Apparatus and method to suppress gain-switched spikes in fiber laser amplifier systems
View Patent ↗Apparatus and method for generating controlled-linewidth laser-seed-signals for high-powered fiber-laser amplifier systems. In some embodiments, the natural chirp (frequency change of laser light over a short start-up time) of a DBR laser diode when driven by pulsed current is used to broaden the linewidth of the laser output, while adjusting the peak current and/or the pulse duration to obtain the desired linewidth.
1. An apparatus comprising:
an optical fiber gain medium having optical gain;
an optical pump source operatively coupled to the optical fiber gain medium to deliver optical pump energy that is stored in the optical fiber gain medium and builds up over time;
a laser-diode pulsed seed source operatively coupled to the optical fiber gain medium, wherein the laser-diode pulsed seed source provides an optical-seed-laser signal to the optical fiber gain medium to be amplified by the optical fiber gain medium and wherein the optical-seed-laser signal has an amplitude that varies over time and that includes laser pulses; and
a pulsed electrical-current source operatively coupled to supply pulsed laser drive current to the laser-diode pulsed seed source, wherein a magnitude of the laser drive current is controlled to suppress gain-switched spikes in the amplitude of the laser pulses.
2. The apparatus of claim 1 , wherein the electrical-current source is controlled to supply current at a level that heats the laser-diode pulsed seed source, but wherein the level is below a lasing-threshold amount of current prior to producing the pulsed laser drive current.
3. The apparatus of claim 1 , wherein the electrical-current source supplies the pulsed laser drive current with an increasing-ramp shape.
4. The apparatus of claim 1 , wherein the electrical-current source limits the pulsed laser drive current such that mode hopping is avoided.
5. The apparatus of claim 1 , wherein the electrical-current source is controlled to supply a continuous-wave (CW) bias current amount at a level as high as possible without exceeding lasing threshold prior to producing the pulsed laser drive current.
6. The apparatus of claim 1 , wherein the apparatus is configured to control the pulsed electrical-current source to supply bias current to the laser-diode pulsed seed source to heat the laser-diode pulsed seed source between pulses of the pulsed laser drive current to suppress mode hopping.
7. The apparatus of claim 1 , wherein the apparatus is configured to control the pulsed electrical-current source to adjust a level of the pulsed drive current until mode hopping is observed, and to then reduce the pulsed drive current level to a value still greater than a lasing-threshold amount of current.
8. A method comprising:
providing an optical fiber gain medium having optical gain;
providing an optical-pump source operatively coupled to the optical fiber gain medium to deliver optical pump energy that is stored in the optical fiber gain medium and builds up over time;
providing a laser-diode pulsed seed source;
connecting an optical-seed-laser signal from the laser-diode pulsed seed source to the optical fiber gain medium, wherein the optical-seed-laser signal has an amplitude that varies over time and that includes laser pulses;
amplifying the optical-seed-laser signal by the optical fiber gain medium;
supplying pulsed laser drive current to the laser-diode pulsed seed source; and
controlling a magnitude of the laser drive current to suppress gain-switched spikes in the amplitude of the laser pulses.
9. The method of claim 8 , wherein the controlling a magnitude of the laser drive current includes controlling the current at a level that heats the laser-diode pulsed seed source, but wherein the level is below a lasing-threshold amount of current prior to producing the pulsed laser drive current.
10. The method of claim 8 , wherein the controlling a magnitude of the laser drive current includes supplying the pulsed laser drive current with an increasing-ramp shape.
11. The method of claim 8 , wherein the controlling a magnitude of the laser drive current includes limiting the pulsed laser drive current such that mode hopping is avoided.
12. The method of claim 8 , wherein the controlling a magnitude of the laser drive current includes supplying a continuous-wave (CW) bias current amount at a level as high as possible without exceeding lasing threshold prior to producing the pulsed laser drive current.
13. The method of claim 8 , further comprising heating the laser-diode seed source between pulses to suppress mode hopping.
14. The method of claim 8 , further comprising:
adjusting a level of the pulsed drive current until mode hopping is observed; and
reducing the pulsed drive current level to a value below the level of mode hopping still greater than a lasing-threshold amount of current.
15. An apparatus comprising:
an optical fiber gain medium having optical gain;
an optical-pump source operatively coupled to the optical fiber gain medium, wherein the optical-pump source is configured to deliver optical-pump energy from the optical-pump source to the optical fiber gain medium, and wherein the delivered optical-pump energy is stored in the optical fiber gain medium and builds up over time;
a laser-diode pulsed seed source configured to emit an optical-seed-laser signal, wherein the optical-seed-laser signal has an amplitude that varies over time and that includes laser pulses;
means for supplying pulsed laser drive current to the laser-diode pulsed seed source; and
means for controlling a magnitude of the laser drive current to suppress gain-switched spikes in the amplitude of the laser pulses.
16. The apparatus of claim 15 , wherein the means for controlling a magnitude of the laser drive current includes means for controlling the current at a level that heats the laser-diode pulsed seed source, but wherein the level is below a lasing-threshold amount of current prior to producing the pulsed laser drive current.
17. The apparatus of claim 15 , wherein the means for controlling a magnitude of the laser drive current includes means for supplying the pulsed laser drive current with an increasing-ramp shape.
18. The apparatus of claim 15 , wherein the means for controlling a magnitude of the laser drive current includes means for limiting the pulsed laser drive current such that mode hopping is avoided.
19. The apparatus of claim 15 , wherein the means for controlling a magnitude of the laser drive current includes means for supplying a continuous-wave (CW) bias current amount at a level as high as possible without exceeding lasing threshold prior to producing the pulsed laser drive current.
20. The apparatus of claim 15 , further comprising:
means for heating the laser-diode seed source between pulses to suppress mode hopping.