摘要： Coherent beam combining (CBC) is one of the methods for power scaling of high power lasers. In the scientific literatures a low power narrow linewidth source is used for CBC, however in this report, a low cost diode laser source (spectral bandwidth <10 MHz) is used to fabricate near diffraction-limited 300 W fiber laser with CBC method. The diode laser is amplified by a preamp fiber amplifier and then divided in to three channels. Each channel is amplified to achieve 120W output with homemade power amplifiers. A 1×3 diffractive optical element is used to combine the output of the amplifiers with ~83% efficiency. Active phase locking is achieved with the stochastic parallel gradient descent (SPGD) method. A major obstacle towards high power narrow-linewidth fiber lasers is stimulated Brillouin scattering (SBS). It has been proven that phase modulation is an effective way to suppress SBS in these kind of lasers. Applying phase modulation to a single frequency laser, splits its spectrum to many spectral lines with the same frequency spacing of the modulation frequency. In this work, we use a sinusoidal signal phase modulation (30 MHz frequency and 10 V amplitude) to suppress SBS effect. The result of this modulation on the spectrum of the laser is illustrated. The maximum achievable output power for each channel without modulation is ~40 W. However, by applying modulation SBS threshold power enhances with a factor of 3. The output power of combined beam versus pump diode current (solid line) is shown. Also the backward output power (dashed line) is illustrated. As it can be seen in the figure the maximum backward power is 110 μW which proves the SBS effect is cancelled.