Research On Optical Add Drop Multiplexer Based On Planar Lightwave Circuit Technology

The progress of optical devices determines the development stage of the All Optical Network (AON), which is the necessary development trend of the optical communication network. Optical Add Drop Multiplexer (OADM), the key component of the Wavelength division Multiplexing (WDM) communication system, marks the development of the AON into ring- or mesh-structure. The OADMs based on Planar Lightwave Circuit (PLC) technology have the advantages of small size, low cost, high performance and accord with the direction of the optical devices toward integration. Therefore, it is of great significance to study the OADMs based on PLC technology.Based on the fundamental theories of the PLCs and the waveguide Bragg gratings (WBGs) as well as the basic principles and simulation methods of a null-coupler-based OADM, some improved design methods for optimizing the performance of the coupler-based OADMs are studied in details. Experimental studies of the fabrication of an OADM are also carried out.The basic principles and simulation methods of a null-coupler-based OADM are studied firstly, especially in the crosstalk of a Y-branch structure and the coupling properties of a tilted grating. The theoretical analysis of a Y-branch structure, based on the combination of normal modes and waveguide modes, is presented for the first time. This method is brief in form and easy to understand. The simulation results are validated by the beam propagation method.A novel design of an OADM based on a tilt-grating-assisted symmetric coupler is proposed. By increasing the similarity of the two normal modes of the symmetric coupler in the grating region, the simultaneous optimization of the self-coupling interactions and cross-coupling interactions ensures that the device can enjoy the low cross-talk and lowback-reflection at both input and add ports.A novel design method of the back-reflection-peak-wavelength, used to lower the back-reflection of the OADMs, is presented. By utilizing the characteristics of the WDM signals, the wavelength to be added and dropped is located within WDM signal channels, while the peak wavelengths of the reflective spectrum are located outside the WDM signal channels, so that the back-reflection of the device will be greatly lowered. Meanwhile, the tolerance in fabrication process is remarkably enlarged. This method, applicable to the different kinds of OADMs, provides a feasible choice in the design of the OADMs with high performance and large process tolerance.An innovative design of a tilt-grating-assisted asymmetric-coupler-based OADM is proposed. By employing the 3-dimmention normal modes of a composite waveguide, the theoretical analysis on the three structures of the OADM device is made to select an optimized one. This, together with the application of the back-reflection-peak-wavelength, enables the OADM device to obtain the low back-reflection and the large process tolerance.The process of UV-written waveguide Bragg grating (WBG) is explored and the properties of the WBGs, made by Phase Mask Method, are systematically studied.The tilt-grating-assisted OADM device based on an asymmetric coupler is fabricated for the first time. The measured results show that the insertion loss is about 7 dB, the crosstalk is about -23 dB, and the return loss is about -22 dB, which also prove the back-reflection-peak-wavelength method. After the results are analyzed, the further measures to improve the performance of the coupler-based OADMs are discussed in details.