Multi-wavelength polarization-maintaining fiber amplifier for FMCW laser radar and its application

Abstract

The present application relates to a multi-wavelength polarization-maintaining fiber amplifier for FMCW laser radar and its application. The scheme includes components such as polarization beam splitter, wavelength division multiplexer, erbium-ytterbium co-doped fiber, etc. The polarization beam splitter separates and combines optical signals, the wavelength division multiplexer demultiplexes the wavelength division multiplexer, the erbium-ytterbium co-doped fiber is used for amplification, the Faraday rotator adjusts the polarization state, the high-power splitter distributes the pump light, the combiner cooperates to form a pump mode, the high-power pump supplies energy, and the control unit can determine the input light intensity, control the power and monitor the temperature. It has the advantages of low cost, small size, high integration, and strong reliability. The wavelength and number of paths can be selected as needed, the power range is 8-20W, the polarization beam splitter extinction ratio is ≥40dB, and the wavelength of the wavelength division multiplexer is 1530-1565nm. It is suitable for the automotive field and solves the problems of the existing technology.

Description

Technical Field

[0001] The present application relates to the field of laser radar technology, and in particular to a multi-wavelength polarization-maintaining fiber amplifier for FMCW laser radar. Background Art

[0002] As an advanced sensor technology, LiDAR plays a vital role in many fields, especially in autonomous driving. Among them, Frequency Modulated Continuous Wave (FMCW) LiDAR has attracted much attention due to its advantages such as high resolution, high precision and strong anti-interference ability.

[0003] In the multi-wavelength usage scenario of FMCW lidar, the existing technology mainly uses multiple polarization-maintaining fiber amplifiers to amplify multiple wavelengths separately, and each wavelength needs to be transmitted through a corresponding polarization-maintaining fiber. Although this method can achieve multi-wavelength amplification and transmission, it has many defects.

[0004] From a cost perspective, the use of multiple polarization-maintaining fiber amplifiers leads to a significant increase in costs. At the same time, the price of polarization-maintaining fibers for transmission is expensive. The use of multiple polarization-maintaining fibers keeps the overall cost high, which severely limits its application in some cost-sensitive fields (such as the automotive industry). In terms of volume, numerous polarization-maintaining fiber amplifiers and multiple polarization-maintaining fibers need to occupy a large space, which is not conducive to the miniaturization design of the equipment. In application scenarios such as automobiles, there are strict restrictions on the volume of the equipment, which makes it difficult for existing technologies to meet the needs of miniaturization of automotive lidars. In addition, multiple amplifiers and optical fibers also bring difficulties to centralized management, increasing the complexity of the system and management costs.

[0005] In summary, the existing FMCW LiDAR multi-wavelength amplification and transmission technology has obvious deficiencies in terms of cost, volume, centralized management, etc. A new technical solution is urgently needed to solve these problems in order to meet the growing market demand, especially the automotive industry's demand for miniaturized, low-cost, and high-reliability LiDAR systems. The present invention is an innovative solution proposed based on this background. Summary of the invention

[0006] The purpose of the present application is to provide a multi-wavelength polarization-maintaining fiber amplifier for FMCW laser radar in order to solve the above-mentioned problems existing in the prior art.

[0007] The core technology of this application is to amplify multiple wavelengths and then mix them, and transmit them through a single polarization-maintaining optical fiber. By sharing high-power pumps, some passive components, and control circuits, and reducing the use of polarization-maintaining optical fibers, the cost of multi-wavelength amplification and transmission of FMCW lidar can be reduced.

[0008] In order to achieve the above application purpose, the present application adopts the following technical solution: A multi-wavelength polarization-maintaining fiber amplifier for FMCW laser radar includes:

[0009] A polarization beam splitter, the input end of which is connected to a multi-wavelength mixed input signal light, and the output end of which outputs a multi-wavelength mixed output signal light, is connected to the wavelength division multiplexer, and is used to separate the multi-wavelength mixed input signal light into optical signals of different polarization states, so that each wavelength optical signal can enter the corresponding amplification link for independent processing, and is used to re-combine the amplified wavelength optical signals of different polarization states into a beam of multi-wavelength mixed output signal light for output;

[0010] The wavelength division multiplexer is used to perform wavelength division operation on the separated multi-wavelength mixed input signal light, so that each wavelength optical signal can enter the corresponding amplification link for amplification and then return to the wavelength division multiplexer for multiplexing, and then output to the polarization beam splitter;

[0011] Erbium-ytterbium co-doped optical fiber, used to form an amplification link;

[0012] A Faraday rotator, located on each amplification link, is used to rotate the polarization state of the reflected light by 90° compared to the incident light;

[0013] High-power splitter, used to evenly distribute the pump light of high-power pump into each amplifier link;

[0014] A beam combiner is provided in each amplification link, located before and / or after the erbium-ytterbium co-doped optical fiber, to form forward or backward or bidirectional pumping, and is used to mix the optical signal and the pump light into one optical fiber;

[0015] High-power pump, used to generate pump light.

[0016] Furthermore, the power of the high-power pump is 8~20W.

[0017] Furthermore, it also includes a control unit, which determines the light intensity threshold of the input multi-wavelength mixed input signal light and turns off the amplification function for the signal light below the threshold.

[0018] Furthermore, the control unit also controls the power of the high-power pump by monitoring the amplified power of each optical signal of the corresponding wavelength to maintain the stability of the output power.

[0019] Furthermore, the control unit calculates the maximum and minimum values ​​of the amplified power of each optical signal of the corresponding wavelength through average comparison, and controls the output power of the high-power pump in real time by comparing the maximum and minimum values ​​with the preset target values, so as to control the power difference of each channel within ±0.5dBm.

[0020] Furthermore, the control unit monitors the internal temperature of the high-power pump and amplifier unit in real time and adjusts the temperature to ensure a constant temperature;

[0021] The amplification link and all devices on the link constitute an amplification unit.

[0022] Furthermore, the extinction ratio of the polarization beam splitter is not less than 40 dB.

[0023] Furthermore, the number of high-power pumps is one or two, one corresponds to forward and backward pumping, and two corresponds to bidirectional pumping.

[0024] Furthermore, the wavelength range of multiplexing and demultiplexing of the wavelength division multiplexer is 1530-1565 nm.

[0025] According to the above-mentioned multi-wavelength polarization-maintaining fiber amplifier for FMCW laser radar, it is applied to automobiles.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1) Cost reduction

[0028] Sharing components saves costs: By sharing high-power pumps, some passive components (such as polarization beam splitters, input detection tubes, etc.) and control circuits (existing circuits for controlling high-power pumps and other components), the repeated purchase of hardware equipment and the material cost can be reduced. The existing polarization-maintaining fiber amplifiers use polarization-maintaining erbium-ytterbium co-doped fibers, while non-polarization-maintaining erbium-ytterbium co-doped fibers are used here. The price of polarization-maintaining erbium-ytterbium co-doped fibers is 5-10 times that of non-polarization-maintaining erbium-ytterbium co-doped fibers. At the same time, the price of polarization-maintaining fibers used for connection is also very expensive.

[0029] Reduce the use of optical fibers and reduce costs: Only a single polarization-maintaining optical fiber is used for transmission, which significantly reduces the optical fiber procurement cost compared to the use of multiple polarization-maintaining optical fibers in the existing technology. In large-scale production and application scenarios, this cost reduction effect is more obvious, making the product more price competitive in the market. The focus is on the advantages of convenient management and reduced size after integration in multi-channel mixing, sharing the polarization-maintaining optical fiber used for input and output optical fibers, sharing high-power pumps, control circuits, drive circuits, etc.

[0030] 2) Improved flexibility

[0031] Wavelength and number of paths can be flexibly selected: different wavelengths and different number of paths can be freely selected within the C-band range according to actual use requirements. This flexibility enables the multi-wavelength polarization-maintaining fiber amplifier of the present invention to better adapt to various complex and changeable application scenarios, and meet the personalized needs of different users for different wavelength and number of paths configurations, without the need to redesign or replace the entire set of equipment for different needs, greatly improving the versatility and adaptability of the equipment.

[0032] 3) Volume reduction

[0033] Sharing components reduces volume: Since multiple key components are shared, the number of overall components is reduced, thereby effectively reducing the size of the device. In application environments with limited space (such as the interior space of a car that has strict requirements on the volume of the LiDAR device), the small size advantage of the present invention is particularly prominent, making it easier to install and integrate into other systems, providing strong support for the miniaturization design of the device and helping to promote the application of LiDAR in more volume-sensitive fields.

[0034] 4) Improved integration

[0035] One-to-one management is convenient and efficient: The LiDAR main control unit only needs one-to-one management, which greatly simplifies the management process and complexity compared to the one-to-many management method in the existing technology. This one-to-one management mode not only reduces the probability of system errors, but also improves management efficiency, allowing the main control unit to obtain and process information from each amplification link more timely and accurately, and achieve precise control of the entire system.

[0036] Centralized power supply and wiring simplify the system: The centralized power supply and wiring design further optimizes the system structure, reduces the complexity and length of wiring, reduces line loss and interference risks, and also facilitates the installation, maintenance and upgrade of the system, improves the overall stability and reliability of the system, and provides a strong guarantee for the long-term stable operation of the system.

[0037] 5) Enhanced reliability

[0038] Reducing the number of optical fibers reduces risks: The multi-wavelength hybrid input and output method reduces the number of optical fibers used and the number of interfaces, thereby reducing the risk of system failures due to problems such as optical fiber damage or loose interfaces. Optical fibers are prone to damage in complex environments (such as vibration, temperature changes, etc.). Reducing the number of optical fibers and interfaces can effectively improve the system's anti-interference ability and stability, ensuring that the LiDAR system can still work reliably in various harsh environments, and improving the overall reliability and service life of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of the structure of this application;

[0040] Figure 2 is the control diagram of this application;

[0041] Figure 3 is a principle block diagram of a forward pumping implementation method of the present application;

[0042] Figure 4 is a principle block diagram of the backward pumping implementation method of the present application;

[0043] Figure 5 It is a principle block diagram of the bidirectional pumping implementation method of the present application. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments in the present application belong to the scope of protection of this application.

[0045] Those skilled in the art should understand that, in the disclosure of the present application, the terms "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, which are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the above terms should not be understood as limiting the present application.

[0046] Each wavelength of the existing FMCW laser radar needs to be amplified by a corresponding polarization-maintaining fiber amplifier to reach the target power and then transmitted through the corresponding polarization-maintaining fiber.

[0047] Based on this, the present invention solves the problems existing in the prior art by using a wavelength division multiplexer.

[0048] Example 1

[0049] like Figure 1-5 As shown, the multi-wavelength polarization-maintaining fiber amplifier for FMCW laser radar includes:

[0050] A polarization beam splitter, the input end of which is connected to a multi-wavelength mixed input signal light, and the output end of which outputs a multi-wavelength mixed output signal light, is connected to the wavelength division multiplexer, and is used to separate the multi-wavelength mixed input signal light into optical signals of different polarization states, so that each wavelength optical signal can enter the corresponding amplification link for independent processing, and is used to re-combine the amplified wavelength optical signals of different polarization states into a beam of multi-wavelength mixed output signal light for output;

[0051] In this embodiment, the polarization beam splitter is an optical element that can separate or combine light according to the polarization state of the light, and is used to separate and combine optical signals of different polarization states to improve the capacity and performance of the optical communication system. Preferably, the extinction ratio of the polarization beam splitter reaches 40dB or higher to ensure the performance and accuracy of the system.

[0052] The wavelength division multiplexer is used to perform wavelength division operation on the separated multi-wavelength mixed input signal light, so that each wavelength optical signal can enter the corresponding amplification link for amplification and then return to the wavelength division multiplexer for multiplexing, and then output to the polarization beam splitter;

[0053] In this embodiment, the main function of the wavelength division multiplexer is to simultaneously transmit multiple optical signals of different wavelengths in one optical fiber, thereby realizing multiplexing and demultiplexing of optical signals and improving the transmission capacity and spectrum utilization of the optical fiber. Preferably, the wavelength range of multiplexing and demultiplexing of the wavelength division multiplexer is: C-band (1530nm-1565nm), and the specific splitting range is adjusted according to the actual situation of the input optical signal.

[0054] Erbium-ytterbium co-doped optical fiber, used to form an amplification link;

[0055] In this embodiment, erbium-ytterbium co-doped fiber is a special optical fiber widely used in the field of optical communication and optical amplification. When high-power pump light is evenly distributed through a high-power splitter to enter each amplification link containing erbium-ytterbium co-doped fiber, the ytterbium ions first absorb the pump light energy and transition to an excited state. Then, the ytterbium ions in the excited state transfer energy to the erbium ions through a non-radiative transition, causing the erbium ions to transition to a higher energy level of the excited state. When the multi-wavelength mixed input signal light enters the erbium-ytterbium co-doped fiber, the erbium ions in the excited state will transition back to the ground state and radiate photons with the same wavelength as the input signal light, thereby achieving amplification of the signal light. Due to the transition radiation characteristics of erbium ions between specific energy levels, the input signal light can obtain sufficient gain when passing through the erbium-ytterbium co-doped fiber to achieve the output power level required by the lidar system. In the present invention, the loss of different components in each amplification link can be compensated by reasonably adjusting the length of each erbium-ytterbium co-doped optical fiber, so that the gain flatness can be controlled within the range of ±0.5dB, ensuring that each wavelength signal can obtain a relatively uniform amplification effect.

[0056] A Faraday rotator, located on each amplification link, is used to rotate the polarization state of the reflected light by 90° compared to the incident light;

[0057] In this embodiment, the Faraday rotator is also called a Faraday rotator. In the present invention, after the multi-wavelength mixed input signal light enters the polarization-maintaining fiber amplifier, it is demultiplexed by the wavelength division multiplexer, and the optical signal of each wavelength enters the corresponding amplification link for amplification. During the transmission of the optical signal along the amplification link, when passing through the Faraday rotator, its polarization state will be precisely rotated. Specifically, the polarization state of the reflected light is rotated by 90° compared with the polarization state of the incident light. This rotation of the polarization state is of key significance for the subsequent processing and transmission of the optical signal.

[0058] High-power splitter, used to evenly distribute the pump light of high-power pump into each amplifier link;

[0059] In this embodiment, the high-power splitter realizes the splitting function based on the principle of light interference or optical coupling, and is mainly used to split one input optical signal into multiple output optical signals according to a specific ratio or method. In the present invention, its function is to evenly distribute the high-power pump light to each amplification link to ensure that each amplification link can obtain appropriate pump energy and realize effective amplification of signals of different wavelengths. It can work stably in a high-power environment, ensure that the optical power after splitting meets the needs of each amplification link, and minimize the power loss and signal distortion in the splitting process.

[0060] A beam combiner is provided in each amplification link, located before and / or after the erbium-ytterbium co-doped optical fiber, to form forward or backward or bidirectional pumping, and is used to mix the optical signal and the pump light into one optical fiber;

[0061] In this embodiment, the beam combiner is also based on the principle of light interference or optical coupling, but the optical path design and working mode are opposite to those of the splitter, and the purpose is to mix the pump light and the optical signal into the optical fiber. Preferably, the position of the beam combiner determines the forward, backward and bidirectional pumping. Figure 3 In the example, the combiner is located before the Erbium-Ytterbium co-doped fiber for forward pumping. Figure 4 In the example, the beam combiner is located after the Er-Yb co-doped fiber for backward pumping. Figure 5 In the scheme, the combiner is located before and after the Er-Yb co-doped fiber for bidirectional pumping.

[0062] High-power pump, used to generate pump light.

[0063] In this embodiment, the main function of the high-power pump is to generate high-power pump light to stimulate particle transitions in the gain medium, thereby achieving amplification of the input optical signal. In the present invention, according to the actual number of paths used and power requirements, the power of the high-power pump can be selected in different specifications such as 8W, 10W, 15W, and 20W. The power of the pump light needs to match the absorption characteristics of the gain medium, the power and wavelength of the signal light, and other factors to ensure that while meeting the signal light amplification requirements, it will not cause damage to the gain medium or other optical components. For example, if the pump light power is too high, it may cause excessive excitation of particles in the gain medium, produce nonlinear effects, and affect the quality of the signal light; if the pump light power is too low, sufficient signal light gain cannot be achieved, and the system performance requirements cannot be met.

[0064] The control unit judges the light intensity threshold of the input multi-wavelength mixed input signal light and turns off the amplification function for the signal light below the threshold.

[0065] In this embodiment, the control unit determines whether there is an optical signal input based on the detection circuit of the input optical signal, and turns off the amplification function if the input optical signal is lower than the threshold value, so as to avoid working when there is no input or the input is too low, which will not meet the use conditions and reduce the life of the device.

[0066] Preferably, when the light intensity of the input optical signal is higher than the threshold, the real-time power control is achieved through the monitoring feedback of each output power (the power of each optical signal of the corresponding wavelength after being amplified) and automatic power control (controlling the high-power pump output power) to maintain the stability of the output power. Since the output power of each channel is different, the control unit calculates the maximum and minimum values ​​through average comparison, and controls the high-power pump output power in real time by comparing the maximum and minimum values ​​with the target value, and controls the power difference of each channel within ±0.5dBm to meet the actual use requirements.

[0067] The control unit monitors the high-power pump and the internal ambient temperature of the entire amplifier unit in real time. If the temperature is too low or too high, the control unit will turn on heating and cooling to control the temperature in real time, so that the temperature is within the controllable range to ensure the indicators and product life. Among them, the amplifier link and all the devices on the link constitute the amplifier unit.

[0068] Among them, the driving circuit of the high-power pump, the components for temperature control, and the sensors for detecting temperature used here are all prior art and will not be described in detail here. The control unit can also be an existing control unit, on which means of power monitoring and temperature control are added. The detection circuit for detecting the presence and luminosity of the optical signal and the circuit for detecting the output power are also prior art means, and are not the technical points to be protected by this application, so they will not be described in detail here.

[0069] The method by which the control unit calculates the maximum and minimum values ​​through average comparison is:

[0070] The control unit samples the output power of each channel multiple times (MS level) in turn through the ADC sampling circuit. The sampled data is then passed through the median average filtering algorithm (continuously collecting N data, removing a maximum value and a minimum value, and then taking the average of the remaining data, and the data value range of N is 3 to 14). The accurate value is obtained after removing interference as much as possible. After obtaining the detection value of this round, the maximum and minimum power data of multiple channels are taken out. After comparing with the target value, the high-power pump output power is adjusted through the automatic power control circuit according to the control logic of controlling the power of each channel within the range of ±0.5dBm of the target value.

[0071] If one or more channels are abnormal in the collected multi-channel output power data, the current round of power adjustment is abandoned, the number of errors is accumulated, and the number of errors is cleared when it returns to normal in the subsequent collection process. When the number of errors exceeds the specified number, it is judged as a device failure. The output can be restarted or shut down according to usage requirements.

[0072] In this way, the present invention can amplify multiple wavelengths and then mix them, and transmit them through a single polarization-maintaining optical fiber. By sharing high-power pumps, some passive components (a polarization beam splitter, an input detection tube), and control circuits, the use of polarization-maintaining optical fibers is reduced to reduce the amplification and transmission costs of multiple wavelengths of FMCW laser radars.

[0073] Example 2

[0074] Applying Example 1 to an automobile, such as Figure 2 As shown, the basic control flow is as follows:

[0075] The multi-wavelength mixed light is input to one port of the polarization beam splitter;

[0076] Multi-wavelength mixed light separates each wavelength to its own amplification link;

[0077] After each wavelength is amplified, it is returned after the polarization state is adjusted through the FRM (Faraday Rotating Mirror);

[0078] Each wavelength returns and mixes again;

[0079] The amplified multi-length mixed light is output from the second port of the polarization beam splitter.

[0080] The parts not described in detail in this application are prior art, so this application does not describe them in detail.

[0081] It is to be understood that the term "one" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element may be one, while in another embodiment, the number of the element may be multiple, and the term "one" should not be understood as a limitation on the quantity.

[0082] Although this article uses more professional terms, it does not exclude the possibility of using other terms. These terms are used only to more conveniently describe and explain the essence of this application; interpreting them as any additional restrictions is contrary to the spirit of this application.

[0083] The present application is not limited to the above-mentioned optimal implementation mode. Anyone can derive other forms of products under the inspiration of this application. However, no matter what changes are made in the shape or structure, all technical solutions that are the same or similar to those of the present application fall within the protection scope of the present application.

Claims

1. A multi-wavelength polarization-maintaining fiber amplifier for FMCW laser radar, characterized in that: include: A polarization beam splitter, the input end of which is connected to a multi-wavelength mixed input signal light, and the output end of which outputs a multi-wavelength mixed output signal light, is connected to the wavelength division multiplexer, and is used to separate the multi-wavelength mixed input signal light into optical signals of different polarization states, so that each wavelength optical signal can enter the corresponding amplification link for independent processing, and is used to re-combine the amplified wavelength optical signals of different polarization states into a beam of multi-wavelength mixed output signal light for output; A wavelength division multiplexer, used for performing wavelength division operation on the separated multi-wavelength mixed input signal light, so that each wavelength optical signal can enter the corresponding amplification link for amplification and then return to the wavelength division multiplexer for multiplexing, and then output to the polarization beam splitter; Erbium-ytterbium co-doped optical fiber, used to form the amplification link; A Faraday rotator, located on each amplification link, is used to rotate the polarization state of the reflected light by 90° compared to the incident light; High-power splitter, used to evenly distribute the pump light of high-power pump into each amplifier link; A beam combiner is provided in each amplification link, located before and / or after the erbium-ytterbium co-doped optical fiber, to form forward or backward or bidirectional pumping, and is used to mix the optical signal and the pumping light into one optical fiber; High-power pump, used to generate pump light.

2. The multi-wavelength polarization-maintaining fiber amplifier for FMCW laser radar according to claim 1, characterized in that: The power of the high-power pump is 8-20W.

3. The multi-wavelength polarization-maintaining fiber amplifier for FMCW laser radar according to claim 1, characterized in that: It also includes a control unit, which determines the light intensity threshold of the input multi-wavelength mixed input signal light and turns off the amplification function for the signal light below the threshold.

4. The multi-wavelength polarization-maintaining fiber amplifier for FMCW laser radar according to claim 3, characterized in that: The control unit also controls the power of the high-power pump by monitoring the amplified power of each optical signal of the corresponding wavelength to maintain the stability of the output power.

5. A multi-wavelength polarization-maintaining fiber amplifier for FMCW laser radar according to claim 4, characterized in that: The control unit calculates the maximum and minimum values ​​of the amplified power of each optical signal of the corresponding wavelength through average comparison, and controls the output power of the high-power pump in real time by comparing the maximum and minimum values ​​with the preset target values, so as to control the power difference of each channel within ±0.5dBm.

6. The multi-wavelength polarization-maintaining fiber amplifier for FMCW laser radar according to claim 4, characterized in that: The control unit monitors the internal temperature of the high-power pump and amplifier unit in real time and adjusts the temperature to ensure a constant temperature; The amplification link and all devices on the link constitute an amplification unit.

7. The multi-wavelength polarization-maintaining fiber amplifier for FMCW laser radar according to claim 1, characterized in that: The extinction ratio of the polarization beam splitter is not less than 40 dB.

8. A multi-wavelength polarization-maintaining fiber amplifier for FMCW laser radar according to any one of claims 1 to 7, characterized in that: The number of the high-power pumps is one or two. When there is one, it corresponds to forward and backward pumping, and when there are two, it corresponds to bidirectional pumping.

9. A multi-wavelength polarization-maintaining fiber amplifier for FMCW laser radar according to any one of claims 1 to 7, characterized in that: The wavelength range of multiplexing and demultiplexing of the wavelength division multiplexer is 1530-1565nm.

10. The use of a multi-wavelength polarization-maintaining fiber amplifier for FMCW laser radar according to any one of claims 1 to 9, characterized in that: Application of multi-wavelength polarization-maintaining fiber amplifier for FMCW lidar in the automotive field.

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