Research on Coupling Alignment Principle of COB Optical Module

Research on Coupling Alignment Principle of COB Optical Module

As a connecting device for photoelectric conversion, optical modules affect the rapid development of the optical communication industry to a certain extent. Today, from 1G SFP, to 10G SFP+, 40G QSFP+, 100G QSFP28, the package types of optical modules are developing in the direction of lower power consumption, smaller size and faster speed. Chip On Board (COB) Technology meets this requirement well.

COB is to paste the optoelectronic bare chip on the PCB board, and use smaller leads to connect the chip and the PCB, thus greatly improving the packaging density. The coupling alignment of the COB optical module is an important step in the packaging process, and it is also a technical difficulty. The quality of the coupling directly affects the yield of the COB optical module.

The purpose of coupling alignment is to find the best coupling position. From a mathematical point of view, it is a function optimization problem. To solve the function optimization problem, numerical solutions and intelligent optimization algorithms are generally used. Among the numerical solutions, the hill-climbing method has been applied to the alignment of lasers and optical fibers, but it can only perform one-dimensional alignment.

In 2006, Chunjing et al. applied the mode search method to solve the problem of automatic alignment of optical fibers, which can search in two degrees of freedom in the X-Y plane. The algorithm has been proven to be highly reliable through experiments, and it is not easy to fall into local optimum, but it only overcomes the X-Y two degrees of freedom. Coupling error for degrees of freedom, not searched along other degrees of freedom. Compared with numerical algorithms, intelligent optimization algorithms generally do not require explicit mathematical expressions for optimization problems in the solution process, so this algorithm is often used to solve complex optimization problems.

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In 2012, Marc Landry et al. proposed an intelligent particle swarm optimization algorithm and applied it to the coupling alignment between two fibers. This algorithm is simple and can search in multiple degrees of freedom at the same time. Experiments show that the algorithm is highly reliable and It is not easy to fall into local optimum.

Research on Coupling Alignment Principle of COB Optical Module

The particle swarm intelligent optimization algorithm still has a certain room for improvement in the search speed, and the adaptive weight particle swarm optimization algorithm has been proved in many studies that the search speed and reliability can be improved by adjusting the weight. However, it is rarely studied in the field of coupling packaging of optical communication devices.

This paper analyzes the coupling alignment principle of the COB optical module, and discusses the influence of various deviations on the coupling efficiency through the actual coupling alignment experiment. Based on the above analysis and research, the particle swarm algorithm with adaptive weight is introduced and used in the coupling alignment process of COB optical modules, and simulation and experimental verification are carried out. The experimental results show that the algorithm greatly improves the coupling pair. The quasi-efficiency and success rate provide theoretical technical support for the precise packaging of COB optical modules.

Coupling Alignment Principle

The principle of COB optical module coupling and alignment is to convert electrical signals into optical signals at the optical transmitting end, drive the vertical cavity surface emitting laser (VCSEL) to emit optical signals, and transmit them into the optical fiber; at the optical receiving end, the intrinsic photodetector (PIN) converts optical signals into electrical signals to achieve electrical-optical-electrical conversion. During this process, both the VCSEL and the PIN need to be optimally positioned to couple to the fiber so that the optical signal can be transmitted efficiently. The bare chips of VCSEL and PIN are mounted on the PCB by bonding and patching.

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The VCSEL’s laser emission direction and the PIN’s receiving light signal direction are both perpendicular to the chip, and the optical fiber is parallel to the PCB board, so the VCSEL is parallel to the PCB board. The chip of /PIN is 90°. Therefore, how to efficiently couple the optical fiber and the chip is the key to the packaging of the COB optical module, and the optical bending method is used in this study.

As shown in Figure 1, taking the light emitting end as an example, the optical path is bent by a reflector, the light emitted by the VCSEL is rotated by 90° through a 45° reflector, and is injected into the fiber through a lens to complete the coupling.

 

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