A 50G PAM4 transmitting laser coaxial packaging structure and method

Abstract

The present invention relates to a coaxial packaging structure and method for a 50G PAM4 transmitting laser. The packaging structure includes a laser diode chip, a converging coupling lens cap, a laser diode gasket, a chip-on-chip gasket, gold bonding wires, a socket, and a high-frequency flexible circuit board. The laser diode chip is fixed to the laser diode gasket to form a chip-on-chip, the chip-on-chip is fixed to the chip-on-chip gasket, the chip-on-chip gasket is fixed to the socket, the high-frequency flexible circuit board is inserted into the socket, the laser diode chip is connected to the high-frequency flexible circuit board via gold bonding wires, and the converging coupling lens cap is fixed to the socket. The laser diode chip emits a Gaussian beam, which is converged by the converging coupling lens cap. The converged light is concentrated into a mode matching a single optical fiber and is incident on a single-mode optical fiber. This packaging structure and method are beneficial for signal optimization and reduce material and packaging costs.

Description

Technical Field

[0001] The present invention belongs to the field of optical fiber communications, and in particular relates to a coaxial packaging structure and method for a 50G PAM4 transmitting laser. Background Art

[0002] As society's thirst for data continues to grow—not only in ever-increasing quantities but also at ever-increasing speeds—older modulation schemes based on NRZ-type encoding are becoming increasingly inadequate. We need to get data from point A to point B as efficiently as possible, whether it's a chip on a PC board or from one end of a long-haul fiber optic cable to the other. The modulation scheme gaining favor in many ways is PAM4.

[0003] PAM4 signals use four different signal levels for transmission, with each symbol period representing two bits of logical information (0, 1, 2, 3). Because PAM4 signals can transmit two bits of information per symbol period, to achieve the same signal transmission capability, the symbol rate of PAM4 signals only needs to be half that of NRZ signals, significantly reducing transmission channel losses. With future technological developments, the possibility of using higher-level PAM8 or even PAM16 signals for information transmission is not ruled out.

[0004] TO (Transistor Outline) refers to the transistor form factor. Early transistors were mostly packaged in coaxial packages, which were later adapted for use in optical communications and became known as TO packages. Coaxial means that the centerlines of all optical paths, from the laser, lens, and optical fiber, are aligned. Therefore, optical components packaged in TO packages are also called coaxial packages. Currently, coaxial components dominate the mainstream optical device market due to their ease of manufacturing and cost advantages. TO-can, meaning "can," houses the laser and detector chips in a can. The numbers TO38, TO46, and TO56 represent the diameter of the can base (TO base), which are 3.8mm, 4.6mm, and 5.6mm, respectively. These three sizes are commonly used in the optical communications industry. The butterfly package (also called BOXPackage) typically has a rectangular housing, a varable tube, low-temperature soldering glass, and high-frequency ceramic sintering. Its structure and functionality are often complex, and it can support wire bonding for all the above components. Its large housing area provides excellent heat dissipation, making it suitable for various data rates and long-distance transmission of up to 80km.

[0005] In the existing technology, the coaxial packaging structure of the PAM4 transmitting laser mainly consists of the laser diode chip LD chip, the convergent coupling lens LENS, the box BOX used to carry and protect the optoelectronic components, the COC submount supporting the COC (Chip on chip), the LD submount supporting the LD chip, the Golden Wire connecting the laser and the RF Circuit, the high-frequency flexible printed circuit FPC (Flexible Printed Circuit), the high-frequency circuit pattern RF Circuit on the high-frequency ceramic, and the high-frequency ceramic RF Ceramic. Its structure is as follows: Figure 1 As shown in the figure, the optical path principle is as follows: the LD chip emits divergent light, which is then converged by a lens. The converged light then passes through a box window and enters a single-mode optical fiber. The circuit principle is as follows: the FPC and driver circuit are connected by soldering; the RF circuit and FPC are connected by soldering; and the LD chip and RF circuit are connected by gold wire bonding. The RF circuit on the RF ceramic is a differential 100-ohm high-frequency signal, capable of NRZ 25G BPS and PAM4 50G BPS. The existing technology faces the following challenges: 50G PAM4 is a high-volume application for 5G base stations. Currently, mass production can only be achieved using a box structure, which results in high material and box packaging costs. Looking back at the coaxial packaging solutions previously used in optical communications, the transmitter socket uses a differential 50-ohm signal output mode. While a 100-ohm differential output from the socket is achievable, this increases the socket volume, approaching a diameter of 9mm, far exceeding the module housing dimensions. Summary of the Invention

[0006] The object of the present invention is to provide a coaxial packaging structure and method for a 50G PAM4 transmitting laser, which is conducive to optimizing signals and reducing material costs and packaging costs.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a 50G PAM4 transmitting laser coaxial packaging structure, including a laser diode chip, a converging coupling lens cap, a laser diode gasket, an on-chip chip gasket, a bonding wire, a tube seat and a high-frequency flexible circuit board, wherein the laser diode chip is fixed on the laser diode gasket to form an on-chip chip, the on-chip chip is fixed on the on-chip chip gasket, the on-chip chip gasket is fixed on the tube seat, the high-frequency flexible circuit board is passed through the tube seat, the laser diode chip is connected to the high-frequency flexible circuit board via a bonding wire, and the converging coupling lens cap is fixed on the tube seat; the laser diode chip emits a Gaussian beam, which is converged by the converging coupling lens cap. The converged light is converged into a mode matching a single optical fiber and is incident on a single-mode optical fiber.

[0008] Furthermore, the converging coupling lens cap is a half-cap structure composed of converging coupling lenses, and the converging coupling lens cap is arranged on the outer side of the laser diode chip to converge the Gaussian beam emitted by the laser diode chip.

[0009] Furthermore, the optical communication wavelength of the laser diode chip is 1310 nm.

[0010] Furthermore, the tube seat is made of Kovar and stainless steel.

[0011] Furthermore, the high-frequency flexible circuit board is a differential 100 ohm high-frequency signal, NRZ 25G Bps, and PAM450G Bps.

[0012] Furthermore, the high-frequency flexible circuit board and the driving circuit are connected together by welding.

[0013] The present invention also provides a 50G PAM4 transmitting laser coaxial packaging method, comprising the following steps:

[0014] 1) SMT: Use silver glue to attach the high-frequency flexible circuit board to the tube holder and bake it to fix it. Use high-temperature eutectic welding to fix the laser diode chip on the laser diode pad to obtain the chip-on-chip, and fix the chip-on-chip on the chip-on-chip pad. Then use silver glue to attach the chip-on-chip pad to the tube holder and bake it to fix it.

[0015] 2) Wire bonding: Using flip wire bonding, use bonding wire to weld from the laser diode pad to the high-frequency flexible circuit board;

[0016] 3) Capping: Use a capping machine to weld the coupling lens cap resistor onto the tube holder.

[0017] Compared with the prior art, the present invention has the following beneficial effects: the present invention reduces one step of electrical connection, and the high-frequency flexible circuit board is directly connected to the laser diode gasket through the bonding wire, which not only improves the high-frequency signal but also reduces the material cost and packaging cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural diagram of the prior art.

[0019] Figure 2 It is a structural diagram of an embodiment of the present invention.

[0020] Figure 3 Schematic diagram of the structure of the converging coupling lens cap and the tube base in an embodiment of the present invention. DETAILED DESCRIPTION

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] like Figure 2 As shown, this embodiment provides a 50G PAM4 transmitting laser coaxial packaging structure, including a laser diode chip 1, a converging coupling lens cap 2, a laser diode gasket 3, an on-chip chip gasket 4, a bonding wire 5, a tube seat 6 and a high-frequency flexible circuit board 7. The laser diode chip 1 is fixed on the laser diode gasket 3 to form an on-chip chip, the on-chip chip is fixed on the on-chip chip gasket 4, the on-chip chip gasket 4 is fixed on the tube seat 6, the high-frequency flexible circuit board 7 is passed through the tube seat 6, the laser diode chip 3 is connected to the high-frequency flexible circuit board 7 through the bonding wire 5, and the converging coupling lens cap 2 is fixed on the tube seat 6; the laser diode chip 1 emits a Gaussian beam, which is converged by the converging coupling lens cap 2. The converged light is converged into a mode matching a single optical fiber and is incident on a single-mode optical fiber.

[0023] The optical communication wavelength of the laser diode chip is 1310 nm.

[0024] like Figure 3 As shown, in this embodiment, the converging coupling lens cap 2 is a half-cap structure composed of a converging coupling lens. The converging coupling lens cap 2 is covered on the outer side of the laser diode chip 1 to converge the Gaussian beam emitted by the laser diode chip 1.

[0025] The tube base 6 is made of Kovar and stainless steel.

[0026] In this embodiment, the value ranges of the dimensional parameters of the converging coupling lens cap 2 and the tube base 6 are:

[0027] 3.3<A<7mm, 0.5<B<6mm, 0<C<3mm, 0<D<5mm, 1<E<6mm, 0.1<F<7mm, 0.5<G<7mm, 0.5<H<7mm.

[0028] The high-frequency flexible circuit board is a differential 100-ohm high-frequency signal, NRZ 25G Bps, PAM4 50G Bps. The high-frequency flexible circuit board is connected to the driving circuit by welding.

[0029] The present invention also provides a 50G PAM4 transmitting laser coaxial packaging method for realizing the above-mentioned packaging structure, comprising the following steps:

[0030] 1) SMT: Use silver glue to attach the high-frequency flexible circuit board to the tube holder and bake it to fix it. Use high-temperature eutectic welding to fix the laser diode chip on the laser diode pad to obtain the chip-on-chip, and fix the chip-on-chip on the chip-on-chip pad. Then use silver glue to attach the chip-on-chip pad to the tube holder and bake it to fix it.

[0031] 2) Wire bonding: Using flip wire bonding, use bonding wire to weld from the laser diode pad to the high-frequency flexible circuit board;

[0032] 3) Capping: Use a capping machine to weld the coupling lens cap resistor onto the tube holder.

[0033] The above are preferred embodiments of the present invention. Any changes made according to the technical solution of the present invention, as long as the resulting functions and effects do not exceed the scope of the technical solution of the present invention, shall fall within the scope of protection of the present invention.

Claims

1. A 50G PAM4 transmitting laser coaxial packaging structure, characterized in that: The laser diode chip comprises a laser diode chip, a convergent coupling lens cap, a laser diode gasket, an on-chip chip gasket, a gold bonding wire, a tube holder, and a high-frequency flexible circuit board. The laser diode chip is fixed on the laser diode gasket to form an on-chip chip, the on-chip chip is fixed on the on-chip chip gasket, the on-chip chip gasket is fixed on the tube holder, the high-frequency flexible circuit board is passed through the tube holder, the laser diode chip is connected to the high-frequency flexible circuit board via a gold bonding wire, and the convergent coupling lens cap is fixed on the tube holder. The laser diode chip emits a Gaussian beam, which is converged by the convergent coupling lens cap. The converged light is converged into a mode matching a single optical fiber and is incident on a single-mode optical fiber. The converging coupling lens cap is a half-cap structure composed of converging coupling lenses. The converging coupling lens cap is arranged on the outer side of the laser diode chip to converge the Gaussian beam emitted by the laser diode chip; The optical communication wavelength of the laser diode chip is 1310nm; The pipe seat is made of Kovar and stainless steel; The high-frequency flexible circuit board is a differential 100-ohm high-frequency signal, NRZ 25G Bps, PAM450G Bps; The high-frequency flexible circuit board and the driving circuit are connected together by welding; The packaging method of the 50G PAM4 transmitting laser coaxial packaging structure includes the following steps: 1) SMT: Use silver glue to attach the high-frequency flexible circuit board to the tube holder and bake it to fix it; use high-temperature eutectic welding to fix the laser diode chip on the laser diode pad to obtain a chip-on-chip, and fix the chip-on-chip on the chip-on-chip pad; then use silver glue to attach the chip-on-chip pad to the tube holder and bake it to fix it; 2) Wire bonding: Using flip wire bonding, use bonding wire to weld from the laser diode pad to the high-frequency flexible circuit board; 3) Capping: Use a capping machine to converge the coupling lens cap resistance welding on the tube seat.

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