| Broadband networks are one of the country's most important infrastructures.In recent years,with the acceleration of 5G commercialization,the whole society is about to enter a deeper era of data.In this wave of great changes from the Internet to the Internet of things,many emerging technologies and industries represented by AR/VR,autonomous driving,industrial Internet,smart city and cloud computing have developed rapidly,and the whole society has accelerated the process of informatization,which all put forward higher requirements for passive devices and optical modules in optical communication systems.The increase of communication services and the abundance of information types force the continuous improvement of communication speed and capacity,and wavelength division multiplexing(WDM)technology is one of the most effective methods to increase the transmission capacity of optical fiber communication system.The reliability of WDM systems is also more demanding in 5G applications.Compared with the existing optical WDM filter element,Volume holographic grating(VHG)filters recorded in holographic recording glass(HRG),which not only has excellent performance like FBG filters,but also has the simple structure like TFF filters.In addition,it has the advantages of high environmental stability and low manufacturing cost.So it has great potential to replace commercial WDM devices.In this thesis,the volume holographic gratings recorded in Photo-thermo-refractive glass are used as optical wavelength division multiplexer elements.The filtering principle and preparation technology of volume holographic gratings are studied theoretically and experimentally.The structure of WDM is designed.Combined with the coupled wave theory,the diffraction characteristics of the transmission and reflection volume holographic gratings are analyzed in detail.It mainly includes the effect of grating period,thickness and refractive index modulation on the wavelength selectivity,peak diffraction efficiency and first diffraction side lobe of grating,and the different diffraction effects of these two kinds of gratings on polarized light are analyzed.A computational model is established for the filtering effect of VHGs.A new type of PTR glass was prepared with a two-step melting process.The double-beam interferometry and two-step heat treatment were used to fabricate VHGs.Following UV exposure at ?=325nm and exposure does of 800 mJ/cm2,the glass is heat treated at 500 ?for 3h to nucleate,with further heating to 530? for 2h to crystallize.Finally,a volume holographic grating with a thickness of 3mm and a period of 1.8 ?m was prepared.The mechanism of grating formation in new HRG was studied.Using the transfer matrix method,the effects of the fringe deformation on the diffraction filtering characteristics were analyzed from the aspect of the fringe ratio and drift.The period,peak diffraction efficiency,refractive index modulation and wavelength selection curve of the prepared VHG were measured.The relative peak diffraction efficiency is 73%,the refractive index modulation is 162ppm,and the half-width of first zero value is about 3nm.The filtering ability was verified by the spectrometer,and the diffraction fringe of the light source was observed.Combined with the diffraction characteristics of VHGs,the series-parallel and multiple VHG wavelength division multiplexers are designed,and the relevant design ideas is given.The former can flexibly realize dense wavelength division multiplexing;The latter can simplify the device structure of the system.The experimental preparation and comparative analysis of the double VHG show that the multiple VHG has a negative effect on the peak diffraction efficiency. |
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