WO2020083033A1 - 可穿戴设备、光模块及其驱动方法 - Google Patents

可穿戴设备、光模块及其驱动方法 Download PDF

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Publication number
WO2020083033A1
WO2020083033A1 PCT/CN2019/110485 CN2019110485W WO2020083033A1 WO 2020083033 A1 WO2020083033 A1 WO 2020083033A1 CN 2019110485 W CN2019110485 W CN 2019110485W WO 2020083033 A1 WO2020083033 A1 WO 2020083033A1
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Prior art keywords
optical module
mondac
current
tracking error
monitoring current
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PCT/CN2019/110485
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English (en)
French (fr)
Inventor
林琳
孙剑
郭子强
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京东方科技集团股份有限公司
北京京东方光电科技有限公司
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Application filed by 京东方科技集团股份有限公司, 北京京东方光电科技有限公司 filed Critical 京东方科技集团股份有限公司
Priority to US16/760,559 priority Critical patent/US11016254B2/en
Publication of WO2020083033A1 publication Critical patent/WO2020083033A1/zh

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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/42—Coupling light guides with opto-electronic elements
    • G02B6/4201—Packages, e.g. shape, construction, internal or external details
    • G02B6/4286—Optical modules with optical power monitoring
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/42—Coupling light guides with opto-electronic elements
    • G02B6/4201—Packages, e.g. shape, construction, internal or external details
    • G02B6/4274—Electrical aspects
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/11—Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/42—Coupling light guides with opto-electronic elements
    • G02B6/4201—Packages, e.g. shape, construction, internal or external details
    • G02B6/4266—Thermal aspects, temperature control or temperature monitoring
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/564—Power control

Definitions

  • the present disclosure relates to optical communication, and more particularly, to a wearable device, optical module, and driving method thereof.
  • Wearable devices such as virtual reality (VR) or augmented reality (AR) devices
  • VR virtual reality
  • AR augmented reality
  • MIPI Mobile Industry Processor Interface
  • HDMI High-Definition Multi-faceted Interface
  • Connect the optical module to transmit through optical fiber then the transmission rate can be easily achieved 40Gbps / 100Gbps, and the upgraded version of 400Gbps is also being tested. Therefore, the use of optical fiber communication is bound to become the main transmission mode of VR or AR equipment.
  • MSA Multi-Source Agreement
  • optical modules small hot-swappable optical transceiver modules
  • MSA unifies the packaging of optical transceivers. Therefore, optical transceivers conforming to MSA are the main forms of current optical transmitters and receivers.
  • a perfect content of the MSA protocol is miniaturization. Due to the miniaturization, the interface density of interface boards is getting higher and higher, so heat dissipation and temperature management have become the focus of attention. As the core of optical fiber access network equipment, the output characteristics of optical modules will be affected by temperature, so temperature compensation becomes the top priority.
  • the temperature compensation methods of the optical module currently include a scaling method, a thermistor compensation method, and a three-temperature fitting method.
  • the scaling method uses curve compensation, but it must provide many sets of experimental curves, which consumes a lot.
  • the thermistor compensation method uses a thermistor to compensate, but because it requires a welding resistor, the accuracy improvement is limited and the data is inaccurate.
  • the three-temperature fitting method fits the universal calibration curve by testing the power of the optical module at three temperature points of normal temperature (25 ° C), high temperature and low temperature, and taking points, but the test platform used is complicated, the test time is long, and it does not have Uniform standards.
  • an optical module including:
  • a light emitting component for emitting light based on the driving current to output optical power
  • a calibration unit for acquiring an original monitoring current feedback value MONDAC before corresponding to the current monitoring current of the light emitting component, and for acquiring a tracking error value TE of the current temperature relative to the reference temperature, and calibrating the original based on the tracking error value Monitor the current feedback value MONDAC before to get the calibrated monitor current feedback value MONDAC after ;
  • the driving current setting unit is used to set the driving current based on the calibrated monitoring current feedback value MONDAC after to control the optical power output by the light emitting component.
  • the calibration unit is configured to linearly calibrate the original monitoring current feedback value MONDAC before based on the tracking error value TE.
  • the calibration unit is configured to perform the calibration according to the following equation:
  • the calibration unit is configured to perform the calibration according to the following equation:
  • the driver is a circuit combining an analog circuit and a micro control unit.
  • the optical module further includes a storage unit for storing the tracking error value TE.
  • the calibration unit is configured to read the tracking error value TE from the storage unit.
  • the original monitoring current feedback value MONDAC before is obtained by collecting an analog quantity Im of the monitoring current of the light emitting component, and performing analog-to-digital conversion on the analog quantity Im.
  • the calibration unit uses a 5-bit register and a shifter to implement the calculation of the following formula:
  • the calibration unit uses an 8-bit shifter to implement the calculation of the following formula:
  • a method for driving an optical module comprising the steps of: obtaining the original monitoring current feedback value MONDAC before corresponding to the current monitoring current of the light emitting component of the optical module; obtaining the current temperature relative A tracking error value TE of the reference temperature; calibrating the original monitoring current feedback value MONDAC before based on the tracking error value TE to obtain a calibrated monitoring current feedback value MONDAC after ; and based on the calibrated monitoring current feedback value MONDAC after
  • the driving current is set to control the optical power output by the light emitting component.
  • calibrating the original monitored current feedback value MONDAC before based on the tracking error value TE includes linearly calibrating the original monitored current feedback value MONDAC before based on the tracking error value TE.
  • calculating the MONDAC after calibrated monitoring current is performed according to the following equation:
  • calculating the MONDAC after calibrated monitoring current is performed according to the following equation:
  • acquiring the tracking error value TE of the current temperature relative to the reference temperature includes reading the tracking error value TE from the storage unit of the optical module.
  • the original monitoring current feedback value MONDAC before is obtained by collecting an analog quantity I m of the monitoring current of the light emitting component and performing analog-to-digital conversion on the analog quantity I m .
  • a wearable device including the optical module according to the first aspect of the present disclosure.
  • FIG. 1 illustrates a schematic structural diagram of an optical module according to an embodiment of the present disclosure.
  • FIG. 2 illustrates a calibration curve according to an example embodiment of the present disclosure.
  • FIG. 3 illustrates a calibration curve according to another example embodiment of the present disclosure.
  • FIG. 4 illustrates a driving method of an optical module.
  • Fig. 5 illustrates the comparison of the output optical power curves of different schemes applied to the optical module.
  • FIG. 6 illustrates an example schematic diagram of a wearable device according to an embodiment of the present disclosure.
  • FIG. 7 illustrates a schematic structural diagram of an optical module according to an embodiment of the present disclosure.
  • Various embodiments are directed to the optical module and its driving method.
  • the internal environment of wearable devices is not well ventilated and heat dissipated, but it is relatively sealed. Therefore, when the optical module is applied to a wearable device, it has the characteristics of high component temperature, but low noise and high transmission signal quality.
  • the present disclosure proposes an optical module used in a wearable device environment such as VR and AR devices and a driving method thereof to maintain the output optical power temperature of the optical module.
  • the optical module is a device that realizes electro-optical conversion. It controls and adjusts the size of the driving current of the light emitting element in the light emitting component to output the desired optical power.
  • the light emitting element can be a light emitting diode, a laser diode, or other current driven light. element.
  • the stability of the output optical power is an important performance index of the optical module.
  • the output optical power of the light emitting component is usually monitored by tracking the backlight current converted by the backlight through a backlight detector (such as a photodiode) inside the light emitting component, so the backlight current is also often This is called monitoring current. Once the monitoring current changes, it is determined that the output optical power has changed. At this time, the drive current of the light emitting component will be adjusted accordingly to perform optical power control to maintain the stability of the output optical power.
  • the tracking characteristics of the backlight detector (which can be expressed by monitoring the change of the current with the output optical power) will change.
  • the backlight detector may still monitor the same monitoring current I m , which generates a tracking error (Tracking Error, also known as tracking error).
  • Track Error also known as tracking error
  • the tracking error is often simplified as the difference between the output optical power when the light emitting component tracks the same monitoring current under two different temperature conditions. Therefore, if a certain temperature is used as the reference temperature, the change in tracking error at different temperatures also reflects the change in output optical power.
  • the change in temperature is generally not considered (that is, the ambient temperature is at a predetermined temperature by default), and a fixed preset tracking characteristic curve is used to characterize the backlight
  • the tracking characteristics of the detector that is: as long as the monitoring current Im is the same, it is considered that the optical power P emitted by the light emitting component is the same, and vice versa.
  • the optical module when the ambient temperature changes from a predetermined temperature to other temperatures, if the optical module always uses the preset tracking characteristic curve (corresponding to a single predetermined temperature) to determine the output optical power of the light emitting component from the monitoring current, tracking error And the output optical power of the light emitting component is misjudged, which results in an error in the control of the drive current of the light emitting component, so it is difficult to achieve the purpose of maintaining the stability of the optical power.
  • FIG. 1 illustrates a schematic structural diagram of an optical module according to an embodiment of the present disclosure.
  • the optical module 100 includes a light emitting assembly 110 and a driver 120.
  • the light emitting component 110 is used to emit an optical signal based on the driving current to output optical power.
  • the light emitting component 110 may generate and maintain a continuous optical power output.
  • the difference between the driving current and the threshold current Ith is relatively stable, the light emitting component 110 can maintain a substantially stable output optical power.
  • the modulation current used to drive the light emitting component 110 is adapted to the bias current and the threshold current, the light signal emitted by the light emitting component 110 can maintain a relatively stable extinction ratio.
  • the light emitting component 110 may include a light emitting element such as a light emitting diode LED or a semiconductor laser diode LD.
  • the light emitting component 110 may include a VCSEL laser (vertical surface cavity emitting laser), an FP laser (Fabry-Perot laser), a DFB laser (distributed feedback laser), or the like.
  • the driver 120 includes a calibration unit 122 and a drive current setting unit 124.
  • the calibration unit 122 is used for acquiring the original monitoring current feedback value MONDAC before corresponding to the current monitoring current of the light emitting component 110; acquiring the tracking error value TE of the current temperature relative to the reference temperature, and linearly calibrating the tracking error value TE based on the tracking error value TE The original monitoring current feedback value MONDAC before to get the calibrated monitoring current feedback value MONDAC after .
  • the tracking error value TE of the current temperature relative to the reference temperature represents the difference between the tracking characteristic of the current temperature and the tracking characteristic of the reference temperature.
  • the tracking characteristic is represented by the ratio of the output optical power to the monitoring current. Accordingly, the tracking error can be expressed by the difference between the ratio of the output optical power of the current temperature and the reference temperature to the monitoring current.
  • the tracking characteristic curve at the reference temperature is the tracking characteristic curve used by the calibration unit 122 to set the drive current.
  • the monitoring current feedback value is a digital value corresponding to the analog monitoring current.
  • the tracking characteristic curve of the reference temperature there is a certain one-to-one correspondence between the monitoring current feedback value and the output optical power of the optical module.
  • the preset tracking characteristic curve adopted by the optical module may be used as the tracking characteristic curve of the reference temperature, and the optical module will search for the output optical power corresponding to the monitoring current feedback value according to the preset tracking characteristic curve, and According to this, the change of the output optical power is judged to perform the corresponding output optical power control.
  • the driving current setting unit 124 is configured to set the driving current based on the calibrated monitoring current feedback value MONDAC after to control the output optical power of the optical signal emitted by the optical emitting component.
  • the setting of the driving current includes the setting of the bias current and the modulation current. You can control the bias current to keep the output optical power stable, and control the modulation current to keep the extinction ratio stable.
  • the setting of the driving current is based on the monitoring current calibrated with the tracking error value, that is, the monitoring current after temperature compensation, rather than the monitoring current obtained directly. Due to the calibration, the collected monitoring current is mapped to the monitoring current at the reference temperature on which the driving current is adjusted, so that the driving current setting unit can more accurately track the change of the output optical power, so as to reduce the control error of the output optical power . Because the control error is reduced, the light emitting module can output stable output optical power. In other words, because the output optical power remains stable with respect to temperature changes, temperature compensation for the output optical power is achieved.
  • the original monitoring current feedback value MONDAC before is obtained by collecting the analog quantity I m of the monitoring current of the light emitting component 110 and performing analog-to-digital conversion on the analog quantity I m .
  • the original value MONDAC before monitoring the current feedback is included with the monitor current I m of analog digital value varying linearly in another embodiment.
  • the original monitoring current feedback value MONDAC before is a digital value that is implemented based on a specific circuit and has a linear relationship with the analog quantity I m of the monitoring current.
  • the calibration unit 122 may acquire the tracking error initial value TE 0 as the tracking error value TE of the current temperature.
  • the initial tracking error TE 0 may be set as the tracking error of the actual tracking characteristic of the optical module at a certain temperature relative to the tracking characteristic of the reference temperature (for example, the preset tracking characteristic adopted by the optical module).
  • the initial tracking error TE 0 can be measured according to the characteristics of the internal components of the optical module (mainly including light emitting components).
  • the manufacturer may be formed inside the optical device module according to the characteristics of each optical module, according to self-test algorithm defined to provide an initial value of the tracking error TE 0, and to provide a predetermined output characterization TE 0 corresponding to the initial value of the tracking error
  • the initial monitoring current feedback value of the optical power is MONDAC 0 .
  • the monitoring current feedback value can be calibrated starting from TE 0 and the initial monitoring current feedback value MONDAC 0 .
  • the TE value at which the test environment temperature of the device is 25 ° C may be used as TE 0
  • the corresponding initial monitoring current feedback value MONDAC 0 may be preset at this time.
  • the output optical power is 1dBm.
  • the calibration unit 122 may also obtain the tracking error value TE of a certain temperature range corresponding to the current temperature as the tracking error value TE of the current temperature.
  • the temperature range may be, for example, high temperature, room temperature (for example, 20 ° C-25 ° C), low temperature, etc., or a temperature interval divided at predetermined intervals, or a temperature interval divided at different intervals according to the main temperature range during operation of the optical module.
  • the tracking error value TE in a certain temperature range can be provided by the manufacturer of the optical module according to the characteristics of the internal device of the respective optical module and according to a custom test algorithm.
  • the calibration unit 122 may also calculate the tracking error value TE of the current temperature based on the tracking error initial value TE 0 and the temperature change value. As mentioned above, the change in the output optical power due to the tracking error can be approximated as a linear relationship, so the tracking error value TE at the current temperature can be a value that changes linearly with temperature from the initial tracking error value TE 0 .
  • the driver 120 may include a storage unit for storing the tracking error initial value TE 0 and the initial monitoring current feedback value MONDAC 0 .
  • the calibration unit 122 acquires the tracking error initial value and the initial monitoring current feedback value MONDAC 0 from the storage unit and starts calibration from there.
  • the storage unit may also store the tracking error value TE corresponding to different temperatures or different temperature ranges, or the calculated tracking error value TE.
  • the tracking error value TE can be obtained by measuring the output optical power of the light emitting component at different temperatures.
  • the output optical power of the optical module has a predetermined normal operating range
  • the monitoring current feedback value MONDAC has a corresponding effective numerical range.
  • the tracking error value TE can also be adjusted (eg, increased or decreased) in a stepwise manner to change the monitoring current
  • the feedback value MONDAC is maintained within this value range, which correspondingly indicates that the output optical power is also within the normal operating range.
  • the MONDAC after calibrated monitoring current feedback value can be converted into a corresponding analog quantity through digital / analog conversion.
  • the driver 120 may be implemented as a circuit in which an analog circuit is combined with a micro control unit (for example, a microcontroller MCU).
  • a micro control unit for example, a microcontroller MCU
  • the calibration unit 122 performs linear calibration according to formula (1):
  • TE is the tracking error value
  • MONDAC before is the monitoring current feedback value before calibration, that is, the original monitoring current feedback value
  • MONDAC after is the monitoring current feedback value after calibration.
  • TE represents the ratio of the output optical power at the current temperature to the output optical power at the reference temperature under the same monitoring current.
  • the calibration unit 122 uses an 8-bit register and a shifter to perform the operation of formula (1).
  • the calibration unit may include a temperature sensor in order to sense the current temperature.
  • the calibration unit may also obtain the current temperature from outside the optical module.
  • FIG. 2 shows a calibration curve corresponding to formula (1), which may correspond to a preset tracking characteristic curve of the optical module, that is, a curve to be calibrated.
  • the X axis represents the monitoring current feedback value MONDAC
  • the Y axis represents the output optical power P of the optical module or the operating current I w of the optical module.
  • the monitoring current feedback value MONDAC and the output optical power are approximately linear.
  • the monitoring current feedback value MONDAC is less than a certain value, it can be considered that the output optical power of the optical module always changes according to the first slope relative to the monitoring current feedback value.
  • the output optical power of the optical module changes according to the second slope with respect to the monitoring current feedback value. That is, the specific value corresponds to the sudden change point of the slope.
  • an 8-bit (ie, range 0 to 127) register may be used to store the monitoring current feedback value MONDAC value, and the setting is such that the maximum value of the 8-bit register, that is, 127 corresponds to the slope change point. It can be understood that when the MONDAC value is greater than 127, two 8-bit registers can be used. In a scenario, the first slope is S, and the second slope is 4S, that is, the second slope is 4 times the first slope.
  • FIG. 2 exemplarily shows two points N and M on the x axis (MON DAC axis), which respectively represent two different monitoring current feedback values MONDAC.
  • the monitoring current feedback value N corresponds to the output optical power P 1
  • the monitoring current feedback value M corresponds to the output optical power P 2 .
  • the collected raw monitoring current feedback value is M.
  • a tracking error occurs when the temperature rises to T2
  • the monitoring current feedback value M is still collected.
  • the optical module will mistakenly believe that the current output optical power is still maintained at the desired optical power Power P 2 , so the drive current is not adjusted, so that the phenomenon of unstable output power will occur.
  • the monitoring current feedback value can be calibrated from M to N, for example, so that the optical module can correctly recognize the change of the output optical power based on the change of the monitoring current feedback value, thereby adjusting the driving current to maintain the output light Power stability. In this way, the output optical power is kept stable with respect to the temperature change, thereby achieving temperature compensation for the optical module.
  • the wearable device has the following two characteristics: 1) Because the space is relatively closed, the ventilation and heat dissipation are not smooth, and the actual application temperature is high; 2) Because the space is limited, the working environment is clean and the noise is low, and the quality of the transmitted signal is good. These two characteristics lead to the change of the output optical power of the optical module relative to the temperature of the wearable device is relatively gentle, so the compensation range does not need to be too large.
  • the compensation range can be reduced for the characteristics of the wearable device, and thus the calibration unit 122 can perform linear calibration using formula (2):
  • TE is the tracking error value
  • MONDAC before is the monitoring current feedback value before calibration, that is, the original monitoring current feedback value
  • MONDAC after is the monitoring current feedback value after calibration.
  • TE represents the ratio of the output optical power at the current temperature to the output optical power at the reference temperature under the same monitoring current.
  • the acquired MONDAC can be represented by 5 bits.
  • a 5-bit register and a shifter may be used to complete the operation of formula (2) to achieve optical power temperature compensation.
  • Fig. 3 shows a calibration curve corresponding to formula (2).
  • P x is the output optical power
  • I w is the operating current of the optical module
  • MONDAC is the monitoring current feedback value.
  • a 5-bit register that is, a storage range of 0 to 31
  • the abscissa 31 represents the maximum value of the 5-bit register, and it is set to the MONDAC value corresponding to the sudden change in slope.
  • FIG. 3 also exemplarily shows two points N ′ and M ′ on the x-axis (MON DAC axis), which respectively represent two different monitoring current feedback values MONDAC and respectively correspond to the optical power P 1 ′ and P 2 '.
  • the slope before the abrupt change point in FIG. 3 is S / 4
  • the slope after the abrupt change point is S, that is, the change in output optical power relative to the change in the monitoring current feedback value It's more gentle.
  • the monitoring current feedback value is calibrated from M 'to N' according to the scheme of formula (2), which can make the optical module track that the output optical power is actually P 1 'instead of P 2 '. Adjust the corresponding drive current. Since the slope shown in FIG. 3 is S / 4, that is, the output optical power changes smoothly, the compensation range is small.
  • this embodiment of the present disclosure realizes a smaller compensation range, and can implement real-time calculation, simplifying operation and saving storage space.
  • the optical module includes a light emitting diode as the light emitting component 110, and a driver 120 composed of a calibration unit 122 and a driving current setting unit 124.
  • the calibration unit 122 may include a photodiode 1222 for receiving a backlight and generating a monitoring current Im according to the backlight, an amplifier A1 for amplifying the monitoring current Im, and an analog-to-digital conversion for converting the amplification result of the monitoring current Im into a digital signal Device (A / D) and single chip microcomputer (MCU, micro control unit) 1221.
  • the photodiode 1222 is used to generate a monitoring current Im under the illumination of the backlight.
  • the monitoring current is amplified by the amplifier A1 and then converted to the original monitoring current feedback value MONDAC before of the current monitoring current through the analog-to-digital converter.
  • the single chip microcomputer 1221 includes a calculator and a memory, in which the tracking error values of different temperatures relative to the reference temperature are stored in the memory, the calculator can obtain the tracking error value TE of the current temperature from the reference temperature according to the current temperature, and from the modulus
  • the converter obtains the original monitoring current feedback value MONDAC before of the current monitoring current, and then obtains the calibrated monitoring current feedback value MONDAC after by calculation according to TE and MONDAC before .
  • the calibration unit 122 is an analog circuit and a combination circuit for the control unit, which is used to obtain the original monitoring current feedback value MONDAC before corresponding to the current monitoring current of the light emitting component, and to obtain the tracking of the current temperature relative to the reference temperature An error value TE, and the original monitoring current feedback value MONDAC before is calibrated based on the tracking error value TE to obtain a calibrated monitoring current feedback value MONDAC after .
  • the driving current setting unit 124 may include a data voltage input circuit, a modulation current circuit, a bias current circuit, an amplifier A3 for providing a reference voltage V ref , and a number for converting the calibrated monitoring current feedback value MONDAC after to an analog signal Analog-to-digital converter (D / A), comparator A2 for comparing the corrected analog signal converted by MONDAC after and the reference voltage V ref .
  • D / A analog signal Analog-to-digital converter
  • the data voltage input circuit includes a first triode V1 and a second triode V2, wherein the collector of the first triode V1 and the collector of the second triode V2 are respectively input to the light emitting component 110
  • the terminal is connected to the output terminal, the base of the first transistor V1 and the base of the second transistor V2 form the data voltage input port, the emitter of the first transistor V1 and the emitter of the second transistor V2 They are used for electrical connection with the third resistor R3.
  • the input terminal of the light emitting component 110 is also electrically connected to the power supply voltage VCC.
  • the modulation current circuit includes a third resistor R3.
  • the bias current circuit includes a third transistor V3 and a fourth resistor R4, wherein the collector of the third transistor V3 is electrically connected to the output end of the light emitting component 110, and the emitter of the third transistor V3 is used for It is electrically connected to the input terminal of the fourth resistor R4, and the output terminal of the fourth resistor R4 is used to be electrically connected to the ground line.
  • the bias current circuit is used to adjust the bias current I BIAS through the light emitting component 110 under the control of the base of the third transistor V3, wherein the modulation current I MON and the bias current I BIAS form the drive current of the optical module .
  • the input terminal of the digital-to-analog converter (D / A) is electrically connected to the output terminal of the single-chip microcomputer 1221, and is used to convert MONDAC after to a corrected analog signal.
  • the two input terminals of the comparator A2 are electrically connected to the output terminal of the digital-to-analog converter (D / A) and the output terminal of the amplifier A3 respectively, and the output terminal of the comparator A2 is electrically connected to the base electrode of the third transistor V3
  • the two input terminals of the amplifier A3 respectively input a signal reference voltage and a DC reference voltage.
  • the amplifier A3 can output the reference voltage V ref according to the signal reference voltage and the DC reference voltage
  • the comparator A2 will output a control signal according to the reference voltage V ref and the corrected analog signal, and the control signal is loaded on the third transistor V3
  • the base electrode adjusts the bias current I BIAS through the light emitting component 110.
  • the driving current setting unit 124 can set the driving current based on the calibrated monitoring current feedback value MONDAC after to control the output optical power of the light emitting component to emit the optical signal.
  • the driver 120 appears as a circuit in which an analog circuit and a micro control unit are combined.
  • FIG. 4 illustrates a driving method of an optical module according to an embodiment of the present disclosure, to implement temperature compensation and output optical power control of the optical module.
  • the driving method of the optical module includes:
  • the original monitoring current feedback value MONDAC before corresponding to the current monitoring current of the light emitting component 110 is acquired.
  • the original monitoring current feedback value can be obtained by collecting the monitoring current of the light emitting component.
  • the monitoring current may be the photocurrent of the photodiode given the reverse voltage of the photodiode.
  • the analog value of the collected monitoring current can be converted to the original monitoring current feedback value through analog-to-digital conversion.
  • the tracking error value TE of the current temperature relative to the reference temperature is obtained.
  • the initial value of the tracking error and the corresponding initial monitoring current feedback value may be acquired, and the calibration operation may be started therefrom.
  • the initial value of the tracking error may be provided by the manufacturer and stored in the optical module in advance, for example, in the storage unit of the driver.
  • step 406 the original monitoring current feedback value MONDAC before is calibrated based on the tracking error value TE to obtain the calibrated monitoring current feedback value MONDAC after .
  • the original monitoring current feedback value MONDAC before is linearly calibrated based on the tracking error value TE to obtain the calibrated monitoring current feedback value MONDAC after .
  • linear calibration is performed based on the following formula:
  • linear calibration is performed based on the following formula:
  • the driving current is set based on the calibrated monitored current feedback value MONDAC after to control the output optical power of the light emitting component.
  • the optical module may control the increase or decrease of the output optical power of the light emitting component by setting a bias current and / or a modulation current to drive the light emitting component, so as to keep the performance index of the optical module stable.
  • the monitoring current feedback value for adjusting the performance index of the optical module is calibrated using the tracking error. Since the calibrated monitoring current feedback value can enable the optical module to more accurately determine the change of the output optical power of the optical module, this allows the automatic power control of the optical module (such as the adjustment of the drive current) to be better adapted to the output light Changes in power to maintain the stability of the output optical power of the optical module relative to temperature changes. This realizes temperature compensation for the optical module and improves the performance of the optical module.
  • FIG. 5 illustrates the output optical power curve of 15 optical modules tested after applying the solution according to the embodiment of the present disclosure.
  • the relationship between the component temperature and the optical module temperature in the test environment is exemplarily shown in Table 1.
  • each point on the curve of the 25 ° C scheme 1 represents the output optical power of each optical module calibrated using the formula (1) at an operating temperature of 25 ° C, while the points on the second curve of the 25 ° C scheme represent the When the operating temperature is 25 ° C, the output optical power of each optical module calibrated according to formula (2) is used.
  • the output optical power after calibration according to the solution of the embodiment of the present disclosure remains stable, which improves the performance of the optical module.
  • the output optical power of some optical modules in the 25 ° C scheme 2 curve is increased.
  • the output optical power value of the optical module is improved at 25 ° C.
  • the optical module whose power is not increased is to balance the contradiction between the extinction ratio and the power; since the improvement of the extinction ratio and the optical power is appropriately compromised according to the scheme of the present disclosure, the optimal performance of the optical module is ensured.
  • Table 2 shows the data information including the output power, monitoring current, threshold current and output current collected by the optical module of the present disclosure during the test.
  • the data information shown is obtained by averaging each optical module.
  • the output power refers to the optical power output from the light emitting diode when the preset current reaches a prescribed modulation current.
  • the monitoring current refers to the photocurrent value of the photodiode at a given photodiode reverse voltage when the specified light-emitting diode output power is given.
  • the threshold current is the current that the light-emitting diode must reach to work properly.
  • the output current refers to the working current corresponding to the output power.
  • the threshold current of the optical module changes greatly.
  • the drive current is adjusted based on the calibrated monitoring current feedback value, so that the output power of the optical module remains basically stable under different temperature conditions of -40 ° C, 25 ° C and 95 ° C , Thereby improving the performance of the optical module.
  • FIG. 6 illustrates an exemplary schematic diagram of a wearable device according to an embodiment of the present disclosure.
  • the wearable device may include VR and AR devices.
  • wearable devices also include other types of personal interaction devices and other small devices developed in the future that require the use of optical communication technology.
  • the wearable device 610 includes an optical module 612 according to an embodiment of the present disclosure, and communicates through the optical module 612.
  • the wearable device is connected to the optical fiber 620 through the optical module 612 for high-speed data stream transmission with the server 630 or other processors, for example.
  • the driver of the optical module and the circuit of the VR device can be integrated as a whole, and the light emitting component (such as a laser and its integrated chip) is directly soldered to the VR Circuit board of the device.
  • Various embodiments of the present disclosure may be implemented by using hardware units, software units, or a combination thereof.
  • hardware units may include devices, components, processors, microprocessors, circuits, circuit elements (eg, transistors, resistors, capacitors, inductors, etc.), integrated circuits, application specific integrated circuits (ASICs), programmable logic Device (PLD), digital signal processor (DSP), field programmable gate array (FPGA), memory unit, logic gate, register, semiconductor device, chip, microchip, chipset, etc.
  • Examples of software units may include software components, programs, applications, computer programs, application programs, system programs, machine programs, operating system software, middleware, firmware, software modules, routines, subprograms, functions, methods, processes, Software interface, application program interface (API), instruction set, calculation code, computer code, code segment, computer code segment, word, value, symbol, or any combination thereof.
  • API application program interface

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Abstract

一种光模块，包括：光发射组件（110）和驱动器（120）。光发射组件（110）用于基于驱动电流发射光信号。驱动器（120）包括：校准单元（122）和驱动电流设置单元（124）。校准单元（122）用于获取对应于光发射组件（110）的当前监视电流的原始监视电流反馈值MONDACbefore，以及用于获取当前温度相对基准温度的跟踪误差值TE，且基于跟踪误差值TE校准原始监视电流反馈值MONDACbefore以得到校准后的监视电流反馈值MONDACafter。驱动电流设置单元（124）用以基于校准后的监视电流反馈值MONDACafter设置驱动电流以控制光发射组件（110）发射光信号的输出的光功率。通过以简单的方式校准监视电流并补偿跟踪误差，更好地对光模块进行温度补偿。

Description

可穿戴设备、光模块及其驱动方法
交叉引用
本公开要求于2018年10月23日提交的申请号为201811238950.2、名称为“光模块及其温度补偿方法”的中国专利申请的优先权，该中国专利申请的全部内容通过引用全部并入本文。
技术领域
本公开涉及光通信，更具体而言，涉及一种可穿戴设备、光模块及其驱动方法。
背景技术
可穿戴设备(例如虚拟现实(VR)或者增强现实(AR)设备)为了获取良好的沉浸感和用户体验，需要用高速数据流传输至服务器或其他处理器。由于传输容量和速率的不断提高，现有的普通传输模式/协议标准MIPI(移动行业处理器接口)、HDMI(高清晰度多面接口)等因传输速率难以超过20Gbps而不能满足使用要求。连接光模块通过光纤传输，则传输速率可以轻松实现40Gbps/100Gbps，且400Gbps升级版也在试验中。因此，采用光纤通信势必会成为VR或者AR设备的主要传输模式。
MSA(Multi-Source Agreement)是小型可热插拔光收发模块(简称光模块)的多源协议。MSA统一了光收发器封装，因此，符合MSA的光收发器是当前光发射机和接收机的主要形式。因为当前使用光模块的设备(例如VR或者AR设备)的尺寸越来越小，为满足新服务和先进技术的需求，MSA协议的一个完善内容是小型化。由于小型化导致接口板的接口密度越来越高，所以散热与温度管理成为关注重点。作为光纤接入网络设备的核心，光模块的输出特性会受到温度的影响，因此，其温度补偿成为重中之重。
光模块的温度补偿方法目前有缩放法、热敏电阻补偿法和三温拟合法。缩放法采用曲线补偿的方式，但是其必须提供许多组实验曲线，消耗巨大。热敏电阻补偿法通过热敏电阻进行补偿，但由于其需要焊接电阻，导致精度提升受限，数据不准确。三温拟合法通过在常温(25℃)、高温与低温三个温度点测试光模块的功率、取点而拟合通用校准曲线，但是其所采用的测试平台复杂，测试时间长，而且不具有统一标准。
发明内容
根据本公开的第一方面，提供了一种光模块，包括：
光发射组件，用于基于驱动电流发射光以输出光功率；和
驱动器，包括：
校准单元，用于获取对应于光发射组件的当前监视电流的原始监视电流反馈值 MONDAC before，以及用于获取当前温度相对基准温度的跟踪误差值TE，且基于所述跟踪误差值校准所述原始监视电流反馈值MONDAC before以得到校准后的监视电流反馈值MONDAC after；和
驱动电流设置单元，用以基于所述校准后的监视电流反馈值MONDAC after设置所述驱动电流以控制所述光发射组件输出的光功率。
可选地，所述校准单元被配置为基于所述跟踪误差值TE线性校准所述原始监视电流反馈值MONDAC before。
可选地，所述校准单元被配置为按照如下方程进行所述校准：
Figure PCTCN2019110485-appb-000001
可选地，所述校准单元被配置为按照如下方程进行所述校准：
Figure PCTCN2019110485-appb-000002
可选地，所述驱动器为模拟电路与微控制单元相组合的电路。
可选地，所述光模块还包括存储单元，用于存储跟踪误差值TE。所述校准单元被配置为从所述存储单元读取所述跟踪误差值TE。
可选地，所述原始监视电流反馈值MONDAC before是通过采集光发射组件的监视电流的模拟量Im，且对该模拟量Im进行模/数转换而得到的。
可选地，所述校准单元采用5比特寄存器和移位器来实现下式的计算：
Figure PCTCN2019110485-appb-000003
可选地，所述校准单元采用8比特移位器来实现下式的计算：
Figure PCTCN2019110485-appb-000004
根据本公开的第二方面，提供了一种光模块的驱动方法，包括以下步骤：获取对应于所述光模块的光发射组件的当前监视电流的原始监视电流反馈值MONDAC before；获取当前温度相对基准温度的跟踪误差值TE；基于所述跟踪误差值TE校准所述原始监视电流反馈值MONDAC before以得到校准后的监视电流反馈值MONDAC after；和基于所述校准后的监视电流反馈值MONDAC after设置所述驱动电流以控制所述光发射组件输出的光功率。
可选地，基于所述跟踪误差值TE校准所述原始监视电流反馈值MONDAC before包括，基于所述跟踪误差值TE线性校准所述原始监视电流反馈值MONDAC before。
可选地，计算校准后的监视电流MONDAC after按照如下的方程进行：
Figure PCTCN2019110485-appb-000005
可选地，计算校准后的监视电流MONDAC after按照如下的方程进行：
Figure PCTCN2019110485-appb-000006
可选地，获取当前温度相对基准温度的跟踪误差值TE包括从所述光模块的存储单元中读取所述跟踪误差值TE。
可选地，所述原始监视电流反馈值MONDAC before是通过采集光发射组件的监视电流的模拟量I m，且对该模拟量I m进行模/数转换而得到的。
根据本公开的第三方面提供了一种可穿戴设备，其包括根据本公开的第一方面的光模块。
附图说明
通过阅读以下的详细说明和仔细查看相关联的附图，这些和其它的特征与优点将是明显的。应当明白，上述的一般性说明和以下的详细说明均仅仅是说明性的，而不是对所要求保护的方面的限制。
图1图示了根据本公开实施例的光模块的结构示意图。
图2图示了根据本公开一个示例实施例的校准曲线。
图3图示了根据本公开另一个示例实施例的校准曲线。
图4图示了一种光模块的驱动方法。
图5图示了光模块应用不同方案的输出光功率曲线的对比。
图6图示了根据本公开实施例的可穿戴设备的示例示意图。
图7图示了根据本公开实施例的光模块的结构示意图。
具体实施方式
各种实施例针对光模块及其驱动方法。与在网络运营商中的常规使用环境不同，可穿戴设备的内部环境通风散热不畅，但相对密封。因此，光模块应用于可穿戴设备时，具有组件温度较高、但噪声较小、传输信号质量高的特点。鉴于此，本公开提出了在诸如VR和AR设备等的可穿戴设备环境中所使用的光模块及其驱动方法，以保持光模块的输出光功率温度。
光模块是实现电光转换的器件，其通过控制调整光发射组件中的发光元件的驱动电流的大小来输出所期望的光功率，其中，发光元件可以为发光二极管、激光二极管或者其他电流驱动的发光元件。输出光功率的稳定性是光模块的重要性能指标。在相关技术中，为保持输出光功率的稳定，通常通过光发射组件内部的背光探测器(例如光电二极管)跟踪经背光转换的背光电流来监视光发射组件的输出光功率，因此背光电流也经常被称为监视电流。一旦监视电流发生变化，就判定输出光功率发生了变化，此时会相应地调整光发射组件的驱动电流来进行光功率控制，以保持输出光功率的稳定。
但是，在实际中，当环境温度发生变化时，背光探测器的跟踪特性(可通过监视电流随输出光功率的变化来表示)会发生变化。举例而言，当温度从T1变化到T2时，尽管光发射组件的输出光功率可能从P变化到P’，但是背光探测器仍可能监测到相同的监视电流I m，这样便产生了跟踪误差(Tracking Error，又称示踪误差)。在相关技术中，跟踪误差常常被简化表示为，光发射组件在两个不同温度条件下跟踪到相同监视电流时，输出光功率间的差异。因此，如果以某一温度为基准温度，则不同温度下的跟踪误差变化也反映了输出光功率的变化。
然而，在现有的光模块中，为实现上的方便，通常不考虑温度的变化(也即将环境温度默认为处于某个预定的温度)，而采用一个固定的预设跟踪特性曲线来表征背光探测器的跟踪特性，即：只要监视电流Im相同，就认为光发射组件发射的光功率P相同，反之亦然。这样，在环境温度从预定温度变化到其他温度时，如果光模块始终采用该预设跟踪特性曲线(对应单个预定的温度)来从监视电流判断光发射组件的输出光功率，就会因跟踪误差的影响而误判光发射组件的输出光功率，导致对光发射组件的驱动电流的控制出现误差，因而难以达到保持光功率稳定性的目的。
发明人认识到，如果将光模块中所采用的预设跟踪特性设定为基准温度的跟踪特性，那么通过补偿其他温度相对于基准温度的跟踪误差，即将其他温度下的监视电流校准到基准温度下的监视电流，光模块即便依据单个跟踪特性曲线，也能正确地判断输出光功率的变化，实现有效的自动功率控制。因为光发射组件能够在不同温度下保持输出光功率的稳定性，由此实现了温度补偿。
图1图示了根据本公开实施例的光模块的结构示意图。该光模块100包括光发射组件110和驱动器120。
光发射组件110用于基于驱动电流发射光信号以输出光功率。在正常工作时，当通过光发射组件110的驱动电流超过阈值电流Ith时，光发射组件110可产生并保持连续的光功率输出。当驱动电流相对于阈值电流Ith的差值相对稳定时，光发射组件110可以保持基本稳定的输出光功率。当用于驱动光发射组件110的调制电流适配于偏置电流和阈值电流时，可以使得光发射组件110发出的光信号保持相对稳定的消光比。在一些实施例中，光发射组件110可以包括发光二极管LED或半导体激光二极管LD等发光元件。在示例中，光发射组件110可以包括VCSEL激光器(垂直表面腔发射激光器)、FP激光器(法布里-珀罗激光器)或DFB激光器(分布式反馈激光器)等。
驱动器120包括校准单元122和驱动电流设置单元124。校准单元122用于获取对应于光发射组件110的当前监视电流的原始监视电流反馈值MONDAC before；获取当前温度相对基准温度的跟踪误差值TE，且基于所述跟踪误差值TE来线性校准所述原始监视电流反馈值MONDAC before以得到校准后的监视电流反馈值MONDAC after。
这里，当前温度相对基准温度的跟踪误差值TE表示当前温度的跟踪特性与基准温度 的跟踪特性的差异。在一些实施例中，跟踪特性通过输出光功率与监视电流的比值来表示。相应地，跟踪误差可以由当前温度和基准温度的输出光功率与监视电流的比值的差异来表示。基准温度下的跟踪特性曲线是校准单元122所基于的用于设置驱动电流的跟踪特性曲线。
监视电流反馈值是与模拟监视电流相对应的数字值。在基准温度的跟踪特性曲线中，监视电流反馈值与光模块的输出光功率存在确定的一一对应的关系。在一些实施例中，可以将光模块所采用的预设跟踪特性曲线作为基准温度的跟踪特性曲线，且光模块将按照该预设跟踪特性曲线查找与监视电流反馈值对应的输出光功率，并据此判断输出光功率的变化以进行相应的输出光功率控制。
驱动电流设置单元124用于基于所述校准后的监视电流反馈值MONDAC after设置所述驱动电流，以控制所述光发射组件发射光信号的输出光功率。在一些实施例，驱动电流的设置包括偏置电流和调制电流的设置。可以通过控制偏置电流来保持输出光功率的稳定，以及通过控制调制电流来保持消光比的稳定。
按照本公开的方案，驱动电流的设置是基于利用跟踪误差值校准后的监视电流，也即经过温度补偿后的监视电流，而非直接采集得到的监视电流。由于通过校准，采集得到的监视电流被映射到调整驱动电流所依据的基准温度下的监视电流，使得驱动电流设置单元能更准确地跟踪输出光功率的变化，以便减小输出光功率的控制误差。因为减小了控制误差，所以光发射组件能够输出稳定的输出光功率。换言之，因为输出光功率相对温度变化保持稳定，所以实现了对输出光功率的温度补偿。
在一个实施例中，原始监视电流反馈值MONDAC before是通过采集光发射组件110的监视电流的模拟量I m，且对该模拟量I m进行模/数转换而得到的。在另一个实施例中，原始监视电流反馈值MONDAC before是随监视电流的模拟量I m而线性变化的数字值。示例性地，原始监视电流反馈值MONDAC before是基于具体电路实现的、与监视电流的模拟量I m成线性关系的数字值。
在一个实施例中，初始地，校准单元122可以获取跟踪误差初始值TE 0作为当前温度的跟踪误差值TE。跟踪误差初始值TE 0可以被设置为在某个温度下光模块的实际跟踪特性相对于基准温度的跟踪特性(例如光模块所采用的预设跟踪特性)的跟踪误差。跟踪误差初始值TE 0可以根据光模块内部器件(主要包括光发射组件)的特性而测量得出。可选地，可以由光模块的厂商根据各自光模块的内部器件的特性，依据自定义的测试算法来提供跟踪误差初始值TE 0，以及提供与该跟踪误差初始值TE 0对应的表征预定输出光功率的初始监视电流反馈值MONDAC 0。可以从TE 0和初始监视电流反馈值MONDAC 0开始进行监视电流反馈值的校准。在一些实施例中，由于设备的初始工作温度可能为25℃，所以可以使用设备测试环境温度为25℃的TE值作为TE 0，且可以预设此时对应的初始监视电流反馈值MONDAC 0表征输出光功率1dBm。
在另一些实施例中，校准单元122还可以获取当前温度所对应的某个温度范围的跟踪误差值TE作为当前温度的跟踪误差值TE。温度范围可以是比如高温、室温(例如20℃-25℃)、低温等，或者是按预定间隔划分的温度区间，或者是依据光模块工作时的主要温度范围划分的间隔不等的温度区间。类似地，某个温度范围的跟踪误差值TE可以由光模块的厂商根据各自光模块的内部器件的特性，依据自定义的测试算法来提供。在一些实施例中，校准单元122还可以通过基于跟踪误差初始值TE 0和温度变化值计算得到的当前温度的跟踪误差值TE。如前所述，由于跟踪误差造成的输出光功率的变化可以近似为一种线性关系，所以当前温度的跟踪误差值TE可以是从跟踪误差初始值TE 0开始随温度而线性变化的值。
在一些实施例中，驱动器120可以包含存储单元，用于存储跟踪误差初始值TE 0和初始监视电流反馈值MONDAC 0。在这些实施例中，校准单元122从存储单元中获取跟踪误差初始值和初始监视电流反馈值MONDAC 0且从其开始校准。在一些实施例中，存储单元还可以存储对应不同温度或者不同温度范围的跟踪误差值TE，或者计算得到的跟踪误差值TE。正如已知的，示例性地，跟踪误差值TE可以通过测量不同温度下光发射组件的输出光功率来获得。
在一些实施例中，光模块的输出光功率具有预定的正常工作范围，且相应地，监视电流反馈值MONDAC具有对应的有效数值范围。这样，当监视电流反馈值MONDAC超出该数值范围(其表明输出光功率可能已超出正常工作范围)时，还可以以步进的方式调整(例如增加或者降低)跟踪误差值TE，以将监视电流反馈值MONDAC维持在该数值范围内，这相应地表明输出光功率也在正常工作范围内。
在一些实施例中，已校准的监视电流反馈值MONDAC after可以被通过数/模转换而转换为对应的模拟量。
在一个实施例中，驱动器120可以被实现为模拟电路与微控制单元(例如单片机MCU)相组合的电路。
在一个实施例中，校准单元122按照公式(1)进行线性校准：
Figure PCTCN2019110485-appb-000007
其中，TE为跟踪误差值，MONDAC before为校准前的监视电流反馈值，即原始监视电流反馈值，MONDAC after为校准后的监视电流反馈值。示例性地，TE表示相同监视电流的条件下，当前温度的输出光功率与基准温度的输出光功率的比值。
示例性地，在一种实现方式中，校准单元122采用8-bit寄存器和移位器来进行公式(1)的运算。
可选地，校准单元可以包括温度传感器，以便感测当前温度。替换地，校准单元也可以从光模块外部获取当前温度。
图2示出了对应公式(1)的一种校准曲线，其可以对应光模块的预设跟踪特性曲线， 也即要被校准到的曲线。这里，X轴(MON DAC轴)表示监视电流反馈值MONDAC；Y轴(I w轴)表示光模块的输出光功率P或者光模块工作电流I w。如图2所示，监视电流反馈值MONDAC和输出光功率之间近似成一次函数关系。当监视电流反馈值MONDAC小于某个特定数值时，可以认为光模块的输出光功率相对于监视电流反馈值一直按照第一斜率变化。当监视电流反馈值大于该特定数值时，光模块的输出光功率相对于监视电流反馈值按照第二斜率变化。也即，该特定数值对应了斜率的突变点。
示例性地，可以使用8比特(即范围0～127)寄存器来存储监视电流反馈值MONDAC值，且设置使得8比特寄存器的最大值，也即127对应斜率突变点。可以理解，当MONDAC值大于127时，可以使用2个8比特寄存器。在一个场景中，第一斜率为S，而第二斜率为4S，也即第二斜率为第一斜率的4倍。
图2中示例性地示出了x轴(MON DAC轴)上的两个点N、M，其分别表示两个不同的监视电流反馈值MONDAC。监视电流反馈值N与输出光功率P 1相对应，而监视电流反馈值M与输出光功率P 2相对应。
假设在温度T1时，当光模块输出期望的光功率P 2时，所采集的原始监视电流反馈值为M。考虑温度上升到T2时出现跟踪误差的情况，也即：可能出现光模块的输出光功率虽然已下降到P 1，但仍采集到监视电流反馈值M的情况。此时，如果不对所采集的原始监视电流反馈值进行校准，则按照图示的跟踪特性曲线，由于监视电流反馈值未变化，光模块将错误地认为目前的输出光功率仍保持在期望的光功率P 2，因而不对驱动电流进行调整，由此会出现输出光功率不稳定的现象。而通过按照本公开的方案，可以将监视电流反馈值例如从M校准到N，使得光模块基于监视电流反馈值的变化而正确认识到输出光功率的变化，由此调整驱动电流以保持输出光功率的稳定。这样使得输出光功率相对于温度变化保持稳定，从而实现了对光模块的温度补偿。
发明人认识到可穿戴设备的内部环境不同于网络运营商所使用的常规环境。具体地，可穿戴设备具有以下两个特点：1)因空间相对密闭，所以通风散热不畅，实际应用温度高；2)因空间有限，所以工作环境干净，噪声小，进而传输信号质量好。这两个特点导致对于可穿戴设备而言，其光模块的输出光功率相对于温度的变化较为平缓，因此补偿范围无需过大。
在一个实施例中，针对可穿戴设备的特点可以缩小补偿范围，且由此校准单元122可以使用公式(2)进行线性校准：
Figure PCTCN2019110485-appb-000008
其中，TE为跟踪误差值，MONDAC before为校准前的监视电流反馈值，即原始监视电流反馈值，MONDAC after为校准后的监视电流反馈值。示例性地，TE表示相同监视电流的条件下，当前温度的输出光功率与基准温度的输出光功率的比值。
在这个实施例中，由于补偿范围缩小，所以所获取的MONDAC可以用5比特来表示。示例性地，在一种实现方式中，可以利用5-bit寄存器和移位器来完成公式(2)的运算，以实现光功率温度补偿。
替换地，由于在数字电路中二进制乘法实现由移位器完成，而"x4"的操作相当于左移2位，且因为在实现公式(2)的运算时无需保留前一次MONDAC值，也即运算结果可以被覆盖，所以在另一实施例中，可以取代5比特寄存器与移位器的组合，而使用单个寄存器(寄存器的最小单元可以是8-bit)来完成公式(2)的计算。也即，在5比特MONDAC值的情况下，由于8比特寄存器中除5比特用于存储MONDAC值外还剩余3比特，所以这3比特可以被直接移位占用来实现二进制乘法。这可以进一步简化操作，节省存储空间。而且，这种迭代操作的算法实现保证了CPU类处理器运算速度最优，仅MCU(微控制单元)平台即可完成实时运算，实现跟踪补偿，而无需MONDAC拟合曲线、查表等。
图3示出了对应公式(2)的一种校准曲线。在图3中，类似于图2，P x为输出光功率，I w为光模块工作电流，MONDAC为监视电流反馈值。这里，采用5比特寄存器(即存储范围是0～31)来存储监视电流反馈值，横坐标31表示5比特寄存器的最大值，且将其设置为对应斜率发生突变的MONDAC值。
图3中同样示例性地示出了x轴(MON DAC轴)上的两个点N’、M’，其分别表示两个不同的监视电流反馈值MONDAC且分别对应于光功率P 1’和P 2’。相比于图2，图3中所示的在斜率突变点之前的斜率为S/4，在斜率突变点之后的斜率为S，也即相对于监视电流反馈值的变化，输出光功率的变化更为平缓。
从图3可见，按照公式(2)的方案将监视电流反馈值从M’校准到N’，可以使光模块跟踪到输出光功率实际上为P 1’而非P 2’，由此而进行相应的驱动电流的调整。由于图3中所示斜率为S/4，也即输出光功率变化平缓，所以补偿范围较小。
本公开的这一实施例针对可穿戴设备的特点，实现了较小的补偿范围，且可以实现实时运算，简化了操作并节省了存储空间。
下面，示例性地提供一种光模块的电路结构示意图，以便进一步地解释和说明本公开提供的光模块的结构和原理。
在该示例中，如图7所示，光模块包括作为光发射组件110的发光二极管，以及由校准单元122和驱动电流设置单元124组成的驱动器120。
其中，校准单元122可以包括用于接收背光并根据背光产生监视电流Im的光电二极管1222、用于放大监视电流Im的放大器A1、用于将监视电流Im的放大结果转化为数字信号的模数转换器(A/D)以及单片机(MCU，微控制单元)1221。光电二极管1222用于在背光的照射下产生监视电流Im，监视电流经过放大器A1放大后，经过模数转换器转变为当前监视电流的原始监视电流反馈值MONDAC before。单片机1221包括计算器和存储器，其中，存储器中存储有不同温度相对基准温度的跟踪误差值，计算器可以根据当前温度而 从存储器中获取当前温度相对基准温度的跟踪误差值TE，并从模数转换器获取当前监视电流的原始监视电流反馈值MONDAC before，然后根据TE和MONDAC before通过计算获得校准后的监视电流反馈值MONDAC after。如此，校准单元122为模拟电路与为控制单元向组合的电路，其用于获取对应于光发射组件的当前监视电流的原始监视电流反馈值MONDAC before，以及用于获取当前温度相对基准温度的跟踪误差值TE，且基于所述跟踪误差值TE校准所述原始监视电流反馈值MONDAC before以得到校准后的监视电流反馈值MONDAC after。
驱动电流设置单元124可以包括数据电压输入电路、调制电流电路、偏置电流电路、用于提供参考电压V ref的放大器A3、用于将校准后的监视电流反馈值MONDAC after转变为模拟信号的数模转换器(D/A)、用于将MONDAC after转换而成的校正后的模拟信号与参考电压V ref进行比较的比较器A2。其中，数据电压输入电路包括第一三极管V1和第二三极管V2，其中，第一三极管V1的集电极和第二三极管V2的集电极分别与光发射组件110的输入端和输出端连接，第一三极管V1的基极和第二三极管V2的基极组成数据电压输入端口，第一三极管V1的发射极和第二三极管V2的发射极分别用于与第三电阻R3电连接。其中，光发射组件110的输入端还与电源电压VCC电连接。调制电流电路包括第三电阻R3，第三电阻R3一端与第一三极管V1的发射极和第二三极管V2的发射极电连接，另一端与接地线电连接，用于提供调制电流I MON的通路。偏置电流电路包括第三三极管V3和第四电阻R4，其中，第三三极管V3的集电极与光发射组件110的输出端电连接，第三三极管V3的发射极用于与第四电阻R4的输入端电连接，第四电阻R4的输出端用于与接地线电连接。偏置电流电路用于在第三三极管V3的基极的控制下调整通过光发射组件110的偏置电流I BIAS，其中，调制电流I MON和偏置电流I BIAS形成光模块的驱动电流。数模转换器(D/A)的输入端与单片机1221的输出端电连接，用于将MONDAC after转化为校正后的模拟信号。比较器A2的两个输入端分别与数模转换器(D/A)的输出端和放大器A3的输出端电连接，比较器A2的输出端与第三三极管V3的基极电连接，放大器A3的两个输入端分别输入信号参考电压和直流参考电压。如此，放大器A3可以根据信号参考电压和直流参考电压而输出参考电压V ref，比较器A2将根据参考电压V ref和校正后的模拟信号输出控制信号，控制信号加载于第三三极管V3的基极以调整通过光发射组件110的偏置电流I BIAS。如此，该驱动电流设置单元124能够基于校准后的监视电流反馈值MONDAC after设置驱动电流以控制所述光发射组件发射光信号的输出光功率。
如此，该示例的光模块中，驱动器120呈现为模拟电路与微控制单元相组合的电路。
图4图示了根据本公开的实施例的光模块的驱动方法，用以实现光模块的温度补偿和输出光功率控制。该光模块的驱动方法包括：
在步骤402，获取对应于光发射组件110的当前监视电流的原始监视电流反馈值MONDAC before。可选地，原始监视电流反馈值可以通过采集光发射组件的监视电流而获取。在一个实施例中，监视电流可以是在给定光电二极管反向电压的情况下该光电二极管的光 电流。所采集的监视电流模拟量可以通过模/数转换而得到原始监视电流反馈值。
在步骤404，获取当前温度相对基准温度的跟踪误差值TE。在一个实施例中，初始地，可获取跟踪误差初始值和对应的初始监视电流反馈值，并从其开始校准操作。可选地，跟踪误差初始值可以由厂商提供，且被预先存储在光模块中，例如存储在驱动器的存储单元中。
在步骤406，基于所述跟踪误差值TE来校准所述原始监视电流反馈值MONDAC before以得到校准后的监视电流反馈值MONDAC after。可选地，基于所述跟踪误差值TE来线性校准所述原始监视电流反馈值MONDAC before以得到校准后的监视电流反馈值MONDAC after。
在一个实施例中，线性校准基于下式来进行：
Figure PCTCN2019110485-appb-000009
在另一个实施例中，线性校准基于下式来进行：
Figure PCTCN2019110485-appb-000010
在步骤408，基于所述校准后的监视电流反馈值MONDAC after设置所述驱动电流以控制所述光发射组件的输出光功率。在示例中，光模块可以通过设置用以驱动光发射组件的偏置电流和/或调制电流，来控制光发射组件输出光功率的增加或者减少，以保持光模块的性能指标稳定。
通过按照本公开实施例的光模块，在温度变化过程中，用于光模块性能指标调整的监视电流反馈值被利用跟踪误差而进行校准。由于校准后的监视电流反馈值能够使光模块更准确地判断光模块的输出光功率的变化，所以这使得光模块的自动功率控制(例如驱动电流的调整)能够更好地适配于输出光功率的变化，从而保持光模块输出光功率相对于温度变化的稳定性。这样实现了对光模块的温度补偿，提升了光模块的性能。
实验显示：采用本公开实施例的方案的光模块在不同温度下的输出光功率稳定。这表明通过补偿跟踪误差值TE来实现功率补偿是可行且有效的。
图5图示了在应用按照本公开实施例的方案后对15个光模块进行测试的输出光功率曲线。在测试环境中的组件温度和光模块温度之间的关系示例性地如表1所示。
表1：组件温度与光模块之间的温度的关系
光发射组件温度 -40℃ 25℃ 95℃
光模块温度 -36℃ 36℃ 114℃
在图5中，25℃方案一曲线上的各点代表在工作温度为25℃时采用公式(1)校准后的各光模块的输出光功率，而25℃方案二曲线上的各点代表在工作温度为25℃时采用按照公式(2)校准后的各光模块的输出光功率。
正如图中示出的，按照本公开实施例的方案进行校准后的输出光功率保持稳定，提升了光模块的性能。
而且，相比于25℃方案一曲线，25℃方案二曲线中的一些光模块，例如光模块1-3、 6-8、10、12的输出光功率增加。这表明，经过按照公式(2)进行温度补偿后，25℃时光模块的输出光功率值得到提升。而功率未提升的光模块是为了平衡消光比与功率的矛盾；由于按照本公开的方案对消光比和光功率的改善进行了适当的折中，所以保证了光模块的性能最优。
如所示的，作为对比，在图5中还给出-40℃经验曲线，-40℃是低温测试的温度。相对于低温下的曲线，25℃方案一曲线和25℃方案二曲线更平稳，表明本公开实施例的方案稳定，可以进行实际应用。
表2给出了本公开的光模块在测试中所采集的包括输出功率、监视电流、阈值电流和输出电流等的数据信息。所示数据信息是对各光模块取均值而得到的。
表2：光模块的测试数据
Figure PCTCN2019110485-appb-000011
这里，输出功率是指在预置的电流达到规定的调制电流时，从发光二极管输出的光功率。监视电流是指在规定的发光二极管输出功率时，在给定光电二极管反向电压时，光电二极管的光电流值。阈值电流是发光二极管正常工作所必须达到的电流。输出电流是指输出功率所对应的工作电流。
从表2可以看出，随着温度的升高，光模块的阈值电流发生了较大的改变。在应用本公开实施例的方案后，通过基于校准的监视电流反馈值来进行驱动电流的调整，使得在-40℃、25℃和95℃的不同温度条件下，光模块的输出功率基本保持平稳，由此提升了光模块的性能。
图6图示了根据本公开实施例的可穿戴设备的示例性示意图。该可穿戴设备可以包括VR、AR设备。但如本领域技术人员所理解的，可穿戴设备还包括其他类型的个人交互设备和未来开发的其他需要使用光通信技术的小型设备。
如图6所示，该可穿戴设备610包括按照本公开实施例的光模块612，且通过光模块612进行通信。在一些实施例中，可穿戴设备例如通过光模块612连接光纤620以便与服务器630或者其他处理器进行高速数据流的传输。
在一些实施例中，当在VR设备中增加光模块时，可以将光模块的驱动器与VR设备的电路整合作为整体，而将光发射组件(例如激光器和其内部集成的芯片)直接焊接至 VR设备的电路板。
本公开的各种实施例可以通过使用硬件单元、软件单元或它们的组合而被实施。硬件单元的示例可包括设备、构件、处理器、微处理器、电路、电路元件(例如，晶体管、电阻器、电容器、电感器等等)、集成电路、专用集成电路(ASIC)、可编程逻辑器件(PLD)、数字信号处理器(DSP)、现场可编程门阵列(FPGA)、存储器单元、逻辑门、寄存器、半导体器件、芯片、微芯片、芯片组等等。软件单元的示例可包括软件构件、程序、应用、计算机程序、应用程序、系统程序、机器程序、操作系统软件、中间件、固件、软件模块、例行程序、子程序、函数、方法、过程、软件接口、应用程序接口(API)、指令集、计算代码、计算机代码、代码段、计算机代码段、单词、值、符号、或它们的任何组合。实施例采用何种方式来实施的决定可以针对给定的实现所希望的，来根据任意数量的因素而变化，诸如想要的计算速率、功率电平、耐热性、处理周期预算、输入数据速率、输出数据速率、存储器资源、数据总线速度、和其它设计或性能约束。
一些实施例可以通过使用表达“一个实施例”或“某个实施例”连同它们的派生词而被描述。这些术语是指结合实施例描述的特定特征、结构或特性被包括在至少一个实施例中。在申请书的各个地方出现的词组“在一个实施例中”不一定必须全都指同一个实施例。
附加地，在上述的详细说明中，可以看到，为了简化公开内容，各种特征在单个实施例中被聚合在一起。这种公开的方法不被解译为反映了所要求保护的实施例需要比在每项权利要求中明确叙述的特征更多特征的意图。相反，正如以下的权利要求反映的，本公开的主题在于少于单个公开的实施例的所有特征。因此，以下的权利要求据此被合并到详细说明中，每项权利要求独自地作为单独的实施例。而且，术语“第一”、“第二”、“第三”等等仅仅被用作为标签，且不打算对它们的对象施加数值要求。
虽然本主题是以特定于结构特征和/或方法动作的语言被描述的，但应当明白，在所附权利要求中限定的主题不是必须限于以上描述的具体特征或动作。相反，上面描述的具体的特征和动作是作为实施权利要求的示例性形式被公开的。

Claims (17)

  1. 一种光模块，包括：
    光发射组件，用于基于驱动电流发射光信号；和
    驱动器，包括：
    校准单元，用于获取对应于光发射组件的当前监视电流的原始监视电流反馈值MONDAC before，以及用于获取当前温度相对基准温度的跟踪误差值TE，且基于所述跟踪误差值TE校准所述原始监视电流反馈值MONDAC before以得到校准后的监视电流反馈值MONDAC after；和
    驱动电流设置单元，用以基于所述校准后的监视电流反馈值MONDAC after设置所述驱动电流以控制所述光发射组件发射光信号的输出光功率。
  2. 根据权利要求1所述的光模块，其中所述校准单元被配置为基于所述跟踪误差值TE线性校准所述原始监视电流反馈值MONDAC before。
  3. 根据权利要求1所述的光模块，其中所述校准单元被配置为按照如下方程进行所述校准：
    Figure PCTCN2019110485-appb-100001
  4. 根据权利要求1所述的光模块，其中所述校准单元被配置为按照如下方程进行所述校准：
    Figure PCTCN2019110485-appb-100002
  5. 根据权利要求1所述的光模块，其中所述驱动器为模拟电路与微控制单元相组合的电路。
  6. 根据权利要求1所述的光模块，还包括存储单元，用于存储所述跟踪误差值TE；所述校准单元被配置为从所述存储单元读取所述跟踪误差值TE。
  7. 根据权利要求1所述的光模块，其中所述原始监视电流反馈值MONDAC before是通过采集光发射组件的监视电流的模拟量I m，且对该模拟量I m进行模/数转换而得到的。
  8. 根据权利要求4所述的光模块，其中所述校准单元采用5比特寄存器和移位器来实现下式的计算：
    Figure PCTCN2019110485-appb-100003
  9. 根据权利要求4所述的光模块，其中所述校准单元采用8比特移位器来实现下式的计算：
    Figure PCTCN2019110485-appb-100004
  10. 一种光模块的驱动方法，包括以下步骤：
    获取对应于所述光模块的光发射组件的当前监视电流的原始监视电流反馈值MONDAC before；
    获取当前温度相对基准温度的跟踪误差值TE；
    基于所述跟踪误差值校准所述原始监视电流反馈值MONDAC before以得到校准后的监视电流反馈值MONDAC after；和
    基于所述校准后的监视电流反馈值MONDAC after设置所述驱动电流以控制所述光发射组件输出的光功率。
  11. 根据权利要求10所述的方法，其中，基于所述跟踪误差值校准所述原始监视电流反馈值MONDAC before包括：
    基于所述跟踪误差值线性校准所述原始监视电流反馈值MONDAC before。
  12. 根据权利要求10所述的方法，其中所述校准按照如下的方程进行：
    Figure PCTCN2019110485-appb-100005
  13. 根据权利要求10所述的方法，其中所述校准按照如下的方程进行：
    Figure PCTCN2019110485-appb-100006
  14. 根据权利要求10所述的方法，其中获取当前温度相对基准温度的跟踪误差值TE包括从所述光模块的存储单元中读取所述跟踪误差值TE。
  15. 根据权利要求10所述的方法，其中所述原始监视电流反馈值MONDAC before是通过采集光发射组件的监视电流的模拟量I m，且对该模拟量I m进行模/数转换而得到的。
  16. 一种可穿戴设备，其包括如权利要求1-9中任一项所述的光模块。
  17. 根据权利要求16所述的可穿戴设备，其中所述可穿戴设备是虚拟现实设备或增强现实设备。
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