Abstract:
A method, apparatus and computer program are disclosed for managing the distribution of optical power to a plurality of optical data devices. The devices can be data storage drives, data replicators, fast optical search devices, or other components that use optical or laser power for their operation. A power management system provides the increased flexibility of monitoring and redirecting optical power (e.g., to provide higher or lower power on demand), which increases the fault-tolerance and performance (e.g., through higher data transfer rates) of a data management system.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to an optical illuminator system, and in particular, to a distribution management and method for delivering optical power to a plurality of optical data devices. 
   2. Background of the Invention 
   Optical power management systems typically require the use of at least one optical power source (e.g., a CW laser, pulsed laser, laser diode, light emitting diode, etc.) for recording, retrieving and manipulating data. Small, relatively low power, low cost solid-state laser diodes with modest optical coherence are the predominant source of optical illumination in existing optical data storage systems. However, the need for shorter wavelength sources to enable greater data storage densities, the need for more powerful sources to enable increased data transfer rates, and the need for sources with longer coherence lengths for holographic data storage and other coherent applications, give rise to the problem of accommodating physically larger, higher power dissipating sources within the limited form factor of an optical device. Further compounding the problem are budgetary constraints that place a limit on the optical source cost per optical data device and the need for a highly reliable source. 
   Lower power, lower quality sources (i.e., sources with higher relative intensity noise, lower coherence length, higher wavelength drift, higher temperature sensitivity, limited wavelength tunability, etc.) limit the performance of optical storage drives and other optical data devices that use optical illumination (e.g., optical data replicators, fast optical search devices, etc.). This performance limitation is a consequence of the trade-off between the total energy required to achieve a desired physical and/or chemical effect while manipulating (e.g., recording, retrieving, processing or copying) data over a given illuminated area, and the time it takes to deliver the required energy. As such, this performance limitation represents a limitation on the optical data device parameters, including data density, capacity, transfer rates, search rates, error rates, integrity, reliability and lifetime. 
   Therefore, it would be desirable to have a system and method for efficiently utilizing a superior laser source despite its larger physical size, increased power and/or cooling demands and greater cost. It would be even more advantageous if such a system and method were capable of automatically detecting and correcting for optical power defects and failures, and optimizing the lifetime of laser sources—all with minimum user intervention. Finally, such a system and method could provide optical power on demand, boosting the performance of optical data devices that received higher performance priority. 
   SUMMARY OF THE INVENTION 
   The present invention provides a method, apparatus and computer program for managing the distribution of optical power from a plurality of (1 to M), high quality, high power optical sources, to a plurality of (1 to N) optical data devices. The optical data devices can be data storage drives, data search engines, data replicators, or other components that use optical power for their operation. Also, the present invention provides a data management system with the increased flexibility of monitoring and redirecting optical power on demand, which increases the fault-tolerance and performance (e.g., through higher data transfer rates) of the data management system. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
       FIG. 1  depicts a block diagram illustrating a fault-tolerant, optical power distribution and management system in accordance with a preferred embodiment of the present invention; 
       FIG. 2  depicts a pictorial representation of an exemplary optical power switch and tunable coupler module that may be used to illustrate principles of the present invention; 
       FIG. 3  depicts a pictorial representation of an exemplary generic optical power switch and tunable coupler module that may be used to illustrate principles of the present invention; 
       FIG. 4  depicts a flowchart of an exemplary process for an optical power monitor to manage the distribution of power levels for a plurality of data devices, in accordance with a preferred embodiment of the present invention; 
       FIG. 5  depicts a pictorial representation of an exemplary equipment rack containing optical data devices, optical power sources, a laser power monitor, and an optical power switch and tunable coupler module, in accordance with a preferred embodiment of the present invention; and 
       FIG. 6  depicts a pictorial representation of an exemplary data management system containing multiple interconnected racks similar to the exemplary equipment rack depicted in  FIG. 5 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   With reference now to the figures, and in particular with reference to  FIG. 1 , a block diagram of a fault-tolerant, optical power distribution and management system is illustrated in accordance with a preferred embodiment of the present invention. Exemplary system  100  includes a plurality of optical power sources which, in this case, are laser power sources  102   a – 102   m  (e.g., where “m” denotes the final or m th  laser power source). Each laser power source  102   a – 102   m  includes a power output connection  103   a – 103   m  and power monitor output connection  105   a – 105   m . Power output connections  103   a – 103   m  are coupled to respective inputs of optical power switch and tunable coupler  104 , and power monitor output connections  105   a – 105   m  are coupled to respective inputs of laser power monitor  108 . Each power output connection  103   a – 103   m  couples the output power of the respective laser power source  102   a – 102   m  to optical power switch and tunable coupler  104 . Each power monitor output connection  105   a – 105   m  relays an electronic signal to laser power monitor  108  that is proportional to the intensity of the respective laser power source  102   a – 102   n . Such a signal is derived from the detection of a small sample of the laser power. Connection  113  couples power redirection signals from laser power monitor  108  to optical power switch and tunable coupler  104 . 
   Exemplary system  100  also includes a plurality of optical data devices  106   a – 106   n  (where “n” denotes the final or nth optical data device). Power output connections  114   a – 114   n  couple the output power of the respective laser power sources  102   a – 102   m  from optical power switch and tunable coupler  104  to selected inputs of optical data devices  106   a – 106   n . As described in more detail below, the actual power levels at output power connections  114   a – 114   n , and the selection of inputs to optical data devices  106   a – 106   n  are performed by optical power switch and tunable coupler  104 , which may select the coupling ratios based on an algorithm, or which may simply use a predetermined coupling ratio. 
   Power monitor output connections  107   a – 107   n  of respective optical data devices  106   a – 106   n  are electronically relayed to respective inputs of laser power monitor  108 . Each power monitor output connection  107   a – 107   n  couples a relatively small percentage of the laser source power received at the respective optical data device  106   a – 106   n  to a photodetector that converts the received intensity into an electronic signal which is then transmitted to laser power monitor  108 . Data connections  116   a – 116   n  transfer data (e.g., storing and retrieving) between optical data devices  106   a – 106   n  and respective input/output (I/O) connections of data management system controller  110 . Output connection  111  of laser power monitor  108  couples fault alert signals (e.g., if any laser power level errors occur) to an input of data management system controller  110 . Output connection  112  of data management system controller  110  couples performance priority signals to an input of laser power monitor  108 . 
   Essentially, laser power sources  102   a – 102   m  and optical data devices  106   a – 106   n  can be mounted on the same equipment rack, where laser sources  102   a – 102   n , optical data devices  106   a – 106   n , and laser power monitor  108  and optical power switch and tunable coupler  104  modules use a similar form-factor in order to facilitate the field replacement of defective units, the upgrade of existing equipment, and the inclusion of additional equipment (e.g., more laser sources, new optical data devices, etc.). Preferably, more than one each module should be available in order to provide the system with the redundancy required for superior fault-tolerance. 
   Alternatively, for example, laser power sources  102   a – 102   m  and optical data devices  106   a – 106   n  can be arbitrarily mounted on different equipment racks, with their respective outputs and inputs coupled together (e.g., via optical power switch and tunable coupler  104 ) with appropriate optical coupling (e.g., optical fiber coupling), as depicted later in  FIG. 6 . In a preferred embodiment, the optical fibers conveying optical power, and conducting wires conveying electrical power and electronic signals, can be bundled together in the same cable, thus simplifying the cabling and facilitating the replacement of modules during repairs or upgrades. In any event, the arrangement, configuration and location of laser power sources  102   a – 102   m , optical data devices  106   a – 106   n , optical power switch and tunable coupler  104 , laser power monitor  108 , and data management system controller  110  in  FIG. 1  are presented for purposes of illustration and description, and are not intended to impose an architectural limitation on the present invention. 
   In those cases when coherent data processing or storage is required, the optical fiber that delivers the optical power can also be used to deliver light to a fiber optic coupler used to split the light at optical data devices  106   a – 106   n  onto a plurality of fibers. The fibers at the output of the coupler can be trimmed in order to match the path length of the two resulting beams of light at the position where they interfere with each other. The resulting matched path lengths render the optical data devices more tolerant to limited coherent lengths possibly provided by laser sources  102   a – 102   n , and are not intended to impose a limitation on the present invention. 
   With reference now to  FIG. 2 , a pictorial representation of an exemplary optical power switch and tunable coupler module is depicted that may be used to illustrate principles of the present invention. For example, optical power switch and tunable coupler module  200  can be used to implement optical power switch and tunable coupler  104  in  FIG. 1  with power coupled from only two laser power sources (i.e., laser power sources  102   a – 102   b ) via input connections  202   a ,  202   b  (i.e., “m” can represent “2” in  FIG. 1 ). For example, 2×1 switch  204  can include at least one fiber optic switch. The fiber optic switch (or switches) can select an input connection  202   a  or  202   b  and thus couple the laser energy (power) present at selected connection  202   a  or  202   b  to an input of 1×N tunable coupler  206 , thus providing fault-tolerance and the possibility to replace a faulty laser without interruption in the delivery of laser power and the associated down-time. Tunable coupler  206  (in combination with switch  204 ), for example, can use “n−1” 1×2 fiber tunable directional couplers to direct the selected laser power received from switch  204  towards one or more optical data devices at a coupling ratio selected by laser power monitor  108 . For example, n−1 TC1400™ series tunable directional couplers (as manufactured by FiberPro) can be used to provide n tunable outputs in a known binary tree configuration. As described in more detail below, for this exemplary embodiment, a laser power monitor (e.g., laser power monitor  108  in  FIG. 1 ) determines the coupling ratio(s) for tunable coupler  206 . 
   With reference now to  FIG. 3 , a pictorial representation of an exemplary, generic optical power switch and tunable coupler module is depicted that may be used to illustrate principles of the present invention. For example, optical power switch and tunable coupler module  300  can be used to implement optical power switch and tunable coupler  104  in  FIG. 1  with power coupled from “m” laser power sources (i.e., laser power sources  102   a – 102   m ) via input connections  302   a – 302   m.    
   Exemplary optical power switch and tunable coupler module  300  includes a plurality of 1×n tunable coupler sections  304   a – 304   m . Each tunable coupler section  304   a – 304   m  can use, for example, “n−1” 1×2 fiber tunable directional couplers to direct the selected laser power received towards one or more optical data devices at a coupling ratio selected by a laser power monitor (e.g., laser power monitor  108  in  FIG. 1 ). Again, for example, n−1 FiberPro™ TC1400 series tunable directional couplers can be used to produce n tunable outputs in a known binary tree configuration. 
   For this example, each m×1 switch  306   a – 306   n  can include at least one fiber optic switch. The fiber optic switch (or switches) can select an individual input connection from one of the tunable coupler sections  304   a – 304   m  and thus couple the laser energy (power) present to an input of a selected device (e.g., one of optical data devices  106   a – 106   n  in  FIG. 1 ) via a respective output connection  308   a – 308   n , without mixing light from different lasers and thus providing fault-tolerance and the possibility to replace a faulty laser without down-time. Again, for this exemplary embodiment, a laser power monitor (e.g., laser power monitor  108  in  FIG. 1 ) can determine the coupling ratio(s) for each tunable coupler section  304   a – 304   m , and which laser(s) to send optical power to each of the optical data devices by controlling switches  306   a – 306   n.    
   For coherent optical data manipulation applications (e.g., holographic data storage), it is important to prevent the (light) energy from two or more laser sources from being combined. However, in the case where coherent illumination is not required, or when the tunable coupler modules  304   a – 304   m  are each capable of producing a tuning range that goes down to a virtually zero output power level (or at least minimal, acceptable leakage) for those optical data devices not being served, the m×1 switches  306   a – 306   n  can be replaced with m×1 optical power combiners (e.g., m×1 fiber couplers used as combiners) at a potentially lower cost. 
   With reference now to  FIG. 4 , a flowchart is depicted of an exemplary process for an optical power monitor to determine a distribution of power levels for a plurality of data devices, in accordance with a preferred embodiment of the present invention. For example, referring also to  FIG. 1 , process  400  can represent a process for laser power monitor  108  to determine a distribution of power levels from laser power sources  102   a – 102   m  to optical data devices  106   a – 106   n . As such, for illustrative purposes only, process  400  is described herein with respect to operations of exemplary fault-tolerant, optical power management system  100  shown in  FIG. 1 . 
   Exemplary process  400  begins by laser power monitor  108  retrieving a (device) performance priority signal from data management system controller  110  via connection  112  (step  402 ). The performance priority signal from data management system controller  110  determines which optical data devices  106   a – 106   n  have a higher performance priority, and therefore, should receive more of the available optical power. Typically, all of optical data devices  106   a – 106   n  can be given equal priorities, and the total power available from laser power sources  102   a – 102   m  can be distributed equally among optical data devices  106   a – 106   n . Additionally, the performance priority signal retrieved from data management system controller  110  can be used as a “flag” to laser power monitor  108  to recognize that an optical data device (e.g., optical data device  106   a ) is not being used (i.e., zero priority assigned by data management system controller  110 ). Consequently, laser power monitor  108  can redirect laser power away from that “flagged” optical data device (e.g., optical data device  106   a ) to one or more of the remaining optical data devices (e.g., optical data devices  106   b – 106   n ). 
   If laser power monitor  108  receives a performance priority signal from data management system controller  110  and determines that a change in the priorities of optical data devices  106   a – 106   n  has occurred (step  404 ), laser power monitor  108  recalculates the normalized coupling ratios for the (e.g., remaining) optical data devices where the priority signal sets the weights of the normalized, weighted coupling ratios (step  406 ). Laser power monitor  108  can then send an appropriate power redirection signal with the recalculated coupling ratios to optical power switch and tunable coupler  104  via connection  113 . 
   Next, for this exemplary embodiment, laser power monitor  108  retrieves the laser output power monitor signals from each laser power source  102   a – 102   m  via power output monitor connections  105   a – 105   m  (step  408 ). Laser power monitor  108  can then determine whether or not a retrieved laser output power monitor signal has a value that is less than or equal to a specified power threshold value (step  410 ). If so, laser power monitor  108  assumes that the particular laser power source associated with that signal is defective. Laser power monitor  108  can then send a power redirection signal (via connection  113 ) to optical power switch and tunable coupler  104 , in order to switch the defective laser power source out of service, and reapportion the power from the remaining laser power sources to optical data devices  106   a – 106   n  (step  412 ). Also, laser power monitor  108  can send an appropriate flag (e.g., fault alert message) to data management system controller  110  via connection  111 , in order to initiate service to replace the defective laser power source (step  414 ). Additionally, in response to receiving a fault alert message, data management system controller  110  can initiate a process to prevent a more catastrophic system failure, such as, for example, backing up system data, flushing buffers, using alternative optical data devices, etc. 
   Next, for this exemplary embodiment, laser power monitor  108  retrieves the power monitor signals from optical data devices  106   a – 106   n  via respective power monitor output connections  107   a – 107   n  (step  416 ). These signals allow laser power monitor  108  to determine how much power from each laser power source  102   a – 102   m  has arrived at a respective optical data device  106   a – 106   n . Additionally, the strengths of these signals can allow laser power monitor  108  to determine the optical losses due to fiber optic connections, switches, and/or couplers involved in those particular laser power flows. 
   In response to receipt of the power monitor signals from optical data devices  106   a – 106   n , laser power monitor  108  can determine whether or not a particular optical data device  106   a – 106   n  has failed (step  418 ). If so, laser power monitor  108  can send an appropriate fault alert signal (e.g., as a flag) to data management system controller  110  via connection  111  (step  420 ). 
   Additionally, the power monitor signals from optical data devices  106   a – 106   n  can be used in a closed feedback process to control the coupling ratios of the tunable coupler module(s) of optical power switch and tunable coupler  104 , and to compensate for temporal fluctuations in optical power losses in the optical power distribution path. For example, laser power monitor  108  can determine from the power monitor signals received from optical data devices  106   a – 106   n  whether or not the coupling ratios being used in the tunable coupler module(s) of optical power switch and tunable coupler  104  are correct, by comparing the power monitor signals received from optical data devices  106   a – 106   n  with a predetermined calculation representing correct coupling ratios preferably derived from performance priority signals received from data management system controller  110  via connection  112  (step  422 ). If laser power monitor  108  determines that one or more of the coupling ratios being used in the tunable coupler module(s) of optical power switch and tunable coupler  104  are incorrect, then laser power monitor  108  can send an appropriate power redirection signal to optical power switch and tunable coupler  104  via connection  113 , in order to reassign the coupling ratios (e.g., by incrementally adjusting the coupling ratios by small amounts) until the desired, correct coupling ratios are achieved (step  424 ). Preferably, these incremental adjustments of the coupling ratios are designed to be small enough to prevent unstable feedback loop behavior, but still large enough to provide a rapid system response (i.e., using control system techniques well-known to those of ordinary skill in the art). 
   Furthermore, the laser power monitor  108  may keep track of the periods of time, duration, and the power levels at which each of laser sources  102   a – 102   m  are used. This information then can be used to keep track of which laser sources are most likely to fail, and preventive maintenance can be requested to data management system controller  110  via connection  111 . The preventive maintenance can be in the form of the preventive replacement of the unit, or its preventive servicing (e.g., replacement of a pump diode module). Also, the laser power monitor  108  can use the laser usage information in order to increase the useful life of each laser by using one (or both) of the following techniques: 1) by guaranteeing that each source is used at least once over a certain period of time; and 2) by equalizing the total energy output of each source by using more of those sources that have been used the least, whenever not in conflict with other data management performance priorities. 
   With reference now to  FIG. 5 , a pictorial representation is depicted of an exemplary equipment rack containing optical data devices, optical power sources, a laser power monitor, and an optical power switch and tunable coupler, in accordance with a preferred embodiment of the present invention. For this exemplary embodiment, equipment rack  500  includes a plurality of optical data device modules  502   a – 502   d  (e.g., including optical data devices similar in structure and function to optical data devices  106   a – 106   n  in  FIG. 1 ), a plurality of optical power source modules  504   a – 504   b  (e.g., including optical power sources similar in structure and function to laser power sources  102   a – 102   m ), an optical power monitor module  506   a  (e.g., including an optical power monitor similar in structure and function to laser power monitor  108 ), and an optical power switch and tunable coupler module  506   b  (e.g., including an optical power switch and tunable coupler similar in structure and function to optical power switch and tunable coupler  104 ). An optical power monitor module  506   a  and a tunable coupler module  506   b  can be packaged together in a single module  506  (as shown in  FIG. 5 ), or they can be packaged in separate modules in an alternative embodiment. 
   Advantageously, as shown, modules  502   a – 502   d ,  504   a – 504   b  and  506   a – 506   b  are mounted in the same equipment rack, with the respective outputs and inputs of modules  502   a – 502   d ,  504   a – 504   b  and  506   a  coupled together via module  506   b  with appropriate optical coupling (e.g., optical fiber coupling). Also, advantageously, modules  502   a – 502   d ,  504   a – 504   b  and  506   a – 506   b  use similar form-factors in order, for example, to facilitate the field replacement of defective units, the upgrade of existing equipment, and the inclusion of additional equipment (e.g., more laser sources, new optical data devices, etc.). As such, a plurality of these modules can be available in order to provide the system with the redundancy required for superior fault-tolerance. 
   Additionally, for a preferred embodiment, the optical fibers conveying optical power between the modules shown in  FIG. 5 , the conducting wires conveying electronic signals (e.g.,  105   a – 105   m  and  107   a – 107   n ), and the conducting wires conveying electrical power to these modules can be bundled together in one cable, which simplifies the cabling and facilitates replacement of the modules during repairs or upgrades. 
   Furthermore, a bundle of optical cables and/or electronic signal wires and/or electrical power cable  508  can be used to interconnect equipment rack  500  to other equipment racks in a data management system. 
   With reference now to  FIG. 6 , a pictorial representation is depicted of an exemplary data management system containing multiple interconnected racks, which are similar to the exemplary equipment rack depicted in  FIG. 5 . For example, exemplary data management system  600  contains a plurality of equipment racks  602 ,  604 ,  606 . However, it should be understood that although only three equipment racks are shown in  FIG. 6 , the present invention is not intended to be so limited, and data management system  600  can contain a number of additional equipment racks similar in structure and function to racks  602 ,  604  and  606 . Preferably, each of racks  602 ,  604 ,  606  is arranged with modules similar in structure and function to modules  502   a – 502   d ,  504   a – 504   b  and  506   a – 506   b  in  FIG. 5 , and coupled together (e.g., via modules similar to module  506   a  in  FIG. 5 ), using optical cable  608  similar to cable  508 , for conveying optical power between the respective outputs and inputs of the modules with appropriate optical coupling. Alternatively, for example, one or more of the modules (e.g., modules  502   a – 502   d  and  504   a – 504   b ) contained in each rack  602 ,  604 ,  606  can be arbitrarily mounted on a different one of racks  602 ,  604 ,  606 , with their respective outputs and inputs coupled together (e.g., via a module such as module  506   b  in  FIG. 5 ) with appropriate optical coupling. 
   It is important to note that while the present invention has been described in the context of a fully functioning fault-tolerant, optical power management apparatus and method for automated data manipulation and storage, those of ordinary skill in the art will appreciate that the processes of the present invention are capable of being distributed in the form of a computer readable medium of instructions and a variety of forms and that the present invention applies equally regardless of the particular type of signal bearing media actually used to carry out the distribution. Examples of computer readable media include recordable-type media such a floppy disc, a hard disk drive, a RAM, CD-ROMs, and transmission-type media such as digital and analog communications links. 
   The description of the present invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.