The Research On Laser Collimation And Coupling Technology In Optical Communication

Free space optical communication is the system which transfers information in the atmosphere, with laser as a carrier. Optical communication attracts extensive attention for its short cycle, low cost, strong anti-electromagnetic capability and good security.This paper studies laser collimation and coupling in the optical communication. We use photonic crystal to realize laser divergence angle collimation, and verify the collimation results we obtained by theory with optical software simulation. Ultra-wideband planar photonic crystal fiber is designed and we research the coupling characteristics of photonic crystal fiber and single mode fiber.Photonic crystal is an artificial photonic band gap material, which is due to the periodical dielectric constant that makes beam generate periodic refractive distribution. Many applications of the photonic crystals rely on the existence of the photonic band gap in a certain frequency range, which provides a new mechanism of light control with widespread attention.The main work of this paper can be included as follow:1. The principle of optical communication and some methods of laser collimation and coupling are introduced and we determine to choose photonic crystal researching in this paper. The development of photonic crystal is briefly recommended. We discuss the main methods of photonic crystals:Plane wave expansion method(PWE), transfer matrix method(TME) and software simulation used by finite difference time domain(FDTD) in photonic crystals.2. We improve the traditional two-dimensional photonic crystal model with the principle of surface modes, and study the effect of beam collimation. Compared with the traditional two-dimensional photonic crystal, a better collimation angle can be obtained by changing the surface of photonic crystal and using the transmission characteristics of far-field distribution analysis collimation effect. The dispersion curve of surface modes and energy band structure of two-dimensional photonic crystal can be calculated by plane expansion method(PWE). The collimated frequency of surface modes is outside the scope of photonic band gap. The software simulation results show that self-collimation effect simulation can be obtained compared with the traditional structure without surface corrugation.3. Ultra-wideband planar photonic crystal fiber is designed with the purpose of reducing the crosstalk code when beam propagates in optical fiber. Analyzing the main factors affecting the dispersion curve, the conclusion is that the air holes radius and the hole space of photonic crystal fiber have a great impact on the dispersion. By altering these parameters to optimize the dispersion curve, Ultra-wideband planar photonic crystal fiber can be obtained. Analyzing the factors influencing the coupling loss of photonic crystal fiber and single mode fiber, we can calculate the coupling losses. At last, we make the ultra-flattened dispersion photonic crystal fiber that we design couple with single mode fiber and calculated the coupling loss.