Research Reflected LiNbO₃ Optical Waveguide Interleaver

Optical interleaver is a key component in dense wavelength division multiplexing system, which can separate optical signal with smaller wavelength space into the optical signal of double wavelength space, thus greatly alleviated the requirements of filtering devices of DWDM system. Nowadays, the research hot spot mainly concentrate on fabricating some dense and effective devices to satisfy the demands in integrated optic system. In this dissertation, a reflection type asymmetric MZI interleaver is proposed, which combine the asymmetric MZ structure and a reflection mirror formed on one end face of the device. The proposed interleaver can greatly reduce the size of the device. The slope angle between the waveguide and reflective film can introduce the required length difference between the two MZ interference arms. While lithium niobate crystal show high reflection effect like metal after being burnished; On the other hand, Due to fabrication error in the fabrication process of the device, the central wavelength may shift. However, the tunable interleaver can compensate the error in the manufacture process and solve this problem. Moreover, tunable optical interleaver can be used as a wavelength-selected switch. Thus, the research on tunable optical interleaver is of great significance. LiNbO3 crystal materials with large electro-optic coefficient are widely used to fabricate the electro optic tunable waveguide devices, but because the refractive difference of LiNbO3 optical waveguide fabricated by annealed proton exchange process is quite small, the size of LiNbO3 optical waveguide interleaver are usually rather large, which is a disadvantage for the fabrication of device. In this dissertation, we use the reflective structure described as above to shorten the device length, and focus on the research on how to achieve the device structure, then, on the basis of which to design electrode to realize its tuning function. The main content of the dissertation include:First, the basic structure of the proposed reflection type asymmetric MZI Interleaver is investigated, and the working principle and output characteristics of the device are presented. Then, the single mode transmission condition of the waveguideis is analyzed. And based this condition the basic structure and the parameters of the 3 dB coupler and asymmetrical arm are investigated, which are the key components of the tunable interleaver. As the input and the output of the devices, the 3 dB coupler greatly affects the performance of the devices. Therefore, the output characteristics of the devices with different couplers having different waveguide gap and length are also analyzed. Moreover, because the arm length difference between the two asymmetric arms directly determines the wavelength space of the output spectrum, the effect of the length difference on the performance of the device is also investigated.Secondly, according to the analysis and design of the different structural parameters, we finish the design of the device, and manufacture the mask. Then we fabricated the waveguides by annealed proton exchange technology and tested the devices. The following are specific experimental work:(1) Successfully fabricate the LiNbO3 S-bend waveguides with different parameters, and measure the transmission characteristics and insertion loss, verify that waveguide with smaller bending radius have greater bending loss; (2) Successfully fabricate the reflection type asymmetric MZI interleaver (without a reflective film), and test the output characteristics and coupling efficiency under the condition of different annealing time, which aim at the realization the ideal splitting ratio; (3) Successfully fabricate the reflection type asymmetric MZI interleaver, and test the output characteristics of the device, and obtain the comb output spectrum, the optical interleaver with FSR of 200 GHz is successfully realized.