Laser control

Abstract

The present description relates to laser control. An example can include a laser having a laser emitter configured to generate a laser beam for a time interval (e.g., a pixel time). The laser can have a compensation and control component configured to receive a predicted laser emitter temperature of the laser emitter, obtain a desired optical power for the time interval, and calculate a compensation current for the time interval using a plurality of light-to-current lookup tables. Individual light-to-current lookup tables can be associated with a specific laser emitter temperature.

Description

Background Art

[0001] Lasers are driven by electric current so that more current equates to more light. However, electric current also causes the laser to self-heat. As the laser heats up, the current required to produce a given amount of light increases. If the emitter temperature of the laser is known, it should be possible to accurately determine the current required for the desired amount of light. Accurate measurement of the emitter temperature of a laser is extremely difficult and takes time. Laser temperature tends to change so rapidly that it is impractical to measure the emitter temperature, or when the emitter temperature is measured, the value is out of date (e.g., inaccurate). The present concept provides methods for predicting laser emitter temperature in near real time (e.g., quickly enough), and methods for determining the current required to obtain the desired amount of light. 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

[0002] The accompanying drawings illustrate implementations of the concepts conveyed in this document. The features of the illustrated implementations may be more readily understood by reference to the following description in conjunction with the accompanying drawings. Wherever possible, the same reference numerals are used in the various drawings to indicate similar elements. In some cases, parentheses are used after the reference numerals to distinguish similar elements. Using reference numerals without associated parentheses is a common method for the element. In addition, the leftmost digit of each reference numeral conveys the figure and associated discussion in which the reference numeral is first introduced.

[0003] Figures 1 to 3 , Figure 5 as well as Figure 7 An example system according to some implementations of the present laser control concepts is shown.

[0004] Figure 4A and Figure 4B Example current-light-temperature relationships according to some implementations of the present laser control concepts are shown.

[0005] Figure 4C Example temperature-optical power relationships according to some implementations of the present laser control concepts are shown.

[0006] Figure 4D Example heating power versus current and temperature relationships according to some implementations of the present laser control concepts are shown.

[0007] Figure 6 Some implementations of the laser control concept are shown. Figure 5 Additional details of some of the elements shown.

[0008] Figure 8 and Fig. 9 An example laser control flow chart according to some implementations of the present laser control concepts is shown. DETAILED DESCRIPTION

[0009] The present description relates to controlling a laser that can be used to generate light (e.g., a laser beam). The laser may include a laser emitter that emits a laser beam. The laser may be driven using an electric current to emit optical power from the laser emitter. However, achieving the desired optical power output depends on the properties of the laser, particularly the temperature of the laser emitter. The temperature of the laser emitter may affect how efficiently the laser converts electrical power into optical power (e.g., the efficiency with which the laser converts electrical energy into optical energy depends on the laser emitter temperature). If the laser is driven by an electric current that is not adjusted to reflect the temperature of the laser emitter, the actual optical power of the laser beam may not match the desired optical power. However, accurately and quickly measuring the temperature of the laser emitter may be difficult or impossible, particularly when the temperature is changing rapidly.

[0010] The present concepts provide a laser emitter temperature prediction model that accurately predicts laser emitter temperature even when the laser emitter temperature is changing rapidly. The laser emitter temperature prediction model can use various sensed laser properties (e.g., laser housing temperature) as input to predict the laser emitter temperature. The predicted laser emitter temperature can be used to calculate an adjusted current or compensation current to drive the laser so that the laser produces an actual optical power that matches (or nearly matches) the desired optical power.

[0011] Guiding Figure 1 An example implementation of some of the present concepts is shown on system 100. System 100 may include a laser 102 that may generate a laser beam 104.

[0012] Traditionally, the desired optical power 106 would be mapped to a current, and this current would be used to drive the laser 102 to produce a laser beam 104 having an actual optical power. This is intended to match the actual optical power of the laser beam to the desired optical power 106. However, the laser emitter temperature can alter the laser efficiency produced by the mapped current and thus result in a large difference between the desired optical power and the actual optical power.

[0013] The system 100 may include a compensation and control component 108, and a laser emitter temperature prediction model 110. The system 100 may also include a laser sensor 112 and a laser beam sensor 114, among other sensors. The laser sensor 112 may sense properties of the laser 102 (e.g., sensed laser properties 116, such as laser housing temperature). The laser beam sensor 114 may sense properties of the laser beam 104 (e.g., sensed laser beam properties 118, such as optical power and / or wavelength). The sensed laser properties 116 and / or the sensed laser beam properties 118 may be used as inputs to the laser emitter temperature prediction model 110 and / or may 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 may predict the laser emitter temperature from the input current.

[0014] 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 use the predicted laser emitter temperature to calculate a compensation current 120 for driving the laser 102. The calculated compensation current can be specific to the predicted laser emitter temperature and can therefore cause the laser beam 104 to have an actual optical power that closely matches the desired optical power 106 (e.g., a small difference).

[0015] In other words, the temperature of the laser emitter significantly affects the optical efficiency of the laser (e.g., the percentage of electrical power input that is converted into optical power). Knowing the laser emitter temperature will allow temperature compensation. However, accurately measuring the temperature of the laser emitter is difficult, especially during rapid temperature changes. Based on more easily sensed laser properties 116, sensed laser beam properties 118, knowledge of the input power history, and / or an understanding of the thermal impedance of the laser, the laser emitter temperature prediction model 110 can predict the laser emitter temperature. (Thermal impedance can reflect the thermal resistance and / or thermal capacitance of the laser over time). The compensation and control component can calculate a compensation current 120 for the desired optical power 106 for the predicted laser emitter temperature. The present technology provides a close match between the desired optical power 106 and the actual optical power of the laser beam 104.

[0016] Figure 2Another example system 100A is shown that includes a laser 102A. In this case, the laser 102A can include a housing 200, a laser emitter 202 (e.g., an emitter), one or more support structures 204, and / or a heat sink 206. The system 100A can also include a display device 208, a compensation and control component 108A, and a laser emitter temperature prediction model 110A. The display device 208 can also include a scanner 210 and a display 212 that can display an image 214 (e.g., a raster image).

[0017] The image 214 may be composed of pixels 216. Note that the image 214 may be composed of many pixels 216, even millions of pixels 216. Only two pixels 216(1) and 216(2) are indicated to avoid clutter on the attached drawing page. The image content 217 may define the desired optical power 106A for each pixel. In operation, the laser 102A may generate a laser beam 104A for a duration (e.g., a pixel time), and the scanner 210 may direct the laser beam to an individual pixel 216(1) for the pixel time. The laser 102A may generate a laser beam 104A for the next pixel time, and the scanner 210 may direct the laser beam to the next pixel 216(2). In many applications, the time interval is very short, such as, for example, 5 nanoseconds (ns).

[0018] By continuously driving the laser 102A for a plurality of pixel times (e.g., in pulses or a continuous wave), successive pixels 216 may be illuminated by the scanner 210. In this example, the pixels 216 may be illuminated along a scan line 218. For example, the laser beam 104A may be used to continuously illuminate the pixels 216 along a scan line 218(1), crossing the illustrated display 212 from left to right. At the end of the scan line 218(1), toward the right hand side of the drawing page, the laser beam 104A may be directed downward to the next scan line 218(2) and continue to illuminate the pixels 216 from right to left along the scan line 218(2). In this manner, scanning of the laser beam 104A may continue until the image 214 covers an area of ​​the display 212. One coverage of an area of ​​the display 212 may be referred to as a frame 220.

[0019] The image content 217 may define the desired optical power 106A for each pixel time at which the laser 102A generates the laser beam 104A. Since there may be millions of pixels in a frame, and individual pixels may be energized at different optical powers to create the image 214, the temperature of the laser emitter 202 may vary significantly during the process of creating a frame. As mentioned above, due to the physical properties of laser emitters, it is not practical to directly measure the emitter temperature of the laser emitter 202 itself, especially at a rate fast enough and accurate enough for the emitter temperature data to be used for pixel-by-pixel compensation. (Recall that the pixel time may be very short, such as 5 nanoseconds). Furthermore, utilizing a single laser emitter temperature for all pixels in a frame does not allow for accurate current compensation for individual pixels, and may result in large differences between the desired optical power and the actual optical power for a pixel.

[0020] The laser emitter temperature prediction model 110A may provide an effective real-time solution that may predict laser emitter temperature as fast as on a pixel-by-pixel basis (e.g., on a pixel-by-pixel time basis). In some implementations, the laser emitter temperature prediction model may predict temperature behavior as a function of time and power at a specific point on the laser 102A, such as the laser emitter 202. In some such examples, the laser emitter temperature prediction model may utilize sensed laser properties (e.g., laser housing temperature) 116A and / or sensed laser beam properties (e.g., wavelength and / or optical power) 118A as inputs to predict laser emitter temperature. In other words, the laser emitter temperature prediction model may model the thermal characteristics and internal temperature of the laser over time.

[0021] In one such example, the temperature of the heat sink 206 may be sensed by the laser sensor 112A and included in the sensed laser attributes 116A. In some cases, the current temperature of the heat sink 206 may be considered the housing temperature of the laser. The laser emitter temperature prediction model 110A may utilize the housing temperature and / or image attributes (e.g., optical power compared to thermal power) to predict the temperature of the laser emitter 202. By knowing or estimating the thermal impedance between the laser emitter 202 and the heat sink 206, the laser emitter temperature prediction model 110A may predict the laser emitter temperature from the housing temperature of the heat sink 206. In this case, thermal impedance can describe heat transfer as follows: heat from the laser emitter 202 (and / or other electronic components of the laser) is conducted through the laser emitter 202 itself, through the materials and interfaces of the laser, such as: through the first interface INT1 to the first support structure 204(1), through the first support structure 204(1), through the second interface INT2 to the second support structure 204(2), through the second support structure 204(2), and through the third interface INT3 to the heat sink 206.

[0022] Figure 2 The number, size and / or shape of the support structures 204 shown, and the associated interfaces, are not intended to be limiting. A variety of variations in the internal structure of the laser 102A are contemplated. Differences in the internal structure can affect the overall thermal impedance between the laser emitter 202 and the point at which the temperature is measured (such as the heat sink 206 in this case). For example, the overall laser system thermal impedance can include the effects of thermal energy flowing to / from nearby electronic devices through multiple pathways. In other words, the overall thermal impedance can include any electronic or non-electronic components or elements that have a significant thermal relationship with the laser emitter. The laser emitter temperature prediction model 110A can use the overall thermal impedance of the laser and the housing temperature as inputs to predict the laser emitter temperature. The following is about Figures 5 and 6 This aspect is described in more detail below. Figure 3 and system 100B provide additional examples of internal laser structures and their overall thermal impedance.

[0023] If desired, the predicted laser emitter temperature generated by the laser emitter temperature prediction model 110A can be used to calculate the compensation current 120A at a pixel-by-pixel rate, and thus any remaining image artifacts can be reduced and / or eliminated. For example, the compensation and control component 108A can receive the desired optical power 106A for the pixel. The compensation and control component 108A can receive the predicted laser emitter temperature of the laser emitter 202 for the pixel from the laser emitter temperature prediction model 110A. The compensation and control component 108A can use the predicted laser emitter temperature to calculate the compensation current 120A that drives the laser 102A for the pixel time that illuminates the pixel. The compensation current 120A can make the actual laser beam optical power (approximately) match the desired optical power 106A.

[0024] Figure 3 Another system 100B is shown that uses multiple laser emitters 202B per laser 102B. Figure 3 As shown, laser 102B is otherwise similar to Figure 2 The system 100B may include a laser 102A and may include a housing 200B, a plurality of laser emitters 202B (in this case, two), a support structure 204B, and a heat sink 206B. The laser beam 104B may be generated by one or more laser emitters 202B of the laser 102B. The system 100B may include a display device 208B, one or more scanners 210B, a compensation and control component 108B, and a laser emitter temperature prediction model 110B. The display device 208B may include a display 212B that may display an image 214B. The image 214B may be composed of pixels 216B. Only two pixels 216B(1) and 216B(2) are indicated to avoid clutter on the drawing page.

[0025] Two laser emitters 202B(1) and 202B(2) are shown in this example, which generate two laser beams 104B. By generating additional laser beams 104B, the two laser emitters 202B can increase the number of scan lines 218B in a single frame 220B. In some cases, the two laser emitters 202B can provide double the density of scan lines 218B, which can produce better image quality. However, using more than one laser emitter 202B can also dramatically increase the complexity of laser emitter temperature prediction. For example, more than one laser emitter 202B can introduce additional variables to the laser emitter temperature prediction problem. For example, the laser emitters 202B can heat each other through the interface INT4. The laser emitters 202B can also be powered differently in time, so that the amount of additional heat contributed by the laser emitters 202B to each other varies in time. The internal structure can affect the overall thermal impedance between the laser emitters 202B and the point of temperature measurement (such as the heat sink 206B). The laser emitter temperature prediction model can reflect the overall thermal impedance to predict the laser emitter temperature. Figure 5 and Figure 6 This aspect is described in more detail.

[0026] Note that the above Figures 1 to 3 Example laser configurations and associated thermal impedances are described. The overall thermal impedance for a given laser configuration may include any number of laser dies, laser emitters, and / or other electronic components (e.g., heat generating components) associated with the laser. The laser die (not explicitly noted) may include one or more laser emitters per laser die. The thermal impedance may reflect the effects of individual heat generating elements (such as laser emitters) in isolation or on each other (e.g., the effect of a laser emitter on an adjacent laser emitter and vice versa). The following is a description of the thermal impedance of a given laser configuration. Figure 5 and Figure 6 The details described can be applied to model the thermal impedance of any component or element that has a thermal relationship with a given laser configuration.

[0027] Continue About Figure 3 As discussed above, the compensation and control component 108B may receive the desired optical power 106B and utilize the predicted laser emitter temperature to correspondingly generate a compensation current 120B. FIG. 4A to FIG. 4D Additional details are provided regarding the relationship between emitter temperature, current supplied to a laser emitter, and light emitted from the laser emitter.

[0028] Figure 4A and Figure 4BA graph 400 is included with example light (e.g., optical power) current (i) curves (LIC) 402. For example, the light-current curve 402 can represent an individual light-current-temperature relationship for a specific laser emitter temperature. The graph 400 includes current on the x-axis and light on the y-axis. The light-current curve 402 can be related to a specific laser emitter temperature. In this case, individual light-current curves 402(1), 402(2), and 402(3) are shown for 25 degrees Celsius, 45 degrees Celsius, and 65 degrees Celsius, respectively. The graph 400 is not necessarily drawn to scale. The graph 400 is for illustration purposes and is not intended to be limiting.

[0029] exist Figure 4A In the graph 400, a vertical dashed line is drawn at an arbitrary current value C1 (current may also be represented as "I"). A horizontal dashed line is drawn at the intersection of the current value C1 with the light-current curves 402 (1) and 402 (3), which correspond to the optical power values ​​L1 and L2. Figure 4A As shown, an increase in laser emitter temperature from 25 degrees Celsius to 65 degrees Celsius can cause a significant decrease in optical power resulting from the same current input to the laser emitter, from L1 down to L2. Therefore, laser emitter temperature can significantly affect laser emitter efficiency. Figure 4A A vertical dashed line at current value C2 may also be included. In an instance where L1 is the desired optical power value for a specific pixel of the displayed image and the laser emitter temperature of the laser is 65 degrees Celsius, the laser emitter will have to drive the laser emitter using a current value of C2 in order to produce the desired optical power value. In this instance, driving the laser using C1 (which corresponds to 25 degrees Celsius) will not maintain the desired optical power. The compensation and control component 108 can utilize the LI curve to compensate or adjust the current to reflect the predicted laser emitter temperature. However, it is unlikely that the LI curve will be available for the predicted emitter temperature for individual time intervals (e.g., the predicted emitter temperature may not exactly match the temperature of any of the known LI curves). The following is about Figure 4B The discussion explains how to determine the current for a predicted emitter temperature that does not correspond to an available LI curve.

[0030] Figure 4B Additional aspects of a light-current (LI) curve 402 are illustrated. The LI curve may reflect known values ​​at specific temperatures (e.g., in this case, 25, 45, and 64 degrees). Values ​​for other temperatures may be interpolated from the known LI curve. Figure 4BAs shown in graph 400(1), at an optical power value of L3, light-current curve 402(1) may be a distance D1 from light-current curve 402(3). Light-current curve 402(2) may be a percentage P1 of distance D1 from light-current curve 402(1), and may be a percentage P2 of distance D1 from light-current curve 402(3). Similarly, at an optical power value of L4, light-current curve 402(1) may be a distance D2 from light-current curve 402(3), light-current curve 402(2) may be a percentage P3 of distance D2 from light-current curve 402(1), and light-current curve 402(2) may be a percentage P4 of distance D2 from light-current curve 402(3). In some cases, even though 45 degrees Celsius is midway between 25 degrees Celsius and 65 degrees Celsius, the light-current curves corresponding to these laser emitter temperatures may not be equally spaced. Figure 4B As depicted in , percentage P1 for distance D1 is relatively less than percentage P2 for distance D1. This is one example of a nonlinear aspect that may be intrinsic to light-current curve 402. Another example may be the difference between percentages at different optical power values. In this example, percentage P1 for distance D1 may be different than percentage D3 for distance D2. In other words, the position of light-current curve 402(2) between light-current curve 402(1) and light-current curve 402(3) may change with optical power. Figure 4C An example of this relationship for a specific laser configuration is shown in .

[0031] Figure 4C A graphical representation of the temperature to index transfer function is shown as graph 400(2). As mentioned above, this graph can serve as a temperature to index LUT reflecting the relationship between optical power or light (vertical axis) and temperature (horizontal axis).

[0032] Figure 4D A graphical representation of thermal or heating power as a function of current and temperature is shown as graph 400(3). This graph can represent a code to power relationship (e.g., the thermal power that must be applied to the laser emitter given a certain combination of compensation current, temperature information, and optical output). Note that Figure 4A-4DThe example graph of can be associated with an example laser configuration (e.g., a laser model). Similar graphs can be constructed for other laser configurations. In this implementation, the compensation and control component 108A can solve the technical problem of maintaining the 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 108A can calculate the compensation current for the laser in a manner that reflects the sensitivity of the laser efficiency to the emitter temperature for a given optical power. The following is about Figure 5 This aspect is discussed in more detail.

[0033] Figure 5 A schematic diagram of components that may implement system 100B is provided. Figure 3 Recall that in system 100B, laser 102B includes two laser emitters 202B(1) and 202B(2). Figure 3 Consistent, on the left side of the page, Figure 5 1 receives the desired optical powers 106B(1) and 106B(2). On the right side of the page, for each pixel, the compensation and control component 108B ultimately calculates compensation currents 120B(1) and 120B(2). Because there are two laser emitters 202B(1) and 202B(2), the compensation and control component 108B generates two compensation currents 120B (e.g., compensation current 120B(1) for laser emitter 202B(1) at the top of the page and compensation current 120B(2) for laser emitter 202B(2) at the bottom of the page). Because there are two laser emitters 202B, the circuit arrangement is largely repeated so that the upper half of the figure is associated with laser emitter 202B(1) and the lower half of the figure is associated with laser emitter 202B(2). The following discussion will emphasize the upper half of the diagram, recognizing that the lower half is similar, and if additional laser emitters are employed, additional sets of circuit devices may be employed, etc. Whenever possible, the upper half of the diagram relating to laser emitter 202B(1) is referred to by "1," and the lower half of the diagram relating to laser emitter 202B(2) is referred to by "2."

[0034] The compensation current 120B may be embodied as a digital code (Code 1) fed to a digital-to-analog converter (DAC) 502 (e.g., DAC 502(1) at the top of the page connected to laser emitter 202B(1) and Code 2 at the bottom of the page connected to DAC 502(2) at the bottom of the page). The DAC converts the digital code into an analog current that is used to cause laser emitter 202B(1) to emit a laser beam (104B(1), Figure 3 ).

[0035] The remainder of the components are related to the compensation and control component 108B. Starting on the left side of the page and arranged vertically, the compensation and control component may include a power accumulator 504, a laser emitter temperature prediction model 110B, an adder 506, a code to power LUT 508, a temperature to index LUT 510, a LI LUT 512, and / or an interpolator 514. The LI LUT may be a lookup table that is populated with data from a light to current curve (LIC) or other calculation mechanism associated with a specific laser emitter temperature (25 degrees and 65 degrees in this example). Figure 4A and Figure 4B The LIC is explained. Although not explicitly shown, a pixel clock may be employed to synchronize the functions of the various components.

[0036] For purposes of explanation, beginning at interpolator 514(1), assume that the interpolator has generated a compensation current 120B (e.g., Code 1), which is fed back to code-to-power LUT 508(1), which optionally receives a predicted laser emitter temperature (T(emitter 1)) from adder 506(1) (described below). Recall that the code generated by interpolator 514(1) commands the analog current produced by DAC 502(1). Given some combination of the compensation current, temperature information, and the optical output power (which may also be estimated), code-to-power LUT 508(1) can infer the thermal power that must have been applied to laser 102B. Figure 4D An example graphical representation of such a code-to-power LUT 508(1) is shown in graph 400(3) of FIG.

[0037] The thermal power value (e.g., Power 1) determined by the code-to-power LUT 508(1) may be fed back to the power accumulator 504(1). (Also note that while the discussion focuses on the upper half of the figure associated with the laser emitter 202B(1), the thermal power may be fed back in a cross-over fashion at 516 so that the upper half of the circuit arrangement receives information about the thermally related laser emitters shown in the lower half (e.g., Power 2, and vice versa). The power accumulator 504(1) may optionally accumulate values ​​representing thermal energy associated with a plurality of previous pixels prior to entry into the laser emitter temperature prediction model 110B. Accumulating thermal energy reduces the complexity of the laser emitter temperature prediction model 110B, but also adds a 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 of the temperature prediction model 110B.

[0038] The laser emitter temperature prediction model 110B(1) can predict the temperature of the laser emitter 202B(1) by modeling the thermal characteristics of the laser 102B as a function of time and thermal power. The thermal power can be the difference between the electrical power for a time interval (and previous time intervals) and the optical power emitted by the laser emitter for the time interval (and previous time intervals) (e.g., any electrical power that is not converted to optical power is converted to thermal power (e.g., heat)). The following is a description of the thermal characteristics of the laser emitter 202B(1) by modeling the thermal characteristics of the laser 102B as a function of time and thermal power. The thermal power can be the difference between the electrical power for a time interval (and previous time intervals) and the optical power emitted by the laser emitter for the time interval (and previous time intervals) (e.g., any electrical power that is not converted to optical power is converted to thermal power (e.g., heat)). Figure 6 This aspect is described in more detail. The temperature rise may be communicated to summer 506. Summer also receives the temperature rise associated with laser emitter 202B(2) from laser emitter temperature prediction model 110B(2) and sensed laser properties 116B (e.g., housing temperature) from laser sensor 112B.

[0039] In this case, the laser sensor 112B may be embodied as a thermistor placed on the housing of the laser, and the sensed laser property 116B may be embodied as the housing temperature of the laser 102B. The adder 506(1) may send the sum of the thermal data (e.g., T(emitter 1)) to the temperature-to-index LUT 510(1). Some implementations may provide additional refinements by supplying the thermal data (e.g., T(emitter 1)) to the code-to-power LUT 508(1) so that the emitter temperature may be considered in the code-to-power function. Alternatively or additionally, the desired optical power 1 may be supplied to the temperature-to-index LUT 510(1) to allow further refinement of the calculation. Figure 4C This aspect is described.

[0040] It is desired that optical power 1 is supplied to LI LUT 512. Recall that any number of multiple LI LUTs may be employed. In one case, for example, light-current curve LUTs 512(1) and 512(3) may correspond to a light-current curve at 25 degrees Celsius, while LI LUTs 512(2) and 512(4) may correspond to a light-current curve at 65 degrees Celsius. In some cases, for example, LI LUTs 512(1) and 512(3) may actually be LI LUTs accessed by both the same interpolators 514(1) and 514(2).

[0041] The outputs from the LI LUT 512 and the temperature-to-index LUT 510 may be provided to, or accessed by, an interpolator 514. As mentioned above, it is possible that the predicted laser emitter temperature matches one of the temperatures in the LI LUT 512. For example, the predicted laser emitter temperature may be 65 degrees, and one of the LILUTs in the LI LUT may relate light (e.g., optical power) to current at 65 degrees. Thus, the interpolator 514 may calculate the compensation current directly from the LI LUT. More likely, however, the predicted laser temperature will not be an exact match. In such a case, the interpolator may interpolate or extrapolate from the available values ​​of the LI LUT to the predicted laser emitter temperature. Recall from the above discussion that this tends not to be a linear function. The temperature-to-index LUT 510(1) may provide a relationship between the available values. For example, the predicted laser emitter temperature may be 45 degrees. The temperature-to-index LUT 510(1) may indicate in percentage that the value of the 45 degree LIC curve is 30% from 25 degrees and 70% from 65 degrees. Thus, the interpolator 514 may calculate the compensation current as (LI) by interpolating between the values ​​of the two LI LUTs. 65° Value-LI 65° 30% of the value of 25° The value of .

[0042] In yet another scenario, the predicted laser emitter temperature may be outside of the available LI LUT 512. For example, continuing with the above example, the predicted laser emitter temperature may be 75 degrees and the LI LUT may be related to 25 degrees and 65 degrees. The temperature to index LUT 510 may provide a percentage improvement over the available LI LUT. For example, the relationship 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 shown in the graph 400(2)( Figure 4C ) is reflected on the index axis of the temperature axis as a value of 161% at the 75 degree point on the temperature axis. As such, the interpolator 514 can extrapolate the compensation current for the desired optical power as 161% of (the value of LI65° - the value of LI65°) + the value of LI25°. In each of the above scenarios, the interpolator 514 can send the compensation current information 120B (code 1) to the digital-to-analog converter (DAC) 502, which can drive the laser 102B (e.g., the laser transmitter 202B (1)).

[0043] Figure 6 Provide with Figure 5Additional details related to the laser emitter temperature prediction models 110B(1), 110B(2), 110B(3), 110B(4) are shown. Among other configurations, each of those laser emitter temperature prediction models 110B can be implemented as a plurality of recursive (sometimes referred to as infinite impulse response, "IIR") filter sub-models 600(1)1, 600(1)2, ... 600(1)N, where each recursive filter sub-model receives a thermal power (e.g., power 1, Figure 5 ) as input and predicts the laser housing temperature as a function of time as a fraction of the upper emitter temperature rise. The laser emitter temperature prediction model 110B can run continuously so that the temperature prediction is always up to date. Figure 5 Recall that in this implementation, the laser emitter prediction model 110B(1) receives a power 1 input from the code-to-power LUT 508 and sends its output as a boost 1+1 to the adder 506(1). Figure 5 The power accumulator 504(1) is discussed but not shown here. For the sake of brevity, these aspects are not revisited here.

[0044] in this case, Figure 5 The laser transmitter temperature prediction model 110B (1) in Figure 6 The effects of thermal impedances (such as the thermal interface or material of the laser) are modeled using a plurality of recursive filter elements referred to as laser emitter temperature prediction submodels 600(1)1-600(1)N. Figure 2 and Figure 3 Examples of materials and interfaces are discussed and indicated. In other words, because a laser may include multiple materials and interfaces that contribute to the overall thermal impedance, multiple laser emitter temperature prediction sub-models may be employed. Because each output of these laser emitter temperature prediction sub-models 600 may predict a portion of the total temperature rise, all of these outputs may be added together using appropriate weighting factors to predict the total temperature rise (e.g., a 1+1 rise).

[0045] continue Figure 6, in this example the individual laser emitter temperature prediction sub-models (e.g., 600(1)1, etc.) may include multiplication functions F1 and F3, addition function F2, coefficients COEFF1 and COEFF2, and temperature register 604. As known to those skilled in the art, they can be used together to create a recursive, single-pole, low-pass filter with a decaying exponential time response. The decay time of each filter can be selected to simulate one of the thermal time constants of the laser thermal impedance. As described above, the thermal impedance in systems 100A and 100B may include many thermal time constants, and each thermal time constant has a different proportional effect on the overall temperature to power relationship. In Figure 6 In the example shown, by using function blocks F5, F6, and F7, the output of each sub-model is multiplied by a weighting factor W before the outputs of all sub-models are added together using F4 (i.e., adder 606(1)). T1 , W T2 and W TN , the proportional contributions of up to "N" sub-model time constants can be matched to the individual time constant contributions that make up the thermal impedance of the actual laser system (eg, 100A).

[0046] Those skilled in the art will appreciate that other arrangements of multiplication functions, addition functions, coefficients, and / or temperature registers may be used for a recursive single-pole low-pass filter having the same decaying exponential time response. Such alternative arrangements may utilize different numbers of multiplication and addition functions and different numbers of coefficients. In other arrangements, weighting factors may be applied at the input to the laser transmitter temperature prediction submodel 600 or incorporated into the coefficient values. In still other arrangements, multiple single-pole filters may be replaced by one or more multi-pole filters. Figure 6 The specific functions shown are not intended to be limiting.

[0047] In this example, for each filter comprising a particular laser emitter temperature prediction submodel 600, a new output is determined by combining a new input value (e.g., Power 1) with the previous filter output value using weighting factors COEFF1 and COEFF2, each determining how much to contribute to the new output value. Temperature registers 604 hold the immediate previous output value to allow this calculation. Recall that the previous output value was also a weighted combination of its input and an even earlier output value, so the submodel 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, as the "inertia" of the filter's previous output values ​​must be "overcome" by the new input.

[0048] When multiple filter (i.e., laser emitter temperature prediction submodel) outputs are summed together, the overall response will remain slow, even though any individual filter may respond faster or slower than the other filters in the combination. This type of behavior matches the general thermal response of laser systems 100A and 100B to any thermal power input. By selecting appropriate time constants for the filters (e.g., laser emitter temperature prediction submodels 600(1)1 to 600(1)N associated with laser emitter temperature prediction model 110B(1), and similar laser emitter temperature prediction submodels associated with other laser emitter temperature prediction models), and selecting appropriate weighting factors (WT1, WT2, ... WTN) specific to each filter, the specific thermal behavior of laser systems 100A and 100B can be matched to a desired level of accuracy. All weighted outputs are summed in adder 606(1) to generate an overall thermal prediction model value (output value of 110B(1), 110B(2), etc.).

[0049] In other words, the temperature rise of the laser emitter above the laser housing temperature may gradually change when driven at a new thermal power level. The laser emitter may eventually reach thermal equilibrium for a constant thermal power level, but it is more likely that the laser emitter will be driven again at a newer thermal power before thermal equilibrium is reached. In a similar manner, the emitter temperature rise predicted by each laser emitter thermal prediction model 110B will depend on the starting laser emitter temperature and will change as the applied thermal power changes. Eventually, the laser emitter temperature prediction model will also reach thermal equilibrium for a constant thermal power level, but if a new thermal power level appears at the input to the laser emitter temperature prediction model, the laser emitter temperature prediction model will predict a new temperature. In this way, the laser emitter temperature prediction model continuously updates its temperature rise prediction based on the applied thermal power.

[0050] The output of the laser emitter temperature prediction model 110B(1) (i.e., the output of adder 606(1)) may be sent to adder 506(1). Note that Figure 6 The laser emitter temperature prediction model 110B(1) is described in detail, but is applicable to the other laser emitter temperature prediction models 110B(2)-110B(4). The laser emitter temperature prediction model 110B(1) captures the thermal effect of the thermal power applied to the laser emitter 202B(1) on itself ( Figure 5 ). The laser emitter temperature prediction model 110B(2) captures the thermal effect on the laser emitter 202B(1) of the thermal power applied to the laser emitter 202B(2). Figure 5As discussed, summer 506(1) receives input values ​​from laser emitter temperature prediction models 110B(1) and 110B(2) and the laser housing temperature, and outputs the temperature of laser emitter 202B(1) (ie, T(emitter 1)).

[0051] Combined Figure 5 and Figure 6 , some of the implementations described above may be distinguished from conventional systems in which optical 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 conventional systems, the LI LUT data is collected as part of the system calibration. For each frame, the measured light is compared to the expected light and the LI LUT is repopulated. A simple algorithm is used to stretch and scale the LI LUT data as a feedback mechanism to align the measured light with the expected light for the next frame. This approach does not compensate for the dramatic temperature fluctuations that can occur within a frame time and typically results in a large difference between the actual or emitted optical power and the expected optical power.

[0052] The present concept may employ a second (or more) LI LUTs (512, 513) containing light-to-current data collected at different temperatures (e.g., 65 degrees and 25 degrees) Figure 5 ). The LI LUT 512 feeds an interpolator 514, which can interpolate between the two LI LUTs based on the index value provided by the temperature-to-index LUT 510. (As a result, no stretching or scaling or reconstructing of either of the two LI LUTs is required.) This multiple LI LUT and interpolator arrangement can form a virtual LUT (e.g., two or more LUTs for a particular temperature and an interpolator that can identify the compensation current for any desired optical output as a function of any temperature). As described above, the interpolator feeds the laser DAC 502. The index value can be a simple function of the predicted laser emitter temperature, or it can be a more complex function of the predicted laser emitter temperature as defined by the temperature-to-index LUT 510. The temperature prediction is based on a laser emitter temperature prediction model of the laser, which can be implemented by the compensation and control component 108.

[0053] In some implementations, the laser emitter temperature prediction model can be based on one or more infinite impulse response (IIR) low pass filters (e.g., laser emitter temperature prediction sub-models) that accept as input a representation of the laser power, apply a system-dependent gain to the laser power, and output a value representing the temperature rise. The temperature rise can be added to the known housing temperature to predict the laser emitter temperature for any instant in time, regardless of how dynamic the temperature rise is. The housing temperature can be provided by a simple thermistor because the temperature tends to change slowly. In another implementation, the housing temperature can be inferred by using an integrated feedback system in which the measured light is compared to the expected light. When the measured light is less than expected, the inferred housing temperature can be increased - and vice versa.

[0054] Several implementations are considered, including alternatives to those mentioned above for determining the housing temperature. Various laser emitter temperature prediction models that model the thermal characteristics of the laser can be adopted. Some of these implementations employ IIR filters. A potentially important point for some IIR implementations is that the emitter temperature prediction IIR filter can include several IIR filter stages, each IIR filter stage representing various thermal impedances that may exist between the laser emitter and the laser housing. Similarly, the virtual LI LUT can be composed of more than 2 (e.g., 3 or 4) physical LUTs. The interpolator can be extrapolated for temperatures outside the range covered by the physical LUT. The temperature to index LUT can benefit from including optical power as an input to enhance accuracy and / or to provide feedback to check the accuracy of compensation and control components.

[0055] Figure 7 A system 100C showing various device implementations is illustrated. Device 700 may be associated with Figure 2 and Figure 3 The display device 208 and / or display device 208B described are similar. Three device implementations are illustrated in this case. Device 700(1) can operate in cooperation with device 700(2). For example, device 700(1) can be embodied as a display device for a personal computer, a television, or a projection display device. Device 700(3) is embodied as a head mounted display device. Individual devices can include a display 702, which can be similar to display 212 and / or display 212B. Device 700 can communicate via one or more networks, such as network 704. Although specific device examples are illustrated for purposes of explanation, the devices can be embodied in any of a myriad of evolving or yet to be developed types of devices.

[0056] Among other things, individual devices 700 may be embodied in one of the two illustrated configurations 706(1) and 706(2). Briefly, configuration 706(1) represents an operating system-centric configuration, and configuration 706(2) represents a system-on-chip configuration. Configuration 706(1) is organized into one or more applications 708, an operating system 710, and hardware 712. Configuration 706(2) is organized into shared resources 714, dedicated resources 716, and interfaces 718 therebetween.

[0057] In either configuration, device 700 may include processor 720, storage 722, compensation and control assembly 108C, and / or laser emitter temperature prediction model 110C. Individual devices may alternatively or additionally include other elements, which are not illustrated or discussed herein for the sake of brevity.

[0058] Device 700(1) and device 700(2) may be considered to operate cooperatively to perform the present concepts. For example, device 700(2) may include processor 720, storage device 722, compensation and control component 108C, and / or an instance of laser emitter temperature prediction model 110C. In this example, device 700(2) may receive sensed laser properties and / or sensed laser beam properties from device 700(1) and send compensation currents to device 700(1). Conversely, devices 700(1) and / or 700(3) may be self-contained devices, both of which include display 702, processor 720, storage device 722, compensation and control component 108C, and an instance of laser emitter temperature prediction model 110C.

[0059] In some implementations, a device such as device 700(3) may include a SoC configuration, such as an application specific integrated circuit (ASIC) that includes the compensation and control component 108C and the laser emitter temperature prediction model 110C. Other device implementations, such as head mounted display device 700(3), may include a processor (such as a CPU and / or GPU) that renders frames, and the compensation and control component 108C and the laser emitter temperature prediction model 110C may also be executed on the same processor or on another processor.

[0060] From one perspective, any device in device 700 can be considered a computer. As used herein, the term "device", "computer" or "computing device" can mean any type of device having a certain amount of processing power and / or storage capacity. Processing power can be provided by one or more processors, which can execute data in the form of computer-readable instructions to provide functionality. Data (such as computer-readable instructions and / or user-related data) can be stored on a storage device (such as a storage device that can be internal or external to the computer). The storage device can include any one or more of volatile or non-volatile memory, hard disk drive, flash memory storage device, optical storage device (e.g., CD, DVD, etc.) and / or remote storage device (e.g., cloud-based storage device). As used herein, the term "computer-readable medium" can include signals. In contrast, the term "computer-readable storage medium" does not include signals. Computer-readable storage media include "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 disk drives, optical disks and / or flash memory).

[0061] As mentioned above, configuration 706(2) may be considered a system-on-chip (SOC) type design. In such a case, the functionality provided by device 700 may be integrated on a single SOC or multiple coupled SOCs. One or more processors may 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). Therefore, the term "processor" as used herein may also refer to a central processing unit (CPU), a graphics processing unit (GPU), a field programmable gate array (FPGA), a controller, a microcontroller, a processor core, or other type of processing device. The compensation and control component 108C and the laser emitter temperature prediction model 110C may be embodied as dedicated resources 716 and / or shared resources 714.

[0062] Typically, any function described herein can be implemented using software, firmware, hardware (e.g., fixed logic circuitry) or a combination of these implementations. As used herein, the term "component" typically represents software, firmware, hardware, entire equipment or network, or a combination of the foregoing. For example, in the case of software implementation, these can represent the program code that performs a specified task when executed on a processor (e.g., one or more CPUs). The program code can be stored in one or more computer-readable storage devices (such as computer-readable storage media). The features and techniques of this component are platform-independent, which means that they can be implemented on various commercial computing platforms with various processing configurations.

[0063] Figure 8 An example laser control method 800 is shown.

[0064] In this case, block 802 may receive a predicted laser emitter temperature of a laser emitter.

[0065] Block 804 may obtain the desired optical power for a time interval (eg, pixel time).

[0066] Block 806 may utilize a plurality of light-to-current lookup tables to calculate the compensation current for the time interval. The individual light-to-current lookup tables may be associated with a specific laser emitter temperature.

[0067] Fig. 9 A laser control method 900 is shown.

[0068] In this case, block 902 may predict the temperature of the laser emitter from the sum of the heat transfer across the components and interfaces of the laser containing the laser emitter. The predicted temperature of the laser emitter may be accurate for lasers employing a single laser emitter and / or lasers employing multiple laser emitters. In configurations with multiple laser emitters, the prediction may factor in the thermal power from each of the laser emitters because the laser emitters tend to heat each other. Therefore, if the predicted temperature of the laser emitter does not take into account the heat gain from other laser emitters, it may be incorrect.

[0069] Block 904 may obtain the desired optical power for the pixel time at which the laser is driven.

[0070] Block 906 may calculate a compensation current to drive the laser emitter for a pixel time by interpolating between the light and current values ​​for the known laser emitter temperature.

[0071] Block 908 may cause the laser emitter to be driven using a compensation current so that the output of the actual optical power of the laser emitter matches the desired pixel time for the pixel time.

[0072] Various examples are described above. Additional examples are described below. One example includes a system comprising: a laser including 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 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 calculate a compensation current to drive the laser based on the predicted laser emitter temperature so that the laser emitter generates a laser beam having an actual optical power that matches the desired optical power.

[0073] Another example may include any of the above and / or following examples, wherein the sensor is a thermal sensor that senses a temperature of a housing of the laser.

[0074] Another example may include any of the above and / or following examples, wherein the laser emitter temperature prediction model models a thermal impedance of the laser from the laser emitter to the housing.

[0075] Another example may include any of the above and / or following examples wherein the thermal impedance reflects an element having a thermal relationship with the laser emitter.

[0076] Another example may include any of the above and / or following examples, wherein the element includes another laser emitter.

[0077] Another example may include any of the above and / or following examples, wherein the laser emitter temperature prediction model may model thermal characteristics and internal temperature of the laser over time.

[0078] Another example may include any of the above and / or following examples, where the laser emitter temperature prediction model may model a specific point on the laser as a function of time and power.

[0079] Another example may include any of the above and / or following examples, wherein the laser emitter temperature prediction model includes a plurality of laser emitter temperature prediction models.

[0080] Another example may include any of the above and / or following examples, wherein individual laser emitter temperature prediction models are associated with individual elements of the laser.

[0081] Another example may include any of the above and / or following examples where the outputs of individual laser emitter temperature prediction models are added together to create an overall thermal value for the laser.

[0082] Another example may include any of the above and / or following examples, wherein the laser emitter includes a plurality of laser emitters.

[0083] Another example may include any of the above and / or following examples wherein the laser emitter temperature prediction model takes into account the thermal effects of individual laser emitters on each other.

[0084] Another example may include any of the above and / or following examples, wherein the compensation and control component includes a plurality of light-to-current lookup tables (LI LUTs) for individual laser emitter temperatures.

[0085] Another example may include any of the above and / or following examples, wherein the compensation and control component includes an interpolator that can interpolate or extrapolate from individual laser emitter temperatures to a predicted laser emitter temperature.

[0086] Another example may include any of the above and / or following examples wherein the compensation and control component includes a temperature to index lookup table showing the change in required drive level as a percentage between or beyond the required level at the individual laser emitter temperature.

[0087] Another example may include any of the above and / or following examples, wherein the compensation and control component calculates the compensation current from the current value of the individual laser emitter temperature using a percentage change.

[0088] Another example includes a system comprising: a laser including a laser emitter configured to generate a laser beam for an interval in 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 the interval in time, and calculate a compensation current for the interval using a plurality of light-to-current lookup tables, wherein an individual light-to-current lookup table is associated with a specific laser emitter temperature.

[0089] Another example may include any of the above and / or following examples, wherein the compensation and control component is configured to perform an interpolation or extrapolation of a specific laser emitter temperature from a light-to-current lookup table to a predicted laser emitter temperature.

[0090] Another example may include any of the above and / or following examples, wherein the interpolation or the extrapolation is non-linear.

[0091] Another example includes a computer-implemented method comprising predicting a temperature of a laser emitter from a sum of time-dependent heat transfer through materials and interfaces of the laser containing the laser emitter, obtaining a desired optical power for a pixel time at which the laser emitter is driven, calculating a compensation current to drive the laser emitter for the pixel time by interpolating between light and current values ​​for the known laser emitter temperature, and causing the laser emitter to be driven using the compensation current so that an actual optical output of the laser emitter matches the desired optical output for the pixel time.

Claims

1. A laser system comprising: A laser including a laser transmitter configured to generate a laser beam; a sensor configured to sense a temperature of a housing of the laser; a laser emitter temperature prediction model capable of modeling a thermal impedance of the laser from the laser emitter to the housing to predict the laser emitter temperature from a sensed temperature of the housing of the laser; as well as A compensation and control component is configured to receive a desired optical power and calculate a compensation current for driving the laser based on a predicted temperature of the laser emitter, the compensation current being calculated for the predicted temperature of the laser emitter so that the laser emitter generates the laser beam having an actual optical power that matches the desired optical power.

2. The laser system of claim 1, wherein the thermal impedance reflects an element having a thermal relationship with the laser emitter.

3. The laser system of claim 2, wherein the element comprises another laser emitter.

4. The laser system of claim 1, wherein the laser transmitter temperature prediction model is capable of modeling thermal characteristics and internal temperature of the laser over time.

5. The laser system of claim 4, wherein the laser emitter temperature prediction model is capable of modeling the laser emitters on the laser as a function of time and power.

6. The laser system of claim 5, wherein the laser emitter temperature prediction model comprises a plurality of laser emitter temperature prediction models.

7. The laser system of claim 6, wherein individual laser emitter temperature prediction models are associated with individual elements of the laser.

8. The laser system of claim 7, wherein the outputs of the individual laser emitter temperature prediction models are added together to create an overall thermal value for the laser.

9. The laser system of claim 1, wherein the laser emitter comprises a plurality of laser emitters.

10. The laser system of claim 9, wherein the laser emitter temperature prediction model is capable of taking into account the thermal effects of individual laser emitters on each other.

11. The laser system of claim 1 , wherein the compensation and control component comprises a plurality of light-to-current look-up tables (LILUTs) for individual laser emitter temperatures.

12. The laser system of claim 11, wherein the compensation and control component includes an interpolator capable of interpolating or extrapolating from the individual laser emitter temperatures to the predicted laser emitter temperature.

13. The laser system of claim 12, wherein the compensation and control component includes a temperature to index lookup table showing the required change in current drive level as a percentage between or beyond the current drive level required at the individual laser emitter temperature.

14. The laser system of claim 13, wherein the compensation and control component utilizes the percentage change to calculate the compensation current from the current drive level of the individual laser emitter temperature.

15. A laser system comprising: A laser including a laser emitter configured to generate a laser beam for time-dependent intervals; The compensation and control components are configured as: receiving a predicted laser emitter temperature of the laser emitter from a laser emitter temperature prediction model capable of modeling a thermal impedance from the laser emitter of the laser to a housing of the laser, Get the expected optical power for the interval, and, calculating a compensation current for the interval using a plurality of light-to-current lookup tables, wherein individual light-to-current lookup tables are associated with available temperature values; The laser transmitter is caused to generate the laser beam having an actual optical power matching the desired optical power.

16. The laser system of claim 15, wherein the compensation and control component is configured to perform an interpolation or an extrapolation from the available temperature value of the light-to-current lookup table to the predicted temperature of the laser emitter.

17. The laser system of claim 16, wherein the interpolation or extrapolation is non-linear.

18. A method for controlling a laser transmitter, comprising: predicting a temperature of the laser emitter from a sum of time-dependent heat conduction through materials and interfaces containing the laser of the laser emitter; obtaining a desired optical power for a pixel time at which the laser emitter is driven; calculating a compensated current to drive the laser emitter for the pixel time by interpolating between light and current values ​​for a known laser emitter temperature; as well as The laser emitter is driven with the compensated current such that an actual optical output of the laser emitter matches the desired optical power for the pixel time.

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