Analysis Of Characteristics Of Gaussian Beam And It’s Applications In Optical Devices

Optical devices are the physical basis for an optical communication system, whoseperformance is important for the whole system. The optical beam emitting from asingle-mode optical fiber can be approximated by a Gaussian beam. Thus, it is necessary toresearch the characteristics of a Gaussian beam and it’s applications in optical devices. Inthis thesis, the coupling characteristics of Gaussian beam and it’s applications in severaloptical devices were analyzed in detail, including wavelength selective switch (WSS),tunable optical filter (TOF) and variable optical attenuator (VOA). Meanwhile, a series ofexperiments were designed for the verification of the theoretical results. The main work ofthis thesis includesBased on coupled-mode theory, the coupling efficiency between two Gaussian beamswere obtained and the influence of several mismatch factors were analyzed. Then theanalysis was extended to the situation of coupling between a circular Gaussian beam and anelliptical one. The condition to reach the maximum coupling efficiency was obtained.The coupling of a dispersed Gaussian beam on a MEMS (Micro-Electro-MechanicalSystems) mirror array was studied. For two different optical devices, WSS and TOF, therelationship between the optical spectrum and the parameters of the MEMS mirror array,such as fill-factor and beam confinement factor, was analyzed. The WSS sample was testedand the measured spectrum meets the simulation results well.For a free-space optics based TOF, a simplified model was established and thetransmission spectrum was obtained also based on coupled-mode theory. The theoreticalresults show that the3dB line width decreases when the beam size improves. Experimentsfor verification were carried out. The measurement results meet the theoretical value well.For the VOA employing on a MEMS torsion mirror, based on the mismatch couplingmodel of Gaussian beam and considering the wavelength dependence of fiber mode size, thecause for wavelength dependent loss (WDL) was obtained. Accordingly, several possibleapproaches for optimization were presented and the final solution was experimentallyverified.The methods mentioned and the results obtained in this thesis are important for the design of optical devices with good specifications, which help to improve the performance ofthe whole optical fiber communication system.