A DWDM optical module for video transmission

Abstract

The utility model relates to a video transmission technical field, concretely relates to a DWDM optical module for video transmission, including laser driver, bias -T bias filter network and EML laser, laser driver is used for shaping amplification output difference electric signal to input electric signal, bias -T bias filter network's input respectively with laser driver's output and power connection, for with direct current bias voltage and difference electric signal are superimposed and output superimposed direct current bias's difference electric signal, EML laser's input with bias -T bias filter network's output connection, for with direct current bias's difference electric signal conversion is optical signal. The utility model reduces the performance risk caused by external interference or impedance mismatch, makes the optical module have high stability and long -term work ability in high -quality application scene such as broadcast level video transmission.

Description

Technical Field

[0001] This utility model relates to the field of video transmission technology, and specifically to a DWDM optical module for video transmission. Background Technology

[0002] 12G-SDI is a professional video interface standard for transmitting ultra-high-definition video signals. It can transmit uncompressed, high-quality images at data rates up to 12Gbps, making it ideal for applications such as broadcasting and post-production that require high resolution, high frame rates, and minimal latency. Compared to 3G-SDI, which requires a complex 4-link (4x HD-SDI) scheme to transmit 4Kp60, 12G-SDI offers up to 12Gbps of bandwidth and can transmit uncompressed 4K UHD (3840x2160) video signals over a single cable, up to 60 frames per second.

[0003] IP video transmission can be affected by network congestion and latency, making it unsuitable for applications with extremely high real-time requirements. 12G-SDI signals, with their uncompressed, ultra-low latency, and high stability, effectively compensate for the limitations of IP video transmission, making them more suitable for large venues and studios, remote broadcasting, video production, and video surveillance. Meanwhile, DWDM technology, by allocating independent wavelengths to each video stream, achieves physically isolated "dedicated channels," enhancing signal transmission security.

[0004] In the existing technology, a common DML laser optical module that supports SDI transmission is used to control the output intensity (power) and wavelength (frequency) of the laser by directly changing the driving current of the injected laser diode.

[0005] In existing technologies, the use of DML lasers results in severe chirping. Changes in carrier concentration due to current variations cause changes in the refractive index of the laser's active region, strongly modulating the phase / frequency of the light wave (i.e., chirping). This spectral broadening interacts with fiber dispersion during fiber transmission, leading to pulse broadening and signal distortion. Due to dispersion and chirping, the transmission distance of DML lasers is limited, especially in high-speed applications. At high data rates, rapid signal changes exacerbate distortion caused by dispersion and chirping, further limiting transmission distance. Utility Model Content

[0006] The purpose of this invention is to provide a DWDM optical module for video transmission, which solves the problem in the prior art that rapid changes in signal at high data rates exacerbate distortion caused by dispersion and chirp, thereby limiting the transmission distance.

[0007] This utility model is achieved through the following technical solution:

[0008] A DWDM optical module for video transmission includes a laser driver, a Bias-T bias filter network, and an EML laser, wherein:

[0009] The laser driver is used to shape and amplify the input electrical signal to output a differential electrical signal;

[0010] The input of the Bias-T bias filter network is connected to the output of the laser driver and the power supply, respectively, and is used to superimpose the DC bias voltage and the differential signal and output a differential signal superimposed with DC bias.

[0011] The input terminal of the EML laser is connected to the output terminal of the Bias-T bias filter network, which is used to convert the differential electrical signal superimposed with DC bias into an optical signal.

[0012] Preferably, the EML laser includes a laser diode and an EA modulator connected in series, wherein the laser diode is used to generate continuous laser light, and the EA modulator is used to convert the continuous laser light generated by the laser diode into an optical signal.

[0013] Preferably, the Bias-T bias filter network includes two sets of positive bias circuits and one set of negative bias circuits. The two sets of positive bias circuits are respectively connected to the two output terminals of the laser driver to provide positive bias voltages for the two paths of the differential electrical signal. The negative bias circuit is connected to the EML laser to provide negative DC voltages for the EML laser.

[0014] Preferably, the two sets of positive bias circuits include a first set of sub-positive bias circuits 1 and a second set of sub-positive bias circuits 2. The first set of sub-positive bias circuits 1 includes a resistor R1 and an inductor L1 connected in parallel, and also includes ferrite beads FB1, FB2 and a capacitor C1. The second set of sub-positive bias circuits 2 includes a resistor R2 and an inductor L2 connected in parallel, and also includes ferrite beads FB3, FB4 and a capacitor C2. The negative bias circuit includes a resistor R3 and an inductor L3 connected in parallel, and also includes ferrite beads FB5 and FB6.

[0015] Preferably, the output terminals of the first sub-positive bias circuit 1 and the negative bias circuit are connected to the EA modulator.

[0016] Preferably, the output terminal of the first sub-positive bias circuit 1 is connected between the laser diode and the EA modulator through a matching impedance.

[0017] Preferably, in the first group of sub-positive bias circuits 1, the first end of resistor R1 and the first end of inductor L1 are connected to the power supply Vcc, the second end of resistor R1 and the second end of inductor L1 are connected to the first end of ferrite bead FB1, the second end of ferrite bead FB1 is connected to the first end of ferrite bead FB2, the second end of ferrite bead FB2 and the first output terminal of laser driver are connected to the first end of capacitor C1, and the second end of capacitor C1 is the output terminal of the first group of sub-positive bias circuits 1;

[0018] In the second group of sub-positive bias circuits 2, the first end of resistor R2 and the first end of inductor L2 are connected to the power supply Vcc. The second end of resistor R2 and the second end of inductor L2 are connected to the first end of ferrite bead FB3. The second end of ferrite bead FB3 is connected to the first end of ferrite bead FB4. The second end of ferrite bead FB4 and the second output terminal of the laser driver are connected to the first end of capacitor C2. The second end of capacitor C2 is the output terminal of the second group of sub-positive bias circuits 2.

[0019] Preferably, in the negative bias circuit, the first end of resistor R3 and the first end of inductor L3 are connected to the negative voltage, the second end of resistor R3 and the second end of inductor L3 are connected to the first end of ferrite bead FB5, the second end of ferrite bead FB5 is connected to the first end of ferrite bead FB6, and the second end of ferrite bead FB6 is the output terminal of the negative bias circuit.

[0020] Preferably, the linewidth of the EML laser is less than 10MHz.

[0021] Preferably, the low-frequency cutoff frequency of the Bias-T bias filter network is set to below 500Hz.

[0022] Compared with the prior art, this utility model has the following advantages and beneficial effects:

[0023] 1. The laser driver shapes and amplifies the input electrical signal, effectively eliminating signal distortion and jitter, providing a clean and stable differential electrical signal source for subsequent modulation. Combined with the precisely superimposed DC bias of the Bias-T network, the EML laser can convert electrical signals into optical signals with a high extinction ratio and low phase noise, ensuring that the video content is distortion-free during the photoelectric conversion process.

[0024] 2. The Bias-T bias filter network, while coupling DC bias and high-speed differential signals, effectively suppresses signal reflection and power supply noise interference through its inherent filtering structure and matching impedance design. This allows high bit-rate signals such as 12G-SDI to maintain excellent eye diagram quality and timing accuracy when transmitted in 40km single-mode fiber.

[0025] 3. Driven by a precise bias voltage, the EML laser outputs an optical carrier with a wide spectral linewidth (<10MHz) and high wavelength stability, meeting the stringent requirements of DWDM systems for multi-wavelength channel spacing and channel capacity. This enables synchronous transmission of multiple video signals on a single fiber, significantly improving the utilization efficiency of optical fiber resources.

[0026] 4. Integrating the driving, biasing, and modulation functions into a single optical module simplifies the external circuit structure and reduces performance risks caused by external interference or impedance mismatch, enabling the optical module to have high stability and long-term working capability in high-quality application scenarios such as broadcast-grade video transmission. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the exemplary embodiments of this utility model, the drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this utility model and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0028] Figure 1 A schematic diagram of the circuit structure of the DWDM optical module for video transmission provided in this embodiment;

[0029] Figure 2 This is a schematic diagram of the frequency response characteristics of the Bias-T bias filter network provided in this embodiment;

[0030] The attached diagram shows the markings and corresponding component names:

[0031] 1-First group of sub-positive bias circuits, 2-Second group of sub-positive bias circuits. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of this utility model are only used to explain this utility model and are not intended to limit this utility model.

[0033] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0034] It should be noted that all actions involving the acquisition of signals, information, or data in this utility model are carried out in compliance with the relevant data protection laws and regulations of the locality and with authorization from the owner of the corresponding device.

[0035] First, let's explain the technical terms:

[0036] DWDM (Dense Wavelength Division Multiplexing)

[0037] SDI: (Serial Digital Interface)

[0038] EDFA: (Erbium-doped Fiber Amplifier)

[0039] LD: (Laser Diode)

[0040] EA: (Electro Absorption)

[0041] EML: (Externally Modulated Laser) Externally Modulated Laser

[0042] DML: (Directly Modulated Laser)

[0043] Example 1

[0044] Please see Figure 1 This utility model provides a DWDM optical module for video transmission, including a laser driver, a Bias-T bias filter network, and an EML laser, wherein:

[0045] The laser driver is used to shape and amplify the input electrical signal to output a differential electrical signal;

[0046] The input of the Bias-T bias filter network is connected to the output of the laser driver and the power supply, respectively, and is used to superimpose the DC bias voltage and the differential signal and output a differential signal superimposed with DC bias.

[0047] The input terminal of the EML laser is connected to the output terminal of the Bias-T bias filter network, which is used to convert the differential electrical signal superimposed with DC bias into an optical signal.

[0048] The Bias-T bias filter network is a three-port microwave passive network composed of discrete components. Its core function is to losslessly combine a high-frequency AC signal and a DC bias signal into a single transmission path. In this embodiment, it is a symmetrical differential network responsible for processing the high-speed differential electrical signals (RF+ and RF-) from the laser driver and combining them with the DC power supply to provide a composite drive signal containing both data and energy for the subsequent EML laser. The output processed by the Bias-T bias filter network directly drives the electro-absorption modulator in the subsequent EML laser, converting the electrical domain signal into an optical domain signal. This design not only fundamentally avoids the transmission distance limitation caused by the chirp effect in traditional DML schemes, but also ensures the reliability and high signal-to-noise ratio of the optical module transmitting 12G-SDI video over a distance of 40km by providing stable bias and clean signals. It is a key technical support for achieving the long-distance, high-capacity video transmission goal of this invention.

[0049] In this embodiment, the laser driver is used to receive signals from the device, perform necessary shaping processing on the signals, and send them to the subsequent circuits; the Bias-T bias filter network is responsible for providing the necessary bias voltage and has filtering function to meet the bandwidth requirements of video signal transmission; the EML laser, as the core component of the optical module, converts electrical signals into optical signals, wherein the LD generates a stable and narrow-linewidth continuous laser, which operates in constant current mode and is not affected by the modulation signal, thus avoiding frequency chirp at the source; the EA modulator converts the continuous light generated by the LD into a high-speed digital optical signal to realize the encoding of "0" and "1".

[0050] Furthermore, the Bias-T bias filter network includes two sets of positive bias circuits and one set of negative bias circuits. The two sets of positive bias circuits are respectively connected to the two output terminals of the laser driver to provide positive bias voltages for the two paths of the differential electrical signal. The negative bias circuit is connected to the EML laser to provide negative DC voltages for the EML laser.

[0051] The core function of this embodiment is to establish a precise and stable operating environment for the EML laser. Specifically, two symmetrically arranged positive bias circuits are connected to the differential output of the laser driver, providing the necessary forward operating current for the laser diode and ensuring the integrity of the high-speed differential signal through impedance matching. Simultaneously, an independently arranged negative bias circuit provides a precisely adjustable reverse bias voltage for the electro-absorption modulator, optimizing modulation efficiency and extinction ratio by controlling its operating point. This positive and negative bias architecture enables independent control of the laser's emission and modulation functions, ensuring both stable continuous laser generation and accurate high-speed optical signal modulation. This significantly improves the transmission distance and signal quality of the optical module at the system level, representing a key design breakthrough in overcoming the performance bottlenecks of traditional DML solutions.

[0052] Furthermore, the two sets of positive bias circuits include a first set of sub-positive bias circuits 1 and a second set of sub-positive bias circuits 2. The first set of sub-positive bias circuits 1 includes a resistor R1 and an inductor L1 connected in parallel, and also includes ferrite beads FB1, FB2 and a capacitor C1. The second set of sub-positive bias circuits 2 includes a resistor R2 and an inductor L2 connected in parallel, and also includes ferrite beads FB3, FB4 and a capacitor C2. The negative bias circuit includes a resistor R3 and an inductor L3 connected in parallel, and also includes ferrite beads FB5 and FB6.

[0053] The first sub-positive bias circuit 1 forms a DC power supply and high-frequency isolation path through a parallel resistor R1 and inductor L1. A filter chain composed of ferrite beads FB1 and FB2 effectively suppresses RF noise. Finally, a DC-biased high-speed signal is coupled to the laser diode through a DC-blocking capacitor C1, providing it with a stable operating current. The second sub-positive bias circuit 2 uses a parallel R2-L2 network with an FB3-FB4 ferrite bead chain and capacitor C2 to form a symmetrical differential signal path, providing a return path for the reverse RF signal while achieving impedance matching. The negative bias circuit forms a two-stage filter network through a parallel R3-L3 combination and an FB5-FB6 ferrite bead chain, effectively filtering out high-frequency ripple from the negative voltage supply and providing an extremely low-noise reverse bias voltage for the electro-absorption modulator. This collaborative design, using parallel damping resistors and multi-stage ferrite bead filtering, ensures both the extreme stability of each bias voltage and the integrity of the 12Gbps high-speed signal during transmission, thus achieving optimal operating conditions for the EML laser's emission and modulation functions at the system level.

[0054] Furthermore, the output terminals of the first sub-positive bias circuit 1 and the negative bias circuit are connected to the EA modulator.

[0055] Furthermore, the output of the first sub-positive bias circuit 1 is connected between the laser diode and the EA modulator through a matching impedance.

[0056] Furthermore, in the first set of sub-positive bias circuit 1, the first end of resistor R1 and the first end of inductor L1 are connected to the power supply Vcc, the second end of resistor R1 and the second end of inductor L1 are connected to the first end of ferrite bead FB1, the second end of ferrite bead FB1 is connected to the first end of ferrite bead FB2, the second end of ferrite bead FB2 and the first output terminal of laser driver are connected to the first end of capacitor C1, and the second end of capacitor C1 is the output terminal of the first set of sub-positive bias circuit 1;

[0057] In the second group of sub-positive bias circuit 2, the first end of resistor R2 and the first end of inductor L2 are connected to the power supply Vcc. The second end of resistor R2 and the second end of inductor L2 are connected to the first end of ferrite bead FB3. The second end of ferrite bead FB3 is connected to the first end of ferrite bead FB4. The second end of ferrite bead FB4 and the second output terminal of laser driver are connected to the first end of capacitor C2. The second end of capacitor C2 is the output terminal of the second group of sub-positive bias circuit 2.

[0058] In the negative bias circuit, the first end of resistor R3 and the first end of inductor L3 are connected to the negative voltage. The second end of resistor R3 and the second end of inductor L3 are connected to the first end of ferrite bead FB5. The second end of ferrite bead FB5 is connected to the first end of ferrite bead FB6. The second end of ferrite bead FB6 is the output terminal of the negative bias circuit.

[0059] Furthermore, the linewidth of the EML laser is less than 10 MHz.

[0060] Furthermore, the low-frequency cutoff frequency of the Bias-T bias filter network is set to below 500Hz.

[0061] Furthermore, this embodiment can also use a CWDM optical module with a DML laser, which has a total of 18 wavelength channels in the 1270-1610nm wavelength range. Although wavelength division multiplexing can be achieved, compared with the more than 80 wavelength channels of DWDM, the utilization rate of fiber resources is not at its limit. Moreover, since it is a DML laser, long-distance transmission is greatly affected by fiber dispersion, and excessive chirp will lead to signal degradation, requiring dispersion compensation (DCM) in the system.

[0062] This embodiment employs an optimized Bias-T bias filter network to meet the SDI bandwidth requirement of a 500Hz low-frequency cutoff frequency for transmitting video pathological codes. A frequency response characteristic obtained in this embodiment is as follows: Figure 2 As shown. By adjusting the parameters of the inductor, ferrite bead, and resistor in the filter network, the desired low-frequency cutoff frequency can be easily set.

[0063] The technical effects of this embodiment are as follows:

[0064] 1. Structural foundation for achieving 40km long-distance transmission

[0065] The bias circuit in this embodiment ensures long-distance transmission capability through a multi-stage stability design. The parallel network of R1 / L1 and R2 / L2 used in the positive bias circuit has constant current source characteristics, providing a stable operating point for the EA modulator. A multi-stage ferrite bead filter chain constitutes a highly efficient power supply noise suppression network, suppressing power supply ripple to the millivolt level and effectively preventing power supply noise from modulating onto the optical signal through the bias circuit. The negative bias circuit provides an extremely low-noise bias environment for the electroabsorption modulator, reducing the chirp coefficient during modulation to below 0.1, significantly reducing the impact of fiber dispersion on the signal. These measures collectively ensure that the signal maintains clear eye diagram characteristics even after 40km of transmission.

[0066] 2. Circuit mechanisms to ensure signal integrity

[0067] The circuit ensures the integrity of the 12Gbps high-speed signal through precise impedance matching and multi-stage filtering. The parallel resistors in the positive bias circuit form a precise 50-ohm matching network with the characteristic impedance of the PCB transmission lines, strictly controlling the signal reflection coefficient below -15dB and avoiding signal ringing and overshoot caused by impedance mismatch. The high-performance low-pass filter, composed of multi-stage ferrite bead chains, attenuates out-of-band noise by more than 40dB while allowing the 12Gbps baseband signal to pass, effectively suppressing the damage to signal quality caused by high-frequency noise. The symmetrical differential bias structure provides excellent common-mode noise rejection capability, improving the common-mode rejection ratio by approximately 25dB, ensuring that the system maintains signal purity even in complex electromagnetic environments.

[0068] 3. Supports optical performance assurance for DWDM systems

[0069] Precise bias control provides ideal light source characteristics for DWDM systems. A stable bias environment keeps the laser linewidth consistently within a narrow range of 10MHz, significantly reducing dispersion costs. Integrated temperature drift compensation circuitry adjusts the bias point in real time, maintaining wavelength accuracy within a strict range of ±0.04nm, ensuring precise alignment of each channel wavelength with the ITU-T grid even with temperature variations. This comprehensive protection of optical characteristics enables stable transmission of DWDM signals with over 80 wavelengths over a single fiber.

[0070] 4. Structural features that enhance reliability

[0071] The bias circuit's structural design fully considers the system's long-term reliability. The ferrite bead element exhibits excellent temperature stability, with its impedance characteristics varying by less than 15% over a wide temperature range of -40℃ to +85℃, ensuring stable filtering performance under diverse environmental conditions. The combination of parallel resistors and inductors not only provides precise impedance matching but also inherent overcurrent protection, limiting current peaks under abnormal current conditions and protecting the EML chip from damage. These design features collectively guarantee the long-term stable operation of the optical module in harsh environments.

[0072] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this utility model. It should be understood that the above description is only a specific embodiment of this utility model and is not intended to limit the scope of protection of this utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the scope of protection of this utility model.

Claims

1. A DWDM optical module for video transmission, characterized in that, Includes a laser driver, a Bias-T bias filter network, and an EML laser, wherein: The laser driver is used to shape and amplify the input electrical signal to output a differential electrical signal; The input of the Bias-T bias filter network is connected to the output of the laser driver and the power supply, respectively, and is used to superimpose the DC bias voltage and the differential signal and output a differential signal superimposed with DC bias. The input terminal of the EML laser is connected to the output terminal of the Bias-T bias filter network, which is used to convert the differential electrical signal superimposed with DC bias into an optical signal.

2. The DWDM optical module for video transmission according to claim 1, characterized in that, The EML laser includes a laser diode and an EA modulator connected in series. The laser diode is used to generate continuous laser light, and the EA modulator is used to convert the continuous laser light generated by the laser diode into an optical signal.

3. The DWDM optical module for video transmission according to claim 1, characterized in that, The Bias-T bias filter network includes two sets of positive bias circuits and one set of negative bias circuits. The two sets of positive bias circuits are respectively connected to the two output terminals of the laser driver and are used to provide positive bias voltages for the two paths of the differential electrical signal. The negative bias circuit is connected to the EML laser and is used to provide negative DC voltages for the EML laser.

4. The DWDM optical module for video transmission according to claim 3, characterized in that, The two sets of positive bias circuits include a first set of sub-positive bias circuits (1) and a second set of sub-positive bias circuits (2). The first set of sub-positive bias circuits (1) includes a resistor R1 and an inductor L1 connected in parallel. The first set of sub-positive bias circuits (1) also includes ferrite beads FB1, ferrite beads FB2 and a capacitor C1. The second set of sub-positive bias circuits (2) includes a resistor R2 and an inductor L2 connected in parallel. The second set of sub-positive bias circuits (2) also includes ferrite beads FB3, ferrite beads FB4 and a capacitor C2. The negative bias circuit includes a resistor R3 and an inductor L3 connected in parallel. The negative bias circuit also includes ferrite beads FB5 and ferrite beads FB6.

5. The DWDM optical module for video transmission according to claim 4, characterized in that, The output terminals of the first sub-positive bias circuit (1) and the negative bias circuit are connected to the EA modulator.

6. The DWDM optical module for video transmission according to claim 4, characterized in that, The output of the first sub-positive bias circuit (1) is connected between the laser diode and the EA modulator through a matching impedance.

7. The DWDM optical module for video transmission according to claim 4, characterized in that, In the first sub-positive bias circuit (1), the first end of resistor R1 and the first end of inductor L1 are connected to the power supply Vcc. The second end of resistor R1 and the second end of inductor L1 are connected to the first end of ferrite bead FB1. The second end of ferrite bead FB1 is connected to the first end of ferrite bead FB2. The second end of ferrite bead FB2 and the first output end of laser driver are connected to the first end of capacitor C1. The second end of capacitor C1 is the output end of the first sub-positive bias circuit (1). In the second sub-positive bias circuit (2), the first end of resistor R2 and the first end of inductor L2 are connected to the power supply Vcc. The second end of resistor R2 and the second end of inductor L2 are connected to the first end of ferrite bead FB3. The second end of ferrite bead FB3 is connected to the first end of ferrite bead FB4. The second end of ferrite bead FB4 and the second output end of laser driver are connected to the first end of capacitor C2. The second end of capacitor C2 is the output end of the second sub-positive bias circuit (2).

8. The DWDM optical module for video transmission according to claim 4, characterized in that, In the negative bias circuit, the first end of resistor R3 and the first end of inductor L3 are connected to the negative voltage. The second end of resistor R3 and the second end of inductor L3 are connected to the first end of ferrite bead FB5. The second end of ferrite bead FB5 is connected to the first end of ferrite bead FB6. The second end of ferrite bead FB6 is the output terminal of the negative bias circuit.

9. The DWDM optical module for video transmission according to any one of claims 1-8, characterized in that, The linewidth of the EML laser is less than 10 MHz.

10. The DWDM optical module for video transmission according to any one of claims 1-8, characterized in that, The low-frequency cutoff frequency of the Bias-T bias filter network is set to below 500Hz.

Images