Method, circuitry and apparatus for outputting a stable optical signal in a dense wavelength division multiplexing device during fast changes of operating conditions
View Patent ↗The disclosure relates to a fast, stable method of output wavelength control in a DWDM optical device, and a circuit configured to perform the method. The method and circuit can control timing and overshoot during conditions of rapid operational changes, such as during power-on or restart of the device. The method and circuit includes optimized APC, TEC and electro-absorption (EA) modulator control hardware and algorithms, to effectively control transient processes. Software and circuitry based on the method(s) are achieved in part by optimizing APC, EA and TEC control algorithms. In combination with hardware/circuit optimization, one can achieve fast turn-on of an optical output signal at a stable wavelength. The method and circuit provides a stable power-up process in which a change of wavelength is small enough to meet DWDM specification requirements, to ensure the elimination and avoidance of crosstalk in adjacent channels in dense wave (sub)systems.
1. A method of generating an output signal in a dense wavelength division multiplexing (DWDM) device, comprising:
providing a bias current to a laser in the DWDM device;
comparing an initial state of a transmitter including the laser to a maximum overshoot value;
reducing the bias current to the laser to prevent or eliminate an overshoot condition of the bias current when the initial state exceeds the maximum overshoot value during power-up of the laser or the DWDM device, so as to prevent a change in output wavelength of the laser that would result in crosstalk; and
optimizing an automatic power control (APC) loop, a thermoelectric control (TEC) loop, and an electro-absorption (EA) modulator control loop in the DWDM device to actively control the bias current during a change of operating conditions in the DWDM device.
2. A dense wavelength division multiplexing (DWDM) device, comprising:
a laser;
an automatic power control (APC) loop, comprising a comparator, an overshoot control circuit, and a bias current control circuit, the APC loop configured to compare an initial state of a transmitter including the laser to a maximum overshoot value, and reduce a bias current to the laser to prevent or eliminate overshoot of the bias current when the initial state exceeds the maximum overshoot value during power-up of the laser or the DWDM device, so as to prevent a change in output wavelength of the laser that would result in crosstalk;
a thermoelectric control (TEC) loop, configured to control one or more thermoelectric characteristics of the laser; and
an electro-absorption (EA) modulator control loop, configured to control an EA modulation of the laser.
3. The method of claim 1 , wherein the DWDM device includes an optical transmitter.
4. The method of claim 3 , wherein the DWDM device is an optical transceiver.
5. The method of claim 4 , wherein the DWDM optical transceiver sets an automatic, adjusted laser bias current control circuit with a predetermined setting, and optimizes the APC and TEC control loops and an operation point of the EA modulator control loop.
6. The method of claim 5 , wherein the DWDM optical transceiver includes a processor and the bias current control circuit, and the processor and the bias current control circuit (i) actively adjust the bias current to prevent or eliminate the overshoot of the bias current and pre-compensate for any expected change in the output wavelength of the laser.
7. The method of claim 1 , wherein optimizing said APC loop, said TEC loop, and said EA modulator control loop includes:
applying power to and initializing the DWDM device;
actively monitoring and controlling the output wavelength and a peak power of the laser within a predetermined range; and
incrementing or decrementing a bias voltage to the EA modulator, pre-offsetting a setting in the TEC loop to compensate for any drift in the output wavelength of the laser, and/or automatically adjusting a setting in the APC loop to control the overshoot in the output wavelength of the laser.
8. The method of claim 1 , further comprising configuring a control interface of said APC loop, said TEC loop, and said EA modulator control loop; and either
if the DWDM device is undergoing a transient process, applying EA, APC, and TEC control to the laser, and after a predetermined length of time, entering a monitor mode; or
if the DWDM device is not in a quick change of operating conditions mode, then directly entering the monitoring mode.
9. The method of claim 1 , wherein the DWDM device sets the bias current in a bias current control circuit, and optimizes APC, TEC and EA modulator control algorithms.
10. A dense wavelength division multiplexing (DWDM) device, comprising:
a laser;
an automatic power control (APC) loop, comprising a comparator, an overshoot control circuit, and a bias current control circuit, the APC loop configured to compare an initial state of a transmitter including the laser to a maximum overshoot value, and reduce a bias current to the laser to prevent or eliminate overshoot of the bias current or an output wavelength of the laser when the initial state exceeds the maximum overshoot value during power-up of the laser or the DWDM device;
a thermoelectric control (TEC) loop, configured to control one or more thermoelectric characteristics of the laser; and
an electro-absorption (EA) modulator control loop, configured to control an EA modulation of the laser.
11. The DWDM device of claim 10 , wherein:
the bias current control circuit provides the bias current to the laser; and
the overshoot control circuit reduces the bias current when the initial state exceeds the maximum overshoot value, and thereby prevents or eliminates the overshoot in the output wavelength of the laser.
12. The DWDM device of claim 11 , wherein the APC loop further includes:
the laser;
a laser monitoring circuit configured to monitor a power, wavelength and/or intensity of the laser; and
a processor unit configured to set an initial state of the bias current control circuit.
13. The DWDM device of claim 12 , wherein the processor unit includes a PID loop providing setting information to the overshoot control circuit, a TEC control block providing setting information to the TEC loop, and an EA control block providing setting information to the EA loop.
14. The DWDM device of claim 12 , wherein the processor unit includes a microcontroller configured to control the APC, TEC and EA modulator control loops.
15. The DWDM device of claim 12 , wherein the TEC loop includes:
a TEC control circuit configured to provide a signal to the laser configured to maintain or adjust one or more thermoelectric characteristics or properties of the laser;
the laser;
the laser monitoring circuit; and
the processor unit.
16. The DWDM device of claim 12 , wherein the EA loop includes:
an EA control circuit configured to provide a signal to the laser configured to maintain or adjust an EA modulation of the laser;
the laser;
the laser monitoring circuit; and
the processor unit.
17. The DWDM device of claim 16 , wherein the EA loop further includes a bias-tee circuit configured to receive an output of the EA control circuit and provide an EA modulation signal to the laser.
18. The DWDM device of claim 10 , wherein the laser comprises a distribution grating laser diode.
19. The DWDM device of claim 10 , wherein the laser further comprises an EA modulator configured to modulate an output of the laser.