Thermal management of laser diode mode hopping for heat assisted media recording
A method and apparatus provide for determining a temperature at a junction of a laser diode when the laser diode is operated in a lasing state that facilitates heat-assisted magnetic recording, comparing the junction temperature and an injection current supplied during the lasing state to stored combinations of junction temperature and injection current, and determining a likelihood of mode hopping occurring for the laser diode during the lasing state based on the comparison to stored combinations of junction temperature and injection current.
1. A method, comprising:
operating a laser diode in a lasing state to facilitate heat-assisted magnetic recording;
determining a voltage differential between a transient voltage lasing state of the laser diode and a constant voltage lasing state of the laser diode;
determining, using the voltage differential, a temperature at a junction of the laser diode when the laser diode is operated in the lasing state;
comparing the junction temperature and an injection current supplied to the laser diode during the lasing state to stored combinations of junction temperature and injection current; and
avoiding a combination of junction temperature and injection current for which mode hopping is likely to occur during the lasing state.
2. The method of claim 1 , wherein the junction temperature is determined using the voltage differential and a proportionality factor.
3. The method of claim 2 , wherein the proportionality factor (K) is characterized by K=(V 1 −V 2 )/(T 2 −T 1 ), where V 1 is a voltage measured during a first state, V 2 is a voltage measured during a second state, T 2 is a temperature measured during the second state, and T 1 is a temperature measured during the first state.
4. The method of claim 1 , wherein determining the voltage differential comprises determining a difference in forward voltage of the laser diode measured before and after applying a pulsed drive current to the laser diode during the lasing state.
5. The method of claim 1 , wherein avoiding comprises adjusting the injection current to avoid the combination of junction temperature and injection current for which mode hopping is likely to occur during the lasing state.
6. The method of claim 1 , wherein avoiding comprises heating or cooling the laser diode to avoid the combination of junction temperature and injection current for which mode hopping is likely to occur during the lasing state.
7. The method of claim 1 , wherein avoiding comprises preheating the laser diode prior to writing data to avoid the combination of junction temperature and injection current for which mode hopping is likely to occur during the lasing state.
8. The method of claim 1 , wherein avoiding comprising heating the laser diode during a non-lasing state.
9. The method of claim 1 , wherein avoiding comprises heating the laser diode during at least a portion of the lasing state and a non-lasing state.
10. A method, comprising:
operating a laser diode in a lasing state to facilitate heat-assisted magnetic recording;
determining a voltage differential between a transient voltage lasing state of the laser diode and a constant voltage lasing state of the laser diode; and
determining, using the voltage differential, a temperature at a junction of the laser diode when the laser diode is operated in the lasing state.
11. The method of claim 10 , wherein the junction temperature is determined using the voltage differential and a proportionality factor.
12. The method of claim 11 , wherein the proportionality factor (K) is characterized by K=(V 1 −V 2 )/(T 2 −T 1 ), where V 1 is a voltage measured during a first state, V 2 is a voltage measured during a second state, T 2 is a temperature measured during the second state, and T 1 is a temperature measured during the first state.
13. The method of claim 10 , wherein determining the voltage differential comprises determining a difference in forward voltage of the laser diode measured before and after applying a pulsed drive current to the laser diode during the lasing state.
14. An apparatus, comprising:
a slider configured for heat-assisted magnetic recording, the slider comprising a laser diode;
a controller configured to calculate a voltage differential between a transient voltage lasing state of the laser diode and a constant voltage lasing state of the laser diode, the controller further configured to determine, using the voltage differential, a temperature at a junction of the laser diode when the laser diode is operated in the lasing state; and
a processor configured to compare the junction temperature and an injection current supplied to the laser diode during the lasing state to stored combinations of junction temperature and injection current, the processor further configured to avoid a combination of junction temperature and injection current for which mode hopping is likely to occur during the lasing state.
15. The apparatus of claim 14 , wherein the controller is configured to determine the junction temperature using the voltage differential and a proportionality factor.
16. The apparatus of claim 15 , wherein the proportionality factor (K) is characterized by K=(V 1 −V 2 )/(T 2 −T 1 ), where V 1 is a voltage measured during a first state, V 2 is a voltage measured during a second state, T 2 is a temperature measured during the second state, and T 1 is a temperature measured during the first state.
17. The apparatus of claim 14 , wherein the controller is configured to determine the voltage differential by determining a difference in forward voltage of the laser diode measured before and after application of a pulsed drive current to the laser diode during the lasing state.
18. The apparatus of claim 14 , further comprising a heater arrangement proximate the laser diode;
wherein the controller is configured to activate the heater arrangement to warm the junction and maintain the junction temperature within a predetermined temperature range associated with a reduced likelihood of mode hopping occurring for the laser diode during the lasing state.
19. The apparatus of claim 18 , wherein the heater arrangement is coupled in a parallel relationship with the laser diode, and wherein the heater arrangement comprises one or more of a diode, a diode arranged in series with a thermistor, and a diode arranged in series with a heater.
20. The apparatus of claim 14 , wherein the controller is configured to modify one or more of an injection current, a laser diode power, and a head position relative to a magnetic recording medium to compensate for a laser diode power variation due to mode hopping.