Optik doğrultu kuplörlerinde performans analizi

Optical fibers are the preferred choice in communication technologies, because of their small losses and high channel capacity due to their broad band width. The abundance of silisium, which is the raw material from which optical fibers are manufactured, in the nature, and occupation of small space, working in harmony with the existing systems, and not being influenced by electromagnetic fields are among the basic properties of optical fibers working at THz frequencies. In optical communication systems, communication in both directions is achieved by using the wavelength division multiplexing mechanism, and increasing the data transmission capacity is aimed. In optical communication networks, which are rapidly spreading, elements such as optical directional couplers, optical fiber sensors, optical amplifiers, optical modulators, optical isolators, optical filters, optical resonators, optical polarisers, optical circulators, optical reflectors, optical attenuators and optical detectors are commonly used. In this study, optical directional couplers are analysed. An optical directional coupler, which is a four-port circuit element being fed by a laser or a light emitting diode at one of the ports and providing data transmission through the other three ports, consists of two parallel optical fibers and two bent or one straight and one bent optical fibers. Evanescent fields influence each other because the distance between the axes of the optical fibers is much smaller than the working wavelength. In this study, coupling mechanism and data transmission of an optical directional coupler is analysed by using the Coupled Mode Theory and Perturbation Theory. The interaction within an optical directional coupler, which consists of nonidentical, slab, parallel, weakly guiding, lossless and bare optical fibers, is analysed for a time dependent term of exp(jZt), and coupling coefficients which are independent of the coordinate z in the propagation direction are determined. Change in the propagation constant because of the coupling and the relation between the coupling coefficients are given, and it is found that the maximum coupling occurs for the synchronous case when modal coupling between the optical fibers is considered. Coupling coefficients for TE and TM modes are determined by using the Maxwell equations and dielectric-dielectric boundary conditions. The change of coupling coefficients with the radius of the second optical fiber is calculated for TE even, TE odd, TM even and TM odd modes, if the transmitted power is 1 mW, the radius of the first optical fiber is 20 Pm, the refractive index of the optical fibers is 1.5, and the refractive index of the surrounding region is 1, for three different propagation constants, at 200 THz. In the analysis, it is observed that the coupling between the TE modes is bigger than that between the TM modes, and that the coupling between the TE even modes is more effective than those between the other modes. Characteristic properties of an optical directional coupler are determined by analysing its performance with OptiSystem 7.0 simulator. A system consisting of a standard continuous wave laser which works at 193.1 THz frequency and has 0 dBm power, and an optical directional coupler with a coupling coefficient of 0.5 is configured and is evaluated with an optical spectrum analyser and an optical power meter. As a natural consequence of the coupler structure, it is observed that the powers at the exit ports are less than that at the entry port. The exit ports of the optical directional coupler are examined with the optical power meter, and it is observed that the total power is -3.010 dBm for both exit ports. When the change of the power values at the exit ports of the optical directional coupler with the coupling coefficient is calculated, it is determined that while the power at the first exit port decreases, the power at the second exit port increases, which is expected because of the working mechanism of the coupler.