Patent Publication Number: US-11031749-B2

Title: Laser control

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of and claims the benefit of U.S. patent application Ser. No. 16/101,179, filed Aug. 10, 2018, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     Lasers are driven by current such that more current equates to more light. However, current also causes the laser to self-heat. As the laser heats, the current required to produce a given amount of light increases. If the laser&#39;s emitter temperature is known, it should be possible to accurately determine the current required for a desired amount of light. Accurate measurement of the laser&#39;s emitter temperature is extremely difficult and takes time. The laser temperature tends to change so rapidly that it&#39;s not practical to measure the emitter temperature or by the time the emitter temperature is measured the value is stale (e.g., inaccurate). The present concepts offer techniques for predicting the laser emitter temperature in near real-time (e.g., fast enough) as well as a method for determining the amount of current required to get the desired amount of light. The high-speed temperature prediction techniques can be applied to laser-based raster image displays to produce high image quality and thereby enhance user satisfaction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate implementations of the concepts conveyed in the present document. Features of the illustrated implementations can be more readily understood by reference to the following description taken in conjunction with the accompanying drawings. Like reference numbers in the various drawings are used wherever feasible to indicate like elements. In some cases, parentheticals are utilized after a reference number to distinguish like elements. Use of the reference number without the associated parenthetical is generic to the element. Further, the left-most numeral of each reference number conveys the FIG. and associated discussion where the reference number is first introduced. 
         FIGS. 1-3, 5, and 7  show example systems in accordance with some implementations of the present laser control concepts. 
         FIGS. 4A and 4B  show example current-light-temperature relationships in accordance with some implementations of the present laser control concepts. 
         FIG. 4C  shows example temperature-optical power relationships in accordance with some implementations of the present laser control concepts. 
         FIG. 4D  shows example heating power versus current and temperature relationships in accordance with some implementations of the present laser control concepts. 
         FIG. 6  shows additional details about some of the elements shown in  FIG. 5  in accordance with some implementations of the present laser control concepts. 
         FIGS. 8 and 9  show example laser control flowcharts in accordance with some implementations of the present laser control concepts. 
     
    
    
     DESCRIPTION 
     This description relates to controlling lasers that can be used to produce light (e.g., a laser beam). A laser can include a laser emitter that emits the laser beam. The laser can be driven with electrical current to emit optical power from the laser emitter. However, achieving a desired optical power output is dependent upon the properties of the laser, especially the temperature of the laser emitter. The temperature of the laser emitter can affect how efficiently the laser converts the electrical power to optical power (e.g., the efficiency of the laser at converting electrical energy into optical energy is dependent on laser emitter temperature). If the laser is driven at an electrical current that is not adjusted to reflect the temperature of the laser emitter, an actual optical power of the laser beam may not match the desired optical power. However, it can be difficult or impossible to accurately and quickly measure laser emitter temperature, especially when the temperature is rapidly changing. 
     The present concepts provide laser emitter temperature prediction models that accurately predict laser emitter temperature even when the laser emitter temperature is rapidly changing. The laser emitter temperature prediction models can utilize various sensed laser properties (e.g., laser case temperature) as input to predict the laser emitter temperature. The predicted laser emitter temperatures can be used to compute adjusted or compensated electrical currents that drive the laser so that the laser produces an actual optical power that matches (or nearly matches) the desired optical power. 
     Introductory  FIG. 1  shows an example implementation of some of the present concepts on a system  100 . System  100  can include a laser  102  that can produce laser beam  104 . 
     Traditionally, a desired optical power  106  would be mapped to an electrical current and the electrical current would be used to drive the laser  102  to produce laser beam  104  that has an actual optical power. The intent is for the actual optical power of the laser beam to match the desired optical power  106 . However, laser emitter temperature can alter the laser efficiency produced by the mapped electrical current and thus result in a large delta between the desired optical power and the actual optical power. 
     The present system  100  can include a compensation and control component  108  and a laser emitter temperature prediction model  110 . System  100  can also include a laser sensor  112  and a laser beam sensor  114 , among other sensors. The laser sensor  112  can sense properties of the laser  102  (e.g., sensed laser properties  116 , such as laser case temperature). The laser beam sensor  114  can sense properties (e.g., sensed laser beam properties  118 , such as optical power and/or wavelength) of the laser beam  104 . The sensed laser properties  116  and/or the sensed laser beam properties  118  can be used as input for the laser emitter temperature prediction model  110  and/or can be used as feedback to check the accuracy of the laser emitter temperature prediction model  110 . In some implementations, the laser emitter temperature prediction model  110  can predict a laser emitter temperature from an input current. 
     The compensation and control component  108  can receive the desired optical power  106  for the laser beam  104 . The compensation and control component  108  can utilize the predicted laser emitter temperature to compute a compensated electrical current  120  for driving the laser  102 . The computed compensated electrical current can be specific to the predicted laser emitter temperature and thus can cause the laser beam  104  to have an actual optical power that closely matches the desired optical power  106  (e.g., small delta). 
     Stated another way, the temperature of the laser emitter greatly affects the optical efficiency of the laser (e.g., the percentage of electrical power input that is converted to optical power). Knowing the laser emitter temperature would allow for temperature compensation. However, it is difficult to accurately measure the temperature of the laser emitter, especially during rapid temperature change. The laser emitter temperature prediction model  110  can predict the laser emitter temperature based upon more readily sensed laser properties  116 , sensed laser beam properties  118 , knowledge of the input power history, and/or understanding of the thermal impedance of the laser. (Thermal impedance can reflect thermal resistance and/or thermal capacitance of the laser over time). The compensation and control component can compute the compensated electrical current  120  for the desired optical power  106  for the predicted laser emitter temperature. This technique provides a close match between the desired optical power  106  and the actual optical power of the laser beam  104 . 
       FIG. 2  shows another example system  100 A that includes a laser  102 A. In this case, laser  102 A can include a case  200 , a laser emitter  202  (e.g., emitter), one or more supporting structures  204 , and/or a heat sink  206 . System  100 A can also include a display device  208 , compensation and control component  108 A and laser emitter temperature prediction model  110 A. Display device  208  can also include a scanner  210  and a display  212  which can display an image  214  (e.g., raster image). 
     The image  214  can be made up of pixels  216 . Note that the image  214  can be made up of many pixels  216 , even millions of pixels  216 . Only two pixels  216 ( 1 ) and  216 ( 2 ) are designated to avoid clutter on the drawing page. Image content  217  can define the desired optical power  106 A for each pixel. In operation, the laser  102 A can generate the laser beam  104 A for a duration of time (e.g., pixel time) and the scanner  210  can direct the laser beam at an individual pixel  216 ( 1 ) for the pixel time. The laser  102 A can generate the laser beam  104 A for the next pixel time and the scanner  210  can direct the laser beam at the next pixel  216 ( 2 ). In many applications, the intervals are very short, such as 5 nanoseconds (ns), for example. 
     Through continued driving of the laser  102 A for multiple pixel times (e.g., in the form of pulses or continuous waves), successive pixels  216  can be illuminated by the scanner  210 . In this example, the pixels  216  can be illuminated along a scan line  218 . For instance, the laser beam  104 A can be used to successively illuminate pixels  216  along scan line  218 ( 1 ), from left to right across the illustrated display  212 . At the end of scan line  218 ( 1 ), toward the right-hand side of the drawing page, the laser beam  104 A can be directed down to the next scan line  218 ( 2 ) and continue illuminating pixels  216  from right to left along scan line  218 ( 2 ). In this manner, scanning of the laser beam  104 A can continue until the image  214  covers the area of the display  212 . One-time coverage of the area of the display  212  can be termed a frame  220 . 
     Image content  217  can define the desired optical power  106 A for each pixel time that the laser  102 A generates the laser beam  104 A. Since there can be millions of pixels in the frame and the individual pixels can be powered at different optical powers to create the image  214  the temperature of the laser emitter  202  can change greatly during the course of creating the frame. As mentioned above, due to the physical nature of the laser emitter, it is not practical to directly measure the emitter temperature of the laser emitter  202  itself, especially at a rate that is fast enough and accurate enough for emitter temperature data to be used to compensate pixel by pixel. (Recall that pixel times can be very short, such as 5 nanoseconds). Further, utilizing a single laser emitter temperature for all pixels in the frame does not allow accurate electrical current compensation for the individual pixels and can result in large deltas between the desired optical power and the actual optical power for the pixels. 
     The laser emitter temperature prediction model  110 A can offer an effective real-time solution that can predict laser emitter temperatures as fast as a pixel-by-pixel basis (e.g., pixel time-by-pixel time basis). In some implementations, the laser emitter temperature prediction model can predict temperature behavior at a particular point on the laser  102 A, such as the laser emitter  202  as a function of time and power. In some such examples, the laser emitter temperature prediction model can utilize sensed laser properties (e.g., laser case temperature),  116 A and/or sensed laser beam properties (e.g., wavelength and/or optical power)  118 A as input to predict the laser emitter temperature. Stated another way, the laser emitter temperature prediction model can model the thermal characteristics and the internal temperature of the laser over time. 
     In one such example, a temperature of heat sink  206  can be sensed by laser sensor  112 A and included in sensed laser properties  116 A. In some cases, the current temperature of the heat sink  206  can be considered as the case temperature of the laser. The laser emitter temperature prediction model  110 A can utilize the case temperature and/or the image properties (e.g., optical power compared to thermal power) to predict the temperature of the laser emitter  202 . The laser emitter temperature prediction model  110 A can predict the laser emitter temperature from the case temperature of the heat sink  206  by knowing or estimating thermal impedances between the laser emitter  202  and the heat sink  206 . In this case, the thermal impedances can describe heat transfer as heat from the laser emitter  202  (and/or other electronic components of the laser) is conducted through the laser emitter  202  itself, across materials and interfaces of the laser, such as through a first interface INT 1  to first supporting structure  204 ( 1 ), through the first supporting structure  204 ( 1 ), across second interface INT 2  to second supporting structure  204 ( 2 ), through the second supporting structure  204 ( 2 ), and across third interface INT 3 , to the heat sink  206 . 
     The number, size, and/or shape of supporting structures  204  and associated interfaces shown in  FIG. 2  is not meant to be limiting. A wide variation in the internal structure of the laser  102 A is contemplated. Differences in the internal structure can affect an overall thermal impedance between the laser emitter  202  and a point of temperature measurement, such as the heat sink  206  in this case. For instance, the overall laser system thermal impedance can include the effects of heat energy flowing to and/or from nearby electronics through multiple pathways. Stated another way, the overall thermal impedance can include any component or element, electronic or not, that has a significant thermal relationship with the laser emitter. The laser emitter temperature prediction model  110 A can utilize the overall thermal impedance of the laser and the case temperature as input to predict the laser emitter temperature. This aspect is described in more detail below relative to  FIGS. 5-6 . An additional example of an internal laser structure and its overall thermal impedance is provided below relative to  FIG. 3  and system  1008 . 
     The predicted laser emitter temperature produced by laser emitter temperature prediction model  110 A can be used to compute a compensated electrical current  120 A at a pixel by pixel rate if desired and thus any remaining image artifacts can be reduced and/or eliminated. For instance, the compensation and control component  108 A can receive the desired optical power  106 A for a pixel. The compensation and control component  108 A can receive the predicted laser emitter temperature of the laser emitter  202  for the pixel from the laser emitter temperature prediction model  110 A. The compensation and control component  108 A can utilize the predicted laser emitter temperature to compute the compensated electrical current  120 A to drive the laser  102 A for the pixel time that illuminates the pixel. The compensated electrical current  120 A can cause the actual laser beam optical power to (approximately) match the desired optical power  106 A. 
       FIG. 3  shows another system  100 B that employs multiple laser emitters  202 B per laser  102 B. As illustrated in  FIG. 3 , laser  102 B is otherwise similar to laser  102 A of  FIG. 2  and can include a case  200 B, multiple laser emitters  202 B (in this case two), supporting structures  204 B, and a heat sink  206 B. Laser beams  104 B can be produced by the one or more laser emitters  202 B of laser  102 B. System  100 B can include display device  208 B, one or more scanners  210 B, compensation and control component  108 B, and laser emitter temperature prediction model  110 B. Display device  208 B can include a display  212 B which can display an image  214 B. The image  214 B can be made up of pixels  216 B. Only two pixels  216 B( 1 ) and  216 B( 2 ) are designated to avoid clutter on the drawing page. 
     In this example, two laser emitters  202 B( 1 ) and  202 B( 2 ) are shown, producing two laser beams  104 B. By generating an additional laser beam  104 B, the two laser emitters  202 B can increase the number of scan lines  218 B in a single frame  220 B. In some cases, the two laser emitters  202 B can provide double the density of scan lines  218 B, which can produce better image quality. However, using more than one laser emitter  202 B can also dramatically increase the complexity of laser emitter temperature prediction. For example, more than one laser emitter  202 B can introduce additional variables into the laser emitter temperature prediction problem. For instance, the laser emitters  202 B can heat each other, through interface INT 4 . The laser emitters  202 B may also be powered differently over time, such that the amount of additional heat the laser emitters  202 B contribute to each other changes over time. The internal structure can affect the overall thermal impedance between the laser emitters  202 B and the point of temperature measurement, such as the heat sink  206 B. The laser emitter temperature prediction model can reflect this overall thermal impedance to predict the laser emitter temperature. This aspect is described in more detail below relative to  FIGS. 5 and 6 . 
     Note that example laser configurations and associated thermal impedances are described above relative to  FIGS. 1-3 . The overall thermal impedance for a given laser configuration can include any number of laser dies, laser emitters, and/or other electronic components (e.g., heat generating components) associated with the laser. Laser dies (not specifically designated) can include one or more laser emitters per laser die. The thermal impedance can reflect the effects of individual heat generating elements, such as the laser emitters, in isolation and on each other (e.g., effect of a laser emitter on adjacent laser emitter and vice-versa). The details described below relative to  FIGS. 5 and 6  can be applied to model thermal impedances of any components or elements that have a thermal relationship with a given laser configuration. 
     Continuing with the discussion relative to  FIG. 3 , the compensation and control component  108 B can receive the desired optical power  106 B and utilize the predicted laser emitter temperature to generate compensated electrical current  120 B accordingly.  FIGS. 4A-4D  offer additional details about the relationships between emitter temperature, electrical current supplied to the laser emitter, and light emitted from the laser emitter. 
       FIGS. 4A and 4B  include a graph  400  with example light (e.g., optical power) electrical current (i) curves (LICs)  402 . The light-current curves  402  can represent individual light-current-temperature relationships for particular laser emitter temperatures, for example. Graph  400  includes electrical current on the x-axis and light on the y-axis. The light-current curves  402  can relate to particular laser emitter temperatures. In this case, individual light-current curves  402 ( 1 ),  402 ( 2 ), and  402 ( 3 ) are shown for 25° C., 45° C., and 65° C., respectively. Graph  400  is not necessarily drawn to scale. Graph  400  is for illustration purposes and is not meant to be limiting. 
     In  FIG. 4A , a vertical dashed line is drawn on graph  400  at an arbitrary electrical current value, C 1  (current can also be represented as ‘I’). Horizontal dashed lines are drawn where the electrical current value C 1  intersects light-current curves  402 ( 1 ) and  402 ( 3 ), corresponding to optical power values L 1  and L 2 . As shown in  FIG. 4A , a laser emitter temperature increase from 25° C. to 65° C. can cause a significant decrease in resultant optical power for the same electrical current input to the laser emitter, from L 1  down to L 2 . Therefore, laser emitter temperature can significantly affect laser emitter efficiency.  FIG. 4A  also includes a vertical dashed line at electrical current value C 2 . In an instance where L 1  is a desired optical power value for a particular pixel of a displayed image, and a laser emitter temperature of the laser is 65° C., the laser emitter would have to be driven with an electrical current value of C 2  in order to produce the desired optical power value. In this instance, driving the laser with C 1  (which corresponded to 25° C.) would not maintain a desired optical power. The compensation and control component  108  can utilize the LI curves to compensate or adjust electrical current to reflect the predicted laser emitter temperature. However, it is unlikely that an LI curve is available for the predicted emitter temperature for an individual interval (e.g., the predicted emitter temperature may not exactly match the temperature of any of the known LI curves). The discussion below relative to  FIG. 4B  explains how to determine an electrical current for a predicted emitter temperature that does not correspond to an available LI curve. 
       FIG. 4B  illustrates additional aspects of light-current (LI) curves  402 . The LI curves can reflect known values at specific temperatures (e.g., in this case, 25, 45, and 65 degrees). Values for other temperature can be interpolated from the known LI curves. On the graph  400 ( 1 ) shown in  FIG. 4B , at an optical power value of L 3 , light-current curve  402 ( 1 ) can be a distance D 1  from light-current curve  402 ( 3 ). Light-current curve  402 ( 2 ) can be a percentage P 1  of the distance D 1  from light-current curve  402 ( 1 ), and can be a percentage P 2  of the distance D 1  from light-current curve  402 ( 3 ). Similarly, at optical power value L 4 , light-current curve  402 ( 1 ) can be a distance D 2  from light-current curve  402 ( 3 ), light-current curve  402 ( 2 ) can be a percentage P 3  of the distance D 2  from light-current curve  402 ( 1 ), and light-current curve  402 ( 2 ) can be a percentage P 4  of the distance D 2  from light-current curve  402 ( 3 ). In some cases, although 45° C. is half-way between 25° C. and 65° C., the light-current curves corresponding to these laser emitter temperatures may not be evenly spaced. For example, as depicted in  FIG. 4B , percentage P 1  of distance D 1  is relatively less than percentage P 2  of distance D 1 . This is one example of a non-linear aspect that can be inherent to the light-current curves  402 . Another example can be differences between the percentages at different optical power values. In this example, percentage P 1  of distance D 1  can be different than percentage P 3  of distance D 2 . Stated another way, the location of light-current curve  402 ( 2 ) between light-current curve  402 ( 1 ) and light-current curve  402 ( 3 ) can change with optical power. An example of this relationship for a particular laser configuration is shown in  FIG. 4C . 
       FIG. 4C  shows a graphical representation of a temperature to index transfer function as graph  400 ( 2 ). This graph can function as a temperature to index LUT that reflects relationships between optical power or light (vertical axis) and temperature (horizontal axis) as mentioned above. 
       FIG. 4D  shows a graphical representation of a thermal or heating power versus current and temperature function as graph  400 ( 3 ). This graph can represent code to power relationships (e.g., the thermal power that must have been applied to the laser emitter given some combination of the compensated electrical current, the temperature information, and the optical output). Note that the example graphs of  FIGS. 4A-4D  can relate to one example laser configuration (e.g., one laser model). Similar graphs can be constructed for other laser configurations. In this implementation, the compensation and control component  108 A can solve the technical problems of maintaining desired optical power of the laser by utilizing the predicted laser emitter temperature provided by the laser emitter temperature prediction model. The compensation and control component  108 A can compute the compensated electrical current for the laser in a manner that reflects the sensitivity of laser efficiency to emitter temperature for a given optical power. This aspect is discussed in more detail below relative to  FIG. 5 . 
       FIG. 5  provides a schematic of components that can implement system  1006 , which was introduced relative to  FIG. 3 . Recall that in system  1006 , laser  1026  includes two laser emitters  202 B( 1 ) and  2026 ( 2 ). Consistent with  FIG. 3 , the compensation and control component  1086  in  FIG. 5  receives the desired optical powers  106 B( 1 ) and  106 B( 2 ) on the left side of the page. For each pixel, the compensation and control component  1086  ultimately computes a compensated electrical current  120 B( 1 ) and  120 B( 2 ) on the right side of the page. Because there are two laser emitters  202 B( 1 ) and  2026 ( 2 ), the compensation and control component  1086  produces two compensated electrical currents  1206  (e.g., compensated electrical current  120 B( 1 ) on the top of the page for laser emitter  202 B( 1 ) and compensated electrical current  120 B( 2 ) on the bottom of the page for laser emitter  2026 ( 2 )). Because there are two laser emitters  2026 , the circuitry is in large part duplicated so that the top half of the FIG. relates to laser emitter  202 B( 1 ) and the bottom half of the FIG. relates to laser emitter  2026 ( 2 ). The discussion that follows will emphasize the top half of the FIG. with the recognition that the bottom half is similar and that if additional laser emitters were employed then additional sets of circuitry could be employed, etc. Where possible, the top half of the FIG. that relates to laser emitter  202 B( 1 ) is referred to with a ‘1’ and the bottom half that relates to laser emitter  2026 ( 2 ) is referred to with a ‘2.’ 
     The compensated electrical current  120 B can be manifest as a digital code (code 1 ) that is fed to a digital to analog converter (DAC)  502  (e.g., DAC  502 ( 1 ) on the top of the page connected to laser emitter  202 B( 1 ) and code 2  to DAC  502 ( 2 ) on the bottom of the page connected to laser emitter  2026 ( 2 )). The DAC converts the digital code to an analog electrical current that is used to cause the laser emitter  202 B( 1 ) to emit the laser beam ( 1046 ( 1 ),  FIG. 3 ). 
     The remainder of the components relate to the compensation and control component  1086 . Starting on the left side of the page and vertically arranged, the compensation and control component can include power accumulators  504 , laser emitter temperature prediction models  110 B, adders  506 , code to power LUTS  508 , temperature to index LUTs  510 , LI LUTs  512 , and/or interpolators  514 . An LI LUT can be a look up table populated with data from a light to current curve (LIC) relating to a specific laser emitter temperature (in this example 25 degrees and 65 degrees) or other computing mechanism. LICs are explained above relative to  FIGS. 4A and 4B . While not specifically illustrated, a pixel clock can be employed to synchronize the function of various components. 
     For purposes of explanation, beginning at interpolator  514 ( 1 ), assume that the interpolator has generated the compensated electrical current  120 B (e.g., code 1 ), which is fed back to code to power LUT  508 ( 1 ) which optionally receives predicted laser emitter temperature (T(emitter 1 )) from adder  506 ( 1 ) (described below). Recall that the code produced by the interpolator  514 ( 1 ) commands an analog electrical current produced by the DAC  502 ( 1 ). The code to power LUT  508 ( 1 ) can infer the thermal power that must have been applied to the laser  1028  given some combination of the compensated electrical current, the temperature information, and the optical output power (which can also be estimated). An example graphical representation of such a code to power LUT  508 ( 1 ) is represented in graph  400 ( 3 ) of  FIG. 4D . 
     The thermal power value (e.g., power 1 ) determined by the code to power LUT  508 ( 1 ) can be fed back to the power accumulator  504 ( 1 ). (Note also that while the discussion is focusing on the top half of the FIG. relating to laser emitter  202 B( 1 ), the thermal power can be fed back in a cross-over manner indicated at  516 , so that the top half of the circuitry receives power information about the thermally related laser emitter shown in the bottom half (e.g., power 2  and vice-versa). The power accumulator  504 ( 1 ) can optionally accumulate values representing the thermal energy associated with multiple previous pixels prior to entering the laser emitter temperature prediction model  1108 . Accumulating the thermal energy reduces the complexity of the laser emitter temperature prediction model  1108  but also adds delay to the predicted temperature output (e.g., T(emitter 1 )). The power accumulator  504  is useful for long temperature time constants that might otherwise require increased complexity in the temperature prediction model  1108 . 
     The laser emitter temperature prediction model  110 B( 1 ) can predict a temperature of the laser emitter  202 B( 1 ) by modeling thermal characteristics of the laser  102 B as a model of time and thermal power. The thermal power can be the difference between the electrical power for the interval (and previous intervals) and the optical power emitted by the laser emitter for the interval (and previous intervals) (e.g., any electrical power that was not converted to optical power was converted to thermal power (e.g., heat)). This aspect is described in more detail below relative to  FIG. 6 . The temperature rise can be delivered to adder  506 . The adder also receives the temperature rise relating to laser emitter  202 B( 2 ) from laser emitter temperature prediction model  110 B( 2 ) and sensed laser properties  116 B (e.g., case temperature) from laser sensor  112 B. 
     In this case, the laser sensor  1128  can be manifest as a thermistor positioned on the laser&#39;s case and the sensed laser properties  1168  can be manifest as a case temperature of the laser  1028 . The adder  506 ( 1 ) can send the sum of this thermal data (e.g., T(emitter 1 )) to the temperature to index LUT  510 ( 1 ). Some implementations can provide additional refinement by supplying the thermal data (e.g., T(emitter 1 )) to the code to power LUT  508 ( 1 ) so that emitter temperature can be considered in the code to power function. Alternatively or additionally, the desired optical power 1  can be supplied to the temperature to index LUT  510 ( 1 ) to allow for further refinement in the computation. This aspect was described above relative to  FIG. 4C . 
     The desired optical power 1  is supplied to the LI LUTs  512 . Recall that any plural number of LI LUTs can be employed. In one case, light-current curve LUTs  512 ( 1 ) and  512 ( 3 ) can correspond to a 25° C. light-current curve, while LI LUTs  512 ( 2 ) and  512 ( 4 ) can correspond to a 65° C. light-current curve, for example. In some cases, LI LUTs  512 ( 1 ) and  512 ( 3 ) can actually be the same LI LUT accessed by both interpolators  514 ( 1 ) and  514 ( 2 ), for example. 
     Output from the LI LUTS  512  and the temperature to index LUTs  510  can be provided to or accessed by the interpolator  514 . As mentioned above, it is possible that the predicted laser emitter temperature matches one of the temperatures of the LI LUTs  512 . For instance, the predicted laser emitter temperature could be 65 degrees and one of the LI LUTs could relate light (e.g., optical power) to electrical current at 65 degrees. Thus, interpolator  514  can compute the compensated electrical current directly from the LI LUT. More likely though, the predicted laser temperature will not be an exact match. In such a case, the interpolator can interpolate or extrapolate from the available values of the LI LUTs to the predicted laser emitter temperature. Recall from the discussion above this tends to not be a linear function. The temperature to index LUT  510 ( 1 ) can provide the relationship between the available values. For instance, the predicted laser emitter temperature may be 45 degrees. The temperature to index LUT  510 ( 1 ) could indicate that percentage-wise, the values of the 45 degree LIC curve are 30% from 25 degrees and 70% from 65 degrees. Thus, the interpolator  514  can compute the compensated electrical current as 30% of (value of LI 65 °−value of LI 25 °)+value of LI 25 ° by interpolating between the values of the two LI LUTs. 
     In still another scenario, the predicted laser emitter temperature may lie outside the available LI LUTs  512 . For instance, continuing with the above example, the predicted laser emitter temperature may be 75 degrees and the LI LUTs can relate to 25 degrees and 65 degrees. The temperature to index LUT  510  can provide percentage-wise increases beyond the available LI LUTs. For instance, the relationships of the temperature to index LUT may indicate that there will be an additional 61% current jump from 65 degrees to 75 degrees. This would be reflected as a value of 161% on the Index axis of graph  400 ( 2 ) ( FIG. 4C ) at the 75-degree point on the temperature axis. As such, the interpolator  514  can extrapolate the compensated electrical current for the desired optical power as 161% of (value of LI65°−value of LI25°+value of LI25°. In each of the above scenarios, the interpolator  514  can send compensated electrical current information  120 B (code 1 ) to digital-to-analog converter (DAC)  502 , which can drive the laser  102 B (e.g., laser emitter  202 B( 1 )). 
       FIG. 6  provides additional detail relating to laser emitter temperature prediction models  110 B( 1 ),  110 B( 2 ),  110 B( 3 ),  110 B( 4 ) shown in  FIG. 5 . Among other configurations, each of those laser emitter temperature prediction models  1108  can be implemented as a multitude of recursive (sometimes called infinite impulse response, ‘IIR’) filter sub-models  600 ( 1 ) 1 ,  600 ( 1 ) 2 , . . .  600 ( 1 )N, each of which receives as input the thermal power (e.g. power 1 ,  FIG. 5 ) applied to the laser and predicts a portion of the emitter temperature rise above the laser case temperature as a function of time. The laser emitter temperature prediction models  1106  can run continuously so the temperature prediction is always up-to-date. Recall from  FIG. 5  that in this implementation the laser emitter prediction model  1106 ( 1 ) receives the power 1  input from the code to power LUT  508  and sends its output to adder  506 ( 1 ) as Rise 1+1. Also, the power accumulator  504 ( 1 ) is discussed above relative to  FIG. 5 , but is not shown here. These aspects are not revisited here for sake of brevity. 
     In this case, the laser emitter temperature prediction model  110 B( 1 ) in  FIG. 5  can employ multiple recursive filter elements referred to as laser emitter temperature prediction sub-models  600 ( 1 ) 1 - 600 ( 1 )N in  FIG. 6  to model the effects of thermal impedances, such as a thermal interface or material of the laser. Examples of materials and interfaces are discussed and designated relative to  FIGS. 2 and 3 . Stated another way, because the laser can include multiple materials and interfaces that contribute to the overall thermal impedance, multiple laser emitter temperature prediction sub-models may be employed. As each output of these laser emitter temperature prediction sub-models  600  can predict a portion of the total temperature rise, all of the outputs can be added together with appropriate weighting factors to predict the total temperature rise (e.g., Rise 1+1). 
     Continuing with  FIG. 6 , in this example individual laser emitter temperature prediction sub-models (e.g.,  600 ( 1 ) 1 , etc.) can include multiplication functions F 1  and F 3 , an addition function F 2 , coefficients COEFF 1  and COEFF 2 , and a temperature register  604 . Together, as is known to those skilled in the art, they can be used to create a recursive, single-pole, low-pass filter that has a decaying exponential time response. The decay time of each filter can be chosen to mimic one of the thermal time constants of the laser thermal impedance. As described above, the thermal impedances in systems  100 A and  100 B can include many thermal time constants and each has an impact on the overall temperature versus power relationship in varying proportions. In the example shown in  FIG. 6 , the proportional contributions of up to “N” sub-models&#39; time constants can be matched to the individual time constant contributions making up the thermal impedance of an actual laser system (e.g.,  100 A) by using function blocks F 5 , F 6 , and F 7  to multiply the output of each sub-model by weighting factors W T1 , W T2 , and W TN  before adding them all together using function F 4  (i.e., Adder  606 ( 1 )). 
     Those skilled in the art know that other arrangements of multiplication functions, addition functions, coefficients, and/or a temperature register can be used to create recursive, single-pole, low-pass filters that have the same decaying exponential time responses. Such alternate arrangements may utilize different numbers of multiplication and addition functions as well as different numbers of coefficients. In other arrangements, the weighting factors can be applied at the inputs to the laser emitter temperature prediction sub-models  600  or incorporated into the coefficient values. In yet other arrangements, the multiple single-pole filters could be replaced by one or more multi-pole filters. The particular functions shown in  FIG. 6  are not meant to be limiting. 
     In this example, for each filter comprising a specific laser emitter temperature prediction sub-model  600 , the new output is determined by combining a new input value (e.g., power 1 ) and the previous filter output value with weighting factors COEFF 1  and COEFF 2  determining how much each contributes to the new output value. Temperature register  604  retains the immediately previous output value to allow this computation. Looking back in time, the previous output value was also a weighted combination of its input and even earlier output values, so the sub-model output reflects the complete history of its input and output values. This means that the output value of any individual filter will follow the input, but only slowly, since the “inertia” of the filter&#39;s previous output values must be “overcome” by new inputs. 
     When multiple filter (i.e., laser emitter temperature prediction sub-model) outputs are summed together, the overall response will remain slow though any individual filter may respond faster or slower than the others in the combination. This type of behavior matches the general thermal response of laser systems  100 A and  100 B to any thermal power inputs. The specific thermal behavior of laser systems  100 A and  1008  can be matched to a desired level of accuracy by choosing appropriate time constants for the filters (e.g., laser emitter temperature prediction sub-models  600 ( 1 ) 1  to  600 ( 1 )N relating to laser emitter temperature prediction model  110 B( 1 ) and similar laser emitter temperature prediction sub-models (not shown) relating to the other laser emitter temperature prediction models) and choosing appropriate weighting factors (W T1 , W T2 , . . . W TN ) specific to each filter. Summing all the weighted outputs in adder  606 ( 1 ) generates the overall thermal prediction model value (the output value of  1106 ( 1 ),  1106 ( 2 ), etc.). 
     Stated another way, the temperature rise of the laser emitter above the laser case temperature may change gradually when driven with a new level of thermal power. The laser emitter may eventually reach a thermal equilibrium for a constant thermal power level, but it is more likely that the laser emitter will be driven with a newer thermal power level yet again before thermal equilibrium is reached. In similar fashion, the emitter temperature rise predicted by each laser emitter thermal prediction model  1106  will depend upon the starting laser emitter temperature and will change as the applied thermal power changes. Eventually, the laser emitter temperature prediction model will also reach an equilibrium value for a constant thermal power level but if a new thermal power level appears at the input to the laser emitter temperature prediction model, it will predict a new temperature. In this way, the laser emitter temperature prediction model is constantly updating its temperature rise prediction based on applied thermal power. 
     The output of laser emitter temperature prediction model  1106 ( 1 ) (i.e., output of adder  606 ( 1 )) can be sent to adder  506 ( 1 ). Note that  FIG. 6  elaborates on laser emitter temperature prediction model  110 B( 1 ) but is applicable to the other laser emitter temperature prediction models  110 B( 2 )- 110 B( 4 ). Laser emitter temperature prediction model  110 B( 1 ) captures the thermal effect of thermal power applied to laser emitter  202 B( 1 ) on itself ( FIG. 5 ). Laser emitter temperature prediction model  110 B( 2 ) captures the thermal effect of thermal power applied to laser emitter  202 B( 2 ) on laser emitter  202 B( 1 ). As discussed relative to  FIG. 5 , adder  506 ( 1 ) receives input values from laser emitter temperature prediction models  110 B( 1 ) and  110 B( 2 ) and the laser case temperature and outputs the temperature (i.e., T(emitter 1 )) of laser emitter  202 B( 1 ). 
     Looking at  FIGS. 5 and 6  collectively, some of the implementations described above can be distinguished from traditional systems where the light data is input to a single LI LUT that outputs a DAC code to drive the laser current to produce the desired optical power. In such a traditional system, the LI LUT data are collected as a part of system calibration. The measured light is compared to the expected light for each frame and the LI LUT is repopulated. A simple algorithm is used to stretch and scale the LI LUT data as the feedback mechanism to align the measured light with the expected light for the next frame. This approach does not compensate for the wild temperature fluctuations that can occur within a frame time and often results in large deltas between the actual or emitted optical power and the desired optical power. 
     The present concepts can employ a second (or more) LI LUT ( 512 ,  FIG. 5 ) containing light to current data collected at different temperatures (e.g. 65 and 25 degrees). The LI LUTs  512  feed interpolator  514  which can interpolate between the two LI LUTs according to an index value provided by temperature to index LUT  510 . (As a result, no stretching or scaling or repopulation of either LI LUTs is required.) This multiple LI LUT and interpolator arrangement can form a virtual LUT (e.g., two or more LUTs for specific temperatures and the interpolator that can identify the compensated electrical current for any desired optical output as a function of any temperature). The interpolator feeds the laser DAC  502  as described above. The index value can be a simple function of the predicted laser emitter temperature or it could be a more complicated function of predicted laser emitter temperature as defined by the Temp-to-Index LUT  510 . Temperature prediction is based on the laser emitter temperature prediction model of the laser, which can be implemented by the compensation and control component  108 . 
     In some implementations, the laser emitter temperature prediction models can be based on one or more infinite impulse response (IIR) low pass filters (e.g., laser emitter temperature prediction sub-models) that accept a representation of laser power as its input, apply a system-dependent gain to this laser power, and output a value representing temperature rise. This temperature rise can be added to the known case temperature to predict a laser emitter temperature for any instant in time regardless of how dynamic the temperature rise is. The case temperature could be provided by a simple thermistor since this temperature tends to change slowly. In another implementation, the case temperature could be inferred by use of an integration feedback system in which measured light is compared to expected light. When the measured light is less than expected, the inferred case temperature can be increased—and vice versa. 
     Several implementations are contemplated including alternatives for determining case temperature to those mentioned above. Various laser emitter temperature prediction models that model thermal characteristics of the laser can be employed. Some of these implementations employ IIR filters. A potentially important point for some IIR implementations is that the emitter temperature prediction IIR filter may include several IIR filter stages, each representing the various thermal impedances that may exist between the laser emitter and the laser case. Also, the virtual LI LUT may be comprised of more than 2 physical LUTs (e.g., 3 or 4). The interpolator may extrapolate for temperatures outside the range covered by the physical LUTs. The temperature-to-index LUT may benefit from including optical power as an input to enhance accuracy and/or to provide feedback to check the accuracy of the compensation and control component. 
       FIG. 7  illustrates an example system  100 C that shows various device implementations. Devices  700  can be similar to display devices  208  and/or  208 B, described above relative to  FIGS. 2 and 3 . In this case, three device implementations are illustrated. Device  700 ( 1 ) can operate cooperatively with device  700 ( 2 ). Device  700 ( 1 ) can be manifest as a display device for a personal computer, a television, or a projection display device, for example. Device  700 ( 3 ) is manifest as a head-mounted display device. Individual devices can include a display  702 , which can be similar to display  212  and/or  212 B. Devices  700  can communicate over one or more networks, such as network  704 . While specific device examples are illustrated for purposes of explanation, devices can be manifest in any of a myriad of ever-evolving or yet to be developed types of devices. 
     Individual devices  700  can be manifest as one of two illustrated configurations  706 ( 1 ) and  706 ( 2 ), among others. Briefly, configuration  706 ( 1 ) represents an operating system centric configuration and configuration  706 ( 2 ) represents a system on a chip configuration. Configuration  706 ( 1 ) is organized into one or more applications  708 , operating system  710 , and hardware  712 . Configuration  706 ( 2 ) is organized into shared resources  714 , dedicated resources  716 , and an interface  718  there between. 
     In either configuration, the devices  700  can include a processor  720 , storage  722 , a compensation and control component  108 C, and/or a laser emitter temperature prediction model  110 C. Individual devices can alternatively or additionally include other elements, which are not illustrated or discussed here for sake of brevity. 
     Devices  700 ( 1 ) and  700 ( 2 ) can be thought of as operating cooperatively to perform the present concepts. For example, device  700 ( 2 ) may include an instance of processor  720 , storage  722 , compensation and control component  108 C, and/or a laser emitter temperature prediction model  110 C. In this example, the device  700 ( 2 ) can receive sensed laser properties and/or sensed laser beam properties from device  700 ( 1 ), and send a compensated electrical current to device  700 ( 1 ). In contrast, devices  700 ( 1 ) and/or  700 ( 3 ) may be self-contained devices that include both an instance of the display  702 , processor  720 , storage  722 , compensation and control component  108 C, and laser emitter temperature prediction model  110 C. 
     In some implementations, a device such as device  700 ( 3 ) could include a SoC configuration, such as an application specific integrated circuit (ASIC) that includes compensation and control component  108 C and laser emitter temperature prediction model  110 C. Other device implementations, such as head-mounted display device  700 ( 3 ) can include a processor, such as CPU and/or GPU, that renders frames and can also execute compensation and control component  108 C and laser emitter temperature prediction model  110 C, on the same processor or on another processor. 
     From one perspective, any of devices  700  can be thought of as computers. The term “device,” “computer,” or “computing device” as used herein can mean any type of device that has some amount of processing capability and/or storage capability. Processing capability can be provided by one or more processors that can execute data in the form of computer-readable instructions to provide a functionality. Data, such as computer-readable instructions and/or user-related data, can be stored on storage, such as storage that can be internal or external to the computer. The storage can include any one or more of volatile or non-volatile memory, hard drives, flash storage devices, optical storage devices (e.g., CDs, DVDs etc.), and/or remote storage (e.g., cloud-based storage), among others. As used herein, the term “computer-readable media” can include signals. In contrast, the term “computer-readable storage media” excludes signals. Computer-readable storage media includes “computer-readable storage devices.” Examples of computer-readable storage devices include volatile storage media, such as RAM, and non-volatile storage media, such as hard drives, optical discs, and/or flash memory, among others. 
     As mentioned above, configuration  706 ( 2 ) can be thought of as a system on a chip (SOC) type design. In such a case, functionality provided by the device  700  can be integrated on a single SOC or multiple coupled SOCs. One or more processors can be configured to coordinate with shared resources  714 , such as memory, storage, etc., and/or one or more dedicated resources  716 , such as hardware blocks configured to perform certain specific functionality. Thus, the term “processor” as used herein can also refer to central processing units (CPUs), graphical processing units (GPUs), field programmable gate arrays (FPGAs), controllers, microcontrollers, processor cores, or other types of processing devices. The compensation and control component  108 C and laser emitter temperature prediction model  110 C can be manifest as dedicated resources  716  and/or as shared resources  714 . 
     Generally, any of the functions described herein can be implemented using software, firmware, hardware (e.g., fixed-logic circuitry), or a combination of these implementations. The term “component” as used herein generally represents software, firmware, hardware, whole devices or networks, or a combination thereof. In the case of a software implementation, for instance, these may represent program code that performs specified tasks when executed on a processor (e.g., CPU or CPUs). The program code can be stored in one or more computer-readable memory devices, such as computer-readable storage media. The features and techniques of the component are platform-independent, meaning that they may be implemented on a variety of commercial computing platforms having a variety of processing configurations. 
       FIG. 8  shows an example laser control method  800 . 
     In this case, block  802  can receive a predicted laser emitter temperature of a laser emitter. 
     Block  804  can obtain a desired optical power for an interval (e.g., pixel time). 
     Block  806  can compute a compensated electrical current for the interval utilizing multiple light to current look up tables. Individual light to current look up tables can relate to specific laser emitter temperatures. 
       FIG. 9  shows an example laser control method  900 . 
     In this case, block  902  can predict a temperature of a laser emitter from a sum of heat transfer across elements and interfaces of a laser containing the laser emitter. The predicted temperature of the laser emitter can be accurate for a laser that employs a single laser emitter and/or a laser that employs multiple laser emitters. In configurations with multiple laser emitters, the prediction can factor the thermal power from each of the laser emitters, since they tend to heat each other. Thus, a laser emitter predicted temperature would likely be incorrect if it did not consider thermal gain from the other laser emitters. 
     Block  904  can obtain a desired optical power for a pixel time that the laser emitter is driven. 
     Block  906  can compute a compensated electrical current to drive the laser emitter for the pixel time by interpolating between light and current values for known laser emitter temperatures. 
     Block  908  can cause the laser emitter to be driven with the compensated electrical current such that an actual optical output of the laser emitter matches the desired optical output for the pixel time. 
     Various examples are described above. Additional examples are described below. One example includes a system comprising a laser that comprises a laser emitter configured to generate a laser beam, a sensor configured to sense a property of the laser, a laser emitter temperature prediction model that is configured to predict a temperature of the laser emitter from the sensed property of the laser, and a compensation and control component configured to receive a desired optical power and to compute a compensated electrical current to drive the laser based upon the predicted laser emitter temperature, the compensated electrical current computed for the predicted laser emitter temperature to cause the laser emitter to generate the laser beam having an actual optical power that matches the desired optical power. 
     Another example can include any of the above and/or below examples where the sensor is a thermal sensor that senses temperatures of a case of the laser. 
     Another example can include any of the above and/or below examples where the laser emitter temperature prediction model models thermal impedance of the laser from the laser emitter to the case. 
     Another example can include any of the above and/or below examples where the thermal impedance reflects elements that have a thermal relationship with the laser emitter. 
     Another example can include any of the above and/or below examples where the elements include another laser emitter. 
     Another example can include any of the above and/or below examples where the laser emitter temperature prediction model can model thermal characteristics and internal temperature of the laser over time. 
     Another example can include any of the above and/or below examples where the laser emitter temperature prediction model can model a particular point on the laser as a function of time and power. 
     Another example can include any of the above and/or below examples where the laser emitter temperature prediction model comprises multiple laser emitter temperature prediction models. 
     Another example can include any of the above and/or below examples where individual laser emitter temperature prediction models relate to individual elements of the laser. 
     Another example can include any of the above and/or below examples where the output of the individual laser emitter temperature prediction models are added together to create an overall thermal value of the laser. 
     Another example can include any of the above and/or below examples where the laser emitter comprises multiple laser emitters. 
     Another example can include any of the above and/or below examples where the laser emitter temperature prediction model considers thermal effects of individual laser emitters on one another. 
     Another example can include any of the above and/or below examples where the compensation and control component comprises multiple light to current look up tables (LI LUT) for individual laser emitter temperatures. 
     Another example can include any of the above and/or below examples where the compensation and control component comprises an interpolator that can interpolate or extrapolate from the individual laser emitter temperatures to the predicted laser emitter temperature. 
     Another example can include any of the above and/or below examples where the compensation and control component comprises a temperature to index look up table that shows the change in drive level needed as a percentage between or beyond the levels needed at the individual laser emitter temperatures. 
     Another example can include any of the above and/or below examples where the compensation and control component utilizes the percentage change to compute the compensated electrical current from the electrical current values of the individual laser emitter temperatures. 
     Another example includes a system comprising a laser comprising a laser emitter configured to generate a laser beam for intervals of time and a compensation and control component configured to: receive a predicted laser emitter temperature of the laser emitter, receive a desired optical power for an interval, and compute a compensated electrical current for the interval utilizing multiple light to current look up tables, wherein individual light to current look up tables relate to specific laser emitter temperatures. 
     Another example can include any of the above and/or below examples where the compensation and control component is configured to perform an interpolation or extrapolation from the specific laser emitter temperatures of the light to current look up tables to the predicted laser emitter temperature. 
     Another example can include any of the above and/or below examples where the interpolation or extrapolation is non-linear. 
     Another example includes a computer-implemented method comprising predicting a temperature of a laser emitter from a sum of time-dependent heat transfers though materials and interfaces of a laser containing the laser emitter, obtaining a desired optical power for a pixel time that the laser emitter is driven, computing a compensated electrical current to drive the laser emitter for the pixel time by interpolating between light and current values for known laser emitter temperatures, and causing the laser emitter to be driven with the compensated electrical current such that an actual optical output of the laser emitter matches the desired optical output for the pixel time.