HIGH MULTIPLEXING OF ALL-SINGLE-MODE-FIBER-LASER USING COHERENT-CAVITY COMBINING SYSTEM

摘要

In this study, we have developed high power fiber laser using coherent-cavity combining (C~3) system. C~3 is a power addition technique that can maintain high beam quality using coupled laser cavities. C3 enables power scaling beyond the limits of single fiber laser. However, the number of laser modules that can be combined in the coupled cavity is limited, one example of the drop of the combined efficiency with number of lasers combined [1, 2]. The cause of that is the mismatch of individual longitudinal modes. Our present work increases the number of coupled laser by precise control of cavity lengths. Laser modules of cavity length are controlled by using an aluminum coated fiber (ACF). It is possible to tune the cavity length accurate to about 10 nm with the ACF controlled by applied electrical power. We have tried completely consisting of the longitudinal modes of two individual fiber lasers in the coupled cavity by the technique with an ACF. In case of uncontrolled cavity length, the spectrum of combined beam formed longitudinal modes group. On the other hand, the spectrum of combined beam having a cavity length difference of much less than 10 μm matched the spectrum of single fiber laser. As a result, two fiber lasers in the coupled cavity by completely consisting of the longitudinal modes are considered single fiber laser. The drop of the combined efficiency occur when the number of lasers combined exceed seven. Therefore, we expect it is possible to combine more fiber lasers with high efficiency by completely consisting of the longitudinal modes.