information is encoded, onto each corresponding active temporal segment of the electrical modulating signal and the output optical signal, only within a specified modulation frequency range that is from about 5 MHz to about 200 MHz.

3. The modulated optical source of claim 1 wherein the idle transmission level is more than about 30. dB lower than the average active transmission level.

4. The modulated optical source of claim 1 wherein the source idle power level, the source average active power level, the idle transmission level, and the average active transmission level result in (i) an average idle power level of the output optical signal during each idle temporal segment that is less than about −30. dBm, and (ii) an average active power level of the output optical signal during each active temporal segment that is greater than about 0. dBm.

5. The modulated optical source of claim 1 wherein the source idle power level, the source average active power level, the idle transmission level, and the average active transmission level result in (i) an average idle power level of the output optical signal during each idle temporal segment that is less than about −37. dBm, and (ii) an average active power level of the output optical signal during each active temporal segment that is greater than about 3. dBm.

6. The modulated optical source of claim 1 wherein the modulated optical source is arranged so that, upon a transition from an idle temporal period to an active temporal period, the output optical frequency varies by less than about 2.0 GHz.

7. The modulated optical source of claim 1 wherein the source idle power level is about equal to the source average active power level.

8. The modulated optical source of claim 1 wherein the light source includes a monitor photodetector arranged so as to receive a portion of the source optical signal and generate therefrom a monitor electrical signal, and the control circuit is arranged and connected so as to control the source idle power level or the source average active power level in response to the monitor electrical signal.

9. The modulated optical source of claim 1 wherein the light source comprises a semiconductor laser.

10. The modulated optical source of claim 9 wherein the light source and the control circuit are arranged so that, during each idle temporal segment, the source optical signal includes laser output of the semiconductor laser.

11. The modulated optical source of claim 10 wherein the control circuit is arranged and connected to the light source so as to apply to the light source, during each idle temporal period, a dithering signal that causes the output optical spectral width to broaden relative to the output optical spectral width during each active temporal period.

12. The modulated optical source of claim 11 wherein the control circuit is arranged so that the dithering signal oscillates at a dithering frequency between about 1.0 MHz and about 5 MHz.

13. The modulated optical source of claim 11 wherein the control circuit is arranged so that the dithering signal results in the output optical spectral width being greater than about 100 MHz FWHM.

14. The modulated optical source of claim 1 wherein the control circuit is arranged and connected so as to attenuate, only during each idle temporal segment, one or more portions of the electrical modulating signal that fall within a specified modulation frequency range.

15. The modulated optical source of claim 1 wherein:

(e′) the control circuit is arranged and connected to the light source so as to cause the light source to produce the source optical signal at a substantially constant source active power level during each active temporal segment, the substantially constant source active power level being about equal to the source average active power level; and

(f′) the control circuit is arranged and connected to the optical modulator so as to result in modulation, during each active temporal segment, of an active transmission level of the optical modulator in accordance with the electrical modulating signal, so that each active segment of the optical output signal encodes the information of the corresponding active temporal segment of the electrical modulating signal.

16. The modulated optical source of claim 1 wherein:

(e′) the control circuit is arranged and connected to the optical modulator so as to cause the optical modulator to transmit the source optical signal at a substantially constant active transmission level during each active temporal segment, the substantially constant active transmission level being about equal to the average active transmission level; and

(f′) the control circuit is arranged and connected to the light source so as to result in modulation, during each active temporal segment, of the source optical signal in accordance with the electrical modulating signal, so that each active segment of the optical output signal encodes the information of the corresponding active temporal segment of the electrical modulating signal.

17. The modulated optical source of claim 16 wherein the light source comprises (i) a directly modulated semiconductor laser or (ii) an externally modulated semiconductor laser source that includes a source laser and a source modulator.

18. The modulated optical source of claim 1 wherein the optical modulator comprises a semiconductor waveguide with a modulator active region, and the modulator active region is arranged so as to alter the transmission level of the optical modulator in response to voltage or current applied by the control circuit.

19. The modulated optical source of claim 18 wherein the control circuit and the modulator active region are arranged so that the optical modulator exhibits the idle transmission level by an electroabsorption effect in response to a negative bias voltage applied by the control circuit to the modulator active region during the idle temporal segments.

20. The modulated optical source of claim 18 wherein the control circuit and the modulator active region are arranged so that the optical modulator exhibits the average active transmission level by an electroabsorption effect in response to a bias voltage applied by the control circuit to the modulator active region during the active temporal segments.

21. The modulated optical source of claim 20 wherein the control circuit and the modulator active region are arranged so that the optical modulator exhibits a modulated active transmission level by an electroabsorption effect in response to active temporal segments of the electrical modulating signal applied by the control circuit to the modulator active region during the active temporal segments.

22. The modulated optical source of claim 18 wherein the control circuit and the modulator active region are arranged so that the optical modulator exhibits the idle transmission level by extraction of charge carriers from the modulator active region by the control circuit during the idle temporal segments.

23. The modulated optical source of claim 18 wherein the control circuit and the active region are arranged so that the optical modulator exhibits the average active transmission level by injection into the modulator active region, or extraction of charge carriers from the modulator active region, by the control circuit during the active temporal segments.

24. The modulated optical source of claim 23 wherein the control circuit and the modulator active region are arranged so that the optical modulator exhibits a modulated active transmission level by injection into the modulator active region, or extraction of charge carriers from the modulator active region, in response to active temporal segments of the electrical modulating signal applied by the control circuit to the modulator active region during the active temporal segments.

25. The modulated optical source of claim 18 wherein the light source comprises a laser active region of the semiconductor waveguide.

26. The modulated optical source of claim 25 wherein the control circuit is arranged so as to deliver a compensating laser current to the laser active region during each active temporal segment, in addition to laser current delivered to the laser active region under control of a monitor photodetector signal.

27. The modulated optical source of claim 1 wherein the control circuit is arranged and connected so as to cause, after each active temporal segment, a shift of the source optical frequency by more than about 5 GHz.

28. The modulated optical source of claim 1 wherein the control circuit is arranged so as to:

(g) detect a transition in the electrical modulating signal from an idle temporal segment to an active temporal segment; and

(h) in response to the detection of part (g), switch, within a specified switch-on time interval that is less than about 0.5 μs, the light source from the idle power level to the active power level and the optical modulator from the idle transmission level to the active transmission level.

29. The modulated optical source of claim 1 wherein the control circuit is arranged so as to:

(g) detect a transition in the electrical modulating signal from an active temporal segment to an idle temporal segment; and

(h) in response to the detection of part (g), switch, within a specified switch-off time interval that is less than about 0.5 μs, the light source from the active power level to the idle power level and the optical modulator from the active transmission level to the idle transmission level.

30. The modulated optical source of claim 29 wherein the detection of part (g) includes detecting a signal level, within a specified modulation frequency range, that remains below a specified switch-off signal threshold during a time interval that exceeds a specified switch-off time threshold that is greater than about 1.0 μs.

31. The modulated optical source of claim 1 wherein the control circuit is arranged so as to:

(g) detect a transition in the electrical modulating signal from an idle temporal segment to an active temporal segment, and that detection includes detecting a signal level within a designated modulation frequency range that exceeds a specified switch-on signal threshold;

(h) in response to the detection of part (g), switch, within a specified switch-on time interval, the light source from the idle power level to the active power level and the optical modulator from the idle transmission level to the active transmission level;

(g′) detect a transition in the electrical modulating signal from an active temporal segment to an idle temporal segment, and that detection includes detecting a signal level within the designated modulation frequency range that remains below a specified switch-off signal threshold during a time interval that exceeds a switch-off time threshold, wherein magnitude of the switch-on signal threshold is greater than magnitude of the switch-off signal threshold; and

(h′) in response to the detection of part (g′), switch, within a specified switch-off time interval, the light source from the active power level to the idle power level and the optical modulator from the active transmission level to the idle transmission level.

32. A method for operating a modulated optical source, the method comprising:

(A) receiving an electrical modulating signal that includes alternating active and idle temporal segments, wherein each one of the active segments of the electrical modulating signal encodes corresponding information; and

(B) producing, using the modulated optical source, in response to the electrical modulating signal, an optical output signal that includes alternating active and idle temporal segments corresponding to the active and idle temporal segments of the electrical modulating signal, wherein each active temporal segment of the optical output signal encodes the information of the corresponding active temporal segment of the electrical modulating signal,

wherein:

(a) the modulated optical source comprises a light source, an optical modulator, and a control circuit operatively coupled to the light source and the optical modulator;

(b) the control circuit is arranged and connected so as to receive the electrical modulating signal;

(c) the modulated optical source is arranged and connected so as to produce, in response to the electrical modulating signal, the output optical signal characterized by an output optical frequency and an output optical spectral width;

(d) the light source and the optical modulator are arranged so that at least a portion of a source optical signal produced by the light source is received by the optical modulator, and the output optical signal comprises one or more portions of the source optical signal that are transmitted by the optical modulator;

(e) the control circuit is arranged and connected (i) to the light source so as to cause the light source to produce the source optical signal at a non-zero source idle power level during each idle temporal segment, and (ii) to the optical modulator so as to cause the optical modulator to transmit the source optical signal at a substantially constant idle transmission level during each idle temporal segment;

(f) the control circuit is arranged and connected (i) to the light source so as to cause the light source to produce the source optical signal at a non-zero source average active power level during each active temporal segment, and (ii) to the optical modulator so as to cause the optical modulator to transmit the source optical signal at an average active transmission level during each active temporal segment, the average active transmission level being higher than the idle transmission level; and

(g) the control circuit is arranged and connected to the light source or the optical modulator so as to result in modulation, during each active temporal segment, of the output optical signal in accordance with the electrical modulating signal, so that each active temporal segment of the output optical signal encodes the information of the corresponding active temporal segment of the electrical modulating signal.