Hybrid integrated correction-free linear frequency modulation DFB laser ranging system and ranging method thereof

Abstract

The invention discloses a hybrid integrated correction-free linear frequency modulation DFB laser ranging system and a ranging method thereof, and relates to the technical field of laser radar ranging. Comprising a hybrid integrated packaging module, a first DFB laser, a second DFB laser, an optical circulator unit, a GPPO high-frequency radio frequency interface and an independent regulation and control unit, the first DFB laser, the second DFB laser and the optical circulator unit are packaged in the hybrid integrated packaging module, and the GPPO high-frequency radio frequency interface is arranged on the hybrid integrated packaging module; according to the hybrid integrated correction-free linear frequency modulation DFB laser ranging system and the ranging method thereof, the sweep frequency linearity of the laser is directly anchored on a radio frequency source of an electric domain through a physical mechanism of sideband locking, so that the sweep frequency linearity of output optical frequency is ensured from the physical level; a complex digital pre-distortion algorithm or expensive photoelectric phase-locked loop hardware is thoroughly omitted, and the system complexity is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of lidar ranging technology, specifically to a hybrid integrated uncorrected linear frequency modulated DFB laser ranging system and its ranging method. Background Technology

[0002] LiDAR, as a high-precision active detection technology, plays a crucial role in fields such as autonomous driving, remote sensing mapping, wind speed measurement, and environmental monitoring. Among them, frequency modulated continuous wave (FMCW) lidar has become a current research hotspot due to its advantages such as high ranging accuracy, high sensitivity, blind-zone-free detection capability, and strong anti-interference ability. FMCW lidar can simultaneously acquire the distance and velocity information of a target in a single measurement and is suitable for miniaturization and integration.

[0003] However, the performance of FMCW lidar is highly dependent on the frequency modulation linearity of the light source. An ideal linearly frequency modulated (Chirp) signal requires the frequency to change linearly with time, but in practical applications, semiconductor lasers (such as DFB lasers) are affected by factors such as thermal effects, carrier concentration changes, driving circuit noise, and external environmental disturbances, and their output frequency often exhibits nonlinearity, which seriously reduces the measurement accuracy and resolution of the system.

[0004] To address the nonlinearity issue of light sources, existing technologies primarily employ nonlinear correction techniques, which include: Predistortion technology: Based on an iterative algorithm, a mapping relationship between frequency and current is constructed to predistort the driving signal. Although it can achieve a certain degree of linearization, the algorithm is complex, sensitive to environmental changes, and has poor real-time performance. Optical phase-locked loop (OPLL) technology: locks the scanning light frequency to a highly stable reference frequency. This method offers high accuracy, but the system hardware structure is complex, costly, and difficult to integrate. Resampling technique: An auxiliary interference optical path is introduced to extract the clock signal and the measurement signal is resampled to eliminate nonlinearity. This method increases the complexity of the optical system and the amount of data in the back-end signal processing. External modulation techniques: Using external modulators (such as SSB modulators and I / Q modulators) to generate linear sweep signals. Although the linearity is good, this introduces expensive and bulky external optical components, which is not conducive to the low cost and miniaturization of the system.

[0005] In addition, traditional single-frequency FMCW lidar is easily affected by atmospheric turbulence and speckle noise on the target surface when operating in actual atmospheric environments, which leads to a decrease in the signal-to-noise ratio of the echo signal and an increase in measurement error. Dual-frequency modulated continuous wave (DF-FMCW) lidar was proposed to solve this problem. It emits two laser beams with a specific frequency difference and uses the correlation of the two wavelengths to suppress the effects of speckle and turbulence.

[0006] Therefore, there is a need for an integrated light source and ranging system that does not require complex nonlinear correction circuits or algorithms, has a simple structure, can resist environmental interference, and has high frequency modulation linearity characteristics, in order to meet the requirements of high precision, low cost, and real-time ranging and imaging. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a hybrid integrated uncorrected linear frequency modulated DFB laser ranging system and its ranging method, which solves the problems mentioned in the background art, such as the complex system structure of existing linear frequency modulated laser sources, the extremely high requirements for the linearity of the driving circuit, and the need to rely on complex digital predistortion algorithms or photoelectric feedback loops for nonlinear correction.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a hybrid integrated uncorrected linear frequency modulated DFB laser ranging system, comprising a hybrid integrated package module, a first DFB laser, a second DFB laser, an optical circulator unit, a GPPO high-frequency radio frequency interface, and an independent control unit. The first DFB laser, the second DFB laser, and the optical circulator unit are packaged inside the hybrid integrated package module, and the GPPO high-frequency radio frequency interface is located on the hybrid integrated package module. The optical circulator unit is located on the optical output path of the first DFB laser and the second DFB laser. After passing through the optical circulator unit, the first DFB laser enters the second DFB laser to form a sideband injection lock before outputting. The GPPO high-frequency radio frequency interface is connected to the first DFB laser and the second DFB laser, and is used to inject linear frequency modulation signals to achieve sideband locking; The independent control unit includes a temperature control circuit and a current drive circuit that independently control the first DFB laser and the second DFB laser, respectively.

[0009] Preferably, the first DFB laser and the second DFB laser are integrated and packaged on the same socket. The first DFB laser and the second DFB laser are connected to the socket's casing pins via wire bonding. Independent control units are used for coarse temperature adjustment and fine current adjustment to set the center beat frequency. .

[0010] Preferably, both the temperature control circuit and the current drive circuit are connected to the injection electrodes of the first DFB laser and the second DFB laser.

[0011] A ranging method for a hybrid integrated uncorrected linear frequency modulated DFB laser ranging system includes the following steps: S1: The temperature and injection current of the first and second DFB lasers are adjusted separately by independent control units to make the wavelength difference between the two lasers equal. Corresponding to the preset center carrier frequency ; S2: Inject a linear frequency modulated microwave signal into the second DFB laser through the GPPO high-frequency radio frequency interface; S3: By utilizing the sideband injection locking effect, the longitudinal mode frequency of the first DFB laser is locked to the modulation sideband of the radio frequency signal; S4: After the first and second DFB lasers are beat-frequency through the 3-port of the optical circulator unit, they directly output a high-linearity frequency-modulated continuous wave (FMCW) signal without the need for additional nonlinear correction algorithms.

[0012] Preferably, the center frequency requirement of the linear frequency modulated microwave signal is reduced by using fine adjustment of current and temperature control, and the nonlinear effects of the first DFB laser and the second DFB laser are eliminated when sweeping frequencies over a wide range by using a sideband injection locking mechanism.

[0013] This invention provides a hybrid integrated uncorrected linear frequency modulated DFB laser ranging system and its ranging method, which has the following beneficial effects: 1. The hybrid integrated uncorrected linear frequency modulated DFB laser ranging system and its ranging method directly anchor the laser's sweep frequency linearity to the radio frequency source in the electric domain through the physical mechanism of "sideband locking". This ensures the sweep linearity of the output optical frequency from a physical perspective, completely eliminating the need for complex digital predistortion algorithms or expensive optoelectronic phase-locked loop hardware, and greatly reducing the system complexity.

[0014] 2. This hybrid integrated uncorrected linear frequency modulated DFB laser ranging system and its ranging method, by employing hybrid integration technology, encapsulates two DFB laser chips (first and second DFB lasers) and coupling components within the same module. Compared to systems built with separate components, this not only significantly reduces size and weight but also significantly enhances resistance to vibration and temperature drift, as well as environmental interference. Furthermore, the independent temperature and current control path design not only enables flexible setting of the center carrier frequency but also allows for fine adjustment and optimization of the injection-locked bandwidth and stability, effectively improving the system's energy efficiency ratio and detection accuracy. This makes it highly suitable for the miniaturization and high-performance applications of lidar systems. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the hybrid integrated uncorrected linear frequency modulation DFB system used in this invention; Figure 2 This is the spectrum of the DFB laser in Embodiment 2 of the present invention when the main laser current is fixed at 86mA, as the laser current changes from 36mA to 41mA. Figure 3 This is the spectrum of the DFB laser in Embodiment 2 of the present invention when the slave laser current is fixed at 41mA and the master laser current changes from 83mA to 88mA. Figure 4 This is the spectrum of the DFB laser in the system when the I1 current is 48mA and the I2 current is 34mA in Embodiment 2 of the present invention. Figure 5 This is the beat frequency spectrum of the DFB laser in Embodiment 2 of the present invention when the I1 current is 48mA and the I2 current is 34mA. Figure 6 The above is a spectrum of the modulation bandwidth of the DFB laser in Embodiment 2 of the present invention, where the I1 current is 48mA, the I2 current is 34mA, and an external linear frequency modulated signal with a center frequency of 23.5GHz and a modulation bandwidth of 3GHz is applied. Figure 7 This is a diagram showing the distance of a 50.38m fiber optic cable measured by a DFB laser in Embodiment 2 of the present invention. Figure 8 This is a diagram showing the distance of a 2027.95m fiber optic cable measured by a DFB laser in Embodiment 2 of the present invention. Figure 9 This is an absolute error analysis diagram of the DFB laser in Embodiment 2 of the present invention when measuring different fiber distances. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Example 1

[0017] Please see Figure 1 This invention provides a technical solution: a hybrid integrated uncorrected linear frequency modulated DFB laser ranging system, comprising a hybrid integrated package module, a first DFB laser, a second DFB laser, an optical circulator unit, a GPPO high-frequency radio frequency interface, and an independent control unit. The first DFB laser, the second DFB laser, and the optical circulator unit are packaged inside the hybrid integrated package module, and the GPPO high-frequency radio frequency interface is located on the hybrid integrated package module. The optical circulator unit is located on the optical output path of the first DFB laser and the second DFB laser. It is used to couple the two laser signals to generate an FMCW signal. After passing through the optical circulator unit, the first DFB laser enters the second DFB laser to form a sideband injection lock before outputting. The GPPO high-frequency radio frequency interface is connected to the first DFB laser and the second DFB laser to inject linear frequency modulation signals to achieve sideband locking; The independent control unit includes temperature control circuits and current drive circuits that independently control the first DFB laser and the second DFB laser, respectively.

[0018] The first and second DFB lasers are mounted on the same high thermal conductivity socket using processes such as eutectic bonding to ensure consistent operating temperatures, effectively reduce device size, and suppress frequency drift. The first and second DFB lasers are connected to the socket's housing pins via wire bonding, and independent control units are used for coarse temperature adjustment and fine current adjustment to set the center beat frequency. .

[0019] The optical circulator unit has three ports: optical circulator port 1 (2-1), optical circulator port 2 (2-2), and optical circulator port 3 (2-3).

[0020] Both the temperature control circuit and the current drive circuit are connected to the injection electrodes of the first DFB laser and the second DFB laser, enabling independent temperature regulation and DC bias current control of the first DFB laser and the second DFB laser, thereby achieving coarse wavelength adjustment, thermal frequency stabilization, and fine power adjustment.

[0021] A ranging method for a hybrid integrated uncorrected linear frequency modulated DFB laser ranging system includes the following steps: S1: The temperature and injection current of the first and second DFB lasers are adjusted separately by independent control units to make the wavelength difference between the two lasers equal. Corresponding to the preset center carrier frequency ; S2: Inject a linear frequency modulated microwave signal into the second DFB laser through the GPPO high-frequency radio frequency interface; S3: By utilizing the sideband injection locking effect, the longitudinal mode frequency of the first DFB laser is locked to the modulation sideband of the radio frequency signal; S4: After the first and second DFB lasers beat through the 3-port (2-3) of the optical circulator unit, they directly output a high-linearity frequency-modulated continuous wave (FMCW) signal without the need for additional nonlinear correction algorithms.

[0022] The center frequency requirement for linear frequency modulated microwave signals is reduced by finely adjusting the current and temperature control, and the nonlinear effects of the first and second DFB lasers during wide-range frequency sweeps are eliminated by using a sideband injection locking mechanism.

[0023] Example 2, see Figures 1-9Based on Embodiment 1, the present invention provides a technical solution: a hybrid integrated uncorrected linear frequency-modulated DFB laser ranging system, in order to achieve high linearity frequency sweep output, firstly requires matching and adjusting the static characteristics of the laser through an external independent control unit.

[0024] like Figure 2 As shown, the first DFB laser is the master laser, and the second DFB laser is the slave laser. Keeping the drive current I1 of the master laser constant at 86mA, adjusting the drive current I2 of the slave laser from 36mA to 41mA results in a frequency shift in the beat frequency. Similarly, as... Figure 3 As shown, by fixing I2 at 41mA and adjusting I1 from 83mA to 88mA, the ability of bidirectional current regulation to control frequency difference was further verified.

[0025] After system optimization, when I1 is set to 48mA and I2 is set to 34mA, the laser spectrum output by the system and the spectrum of its generated static beat frequency signal are as follows: Figure 4 and Figure 5 As shown in the figure. At this point, the beat frequency spectrum signal is stable and has a high signal-to-noise ratio, and it is established as the operating point for subsequent linear frequency modulation experiments.

[0026] During the verification of linear frequency modulation characteristics, a linearly swept radio frequency signal with a center frequency of 23.5 GHz and a modulation bandwidth of 3 GHz was injected into the second DFB laser through a GPPO high-frequency interface. This invention utilizes the sideband locking effect to force the second DFB laser to lock onto the sideband of the radio frequency reference signal. Due to the extremely high phase stability and linearity of the radio frequency source itself, the frequency-modulated signal generated by the second DFB laser directly cancels the inherent electrothermal nonlinearity of the semiconductor laser through a physical locking mechanism. Figure 6 As shown, after loading the modulation signal at the above operating point, the modulation bandwidth spectrum of the system output is uniform and flat, proving that the system can obtain a wideband and highly linear frequency-modulated continuous wave output without the need for complex resampling algorithms or predistortion iterative correction.

[0027] To verify the lidar ranging performance of this system, this embodiment verifies it through ranging experiments on optical fibers of different lengths. Based on the principle of linear frequency modulation (LFM) ranging, the system's output optical signal is split into reference and probe light by a 1:99 beam splitter. The probe signal enters the fiber under test. The probe signal propagates in the fiber and is reflected back at the end, incurring a time delay with the local oscillator signal. , Through formula as well as (in The measured equivalent distance of the optical fiber, At the speed of light, For the frequency sweep period, The beat frequency, (For the sweep bandwidth), the fiber length can be accurately extracted; In short-distance and medium-distance measurement experiments, such as Figure 7 As shown, when probing a 50.38m long optical fiber, the peak values ​​of its beat frequency signal after Fast Fourier Transform (FFT) are sharp and clear. This indicates that the system output sweep frequency signal has extremely high linearity, and there is no phenomenon of spectral broadening or decreased ranging resolution due to sweep frequency nonlinearity.

[0028] In long-distance measurement verification, such as Figure 8 As shown, tests were conducted on a long-distance optical fiber of 2027.95m, and the system was still able to extract a distance characteristic peak with a high signal-to-noise ratio. This result strongly demonstrates that the hybrid integrated packaging structure can effectively suppress phase noise and ensure the system's detection capability over ultra-long distances.

[0029] Finally, through statistical analysis of the fiber optic ranging experimental data at distances of 10.1m, 13.15m, 15.13m, 50.38m, 100.55m, 150.89m, and 2027.94m, the following results were obtained: Figure 9 The system's absolute error distribution is shown in the diagram. Experimental data demonstrate that the measurement results of the system of this invention closely match the physical true values, with the absolute error remaining at a low level throughout the entire measurement range. Because the hybrid integration technology places the two lasers in the same heat sink environment, the impact of ambient temperature fluctuations on the beat frequency is significantly reduced. In summary, this invention, through physical-level frequency locking and hybrid integration technology, solves the problems of large size and complex correction algorithms required in traditional FMCW systems, enabling stable and high-precision real-time ranging applications.

[0030] In summary, this hybrid integrated uncorrected linear frequency modulated (FMCW) laser ranging system and method, during operation, involves adjusting the temperature and bias current of DFB1 and DFB2 separately via an external independent control unit. This controls the center wavelength difference between the two DFB lasers, ensuring that the frequency difference between the two lasers equals the center frequency of the injected linear frequency modulated microwave signal. Subsequently, a radio frequency (RF) signal with power and frequency meeting the locking condition is injected into the DFB2 laser via a GPPO interface using a linear frequency modulated signal source. This locks the longitudinal mode frequency of the DFB1 laser onto the modulation sideband of the DFB2 laser. Due to the locking effect, the frequency of the DFB1 laser will linearly change following the RF sideband of the DFB2 laser, resulting in a high-linearity linear frequency modulated continuous wave (FMCW) signal directly at the output. The entire process requires no pre-distortion correction of the drive current.

[0031] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A hybrid integrated uncorrected linear frequency modulated DFB laser ranging system, characterized in that: It includes a hybrid integrated package module, a first DFB laser, a second DFB laser, an optical circulator unit, a GPPO high-frequency RF interface, and an independent control unit. The first DFB laser, the second DFB laser, and the optical circulator unit are packaged inside the hybrid integrated package module, and the GPPO high-frequency radio frequency interface is located on the hybrid integrated package module. The optical circulator unit is located on the optical output path of the first DFB laser and the second DFB laser. After passing through the optical circulator unit, the first DFB laser enters the second DFB laser to form a sideband injection lock before outputting. The GPPO high-frequency radio frequency interface is connected to the first DFB laser and the second DFB laser, and is used to inject linear frequency modulation signals to achieve sideband locking; The independent control unit includes a temperature control circuit and a current drive circuit that independently control the first DFB laser and the second DFB laser, respectively.

2. The hybrid integrated uncorrected linear frequency modulated DFB laser ranging system according to claim 1, characterized in that: The first and second DFB lasers are integrated and packaged on the same socket. The first and second DFB lasers are connected to the socket's housing pins via wire bonding. Independent control units are used for coarse temperature adjustment and fine current adjustment to set the center beat frequency. .

3. The hybrid integrated uncorrected linear frequency modulated DFB laser ranging system according to claim 1, characterized in that: Both the temperature control circuit and the current drive circuit are connected to the injection electrodes of the first DFB laser and the second DFB laser.

4. The ranging method of a hybrid integrated uncorrected linear frequency modulated DFB laser ranging system according to claim 1, characterized in that: Includes the following steps: S1: The temperature and injection current of the first and second DFB lasers are adjusted separately by independent control units to make the wavelength difference between the two lasers equal. Corresponding to the preset center carrier frequency ; S2: Inject a linear frequency modulated microwave signal into the second DFB laser through the GPPO high-frequency radio frequency interface; S3: By utilizing the sideband injection locking effect, the longitudinal mode frequency of the first DFB laser is locked to the modulation sideband of the radio frequency signal; S4: After the first and second DFB lasers are beat-frequency through the 3-port of the optical circulator unit, they directly output a high-linearity frequency-modulated continuous wave (FMCW) signal without the need for additional nonlinear correction algorithms.

5. The ranging method of a hybrid integrated uncorrected linear frequency modulated DFB laser ranging system according to claim 4, characterized in that: In this process, temperature control circuits and current drive circuits are used to finely adjust the current and temperature control to reduce the center frequency requirement of the linear frequency modulated microwave signal. The sideband injection locking mechanism is used to eliminate the nonlinear effects of the first DFB laser and the second DFB laser during wide-range frequency sweep.

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