High bandwidth EML substrate

Abstract

The present invention relates to a high-bandwidth EML substrate, comprising a PCB board, a CUW substrate, and an ALN ​​substrate; wherein the PCB board processes high-speed digital signals; the ALN substrate has two sides, front and back, wherein a circuit for processing high-speed analog signals is arranged on the front of the ALN substrate; one side of the back of the ALN substrate has a step-shaped depression in the thickness direction, an EML chip is arranged in the step-shaped depression, the depth of the step-shaped depression is greater than the thickness of the EML chip, so that when the EML chip is soldered to the step-shaped depression in the form of a gold-tin solder ball, the EML chip does not expose the back of the ALN substrate; the non-step-shaped depression part of the back of the ALN substrate is attached to the CUW substrate in a manner that is conducive to heat conduction; the CUW substrate is connected to the PCB board, so that the ALN substrate and the PCB board are not in direct contact with each other. The present invention can optimize the ‑3dB bandwidth of the high-speed link of the EML substrate from the existing 40GHz to more than 70GHz.

Description

Technical Field

[0001] The present invention relates to a photoelectric conversion device in optical fiber communication, belongs to the field of optical communication technology, and specifically relates to a high-bandwidth EML (Electroabsorption Modulated Laser) substrate structure. In particular, it relates to a high-bandwidth EML substrate with a -3dB bandwidth greater than 70GHz, which is suitable for the high-speed link requirements of the next-generation single-wavelength 200G optical module. Background Art

[0002] In recent years, the continuous development of cloud computing and data centers has led to an increasing demand for short-distance broadband transmission. The replacement of 5G communications and changes in communication architecture will soon lead to an explosion of big data, requiring data center optical modules to have higher and higher rates. The single-channel rate of optical modules has developed from 10Gb / s to today's 100Gb / s and the future 200Gb / s, and the bandwidth demand for optical module high-speed links is also increasing. In short-distance applications, although directly modulated lasers (DMLs) have the advantages of low cost and low power consumption, their modulation bandwidth and transmission distance are limited by relaxation oscillation frequency and frequency chirp. Compared with DMLs, electro-absorption modulated lasers (EMLs) have advantages in chirp effect, extinction ratio, eye diagram, jitter, transmission distance and other performance, and can achieve higher rates and longer distances.

[0003] The EML is a monolithic integration of a distributed feedback (DFB) laser and an electro-absorption (EA) modulator. The DFB laser part uses a multi-quantum well active region to provide gain and a grating to select the lasing wavelength to ensure single-mode operation. The EA modulator uses the quantum confined Stark effect (QCSE) of the quantum well material under an external electric field to modulate the intensity of the laser output light.

[0004] However, the technical solution of the EML substrate in the prior art places the driving circuit, high-frequency coupling capacitor, and high-speed bias-T circuit on the PCB board, and the EML chip is bonded to the ALN (aluminum nitride) substrate through silver glue, and the ALN substrate is placed on the CUW (copper tungsten) substrate, and the CUW substrate is bonded to the PCB through black glue. The PCB and the EML substrate are connected through the gold wire WB1, and the EML impedance matching capacitor and resistor on the ALN substrate are connected to the EML chip through the gold wire WB2. In this technical solution, the components on the PCB and the components on the ALN substrate are distributed in a scattered manner, the high-speed loss of the PCB board is large, and the insertion loss of some high-speed traces on the PCB board is large, which affects the bandwidth; and the WB pads and WB gold wires connecting the PCB, ALN substrate, and EML chip have equivalent inductance, which has become a bottleneck limiting the high-speed transmission of the link. In summary, the current high-speed link solution bandwidth is already very difficult to achieve 40GHz, and the room for improvement is limited, which cannot meet the performance requirements of the next-generation single-wavelength 200G optical module with a -3dB bandwidth greater than 70GHz.

[0005] Specifically, when the current 100G optical module adopts PAM4 modulation, the -3dB bandwidth of its high-speed link is required to be controlled within 40GHz; when the rate of a single channel is increased to 100Gb / s, that is, the single-wave transmission rate of the optical module reaches 200G, in order to meet the transmission requirements of 4-channel 800G and 8-channel 1.6T optical modules, the -3dB bandwidth requirement of its high-speed link is around 70GHz. The current high-speed link connection solution will not be able to meet this high bandwidth requirement, and new technological breakthroughs are needed. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a high-bandwidth EML substrate, including a PCB board, a CUW substrate, and an ALN ​​substrate; wherein the ALN substrate is arranged on the CUW substrate, and the CUW substrate is connected to the PCB board, so that the ALN substrate and the PCB board are not in direct contact with each other; the PCB board processes high-speed digital signals; the ALN substrate has a front and a back side, wherein a circuit for processing high-speed analog signals is arranged on the front side of the ALN substrate; one side of the back side of the ALN substrate has a recess in the thickness direction, and an EML chip is arranged in the recess, and the depth of the recess is greater than the thickness of the EML chip, so that when the EML chip is soldered to the recess in the form of a gold-tin solder ball, the EML chip does not expose the back side of the ALN substrate; the EML chip is electrically connected to the front side of the ALN substrate through a gold wire via; the non-step-shaped recessed portion on the back side of the ALN substrate is bonded to the CUW substrate in a manner that is conducive to heat conduction.

[0007] In the above technical solution, the ALN substrate is an aluminum nitride substrate, and the CUW substrate is a copper tungsten substrate.

[0008] In the above technical solution, the ALN substrate is bonded to the CUW substrate by silver glue; and the CUW substrate is connected to the PCB board by black glue.

[0009] In the above technical solution, the depression of the EML chip on the back side of the ALN substrate is a step-shaped depression; the EML chip is arranged in the enclosed space between the step-shaped depression on the back side of the ALN substrate and the CUW substrate, and the gap between the EML chip and the enclosed space is filled with thermally conductive silver glue.

[0010] In the above technical solution, an ODSP circuit is arranged on the PCB board, and the ODSP circuit includes an optical DSP chip.

[0011] In the above technical solution, the circuit for processing high-speed analog signals arranged on the front side of the ALN substrate includes a high-frequency coupling capacitor, an impedance matching resistor, a coupling capacitor, a driving circuit, and a bias T circuit.

[0012] In the above technical solution, the ODSP circuit connects the electrical signal to the front side of the ALN substrate through a connecting line, connects the data transmission pins TD+ and TD- of the driving circuit, and the output of the driving circuit is connected to the via through a high-frequency coupling capacitor, and the two ends of the high-frequency coupling capacitor are respectively connected to the positive voltage VCC and the negative voltage VEE of the power supply through a bias T circuit.

[0013] In the above technical solution, the high-frequency driving signal, power ground GND, and laser bias signal on the front side of the ALN substrate are respectively led to the back side of the ALN substrate through vias, and connected to the EML chip through corresponding solder balls.

[0014] In the above technical solution, the bias T circuit connected to VCC includes a resistor and a low-frequency inductor connected in parallel and then connected in series with a high-frequency magnetic bead.

[0015] In the above technical solution, the bias T circuit connected to VEE includes a resistor and a low-frequency inductor connected in parallel and then connected in series with a high-frequency magnetic bead.

[0016] The present invention has achieved the following technical effects:

[0017] 1. The present invention replaces the process of connecting EML chips with gold wires, which causes bandwidth limitation in the prior art, with high-speed solder balls, thereby eliminating the influence of the wire inductance effect caused by the gold wire connection and increasing the substrate bandwidth;

[0018] 2. The present invention migrates the high-speed devices for processing high-frequency analog signals arranged on the PCB board in the prior art to the ALN substrate, thereby shortening the distance between the various high-speed devices and reducing the insertion loss;

[0019] 3. The present invention replaces the high-speed routing on the PCB board in the prior art with the high-speed routing on the ALN substrate. Since the insertion loss of the high-speed routing on the ALN substrate is much smaller than that of the routing on the PCB board, the high-speed bandwidth is further improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A top view of the high-bandwidth EML substrate structure of the present invention;

[0021] Figure 2 It is a side view of the high-bandwidth EML substrate structure of the present invention.

[0022] Markings in the figure: 10-PCB board, 20-CUW substrate, 30-ALN substrate, 40-bias-T circuit, 50-EML chip, 11-ODSP circuit, 12-connecting wire, 31-high-frequency coupling capacitor, 32-impedance matching resistor, 33-coupling capacitor, 34-driving circuit, 35-via, 41-resistor, 42-low-frequency capacitor, 43-high-frequency magnetic bead, 44-resistor, 45-low-frequency capacitor, 46-high-frequency magnetic bead, 51-solder ball, 52-power GND solder ball, 53-laser bias signal solder ball, 54-silver glue. DETAILED DESCRIPTION

[0023] In order to facilitate those skilled in the art to understand and implement the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0024] In order to optimize the -3dB bandwidth of the high-speed link of the EML substrate of the optical module from the current 40GHz to more than 70GHz, so that the single-wave transmission rate of the optical module can reach 200G, to meet the transmission requirements of 4-channel 800G and 8-channel 1.6T optical modules, the present invention provides a high-bandwidth EML substrate, such as Figure 1-2 As shown, it includes a PCB board 10, a CUW substrate 20, and an ALN ​​substrate 30, wherein the ALN substrate 30 is bonded to the CUW substrate 20 by silver glue, and the CUW substrate 20 and the PCB board 10 are connected by black glue, so that the ALN substrate 30 and the PCB board 10 are not in direct contact with each other.

[0025] The ALN substrate 30 has two sides, a front side and a back side, wherein a high-frequency coupling capacitor 31, an impedance matching resistor 32, a coupling capacitor 33, a driving circuit 34, and a bias-T circuit 40 are arranged on the front side of the ALN substrate 30, and one side of the back side of the ALN substrate 30 has a step-shaped depression in the thickness direction, and the EML chip 50 is arranged in the step-shaped depression, and the depth of the step-shaped depression is greater than the thickness of the EML chip 50, so that when the EML chip 50 is soldered to the step-shaped depression in the form of a gold-tin solder ball, the EML chip 50 does not expose the back side of the ALN substrate 30. Preferably, a certain distance is spaced between the top of the EML chip 50 and the back side of the ALN substrate 30; the non-step-shaped depression portion on the back side of the ALN substrate 30 is bonded to the CUW substrate 20 in a manner that is conducive to heat conduction. Preferably, according to Figure 1 As shown, from a top view, the area of ​​the CUW substrate 20 is larger than the area of ​​the ALN substrate 30; that is, after the ALN substrate 30 is attached to the CUW substrate 20, from a top view, the CUW substrate 20 has a certain extension protrusion in the surrounding direction of the ALN substrate 30; according to Figure 2 As shown, the EML chip 50 is disposed in the enclosed space between the stepped recess on the back side of the ALN substrate 30 and the CUW substrate 20 . Preferably, a heat-conductive silver paste 54 is used to fill the space between the EML chip 50 and the CUW substrate 20 .

[0026] An ODSP circuit 11 is provided on the PCB board 10. The ODSP circuit 11 is an optical DSP circuit, including an optical DSP chip. The ODSP circuit 11 connects an electrical signal to the front of the ALN substrate 30 through a connecting line 12. The electrical signal connected by the connecting line 12 includes at least a TD+ signal, a TD- signal, a GND and a laser bias (Laser Bias) signal. Preferably, a signal ground line GND or a power ground line GND is also correspondingly provided on both sides of the signal line connecting the data transmission pins TD+ and TD- of the drive circuit 34. The output of the drive circuit 34 is connected to the via 35 through a high-frequency coupling capacitor 31. The two ends of the high-frequency coupling capacitor 31 are connected to the positive power supply voltage VCC and the negative power supply voltage VEE through a bias-T circuit 40 (i.e., a bias T circuit). The bias-T circuit 40 connected to VCC includes a resistor 41 and a low-frequency inductor 42 connected in parallel and then connected in series with a high-frequency magnetic bead 43. The bias-T circuit 40 connected to VEE includes a resistor 44 and a low-frequency inductor 45 connected in parallel and then connected in series with a high-frequency magnetic bead 46. The via 35 is also connected to the power ground GND through the resistor 32 and the coupling capacitor 33, thereby leading the power ground GND on the front of the ALN substrate 30 to the EML chip 50 on the back of the ALN substrate 30. The via 35 also connects the EML chip 50 on the back of the ALN substrate 30 with the high-frequency coupling capacitor 32 on the front of the ALN substrate 30 for electrical signal connection; the high-frequency drive signal, the power ground GND, and the laser bias (Laser Bias) signal can be optionally led from the front of the ALN substrate 30 to the back of the ALN substrate 30 through three vias 35, and connected to the EML chip 50 through the solder ball 51, the power GND solder ball 52, and the laser bias signal solder ball 53 respectively.

[0027] It can be seen that the PCB board 10 and the electronic devices thereon are mainly used for processing high-speed digital signals, the ALN substrate 30 is an aluminum nitride substrate, and the CUW substrate 20 is a copper tungsten substrate. The electronic devices on the ALN substrate 30 are mainly used for processing high-speed analog signals and photoelectric conversion. The ALN substrate 30 itself also acts as a heat sink, and the CUW substrate 20 mainly plays the role of supporting heat dissipation.

[0028] The present invention arranges the components (such as high-frequency coupling capacitor 31, impedance matching resistor 32, coupling capacitor 33, driving circuit 34, bias-T circuit 40, EML chip 50) for processing high-frequency analog signals on ALN ​​substrate 30 through the above technical solution, and each high-frequency component is connected through the high-speed routing on ALN ​​substrate 30. ALN substrate 30 is formed into an inverted step shape relative to CUW substrate 20, and the high-speed routing is connected from the front of ALN substrate 30 to the step depression on the back of ALN substrate 30 through one or more gold wire perforations 35 to form gold-tin solder balls 51, power GND solder balls 52, and laser bias signal solder balls 53. EML chip 50 is reversely soldered under the step, and the high-speed RF link, power GND, and laser bias signal required for the operation of EML chip 50 are connected to ALN substrate 30 through gold-tin solder balls 51, power GND solder balls 52, and laser bias signal solder balls 53. Therefore, the present invention has the following technical effects:

[0029] 1. The process of gold wire connection (WB) EML chip that causes bandwidth limitation in the prior art is replaced by high-speed solder balls, eliminating the influence of wire inductance effect caused by gold wire connection and increasing substrate bandwidth;

[0030] 2. The high-speed devices for processing high-frequency analog signals arranged on the PCB in the prior art are migrated to the ALN substrate, so that the distance between each high-speed device is shortened and the insertion loss is reduced;

[0031] 3. The high-speed routing on the PCB board in the prior art is replaced with the high-speed routing on the ALN substrate. Since the insertion loss of the high-speed routing on the ALN substrate is much smaller than that of the routing on the PCB board, the high-speed bandwidth is further improved.

[0032] Therefore, the present invention can optimize the -3dB bandwidth of the high-speed link of the EML substrate from the existing 40GHz to greater than 70GHz, so that the single-wave transmission rate of the optical module can reach 200G, to meet the transmission requirements of 4-channel 800G and 8-channel 1.6T optical modules.

[0033] Those skilled in the art should understand that, in the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0034] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. Those skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

[0035] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A high-bandwidth EML substrate, comprising a PCB board, a CUW substrate, and an ALN ​​substrate; wherein: The ALN substrate is arranged on the CUW substrate, and the CUW substrate is connected to the PCB board, so that the ALN substrate and the PCB board are not in direct contact with each other; the characteristics are: The PCB board processes high-speed digital signals; The ALN substrate has a front and a back side, wherein a circuit for processing high-speed analog signals is arranged on the front side of the ALN substrate; one side of the back side of the ALN substrate has a depression in the thickness direction, in which an EML chip is arranged, and the depth of the depression is greater than the thickness of the EML chip, so that when the EML chip is soldered to the depression in the form of a gold-tin solder ball, the EML chip does not expose the back side of the ALN substrate; the EML chip is electrically connected to the front side of the ALN substrate through a gold wire via; the non-step-shaped depression portion on the back side of the ALN substrate is bonded to the CUW substrate in a manner that is conducive to heat conduction.

2. The high-bandwidth EML substrate according to claim 1, wherein: The ALN substrate is an aluminum nitride substrate, and the CUW substrate is a copper tungsten substrate.

3. The high-bandwidth EML substrate according to claim 2, wherein: The ALN substrate is bonded to the CUW substrate by silver glue; the CUW substrate is connected to the PCB board by black glue.

4. The high-bandwidth EML substrate according to claim 3, characterized in that: The depression on the back side of the ALN substrate in which the EML chip is arranged is a step-shaped depression; the EML chip is arranged in an enclosed space between the step-shaped depression on the back side of the ALN substrate and the CUW substrate, and a gap between the EML chip and the enclosed space is filled with thermally conductive silver glue.

5. The high-bandwidth EML substrate according to claim 1, wherein: The PCB board is provided with an ODSP circuit, and the ODSP circuit includes an optical DSP chip.

6. The high-bandwidth EML substrate according to claim 5, characterized in that: The circuit for processing high-speed analog signals arranged on the front side of the ALN substrate includes a high-frequency coupling capacitor, an impedance matching resistor, a coupling capacitor, a driving circuit, and a bias T circuit.

7. The high-bandwidth EML substrate according to claim 6, wherein: The ODSP circuit connects the electrical signal to the front of the ALN substrate through a connecting line, connects the data transmission pins TD+ and TD- of the driving circuit, and the output of the driving circuit is connected to the via through a high-frequency coupling capacitor, and the two ends of the high-frequency coupling capacitor are respectively connected to the positive power supply VCC and the negative power supply VEE through a bias T circuit.

8. The high-bandwidth EML substrate according to claim 7, wherein: The high-frequency driving signal, power ground GND, and laser bias signal on the front side of the ALN substrate are respectively led to the back side of the ALN substrate through vias, and are connected to the EML chip through corresponding solder balls.

9. The high-bandwidth EML substrate according to claim 8, characterized in that: The bias T circuit connected to VCC includes a resistor and a low-frequency inductor in parallel and then connected in series with a high-frequency ferrite bead.

10. The high-bandwidth EML substrate according to claim 8, wherein: The bias T circuit connected to VEE includes a resistor and a low-frequency inductor in parallel connected in series with a high-frequency ferrite bead.

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