# US 12,347,472 B1 · Positive laser bias electrical control architecture for dark laser heating in heat assisted magnetic recording > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,347,472 B1 - Document ID: US12347472B1 - Status: Granted - Kind: B1 - Application number: 18/402,926 - Filed: 2024-01-03 - Published: 2025-07-03 - Granted: 2025-07-01 - Earliest claimed: 2024-01-03 - Assignees: Western Digital Technologies, Inc. - Applicants: Western Digital Technologies, Inc. - Inventors: John T. Contreras; Joey M. Poss - Web page: https://patentgrep.com/patent/US12347472B1 ## CPC - G11B 7/1267: Power calibration - G11B 5/012: Recording on, or reproducing or erasing from, magnetic disks (G11B17/00, G11B19/00 take precedence) - G11B 13/08: using near-field interactions or transducing means and at least one other method or means for recording or reproducing - G11B 2005/0021: {Thermally assisted recording using an auxiliary energy source for heating the recording layer locally to assist the magnetization reversal} - G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R) ## Abstract Various illustrative aspects are directed to a data storage device comprising a disk, a read/write head configured to read data from and write data to the disk, a laser diode (LD) coupled to a near field transducer (NFT) configured to heat an area of the disk near the read/write head, an asymmetric LD driver configured to drive the LD, and one or more processing devices configured to: preheat the LD to a target temperature, wherein the preheating comprises: generating at least one bias pulse conforming to one or more tunable parameters, based at least in part on the target temperature; and applying, using the asymmetric LD driver, the at least one bias pulse to the LD such that no optical response is produced by the LD; and initiate a write operation for writing data to the disk. ## Claims ### Claim 1 A data storage device comprising: a disk; a read/write head configured to read data from and write data to the disk; a laser diode coupled to a near field transducer (NFT) configured to heat an area of the disk near the read/write head; an asymmetric laser diode driver configured to drive the laser diode; and one or more processing devices or components configured, individually or in combination, to: preheat the laser diode to a target temperature, wherein the preheating comprises: generating, based at least in part on the target temperature, at least one bias pulse conforming to a plurality of tunable parameters, the plurality of tunable parameters including one or more amplitude parameters, wherein the one or more amplitude parameters comprise one or more of: (1) a first laser diode bias current (IP) greater than a lasing threshold current, (2) a second laser diode bias current (IN) lower than the lasing threshold current, (3) a first duration (TPD), and (4) a second duration (TND); and applying, using the asymmetric laser diode driver, the at least one bias pulse to the laser diode such that no optical response is produced by the laser diode; and initiate a write operation for writing data to the disk. ### Claim 2 (depends on 1) The data storage device of claim 1, wherein the plurality of tunable parameters further comprise one or more overshoot parameters, and wherein the one or more overshoot parameters comprise: a first overshoot amplitude current (OSAP), wherein OSAP corresponds to a positive overshoot compensation greater than IP; a first overshoot duration (TOPD); a second overshoot amplitude current (OSAN), wherein OSAN corresponds to a negative overshoot compensation lower than IN; and a second overshoot duration (TOND). ### Claim 3 (depends on 2) The data storage device of claim 2, wherein generating the at least one bias pulse comprises: generating a plurality of current pulses, including at least: a first current pulse spanning the first duration (TPD), the first current pulse including a first overshoot portion spanning the first overshoot duration (TOPD), wherein a corresponding bias current associated with the first current pulse is greater than the lasing threshold current; and a second current pulse spanning the second duration (TND), the second current pulse including a second overshoot portion spanning the second overshoot duration (TOND), wherein a corresponding bias current associated with the second current pulse is lower than the lasing threshold current. ### Claim 4 (depends on 3) The data storage device of claim 3, wherein: TPD is shorter than a turn-on delay for the laser diode; TOPD is shorter than TPD; TOND is shorter than TND; and TND is shorter than TPD. ### Claim 5 (depends on 1) The data storage device of claim 1, wherein the asymmetric laser diode driver comprises an asymmetric Bipolar Complementary Metal-Oxide Semiconductor (BiCMOS) driver. ### Claim 6 (depends on 5) The data storage device of claim 5, wherein the asymmetric laser diode driver is driven by positive current pulses and negative current pulses, and wherein the positive current pulses have an amplitude that is greater in magnitude than an amplitude of the negative current pulses. ### Claim 7 A data storage device comprising: a disk; a read/write head configured to read data from and write data to the disk; a laser diode coupled to a near field transducer (NFT) configured to heat an area of the disk near the read/write head; an asymmetric laser diode driver configured to drive the laser diode, wherein the asymmetric laser diode driver comprises: a first current mirror for controlling at least an overshoot amplitude for positive or rising transitions of a positive bias current applied to the laser diode; and a second current mirror for controlling at least an overshoot amplitude for negative or falling transitions of a negative bias current applied to the laser diode; and one or more processing devices or components configured, individually or in combination, to: preheat the laser diode to a target temperature, wherein the preheating comprises: generating at least one bias pulse conforming to one or more tunable parameters, based at least in part on the target temperature; and applying, using the asymmetric laser diode driver, the at least one bias pulse to the laser diode such that no optical response is produced by the laser diode; and initiate a write operation for writing data to the disk. ### Claim 8 (depends on 7) The data storage device of claim 7, further comprising: an oscillator coupled to the asymmetric laser diode driver, the oscillator configured to provide a first pulse width modulation (PWM) signal and a second PWM signal to the asymmetric laser diode driver; wherein the one or more processing devices or components are further configured, individually or in combination, to: identify a delay between the first and the second PWM signal; receive, from the first current mirror, a first signal corresponding to a laser diode bias current above a lasing threshold current; receive, from the second current mirror, a second signal corresponding to a laser diode bias current below the lasing threshold current; and receive one or more external reference timing (ERT) signals for controlling a handoff between the asymmetric laser diode driver and the first and the second current mirrors. ### Claim 9 (depends on 8) The data storage device of claim 8, wherein: identifying the one or more overshoot parameters further comprises determining a first overshoot duration (TOPD) and a second overshoot duration (TOND), based at least in part on the identified delay; and generating the at least one bias pulse is further based at least in part on controlling the handoff. ### Claim 10 (depends on 9) The data storage device of claim 9, wherein the one or more processing devices or components are further configured, individually or in combination, to calibrate a positive portion of a duty cycle, and wherein calibrating the positive portion of the duty cycle comprises: calibrating a first duration (TPD) during which the laser diode bias current is greater than the lasing threshold current; and calibrating the first overshoot duration (TOPD) during which the laser diode bias current is greater than a positive peak laser current (IP), and wherein the first duration (TPD) is longer than or includes the first overshoot duration (TOPD). ### Claim 11 (depends on 10) The data storage device of claim 10, wherein the peak laser current (IP) is based at least in part on the target temperature, and wherein the target temperature corresponds to a steady-state temperature associated with the write operation. ### Claim 12 (depends on 8) The data storage device of claim 8, wherein the one or more ERT signals comprise a plurality of ERT signals, and wherein the plurality of ERT signals are used to calibrate at least a positive portion of a duty cycle and a negative portion of the duty cycle. ### Claim 13 (depends on 12) The data storage device of claim 12, wherein calibrating the negative portion of the duty cycle comprises: calibrating a first duration (TND) during which the laser diode bias current is lower than the lasing threshold current, and calibrating a first overshoot duration (TOND) during which the laser diode bias current is lower than a negative peak laser current (IN), and wherein the first duration (TND) is longer than or includes the first overshoot duration (TOND). ### Claim 14 A method for operating a data storage device configured for heat-assisted magnetic recording using a laser diode, the method comprising: preheating the laser diode to a target temperature, wherein the preheating comprises: generating, based at least in part on the target temperature, at least one bias pulse conforming to a plurality of parameters, the plurality of tunable parameters including one or more amplitude parameters, wherein the one or more amplitude parameters comprise one or more of: (1) a first laser diode bias current (IP) greater than a lasing threshold current, (2) a second laser diode bias current (IN) lower than the lasing threshold current, (3) a first duration (TPD), and (4) a second duration (TND); and applying, using an asymmetric laser diode driver, the at least one bias pulse to the laser diode such that no optical response is produced by the laser diode; and initiating a write operation for writing data to a disk of the data storage device. ### Claim 15 (depends on 14) The method of claim 14, wherein the plurality of tunable parameters further include one or more overshoot parameters, and wherein the one or more overshoot parameters comprise: a first overshoot amplitude current (OSAP), wherein OSAP corresponds to a positive overshoot compensation above IP; a first overshoot duration (TOPD), wherein TOPD is shorter than TPD; a second overshoot amplitude current (OSAN), wherein OSAN corresponds to a negative overshoot compensation below IN; and a second overshoot duration (TOND), wherein TOND is shorter than TND. ### Claim 16 (depends on 15) The method of claim 15, wherein generating the at least one bias pulse comprises: generating a plurality of current pulses, including at least: a first current pulse spanning the first duration (TPD), the first current pulse including a first overshoot portion spanning the first overshoot duration (TOPD), wherein a corresponding bias current associated with the first current pulse is above the lasing threshold current; and a second current pulse spanning the second duration (TND), the second current pulse including a second overshoot portion spanning the second overshoot duration (TOND), wherein a corresponding bias current associated with the second current pulse is below the lasing threshold current. ### Claim 17 (depends on 14) The method of claim 14, wherein the asymmetric laser diode driver comprises an asymmetric Bipolar Complementary Metal-Oxide Semiconductor (BiCMOS) driver. ### Claim 18 (depends on 17) The method of claim 17, wherein the asymmetric laser diode driver is driven by positive current pulses and negative current pulses, and wherein the positive current pulses have an amplitude that is greater in magnitude than an amplitude of the negative current pulses. ### Claim 19 (depends on 14) The method of claim 14, further comprising: receiving a plurality of external reference timing (ERT) signals; receiving a first pulse width modulation (PWM) signal and a second PWM signal; identifying a delay between the first and the second PWM signal; and identifying a plurality of overshoot parameters, and wherein identifying the one or more overshoot parameters further comprises determining a first overshoot duration (TOPD) and a second overshoot duration (TOND), based at least in part on the identified delay. ### Claim 20 (depends on 19) The method of claim 19, wherein generating the at least one bias pulse further comprises: calibrating a first duration (TPD) during which a laser diode bias current associated with the at least one bias pulse is above a lasing threshold current, based on at least one of the plurality of ERT signals; calibrating the first overshoot duration (TOPD) during which the laser diode bias current is above a first laser current (IP); calibrating a second duration (TND) during which the laser diode bias current is below the lasing threshold current, based on at least one of the plurality of ERT signals; and calibrating the second overshoot duration (TOND) during which the laser diode bias current is below a second laser current (IN); and wherein the lasing threshold current is lower than the first laser current (IP) and greater than the second laser current (IN). ### Claim 21 One or processing devices comprising: means for preheating a laser diode of a data storage device to a target temperature, wherein the data storage device is configured for heat-assisted magnetic recording using the laser diode, and wherein the means for preheating comprises: means for generating, based at least in part on the target temperature, at least one bias pulse conforming to a plurality of tunable parameters, the plurality of tunable parameters including one or more amplitude parameters, wherein the one or more amplitude parameters comprise one or more of: (1) a first laser diode bias current (IP) greater than a lasing threshold current, (2) a second laser diode bias current (IN) lower than the lasing threshold current, (3) a first duration (TPD), and (4) a second duration (TND); and means for applying the at least one bias pulse to the laser diode such that no optical response is produced by the laser diode; and means for initiating a write operation for writing data to a disk of the data storage device. ### Claim 22 A data storage device comprising: a disk; a read/write head configured to read data from and write data to the disk; a laser diode (LD) coupled to a near field transducer (NFT) configured to heat an area of the disk near the read/write head; an asymmetric LD driver configured to drive the LD, wherein the asymmetric LD driver comprises an asymmetric Bipolar Complementary Metal-Oxide Semiconductor (BiCMOS) driver; and one or more processing devices or components configured, individually or in combination, to: preheat the laser diode to a target temperature, wherein the preheating comprises: generating at least one bias pulse conforming to one or more tunable parameters, based at least in part on the target temperature; and applying, using the asymmetric LD driver, the at least one bias pulse to the laser diode such that no optical response is produced by the laser diode; and initiate a write operation for writing data to the disk.