Optical alignment is very critical in optoelectronics packaging. A slight offset in any direction may affect the performance of the photonic devices. Recently, the passive alignment method of optical fibers becomes more popular because of its low cost and high throughput advantages. In conventional optical fiber passive alignment, the position of the fiber is defined by the V-groove geometry and the adhesive is dispensed in a glob-top manner. A cover plate is usually required to press the fiber against the V-groove side walls in order to overcome the buoyancy effect by the adhesive. Even though the alignment yield can be improved by the cover plate, the applied compressive stress may deform the fiber and, hence, affect the optical properties of the fiber. In addition, it may also lead t...[ Read more ]

Optical alignment is very critical in optoelectronics packaging. A slight offset in any direction may affect the performance of the photonic devices. Recently, the passive alignment method of optical fibers becomes more popular because of its low cost and high throughput advantages. In conventional optical fiber passive alignment, the position of the fiber is defined by the V-groove geometry and the adhesive is dispensed in a glob-top manner. A cover plate is usually required to press the fiber against the V-groove side walls in order to overcome the buoyancy effect by the adhesive. Even though the alignment yield can be improved by the cover plate, the applied compressive stress may deform the fiber and, hence, affect the optical properties of the fiber. In addition, it may also lead to reliability issues. In the present study, a modified passive alignment method of optical fibers is introduced. An innovative silicon optical bench (SiOB) is designed. This method offers a self alignment capability of optical fibers. A “reservoir” is placed next to the V-groove for epoxy dispensing and the “canal” is used to divert the excess epoxy away.

As the cover plate is not used in this modified method, there are other processing parameters affecting the epoxy flow and the alignment yield which include the epoxy dispensing volume, epoxy viscosity and the surface quality of V-groove walls. In the present study, four different epoxies with different amount of dispensing volume are investigated. A 4 x 4 test matrix is designed. It is found that the alignment yield may decrease when either the dispensing volume or viscosity of the epoxy increases.

Moreover, the alignment yield may depend on the V-groove side wall roughness. A parametric study was conducted to investigate the relationship between the V-groove side wall roughness and the optical fiber alignment yield. The surface roughness is measured with a high resolution optical profiler. The surface morphology is also inspected under scanning electron microscope. The result of parametric study shows that the alignment yield and the flow length decrease as the V-groove wall roughness increases.

Flow control is another objective of this study. The flow length of epoxy is an important issue in the modified passive alignment method. If the flow length is not well-controlled, the epoxy might flow over and cover the face of the fiber-end, affecting the optical properties. The flow control can be evaluated by the flow distance in a period of time. However, this method is not always reliable. An innovative design of flow stopper is introduced to control the epoxy flow length. The flow stopper is fabricated with the V-groove at the same time. The epoxy can be halted by a flow stopper effectively. However, the flow stopper geometry may be altered due to the convex corner undercutting in the anisotropic etching of silicon. In this study, different compensation methods were investigated. The performance of the compensation scheme and the relationship between the etching depth and the compensation mask area were studied. The developed technology may be integrated with the chip-on-chip 3D optical interconnection when the device chip on the SiOB covers a portion of the V-grooves and the control of epoxy flow length is not visible.