阅读说明：本技术 具有改进的脉冲形状和减少的频率啁啾的脉冲光发射器 (Pulsed light emitter with improved pulse shape and reduced frequency chirp ) 是由 阚家溪 布沙·依卜 于 2020-01-16 设计创作，主要内容包括：光发射器的设计,其生成在所生成的激光脉冲中具有改进的光波形形状的激光脉冲,并为光发射器的光啁啾提供补偿。这种脉冲光发射器可用于多种应用,包括光探测和测距系统(LiDAR)和其他光学感测系统,诸如光时域反射仪(OTDR)系统,和光通信系统。(The design of a light emitter that generates laser pulses with improved optical waveform shapes in the generated laser pulses and provides compensation for the light chirp of the light emitter. Such pulsed light emitters may be used in a variety of applications, including optical detection and ranging systems (LiDAR) and other optical sensing systems, such as Optical Time Domain Reflectometer (OTDR) systems, and optical communication systems.)

1. A pulsed light emitter, comprising:

a laser generating laser pulses in response to an electric laser control pulse signal;

a laser drive circuit coupled to the laser to apply the electrical lasing control pulse signal to the laser for generating the laser pulses;

a first electrical pulse generator to generate a first electrical pulse signal having a first pulse amplitude and a first pulse width in time;

a second electrical pulse generator to generate a second electrical pulse signal having a second pulse amplitude less than the first pulse amplitude and high enough to cause the laser drive circuit to trigger a laser firing operation in the laser, the second pulse width in time being greater than the first pulse width, the pulse leading edge preceding the pulse leading edge of the first electrical pulse signal; and

a signal mixer is coupled to the first and second electrical pulse generators to receive the first and second electrical pulse signals and combine the first and second electrical pulse signals to generate a laser driver control pulse signal, the signal mixer also coupled to the laser driver circuit to apply the laser driver control pulse signal to the laser driver circuit to cause the laser driver circuit to generate the electrical laser control pulse signal.

2. The pulsed light emitter according to claim 1, comprising a control circuit coupled to said first and second pulse generators to turn off said first and second pulse generators together after completion of the generation of said first and second electrical pulse signals to reduce noise.

3. The pulsed light emitter of claim 1, comprising control circuitry coupled to said first and second pulse generators to adjust said first and second pulse amplitudes and a time delay between said first and second electrical pulse signals to reduce chirp or distortion in said generated laser pulses.

4. The pulsed optical transmitter of claim 1, wherein the second electrical pulse generator is configured to operate in tuning the time difference between the second amplitude and the time delay between the first and second electrical pulse signals.

5. A light detection and ranging (LiDAR) system including a light emitter for generating laser pulses to light sense one or more targets, the light emitter comprising:

a laser generating laser pulses in response to an electric laser control pulse signal;

a laser driver circuit coupled to the laser to apply the electrical lasing control pulse signal to the laser for generating the laser pulses;

a first electrical pulse generator to generate a first electrical pulse signal having a first pulse amplitude and a first pulse width in time;

a second electrical pulse generator to generate a second electrical pulse signal having a second pulse amplitude less than the first pulse amplitude and high enough to cause the laser drive circuit to trigger a laser firing operation in the laser, the second pulse width in time being greater than the first pulse width, the pulse leading edge preceding the pulse leading edge of the first electrical pulse signal; and

a signal mixer is coupled to the first and second electrical pulse generators to receive the first and second electrical pulse signals and combine the first and second electrical pulse signals to generate a laser driver control pulse signal, the signal mixer also coupled to the laser driver circuit to apply the laser driver control pulse signal to the laser driver circuit to cause the laser driver circuit to generate the electrical laser control pulse signal.

6. The LiDAR system of claim 5, wherein the light emitter includes control circuitry coupled to the first and second pulse generators to turn off the first and second pulse generators together after the generation of the first and second electrical pulse signals is complete to reduce noise.

7. The LiDAR system of claim 5, wherein the light emitter comprises control circuitry coupled to the first and second pulse generators to adjust the first and second pulse amplitudes and a time delay between the first and second electrical pulse signals to reduce chirp or distortion in the generated laser pulses.

8. The LiDAR system of claim 5, wherein the second electrical pulse generator is configured to operate in tuning the time difference between the second amplitude and the time delay between the first and second electrical pulse signals.

9. An Optical Time Domain Reflectometry (OTDR) system, comprising an optical transmitter including an optical transmitter to generate laser pulses for optical sensing, the optical transmitter comprising:

a laser generating laser pulses in response to an electric laser control pulse signal;

a laser driver circuit is coupled to the laser to apply the electrical lasing control pulse signal to the laser for generating the laser pulses;

a first electrical pulse generator to generate a first electrical pulse signal having a first pulse amplitude and a first pulse width in time;

a second electrical pulse generator to generate a second electrical pulse signal having a second pulse amplitude less than the first pulse amplitude and high enough to cause the laser drive circuit to trigger laser operation in the laser, the second pulse width in time being greater than the first pulse width, the pulse leading edge preceding the pulse leading edge of the first electrical pulse signal; and

a signal mixer is coupled to the first and second electrical pulse generators to receive the first and second electrical pulse signals and combine the first and second electrical pulse signals to generate a laser driver control pulse signal, the signal mixer also coupled to the laser driver circuit to apply the laser driver control pulse signal to the laser driver circuit to cause the laser driver circuit to generate the electrical laser control pulse signal.

10. The OTDR system of claim 9, wherein said optical transmitter includes control circuitry coupled to said first and second pulse generators to turn off said first and second pulse generators together after generation of said first and second electrical pulse signals is complete to reduce noise.

11. The OTDR system of claim 9, wherein the optical transmitter includes control circuitry coupled to the first and second pulse generators to adjust the first and second pulse amplitudes and the time delay between the first and second electrical pulse signals to reduce chirp or distortion in the generated laser pulses.

12. The OTDR system of claim 9, wherein said second electrical pulse generator is configured to operate in tuning the time difference between said second amplitude and the time delay between said first and second electrical pulse signals.

13. A method for operating a pulsed optical transmitter to generate laser pulses, comprising:

operating a first electrical pulse generator to generate a first electrical pulse signal having a first pulse amplitude and a first temporal pulse width in time, and a second electrical pulse generator to generate a second electrical pulse signal having a second pulse amplitude less than the first pulse amplitude and a second pulse width greater in time than the first pulse width;

turning off the first and second electrical pulse generators together after generating the first and second electrical pulse signals;

combining the first and second electrical pulse signals to generate a laser driver control pulse signal;

applying the laser driver control pulse signal to a laser diode to generate laser pulses; and

applying the leading and leading portions of the second electrical pulse signal to generate the laser driver control pulse signal to drive the laser diode to emit laser light in the absence of the first electrical pulse signal, while delaying the first electrical pulse signal in time to a later time to combine the first and the second electrical pulse signals to drive the laser diode to generate laser pulses in response to the delayed first electrical pulse signal.

14. The method of claim 13, comprising:

adjusting the first and second pulse amplitudes and the time delay between the first and second electrical pulse signals to reduce chirp or distortion in the generated laser pulse.

15. The method of claim 13, comprising:

adjusting the second amplitude to reduce chirp or distortion in the generated laser pulse.

16. The method of claim 13, comprising:

adjusting a time delay between the first and second electrical pulse signals to reduce chirp or distortion in the generated laser pulse.

Technical Field

This patent document provides a design of an optical transmitter that uses laser pulses to generate laser pulses for a variety of applications.

Summary of the invention

This patent document provides a design of an optical transmitter that generates laser pulses with improved optical waveform shapes in the generated laser pulses and provides compensation for optical chirp in the generated laser pulses. In addition, the designs disclosed herein for the light emitters may be used to maintain a constant transverse beam width of the laser output. Such pulsed light emitters may be used in a variety of applications, including optical detection and ranging systems (LiDAR) and other optical sensing systems, such as Optical Time Domain Reflectometer (OTDR) systems, and optical communication systems.

In one aspect, the techniques disclosed herein may be implemented to provide a pulsed light emitter comprising a laser to generate laser pulses in response to an electrical lasing control pulse signal; a laser drive circuit coupled to the laser to apply an electrical laser control pulse signal to the laser for generating laser pulses; a first electrical pulse generator to generate a first electrical pulse signal having a first pulse amplitude and a first pulse width in time; a second electrical pulse generator to generate a second electrical pulse signal having a second pulse amplitude that is less than the first pulse amplitude and high enough to cause the laser drive circuit to trigger a laser firing operation in the laser, the second pulse width being greater in time than the first pulse width, the leading edge of the pulse preceding the leading edge of the pulse of the first electrical pulse signal; a signal mixer is coupled to the first and second electrical pulse generators to receive and combine the first and second electrical pulse signals to generate a laser driver control pulse signal, the signal mixer also being coupled to the laser driver circuit to apply the laser driver control pulse signal to the laser driver circuit to cause the laser driver circuit to generate the electrical laser control pulse signal.

In another aspect, the techniques disclosed herein may be implemented to provide a pulsed light emitter comprising a laser generating laser pulses in response to an electrical lasing control pulse signal; a laser driver circuit coupled to the laser to apply an electrical laser control pulse signal to the laser for generating laser pulses; a first electrical pulse generator to generate a first electrical pulse signal based on a clock signal, the first electrical pulse signal having a first pulse amplitude and a first pulse width in time; a second electrical pulse generator to generate a second electrical pulse signal based on the same clock signal as the first electrical pulse generator, the second electrical pulse generator configured to cause the second electrical pulse signal to have a second pulse amplitude that is less than the first pulse amplitude and a second pulse width that is greater in time than the first pulse width; and a signal mixer coupled to the first and second electrical pulse generators to receive and combine the first and second electrical pulse signals to generate a laser driver control pulse signal, the signal mixer further coupled to the laser driver circuit to apply the laser driver control pulse signal to the laser driver circuit to cause the laser driver circuit to generate the electrical laser control pulse signal.

In another aspect, the techniques disclosed herein may be implemented to provide a method for operating a pulsed light emitter to generate laser pulses. The method may include operating and applying a common clock signal to a first electrical pulse generator to generate a first electrical pulse signal having a first pulse amplitude and a first pulse width in time, and a second electrical pulse generator to generate a second electrical pulse signal having a second pulse amplitude less than the first pulse amplitude and a second pulse width greater in time than the first pulse width; turning off the first and second electrical pulse generators together after generating the first and second electrical pulse signals; combining the first and second electrical pulse signals to generate a laser driver control pulse signal; and applies a laser driver control pulse signal to the laser diode to generate laser pulses.

In another aspect, the techniques disclosed herein may be implemented to provide a method for operating a pulsed light emitter to generate laser pulses. The method comprises operating a first electrical pulse generator to generate a first electrical pulse signal having a first pulse amplitude and a first pulse width in time, and a second electrical pulse generator to generate a second electrical pulse signal having a second pulse amplitude less than the first pulse amplitude and a second pulse width greater in time than the first pulse width; turning off the first and second electrical pulse generators together after generating the first and second electrical pulse signals; combining the first and second electrical pulse signals to generate a laser driver control pulse signal; applying a laser driver control pulse signal to a laser diode to generate laser pulses; and applying the leading edge and the leading portion of the second electrical pulse signal to generate a laser driver control pulse signal to drive the laser diode to lase in the absence of the first electrical pulse signal, while delaying the first electrical pulse signal in time to a later time to combine the first and second electrical pulse signals to drive the laser diode to generate a laser pulse in response to the delayed first electrical pulse signal.

Those and other implementations are described in more detail in the figures, the specification, and the claims.

Drawings

Fig. 1 shows an example of a pulsed laser diode with driving electronics.

Fig. 2 includes fig. 2A-2D and illustrates examples of optical chirp and waveform distortion in the pulsed laser diode of fig. 1 and its driving electronics.

Fig. 3A shows an example of a pulsed light emitter architecture including two pulse generators to reduce optical chirp and waveform distortion.

Fig. 3B also shows the relationship between the operating pulses and the pre-pulse (pre-pulse) of the two pulse generators in fig. 3A, and the tuning of the pre-pulse with respect to the operating pulses.

Fig. 4 includes fig. 4A-4D and illustrates an example for operating the two pulse generators of fig. 3A to provide optical chirp compensation in the laser output of a laser diode with drive electronics based on the examples of fig. 3A and 3B.

Detailed Description

This patent document provides a design of an optical transmitter that uses laser pulses to generate laser pulses for a variety of applications.

Fig. 1 shows an example of a typical pulsed laser emitter used in a variety of applications. In this example, a Laser Diode (LD)110 is coupled to a driver circuit that includes a clock circuit 102, a pulse generator circuit 104, and a Laser Diode Driver (LDD). The drive circuit is designed as a current pulse generator that drives the laser diode 110 to generate laser pulses. This type of pulse modulated diode laser tends to experience or exhibit undesirably large distortion, undesirably large chirp in frequency, and undesirably large width of the output laser beam during laser current conversion when the drive current is varied from a low current below a threshold current (when the laser diode is operated in a lasing mode, generating analog emissions in response to the drive current) to a greater current above the threshold current (when the laser diode is operated in a lasing mode, amplification of the analog emissions exceeds optical loss). When the drive current is a low current lower than the threshold current, the laser diode is operated in the excitation mode, generating analog emission, but the presence of spontaneous emission at a low current lower than the threshold current results in output light of the laser beam having both a broad spectrum and a broad lateral beam width due to the lack of laser emission operation in the laser diode. During this current conversion, the optical signal or laser output from the laser diode may be distorted (distorted) from its original electrical signal waveform, and the emitted or generated optical frequency in the laser output from the laser diode may exhibit significant variation in the form of frequency chirp. Further, the lateral beam width of the laser diode output changes from a wide beam width when the drive current is below the threshold current to a narrow and directed beam width when the drive current is above the threshold current and causes the laser diode to operate in a lasing mode.

Fig. 2 illustrates the operation of the laser transmitter of fig. 1. Fig. 2 includes fig. 2A, 2B, 2C, and 2D. Fig. 2A shows that the single pulse generator 104 of fig. 1 generates an electrical pulse signal having a desired pulse amplitude, pulse shape, and pulse duration, which is used to drive the laser diode 110 to generate laser pulses that ideally have the same or nearly the same pulse shape and pulse duration. However, the optical frequency of the generated optical pulses contains undesirable optical chirp in frequency due to the transition caused by the leading edge of the electrical pulse signal used to drive the laser diode 110. As a result, the optical pulse generated by the laser diode 110 is distorted from the original electrical signal waveform, and the temporal shape (temporal shape) of the generated optical pulse is also distorted. Such optical chirp at the laser diode output frequency can cause distortion of the optical receiver output signal that depends on the optical path and the performance of the optical receiver.

Fig. 2B shows an example of the dependence of the optical power output of a laser diode designed based on single pulse generation 104 with respect to the amplitude of the drive current pulse applied to the laser diode in fig. 1. Drive current pulse (I)_LD) From below the lasing current threshold (I)_THRESHOLD) A low value of the amplitude increases as indicated by the initial time when the laser diode is in the spontaneous emission mode, at which time the emitted output optical power is less than P_THRESHOLDA wide beam width and a wide spectral range of light. Subsequently, a current pulse (I) is driven_LD) Continues to increase to the lasing current threshold (I)_THRESHOLD) Above the amplitude of P, the light emission in the laser diode is changed from a spontaneous emission mode to a laser emission mode in which the laser diode emits light having a narrow beam width and a narrower spectral range and an output optical power greater than P_THRESHOLDThe laser of (1). Fig. 2C shows the light intensity of the laser diode output as a function of time, which shows the laser pulse shape in the time domain. FIG. 2D also illustrates the change in spectral range of the laser diode output over time when driven by a single current pulse, showing a wide initial spectral range when the laser diode is in a spontaneous emission mode and when the laser diode is in a lasing modeA narrower spectral range.

This patent document discloses a novel pulsed laser diode emitter with drive electronics that can be used to reduce the aforementioned optical output waveform distortion, optical chirp, and output beam width. The drive electronics for the laser diode disclosed herein are designed to generate two drive current pulses to the laser diode: a normal pulse current and a pre-pulse current, which are added together to generate a drive current pulse for driving the laser diode. The pre-pulse signal may be used to change the laser diode from an excitation mode to a lasing mode at low optical power levels. This is achieved by a combination of techniques. First, the amplitude of the pre-pulse signal is generated to generate a drive current amplitude just above the laser current threshold at which the laser diode operates in the lasing mode, but at a level not much above the threshold. Second, the pre-pulse signal has a pulse duration that is longer than a desired pulse duration for operating the pulse to generate a desired laser pulse through the laser diode. Third, triggering the leading edge of the pre-pulse signal temporally before the leading edge of the operating pulse, causing the laser diode to be driven with the pre-pulse signal before the leading edge of the operating pulse arrives to switch from spontaneous emission to laser emission, such that when generating current to drive the laser diode using the operating pulse, the laser diode is already operated in the lasing mode, and the operating pulse adds drive current to the laser diode in a pulse shape and pulse duration tailored for the desired laser pulse output. Fourth, the trailing edge of the pre-pulse signal and the trailing edge of the operation pulse are transmitted to coincide in time, so that both pulse signals are turned off at the same time. As a result of using a combination of the pre-pulse signal and the normal pulse signal when driving the laser diode, large optical distortion and optical chirp will also occur at lower power levels. Therefore, these large optical distortions, frequency chirps, and large beam widths produced during the conversion of the pre-pulse signal will have little effect on the light emission system using laser diodes driven in this manner. Various laser emitting systems, such as OTDR and LIDAR systems, may benefit from the laser emitter techniques disclosed herein.

Fig. 3A shows an example of a pulsed light emitter architecture that includes two pulse generators to reduce unwanted optical chirping, unwanted waveform distortion, and unwanted wide beamwidth. Such an optical transmitter 300 in the example of fig. 3A includes a clock generator 302 that generates a clock signal and two pulse generators, pulse generator 1(304) and pulse generator 2(303), that are electrically coupled to the clock generator 302 to receive the same clock signal from the clock generator 302 and to generate first and second electrical pulse signals based on the same clock signal. The signal mixer 305 is coupled to receive the first and second electrical pulse signals from the pulse generators 1(304) and 2(303) to add the two pulse signals to each other to generate a control pulse signal to a downstream Laser Diode Driver (LDD) circuit 306. A Laser Diode Driver (LDD) circuit 306 is coupled to receive the LDD control pulse signal from the signal mixer 305 and to generate an LDD driver signal in response to the received LDD control pulse signal. A Laser Diode (LD)310 is coupled to the LDD circuit 306 and is activated by LDD driver signals to generate laser pulses as the optical output of the optical transmitter 300.

The pulse generated by the first generator 304 (pulse generator 1) is an operating pulse signal having an amplitude high enough to operate the laser diode 310 above its laser emission threshold. The second generator 303 (pulse generator 2) generates a low-amplitude pulse signal wider than the operation pulse signal in time, for example, in the preceding time. Both pulse generators 1(304) and 2(303) may be controlled or operated to turn off the pulse signal at the same edge time. This operation of both pulse generators 1(304) and 2(303) can reduce background noise compared to some other optical transmitters for pulse generation where a continuous laser bias current is applied all the time and the amplitude is slightly above the laser threshold. This method of simultaneously turning off the pre-pulse and operating both trailing edges of the pulse signal may be advantageous in LiDAR and OTDR measurements of targets located at short distances. With this dual pulse generator system to drive the laser diode, the laser chirp and waveform will be reduced with some background noise. Thus, when using such pulsed light emitters, the techniques disclosed herein may be used to improve the system sensitivity, receiver detection accuracy, and dynamic range of a LiDAR system.

In another aspect of the pulsed optical transmitter in fig. 3A, the pulses from pulse generators 2(303) and pulses from pulse generators 1(304) may be tuned in amplitude and time delay to pre-shape the drive pulses of laser diode 310 to shape the optical waveform of the pulsed laser output from laser diode 310 and compensate for laser chirp and pulse distortion in a variety of applications. Examples of applications for such pre-forming include, for example, during free-space light transmission due to the presence of hydrogen from water. This tuning may be achieved by using a control circuit coupled to the first and second pulse generators 304 and 303 to control the operation of the generators, including turning them off together after the generation of the first and second electrical pulse signals is completed, respectively, in response to the same clock signal. In the illustrated example, the tuning may be performed using the same clock circuit 302. In particular, the amplitude and pulse duration of the pre-pulse signal may be tuned or adjusted while maintaining the pulse shape, pulse amplitude, or pulse duration of the operating pulse, as based on the particular design used to generate the laser pulses produced by the laser diode 310.

Fig. 3B also shows the relationship between the operating pulses and the pre-pulse signals generated by the two pulse generators 304 and 303 in fig. 3A. The operating pulse and the pre-pulse signals generated by the two pulse generators 304 and 303 may be voltage or current signals and mixed together to generate a common signal to the LLD306, in response to which the LLD306 generates a drive current pulse that drives the laser diode 310 for generating the laser pulse 312. As shown in fig. 3B, the pulses and pre-pulse signals generated by the two pulse generators 304 and 303 both have signal amplitudes corresponding to a drive current to the laser diode 310 that is higher than the laser threshold current of the threshold laser output power. However, their amplitudes are different. The amplitude of the pre-pulse signal is set to be just above the level of the lasing threshold current corresponding to the threshold laser output power so that in the absence of an operating pulse, the pre-pulse signal alone can cause the LDD306 to drive the laser diode 310 in the lasing mode, but to output at a low power in the lasing mode. The amplitude of the operating pulse signal is also set to be above the level of the laser threshold current corresponding to the threshold laser output power, but is set to be higher than the amplitude of the pre-pulse signal. As also shown in fig. 3B, the leading edge of the pre-pulse signal is first initiated and has a pulse duration that is longer than the desired pulse duration for operating the pulse to generate the desired laser pulse by the laser diode. Thus, the pulse-to-pulse leading edge causes the laser diode to undergo a transition from spontaneous emission to lasing at a relatively low optical power slightly above the laser threshold level. With this design, after the laser diode has been in the laser emission mode due to the pre-pulse signal, the arrival of the operation pulse signal will more efficiently convert the energy of the drive current increased by the operation pulse signal into the laser output.

Fig. 3B also shows that the time difference between the leading edge t1 of the pre-pulse signal and the leading edge t2 of the operating pulse signal is tunable or adjusted. Since both signals have the same trailing edge t3, the duration of the pre-pulse signal can be tuned to tune or adjust the time difference between t1 and t 2. Furthermore, the amplitude of the pre-pulse signal may also be tuned. These two tunings of the pre-pulse signal can be used to optimize the reduction of waveform distortion or optical chirp in the laser diode output pulses for a given operating pulse signal. The pulse shape, amplitude, or duration of the operating pulse may be specifically designed for the desired pulse shape, amplitude, or duration of the laser output pulse.

In an implementation, generator 1 and generator 2 may be triggered or controlled using the same clock circuit 302. The pulse amplitude and width of the generator 1 will generate the light pulses of the desired light signal. The pulse amplitude of the generator 2 will generate a small laser current just above the laser threshold. The pulse width of generator 2 is wider than the pulse width from generator 1. By transforming the amplitude and pulse width of the generator 2, an optimal optical transmitter signal with a small optical chirp and beam width can be generated.

Fig. 4 illustrates an example of chirp compensation based on the tuning of the dual pulse generator optical transmitter in fig. 3. The wavelength is shifted when the pulse from the pulse generator 2 is applied, but the peak power is very small compared to the main pulse generated by the pulse generator 1. When the main pulse from the pulse generator 1 is applied, the wavelength becomes constant with high peak optical power. Therefore, the transient chirp is very small and negligible. Similar to fig. 2, fig. 4 includes fig. 4A, 4B, 4C, and 4D for comparison with fig. 2A, 2B, 2C, and 2D, respectively. Comparing fig. 4C and 2C, the light pulse in fig. 4C shows significantly less distortion than the light pulse in fig. 2C, due to the use of a pre-pulse signal for pre-driving the laser diode in the laser firing mode before the arrival of the operating pulse responsible for generating the desired laser output pulse.

While this patent document contains many specifics, these should not be construed as limitations on the scope of any invention or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular inventions. Certain features that are described in this patent document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

Only a few implementations and examples are described, and other implementations, enhancements, and variations can be made based on what is described and illustrated in this patent document.