How to fully apply the characteristics and advantages of light in numerical computation is an important issue that attracts many scholars. Though much research has been done in this field, how to design and realize specific applications or devices is still an issue to be solved. Based on this, we present an architecture and implementation method of modified signed-digit (MSD) optical adder from the point of applicability. In the implementation, we fully consider the different procedures of the MSD addition which including optical logical operation, results decoding, special storage area design, data feedback, control of light path, etc. Meanwhile, we also introduce pipeline mechanism which guarantees that the addition operation is an automatic and continuous process. This is a carry free adder design method which guarantees the addition has high data throughput. It is very suitable to fulfill the large-scale numerical computation. The experiment shows, the MSD adder not only has a reasonable and correct design, but also has high throughput rate, can work efficiently and steadily.