# Patent

## Title
Optical storage system divider based draw verification

## Abstract

An optical storage system includes an optical head and controller arrangement. The arrangement is configured to write data to an optical medium via a higher power main beam, to read, directly after writing, feedback from the medium containing the written data and noise resulting from the higher power main beam, to remove the noise from the feedback by dividing the feedback with data indicative of the higher power main beam, and to generate output indicative of the written data.

## Background
TECHNICAL FIELD
This disclosure relates to techniques for real-time verification of written data in an optical storage system.
BACKGROUND
Optical recording devices such as optical disk and optical tape drives commonly use an Optical Pickup Unit (OPU) or read/write head to write and retrieve data from associated optical media. Conventional OPUs may utilize different wavelength semiconductor laser diodes with complex beam path optics and electromechanical elements to focus and track the optical beam within one or more preformatted tracks on the medium to write or store the data and subsequently read the data. Data written to the medium with a laser at higher power may be verified in a separate operation or process after writing using a lower laser power, or may be verified during the write operation by another laser or laser beam. The ability to read and verify the data during the write operation may be referred to as Direct Read After Write (DRAW).
Current OPUs may use a diffraction grating or similar optics in the laser path to generate three beams from a single laser element including a higher power beam used for reading/writing data and for focusing, and two lower power satellite beams used for tracking. The three beams are focused to three corresponding spots on the surface of the optical storage medium used by the various optical and electromechanical elements of the OPU. In general, the higher power spot is positioned in the center or middle between the two satellite spots. In addition to reading/writing data and focusing, the center spot may also be used for one particular type of tracking operation in some applications. The lower power satellite spots generated from the lower power side beams are typically used for another type of tracking operation for specific types of media.
SUMMARY
Optical storage systems and methods of performing direct read after write for the same utilize circuitry and/or controllers configured to process data read directly after writing to remove noise introduced by the writing. Because the writing process involves high-frequency writing strategy pulses in the laser's optical power for creating the crystal phase change on the optical recording layer of the media, the direct read laser power signal from the laser light sensor during the write contains modulation of the written data and the high-frequency writing pulses. Division of the read signal by the writing strategy signal, for example, can cancel out the noise to recover and verify the written data. The delay or bias associated with the signals may be tuned to improve the signal quality associated with the recovered data.
In one embodiment, an optical storage system includes an optical head that splits a light beam into a higher power main beam and at least one lower power side beam, and a controller. The controller alters an optical medium via the higher power main beam to write data to the medium while processing a first signal resulting from the at least one lower power side beam being reflected from the medium and a second signal resulting from scatter of the higher power main beam to remove noise from the first signal caused by the higher power main beam to generate output indicative of the data directly after writing.
In another embodiment, an optical storage system includes an optical head and controller arrangement that writes data to an optical medium via a higher power main beam, reads, directly after writing, feedback from the medium containing the written data and noise resulting from the higher power main beam, removes the noise from the feedback by dividing the feedback with data indicative of the higher power main beam, and generates output indicative of the written data.
In yet another embodiment, a method for performing direct read after write on an optical medium includes splitting a light beam into a higher power main beam and at least one lower power side beam, and writing data to the medium by altering the medium via the higher power main beam. The method also includes, while performing the writing, processing a first signal resulting from at least one of the lower power side beams being reflected from the medium and a second signal resulting from scatter of the higher power main beam to remove noise from the first signal caused by the higher power main beam, and generating output resulting from the processing indicative of the data.



BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B are block diagrams illustrating operation of an example optical data storage system or method with direct read after write (DRAW) capability.
FIG. 2 is a block diagram illustrating operation of the optical pickup unit (OPU) of FIGS. 1A and 1B having a coherent light beam split or divided into a center beam and two satellite or side beams to provide DRAW capability.
FIGS. 3A through 3C are diagrams illustrating components associated with RF and FM signal wave forms, and the result of their division.
FIG. 4 is another block diagram illustrating operation of the example optical data storage system of FIGS. 1A and 1B.
FIG. 5 is a block diagram illustrating an example DRAW demodulation circuit.
FIG. 6 is a plot comparing, for the same data, a read signal generated during a read operation (top waveform) and a DRAW division output signal generated by the DRAW demodulation circuit of FIG. 5 during a write operation (bottom waveform).



DETAILED DESCRIPTION
Various embodiments of the present disclosure are described herein. However, the disclosed embodiments are merely exemplary and other embodiments may take various and alternative forms that are not explicitly illustrated or described. The Figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one of ordinary skill in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of this disclosure may be desired for particular applications or implementations.
The processes, methods, logic, or strategies disclosed may be deliverable to and/or implemented by a processing device, controller, or computer, which may include any existing programmable electronic control unit or dedicated electronic control unit. Similarly, the processes, methods, logic, or strategies may be stored as data and instructions executable by a controller or computer in many forms including, but not limited to, information permanently stored on various types of articles of manufacture that may include persistent non-writable storage media such as ROM devices, as well as information alterably stored on writeable storage media such as floppy disks, magnetic tapes, CDs, RAM devices, and other magnetic and optical media. The processes, methods, logic, or strategies may also be implemented in a software executable object. Alternatively, they may be embodied in whole or in part using suitable hardware components, such as Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), state machines, controllers or other hardware components or devices, or a combination of hardware, software and firmware components.
Referring now to FIGS. 1A and 1B, block diagrams illustrating operation of an example optical data storage system or method with direct read after write (DRAW) capability are shown. FIG. 1A is a side view diagram and FIG. 1B is a top or plan view diagram. In this embodiment, optical data storage system 10 is an optical tape drive 12 that receives an optical data storage medium 14, which is an optical tape 16. While illustrated and described with reference to an optical tape drive, those of ordinary skill in the art will recognize that the teachings of the present disclosure may also be applied to various other types of optical data storage devices that may use various types of write-once or re-writable optical media, such as optical discs. The optical tape 16 is a 1⁄2 inch (12.7 mm) wide tape having a plurality of tracks 36 generally extending across the width of the tape and may vary in length depending on the desired storage capacity and performance characteristics as illustrated and described in greater detail herein. Other tape configurations and dimensions, however, are also possible. The optical tape 16 may be wound on an associated spool 17 contained within a protective case or cartridge 18 that is manually or automatically loaded or mounted in the optical tape drive 12. Transport mechanism 24 moves the optical tape 16 through a carriage and past at least one optical pickup unit (OPU) or optical head 20 to a take-up spool 22 that typically remains within the tape drive 12. The OPU 20 writes data to, and reads data from, the optical tape 16 as the transport mechanism 24 moves the optical tape 16 between the cartridge 18 and take-up spool 22 in response to at least one controller and associated electronics 26. As explained in greater detail below, data may be read/written to the optical tape 16 in one or more of the tracks 36 in a serpentine fashion as the tape travels in either direction past the OPU 20, i.e., either from the cartridge 18 to the take-up spool 22, or from the take-up spool 22 to the cartridge 18.
The optical head 20 may include associated optics and related electromechanical servo controlled devices, represented generally by reference numeral 30, that split or divide a light beam, such as a laser beam, into two or more beams that are focused to corresponding spots on the storage medium 16 for reading/writing data as illustrated and described in greater detail with reference to FIG. 2. Various servo mechanisms (not specifically illustrated) may be used to position/align the beams with a selected one of the tracks 36 on the optical tape 16.
FIG. 2 is a block diagram illustrating operation of the optical pickup unit (OPU) 20 having a coherent light beam split or divided into a center beam 40 and two satellite or side beams 44, 48 to provide DRAW capability. The beams 40, 44, 48 may be generated by a single or common coherent light source, such as a laser diode, for example. The source beam travels through associated optics, that may include a diffraction grating, for example, to divide or split the source beam into the center beam 40, first side beam 44, and second side beam 48 and to focus the beams to corresponding spots 50, 54, and 58, respectively, on the surface of the optical tape 16 within a selected one of the tracks 36. The three optical spots 50, 54, and 58 are manipulated by various optical and electrometrical elements of the OPU 20 to write and retrieve data from the optical tape 16.
The optical elements used to split the source beam and focus the resulting beams to the spots 50, 54, and 58 may be designed to provide higher power to the center beam 40 and center spot 50 with lower power to the side beams 44, 48 and associated spots 54, 58. For example, the center spot 40 may contain about 90% of the source beam power with the side beams 44, 48 dividing the remaining 10% of the source beam power. The center beam 40 is modulated by the OPU 20 to generate write marks 60 during writing of data to the optical tape 16, which may require about ten times more average power than to read previously stored data (such as about 7 mW to write data and about 0.3 mW to read data, for example). As such, if the source beam is modulated and produces sufficient power for writing data using the center beam/spot 40/50, the side beams 44, 48 will be modulated in a like manner but will contain insufficient power to alter the tape 16.
In this embodiment, the spots 50, 54, and 58 are mechanically aligned in the OPU manufacturing process to correspond to the axes of the data tracks 36. In addition, the satellite spots 54, 58 are generally symmetrically positioned relative to the center spot 50 so that transit distance (d) of the tape 16 between the center spot 50 and either of the satellite/side spots 54, 58 is substantially the same. Other embodiments may include a distance (d) of between about 10-20 μm—although other distances are also contemplated.
Certain conventional optical storage devices use the center spot 50 from the higher power emitting beam 40 for reading, writing, and focusing in addition to one type of tracking operation. The satellite spots 54, 58 formed by the lower power side beams 44, 48 are used for another type of tracking for specific types of media. In these applications, the side spots 54, 58 may not be aligned with one another, or with the center spot 50 along a single one of the tracks 36.
As previously described, the source laser beam is operated at a higher power (relative to operation during a data read/retrieval) and modulated to write the data marks 60 on a selected one of the tracks 36 on the optical tape medium 16. However, only the center beam 40 emits enough power to the optical tape 16 to actually alter the structure of the optically active layer. The satellite beams 44, 48, having much lower power as determined by the diffraction grating power distribution, do not alter the tape 16. They, however, have enough power after being reflected from the optical tape 16 to detect the data marks 60. Therefore depending on the direction of travel of the optical tape 16, the reflection from one or both of the associated satellite spots 54, 58 can be detected by the OPU 20 and used to verify the data marks 60 directly after being written by the main beam/spot 40/50 to provide DRAW operation. While the reflected beam associated with one of the satellite beams 44, 48 (depending on the direction of travel of the tape 16) contains information associated with the data marks 60 on the tape medium 16, the reflected beam is heavily contaminated by the modulation of the center beam 40 and other noise sources and generally exhibits a very low signal to noise ratio (SNR).
Here, some of the DRAW systems and algorithms contemplated use a demodulation/division method to verify written data during the write operation in real-time. For example during the write operation, the written data is decoded (read) from a reflected laser light signal by a high frequency demodulation circuit (divider circuit). Then, the signal quality of the decoded written data can be calculated by a Bit-Error-Rate (BER) detector in order to verify the written data. As a result, the time between data writing and data decoding in this example is less than 1 msec.
As mentioned above, data written by the main spot 50 could be read back by one of the satellite spots 54, 58 after a few micro seconds. The satellite spots 54, 58, however, only have a fraction of the light intensity of the main spot 50. Thus, the light intensity signal detected by either one of the satellite spots 54, 58 is modulated (distorted) with high-frequency laser pulses used for writing. In order to better decode the written data, the satellite spot reflected laser light intensity signal (referred to as the RF signal) can be demodulated from the main spot writing laser pulse signal (referred to as the FM signal as it can be measured by a laser light front monitor detector) using, for example, a DRAW demodulation circuit in order to reverse the modulation caused by the writing pulsation of the laser diode. Also, frequency responses of the RF signal and FM signal can be matched by applying a matched filter before the demodulation. A filter and high-frequency demodulator, therefore, can be designed for decoding and verifying written data during the write operation. Thus, the demodulation and verification of written data can be in real-time.
Certain DRAW circuits contemplated herein require much less calculation cost by using a high frequency demodulator (e.g., analog high speed divider). This enables the operation of DRAW for multiple channels (e.g., 24 channels) simultaneously. Other advantages may include small size, low cost, and high speed for multi-channel designs.
FIG. 3A shows that the RF signal detected by a corresponding RF chip (e.g., a photodetector chip, PDIC, placed at the end of the reflected optical light path of the OPU 20) not only contains data associated with the written mark being read but also the writing strategy waveform embodied by the main spot 50 at the time the written mark was being read. That is, the RF signal is subject to noise introduced by the writing strategy waveform. FIG. 3B shows that the FM signal detected by a corresponding FM chip (e.g., a front monitor chip, FMIC, placed at the laser light output path of the OPU 20) from the scatter associated with the center beam 40 is essentially the writing strategy waveform. FIG. 3C shows that the division of the RF signal by the FM signal via a DRAW circuit yields the written mark.
A voltage of the RF signal, VRF, can be represented as

VRF=kRF×φ×R  (1)

where kRF is a constant associated with the RF chip, φ is the writing strategy modulated light intensity, and R is the changed reflectivity of the medium indicative of a written mark. And, a voltage of the FM signal, VFM, can be represented as

VFM=kFM×φ  (2)

where kFM is a constant associated with the FM chip. Dividing (1) by (2) yields k× R, where k is kRF/kFM. Because kRF and kFM are known, R can be obtained free of influence from VFM.

FIG. 4 shows the OPU 20 and an FMIC chip 23 arranged to receive laser light from a laser diode 21. That is, the FM signal from the FMIC chip 23 represents the direct light output of the laser diode 21 without any modification by the OPU 20 or media 16. And, a PDIC chip 25 is arranged to receive light reflected from the media 16 and through the OPU 20.
FIG. 5 shows the at least one controller and associated electronics 26 implementing an analog DRAW demodulation circuit 62 to perform the signal division described above. In this example, the circuit 62 includes an RF signal input stage 64, a direct current (DC) bias 66, an all-pass delay filter 68, and a low pass filter 70. The circuit 62 also includes an FM signal input stage 72, a low pass filter 74, a multiplier 76, an op-amp 78, an inverter 80, and a DRAW division output 82. The signal process flow associated with the RF signal is the input stage 64 to the DC bias 66, the DC bias 66 to the all-pass delay filter 68, the all-pass delay filter 68 to the low pass filter 70, and the low pass filter 70 to the op-amp 78. The sequence of these elements, however, may be rearranged as necessary. The low pass filter 70, for example, may come before the DC bias 66, etc. The signal process flow associated with the FM signal is the input stage 72 to the low pass filter 74, the low pass filter 74 to the multiplier 76, and the multiplier 76 to the op-amp 78. The final leg of the signal process flow is the op-amp 78 to the multiplier 76 and to the inverter 80, and the inverter 80 to the DRAW division output 82. FIG. 5 shows but one example of a demodulator or divider arrangement that includes a multiplier, op-amp, and inverter. Any suitable such arrangement, however, may be used. And although the elements of the DRAW demodulation circuit 62 are shown to be implemented in analog form, they of course may be implemented in digital form. In embodiments that implement at least the RF path in digital form, the all-pass delay filter 68 may take the form of a Farrow structure phase delay interpolator, which may allow for finer delay adjustment relative to other delay operations.
To better align the RF and FM signals for division, the DC bias 66 applies a DC bias to the RF signal. In the example of FIG. 5, the bias is +1.3 volts. This value, however, may change depending on design considerations, medium configuration, etc. Also due to the differing frequency responses of the RF and FM chips associated with the OPU 20, the all-pass delay filter 68 applies a delay to the DC biased RF signal for synchronization purposes. In other embodiments, the all-pass delay filter 68 may be in the FM signal path. The frequency associated with the writing strategy can be on the order of 165 megahertz. This value, however, may change with tape speed, writing speed, etc. As such, the low pass filters 70, 74 filter out frequency content associated with the RF and FM signals respectively, in this example, greater than 50 megahertz for better performance in the demodulation stage. This value may also change with tape speed, writing speed, writing strategy pattern, etc. A calibration procedure may be performed to select the appropriate bias and delay values prior to operating at run time.
FIG. 6 shows the similarity between a read signal generated during a read operation (top waveform) and, for the same data, a DRAW division output signal generated by DRAW division output 82 during a write operation (bottom waveform).
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure and claims. As previously described, the features of various embodiments may be combined to form further embodiments that may not be explicitly described or illustrated. While various embodiments may have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics may be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.

## Claims

1. An optical storage system comprising:
an optical head configured to split a light beam into a higher power main beam and at least one lower power side beam; and
a controller configured to alter an optical medium via the higher power main beam to write data to the medium while processing a first signal resulting from the at least one lower power side beam being reflected from the medium and a second signal resulting from scatter of the higher power main beam to remove noise from the first signal caused by the higher power main beam to generate output indicative of the data directly after writing, wherein the processing includes dividing the first signal by the second signal.

2. The system of claim 1, wherein the processing includes filtering the first signal to delay the first signal prior to the dividing.

3. The system of claim 2, further comprising a Farrow structure phase delay interpolator to filter the first signal to delay the first signal.

4. The system of claim 1, wherein the processing includes filtering the first and second signals to remove frequency content therefrom greater than a threshold prior to the dividing.

5. The system of claim 1, wherein the controller includes analog circuitry to perform the processing.

6. The system of claim 1, wherein the optical medium is an optical tape.

7. An optical storage system comprising:
an optical head and controller arrangement configured to write data to an optical medium via a higher power main beam, to read, directly after writing, feedback from the medium containing the written data and noise resulting from the higher power main beam, to remove the noise from the feedback by dividing the feedback with data indicative of the higher power main beam, and to generate output indicative of the written data.

8. The system of claim 7, wherein the arrangement includes analog or digital circuitry configured to perform the dividing.

9. The system of claim 7, wherein the arrangement is further configured to perform a delay operation on the feedback or the data indicative of the higher power main beam prior to the dividing.

10. The system of claim 7, wherein the arrangement is further configured to perform a filter operation on the feedback and the data indicative of the higher power main beam to remove frequency content therefrom greater than a threshold prior to the dividing.

11. They system of claim 7, wherein the arrangement is configured to split a light beam into the higher power main beam and a lower power side beam.

12. The system of claim 11, wherein the arrangement is further configured to generate the feedback via the lower power side beam.

13. The system of claim 7, wherein the optical medium is an optical tape.

14. A method for performing direct read after write on an optical medium, comprising:
splitting a light beam into a higher power main beam and at least one lower power side beam;
writing data to the medium by altering the medium via the higher power main beam;
while performing the writing, processing a first signal resulting from at least one of the lower power side beams being reflected from the medium and a second signal resulting from scatter of the higher power main beam to remove noise from the first signal caused by the higher power main beam, wherein the processing includes dividing the first signal by the second signal; and
generating output resulting from the processing indicative of the data.

15. The method of claim 14, wherein the processing includes filtering the first signal to delay the first signal prior to the dividing.

16. The method of claim 15, wherein the filtering the first signal to delay the first signal is by a Farrow structure phase delay interpolator.

17. The method of claim 14, wherein the processing includes filtering the first and second signals to remove frequency content therefrom exceeding a threshold prior to the dividing.

18. The method of claim 14, wherein the processing includes altering a direct current bias of the first signal prior to the dividing.

19. The method of claim 14, wherein the processing is performed via analog and digital circuitry.

20. The method of claim 14, wherein the optical medium is an optical tape.