This work, studies the behaviour of the laser rays which comes out of the semiconductor laser that has direct modulation frequencies. And as the semiconductor laser is regarded as one of the non-linear systems, so Volterra series method has been used to transform the output of the laser to spectrum, which consists of first order, second order, third order, the second and the third order will be responsible for the occurring of the harmonic and intermodulation distortions. Consequently these distortions will affect the first order. To decrease these distortions, an optical interference filter with the characteristics below has been designed: cut off frequency=2.9GHz, filter angle ( )=48.33o,filter length(L)=0.6711mm, reflectivities (R) = 0.98, reflective index (n) = 1.54. This filter is going to remove or decrease the orders that are not lying at the same location of the fundamental order whereas the orders that lie at the same location of the fundamental order will be decreased by making use of the optical interference filter characteristics which is the process of reflecting part of the rays that fall on the filter and then are reflected back to the laser cavity, this process is called the electro-optical feedback. If these reflected rays were at the same phase with the rays emitted from the laser cavity _constructive interaction_, the third order would be decreased. The interference process will be controlled by having control over the filter angle which is controlled through the piezo electric material. So the difference between the fundamental and third orders is _11dB, -14dB, and _9dB when the injection current is modulated by (2.9 GHz), (2.9 and 3GHz), and (2.9, 3, and 3.1 GHz) respectively. We can get the simulation results by using the Simnlink Matlab 7.0 program and Matlab 7.0 M-files programs.