Image modulation VCSEL method
By using triangular wave PWM signal to drive VCSEL, combined with image preprocessing and real-time feedback system, the problem of insufficient modulation depth in the prior art is solved, and a higher signal linearity and dynamic range is achieved, and the quality and efficiency of data transmission are improved.
Patent Information
- Application Number
- CN202411466974.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-21
- Publication Date
- 2025-01-03
AI Technical Summary
The prior art has shortcomings in improving the modulation depth of image modulation VCSEL, which is difficult to meet the needs of modern high-speed data transmission, especially in terms of high data rates and signal-to-noise ratios.
VCSEL is driven by triangular wave pulse width modulation (PWM) signals, and ensures smoothness of the signal by pre-processing images, generating high-resolution PWM signals, low-pass filtering and signal amplification, independently driving the VCSEL array, real-time monitoring and adjustment of the photodetector feedback system Sex and stability.
Significantly reduce high-frequency harmonic generation, improve modulation depth and signal linearity, enhance the dynamic range and delicateness of image modulation, improve the reliability and accuracy of data transmission, and reduce system complexity and cost.
Smart Images
Figure CN119254345A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the field of optical communication technology, and in particular to a method for image modulation of a VCSEL. Background Art
[0002] In data centers and supercomputers, large amounts of data need to be transmitted in parallel. Using an image-modulated VCSEL (Vertical Cavity Surface Emitting Laser) array, multiple data streams can be modulated and transmitted simultaneously, thereby increasing the total bandwidth. The image-modulated VCSEL array can process multiple data streams simultaneously, significantly increasing the total bandwidth of the system and meeting the needs of high-speed data transmission. Compared to traditional electronic interconnects, optical interconnects have lower power consumption. Image-modulated VCSELs further reduce the power consumption of the system through efficient light modulation and transmission.
[0003] In the application of image modulation VCSEL, increasing the modulation depth is of great significance. Increasing the modulation depth can increase the strength of the signal, thereby improving the signal-to-noise ratio (SNR) of the system. A higher SNR can better resist the noise and interference encountered during transmission and ensure the integrity of the data. In addition, a larger modulation depth allows more information to be encoded, which is crucial for scenarios where large amounts of data need to be transmitted.
[0004] Traditional methods for improving the modulation depth of image modulation VCSEL include optimizing the driving circuit, controlling the temperature, using feedback control, using pre-distortion technology, etc. These methods have achieved certain results. For example, using a high-precision current source and a high-speed driving current makes the current provided to the VCSEL more stable and accurate, reduces the noise of the current source and improves the response speed, which can improve the modulation depth to a certain extent. For another example, by modeling the nonlinear characteristics of the VCSEL and performing pre-distortion processing in the input signal, the linearity and depth of the modulated signal can also be improved to a certain extent.
[0005] Modern communication systems are experiencing unprecedented growth in data traffic, including Internet traffic, cloud computing, big data processing, video streaming, etc. These applications require high-speed and reliable data transmission channels. The existing traditional modulation methods are unable to cope with these high data rates. It is necessary to explore new modulation methods to improve the modulation depth of image modulation VCSEL and support higher data transmission efficiency. Summary of the invention
[0006] To solve the above problems, the present invention provides a method for image modulation VCSEL, including step 1, preprocessing the image; step 2, generating a PWM (pulse width modulation) signal; step 3, converting the PWM signal into an analog voltage signal, and generating a current for driving the VCSEL according to the analog voltage signal; step 4, current driving the VCSEL; wherein the PWM signal is a triangular wave signal.
[0007] The reason why the PWM signal is a triangular wave and can increase the modulation depth is that it can significantly reduce the generation of high-frequency harmonics. Compared with the square wave signal, the spectral components of the triangular wave are smoother and more continuous, reducing the intensity of the high-frequency components. When using a triangular wave signal to drive the VCSEL, there are fewer high-frequency noise and distortion components in the signal, thereby improving the purity of the signal and the response accuracy of the VCSEL. The reduction of high-frequency harmonics directly increases the modulation depth, because the main frequency components of the signal are more easily captured and responded to by the VCSEL, reducing unnecessary signal loss and energy dissipation.
[0008] Furthermore, step 1 includes converting the image pixel values into grayscale values. Converting the image into grayscale values simplifies the data processing complexity. Grayscale images retain the brightness information of the image, which is the most critical visual feature. This increases the processing speed and reduces the bandwidth requirements, resulting in a significant improvement in the performance and efficiency of the image modulated VCSEL.
[0009] Furthermore, step 1 also includes noise filtering and contrast enhancement. Noise filtering can improve the signal-to-noise ratio of the image, making useful image information more prominent. The important features and details in the image with a high signal-to-noise ratio are clearer, which is of great significance for subsequent image modulation and transmission. By filtering the noise in the image, the bit error rate can be effectively reduced to ensure the reliability and accuracy of data transmission. Contrast enhancement can make the details in the image more obvious, especially in areas where the grayscale value changes are not obvious. The enhanced contrast can highlight the edge and texture features in the image, making the image clearer and more layered. In addition, contrast enhancement can also expand the dynamic range of the image, so that the details of the bright and dark areas can be fully displayed, ensuring high-quality modulation effects at different brightness levels and improving the overall image quality.
[0010] Furthermore, step 2 includes using a digital signal processor (DSP) to generate a PWM signal from the image data. The DSP can accurately process complex signals and generate high-resolution PWM signals, thereby improving the accuracy and depth of modulation. In addition, the DSP has the characteristics of high programming flexibility and can adjust the PWM parameters in real time to adapt to different image characteristics and application requirements.
[0011] Furthermore, step 3 includes low-pass filtering and signal amplification. The low-pass filter can effectively remove high-frequency noise and interference in the PWM signal to ensure the smoothness and stability of the signal; the low-pass filter converts the discrete PWM signal into a continuous analog voltage signal, avoiding rapid changes and jitters of the signal, making the current driving the VCSEL more stable, thereby achieving more precise light output control. Signal amplification can increase the strength of the analog voltage signal after filtering, ensuring that the signal has sufficient amplitude to drive the VCSEL, thereby obtaining the required light output power and modulation depth.
[0012] Furthermore, the PWM signal is multi-channel, and the VCSEL is a VCSEL array, and each VCSEL is driven by a corresponding PWM current signal. Each VCSEL is driven by a separate PWM signal, and each VCSEL is independently and accurately controlled. The luminous intensity of each VCSEL can be flexibly adjusted according to different image pixels or signal requirements, thereby achieving high-resolution image modulation and output. Multi-channel PWM signal drive can restore image details more meticulously, improve overall image quality, reduce image distortion, and ensure high-quality image reproduction.
[0013] Furthermore, it also includes a photodetector and a feedback system, which uses the photodetector to monitor the output light intensity of the VCSEL in real time, and adjusts the duty cycle of the PWM signal through the feedback system to ensure the stability and accuracy of the output light intensity. The photodetector monitors the output light intensity of the VCSEL in real time and can quickly detect any fluctuations or deviations in light intensity. Through the feedback system, the duty cycle of the PWM signal can be adjusted in time to compensate for these fluctuations and ensure the stability of the output light intensity of the VCSEL.
[0014] Furthermore, the frequency of the triangular wave signal is greater than 200KHz and less than 10MHz. The high-frequency triangular wave signal (greater than 200KHz) can drive the VCSEL faster, allowing it to quickly respond to changes in the input signal. The frequency range below 10MHz can effectively avoid high-frequency noise and electromagnetic interference, thereby improving the stability and reliability of the system. In addition, the moderate frequency range can ensure that the triangular wave signal is not easily distorted during transmission and maintains its original waveform characteristics, thereby accurately controlling the luminous intensity of the VCSEL and improving the modulation accuracy.
[0015] Furthermore, the amplitude of the triangle wave signal is greater than 0 V and less than 3.3 V. The amplitude range is set between 0 V and 3.3 V, which is compatible with the operating voltage range of most digital circuits and microcontrollers, ensuring the compatibility and safety of system design and preventing excessive voltage from damaging the circuit and VCSEL.
[0016] Furthermore, the triangular wave signal is a symmetrical triangular wave. The symmetrical triangular wave signal has the characteristics of linear rise and fall, which makes the duty cycle adjustment of the PWM signal more uniform and smooth, avoids the modulation nonlinearity and distortion that may be caused by the asymmetrical waveform, and improves the quality of the modulated signal. The symmetrical triangular wave signal is easy to design and analyze, and its spectral characteristics are clear, which helps to simplify the design process and signal processing of the system, and effectively reduces the complexity of debugging and optimization. In addition, the symmetrical shape ensures the consistency of the driving signal throughout the cycle, reduces the error accumulation within the cycle, improves the modulation accuracy and stability of the system, and ensures that the output light intensity of the VCSEL is more stable and accurate.
[0017] Beneficial effects of the present invention: (1) As described above, the present invention significantly reduces the generation of high-frequency harmonics and improves the modulation depth.
[0018] (2) The PWM triangular wave signal used in the present invention improves the linearity of the signal. The linear rising and falling slopes of the triangular waveform make the signal change more uniform and predictable. This linear change characteristic can better match the linear response range of the VCSEL, reduce nonlinear distortion and uneven power distribution problems, and ensure that the output light intensity of the VCSEL is proportional to the input electrical signal, thereby achieving deeper and more precise modulation.
[0019] (3) The PWM triangle wave signal used in the present invention effectively improves the dynamic range of the VCSEL modulation system. The symmetry and continuous change characteristics of the triangle wave signal enable the VCSEL to obtain a wider dynamic range within the entire signal cycle. This helps to more finely modulate image data of different gray levels, enhance the delicacy and layering of image modulation, and improve image quality and transmission effect.
[0020] (4) The PWM triangular wave signal used in the present invention has a filtering effect: since the spectral characteristics of the triangular wave are more concentrated and have fewer high-frequency harmonics, the design of the filter can be simpler and more efficient. This not only reduces the complexity and cost of the system, but also improves the signal processing speed and stability, thereby facilitating the overall performance improvement of the VCSEL modulation system.
[0021] Based on the above beneficial effects, the present invention has good application prospects in the field of optical communication technology. BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Figure 1 A schematic diagram of a method for image modulation of a VCSEL. DETAILED DESCRIPTION
[0023] In order to make the objectives, technical solutions and advantages of the present application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and examples.
[0024] The present invention provides a method for image modulation VCSEL, such as Figure 1 As shown, the method includes step 1, preprocessing the image; step 2, generating a PWM signal; step 3, converting the PWM signal into an analog voltage signal, and generating a current to drive the VCSEL according to the analog voltage signal; step 4, the current drives the VCSEL. Wherein, the PWM signal is a triangular wave signal. The detailed description of each step is as follows: Step 1: Preprocess the image.
[0025] First, obtain the original image to be modulated. The original image can be a color image (such as RGB format) or a grayscale image. If the original image is a color image, it needs to be converted into a grayscale image. The calculation formula is: Gray=0.299×R+0.587×G+0.114×B. Each pixel value of the grayscale image is between 0 and 255. Then, according to the noise type and characteristics of the image, select a suitable filtering method to process the grayscale image to obtain a smoothed image after noise filtering. The filtering methods that can be used are mean filtering, median filtering, and Gaussian filtering. Mean filtering is to smooth the image and reduce noise by replacing each pixel value in the image with the average value of its neighboring pixel values; median filtering is to replace each pixel with the median value of its domain pixel value, which is particularly effective in removing salt and pepper noise; Gaussian filtering is to use Gaussian function to weight the neighboring pixel values to smooth the image while retaining edge information. Then, the image contrast is enhanced by modulating the grayscale distribution of the image; the grayscale range of the image is stretched by histogram equalization, making the dark and bright details of the image clearer, which includes counting the number of pixels of each grayscale value in the image to obtain the grayscale histogram, calculating the cumulative distribution function based on the grayscale histogram, and mapping the original grayscale value to the new grayscale value through the cumulative distribution function, thereby adjusting the grayscale distribution of the image. On the basis of global histogram equalization, adaptive histogram equalization is applied to locally process the image, and excessive enhancement and noise amplification are avoided by limiting the contrast enhancement amplitude, which includes dividing the image into multiple small blocks, performing histogram equalization on each small block, setting a contrast limit threshold to avoid excessive contrast enhancement in the local area, and performing difference and fusion on the processed small blocks to obtain an overall enhanced image.
[0026] Step 2: Generate PWM signal DSP converts the grayscale value into the duty cycle of the PWM signal. The PWM signal represents different grayscale values by adjusting the pulse width (duty cycle). The higher the grayscale value, the larger the duty cycle; the smaller the grayscale value, the smaller the duty cycle. Specifically, the grayscale value is normalized to between 0 and 1, and a PWM signal with a corresponding duty cycle is generated based on this normalized value. For example, a pixel with a grayscale value of 128 is normalized to 0.5, and the corresponding PWM signal duty cycle is 50%.
[0027] In order to generate a triangular waveform PWM signal, the DSP needs to generate a high-frequency triangular wave signal as a reference signal. The frequency of the triangular wave signal is set between 200kHz and 10MHz to ensure sufficient response speed and signal stability. This frequency range can meet the needs of high-speed data transmission while avoiding high-frequency noise interference. The amplitude of the triangular wave is set between 0V and 3.3V, which is compatible with most digital circuits and VCSEL drive circuits. In addition, the triangular wave signal is a symmetrical triangular wave.
[0028] DSP compares the duty cycle corresponding to each gray value with the triangular wave signal. In each cycle, DSP compares the input gray value with the voltage of the current triangular wave signal. When the voltage of the triangular wave signal is higher than the voltage corresponding to the gray value, it outputs a high level; otherwise, it outputs a low level. The PWM signal generated by this comparison will change with the shape of the triangular wave within a cycle to form a modulated signal.
[0029] The generated PWM signal is a multi-channel signal, each corresponding to a pixel in the image or a VCSEL in the VCSEL array. This multi-channel PWM signal ensures that each VCSEL can be independently modulated according to the grayscale value of the corresponding image pixel. In this way, the VCSEL array can be accurately controlled so that its luminous intensity is highly matched with the image data, achieving the purpose of image modulation.
[0030] In this step, increasing the slope of the triangular wave signal can enhance the modulation speed, but a too fast slope will cause signal overshoot and ringing, which will affect the stability of the output optical signal of the VCSEL. At the same time, a too large slope will increase electrical noise and affect the purity of the signal. Therefore, it is necessary to smoothly control the slope to ensure the stability of the system and the purity of the signal while maintaining a high modulation speed. Therefore, when generating a triangular wave signal, a low-pass filter is used to remove high-frequency noise in the signal to ensure the smoothness of the waveform; in addition, a damping network, such as an RC or RL circuit, is added to the triangular wave generation circuit to slow down the too fast slope of the voltage change and eliminate possible overshoot and ringing. Specifically, the damping network adjusts the energy distribution in the signal transmission by introducing resistors, capacitors or inductors into the circuit: when the voltage or current changes too fast, the damping element absorbs excess energy, slows down the transient response, and avoids overshoot; at the same time, the damping network suppresses the ringing effect and makes the signal stable; by adjusting the damping coefficient, the speed of change of the voltage or current can be effectively controlled, the oscillation can be reduced, and the stability of the system can be improved.
[0031] Step 3: Convert the PWM signal into an analog voltage signal, and generate a current for driving the VCSEL according to the analog voltage signal.
[0032] First, the PWM signal is passed through a low-pass filter. The PWM signal is a high-frequency square wave signal, and its duty cycle corresponds to the grayscale value of the image pixel. In order to convert this discrete digital signal into a continuous analog voltage signal, a low-pass filter is required. The function of the low-pass filter is to eliminate the high-frequency components in the PWM signal and retain only the low-frequency components, thereby smoothing the square wave into a corresponding DC level. The design of the low-pass filter is crucial, and its cutoff frequency should be selected according to the frequency of the PWM signal and the required signal bandwidth. Usually, the cutoff frequency is set at one-tenth to one-twentieth of the PWM signal frequency to ensure smooth conversion of the signal while retaining sufficient bandwidth to respond to changes in image data.
[0033] The analog voltage signal obtained after passing through the low-pass filter is proportional to the grayscale value of the original image. These voltage signals represent different light intensity levels and are directly used to control the luminous intensity of the VCSEL. However, the signal after the low-pass filter may need further amplification to meet the voltage and current requirements of the VCSEL driver. Therefore, a signal amplifier is required to increase the voltage and power of the signal.
[0034] The amplifier needs to have sufficient bandwidth and linearity to ensure that the amplified signal accurately reflects the original analog voltage signal. At the same time, the gain of the amplifier needs to be adjusted according to the operating characteristics of the VCSEL to provide an appropriate drive current. Generally, the gain of the amplifier should be adjustable to adapt to different operating conditions and image modulation requirements. Choosing a low-noise, high-linearity amplifier can ensure that the signal will not be distorted or introduce additional noise during the amplification process, thereby maintaining the accuracy and stability of image modulation.
[0035] The amplified analog voltage signal is used to drive the VCSEL. The luminous intensity of the VCSEL is proportional to the driving current, which is controlled by the amplified voltage signal. By adjusting the gain of the amplifier and the characteristics of the filter, the light output of the VCSEL can be precisely controlled to be highly consistent with the input image data. In this way, high precision and high stability of image modulation can be achieved.
[0036] Step 4: Apply current to drive the VCSEL.
[0037] The luminous intensity of the VCSEL is adjusted according to the driving current to achieve optical modulation of the image signal.
[0038] Preferably, the image modulation VCSEL method of the present invention further includes a photodetector and a feedback system. The photodetector may be a photodiode or a photoelectric diode. The photodetector is installed near the radiation area of the VCSEL to ensure that it can accurately receive the output light signal of the VCSEL. The photodetector is connected to the feedback system so that the output signal of the photodetector is transmitted to the feedback system for processing. The output light intensity of the VCSEL is monitored in real time using the photodetector, and the duty cycle of the PWM signal is adjusted through the feedback system to ensure the stability and accuracy of the output light intensity.
[0039] Preferably, the PWM signal can also be a pulse sequence. The PWM pulse sequence can switch very quickly and can generate more pulses per unit time, thereby increasing the resolution of the modulation signal, more accurately controlling the brightness of the light source, and improving the depth of modulation. In addition, since the PWM pulse sequence can represent different signal levels by adjusting the width of the pulse, it has a large modulation range. Compared with traditional modulation methods, the PWM pulse sequence can achieve a larger signal dynamic range and can adjust the output of the light source over a wider range. In addition, the PWM pulse sequence has a strong anti-interference ability against noise and interference. This makes the modulated signal more stable and less susceptible to the influence of the external environment, ensuring the accuracy and reliability of the modulation.
[0040] In the image modulation process, the duty cycle of the PWM signal determines the luminous intensity of the VCSEL: a higher duty cycle corresponds to a greater light intensity, and a lower duty cycle corresponds to a smaller light intensity. Preferably, the contrast of the image is improved by dynamically adjusting the duty cycle of the PWM signal. In the dynamic adjustment, the duty cycle of the PWM signal is not fixed, but changes in real time according to the grayscale values of different pixels in the image: for pixels with higher brightness, the duty cycle increases, so that the light intensity emitted by the VCSEL is higher, and the details and brightness of the bright area are enhanced; for dark areas, the duty cycle decreases, so that the luminous intensity is reduced, and the details of the dark area are retained without overexposure. This dynamic adjustment is completed through DSP, and the system produces a corresponding PWM signal based on the grayscale information of the input image. Each pixel of the image corresponds to a different duty cycle, and the light intensity accurately matches the pixel brightness. This method enhances the contrast between light and dark in the image, making the bright part brighter and the dark part deeper, improving the overall contrast, and making the brightness distribution more natural and rich, enhancing the visual hierarchy, and improving the image quality of the system.
[0041] In summary, the present invention provides a method for image modulation VCSEL, including step 1, preprocessing the image; step 2, generating a PWM (pulse width modulation) signal; step 3, converting the PWM signal into an analog voltage signal, and generating a current for driving the VCSEL according to the analog voltage signal; step 4, current driving the VCSEL; wherein the PWM signal is a triangular wave signal. The present invention adopts a PWM triangular wave signal to significantly reduce the generation of high-frequency harmonics, improve the linearity of the signal, increase the dynamic range of the VCSEL modulation system, and enhance the modulation depth, and has good application prospects in the field of optical communication technology.
[0042] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.
Claims
1. A method for image modulation VCSEL, comprising step 1, preprocessing an image; step 2, generating a PWM signal; step 3, converting the PWM signal into an analog voltage signal, and generating a current for driving the VCSEL according to the analog voltage signal; step 4, the current drives the VCSEL; characterized in that: The PWM signal is a triangle wave signal.
2. The method for image modulation VCSEL according to claim 1, characterized in that: Step 1 involves converting image pixel values into grayscale values.
3. The method for image modulation VCSEL according to claim 2, characterized in that: Step 1 also includes noise filtering and contrast enhancement.
4. The method for image modulation VCSEL according to claim 1, characterized in that: Step 2 includes using a digital signal processor to generate a PWM signal from the image data.
5. The method for image modulation VCSEL according to claim 1, characterized in that: Step 3 includes low-pass filtering and signal amplification.
6. The method for image modulation VCSEL according to claim 1, characterized in that: The PWM signal is multi-channel, the VCSEL is a VCSEL array, and each VCSEL is driven by a corresponding PWM current signal.
7. The method for image modulation VCSEL according to claim 1, characterized in that: It also includes a photodetector and a feedback system. The photodetector is used to monitor the output light intensity of the VCSEL in real time. The duty cycle of the PWM signal is adjusted through the feedback system to ensure the stability and accuracy of the output light intensity.
8. The method for image modulating VCSEL according to any one of claims 1 to 7, characterized in that: The frequency of the triangular wave signal is greater than 200 KHz and less than 10 MHz.
9. The method for image modulation VCSEL according to claim 8, characterized in that: The amplitude of the triangular wave signal is greater than 0V and less than 3.3V.
10. The method for image modulation VCSEL according to claim 9, characterized in that: The triangular wave signal is a symmetrical triangular wave.