| Abstrakt: |
The feasibility of achieving efficient coupling between an optical fiber and a periodically poled lithium niobate (PPLN) waveguide in an ideal optical system was theoretically analyzed using a finite element simulator. Divergence of single-mode polarization-maintaining fiber and lensed fiber in space was simulated. Direct end-face coupling simulations were conducted for a PPLN ridge waveguide with a cross-sectional size of 10 μm x 10 μm and a length of 20 mm, involving two different types of fibers. It is found that despite the lensed fiber achieving a coupling efficiency of up to 95%, its fundamental mode contribution is less than 5%. Given that PPLN frequency-doubling devices primarily rely on the laser's fundamental mode for operation, this renders the coupling efficiency of the lensed fiber relatively low in practical applications. In contrast, ordinary single-mode fiber exhibits a significantly higher fundamental mode contribution of 93. 8%, demonstrating its superior performance. Therefore, this study selects ordinary single-mode fiber for encapsulation testing with PPLN ridge waveguides. The experimental results show that when the maximum pump power output from the fiber amplifier reaches 1. 6 W, the calculated input pump power, after deducting the coupling losses between the input fiber and the waveguide, stands at 1. 2 W. The fiber-to-waveguide coupling efficiency is 75%, slightly exceeding the currently known advanced value of 72%. At a temperature of 24. 8 °C, with an input power of 1. 2 W at the fundamental wavelength of 1 560 nm, the maximum output of frequency-doubled light is 653 mW. The optical-to-optical conversion efficiency reaches 54. 4%, with a normalized conversion efficiency of 20. 2% / (W·cm²). [ABSTRACT FROM AUTHOR] |
