Designs And Characteristics Analysis Of Non-polarizing Beam Splitters

When used at oblique incident angle, the reflectance and transmittance of thin films exhibit strong polarization effects, particularly for the films inside a glass cube. However, for many applications this effect is undesirable and should be reduced. Up till now, beam splitters (BSs) with non-polarizing effects both in amplitudes and phases have not been reported. Reflection-induced retardance of non-polarizing beam splitters (NPBSs) has been neglected all along. Moreover, almost all of the related reports published on NPBSs focus on the applications in visible band. Meanwhile, however, the demands of infrared NPBSs increase with the development of modern optical technology. The status of NPBSs research can not obviously keep up with the demands of the engineering. Thirdly, the working spectrum widths of NPBSs reported is limited to 200nm, far from the demand of some projects. These problems mentioned above are investigated and discussed in this dissertation. Therefore, the work is significant in both theoretical aspect and engineering applications.The development of NPBSs is elaborated and the ways of NPBS's technology, especially Gilo's theory are discussed. With the use of characteristic matrices, the NPBSs in visible band are calculated, which prepares for infrared NPBSs.The paper concentrates on the investigation of the phase properties of NPBSs. The NPBSs proposed here can satisfy the targets in both aspects of amplitudes and phases. The design methods of NPBSs for infrared band are explored and six design schemes are proposed and digitally verified. Also the design methods for extending the NPBSs' band are investigated and the designs of NPBS with 300nm band width are achieved.The main points included in this dissertation are as follows:(1) New NPBSs in infrared band are investigated for different glass substrates, such as ZF-7 glass and K9 glass, respectively. Both NPBS utilizing the principle of frustrated total internal reflection (FTIR) and mental-dielectric NPBS can satisfy non-polarizing target in amplitudes, however, their reflection-induced retardances are undesired.(2)Non-polarizing beam splitters in an unsymmetrical glass cube are proposed and theoretically investigated for the first time, and new applied examples are explored. To realize the characters of 50% reflectance and 50% transmittance at specified wavelength for both polarization components with an error less than 2%, the Needle optimization technique is used to optimize the thicknesses of each film in the design procedures with the results that an error is less than 2% and the width of the non-polarizing band is 20nm. Moreover, the effects of some important parameters, including the incident angle and the material indices, on the NPBS composed of ZnS, Al₂O₃ and SiO₂ are investigated.(3)Based on reflection phase shift properties of FTIR layer, polarizing beam splitters (PBS) and NPBS can be achieved. Novel method in solving non-polarizing condition in FTIR layers is proposed and the new designs of ultra-broadband NPBS composed of K9 glass cube and MgF₂ show 50% reflectance and 50% transmittance for both polarization states between 400nm and 700nm with the error less than 2%, but the difference between p-component and s-component is 2.30% greater than 2%. The most attractive feature is that the layer number of this design is eight enough less to fabricate NPBS.(4)At last, metal-dielectric NPBSs are investigated and two new designs are given, applied to the visible wavelength band and the infrared wavelength band, respectively. Non-polarizing band width of NPBs for visible band is 100nm, in which the beam splitter ratio and reflection-induced retardance obtain our targets. The reflection-induced retardance of NPBS for infrared band accords with our targets greatly and the differences between both components reflectance and the target reflectance is less than 2%, but the reflectance difference between p-component and s-component is 2.169% beyond our limitation at 1260nm. The beam splitter ratio and reflection-induced retardance of NPBS for infrared band obtain our targets in the range of 80nm.According to the need of the orthoconjugate reflector current sensor, the NPBS for infrared band is manufactured. The experimental results show that the beam splitter ratio is very close to 1:1 and the reflection-induced retardance is less than 5 degree. All these demonstrate that our designs are feasible.