Laser power monitoring in a heat-assisted magnetic recording device using a resistive sensor and high-frequency laser modulation
An apparatus comprises a light source configured to generate light, and a modulator coupled to the light source and configured to modulate the light above a predetermined frequency. A slider is configured for heat-assisted magnetic recording and to receive the modulated light. A resistive sensor is integral to the slider and subject to heating by absorption of electromagnetic radiation and conduction of heat. Measuring circuitry is coupled to the resistive sensor and configured to measure a response of the resistive sensor due to absorbed electromagnetic radiation and not from the heat conduction. The measuring circuitry may further be configured to determine output optical power of the light source using the measured resistive sensor response.
1. A method, comprising:
modulating light generated by a light source situated in, at, or near a slider above a predetermined frequency, the slider comprising a resistive sensor;
communicating the modulated light from the light source, through the slider, and to an intended focus location of the slider;
heating the resistive sensor by absorption of electromagnetic radiation and conduction of heat from heat sources proximate the resistive sensor;
producing, by the resistive sensor in response to the modulated light above the predetermined frequency, a response due to absorption of the electromagnetic radiation by the resistive sensor and not from the conducted heat; and
measuring the response of the resistive sensor due to the absorbed electromagnetic radiation and not from the conducted heat.
2. The method of claim 1 , wherein measuring comprises measuring the response of the resistive sensor as a function of the modulation frequency.
3. The method of claim 1 , wherein measuring comprises measuring the response of the resistive sensor at or near the predetermined frequency.
4. The method of claim 1 , wherein:
the predetermined frequency defines a transition frequency between a low-frequency regime and a high-frequency regime;
the response produced by the resistive sensor in the low-frequency regime is due to electromagnetic radiation absorption and conduction of heat; and
the response produced by the resistive sensor in the high-frequency regime is due electromagnetic radiation absorption and not from conduction of heat.
5. The method of claim 1 , wherein:
the predetermined frequency defines a transition frequency between a low-frequency regime and a high-frequency regime;
the response produced by the resistive sensor in the low-frequency regime has a first narrow-band power that decreases with increasing modulation frequency; and
the response produced by the resistive sensor in the high-frequency regime has a second narrow-band power that is substantially independent of modulation frequency.
6. The method of claim 1 , wherein:
the predetermined frequency defines a transition frequency between a low-frequency regime and a high-frequency regime;
the response produced by the resistive sensor in the low-frequency regime has a first AC component due to electromagnetic radiation absorption and a second AC component due to heat conduction; and
the response produced by the resistive sensor in the high-frequency regime includes the first AC component and is substantially devoid of the second AC component.
7. The method of claim 1 , wherein measuring comprises measuring an average amplitude of the resistive sensor response.
8. The method of claim 1 , further comprising determining output optical power of the light source using the measured resistive sensor response.
9. The method of claim 1 , further comprising detecting one or both of a change in spacing and contact between the slider and a magnetic recording medium using the resistive sensor.
10. The method of claim 1 , wherein the modulation frequency of the light is greater than about 500 KHz.
11. An apparatus, comprising:
a light source configured to generate light;
a modulator coupled to the light source and configured to modulate the light above a predetermined frequency;
a slider configured for heat-assisted magnetic recording and to receive the modulated light;
a resistive sensor integral to the slider and subject to heating by absorption of electromagnetic radiation and conduction of heat, the resistive sensor configured to produce a response due to absorption of the electromagnetic radiation by the resistive sensor and not from the heat conduction in response to the modulated light above the predetermined frequency; and
measuring circuitry coupled to the resistive sensor and configured to measure the response of the resistive sensor due to absorbed electromagnetic radiation and not from the heat conduction.
12. The apparatus of claim 11 , wherein the measuring circuitry is configured to measure the response of the resistive sensor as a function of the modulation frequency.
13. The apparatus of claim 11 , wherein the measuring circuitry is configured to measure the response of the resistive sensor at or near the predetermined frequency.
14. The apparatus of claim 11 , wherein the measuring circuitry is configured to measure an average amplitude of the resistive sensor response.
15. The apparatus of claim 11 , wherein:
the predetermined frequency defines a transition frequency between a low-frequency regime and a high-frequency regime;
the response produced by the resistive sensor in the low-frequency regime is due to electromagnetic radiation absorption and conduction of heat; and
the response produced by the resistive sensor in the high-frequency regime is due electromagnetic radiation absorption and not from the heat conduction.
16. The apparatus of claim 11 , wherein:
the predetermined frequency defines a transition frequency between a low-frequency regime and a high-frequency regime;
the response produced by the resistive sensor in the low-frequency regime has a first narrow-band power that decreases with increasing modulation frequency; and
the response produced by the resistive sensor in the high-frequency regime has a second narrow-band power that is substantially independent of modulation frequency.
17. The apparatus of claim 11 , wherein:
the predetermined frequency defines a transition frequency between a low-frequency regime and a high-frequency regime;
the response produced by the resistive sensor in the low-frequency regime has a first AC component due to electromagnetic radiation absorption and a second AC component due to heat; and
the response produced by the resistive sensor in the high-frequency regime includes the first AC component and is substantially devoid of the second AC component.
18. The apparatus of claim 11 , wherein the measuring circuitry is further configured to determine output optical power of the light source using the measured resistive sensor response.
19. The apparatus of claim 11 , further comprising a detector coupled to the resistive sensor, the detector configured to detect one or both of a change in spacing and contact between the slider and a magnetic recording medium using the resistive sensor.
20. The apparatus of claim 11 , wherein the modulation frequency of the light is greater than about 500 KHz.