Narrow-linewidth blue-light semiconductor laser for underwater distance measurement

Abstract

The utility model discloses a narrow-linewidth blue-light semiconductor laser for underwater distance measurement. The narrow-linewidth blue-light semiconductor laser comprises a blue-light single-tube chip, a fast and slow axis integrated mirror, a gradient refractive index type volume grating and an optical isolator which are sequentially arranged along a straight line, meanwhile, in order to facilitate stability control, a hardware control structure based on an ADN8834 chip and a controller is provided. The laser is simple in structure, small in size, low in calibration difficulty, good in output spectrum quality and convenient for stability control, and can be applied to an FWCM laser radar to realize high-precision underwater distance measurement.

Description

TECHNICAL FIELD

[0001] The utility model relates to the technical field of laser, more particularly to a narrow line width blue light semiconductor laser for underwater ranging. BACKGROUND

[0002] Autonomous Underwater Vehicle (AUV) has become an important means of ocean exploration and underwater target detection and identification, and a low-power, small underwater laser ranging system is essential for the environmental perception ability of small AUVs.

[0003] At present, the existing laser radar based on pulse time of flight for ranging is not suitable for small platforms such as AUVs due to its high power consumption, large size and other defects; in the FWCM laser radar, the distance resolution is only related to the frequency modulation range of the laser, and because the sensitivity of coherent detection is very high, low-power and small semiconductor lasers can be used in the FWCM laser radar, and applied in scenes with very high requirements for size, weight and power consumption.

[0004] The tunable single-mode narrow line width semiconductor laser is the basis of the FWCM laser radar, and because the absorption of seawater to the detection light will affect the signal and thus shorten the detection distance, the blue-green light band located in the seawater "transmission window" is selected.

[0005] Because the blue light wavelength is short, the required distributed feedback period is small, and the semiconductor etching process required for the common DFB single-frequency narrow line width laser in the near-infrared wavelength is difficult to realize in the blue wavelength. At present, a phase shift grating is added in the DFB structure of the laser to realize 450nm single-mode laser, but its laser line width is about 3GHz, the coherence length is short, and it is difficult to meet the FWCM ranging requirements of a certain length.

[0006] Another kind of laser adopts intracavity frequency doubling technology of titanium sapphire laser to realize it, but its stability is poor, the volume is large, and the structure is complex, which is difficult to carry on the small platform.

[0007] Therefore, in view of the above-mentioned needs, an external cavity narrow line width blue light semiconductor laser is proposed, but the existing external cavity narrow line width blue light semiconductor laser still has the problem of large volume, and when the optical elements are installed and placed, it will cause the problems of difficult adjustment and optical path correction. Utility model content

[0008] Therefore, in view of the above-mentioned needs, an external cavity narrow line width blue light semiconductor laser is proposed, but the existing external cavity narrow line width blue light semiconductor laser still has the problem of large volume, and when the optical elements are installed and placed, it will cause the problems of difficult adjustment and optical path correction.

[0009] In order to achieve the above-mentioned purpose, the utility model adopts the following technical scheme: In order to achieve the above-mentioned purpose, the utility model adopts the following technical scheme:

[0010] A narrow-linewidth blue semiconductor laser for underwater ranging includes a blue single-tube chip, a fast and slow axis integrated mirror, a graded-index volume grating, and an optical isolator arranged sequentially in a straight line; a reflective volume Bragg grating is deposited on the surface of the graded-index volume grating near the optical isolator; the other end of the optical isolator is connected to a collimator fiber.

[0011] To ensure that the divergence angle and beam quality of the laser spot are similar, this application first performs fast and slow axis collimation, that is, using an integrated fast and slow axis collimation lens to focus and collimate the beam. Then, a graded-index volume grating is added, and the beam is refocused and collimated by a graded-index lens in front of the volume grating, further compressing the dead zone and improving its beam quality. A reflective volume Bragg grating provides synchronous external cavity feedback for the beam, thereby achieving wavelength locking and narrowing the spectral linewidth. Finally, the laser after external cavity feedback is coupled into an optical fiber through an optical isolator for unidirectional transmission.

[0012] Furthermore, the blue light single-tube chip has a wavelength of 447nm and a front-side reflectivity of 0.02%.

[0013] Furthermore, the diffraction efficiency of the reflective volume Bragg grating is 15% ± 3%, and the diffraction wavelength is 443.8 ± 0.1 nm.

[0014] Furthermore, the blue light single-tube chip, the fast and slow axis integrated mirror, the graded refractive index volume grating, and the optical isolator are arranged in an independent internal cavity.

[0015] In this application, by using an integrated fast and slow axis mirror, the device structure can be further simplified and its size reduced while ensuring beam quality; furthermore, by using a graded refractive index volume grating to focus the beam and then performing external cavity feedback, the beam quality can be effectively improved, achieving stable transmission while simplifying the device calibration work and reducing the difficulty of assembly and adjustment; at the same time, in terms of fiber coupling, by using an optical isolator, the output light is transmitted unidirectionally, reducing the damage of reflected light to the device.

[0016] As can be seen from the above technical solutions, the narrow-linewidth blue semiconductor laser for underwater ranging disclosed in this utility model is not only simple in structure, small in size, and easy to calibrate, but also has good output spectral quality, and can be applied to FWCM lidar to achieve high-precision underwater ranging.

[0017] To further optimize the above technical solution, a thermistor and a thermoelectric cooler are installed in the inner cavity.

[0018] Furthermore, one end of the thermistor is grounded, and the other end is connected to the ADN8834 chip, while the two ends of the thermoelectric cooler are connected to the ADN8834 chip respectively.

[0019] Specifically, one end of the thermistor is grounded, and the other end is connected to the IN1N pin of the ADN8834 chip. The positive terminal of the thermoelectric cooler is connected to the LDR pin of the ADN8834 chip, and the negative terminal is connected to the SW pin of the ADN8834 chip.

[0020] Furthermore, the ADN8834 chip is also connected to a controller to generate a thermoelectric cooler control signal based on the collected temperature of the thermistor and a preset temperature.

[0021] Furthermore, a button module is connected to the input terminal of the controller.

[0022] Furthermore, the output of the blue LED single-tube chip is connected to the input of the controller through a current sampling circuit and an A / D conversion module, and the output of the controller is connected to the input of the blue LED single-tube chip through a D / A conversion module and a constant current source drive module.

[0023] This application further provides a hardware structure framework for implementing laser temperature control and current drive, providing hardware support for its temperature control and current drive, thereby facilitating the improvement of laser stability.

[0024] This architecture facilitates fine-tuning of the laser's operating temperature range, allowing the laser to quickly stabilize at the new temperature point after a temperature change. Simultaneously, the architecture facilitates providing a stable current output, ensuring the laser receives constant current drive during operation. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0026] Figure 1 The attached diagram is a schematic diagram of an external cavity semiconductor laser.

[0027] Figure 2 The attached diagram shows an example of the pin connections for the ADN8834 chip.

[0028] Figure 3 The attached figure is a schematic diagram of the peripheral hardware connection structure of an external cavity semiconductor laser. Detailed Implementation

[0029] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0030] Example 1

[0031] This utility model discloses an external cavity semiconductor laser for FWCM lidar, which addresses the need for small size and high stability in underwater ranging.

[0032] Reference Figure 1 , Figure 1 This is a schematic diagram of the laser's structure;

[0033] The laser includes a blue single-tube chip 1, a fast and slow axis integrated mirror 2, a graded refractive index volume grating 3, and an optical isolator 4 arranged in a straight line in sequence; a reflective volume Bragg grating is deposited on the surface of the graded refractive index volume grating 3 near the optical isolator; the other end of the optical isolator 4 is connected to a collimator fiber.

[0034] After the blue light single-tube chip 1 emits laser light, the beam is collimated and focused by the fast and slow axis integrated mirror 2 and the graded refractive index volume grating 3. Then, the reflective volume Bragg grating performs wavelength locking and linewidth narrowing on the spatially combined laser beam to improve the output spectral characteristics. The graded refractive index lens in front of the grating simplifies the calibration difficulty.

[0035] Specifically, in order to ensure that the divergence angle and beam quality of the combined beam spot are close and to further simplify the laser structure, this application uses an integrated fast and slow axis collimation lens 2 to compress the divergence angle of the laser beam in the fast and slow axis directions, and compresses the laser volume through integrated design. At the same time, the divergence angle of the laser fast and slow axes after optical collimation will be significantly reduced, ensuring the transmission quality of the beam.

[0036] After spatial beam combining, a reflective volume Bragg grating (RVBG) is added to the optical system to provide external cavity feedback for synchronous beam combining of the laser beams. This achieves wavelength locking and narrowing of the spectral linewidth. The reflective volume Bragg grating used has a diffraction efficiency of 15% ± 3% and a diffraction wavelength of 443.8 ± 0.1 nm. The RVBG, as external cavity optical feedback, can feed back light of a specific wavelength to the output region, reducing the light loss at that wavelength. This facilitates mode competition with other wavelengths, prioritizing reaching the threshold for laser output, enabling the laser to output a single wavelength mode and achieving external cavity wavelength locking. Simultaneously, the RVBG effectively improves the output spectral quality.

[0037] Furthermore, in this embodiment, a graded-index volume grating 3 is used in the selection of the reflective volume Bragg grating. A graded-index lens is used in front of the grating to focus and collimate the input light, which further improves the beam quality and simplifies the calibration work of the device, reducing the difficulty of assembly and adjustment. At the same time, the use of an optical isolator 4 not only couples the input light, but also allows only unidirectional transmission of the output light, preventing reflected light in the system from damaging the device performance.

[0038] In one embodiment, in order to reduce power consumption, a blue single-tube chip 1 with a wavelength of 447nm (Hurricane Core Technology COS package, model JX-CCB-450-5000) is used, and the front-end surface reflectivity is reduced to 0.02% to further narrow the output spectral linewidth of the semiconductor laser and improve the external cavity efficiency.

[0039] This novel approach achieves narrow-linewidth, high-power laser output through a combination of external cavity feedback technology and fiber coupling technology. Furthermore, by integrating fast and slow axis collimating lenses, the structure is further simplified and compressed, enabling it to be mounted on an AUV.

[0040] Example 2

[0041] In this embodiment, the blue single-tube chip 1, the fast and slow axis integrated mirror 2, the graded refractive index volume grating 3, and the optical isolator 4 are arranged in an independent internal cavity. Simultaneously, a thermistor and a thermoelectric cooler are installed in the internal cavity to construct the hardware structure for laser temperature control and current drive, providing hardware support for improving laser stability.

[0042] In one embodiment, the ADN8834, a high-output-efficiency switch-mode single-chip TEC controller from Analog Devices (ADI), is used. The ADN8834 simplifies peripheral configuration while ensuring high accuracy and fast response in temperature control. For easy temperature monitoring, one end of the thermistor is grounded, and the other end is connected to the ADN8834 chip. The two ends of the thermoelectric cooler are also connected to the ADN8834 chip.

[0043] In this embodiment, the pinout and connection relationships of the ADN8834 chip are as follows: Figure 2 As shown, one end of the thermistor is grounded and the other end is connected to the IN1N pin (22) of the ADN8834 chip. The positive terminal of the thermoelectric cooler is connected to the LDR pin (17) of the ADN8834 chip, and the negative terminal is connected to the SW pin (14) of the ADN8834 chip.

[0044] To further optimize the above technical solution, such as Figure 3 As shown, another ADN8834 chip is connected to a controller.

[0045] In a preferred embodiment, the OUT1 pin (21) of the ADN8834 chip is connected to the input terminal of the controller through an A / D conversion module, while the IN2P pin (24) is connected to the output terminal of the controller through a D / A conversion module.

[0046] The working principle is as follows:

[0047] The voltage signal from the thermistor is amplified by the ADN8834 chip and then converted into a digital signal by the A / D conversion module, which is then input to the controller. The controller generates a control signal, which is output to the D / A conversion module to convert the control signal into an analog signal and transmit it to the ADN8834 chip. The ADN8834 chip outputs a control signal to the thermoelectric cooler (TEC) based on the received analog signal, adjusting the magnitude and direction of the current flowing through the TEC. When the temperature of the negative temperature coefficient (NTC) thermistor is lower than the target temperature, the TEC driver will drive the TEC to output a current of a certain amplitude in the heating direction. When the temperature of the NTC thermistor is higher than the target temperature, the TEC driver will reduce the TEC current or reverse the current direction, ultimately heating or cooling the laser and causing the laser temperature to approach the set value, thereby achieving precise temperature control.

[0048] In one embodiment, a preset temperature value is input to the controller, and a deviation value is obtained by comparing the converted digital signal with the preset value. Then, a control signal is generated based on the deviation value.

[0049] It should be noted that this method is only one of the controller implementation methods, and other methods may be used in other embodiments, which are not limited here. Meanwhile, this application aims to provide a hardware structure to facilitate laser temperature control.

[0050] Furthermore, to facilitate the input of preset temperature values, a button module is connected to the input terminal of the controller for user operation.

[0051] In one embodiment, to facilitate stable current driving, the output terminal of the blue LED single-tube chip is connected to the input terminal of the controller through a current sampling circuit and an A / D conversion module, and the output terminal of the controller is connected to the input terminal of the blue LED single-tube chip through a D / A conversion module and a constant current source driving module.

[0052] The current sampling circuit in this application is a common sampling circuit in the prior art. For example, the 3PA1030ADC chip manufactured by Enrico Corporation is used for sampling, which will not be described in detail here.

[0053] Preferably, the constant current source drive module includes, in sequence, a low-pass filter unit, a gain amplification unit, and a negative feedback voltage-controlled current source; the working process includes:

[0054] The analog signal converted by the D / A converter module first undergoes low-pass filtering to remove potential high-frequency noise and ensure signal purity. After filtering, it undergoes various gain adjustments to adapt to different driving requirements and achieve optimal driving performance. The processed analog signal is then fed into a negative feedback voltage-controlled current source. This current source provides precise driving control of the semiconductor laser, ensuring stable operation within the constant current circuit. This method enables fine-tuning of the control voltage in the constant current circuit, thereby ensuring the laser's output power and stability.

[0055] This application can assist lasers in operating within a suitable temperature range and facilitate the provision of stable current to blue single-tube chips, enabling them to achieve high power, high beam quality, high stability, and miniaturization, thus making them suitable for use in FMCW lidar and mounted on AUV platforms.

[0056] Furthermore, the narrow-linewidth blue semiconductor laser proposed in this application has a long coherence length, simple structure, and high stability in underwater ranging. It is not easily affected by external stress and temperature changes, and can simultaneously meet the requirements of small size and underwater ranging of FMCW lidar.

[0057] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0058] The above description of the disclosed embodiments enables those skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A narrow-linewidth blue semiconductor laser for underwater ranging, characterized in that, It includes a blue light single-tube chip, a fast and slow axis integrated mirror, a graded refractive index volume grating, and an optical isolator arranged sequentially in a straight line; a reflective volume Bragg grating is deposited on the surface of the graded refractive index volume grating near the optical isolator; the other end of the optical isolator is connected to a collimator fiber.

2. The laser according to claim 1, characterized in that, The blue LED single-tube chip has a wavelength of 447nm and a front-side reflectivity of 0.02%.

3. The laser according to claim 1, characterized in that, The diffraction efficiency of the reflective volume Bragg grating is 15% ± 3%, and the diffraction wavelength is 443.8 ± 0.1 nm.

4. The laser according to claim 1, characterized in that, The blue light single-tube chip, the fast and slow axis integrated mirror, the graded refractive index volume grating, and the optical isolator are arranged in an independent internal cavity.

5. The laser according to claim 4, characterized in that, The inner cavity is equipped with a thermistor and a thermoelectric cooler.

6. The laser according to claim 5, characterized in that, One end of the thermistor is grounded, and the other end is connected to the ADN8834 chip. The two ends of the thermoelectric cooler are connected to the ADN8834 chip respectively.

7. The laser according to claim 6, characterized in that, The ADN8834 chip is also connected to a controller.

8. The laser according to claim 7, characterized in that, The controller's input terminal is connected to a button module.

9. The laser according to claim 1, characterized in that, The output of the blue LED single-tube chip is connected to the input of the controller through a current sampling circuit and an A / D conversion module. The output of the controller is connected to the input of the blue LED single-tube chip through a D / A conversion module and a constant current source drive module.

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