Common cathode laser driving circuit

• US 10,461,498 B2
• Filed: 10/01/2018
• Issued: 10/29/2019
• Est. Priority Date: 06/23/2017
• Status: Active Grant

• Current Assignee: Google LLC (Alphabet Inc.)
• Original Assignee: Google LLC (Alphabet Inc.)
• Inventors: Zhang, Tao, Du, Liang, Zhao, Xiangjun, Jiang, Changhong Joy, Lam, Cedric Fung, Yin, Shuang, Barratt, Adam Edwin Taylor
• Primary Examiner(s): Carter, Michael
• Application Number:
  US16/148,526
• Publication Number:
  US 20190036302A1
• Time in Patent Office: 393 Days
• CPC Class Codes: H01S 5/042 Electrical excitation ; Circuits therefor monolithically integrated laser drive components H01S5/0261
• CPC Class Codes: H01S 5/0428 for applying pulses to the laser
• CPC Class Codes: H01S 5/06256 with DBR-structure
• CPC Class Codes: H01S 5/068 Stabilisation of laser output parameters H01S5/0625 takes precedence
• CPC Class Codes: H01S 5/125 Distributed Bragg reflector [DBR] lasers
• CPC Class Codes: H01S 5/3013 AIIIBV compounds
• CPC Class Codes: H04B 10/2589 Bidirectional transmission
• CPC Class Codes: H04B 10/40 Transceivers
• CPC Class Codes: H04J 14/0265 Multiplex arrangements in bidirectional systems, e.g. interleaved allocation of wavelengths or allocation of wavelength groups
• CPC Class Codes: H04J 14/0282 WDM tree architectures

Abstract

A method for biasing a tunable laser during burst-on and burst-off states through a common-cathode laser driving circuit includes delivering a bias current to an anode of a gain-section diode having a shared substrate with the laser, and receiving a burst mode signal indicative of a burst-on state or a burst-off state. When the burst mode signal is indicative of the burst-off state, the method includes sinking a sink current away from the anode of the gain-section diode. The sink current is less than the bias current delivered to the anode of the gain-section diode. When the burst mode signal transitions to be indicative of the burst-on state from the burst-off state, the method includes ceasing the sinking of the sink current away from the anode of the gain-section diode, and delivering an overshoot current to the anode of the gain-section diode to accelerate heating of the gain-section diode.

Claims

1. A method comprising:

delivering, by a laser driving circuit, a bias current to an anode of a gain-section diode disposed on a shared substrate of a tunable laser;

receiving, at the laser driving circuit, a burst mode signal indicative of a burst-on state or a burst-off state;

when the burst mode signal is indicative of the burst-off state, sinking, by the laser driving circuit, a sink current away from the bias current at the anode of the gain-section diode, the sink current less than the bias current delivered to the anode of the gain-section diode; and

when the burst mode signal is indicative of the burst-on state, modulating, by the laser driving circuit, the tunable laser by a capacitively coupled modulation stage of the laser driving circuit to the anode of the gain-section diode, resulting in an alternating current (AC) modulation current.

2. The method of claim 1, further comprising, when the burst mode signal transitions to be indicative of the burst-on state from the burst-off state:

ceasing, by the laser driving circuit, the sinking of the sink current away from the bias current at the anode of the gain-section diode; and

delivering, by the laser driving circuit, an overshoot current to the anode of the gain-section diode to accelerate heating of the gain-section diode.

3. The method of claim 2, further comprising delivering, by the laser driving circuit, the overshoot current to the anode of the gain-section diode for a transition period of time after commencement of the burst-on state, the transition period of time less than a burst-on period of time corresponding to a duration of the burst-on state.

4. The method of claim 3, wherein the laser driving circuit comprises an accelerating heating stage capacitively coupled to the anode of the gain-section diode to deliver the overshoot current to the anode of the gain-section diode, the heating stage comprising one of a metal-oxide-semiconductor field-effect transistor (MOSFET) or a Bipolar Junction Transistor (BJT) connected to a burst mode signal source and first and second resistors, a ratio of the first and second resistors proportional to a magnitude of the overshoot current.

5. The method of claim 1, wherein when the burst mode signal is indicative of the burst-off state, the gain-section diode receives a diode current equal to the bias current minus the sink current.

6. The method of claim 1, further comprising receiving, at the laser driving circuit, a sink current adjustment from a sinking stage of the laser driving circuit, the sink current adjustment configured to adjust the sink current.

7. The method of claim 6, wherein the sinking stage comprises a differential pair of first and second MOSFETs, each MOSFET connected to a burst mode signal source, the first MOSFET connected to a resistor, the resistor connected to a voltage source, the second MOSFET connected to an inductor connected to the anode of the gain-section diode.

8. The method of claim 7, wherein:

the first MOSFET is turned off and the second MOSFET is turned on to sink the sink current away from the anode of the gain-section diode when the burst mode signal is indicative of the burst-off state; and

the first MOSFET is turned on and the second MOSFET is turned off to cease sinking of the sink current away from the anode of the gain-section diode when the burst mode signal is indicative of the burst-on state.

9. The method of claim 6, wherein the sinking stage comprises a differential pair of first and second BJTs, each BJT connected to a burst mode signal source, the first BJT connected to a resistor, the resistor connected to a voltage source, the second BJT connected to an inductor connected to the anode of the gain-section diode.

10. The method of claim 9, wherein:

the first BJT is turned off and the second BJT is turned on to sink the sink current away from the anode of the gain-section diode when the burst mode signal is indicative of the burst-off state; and

the first BJT is turned on and the second BJT is turned off to cease sinking of the sink current away from the anode of the gain-section diode when the burst mode signal is indicative of the burst-on state.

11. The method of claim 1, wherein the modulation stage comprises a differential pair of first and second MOSFETs, each MOSFET connected to a burst mode signal source and a data signal source, the first MOSFET connected to a first resistor, the first resistor connected to a voltage source, the second MOSFET connected by a capacitor to the anode of the gain-section diode.

12. The method of claim 11, wherein the second MOSFET is connected to a second resistor connected to a variable voltage source.

13. The method of claim 1, wherein the modulation stage comprises a differential pair of first and second BJTs, each BJT connected to a burst mode signal source and a data signal source, the first BJT connected to a first resistor, the first resistor connected to a voltage source, the second BJT connected by a capacitor to the anode of the gain-section diode.

14. The method of claim 13, wherein the second BJT is connected to a second resistor connected to a variable voltage source.

15. The method of claim 1, wherein the tunable laser comprises a multi-section tunable laser.

16. A common-cathode laser driving circuit comprising:

a voltage source configured to deliver a bias current to an anode of a gain-section diode disposed on a shared substrate of a tunable laser;

a sinking stage configured to receive a burst mode signal indicative of a burst-on state or a burst-off state, the sinking stage configured to;

when the burst mode signal is indicative of the burst-off state, sink a sink current away from the bias current at the anode of the gain-section diode, the sink current less than the bias current received by the anode of the gain-section diode; and

when the burst mode signal is indicative of the burst-on state, cease the sinking of the sink current away from the bias current at the anode of the gain-section diode; and

a modulation stage capacitively coupled to the anode of the gain-section diode, the modulation stage configured to output an alternating current (AC) modulation current when the burst mode signal is indicative of the burst-on state.

17. The laser driving circuit of claim 16, wherein when the burst mode signal is indicative of the burst-off state, the gain-section diode receives a diode current equal to the bias current minus the sink current.

18. The laser driving circuit of claim 16, wherein the sinking stage comprises a differential pair of first and second metal-oxide-semiconductor field-effect transistors (MOSFETs), each MOSFET connected to a burst mode signal source, the first MOSFET connected to a resistor, the resistor connected to a voltage source, the second MOSFET connected to an inductor connected to the anode of the gain-section diode.

19. The laser driving circuit of claim 18, wherein:

the first MOSFET is turned off and the second MOSFET is turned on to sink the sink current away from the anode of the gain-section diode when the burst mode signal is indicative of the burst-off state; and

the first MOSFET is turned on and the second MOSFET is turned off to cease the sinking of the sink current away from the anode of the gain-section diode when the burst mode signal is indicative of the burst-on state.

20. The laser driving circuit of claim 16, wherein the sinking stage comprises a differential pair of first and second Bipolar Junction Transistors (BJTs), each BJT connected to a burst mode signal source, the first BJT connected to a resistor, the resistor connected to a voltage source, the second BJT connected to an inductor connected to the anode of the gain-section diode.

21. The laser driving circuit of claim 20, wherein:

the first BJT is turned off and the second BJT is turned on to sink the sink current away from the anode of the gain-section diode when the burst mode signal is indicative of the burst-off state; and

the first BJT is turned on and the second BJT is turned off to cease the sinking of the sink current away from the anode of the gain-section diode when the burst mode signal is indicative of the burst-on state.

22. The laser driving circuit of claim 16, wherein the modulation stage comprises a differential pair of first and second MOSFETs, each MOSFET connected to a burst mode signal source and a data signal source, the first MOSFET connected to a first resistor, the first resistor connected to a voltage source, the second MOSFET connected by a capacitor to the anode of the gain-section diode.

23. The laser driving circuit of claim 22, wherein the second MOSFET is connected to a second resistor connected to a variable voltage source.

24. The laser driving circuit of claim 16, wherein the modulation stage comprises a differential pair of first and second BJTs, each BJT connected to a burst mode signal source and a data signal source, the first BJT connected to a first resistor, the first resistor connected to a voltage source, the second BJT connected by a capacitor to the anode of the gain-section diode.

25. The laser driving circuit of claim 24, wherein the second BJT is connected to a second resistor connected to a variable voltage source.

26. The laser driving circuit of claim 16, wherein the sinking stage is configured to output a sink current adjustment, the sink current adjustment configured to adjust the sink current.

27. The laser driving circuit of claim 16, wherein the tunable laser comprises a multi-section tunable laser.