The COMOSOL multiphysicsis used to design various optical systems, including the design of the acousto-optic modulator system. Its work depends on the special inputs of the program, such as the characteristics of the laser used and the frequencies of the sound waves. A square modulator was designed with dimensions 3x3 mm, and a quartz crystal was used, in which the interaction of light and sound occurs. Different number of orders diffraction are generated called the Bragg angle, and their number varies with different inputs. The modulator is created by entering the value of the radio frequency up to 100 volts. Through our results, the efficiency increases at the frequency of 400 kHz after changing the frequencies of 200, 300 and 400 kHz. The values of the stress are: 1.24 × 106 P a, 1× 106 P a, 3.8× 106 P a, and the estimated shift is about 0.7, 0.4 and 0.9 mm, there were three frequency values considered: 200, 300, and 400 kHz. respectively. The far field shape show two orders are appeared at 200 kHz and 300 kHz frequencies they are: zero order and first order but they are different in the value of Bragg angles but in 400 kHz shown approximate three orders, they are: zero, first, and new generation of second order with the different in the value of Bragg angles.

Second harmonic generation (SHG) is a phenomenon observed in nonlinear optics that leads to frequency duplication for a high intensity laser incident on nonlinear crystal using BBO crystal. The SHG yield is achieved when the photons interact with a nonlinear optical material and effectively combine to form new photons with double frequency, and therefore double energy and half wavelength. This paper is concerned with the establishment of an SHG experiment to govern the process of producing half-wavelength laser beam from the input one. The theoretical effort was extended to compute the efficiency by using MATLAB software based on mathematical relationships. The values of the conversion maximum efficiencies, which were computed as a function of the input and output powers of the theoretical computations, were 15.6% and 16%  at input and output power values of 0.6 and 0.1, respectively. The experimental results of the laser source of 532nm wavelength (fundamental frequency was 0.563x1015s-1) gave a half wavelength of 266nm (double frequency was 1.126x1015s-1). The conversion efficiencies, computed as a function of the input and output powers of the experimental measurements, were 14.32% and 12.97%, respectively.

This paper describes the concept and simulation of an fiber Bragg grating. Simulation of the transmission system have been analized using simulator OptiSystem, based on different parameters. Show there parameters are investigated by simulating a communication device model and using the most suitable system settings which include input power (dBm), fiber cable length (km) and attenuation coefficient (dB / km) in the cable segment; Namely, signal strength (dB), noise power (dB), receiver output (watts). The power values (-5.299 dB) and (-2.6635 dB) are found in which regions, which decrease as the number of network regions in the fiber increases, thus increasing the density efficiency (16.316) and (75.5192) as well as the number of fiber regions (FBG). Keywords: Principle of FBG, Reflectivity And Tramsmission Spectrum in FBG, Periodic in FBG, Optisystem, Attenuation Coefficient.