Unipolar bias differential driven two-section electroabsorption modulator, bias system

Abstract

The application discloses a single polarity bias differential drive two-section electro-absorption modulator, which comprises a differential drive circuit, a first differential output end and a second differential output end; an electro-absorption modulator component, at least comprising a first section electro-absorption modulator and a second section electro-absorption modulator; a connecting capacitor, connected between the low end of the first section electro-absorption modulator and the low end of the second section electro-absorption modulator; a bias power supply; a bias node, the low end of the first section electro-absorption modulator and the low end of the second section electro-absorption modulator being respectively coupled to the bias node, and the bias node being connected to the bias power supply; and a coupling capacitor, connected between the bias node and the ground. The application can save a bias T network and a bias power supply, simplify packaging and save cost, and meanwhile, the high-frequency performance is improved by shortening a transmission line and removing a blocking capacitor in a signal path.

Description

Technical Field

[0001] This invention relates to the field of electroabsorption modulator technology, and more particularly to a two-stage electroabsorption modulator and bias system with unipolar bias differential drive. Background Technology

[0002] The modulator driver typically employs a differential circuit, as shown in Figure 1(a). This circuit has two inverting outputs (OutP / OutN), with a virtual / true ground at their common node. Traditional electroabsorption modulators (EAMs) operate in a single-ended mode, generally with a reverse-biased structure, as shown in Figure 1(b). The modulation diode has only one electrode that can be connected, driven by one output (OutP) of the driver, while the other output (OutN) is terminated. In this structure, the driver can only utilize half of its available voltage.

[0003] Another approach is to drive the electroabsorption modulator (EAM) from two electrodes and apply a differential voltage, as shown in Figure 1(c). Although the differentially driven electroabsorption modulator (EAM) can utilize the differential power supply voltage to improve modulation efficiency, the frequency bandwidth of the modulator will be severely affected because both the source resistance and the termination resistance are doubled.

[0004] Meanwhile, US Patent 6,914,706B2 proposes a superior differential drive structure that improves the overall performance of an electroabsorption modulator (EAM). In this prior art, the modulator is divided into two segments, both fabricated on the same waveguide, and both are connected in series electrically and optically, as shown in Figures 1 and 6 of the patent specification. In this case, to achieve the same modulation efficiency as the aforementioned differential structure, the frequency response of the series-connected two-segment modulator structure is approximately 1.5 to 1.8 times that of the single-segment modulator, because its capacitance is reduced by half. This prior art, through its "two-segment series" design, optimizes frequency performance while ensuring modulation efficiency, providing a better option for high-speed transmission scenarios, but still suffers from problems such as the complexity of the bias circuit that requires improvement.

[0005] The two-stage differential electroabsorption modulator (EAM) device in US Patent 6,914,706B2 has two limiting factors in practical applications: The first factor is that each segment of the modulator in the signal path from the differential drive circuit to the EAM requires a bias T-network to fuse the modulator's DC bias with the high-speed signal.

[0006] The second factor is that the complementary ports of the differential drive source must be connected to the complementary diodes of the two electro-absorption (EA) modulators, and the DC bias must be connected to the anode and cathode of the modulator diodes, respectively. Therefore, this structure requires two independent bias power supplies, one positive and one negative. The presence of the bias T-network increases circuit complexity and board space, and its inherent characteristics may introduce signal loss and degrade radio frequency (RF) performance. Furthermore, the requirement for dual positive and negative power supplies further increases system cost and integration difficulty. These problems are amplified, especially in multi-channel scenarios, becoming a key bottleneck restricting the large-scale application of the device.

[0007] In summary, the root cause of these two limitations in the prior art lies in the requirement for two independently biased electroabsorption modulator (EAM) segments for each device. To avoid or alleviate these limitations, this invention proposes an alternative biasing scheme called dual low-side biasing. This dual low-side biasing scheme eliminates the need for a bias T-type circuit and can use a single-polarity (positive or negative) bias power supply to replace the original dual positive and negative power supplies. (Note: The core contradiction in the prior art lies in the conflict between the "independent biasing requirement" and "system complexity and performance loss." That is, the existence of the bias T-type circuit introduces additional signal loss and space occupation, while the dual-polarity power supply increases system cost and integration difficulty. The dual low-side biasing scheme proposed in this invention solves these two problems at their root by reconstructing the biasing path, providing key technical support for EAM applications in high-speed, multi-channel scenarios.) Summary of the Invention

[0008] The purpose of this invention is to provide a two-stage electroabsorption modulator and bias system with unipolar bias differential drive. By integrating two on-chip decoupling capacitors and applying dual low-end bias to the two electroabsorption modulators respectively, one stage is biased to the virtual ground on the load side, and the other stage is biased to the electroabsorption modulator side, thereby realizing the biasing of the two modulators with a unipolar bias power supply.

[0009] To achieve the above objectives, the following technical solution is adopted: A unipolar biased differential driven two-stage electroabsorption modulator, comprising: A differential drive circuit has a first differential output terminal and a second differential output terminal; An electroabsorption modulator assembly includes at least a first electroabsorption modulator and a second electroabsorption modulator; the high-side of the first electroabsorption modulator is connected to a first differential output terminal, and the high-side of the second electroabsorption modulator is connected to a second differential output terminal. A connecting capacitor is connected between the low end of the first electroabsorption modulator and the low end of the second electroabsorption modulator. Bias power supply; A bias node is provided, wherein the low end of the first electroabsorption modulator and the low end of the second electroabsorption modulator are respectively coupled to the bias node, and the bias node is connected to the bias power supply. Coupling capacitors are connected between the bias node and ground to decouple the bias node and connect the bias line to ground.

[0010] Furthermore, a low-frequency decoupling capacitor is connected in parallel between the bias node and ground.

[0011] Furthermore, the low end of the first electroabsorption modulator and the low end of the second electroabsorption modulator are respectively coupled to the bias node via gold wire bonding.

[0012] Furthermore, a first load resistor is provided between the first differential output terminal and ground, and a second load resistor is provided between the second differential output terminal and ground.

[0013] Furthermore, the first and second electroabsorption modulators are part of a semiconductor chip, which is mounted on a carrier and coupled to the bias power supply and the differential output terminal of the differential drive circuit respectively via gold wire bonding.

[0014] A multi-segment electroabsorption modulator differential drive low-side bias system, including A differential drive circuit has a first differential output terminal and a second differential output terminal; N-segment electroabsorption modulator, where N≥3; A bias node is connected to a bias power supply, and a decoupling capacitor connected in parallel with ground is provided in the bias line to decouple the bias node from ground. The N-segment electroabsorption modulator is configured as a positive arm and a negative arm of a differential path, the positive arm and the negative arm are connected in series, and the lower ends of the positive arm and the negative arm are both connected to a bias node so as to provide bias to the lower end of the N-segment electroabsorption modulator through a bias power supply.

[0015] By adopting the above solution, the beneficial effects of the present invention are: This invention eliminates the need for a bias T-type network, saving costs. At the same time, by shortening the transmission line and removing blocking capacitors in the signal path, it can improve high-frequency performance and support multi-channel integration. Furthermore, a single-polarity (positive or negative) bias power supply can replace the dual positive and negative power supplies required by a two-stage electroabsorption modulator (EAM), and it can be extended to multi-stage device applications, making it widely applicable. Attached Figure Description

[0016] Figure 1(a) is a differential circuit diagram of an EAM driver with two inverting output terminals; Figure 1(b) is a schematic diagram of EAM in single-ended drive mode; Figure 1(c) is a schematic diagram of EAM in differential drive mode; Figure 2 This is a schematic diagram of the EAM circuit with two-stage cascaded differential drive mode according to the present invention; Figure 3 This is a schematic diagram of the bias circuit in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of the bias circuit in Embodiment 2 of the present invention; Figure 5 This is a schematic diagram of the bias circuit for the multi-segment cascaded differential drive mode EAM of the present invention, namely, Example 3. Detailed Implementation

[0017] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0018] This invention provides a unipolar biased differential driven two-stage electroabsorption modulator, comprising: A differential drive circuit has a first differential output terminal and a second differential output terminal; An electroabsorption modulator assembly includes at least a first electroabsorption modulator and a second electroabsorption modulator; the high-side of the first electroabsorption modulator is connected to a first differential output terminal, and the high-side of the second electroabsorption modulator is connected to a second differential output terminal. A connecting capacitor is connected between the low end of the first electroabsorption modulator and the low end of the second electroabsorption modulator. Bias power supply; A bias node is provided, wherein the low end of the first electroabsorption modulator and the low end of the second electroabsorption modulator are respectively coupled to the bias node, and the bias node is connected to the bias power supply. Coupling capacitors are connected between the bias node and ground to decouple the bias node and connect the bias line to ground.

[0019] A decoupling capacitor is connected in parallel between the bias node and ground; the low ends of the first and second electroabsorption modulators are coupled to the bias node via gold wire bonding; a first load resistor is provided between the first differential output terminal and ground, and a second load resistor is provided between the second differential output terminal and ground; the first and second electroabsorption modulators are part of a semiconductor chip, which is mounted on a carrier and coupled to the bias power supply and the differential output terminal of the differential drive circuit via gold wire bonding.

[0020] like Figure 2 As shown, the solution proposed in this invention is a dual low-end bias structure. Figure 2EA1 and EA2 are the first EAM modulator S1 and the second EAM modulator S2, respectively. The bias voltage Vb starts from node N1, is directly coupled to ground through coupling capacitor Cmim, and provides bias voltage to the low end of the first EAM modulator S1 through node N2 and to the low end of the second EAM modulator S2 through node N3. The first and second EAM modulators (S1 and S2) are decoupled by a connecting capacitor Cconn connected in series.

[0021] This dual low-end bias structure not only retains all the advantages of the low-end bias scheme, but also achieves an additional key improvement: a single polarity (positive or negative) bias power supply can replace the dual positive and negative power supplies required for two-stage EAM.

[0022] In addition, a multi-segment electroabsorption modulator differential drive low-side bias system is also provided, including: A differential drive circuit has a first differential output terminal and a second differential output terminal; N-segment electroabsorption modulator, where N≥3; A bias node is connected to a bias power supply, and a decoupling capacitor connected in parallel with ground is provided in the bias line to decouple the bias node from ground. The N-segment electroabsorption modulator is configured as a positive arm and a negative arm of a differential path, the positive arm and the negative arm are connected in series, and the lower ends of the positive arm and the negative arm are both connected to a bias node so as to provide bias to the lower end of the N-segment electroabsorption modulator through a bias power supply.

[0023] The following is a detailed description using specific embodiments: Example 1: As shown in Figure 3, this example illustrates a low-side bias implementation of an electroabsorption modulator (EAM) 620: a DC bias voltage 630 is connected to node 660 (which is connected to one electrode of the EAM), while a high-speed AC modulation signal 610 is connected to node 650 through a coupling capacitor. This scheme does not require the use of a bias-T circuit.

[0024] In this structure, the DC bias voltage 630 applied to electrode 660 is directly grounded through capacitor Cmim, so the side where this electrode is located is the "low end"; while the high-speed AC modulation signal 610 is grounded through peak inductor 640 and load resistor Rload 670, so the signal input side is the "high end".

[0025] Specifically, the low-side bias is achieved by setting capacitor Cmim 680 in the bias line: capacitor Cmim 680 is connected in parallel with decoupling capacitor Cext 690 and is directly grounded. This bias scheme can not only remove the bulky bias T-network from the circuit design and simplify the packaging process, but also support multi-channel integration; at the same time, by shortening the transmission line and removing the blocking capacitor in the signal path, high-frequency performance can be significantly improved.

[0026] Example 2: This example demonstrates a differential drive low-side bias circuit suitable for a two-stage electroabsorption modulator (EAM). This circuit eliminates the need for two bias T-type circuits and two bias power supplies of different polarities.

[0027] like Figure 4 As shown, the first EAM modulator 701 and the second EAM modulator 702 are connected by a capacitor located between the two differential output terminals 703 and 704 of the modulator and driver; the first EAM modulator 701 and the second EAM modulator 702 are connected in series by a connecting capacitor 705 to achieve decoupling.

[0028] The node (first node 720) between the low end of the first EAM modulator 701 and the connecting capacitor 705 is coupled to the third node 710 and connected to the bias power supply 708 through the third node 710; the node (second node 730) between the low end of the second EAM modulator 702 and the connecting capacitor 705 is also coupled to the third node 710 and connected to the bias power supply 708 through this node.

[0029] also, Figure 4 The inductor in the diagram represents the gold wire bond: the first EAM modulator 701 and the second EAM modulator 702 are part of a semiconductor chip, which is mounted on a carrier and coupled to the bias power supply 708 and the output terminals 703 and 704 of the driver respectively via gold wire bonding.

[0030] Correspondingly, the low-side bias is also achieved by setting a capacitor (Cmim 706) in the bias line, which is connected in parallel with the decoupling capacitor (Cext 707) and directly grounded.

[0031] The dual low-end bias scheme uses nodes 720 and 730 to bias the low ends of the first and second EAM modulators respectively; while the two differential high-speed AC modulation signals (703, 704) are connected to the high ends of the two modulators through nodes 721 and 731, and grounded through load resistors (722, 732).

[0032] The aforementioned capacitors 705 and 706 and resistors 722 and 733 can all be integrated on the chip.

[0033] This biasing scheme not only removes the bulky bias-T network, but also powers both EAM modulators with a single bias power supply, reducing the number of pads connected to external circuits and thus simplifying the packaging process in application scenarios.

[0034] Example 3: This example demonstrates a multi-segment electroabsorption modulator (EAM), such as... Figure 5 As shown, the EAM contains N-segment modulators, where N ≥ 3 and is an integer.

[0035] Although the two-segment EAM circuit shown above only demonstrates two modulators, it can be used in conjunction with a multi-segment EAM for better performance. This is because in a two-segment series EAM structure, the load draws photocurrent, causing a voltage drop and resulting in a degree of "de-biasing." Therefore, if the photocurrents of the first and second EAM modulators (701, 702) are different, there will be a slight difference in the reverse bias voltages of the two modulators. To balance the photocurrents of the two modulators, a multi-segment EAM design with N≥3 is a better choice.

[0036] In this embodiment, the length of each EAM segment is optimized: the total photocurrent generated by all EAM segments connected to one side of the differential drive circuit is equal to the total photocurrent generated by all EAM segments connected to the other side of the driver, thereby achieving symmetrical driving of the differential drive circuit.

[0037] In this embodiment, a four-segment electroabsorption modulator (EAM) is used as an exemplary structure, and its equivalent circuit is as follows: Figure 5 As shown, this EAM consists of four electrically absorbing (EA) waveguides, and the specific connection method is as follows: The first EAM (800) and the third EAM (802) are connected in parallel to form the negative arm of the differential path; the second EAM (801) and the fourth EAM (803) are connected in parallel to form the positive arm of the differential path; the positive arm and the negative arm are connected in series.

[0038] For those skilled in the art, the definitions of positive and negative arms can be flexibly interchanged according to actual application needs, and this design has good adaptability.

[0039] Accordingly, the low-side bias is achieved by connecting node 810 to the bias power supply and setting a decoupling capacitor in parallel in the bias line so that node 810 is directly grounded.

[0040] The dual low-end bias scheme provides bias to the low ends of the two pairs of electro-absorption modulator (EAM) segments through node 810; and the two pairs of EAM segments are connected between the differential outputs of the driver through capacitors and separated by decoupling resistor 820.

[0041] In summary, the design of the "parallel decoupling capacitor" in this embodiment not only continues the core logic of "using a single capacitor to achieve bias supply and DC isolation" in the previous embodiment, but also further enhances the stability of the bias voltage and reduces noise interference by connecting multiple capacitors in parallel. The addition of the decoupling resistor 820 addresses the crosstalk problem between segments of the multi-segment EAM, ensuring that the two pairs of EAM segments can independently respond to differential modulation signals while sharing the bias power supply, ultimately achieving symmetrical drive and photocurrent balance.

[0042] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A two-stage electroabsorption modulator with unipolar bias differential drive, characterized in that, include A differential drive circuit has a first differential output terminal and a second differential output terminal; An electroabsorption modulator assembly includes at least a first electroabsorption modulator and a second electroabsorption modulator; The high-side of the first electroabsorption modulator is connected to the first differential output terminal, and the high-side of the second electroabsorption modulator is connected to the second differential output terminal. A connecting capacitor is connected between the low end of the first electroabsorption modulator and the low end of the second electroabsorption modulator. Bias power supply; A bias node is provided, wherein the low end of the first electroabsorption modulator and the low end of the second electroabsorption modulator are respectively coupled to the bias node, and the bias node is connected to the bias power supply. Coupling capacitors are connected between the bias node and ground to decouple the bias node and connect the bias line to ground.

2. The two-stage electroabsorption modulator with unipolar bias differential drive according to claim 1, characterized in that, A decoupling capacitor is also connected in parallel between the bias node and ground.

3. The two-stage electroabsorption modulator with unipolar bias differential drive according to claim 2, characterized in that, The low end of the first electroabsorption modulator and the low end of the second electroabsorption modulator are respectively coupled to the bias node via gold wire bonding.

4. The two-stage electroabsorption modulator with unipolar bias differential drive according to claim 1, characterized in that, A first load resistor is provided between the first differential output terminal and ground, and a second load resistor is provided between the second differential output terminal and ground.

5. The two-stage electroabsorption modulator with unipolar bias differential drive according to claim 1, characterized in that, The first and second electroabsorption modulators are part of a semiconductor chip, which is mounted on a carrier and coupled to the bias power supply and the differential output terminal of the differential drive circuit respectively by gold wire bonding.

6. A multi-segment electroabsorption modulator differential drive low-end bias system, characterized in that, include A differential drive circuit has a first differential output terminal and a second differential output terminal; N-segment electroabsorption modulator, where N≥3; A bias node is connected to a bias power supply, and a decoupling capacitor connected in parallel with ground is provided in the bias line to decouple the bias node from ground. The N-segment electroabsorption modulator is configured as a positive arm and a negative arm of a differential path, the positive arm and the negative arm are connected in series, and the lower ends of the positive arm and the negative arm are both connected to a bias node so as to provide bias to the lower end of the N-segment electroabsorption modulator through a bias power supply.

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